Backfocusing? Need second opinion!

photoguy6405 wrote in post #6851298
Thanks for the answers. I learned something new today. Now I can go back to bed.

Anyway, sometimes I have issues with focusing close-up and have always blown it off as me and my eyes. Are these focusing charts easy to obtain?

Regarding close-ups: be careful that you don't get too close, because the camera won't be able to deliver sharp images anymore when you are closer than MFD.

Focusing charts are very easy to obtain.
Here is the one that everybody uses: http://focustestchart.​com/chart.html
Another method of testing AF: http://www.komar.org/f​aq/camera/auto-focus-test/

Generally, test charts for testing lens sharpness need to be bought. Here are a few:
http://www.aig-imaging.com/mm5/mercha​nt.mvc

One for free: http://www.graphics.co​rnell.edu/~westin/misc​/res-chart.html

Article on lens testing: http://www.sciencebudd​ies.org …hoto_p001.shtml​?from=Home

Some theoretical stuff on lenses:
http://photo.net/learn​/optics/lensTutorial

Anyway, HTH, kind regards, Wim

A better and easier test will be the battery test.
focus point is the middle battery

FlyingPhotog wrote in post #6852086
"Focusing Close Up" .. Maybe you're up against the MFD (minimum focus distance) for the lens in question?

I do do that on occasion, and increase the distance accordingly. That aspect I'm aware of when it happens.

Hi everyone. Thanks for the info. I'm the one who sold him the 85mm. I never had a problem with it, but I never tested it. Once I get it back I'll do some tests of my own and check the warranty status.

speedy_2 wrote in post #6859314
Hi everyone. Thanks for the info. I'm the one who sold him the 85mm. I never had a problem with it, but I never tested it. Once I get it back I'll do some tests of my own and check the warranty status.

Good on you for stepping up and wanting to work it out...

Everything's on the way back to their respective owners. Thanks speedy

nightcat wrote in post #6849452
This is usually a lens problem, not a camera problem. Is this a Canon lens? Is it still under warantee? If so, send it in for adjustment.

In my case this was a camera problem, luckily I discovered it quickly after buying and Canon calibrated it for $15 shipping (guess I didn't **** enough or it would be free shipping both ways).

I used the same test, and another one - basically a modified battery test, that I do after I run this chart test. I take a sheet of paper with sharp black on white text, cut three little tabs about 1.5" long and 3/4" wide, then glue each to a battery (or anything you can stand upright). This way the text is crisper than what you get on a battery, and the flash doesn't cause as much glare. I position batteries and camera on the same table, and shoot away.

If both tests show back or front focusing you know you have a problem.

ef2 wrote in post #6860111
Everything's on the way back to their respective owners. Thanks speedy

Thanks again.

Luckily, I'm pretty sure it is still under warranty. So if it does test out bad with me, it'll be on it's way to Canon soon after. If you still want to trade after I get it resolved, let me know!!!!

Ok. Got the lens today and did a test. Both on my few year old XT @ f/1.8

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Your sample resembles my test with the XT. Focus seems alot better than my 1D, 1Ds, and 5D.

speedy_2 wrote in post #6871177
Ok. Got the lens today and did a test. Both on my few year old XT @ f/1.8

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The focus chart doesn't look anything like your 5d Test. I don't know. The tape measure does seem to show it focusing more at 15 1/2 inches rather than the 16 I focused on. You guys think I should send it off??

The focus test chart looks OK to me. The tape measure test proves nothing, I'm afraid. You really need an unambiguous single thing to focus on at the focus point. With your tape measure test the camera can quite legitimately choose to focus on anything in it's 'target area', and this extends considerably beyond the box around the focus point in the viewfinder.

gcogger wrote in post #6875378
The focus test chart looks OK to me. The tape measure test proves nothing, I'm afraid. You really need an unambiguous single thing to focus on at the focus point. With your tape measure test the camera can quite legitimately choose to focus on anything in it's 'target area', and this extends considerably beyond the box around the focus point in the viewfinder.

I'm new but have never heard that. Are you saying that even with the one center focus point selected that the camera is still using the other focus points (boxes) or that the focus sensors actually extend beyond the edge of the box?

Pilot Dane wrote in post #6875471
I'm new but have never heard that. Are you saying that even with the one center focus point selected that the camera is still using the other focus points (boxes) or that the focus sensors actually extend beyond the edge of the box?

Most cameras have sensors that do extend slightly outside of the boxes..... Particullary the centre point

This image sorta shows what I am trying to say....
http://img.imaging-resource.com/PRODS/E40​D/ZAFSENSORS.JPG
(you have to click then refresh as I don't think they want direct embedding or whatever)

Pilot Dane wrote in post #6875471
I'm new but have never heard that. Are you saying that even with the one center focus point selected that the camera is still using the other focus points (boxes) or that the focus sensors actually extend beyond the edge of the box?

The sensitive area for a focus 'point' extends well outside the box. Here's an example of the areas covered (shown in red) for the older 7-point system, although the principle is the same on the newer ones.

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strobe monkey wrote in post #6852806
A better and easier test will be the battery test.

or my Stanley test:

How do you know if it's the lens that is at fault or the body? (Apart from trying the suspect lenses on another body and the suspect body with other lenses...)