Crop cameras, crop factors, focal length, FOV, DOF and other mysteries and beliefs.

[jgoetz4]

Yes but with a 1.6 crop the 10-22 works out to be just about a 16-35. However for approximately the same price as the 10-22 you can get the 17-40 F4L to cover just about the same range.

Good Morning,
I will pass along what I have read on other forums regarding 'crop factors'.
It's not a true magnification from what I gather, but rather crops off the image. It was best explained to me that an individual is looking at a tree through 2 different windows, one measuring 24" x 36" , and the second measuring 15" x 23". The tree is still the same distance in the second window, just cropped.
Have a good day :D
Jim...

[dmmattix]

Good Morning,
I will pass along what I have read on other forums regarding 'crop factors'.
It's not a true magnification from what I gather, but rather crops off the image. It was best explained to me that an individual is looking at a tree through 2 different windows, one measuring 24" x 36" , and the second measuring 15" x 23". The tree is still the same distance in the second window, just cropped.
Have a good day :D
Jim...

Since my screw up started this...

The crop concept and name came from the concept of cropping in digital editing and before that cropping with the easel while printing in the darkroom. To take your example just a bit differently. If you stood in a spot and had both a 40D and a 5D with a 50mm lens and photographed a tree far enough away to fill the viewfinder of the 5D with both cameras and the same lens. You then print both images uncropped within Photoshop. The tree in the shot from the 5D would fill the picture while the shot from the 40D would not show the entire tree.

I have never tested it but I suspect a teleconverter has a similar effect as does a digital zoom on many point and shoots.

What does not change is the perspective and I do not feel qualified to explain that completely (I am sure someone like Ziggy will).

[jgoetz4]

Since my screw up started this...

The crop concept and name came from the concept of cropping in digital editing and before that cropping with the easel while printing in the darkroom. To take your example just a bit differently. If you stood in a spot and had both a 40D and a 5D with a 50mm lens and photographed a tree far enough away to fill the viewfinder of the 5D with both cameras and the same lens. You then print both images uncropped within Photoshop. The tree in the shot from the 5D would fill the picture while the shot from the 40D would not show the entire tree.

I have never tested it but I suspect a teleconverter has a similar effect as does a digital zoom on many point and shoots.

What does not change is the perspective and I do not feel qualified to explain that completely (I am sure someone like Ziggy will).:
Good Afternoon,
Interesting discussions going on here :thumb
http://www.fredmiranda.com/forum/topic/612465/1#5404848
Just scroll down the page.
Have a good day :D
Jim...

[ziggy53]

Do I take it that people would appreciate an explanation, with examples, of the relationship between "crop factor", Field-of-View/Angle-of-View, focal length, chip sizes, relative magnification and total magnification?

[dmmattix]

Do I take it that people would appreciate an explanation, with examples, of the relationship between "crop factor", Field-of-View/Angle-of-View, focal length, chip sizes, relative magnification and total magnification?

I for one would like to hear the relative vs total magnification differences.
:dunno

[jgoetz4]

Do I take it that people would appreciate an explanation, with examples, of the relationship between "crop factor", Field-of-View/Angle-of-View, focal length, chip sizes, relative magnification and total magnification?

Good Afternoon Ziggy,
That might help to explain things a bit :thumb I've heard arguments both ways that suggest: 1) it's only an FOV equivalent to a 1.6 magnification ( that's how I remember the tree picture being the same distance in both windows, just cropped) or 2) it is a magnification but it cannot equal the same resolution as the true magnification. Physics is involved in one these scenarios :wink Thanks.
Have a good afternoon :D
Jim...

[ziggy53]

OK, I'll build something. Give me a week or so to build an animation and do some comparative examples. I'll propose some definitions and standards which, if I do my job properly, should clarify some things and get us all talking in a similar fashion.

I'll leave a link here, but it will be a new thread somewhere.

[dmmattix]

OK, I'll build something. Give me a week or so to build an animation and do some comparative examples. I'll propose some definitions and standards which, if I do my job properly, should clarify some things and get us all talking in a similar fashion.

I'll leave a link here, but it will be a new thread somewhere.

Excellent and thanks Ziggy.

[ccpickre]

I don't know if it's been mentioned, but wouldn't a used 5D be better for landscape photography? (or did they say widlife specifically)

I would think the nature of the full frame sensor would work better for Landscape/nature.

As for wildlife, I guess the 40D is nice, but if you already have the 20D get a used 5D for nature and landscape.

That's just me though, I am really wanting a 5D now. Got an Xti, and a 40D and now i want more. My dad has started me down a viscious cycle of never ending camera addictions (I already want the XSi and 5D MkII now. Plus a 1DS MkIII. I even have a jonsing for the D300 or D3, whichever is the better one. And don't get me started on lenses)

[NeilL]

Hi ziggy53

Many thanks for your very generous offer.

I'm very much looking forward to coming to grips with these tricky issues - I'm sure I will with your help!

Neil



OK, I'll build something. Give me a week or so to build an animation and do some comparative examples. I'll propose some definitions and standards which, if I do my job properly, should clarify some things and get us all talking in a similar fashion.

I'll leave a link here, but it will be a new thread somewhere.

[jgoetz4]

Morning Folks,
Here's one for the road until Ziggy shows his demonstration :thumb
Have a good day :D
Jim...

http://forums.dpreview.com/forums/readflat.asp?forum=1029&message=26418186&q=1+6x+crop+factor&qf=m
Re: Crop Question NEW
santa (http://forums.dpreview.com/forums/postersprofile.asp?forum=1029&message=26421863) - 1 month ago
This is one of the most widely misunderstood issues with regard to DSLR's. Your understanding is correct. I can't speak authoritatively to the third question, but people who say "my 400mm lens is really a 640 on my camera" just don't get it. As one person pointed out recently, if all it took to turn a 400mm lens into a 2000mm lens was to use a smaller sensor, we'd all have super telephoto cameras with tiny sensors. The only thing the smaller sensor does is record less field of view. You can compare how many pixels are in a 1.6 to how many are in a 1.0 and talk pixel density and such but those are really separate issues. Just keep in mind a 400mm lens is still a 400mm lens on either camera; on a full crop it shows all of the image it sees. On a 1.6 crop, it simply is able to record less of the image on the sensor. Nothing more, nothing less.

[COMPLAINT] (http://forums.dpreview.com/forums/report.asp?forum=1029&message=26421863)
[REPLY] (http://forums.dpreview.com/forums/message.asp?forum=1029&parent=26421863&thread=26418186&quote=0) [QUOTE] (http://forums.dpreview.com/forums/message.asp?forum=1029&parent=26421863&thread=26418186&quote=1)

[kdog]

The only thing the smaller sensor does is record less field of view. You can compare how many pixels are in a 1.6 to how many are in a 1.0 and talk pixel density and such but those are really separate issues. Just keep in mind a 400mm lens is still a 400mm lens on either camera; on a full crop it shows all of the image it sees. On a 1.6 crop, it simply is able to record less of the image on the sensor. Nothing more, nothing less.


Well, that's one way of looking at it. Here's another. By definition, the longer the lens, the narrower the field of view. So by saying "less of the field", that's the same as saying longer focal length. That narrower field is applied to entire sensor resolution. So pixel quality issues aside, isn't that really higher magnification? :dunno

[ccpickre]

Well, that's one way of looking at it. Here's another. By definition, the longer the lens, the narrower the field of view. So by saying "less of the field", that's the same as saying longer focal length. That narrower field is applied to entire sensor resolution. So pixel quality issues aside, isn't that really higher magnification? :dunno
Higher mag at the sacrifice of distance though. I think it's more of an "it imitates" the "xxx" length, it doesn't actually extend to it. A 600 on a full body would still be 600, while a 400 on a crop would still be 400 with the 600 field.

At least that's how I've always pictured it.

[dmmattix]

Higher mag at the sacrifice of distance though. I think it's more of an "it imitates" the "xxx" length, it doesn't actually extend to it. A 600 on a full body would still be 600, while a 400 on a crop would still be 400 with the 600 field.

At least that's how I've always pictured it.

I had been waiting for Ziggy's more detailed explanation but since the topic has opened up again. ..:rolleyes

The only thing I had a problem with in Jim's original description was the 'magnification' statement. I believe the crop deal works for the picture like the Teleconverters do. The crop sensor only covers a portion of the image circle provided by full frame lense hence the name 'crop'. The TC works like a magnifying glass to make that image circle bigger and the sensor covers less of it hence cropping also. I am sure someone will correct me if I am wrong (like that has never happened) on the TC issue but from when I used one on a Pentax Spotmatic that was the way it worked.

What I am hoping Ziggy's explanation will cover is more the perspective and depth of field issues that neither the TC or the crop sensor impact. In that sense a 300mm lens is still a 300mm lens.

Regards,

[jgoetz4]

I had been waiting for Ziggy's more detailed explanation but since the topic has opened up again. ..:rolleyes

The only thing I had a problem with in Jim's original description was the 'magnification' statement. I believe the crop deal works for the picture like the Teleconverters do. The crop sensor only covers a portion of the image circle provided by full frame lense hence the name 'crop'. The TC works like a magnifying glass to make that image circle bigger and the sensor covers less of it hence cropping also. I am sure someone will correct me if I am wrong (like that has never happened) on the TC issue but from when I used one on a Pentax Spotmatic that was the way it worked.

What I am hoping Ziggy's explanation will cover is more the perspective and depth of field issues that neither the TC or the crop sensor impact. In that sense a 300mm lens is still a 300mm lens.

Regards,
Good Afternoon,
While you are waiting for Ziggys examples and explanations concerning this issue, why not visit the above link to dpreview.com and do some research yourself. That's why I posted it.
Have a good day :D
Jim...

[kdog]

Good Afternoon,
While you are waiting for Ziggys examples and explanations concerning this issue, why not visit the above link to dpreview.com and do some research yourself. That's why I posted it.
Have a good day :D
Jim...

Reading an anonymous person's opinion posted on the internet doesn't exactly qualify as research.

Cheers,
-joel

[dmmattix]

Good Afternoon,
While you are waiting for Ziggys examples and explanations concerning this issue, why not visit the above link to dpreview.com and do some research yourself. That's why I posted it.
Have a good day :D
Jim...

I actually HAVE read it. It actually agrees with my magnification point. The real issue they were discussing was the quality that comes from that magnification (specifically the blur). From the shots that we see around here shot with 10D/20D/30D/40D/Digital Rebel/D100/D200/etc I believe the blur issue is pretty well contained. Again we have the same issues when we put 1.4TC's on telephotos, shoot with crop cameras, well hopefully you get my drift.

I don't like religious discussions because both sides claim they win and nothing ever gets resolved so I will be awaiting Ziggy's presentation and use it to hopefully improve my knowledge.

Regards,

[kdog]

I actually HAVE read it. It actually agrees with my magnification point. The real issue they were discussing was the quality that comes from that magnification (specifically the blur). From the shots that we see around here shot with 10D/20D/30D/40D/Digital Rebel/D100/D200/etc I believe the blur issue is pretty well contained.

What blur issue? Are you saying that pictures taken with telephoto lenses on crop sensor cameras are any less sharp than those taken with a full frame camera? :huh

[jgoetz4]

What blur issue? Are you saying that pictures taken with telephoto lenses on crop sensor cameras are any less sharp than those taken with a full frame camera? :huh

I think he means bokeh. The out of focus areas.
Have a good day :D
Jim...

[jgoetz4]

I actually HAVE read it. It actually agrees with my magnification point. The real issue they were discussing was the quality that comes from that magnification (specifically the blur). From the shots that we see around here shot with 10D/20D/30D/40D/Digital Rebel/D100/D200/etc I believe the blur issue is pretty well contained. Again we have the same issues when we put 1.4TC's on telephotos, shoot with crop cameras, well hopefully you get my drift.

By adding a tc, you magnify the image with optics, not just a crop.

I don't like religious discussions because both sides claim they win and nothing ever gets resolved so I will be awaiting Ziggy's presentation and use it to hopefully improve my knowledge.

I don't believe religion has anything to do with it :wink I have
seen examples and heard arguments both ways and I believe that the magnification is 'interpolated' with the DOF of a 1.6x lens. It sounds like you will take Ziggy's word as Gospel when he shows his examples. Oh, wait a minute, maybe this does have something to do with religion :rofl
Have a good day :D
Jim...
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[ziggy53]

I created a new thread for this discussion because we pretty well trashed the previous thread. :D

Please continue the discussion here but remember to keep it on topic and civil.

[jgoetz4]

I created a new thread for this discussion because we pretty well trashed the previous thread. :D

Please continue the discussion here but remember to keep it on topic and civil.

Good Afternoon Ziggy,
You know we are all civil :barb Just trying to show links to both sides of the issue and let the members judge for themselves. There were some really heated, name calling debates last year over at dpreview.com. That's not called for on any level. After all, we are here to help, learn and share :thumb
Have a good day :D
Jim...

[jgoetz4]

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Quote:
Originally Posted by jgoetz4
Good Afternoon,
While you are waiting for Ziggys examples and explanations concerning this issue, why not visit the above link to dpreview.com and do some research yourself. That's why I posted it.
Have a good day :D
Jim...


Reading an anonymous person's opinion posted on the internet doesn't exactly qualify as research.

No it doesn't, but the internet itself is an excellent place to start, and dpreview.com is an excellent place to start with.
Have a good day :D
Jim...
Cheers,
-joel
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[claudermilk]

I suspect part of the issue with suggesting using DPR is, while I'm sure there are a number of knowledgeable users there, it's generally considered a toll den and better avoided by those wishing to carry on meaningful discussions.

My understanding of the whole crop thing is it isn't true magnification. You are just cropping out the center of the image circle, which give the same FOV of a longer lens and the impression of magnification. So on a 1.6 crop sensor a 50mm lens gives approximately the same FOV of an 85mm lens. The perspective stays the same since you have not moved. Bokeh will be different & DOF will be different. But it's still an image projected by a 50mm lens. In the end, I don't worry too much about it, I just put the lens that I know will give me the framing I want on the camera and shoot the image I am after (or at least try...).

[jgoetz4]

I suspect part of the issue with suggesting using DPR is, while I'm sure there are a number of knowledgeable users there, it's generally considered a toll den and better avoided by those wishing to carry on meaningful discussions.

My understanding of the whole crop thing is it isn't true magnification. You are just cropping out the center of the image circle, which give the same FOV of a longer lens and the impression of magnification. So on a 1.6 crop sensor a 50mm lens gives approximately the same FOV of an 85mm lens. The perspective stays the same since you have not moved. Bokeh will be different & DOF will be different. But it's still an image projected by a 50mm lens. In the end, I don't worry too much about it, I just put the lens that I know will give me the framing I want on the camera and shoot the image I am after (or at least try...).
Good Morning Chris,
This is taken from Wikipedia
Digital Photography Review
From Wikipedia, the free encyclopedia
(Redirected from Dpreview.com)

Digital Photography Review (established November 1998) is a website about digital cameras and digital photography. The website has reviews of digital cameras, buying guides, user reviews, and very active forums for the individual cameras as well as general photography forums. The website has a large database with information about the individual digital cameras.

www.dpreview.com is one of the top 1000 most visited websites on the Internet, according to Alexa Internet[1]. The website itself claims that "These days the site is one of, if not the, premium digital photography site with an audience of seven million unique visitors a month reading over one hundred million pages"[2].
I guess with that many monthly visitors, there are bound to be a few trolls along with thousands of 'knowledgeable users' :wink
Have a good day :D
Jim...

[kdog]

My understanding of the whole crop thing is it isn't true magnification. You are just cropping out the center of the image circle, which give the same FOV of a longer lens and the impression of magnification. So on a 1.6 crop sensor a 50mm lens gives approximately the same FOV of an 85mm lens. The perspective stays the same since you have not moved. Bokeh will be different & DOF will be different. But it's still an image projected by a 50mm lens. In the end, I don't worry too much about it, I just put the lens that I know will give me the framing I want on the camera and shoot the image I am after (or at least try...).

This is basically what several folks above said as well. What it overlooks is the fact that this reduced FOV is projected over the entire sensor, giving you a higher pixel density. Pixel density is very important because it's what gives you detail in the shot. In order to get the same pixel density as the crop body camera in its reduced FOV, you'd have to compare it to a full frame camera with crop-factor times more pixels. So in the case of the Canon 40D, you'd have to compare it to a 16.1 MP full frame camera. In that case, you could truly crop the image from the full-frame and end up with the same magnification as the crop-body for the same FOV. The only camera that fits that bill is the Canon Mark 3 1DS. For all other cameras in the Canon line, the 40D gives the most magnification, given equal lenses, at equal levels of detail.

[KED]

Do I take it that people would appreciate an explanation, with examples, of the relationship between "crop factor", Field-of-View/Angle-of-View, focal length, chip sizes, relative magnification and total magnification?
Would you do some kind of "top of the forum" announcement when it's ready? This is one weird thread (no offense to anyone intended), and I'd prefer to wait for your authoritative explanation.

[jthomas]

This is a very simple concept, and I don't understand why people have so much trouble with it. I think they try to make it harder than it is.

Please consider the diagram below. Circle "A" is the image circle thrown on the plane of the sensor by a standard lens.

Rectangle "B" represents the "full-frame" sensor of a few currently available DSLR's (Canon 5D, Nikon D3, etc.) which is very close to the size of the sensitive region of a frame of 35mm film.

Rectangle "C" represents the size of the sensor of most DSLRs (Canon 30D, Nikon D200, etc.).

Obviously "C" will record only the center of the image, and will give the same effect as using a lens with a longer focal length.

That's all there is to it (if both sensors have the same number of pixels).

http://fish-n-float.smugmug.com/photos/259971898_gkCHJ-L.jpg

[kdog]

Obviously "C" will record only the center of the image, and will give the same effect as using a lens with a longer focal length.

That's all there is to it (if both sensors have the same number of pixels).

Bingo. That's exactly what I was trying to say, although you said it more concisely. :D

[NeilL]

This is basically what several folks above said as well. What it overlooks is the fact that this reduced FOV is projected over the entire sensor, giving you a higher pixel density. Pixel density is very important because it's what gives you detail in the shot. In order to get the same pixel density as the crop body camera in its reduced FOV, you'd have to compare it to a full frame camera with crop-factor times more pixels. So in the case of the Canon 40D, you'd have to compare it to a 16.1 MP full frame camera. In that case, you could truly crop the image from the full-frame and end up with the same magnification as the crop-body for the same FOV. The only camera that fits that bill is the Canon Mark 3 1DS. For all other cameras in the Canon line, the 40D gives the most magnification, given equal lenses, at equal levels of detail.

Good post. Thanks.

[jgoetz4]

Morning Folks :thumb
The following link provides a very good in depth look at these issues. Make a pot of coffee, turn off your cell phones and prepare to spend some time reading this article. It is a bit lengthy, but very detailed.
Have a good day :D
Jim...
http://www.digitaldingus.com/articles/fov/fovef.php (http://www.digitaldingus.com/articles/fov/fovef.php)

[cmason]

jthomas, I thought your picture most helpful, and took the liberty to alter it slightly for what I think adds to the understanding...please forgive my liberties with your image, as well as my own crude adoption:

An image on a full frame will be seen as this:

http://digitalmason.smugmug.com/photos/260145477_WvFxf-M.jpg


While on a crop camera, though the lens is not providing more magnification, the effect is similar. In order to get the subject in the full view of the crop camera, one needs to widen the view. Thus the same lens, on each camera, captures a different field of view, requiring a wide lens on the crop camera for the same view. Likewise, this has the opposite 'benefit' when using a zoom lens, as the crop camera offers more 'zoom' if you will:

http://digitalmason.smugmug.com/photos/260145484_fnh2j-M.jpg

forgive the artwork here, I had only powerpoint at my disposal...blame it on the tool, not the artist LOL

[jgoetz4]

jthomas, I thought your picture most helpful, and took the liberty to alter it slightly for what I think adds to the understanding...please forgive my liberties with your image, as well as my own crude adoption:

An image on a full frame will be seen as this:

http://digitalmason.smugmug.com/photos/260145477_WvFxf-M.jpg


While on a crop camera, though the lens is not providing more magnification, the effect is similar. In order to get the subject in the full view of the crop camera, one needs to widen the view. Thus the same lens, on each camera, captures a different field of view, requiring a wide lens on the crop camera for the same view. Likewise, this has the opposite 'benefit' when using a zoom lens, as the crop camera offers more 'zoom' if you will:

http://digitalmason.smugmug.com/photos/260145484_fnh2j-M.jpg

forgive the artwork here, I had only powerpoint at my disposal...blame it on the tool, not the artist LOL

Good Morning :thumb
Kinda like viewing a tree side by side through 2 different windows. One measures 36" x 24" and the second measures 24" x 15". The tree is still the same size and distance in both windows, however, the view through the second window is showing only part of the tree.
Have a good day :D
Jim...

[kdog]

Good Morning :thumb
Kinda like viewing a tree side by side through 2 different windows. One measures 36" x 24" and the second measures 24" x 15". The tree is still the same size and distance in both windows, however, the view through the second window is showing only part of the tree.
Have a good day :D
Jim...

You may be viewing a smaller portion of the tree, but you are viewing it at greater magnification. That article that you referenced in your previous post describes it here:

"The D100 has a 1.5x FOV Crop. What does this mean? Well, it means any 35mm lens you put on your D100, will automatically magnify your image by 1.5. Looking at it another way, it also means you add 50% more focal length or "zoom power". The smaller the CCD in relation to film, the larger the magnification ratio. Again, why? Since the CCD is smaller than the 35mm film size, the image is magnified automatically, because a 35mm lens that is being put on it, has a much larger image circle. "

Magnify

Cheers,
-joel

[evoryware]

save us ziggy! :rofl

[k2c1959]

save us ziggy! :rofl

LOL, NO KIDDING
not rocket science..:scratch :rofl

[jgoetz4]

You may be viewing a smaller portion of the tree, but you are viewing it at greater magnification. That article that you referenced in your previous post describes it here:

"The D100 has a 1.5x FOV Crop. What does this mean? Well, it means any 35mm lens you put on your D100, will automatically magnify your image by 1.5. Looking at it another way, it also means you add 50% more focal length or "zoom power". The smaller the CCD in relation to film, the larger the magnification ratio. Again, why? Since the CCD is smaller than the 35mm film size, the image is magnified automatically, because a 35mm lens that is being put on it, has a much larger image circle. "

Magnify

Cheers,
-joel

Good Morning :thumb
So then basically, the smaller the sensor the more magnification ? If using the Geometry that was mentioned in the article to obtain the x factor, you could theoretically design a small enough sensor to have an equivalent of say 2000mm using an 500mm lens ? That would mean a 4x crop as compared to a 1.6 crop on most cameras today. Is that a correct statement ?
Have a good day :D
Jim...

[kdog]

Good Morning :thumb
So then basically, the smaller the sensor the more magnification ? If using the Geometry that was mentioned in the article to obtain the x factor, you could theoretically design a small enough sensor to have an equivalent of say 2000mm using an 500mm lens ? That would mean a 4x crop as compared to a 1.6 crop on most cameras today. Is that a correct statement ?
Have a good day :D
Jim...

Yup. The only catch is that sensors with higher pixel densities tend not to produce the same image quality as sensors with bigger pixels. By quality, I'm talking more in terms of color tones and maybe noise, as opposed to sharpness. Sharpness to me is dictated by focus and pixel density, both of which you can get with a dense sensor. But there is a point of diminishing returns by using a smaller sensor.

[jgoetz4]

Good Afternoon :thumb
Very Interesting. The text below was taken from another web site where trolls are known to roam :rofl
Have a good afternoon :D
Jim...

John down under (http://forums.dpreview.com/forums/postersprofile.asp?forum=1002&message=26729092) - 2 weeks ago
Myth: Higher crop factor camera (smaller image sensor) means greater magnification for the same focal length lens.
Reason: Magnification has a specific meaning in photography. It means the size (eg in mm) of the subject projected onto the image sensor plane (or film plane) compared to the actual size of the subject itself (eg in mm). The size of the sensor is irrelevant as it doesn't affect the size of the projection. 1:1 magnification (true macro) means that an object that is x mm wide will be projected at a size of the same x mm at the sensor plane. The crop factor of the camera will then determine how much of the sensor/frame is filled by that subject.
In practical terms: All that aside, using a lens of the same FL at the same distance from the subject with a more cropped camera will result in the subject filling more of the captured frame. It's common to state what FL lens would be needed on a FF camera to provide the same framing from the same shooting distance as the lens in question on the cropped body. The issue of magnification is only one of terminology.

Myth: f-stop is the same as aperture.

Reason: The aperture is the size (diameter) of the iris/opening between the aperture blades that lets light through the lens. f-stop or f/ratio is a ratio between the focal length of the lens and the size of the aperture.
In practical terms: f-stop is easy to set and know, whereas aperture has to be calculated, so aperture isn't generally used. However, image sensor pixel density aside, depth of field is largely determined by focus distance and aperture (not f-stop). Larger focus distance mens larger DOF. Larger aperture means smaller DOF. For a given FL, increasing the f-stop reduces the aperture size and increases DOF. Likewise, for a given f-stop, increasing FL increases the size of the aperture and decreases DOF. In both cases, the same focus distance is assumed.

Myth: When shooting from the same position, changing the lens FL or changing the camera crop factor change the image perspective.
Reason: Perspective is the relationship between the elements of the image, not how the image is framed. When shooting from the same spot, the elements of the image are exactly the same with respect to each other as each path from the lens to any part of the scene can't change.
In practical terms: A longer lens from the same position won't foreshorten the perspective when compared with using a wider angle lens on a cropped body from the same position. If the f-stop isn't changed, DOF will change, with the longer lens resulting in a shallower DOF. However, the relative sizes of elements in the scene won't change, even if the framing of the scene changes from this same position because the difference in FL doesn't match the change in crop size. Paths of light from the parts of the scene to the camera can't alter when shooting from the same position and change perspective.

Myth: More cropped cameras with the same subject framing don't provide greater DOF for the same f-stop.
Reason: To keep the subject framing the same while changing the camera crop size, you either change the FL while keeping the camera in the same place, or move the camera while keeping the lens FL the same. Keeping the camera in the same place not only retains subject framing, but also retains the perspective in the scene. The shorter FL you need on the more cropped camera for the same framing as the longer lens on the les cropped camera means that for a constant f-stop, the longer lens has a larger aperture, meaning a shallower DOF on the less cropped body. If the same FL lens is used and subject framing is retained by backing up with the more cropped body (which also changes the perspective), the increased focus distance means a greater DOF for the more cropped body.
In practical terms: It's important to specify f-stop and framing (and to some extent perspective) conditions when stating whether DOF is different for different crop cameras.
--
Cheers from John from Adelaide, South Australia
John Harvey Photography http://johnharvey.com.au (http://johnharvey.com.au/)
Canon 40D, Canon 20D & Fuji F10

[dmmattix]

Yup. The only catch is that sensors with higher pixel densities tend not to produce the same image quality as sensors with bigger pixels. By quality, I'm talking more in terms of color tones and maybe noise, as opposed to sharpness. Sharpness to me is dictated by focus and pixel density, both of which you can get with a dense sensor. But there is a point of diminishing returns by using a smaller sensor.

From what I have read it is actually the noise which is manifested in the bleeding of color data between ajacent pixels. They (Nikon/Canon) have gotten better with it as witnessed by the progression from the D30(3 MegaPixel) to 450D (12 MegaPixel) sensors on the same sensor real estate but there exists probably a limit to how far they can go.

[ziggy53]

Rather than try to agree with any particular group, I will attempt to explain several different understandings and misunderstandings, and define terminology (some new) to which I will ask the reader to accept for the sake of the explanation.

Once we start talking in common terms, I think everything will fall into place. The key will be the understanding and acceptance of the terms, especially as they are used in the context of the discussion.

I will be showing examples* to actually demonstrate the principles involved. Rather than try to convince anyone that there is a single way to look at these issues, I will try to explain why differing views exist. The point of my discussion will be that of understanding relationships and the reader will be allowed to draw their own conclusions.

(*The examples will include photographs, illustrations and simple mathematics. All should be fairly simple for people to prove and duplicate for themselves, if necessary.)

[Martyn]

jthomas, I thought your picture most helpful, and took the liberty to alter it slightly for what I think adds to the understanding...please forgive my liberties with your image, as well as my own crude adoption:

An image on a full frame will be seen as this:

http://digitalmason.smugmug.com/photos/260145477_WvFxf-M.jpg


While on a crop camera, though the lens is not providing more magnification, the effect is similar. In order to get the subject in the full view of the crop camera, one needs to widen the view. Thus the same lens, on each camera, captures a different field of view, requiring a wide lens on the crop camera for the same view. Likewise, this has the opposite 'benefit' when using a zoom lens, as the crop camera offers more 'zoom' if you will:

http://digitalmason.smugmug.com/photos/260145484_fnh2j-M.jpg

forgive the artwork here, I had only powerpoint at my disposal...blame it on the tool, not the artist LOL


WOW, Image C is like most of my pics.
If I get a full frame camera will it stop all the heads being cutoff in all my photos?

[cmason]

WOW, Image C is like most of my pics.
If I get a full frame camera will it stop all the heads being cutoff in all my photos?

you bet..but you have to first sign the secret agreement NOT to push the 'world peace' button on the back of that new camera...if everyone pushed that...well it would put all those war press photogs out of business you know.

[jww]

WOW, Image C is like most of my pics.
If I get a full frame camera will it stop all the heads being cutoff in all my photos?

LOL!

...possibly, but it might be cheaper to have them all duck a bit. :wink

[ulrikft]

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

This is an interesting article

[jthomas]

Morning Folks :thumb
The following link provides a very good in depth look at these issues. Make a pot of coffee, turn off your cell phones and prepare to spend some time reading this article. It is a bit lengthy, but very detailed.
Have a good day :D
Jim...
http://www.digitaldingus.com/articles/fov/fovef.php (http://www.digitaldingus.com/articles/fov/fovef.php)
Well, I see that this author has several diagrams similar to mine, but his explanation is much longer. He seems to subscribe to the old principle "never say in ten words what you can say in 100".

Seriously, though, he does discuss more aspects of the problem than I did in my brief post. In my view, he also overcomplicates it.

[ziggy53]

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

This is an interesting article

Ulrik,

Yes, that is an excellent article and I will reference it as one of my sources for my discussion.

[jgoetz4]

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm

This is an interesting article

Good Morning,
Yes that is a very interesting article. Perhaps a more appropriate name would be a 1.5x or 1.6x DOF crop :thumb
Have a good day :D
Jim...

[jgoetz4]

Well, I see that this author has several diagrams similar to mine, but his explanation is much longer. He seems to subscribe to the old principle "never say in ten words what you can say in 100".

Seriously, though, he does discuss more aspects of the problem than I did in my brief post. In my view, he also overcomplicates it.

Good Afternoon :D
The diagrams are similiar to yours, mine, and countless others as well, & the longer, detailed explanation may be necessary to some people that still had questions about that issue :thumb

Have a good afternoon :smile6
Jim...