Sigma 70-200mm EX front focus on 10D

[Shing]

I ran the focusing test (downloaded from the Internet) with all my lens on the 10D. I found all the shots of my Sigma 70-200mm EX f2.8 were front focus (about 2.5cm). My other lens were no problem. Here are all lens used:

Canon EF 50mm f1.4
Canon EF 85mm f1.8
Canon EF 24-85mm f3.5-f4.5
Canon EF 70-300mm IS
Sigma 14mm EX f2.8
Sigma 70-200mm EX f2.8

I took 5 shots with AF and 1 with Manual focus with each lens. Only the Sigma 70-200mm have the front focus problem. Any body have the Sigma 70-200mm with 10D tested?

My Sigma 28-300mm was being rechip for 10D by Sigma Imaging in UK. The lens was having focus problem as well.

Any comment would be greatfully recieved.

Many thanks.....

-Shing-

[topeju]

shing wrote:
I ran the focusing test (downloaded from the Internet) with all my lens on the 10D. I found all the shots of my Sigma 70-200mm EX f2.8 were front focus (about 2.5cm). My other lens were no problem. Here are all lens used:


Have you stolen my 10D? :) Seriously, I'm having the exact same problem, my 10D front focuses by pretty much the same amount with the Sigma 70-200/2.8, but focus is spot-on with my other lenses (all Canon).

I emailed Sigma a week and a half ago and received this response:

From Sigma International Division:
1. The lens itself cannot change or adjust the Auto Focus point of the lens, since AF is controlled by AF line sensor and its algorithm in the camera. Although, AF accuracy of the modern SLR cameras has been improved very much, it is still not accurate as Manual Focus. That is a reason most of the professional photographers do not use AF of the camera.

2. AF accuracy will vary depend on the type of the lens. Generally, faster aperture, tele-zoom lens, such as 70-200mm F2.8 and wide angle zoom lens would be not accurate like standard lens.
To prove this analysis, please test Canon 70-200mm F2.8 or Canon 17-35mm F2.8. You will see the similar AF Shift phenomenon.

3. Since EOS-5 has 5 horizontal sensors, it does not affect by the test chart positioned in 45degree to the lens axis. On the other hand, EOS10D has 5 horizontal sensors, plus one sensor at the upper part of the finder and one sensor at the lower part of the finder, which cause the disturbance of the AF sensing with peripheral subjects. That is the reason your EOS5 has better test results compared to EOS 10D.

4. Different AF point is caused by focusing direction ( i.e. from infinity to the subject or near distance to the subject) is inevitable, but acceptable, because the difference of two focus points is due to the depth of the focus. Generally, AF of SLR cameras will not stop the center of the depth of focus, but stop the threshold of the depth of focus, especially with small low contrast subjects, such as the test charts.

As the conclusion, Sigma 70-200mm F2.8EX has no problem with AF Mechanism of the lens.


I haven't had the opportunity to test my 10D with any fast Canon lenses so I can't compare the AF performance with them. Anyone in SW Finland got one so we could do a quick test? Rajala (a local camera store) didn't have any when I was there.

According to item 3 in their response, I think they were assuming I was using all focus points and not just one. If I had been using all focus points, I would understand the end result might be off, but I was only using the center focus point. Oh well.

I think their item 4 is also due to some misunderstanding, as in my original message to Sigma I stated that I get the same front focus irregardless to whether I start AF from infinity or from the minimum focus distance.

BTW, I also inquired as to why my EOS 5 turns the focus much faster (and reliably) than the 10D, and the answer was:

All EOS cameras including EOS-5 have +/- 0.05mm depth of field. However, Canon has received a lot of complains regarding the "near focus and far focus" of AF with D30 as well as D60, because it is easy to check AF accuracy by PC but not easy by film.
Therefore, Canon had to change the depth of focus of EOS10D from +/-0.05 to +/- 0.035mm, which has more accurate AF than +/-0.05 but requires slower AF speed compared to EOS-5.


I guess I'll have to email Sigma again.

[Shing]

Hi Tom,
Thanks for the reply and the information regarding the reply from Sigma.
I have sent a email to Sigma but havn't got a reply from them yet. I have been use the Sigma 70-200mm lens with Canon D30 and D60 in the past 2 years I previous own. I didn't find the focus problem. It may be that I didn't aware of it at all. I won't trust the 70-200mm lens with my 10D untill the focus problem have been solved or I use it with manual focusing.
I got a Canon EOS 3 and I am going to test the lens with it when I have time. So far I see no problem with the Canon 70-200mm L yet. If Sigma can't do anything about it. I may sell my lens and buy the Canon len instead.

Anyway, thanks for the information and good luck for yours. I hope you would get another reply from the Sigma.

Cheers..

-Shing-

[bluebomberx]

I haven't tested my lens with the line chart as of yet. When using only the center AF point, my Sigma 70-200 f/2.8 EX HSM focuses fine at 200mm. It focuses fine at 400mm with the Sigma 2x APO teleconverter attached. I will have to check the other focal lengths to see if this is an area of concern for me.

-Richie

[CyberDyneSystems]

I just got this lens (70-200mm 2.8 Sigma) and then the Sun came out. :D

I'll let you know my results this evening!

[CyberDyneSystems]

Well,.. the sun wasn't up for long but I gave it a lite work out! :D

This is the most responsive lens I've had on the camera to date. I like it!

I am not seeing any focus issues in my casual photographs. Portraits of the twins (retrievers) look perfect.

Of course I had a few out of focus shots,. but these were ratre and were trying to get moving targets,. flying birds etc. More a matter of focus lock than front or back focus.

I have no experience with Canon's "best" to compare it to. But,. as I said,. it is the fastes focusing lens I've used so far, and it takes great pictures :D

[topeju]

CyberDyneSystems wrote:
... But,. as I said,. it is the fastes focusing lens I've used so far ...

Hmm, that's weird, because for me the lens focuses real slow, and the Sigma people even explained why. Looks like I got a bad apple. :(