micro-adjustable cameras.Question-

[fairy bombs]

Hello.

I have a Canon 50D,I use it with a Canon 400 L prime F 5.6,there may be a slight focus issue,where the images are not seeming to be as crisp as when I used the lens on my 450D.

This new 50D has 'micro adjust' so if I read the book,and after some tests feel there is a issue,If I adjust the camera with the lens on.What calibrates?? i.e is the camera programed when that lens is on,or is the lens programed??,So if I use the lens on a different camera-will in act like its on the 50D,or be 'its self'

[agb]

It's the camera, and it remembers the lens so that when it is on that camera body the body "calibrates" to that lens. I don't think lenses have memories.
So if you put that lens on a different body and it has a focus issue that body would also have to be micro adjusted to suit.

[arthurking83]

Also the lens that is used to calibrate the camera at the time of calibration, is not unique either.
That is, the camera will automatically adjust to the calibrated amount if a lens of the same type(but the not the same physical lens) is attached, even tho this other lens may not requuire the same adjusmtment.

of course not many people have two copiees of the same lens,so this issue is not a major one to worry about.

[gqtuazon]

I normally do this just to make sure if my lenses AF is spot on. It's a little harder to estimate for zoom lenses but it's easier for prime lenses with larger aperture. Try to focus as close as possible so that the DOF is a lot thinner. A simple battery test. My focus point was on the middle battery. You'll need a sturdy tripod to do this. I had to program one of my lenses to +5 on this test. Once you've save the data on the camera, then the camera will remember that particular lens whenever it is mounted.

http://images.nikonians.org/galleries/data/16870/battery_test.jpg

[ricktas]

There is a focus chart available here (http://focustestchart.com/focus21.pdf) (PDF file), and information on how to test your lenses is included in the link PDF, whilst for a D70, the concept is the same for all cameras

[fairy bombs]

Thanks all,thanks Glenn-that is a very nifty idea with the batteries!,thanks Rick for link

[arthurking83]

Glen's image indicates oneof the best ways to check for focusing accuracy, except for one small issue!
Don't only try this(or any other method at minimum focus distance, which is the first thing everyone is inclined to do!
Focusing innacuracies sometimes show themselves up at different focus distances , that is, for a given lens, at a given focal legth, it may focus perfectly at one focus distance point, and differently at another.

Best to check for focusing innacuracies at a focus distance most likely to be used for that lens/focal length.

The other issue I wanted to raise about Glenn's battery setup is to line up the batteries in a manner where they are arranged in a v shaped lineup(either behind the central battery, or in front .. doesn't matter, but they should be lined up in a v shape, to help ensure against setup errors. The need to eliminate any setup error in having the camera square on to the setup is important, if reliable results are to be expected.

But!.. over the years, I've found this method to be more indicative of real world usage than using the printed test patterns shot at 45° at close distances. And again!!! it's important to check for errors when shooting at usual distances to the subject matter, rather than just looking for errors in focusing accuracy.

[Wobbles]

There is a focus chart available here (http://focustestchart.com/focus21.pdf) (PDF file), and information on how to test your lenses is included in the link PDF, whilst for a D70, the concept is the same for all cameras

Thanks Rick, I hadn't seen that one before, it looks a lot simpler method. Similar to Arthur's comment though, all the other "do-it-yourself" methods I've seen recommend that "Camera-to-subject distance should be no less than 50 times the focal length of the lens. For a 50mm lens, that would be at least 2.5 meters"... believe me that got pretty tricky when trying to check my 400L !:eek:

Here's one where you use an image on your monitor:
http://www.northlight-images.co.uk/article_pages/cameras/1ds3_af_micoadjustment.html

Cheers
John

[Speedway]

Thanks for this post Glenn. I have been trying to work out a way to test my 150-500 and this has given me a few ideas to try. Arthur the only problem with the V formation is that if the lens is front focusing it would not give any indication of how much.
Keith.
Ps finally got this to post (Ipstar satellite constantly dropping out).

[arthurking83]

...... Arthur the only problem with the V formation is that if the lens is front focusing it would not give any indication of how much.
Keith.
...

Yep! Totally agree, except for one small point. If you don't see any focus at all in any of the subject matter behind the expected plane of focus, you reset the lineup in the opposite direction :p

I've made this same mistakes, thinking that it was better to do it all quick, and then get out and test it all, but I soon found out that if you are focused close up (as most people wrongly are prone top start out doing), and also not square on to the subject, you can introduce user setup errors in the test procedure. If the test procedure is set up to produce variable results, you won't get consistent results.

My Tammy 28-75mm was hard to work out due to this error in test setup, but now I've figured it out properly.
My only other lens(Nikon 80-200/2.8) also needed adjustment, as it was backfocusing by a fair amount, and I used the usual procedures as most people do to test for focus accuracy. I was then explained a better(more reliable test setup) and then re did the Tammy lens too. the Nikon still turned out to produce the same results, but the Tammy focuses with different innacuracies at different focus distances.