How to do AF Microadjustment (50D)

[Scott_Quier]

You have this beautiful camera (the 50D) and a host of lenses. But, you mount a lens and take a picture. And you're a pixel-peeper (like me) and the image doesn't have that stellar sharpness you were hoping for. What do you do?

In the past is was the whole send the lens in for calibration, get it back, still not sharp, complain, "Oh, you need to send in the lens and the camera" ....

Not any more. You can do it all by and for yourself. And you can do it without doing anything dangerous to you camera - none of that "clean the sensor trauma."

The following are the steps I've arrived at to get the job done in the quickest time possible. I've had to develop this because the routine found here didn't work for me. I used it to attempt to dial in a 50mm f/1.4 and the result was a serverly front-focusing lens - not a goodness.

Note: In these images, the focus point is on the center of the nearly healed over know near the center of the crops.

The steps:

1. Mount your lens.
2. Set your camera to Av mode, RAW only, and set the aperture to the maximum provided by your lens. I suggest RAW as this avoids all the processing (sharpening, in particular) the camera will do when generating JPGs.
3. Find a subject that has a variable distance from you camera - I use a tree trunk in my back yard. I focus on a spot on the trunk of the tree about half way between the "front surface" (from my perspective) of the trunk and the very edge. Doing this allows me to compare where on the trunk of the tree the camera/lens is actually focusing with where I had intended it to focus. When these two points coincide, I know I have achieved a proper adjustment. Working with only a flat, square on surface can only tell you that you have (or don't have) focus.
4. Determine the "usual" distance from you subject you use your lens and setup your tripod that distance from your target.
5. Find out how to set the AF Microadjustment - it's on page 180 (and following) of your instruction manual. Since it's already written up for you, I shan't repeat it here. Be sure to use the "Adjust by lens" option.
6. Set the adjustment value to -20. Take a shot. Repeat these steps for adjustment values -15, -10, -5, 0, 5, 10, 15, and 20. Nine images in all.
7. Download all 9 of these images to your computer.
8. Using ACR:
   • Load all the images
   • Select them all
   • Turn off the sharpening
   • Zoom to 100%
   • Using the cropping tool, select most of the image (roughly 98% of what is displayed)
   • Save these crops to "high" resolution jpgs. I had nine of them. In terms of sharpest focus (which was on that vertical cut in the center of the images), these are the best 3 (let's assume them to be -10, -5, 0):
     Front focused:
     
     
     Just about there
     
     and, back-focused
     
9. I then use the Windows Picture and Fax viewer (that's why the conversion to JPG) and cycle through them quickly to find the one that is sharpest at the point of focus.
10. Determine which AF Microadjustment factor was used for that image (it's a counting game, the first one is -20, the second is -15, etc - not exactly rocket science).
11. Insert your CF card back into the camera (you are using a CF card reader, right - it's just easier to do so) and format the card.
12. Using the value determined in step 10, count backwards 3 and set your AF Microadjustment value. For example, say your sharpest was -5, set your AF Microadjustment value to -8.
13. Remount your camera on the tripod and take a series of 7 more images, this time stepping the AF Microadjustment value by only 1.
14. Repeat steps 8 through 10 to determine the "optimal" AF Microadjustment value. These are the single step images I got:
    • -8
      
      
      
    • -7
      
      
      
    • -6
      
      
      
    • -5
      
      
      
    • -4
      
      
      
    • -3
      
      
      
    • -2
      
15. As you can see, the focus is moving further and further from the camera as you step through the images, the sharpest one being (to my eyes at least) -3. Set your AF Microadjustment according to your results.
16. Grab your next lens and repeat steps 1 through 15

As a final note, something that has taken me a while to wrap my head around. Setting the AF Microadjustment value more "Forward" moves your focus point closer to the camera and "Backward" moves the focus point further from the camera. So, if the ground in front of your model is sharp and the model isn't, you will need to dial in more positive values, moving the pointer in the "Backward" direction. Think "Pull Forward, Push Back".

[jeffreaux2]

Okay Scott....You are the man!!!

Im sure I will have questions....but this will be a tremendous help.

Thanks!


Say, one question I do have....

I fully understand calibrating it at a distance you normally use the lens for.....I follow that line of thinking perfectly. I am just curious how well the lens performs after the fact over a wide range of distances. Acceptable?

[Shootin1st]

Great info and a perfect example of what to use!

[Scott_Quier]

Originally Posted by jeffreaux2

Okay Scott....You are the man!!!

Im sure I will have questions....but this will be a tremendous help.

Thanks!


Say, one question I do have....

I fully understand calibrating it at a distance you normally use the lens for.....I follow that line of thinking perfectly. I am just curious how well the lens performs after the fact over a wide range of distances. Acceptable?

Ahhhh I don't know if you me or are just because you think it'll get you what you want

But, to answer your question - I'll probably have an opportunity to find out tomorrow - it's dark out right now. I suspect that it'll all be good given the margin of error we've all been having to deal with all along. How's about you do the test as well as me and we can compare notes? There's an idea

What was interesting is that my 17-55 was off 3, my 70-200 f/2.8 IS was off zero (0), and my 24-105 f/4 was off 8 (all front-focusing) and the offset for each lens was the same on both cameras. That would seem lend credibility to the concept that a lens might need to be calibrated.

[Scott_Quier]

Originally Posted by Shootin1st

Great info and a perfect example of what to use!

Glad you liked the information. I hope you find it useful. I selected a tree trunk because I have a few in the backyard, there was ample light, and because it provided a high-contrast target to make the focusing as accurate as possible each time since this was not an attempt to test the focusing system but to calibrate/adjust it.

[Scott_Quier]

Originally Posted by jeffreaux2

I fully understand calibrating it at a distance you normally use the lens for.....I follow that line of thinking perfectly. I am just curious how well the lens performs after the fact over a wide range of distances. Acceptable?

Yes, quite acceptable!

Here are some 100% crops (800px x 800px) All photos are SOOC - no sharpening, WB correction, contrast ... nothing.

These are 17mm, 33mm, and 55mm (all at f/2.8) taken from about 5 feet from the subject - which is about 1/2 of the shortest distance I would normally be using this lens.


These are 17mm, 35mm, and 55mm (again, all at f/2.8) taken from about 45 feet (effectively infinity focus). The 17mm crop appears to be a bit soft - I think it's because I wasn't taking the time to do this right. I noticed the same thing with the 35mm shot and went out to re-do it (which accounts for the different WB - I didn't correct for WB in any of these shots) becuase I wasn't happy with it (it back-focused pretty bad). The second time around it worked well. So, I think the 17mm shot here is also pilot error.


The entire gallery with all the original sized images can be viewed here

[jeffreaux2]

Okay, I gave it a shot.

First go 'round with 17-55mm which, by the way, was my sharpest lens on my XTi.

1- adjustment at zero.



+5


+10



Then the fine tuning...settled on this a plus 4 ( a different crop, but this is 100% not the previous 3)




Then 85mm F1.8

zero


plus 5


plus10


Fine tune at +6




I hope to pick up where I left off with the 70-200 tommorrow. If I have better light tommorrow I may do a double check on these against tree bark like you did.

[Scott_Quier]

A couple of notes on what I see.

• 17-55, I think you did well here (I say that like I'm some sort of expert). Your selected adjustment appears to be sharper than the "intemediate" (0, 5, 10) shots.
• 85mm - it appears you didn't do such a good job with this one. To my eyes, you "0" shot is sharpest of all those presented.
• There are at least 2 reasons to use a tree rather than a flat sign:
  1. Lots of contrast without the huge contrast you have in your sign - may lead to less CA and, thus, less confusion.
  2. Shooting a landmark on the appearant edge of the tree trunk allows you to judge not only the focus, but also whether the adjustment is front or back focusing. That little bit of information helped me a lot in dialing in the "proper" adjustment.

[jeffreaux2]

Originally Posted by Scott_Quier

A couple of notes on what I see.

• 17-55, I think you did well here (I say that like I'm some sort of expert). Your selected adjustment appears to be sharper than the "intemediate" (0, 5, 10) shots.
• 85mm - it appears you didn't do such a good job with this one. To my eyes, you "0" shot is sharpest of all those presented.
• There are at least 2 reasons to use a tree rather than a flat sign:
  1. Lots of contrast without the huge contrast you have in your sign - may lead to less CA and, thus, less confusion.
  2. Shooting a landmark on the appearant edge of the tree trunk allows you to judge not only the focus, but also whether the adjustment is front or back focusing. That little bit of information helped me a lot in dialing in the "proper" adjustment.

Good points. The CA was very distracting. Ill give it another shot. What distance and focal length did you use on the 17-55? 70-200?

[Scott_Quier]

Originally Posted by jeffreaux2

Good points. The CA was very distracting. Ill give it another shot. What distance and focal length did you use on the 17-55? 70-200?

Working from memory (gotta remember that as you age memory is the second thing to go and I don't remember the first), for the 17-55, I think the distance was right about 10' to 15' and the 70-200 was a about 30'.

Oh, and I used 55mm on the 17-55 and 135mm focal length on the 70-200. Don't ask why for the 17-55 (I may have to revisit that), but the 135 was an attempt at an "average" use focal length for that lens.

[jeffreaux2]

Well, I rechecked the 17-55 and the 85. Practical use will tell me whether it needs to be revisited. I also worked on the 70-200.

Here is what I got.....

This is zero on the 85mm....that was in question on the previous posts. Quite soft.


This is where I set it...plus 5. It was hard to make a call between 5 and 6 (my previous setting)




That final plus 5 setting is a 100% crop from this photo.


The 17-55 plus 4 confirmed.


The original frame for the plus three on the 17-55 shot above.



And finally the 70-200. This surprised me some. It was a tad softer than the 17-55 on my XTi. I had all along just taken it as user error....however zero in it was quite soft. I ended up keeping it at plus 6. This is the plus 6 100%crop.


and the image it was cropped from



As I said time...and practical use will tell whether I have achieved anything good, but I think an important point is that Canon has given us an excellent tool. There is quite a bit of difference from one end of the scale to the other....quite a bit of room there for adjustment rather than sending the lenses in for service. Worse case scenario....I set them all back to zero and give it another try!


Thanks Scott. Its a good method. I have a sports shooting friend coming over Wednesday and we are going to dial his glass in as well!

[Scott_Quier]

The full-sized images look very sharp.

The crops ... not having seen all the crops .... it's hard to tell. An improvement in your technique might be, in the first full-sized image, to focus on the left-edge of the lichen just to the left and below the 100% crop rectangle. This would greatly improve one's abilty to determine exactly the position of the plane of focus. This helped me to take the guess work out of my example in post #1.

Like you say, it's the real-life photographs that are going to tell the whole story.

[KED]

Originally Posted by Scott_Quier

You have this beautiful camera (the 50D) and a host of lenses. But, you mount a lens and take a picture. And you're a pixel-peeper (like me) and the image doesn't have that stellar sharpness you were hoping for. What do you do?

I have a 1d Mk III that also allows for AF microadjustment, and I came across a thread here for a reasonably affordable product that's meant to make the process even more precise, particularly if one lacks such a photogenic tree in the back yard. The link is www.rawworkflow.com; mine shipped today and I should have it later this week. I am NOT endorsing it as an alternative to your method (not yet anyway), but it was glowingly endorsed by sources whose opinions matter to me (Luminous Landscape for one) so I am optimistic.

Apparently this device can also be rented, which I learned after placing my order; that's probably worth considering.

[Scott_Quier]

Originally Posted by KED

I have a 1d Mk III that also allows for AF microadjustment, and I came across a thread here for a reasonably affordable product that's meant to make the process even more precise, particularly if one lacks such a photogenic tree in the back yard. The link is www.rawworkflow.com; mine shipped today and I should have it later this week. I am NOT endorsing it as an alternative to your method (not yet anyway), but it was glowingly endorsed by sources whose opinions matter to me (Luminous Landscape for one) so I am optimistic.

Apparently this device can also be rented, which I learned after placing my order; that's probably worth considering.

Yup - at either $80 or $140. Hmmmm .... not to throw cold water on this product, but I think I'll take the tree or any other textured surface I can find.

[jeffreaux2]

Well heres something I know nothing about....bird photography!!! But it does fortify one thing.....

Taken with the 70-200 after going through the micro-adjust per this thread.




That shot was taken at 200mm with the 70-200....F2.8....ISO400....1/250th. After I finished my tests, I went out back to get the camera and tripod picked up and there were several of these guys eating in the bird feeder. Anyway, it is a 100% crop taken from the image below.....


Now theres some practical useage.....of course one shot proves little....but still....

[Scott_Quier]

Originally Posted by jeffreaux2

Taken with the 70-200 after going through the micro-adjust per this thread.



Now theres some practical useage.....of course one shot proves little....but still....

I think it proves that you got a very, very well focused photograph of a Cardinal

[jeffreaux2]

Well I have a few more shots....the last I intend to post here...I promise....but bare with me.


I admittedly also know zero about floral photography, and am not really trying to learn, but I shot these thinking it might be a good practical test. Each of these was taken at very near the close focus distance of each lens and at its widest aperture. My thinking was that this would represent the thinnest DOF I might encounter and that if I were having front...or back focus issues that might be related to my tinkering it would be apparent at these settings. It was quite windy, so I kept ISO high enough to freeze things....but this of course varied from glass to glass. These have had some pp done on them that included some sharpening. Nothing crazy, but just a bit of what I normally do with images anyway. These are not cropped however, but rather websized copies of the original frames.

1- Canon 85mm F1.8- I have never been treated to the sharpness I have seen this lens produce for other folks. This looks promising though.


2-The 17-55 F2.8IS. This was previously my sharpest lens and looks to be sharp on the 50D as well.


3-Lastly the 70-200 F2.8L IS Nice!

[Scott_Quier]

Yes! That 85mm f/1.8 is looking very promising! It will be interesting to see what you get when you shoot "real" photos.

[jrnylst]

Wow. This has been eye-opening. I just returned a rental zoom lens yesterday that I was very disappointed with because I couldn't get the sharpness out of it on autofocus that I can get from my fixed telephoto lens. I wound up manually focussing it most of the final week of the rental. I thought the quality of a zoom lens vs. a fixed lens was the problem. Maybe I needed to go through this process?

I'm using a Nikon D300. After 10 months, I'm still learning how to use it. Are the steps going to be similar to what you've explained for a Canon?

[jeffreaux2]

Originally Posted by jrnylst

Wow. This has been eye-opening. I just returned a rental zoom lens yesterday that I was very disappointed with because I couldn't get the sharpness out of it on autofocus that I can get from my fixed telephoto lens. I wound up manually focussing it most of the final week of the rental. I thought the quality of a zoom lens vs. a fixed lens was the problem. Maybe I needed to go through this process?

I'm using a Nikon D300. After 10 months, I'm still learning how to use it. Are the steps going to be similar to what you've explained for a Canon?

While I am not familiar with the Nikon system at all, I would imagine the method would work. Why don't you give it a shot, and post up your results......just in case...you know....another Nikonian needs the inspiration? Worse case, you arent satisfied with the results.....just set exerything back to factory specs.