Im Cheap--Do-it youself AFMA Contraption

[bob williams]

Thanks HD---I'll keep that in mind

[Sheiky]

Bob, I used an even simpler method for my 50mm f1.4
I printed a long black rectangle on a white a4 size paper(Capitol I would do the same trick). I pasted it to a door which was level.
I aligned my tripod and camera at about 2m(7 feet) which I assumed was the most used distance of the lens. In other words, the distance which I though would be most important to my shooting style.
Obviously I didn't have a ruler so I couldn't easily spot if my lens was front focusing or back focusing. I knew that it had a front frocus issue so I just took shots from AFMA 0 to AFMA 20 and I compared the shots on 100% view on my computer. Up till this day it has worked perfectly for me and it only cost me 1 sheet of paper
My 24-105 f4L needed a +4 and my Sigma 50mm f1.4 needed +13. My 70-200 f4L IS was spot on. The 100mm L macro had a different story. It was spot on at 1:1 to 1:2 macro settings, however for portraits it needed a +4 AFMA. Since I rarely used AF during macro, I used +4 on that lens as well.

As far as I'm concerned the Lens Allign couldn't do a better job. I'm pretty confident that I'm no more off than +- 1 which for me isn't a problem at all. With the Lens Allign I'm pretty sure that your method could also cost you +- 1 so in my opinion save the 150$.

Jan

[jrw]

I'm pretty cheap too. Would suggest two possible changes. One, replace the ruler with another that has finer graduations. Two, change the angle the ruler sits at. By making it more vertical, the existing graduations would have finer resolution.

JRW

[jrw]

Realized that I ought to elaborate a bit more. Am familiar with using rulers to set up vision inspection camera systems when the actual parts aren't available to use. Have found that satin finish rulers are best. The graduations I prefer are engraved and then black filled with a low lustre pigment. Have also used the same rulers to adjust micro focus. Using live view and manual focus, I focus on one specific measurement line or a target aligned with the ruler depending on what I am setting up. Take a picture. Turn on auto focus and compare the results of a few pictures. This is faster to do when tethered as it is also possible to adjust the focus from the PC. If the results are not close enough to keep me happy, I also know which way to adjust and just record the amount of adjustment required for adjusting in the camera settings. One other problem I experienced once when I had the ruler further away, was a pixelation issue which caused grief in assessing the results. The ruler was too close to horizontal which caused the relative width of the graduations to drop below one pixel width on the sensor. The separation of the markings was also very small in the images. Changing the ruler angle increased the apparent width of the markings in the images, while at the same time the separation increased for better resolution of the focos. It might be a good idea for you to back calculate the pixel resolution in millimetres using your sensor specs along with the image circle dimensions for the lens combined with the optical angle of view. Pixel peeping on one of the markings in an image would also give you a different path to the same information with no math involved.

[HDNitehawk]

As far as I'm concerned the Lens Align couldn't do a better job. I'm pretty confident that I'm no more off than +- 1 which for me isn't a problem at all. With the Lens Align I'm pretty sure that your method could also cost you +- 1 so in my opinion save the 150$.

Jan

Jan

Your method will work, however it takes longer to get the same results. It is a method I used for a long time.

What I see as one of the real benefits of the ruler is that it tells you what your DOF is doing overall. I don't agree that the LensAllign would cost you +/- 1, I would agree your camera will vary that much though. You can be +1/-1 and you will still have quit a few pics in focus, just as if you were dead on. There will be two reasons for this, one is that your AF system isn't pin point accurate, when you move forward or back you end up with either shots that were a bit back focused at dead center coming in to sharp focus or vice/versa for front focus if you go the other way. The other reason is that depending on your lens, your DOF still covers the target.

I would also say, that with the 500mm the +/- 1 matters more than with many other lenses. The wider the lens the wider the DOF, and of course a wider DOF is more forgiving. With the 500mm if you are shooting birds or small wildlife it is a narrow DOF, the fine detail of an eye can be one of the most important aspects of a shot. Luckily, I have found that the big telephoto's are the easiest to get dead on of all the lenses. They are much more accurate and consistent than any other lens I own. If you are a little off one way or the other your keeper rate will start to fall.

I still think Bob's configuration will work. The only thing I see left is he hasn't incorporated a way to easily square and align the target. The lensalign uses two holes that you peep through to get alignment. I think there would be a way to overcome that, with a little surveying and carpentry know how.

Bob, one other note. If you decided to buy a lensalign, you wouldn't have to buy the $150 version unless you wanted to test at the longer distances. They also sell the ruler and face plate as add on's, so if you think you need them later you can order it separate.

Rick