Hyperfocal distance question

acowanacowan Registered Users Posts: 156 Major grins
edited December 7, 2009 in Landscapes
Before I get directed to the innumerable sites explaining hyperfocal distance let me say that I've read most of them already and even scanned through a few today in hopes of finding an answer to my question. Here is my question: When measuring or estimating the distance of the nearest object in the frame (to then determine the hyperfocal distance) should it be measured angularly or laterally? In other words, should I imagine a line from the nearest point going up (at an angle) to the front of the lens (or to the sensor plane) OR should I imagine the nearest point as a focal plane that is parallel to the sensor plane and the resulting distance (measured between these two imaginary planes) is then doubled to obtain my hyperfocal focusing distance...? If my explanations are unclear then please let me know...I don't think there would be a dramatic difference using either method but I have yet to assiduously practice this.

Comments

  • squirl033squirl033 Registered Users Posts: 1,230 Major grins
    edited December 6, 2009
    acowan wrote:
    Before I get directed to the innumerable sites explaining hyperfocal distance let me say that I've read most of them already and even scanned through a few today in hopes of finding an answer to my question. Here is my question: When measuring or estimating the distance of the nearest object in the frame (to then determine the hyperfocal distance) should it be measured angularly or laterally? In other words, should I imagine a line from the nearest point going up (at an angle) to the front of the lens (or to the sensor plane) OR should I imagine the nearest point as a focal plane that is parallel to the sensor plane and the resulting distance (measured between these two imaginary planes) is then doubled to obtain my hyperfocal focusing distance...? If my explanations are unclear then please let me know...I don't think there would be a dramatic difference using either method but I have yet to assiduously practice this.

    measure line of sight, which is what the camera sees. don't worry about angles... you're confusing sighting a camera with sighting a rifle, where the bullet drop is different on a slant than it would be for the same distance horizontally. there is no "drop" to light, so using the slant range is the correct way to do it.

    also, hyperfocal distance is determined by the aperture and focal length, not the distance to any object in the frame, or by doubling the distance from the sensor plane to the object. the formula for hyerfocal distance is as follows:

    focal length squared, divided by the f-number x .03. this results in a fairly large number in mm. divide that by 1000 to get the hyperfocal distance in meters. multiply THAT by 3.3 to get feet.

    example: you're shooting at 50mm, f/8. 50mm squared is 2500. so divide 2500 by (8x.03). 8x.03 is .24, so you have 2500/.24, or 10416. divide that by 1000, you get about 10 meters, a bit over 33 feet. if you then focus at 10 meters, anything between half that distance (about 17 feet) and infinity will be in focus.
    ~ Rocky
    "Out where the rivers like to run, I stand alone, and take back something worth remembering..."
    Three Dog Night

    www.northwestnaturalimagery.com
  • acowanacowan Registered Users Posts: 156 Major grins
    edited December 6, 2009
    Rocky,

    Thanks for the reply. You bring up another point of interest for me...Which comes first: the minimum focusing distance estimate or the aperture setting. I know that the hyperfocal distance is based on the focal length, circle of confusion and aperture but wouldn't you base your aperture setting on the distance? If the goal is to get foreground through infinity in focus wouldn't the minimum focusing distance dictate the aperture rather than the aperture telling you where to manually focus? In other words, if I were to take a shot I would first estimate the distance, then consult my hyperfocal chart and set my focus manually rather than setting my aperture and then basing my focusing distance on aperture..the former is the correct approach, right?
  • squirl033squirl033 Registered Users Posts: 1,230 Major grins
    edited December 6, 2009
    acowan wrote:
    Rocky,

    Thanks for the reply. You bring up another point of interest for me...Which comes first: the minimum focusing distance estimate or the aperture setting. I know that the hyperfocal distance is based on the focal length, circle of confusion and aperture but wouldn't you base your aperture setting on the distance? If the goal is to get foreground through infinity in focus wouldn't the minimum focusing distance dictate the aperture rather than the aperture telling you where to manually focus? In other words, if I were to take a shot I would first estimate the distance, then consult my hyperfocal chart and set my focus manually rather than setting my aperture and then basing my focusing distance on aperture..the former is the correct approach, right?

    aperture is used to control depth of field. minimum focus distance is determined by the mechanics and focal length of the lens, and has nothing to do with it (as a practical matter, the hyperfocal distance for any given lens is well beyond the mininum focus distance, so don't worry about it). to obtain maximum depth of field, you want a relatively small aperture - f/8 through maybe f/16 (beyond f/16 you risk image softening due to diffraction limiting). set your aperture for maximum DOF, then calculate the hyperfocal distance.

    you have to set aperture first, because the hyperfocal distance is dependent on the aperture as part of the calculation. you can't determine that distance until you know the aperture you'll be shooting at. you first calculate or estimate hyperfocal distance based on the lens focal length and aperture, THEN compose the shot and focus at the hyperfocal distance.

    if you have a hyperfocal chart, as i do, you can set up the aperture and focal length to get the composition and DOF you want, then consult your chart, and focus (manual or auto, doesn't matter) at the hyperfocal distance for the lens settings you're using.
    ~ Rocky
    "Out where the rivers like to run, I stand alone, and take back something worth remembering..."
    Three Dog Night

    www.northwestnaturalimagery.com
  • squirl033squirl033 Registered Users Posts: 1,230 Major grins
    edited December 6, 2009
    BTW, i took a peek at your website... some nice stuff there. i love central Idaho and the Sawtooths, but haven't had as much time there with my cameras as i'd like. spent a week at Redfish Lake in 2007, but there were so many fires back in the mountains that year that the smoke messed up most of the scenery... :cry but it's on my list of places to go back to!
    ~ Rocky
    "Out where the rivers like to run, I stand alone, and take back something worth remembering..."
    Three Dog Night

    www.northwestnaturalimagery.com
  • acowanacowan Registered Users Posts: 156 Major grins
    edited December 7, 2009
    Rocky,

    Thanks again for the reply. I'll be heading out this week taking some photos. I'll make sure to take my chart and notes along with the pics so I can remember how I determined the settings and focusing.

    Also, thanks for the compliment on the site. I looked over yours as well and really like the Gale Creek shots and Washington coast shots (the rest weren't too shabby either :D ). I've only been in Idaho for 3 1/2 years but I've befriended some like-minded hikers and have really gotten to explore. The central mountains and the Owyhees give endless photographic possibilities.
  • kwalshkwalsh Registered Users Posts: 223 Major grins
    edited December 7, 2009
    Hi Aaron,

    I think you are on the correct track.

    First off, strictly speaking to your first question the measurement to make is the distance to the plane containing the foreground subject - that is not the line of sight, but as you describe in your first post the distance from the lens front nodal point to a plane parallel to the sensor that contains the foreground object. For ideal optics this is how planes of focus work, they are always parallel to the sensor (with the caveat that the lens axis is normal to the sensor, with view cameras or TS lenses this is not true and the plane of focus is under the control of the photographer).

    EXCEPT - as you point out for most cases the difference between this measurement and a simple line of sight distance is small enough to be completely ignored - remember, we are talking about a circle of confusion size here and 10 or 20 percent really isn't making a huge difference. In the one case that the measurement error is not that small - very wide angle lenses with extremely close foregrounds - there is the problem of field curvature. Most UWA lenses do not have a flat field of focus, the field of focus is curved like a spherical surface and thus all bets are off as to exactly what the DOF is for a given composition - you'll need to add a bit more fudge factor or examine with a DOF preview or test exposure.

    In summary, to your first question, for all practical purposes you can just measure the line of sight distance to the foreground subject even though that is not strictly correct and things are more complicated. Don't get wrapped around the axle with accurate measurements, DOF tables are just guides to help you determine what is possible and where to start.

    As far as your second question, how to set up the focus and determine the working aperture for a hyperfocal shot (i.e. infinity and a foreground both acceptably sharp) you are again pretty much on track. Focus at twice the distance of the foreground. Look up the aperture required for a hyperfocal distance of twice the distance of the foreground. Take your shot, examine it and decide if you need to adjust things. Pay close attention to the definition of hyperfocal distance - it is the distance at which you can focus the lens and still have infinity be "acceptably" sharp. This means your foreground subject isn't at the hyperfocal distance but rather at one half the hyperfocal distance, it is the lens that is focused at the hyperfocal distance. This confusses people frequently and can result in an unexpected factor of two.

    Do not overlook diffraction. At some point the aperture becomes too small and even the in focus areas of the image become soft on account of diffraction. For four-thirds you'll start to see pixel level detail start to fall off by about F/8. Of course if you don't stare at your images at 100% on your monitor and instead print them at normal sizes then you can of course push things further. Just how far you can push it all comes down to what you think is "acceptable".

    Finally, and this is critical, there is the question of "acceptably" sharp. What exactly is "acceptable"? Well, for essentially all DOF tables you'll find they use a circle of confusion based on viewing a print at a "normal" viewing distance (considered to be standing a distance equal to the diagonal away from the print). In these days of 100% pixel peeping and inexpensive giant enlargements (people tend to view very large prints at closer than the diagonal hence invalidating the DOF table assumptions) you'll often find the circle of confusion used in the tables to be unacceptably soft. In fact, the frequently used CoC size used in most online DOF calculators or tables is so large that it is equivalent to the diffraction effects of shooting at F/22 on four-thirds. F/22 on four-thirds is considered by most people to be total mush, in fact if you look at most lens test reviews the results at F/22 are pretty much in the "unacceptable" category. As noted above, at pixel level you start to see diffraction at F/8 on four-thirds. So, the DOF tables you'll get online are often based on a level of "sharpness" that most people in the digital pixel peeping age find decidedly "unacceptable".

    This results in great frustration to many people first trying to control DOF with tables, they discover that rather than getting a "sharp" foreground and background what they instead get is a "blurry" foreground and background and a sharp midground. This comes down to what was thought to be "acceptable". As a rough guide, if what you care about is pixel level sharpness rather than the ages old definition of "acceptably" sharp then you need to adjust standard tables by about a factor of three for the current crop of four-thirds and micro-four-thirds cameras. That is, in a table of hyperfocal distances either multiply those distances by a factor of three (resulting in less DOF for a given aperture) or multiply the apertures by a factor of three (requiring an even smaller aperture for a desired DOF). Most table generators allow you to type in your own CoC. For four-thirds or micro-four-thirds where you want pixel level sharpness a good number to use is about 0.006mm (you'll note this is about three times smaller than what is used by most sites/software when you select the four-thirds format).

    Getting back to diffraction, what is the smallest "acceptable" aperture to use is related to your CoC choice in the table. If you are using a "large" CoC then you should feel free to use a small aperture. This is often overlooked, you'll frequently see people online saying "never shoot smaller than F/8 or diffraction will kill you" even though they are using a DOF table that has a CoC equivalent to diffraction at F/22!!! When pushing extremely deep DOFs you are going to have to make a trade-off and potentially accept softness from diffraction to get that deep DOF. Make sure you understand this trade-off and adjust your tables accordingly, look up the equation for the diffraction Airy disk and understand it. Also, for static scenes consider focus stacking as a good way to have your cake and eat it too.

    I can not emphasize enough, before using a DOF table or calculator make sure you understand what circle of confusion you consider acceptable. Once you figure that out and build the table you will find using it to be quick and easy and give you good results. On the other hand, if you don't make sure your table has been calculated to match your expectations you are going to be frequently frustrated...

    Ken
  • squirl033squirl033 Registered Users Posts: 1,230 Major grins
    edited December 7, 2009
    "the measurement to make is the distance to the plane containing the foreground subject - that is not the line of sight, but as you describe in your first post the distance from the lens front nodal point to a plane parallel to the sensor that contains the foreground object."

    i think you're making things more complicated than they need to be. for all intents and purposes - we can ignore parallax, since it doesn't add enough to even measure at most hyperfocal ranges - the distance between the lens and the object you're focusing on IS in fact "line of sight", as in, straight, unobstructed, and independent of any slope in the geography. getting wrapped up in "planes", while correct in the most precise, technical sense, merely confuses the issue for most people. they think in terms of objects, not invisible planes parallel to the sensor.

    "Focus at twice the distance of the foreground. Look up the aperture required for a hyperfocal distance of twice the distance of the foreground."

    technically, this is backwards. the hyperfocal distance for a given focal length and aperture is totally unrelated to the distance to any object in the image. it is a fixed distance which remains the same until you change the lens settings. if you're shooting 50mm at f/8, the hyperfocal distance is about 10 meters, no matter where you aim the camera.

    as a practical matter, you can *usually* achieve an acceptable result doing it backwards as you describe above, but understand that by focusing on your subject first, you may find that the foreground is either closer or farther away than the correct hyperfocal distance allows for. if it's farther away, it doesn't matter; focus at the correct hyperfocal distance and the foreground subject will be clear. if it's too close, you have to move, or adjust your lens settings to produce a hyperfocal distance that is correct for the foreground.

    the CoC is defined as "the largest blur circle that will still be perceived by the human eye as a point when viewed at a distance of 25 cm" - about 10 inches. the generally accepted CoC for most hyperfocal distance calculations is .03mm for a full-frame camera, .018mm for APS sensors, and .015mm for a 4/3 sensor. while you might be able to notice an aberration that small pixel-peeping at 100%, you won't see it on most print sizes, unless you look at the print with a loupe or blow it up the size of a door, in which case the whole thing is likely to look like crap anyway. the limits of printer technology will make the print "fuzzy" long before you'll notice any degradation as a result of CoC variations. in any case, understand that the minimum CoC is largely determined by the optics in your lens and the visual acuity of the viewer. this is where using top-grade lenses comes in... CoC as a practical matter is greatly affected by the sharpness of focus, and sharper, clearer lenses focus more accurately, so the CoC will be smaller than for cheaper, less precisely ground glass.
    ~ Rocky
    "Out where the rivers like to run, I stand alone, and take back something worth remembering..."
    Three Dog Night

    www.northwestnaturalimagery.com
  • acowanacowan Registered Users Posts: 156 Major grins
    edited December 7, 2009
    Ken,

    I've used Bob Atkins' CoCs when computing my own charts. That is, I've used 0.01845mm for 1.6x (since I use a Canon 30D) and I went ahead and put a full frame table on the same sheet using a CoC of 0.0295mm.

    As far as "acceptable" sharpness goes (I hope we're not opening up a can of worms...) I haven't blown up any of my pictures too much (16x20) and I've been pretty pleased with the results. I've found that my own software sharpening techniques have been the ultimate make or break as far as acceptable sharpness (to myself) goes.

    I'm not a pixel peeper by any means; I'm more concerned with the overall end result. However, when I see nice enlargements (such as at Zion Lodge, Tom Till's Gallery and Mark Lisk's gallery) I do tend to put my face close to the glass just to see the detail. This is just a meaningless aside, though.

    I have unwittingly shot a heavy majority of my pictures at F/16 being more aware of tiny aperture=more DOF and being ignorant of diffraction. I'll still probably shoot F/16 from time to time (as I said, I find my results acceptable) but will probably try to stay more between F/8 and F/11 for diffraction's sake and become even more deliberate in the field while applying hyperfocal focusing techniques.
  • squirl033squirl033 Registered Users Posts: 1,230 Major grins
    edited December 7, 2009
    acowan wrote:
    Ken,

    I've used Bob Atkins' CoCs when computing my own charts. That is, I've used 0.01845mm for 1.6x (since I use a Canon 30D) and I went ahead and put a full frame table on the same sheet using a CoC of 0.0295mm.

    As far as "acceptable" sharpness goes (I hope we're not opening up a can of worms...) I haven't blown up any of my pictures too much (16x20) and I've been pretty pleased with the results. I've found that my own software sharpening techniques have been the ultimate make or break as far as acceptable sharpness (to myself) goes.

    I'm not a pixel peeper by any means; I'm more concerned with the overall end result. However, when I see nice enlargements (such as at Zion Lodge, Tom Till's Gallery and Mark Lisk's gallery) I do tend to put my face close to the glass just to see the detail. This is just a meaningless aside, though.

    I have unwittingly shot a heavy majority of my pictures at F/16 being more aware of tiny aperture=more DOF and being ignorant of diffraction. I'll still probably shoot F/16 from time to time (as I said, I find my results acceptable) but will probably try to stay more between F/8 and F/11 for diffraction's sake and become even more deliberate in the field while applying hyperfocal focusing techniques.

    Aaron, you're generally fine at f/16... diffraction limiting doesn't usually become an issue till you get to f/20 or smaller. it may be present at wider apertures than that, but you can't see it, much less measure it outside of an optical laboratory.

    i'm like you... all about the final result, how an image looks in print. most of my prints are between 8x12 and 16x20, but i do 16x24 or 20x30 occasion, and have done up to 30x40 once or twice (most people don't buy prints larger than 16x20 very often, at least not the kind of photos i do...). like you said, the image resizing software/process will cause far more degradation in the image than CoC or diffraction limiting, so as a practical matter, both of those effects are mostly academic.

    generally speaking, smaller sensors achieve greater DOF than larger ones, but from my experience shooting both APS-c and full frame, somewhere between f/8 and f/13-16 seems to be the sweet spot. i get plenty of DOF, even for landscapes, and there's no sign of diffraction limiting. since most of my landscape work is done between 24mm and 50mm on a FF body, the whole hyperfocal thing is largely a non-issue... the hyperfocal distances are such that pretty much wherever i focus at f/11 or f/13, the important bits are sharp and clear.

    anyway, don't get too wrapped up in all this academic mumbo-jumbo. use your hyperfocal chart and do whatever works best for you. shoot to produce good prints at the sizes you like best, and don't worry too much about the rest, unless you're trying to impress people who care more about technique than results. it's kinda like back in the 70's, when home stereo manufacturers were touting super-low distortion numbers for their amplifiers. the sales guys would blather on about .003% total harmonic distortion, and people would get all excited, because they didn't know that audio distortion has to be about 100x that level before the human ear can even detect it!
    ~ Rocky
    "Out where the rivers like to run, I stand alone, and take back something worth remembering..."
    Three Dog Night

    www.northwestnaturalimagery.com
  • kwalshkwalsh Registered Users Posts: 223 Major grins
    edited December 7, 2009
    squirl033 wrote:
    "the measurement to make is the distance to the plane containing the foreground subject - that is not the line of sight, but as you describe in your first post the distance from the lens front nodal point to a plane parallel to the sensor that contains the foreground object."

    i think you're making things more complicated than they need to be... they think in terms of objects, not invisible planes parallel to the sensor.
    Indeed, as I said in my post, use LOS as it is easy and close enough. But technically it is about image planes and that was what the OP was asking. So I answered it and then explained why he should just use LOS instead. A person using a copy stand, however, would understand LOS is not strictly the correct measurement...
    "Focus at twice the distance of the foreground. Look up the aperture required for a hyperfocal distance of twice the distance of the foreground."

    technically, this is backwards.
    Technically this is exactly how you keep infinity and a foreground in focus. Nothing backwards about it at all. There is no "forwards" or "backwards" to maintaining DOF. You can look up what your DOF is at a given aperture, or you can look up what aperture you need to get a given DOF. Which makes sense is a matter of perspective to the photographer.
    the hyperfocal distance for a given focal length and aperture is totally unrelated to the distance to any object in the image. it is a fixed distance which remains the same until you change the lens settings. if you're shooting 50mm at f/8, the hyperfocal distance is about 10 meters, no matter where you aim the camera.
    Indeed, but the OP's question is how to determine where to focus and what aperture to use to keep a foreground and infinity in focus. In that context, your approach is a bit more iterative and perhaps "backwards" but it will work out just the same in the end.
    as a practical matter, you can *usually* achieve an acceptable result doing it backwards as you describe above, but understand that by focusing on your subject first, you may find that the foreground is either closer or farther away than the correct hyperfocal distance allows for. if it's farther away, it doesn't matter; focus at the correct hyperfocal distance and the foreground subject will be clear. if it's too close, you have to move, or adjust your lens settings to produce a hyperfocal distance that is correct for the foreground.
    Re-read my post, it is the approach to exactly in one step keep a foreground and infinity in focus. Perhaps I didn't describe it well, but no there are no further adjustments to the approach I describe. Focus at twice the foreground distance and then adjust the aperture as small as necessary (either by examination of a table, examination in a DOF preview, or examination of a test exposure). Your description, also valid, is more applicable to a street shooter who doesn't want to think about focusing. The OP (I think) is like most landscape shooters not randomly shooting at things at varying distances but is instead trying to ensure a foreground and background are both sharp for a carefully composed image and he wants to know what aperture he needs to shoot to do this.
    the CoC is defined as "the largest blur circle that will still be perceived by the human
    eye as a point when viewed at a distance of 25 cm" -
    about 10 inches.
    I have never seen such a definition, don't know where you are quoting it, and it must in fact be wrong or improperly excerpted because it makes no statement as to the enlargement size. You'll notice my definition is enlargement independent (based on print diagonal) and is the one found in most any photography book. Your definition is appropriate for the standard at an 8x10 enlargement, being equivalent to the 1/diagonal standard.

    And yeah, as was the entire point of my post, the photographer needs to decide what CoC they want to use. Guys using a 60MP Phase One intending to print 40" enlargements viewed at 12 inches are not going to be happy with the standard CoC. Similarly, outputing to the web one can get much more DOF with a much larger CoC. Different horses, different courses, my point was know what you are doing and don't just print out a DOF table from the web and run with it. (Although, in fairness, running with "standard" CoC works very well for most applications, hence its wide adoption).

    Ken
  • kwalshkwalsh Registered Users Posts: 223 Major grins
    edited December 7, 2009
    acowan wrote:
    I've used Bob Atkins' CoCs when computing my own charts. That is, I've used 0.01845mm for 1.6x (since I use a Canon 30D) and I went ahead and put a full frame table on the same sheet using a CoC of 0.0295mm.

    As far as "acceptable" sharpness goes (I hope we're not opening up a can of worms...) I haven't blown up any of my pictures too much (16x20) and I've been pretty pleased with the results.
    Perfect, then you already know exactly what you need to! Basically, that Bob Atkin's CoCs (he uses the "standard" 1/diagonal) meet what you want.
    I'm not a pixel peeper by any means; I'm more concerned with the overall end result.
    Yeah, that was all I was saying, make sure you know what your "end result" is! Sounds like you've got a good handle on it already.
    However, when I see nice enlargements (such as at Zion Lodge, Tom Till's Gallery and Mark Lisk's gallery) I do tend to put my face close to the glass just to see the detail. This is just a meaningless aside, though.
    Yep, and as such the guys making those huge enlargements that we all love to stand right next to and practically swim in have to use a smaller CoC when calculating DOF and are way more sensitive to camera shake (very heavy tripod). Personally, I'm glad I never print very big so I don't worry about all that (the standard CoC's are what I usually use as well - not a big pixel peeper).
    I have unwittingly shot a heavy majority of my pictures at F/16 being more aware of tiny aperture=more DOF and being ignorant of diffraction. I'll still probably shoot F/16 from time to time (as I said, I find my results acceptable) but will probably try to stay more between F/8 and F/11 for diffraction's sake and become even more deliberate in the field while applying hyperfocal focusing techniques.
    On APS-C F/16 isn't a big deal at all for reasonable enlargement. But yeah, if you don't need it for DOF you'll get just a bit more resolution slightly lower. Again, I wouldn't sweat it so much. That was the whole point of my detailed post, just think in the context of your final output. Don't get caught up chasing that last little bit of sharpness in the capture if you don't need it.

    Oh, and yeah, for almost any modest print size the output sharpening technique you use is going to make a bigger impact to the viewer than any optics, diffraction, or other pixel peeping nuances are...

    Ken

    P.S. Sorry for including the not applicable four-thirds numbers in my previous post. For some reason I thought I was off in one of the 4/3 forums (I had multiple tabs open) and forgot I was in the Landscape forum!
  • squirl033squirl033 Registered Users Posts: 1,230 Major grins
    edited December 7, 2009
    "I have never seen such a definition, don't know where you are quoting it, and it must in fact be wrong..."

    so, because you haven't seen something, you automatically dismiss it as wrong? that's pretty arrogant, don't you think?

    you are correct that the mathematical calculations for CoC are in fact dependent on print size - as one factor - but from the standpoint of someone actually looking at a print, the definition i posted is accurate. obviously, the CoC changes with print size and viewing distance, but the concept remains the same - to the human eye, CoC is the largest blur circle that will still be perceived as a "point" for any given print size or viewing distance. and in the real world, printing aberrations, degradation due to software resizing, lighting and paper quality of the print will have far more effect on perceived sharpness than whether you use .015mm or .03mm in the CoC calculation.

    and no, i am not a "street shooter who doesn't want to think about focusing". i am primarily a landscape shooter who is VERY concerned with proper focus and depth of field (at print sizes of 20x30, yeah, it does matter), and i have no difficulty achieving either one. i am also a pragmatist who believes light, composition, and good optics are much more critical to the final result than how much effect a different CoC number will have on hyperfocal distance, especially since that effect will be unnoticeable in any meaningful way on the print.
    ~ Rocky
    "Out where the rivers like to run, I stand alone, and take back something worth remembering..."
    Three Dog Night

    www.northwestnaturalimagery.com
  • kwalshkwalsh Registered Users Posts: 223 Major grins
    edited December 7, 2009
    squirl033 wrote:
    "I have never seen such a definition, don't know where you are quoting it, and it must in fact be wrong..."

    so, because you haven't seen something, you automatically dismiss it as wrong? that's pretty arrogant, don't you think?
    Actually, what I've seen in print in numerous books in the past few decades is contrary to your definition as they all make it very clear that enlargement size and viewing distance combined with human visual accuity is what sets an acceptable CoC. And you took my quote out of context by chopping off "or improperly excerpted". Clearly, as you illustrated, you know exactly what is relevant to CoC - it just wasn't contained in your quoted (from where?) definition. In any case, sorry if you didn't like my phrasing, I can see it seems inappropriately absolute.
    you are correct that the mathematical calculations for CoC are in fact dependent on print size - as one factor - but from the standpoint of someone actually looking at a print, the definition i posted is accurate. obviously, the CoC changes with print size and viewing distance, but the concept remains the same - to the human eye, CoC is the largest blur circle that will still be perceived as a "point" for any given print size or viewing distance. and in fact, printing aberrations, degradation due to software resizing, lighting and paper quality of the print will have far more effect on perceived sharpness than whether you use .015mm or .03mm in the CoC calculation.
    100% completely and entirely agree with everything except the very last point. The last point, size of the CoC, is very important in certian applications - particularly gigantic enlargements from very high resolution sensors and lenses. Certainly not the type of thing I or most anyone around here shoots...
    and no, i am not a "street shooter who doesn't want to think about focusing". i am primarily a landscape shooter who is VERY concerned with proper focus and depth of field, and i have no difficulty achieving either one. get down off your high horse and into the real world once in a while... the change will do you good.
    I never said you were. I said that there are two completely valid ways to getting a foreground and infinity in focus. One is, set the aperture and focus based on a hyperfocal distance and then shoot. This is excellent for a street shooter. It also works just fine for a landscape shooter as long as you measured the distance to the subject and set the focus properly. People using it every day for years and years. Nothing wrong at all with it. Works wonderfully on manual focus lenses with DOF scales printed on them (or view cameras with scales on the rails) and is incredibly fast to setup in those cases where you have distance scales available.

    The other way is too treat it like any other DOF problem. In that context (keeping infinity and the foreground in focus) if you focus at the point twice the distance of the foreground then infinity and the foreground will have exactly equal blur circles regardless of aperture setting. Then you dial down the aperture to get those blur circles below what you've decided is the acceptable CoC. You can determine that aperture by using a table or by visual inspection (DOF preview, loupe on ground glass, test exposure and zoom, etc. etc.). The practical end result is the same as the hyperfocal technique - foreground and infinity in focus - with the slight but not significant difference that technically this later method keeps the blur circles of the foreground and background the same and is thus slighty more optimal in a completely unpragmatic sense. What is really useful about it is that in a day and age where sadly most lenses omit distance scales you can still quickly set this up. Our visual system is very good at relative measurements - so twice as far as the foreground is usually an easy place to set focus - even with AF on a lens with no distance scale. And if you lack the hyperfocal table you can still quickly visually determine the necessary aperture. The point is even though "hyperfocal distance" changes with aperture the "optimal" focus point for keeping infinity and a foreground in focus is always twice the foreground distance regardless of aperture (see the formula for blur radius).

    In the end, trying to get both the foreground and background below a certain CoC is achieved with either method equally well. One technique works well for some photographers with certain equipment, the other better for others with different equipment. One person's "forwards" is another person's "backwards".

    I don't see why you read so much into it. Try not to be so easliy offended, it is just some optics equations available in hundreds of books and websites. It has nothing to do with ones motivation, artistic merit or any other such thing. No one, especially me, is calling anything like that into question. If I was too snarky in pointing out your CoC definition didn't seem complete to me I'm sorry. My original post contained the basis for what most CoC tables are based in it, you posted something else that seemed incomplete to me and is not the complete basis for what most CoC tables are based on. That was all I was correcting. I'll gently suggest that if I have inadvertently climbed upon some horse I will gladly get down and help you extract whatever bug crawled up your posterior. :)

    Anyway, I suspect the OP's question was answered a long time ago, and really this thread has moved well beyond what is relevant to the "Landscape" forum...

    Ken
  • squirl033squirl033 Registered Users Posts: 1,230 Major grins
    edited December 7, 2009
    kwalsh wrote:
    Actually, what I've seen in print in numerous books in the past few decades is contrary to your definition as they all make it very clear that enlargement size and viewing distance combined with human visual accuity is what sets an acceptable CoC. And you took my quote out of context by chopping off "or improperly excerpted". Clearly, as you illustrated, you know exactly what is relevant to CoC - it just wasn't contained in your quoted (from where?) definition. In any case, sorry if you didn't like my phrasing, I can see it seems inappropriately absolute.


    100% completely and entirely agree with everything except the very last point. The last point, size of the CoC, is very important in certian applications - particularly gigantic enlargements from very high resolution sensors and lenses. Certainly not the type of thing I or most anyone around here shoots...

    I never said you were. I said that there are two completely valid ways to getting a foreground and infinity in focus. One is, set the aperture and focus based on a hyperfocal distance and then shoot. This is excellent for a street shooter. It also works just fine for a landscape shooter as long as you measured the distance to the subject and set the focus properly. People using it every day for years and years. Nothing wrong at all with it. Works wonderfully on manual focus lenses with DOF scales printed on them (or view cameras with scales on the rails) and is incredibly fast to setup in those cases where you have distance scales available.

    The other way is too treat it like any other DOF problem. In that context (keeping infinity and the foreground in focus) if you focus at the point twice the distance of the foreground then infinity and the foreground will have exactly equal blur circles regardless of aperture setting. Then you dial down the aperture to get those blur circles below what you've decided is the acceptable CoC. You can determine that aperture by using a table or by visual inspection (DOF preview, loupe on ground glass, test exposure and zoom, etc. etc.). The practical end result is the same as the hyperfocal technique - foreground and infinity in focus - with the slight but not significant difference that technically this later method keeps the blur circles of the foreground and background the same and is thus slighty more optimal in a completely unpragmatic sense. What is really useful about it is that in a day and age where sadly most lenses omit distance scales you can still quickly set this up. Our visual system is very good at relative measurements - so twice as far as the foreground is an easy place to set focus. And if you lack the hyperfocal table you can still quickly set the aperture without changing focus. The point is even though "hyperfocal distance" changes with aperture the "optimal" focus point for keeping infinity and a foreground in focus is always twice the foreground distance (see the formula for blur radius).

    I don't see why you read so much into it. Try not to be so easliy offended, it is just some optics equations available in hundreds of books and websites. It has nothing to do with ones motivation, artistic merit or any other such thing. No one, especially me, is calling anything like that into question. If I was too snarky in pointing out your CoC definition is not a definition at all then I'm sorry. My original post contained the basis for what most CoC tables are based in it, you posted something else that is in fact incomplete and is not the basis for what most CoC tables are based on. That was all I was correcting. I'll gently suggest that if I have inadvertently climbed upon some horse I will gladly get down and help you extract whatever bug crawled up your posterior. :)

    Anyway, I suspect the OP's question was answered a long time ago, and really this thread has moved well beyond what is relevant to the "Landscape" forum...

    Ken


    missing the DOF scales on lens barrels is rather a peeve of mine as well... i used them all the time back when i shot film. i don't for the life of me understand why - other than saving a buck - the lens makers decided to leave them off.

    my point about hyperfocal calculations was simply that the hyperfocal distance is not determined by the distance to the subject - in fact has nothing to DO with it - and the formula for calculating it produces the same result for any given aperture and focal length, regardless of where the foreground is. the hyperfocal distance for a 50mm lens at f/8 (using .03mm CoC) is about 10 meters, regardless of how far away your foreground is. how you use that information is up to you...

    the idea that focusing at twice the distance of the foreground subject will keep everything in focus is much like the old "sunny 16" rule... useful as a general guideline if you have nothing else to go on. and like most rules of thumb, it will usually produce acceptable results for taking quick shots without thinking about it, but it's not necessarily the best way to go about it if you want the best possible outcome.

    as for my definition of CoC (which is not mine at all, actually), that was a purely pragmatic - as opposed to mathematical - definition based on how the human eye perceives sharpness and clarity. while it does not in and of itself contain the mathematical formulae to calculate CoC, it does express what CoC is from a visual standpoint. the actual CoC depends to no small degree on the size of the sensor and the size of the print, and visual acuity of the viewer, all of which can vary greatly. a lot of people have spent a lot of time figuring out that .018mm is a good all-round number to use for APS-c sensors, and .03mm works well for full-frame sensors. i think i'll go with their numbers.

    and no, i'm not offended. i know what works, and how to use it, and that's all that matters to me.
    ~ Rocky
    "Out where the rivers like to run, I stand alone, and take back something worth remembering..."
    Three Dog Night

    www.northwestnaturalimagery.com
  • kwalshkwalsh Registered Users Posts: 223 Major grins
    edited December 7, 2009
    squirl033 wrote:
    my point about hyperfocal calculations was simply that the hyperfocal distance is not determined by the distance to the subject - in fact has nothing to DO with it
    Agree!
    the idea that focusing at twice the distance of the foreground subject will keep everything in focus is much like the old "sunny 16" rule... useful as a general guideline if you have nothing else to go on. and like most rules of thumb, it will usually produce acceptable results for taking quick shots without thinking about it, but it's not necessarily the best way to go about it if you want the best possible outcome.
    Actually, for the very specific case of keeping infinity (not just any background, but specifically infinity) and a foreground equally in focus (or equally blurred for that matter) twice the foreground distance is exact - not a rule of thumb. But, yeah, like nearly everything in photography if you have to get out rulers and a calculator it probably is at the point of dimishing returns...
    i think i'll go with their numbers.
    Those are the ones I use, but I've seen a number of "peepers" say things like "hyperfocal shooting is just a sure way to get nothing in focus" because they don't understand CoC and how it relates to hyperfocal distances and viewing/enlargement. That's more what I was on about. Like you said, the "standard" numbers have the pragmatic backing of years of use by many photographers.
    and no, i'm not offended. i know what works, and how to use it, and that's all that matters to me.
    Spot on!

    Ken
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