100MM F2.8 Macro Lens test - Opinions sought

[fudgeworth]

Hi,

I've just tested my new 350xt (350d) / 100mm f2.8 Macro lens with the following result. Do you think it's acceptable?

http://www.pbase.com/image/45732700

I recently returned a Tamron 28-75 that was front focussing worse than this. They're the only two lens I've tried on this body. I'm now concerned the body is front focussing.

Thanks,

Fudge

[Bluedog]

The odds of finding one better than that are probably very slim. My Sigma 18-125mm back focuses at certain times but has produced some very nice results.

and is that @ a true 45 degree angle?

[fudgeworth]

I'm not sure how close it was to 45. I roughly guesstimated it with an A4 folded diagonally in half. Maybe plus or minus 10 degrees, but I doubt that would make much difference. If the text in front is clearer than the text in the centre, then it's front focussing at any angle.

And if the AF doesn't give you a precise bearing at f2.8, then it's completely useless isn't it? There's not much room for error at that aperture.

Otherwise all your pics will be soft.


Fudge

[TheObiJuan]

Remember to try the test using manual focus. At f/2.8 there is a very shallow depth of field. The center AF point is almost an aproxomation of where the camera will focus. It is normal with canon's cheaper dslrs.
The cross type sensor may focus slightly above or below the af point. This is why when testing lenses it is wise to manually focus.
Also, your picture is not bad at all. If the 10 below the center line was sharp, then that would equal a problem.

Open the picture in zoombrowser and click the button on the top right to see the focus points btw.

[fudgeworth]

Thanks for your tip on ZoomBrowser. I didn't realize you could do that. Checking confirmed the autofocus point was correctly centred.

I reshot the test in both AF:

http://www.pbase.com/fudgeworth/image/45741566

and

MF:

http://www.pbase.com/fudgeworth/image/45741714

Oddly the Manual focus favours the front as well, but as you can see, not quite as much. Now why would that be?

Fudge

[TheObiJuan]

the slight front focus really is a non issue. If you up it to f/4 it will be gone, since the depth of field increases.
The camera's center af point doesn't always focus in the center, it focuses slightly above or below the point. This seems to be happening here.

[fudgeworth]

I'm afraid I don't really buy your logic.

I take a picture of someone's face, focussing on their forehead and their entire face, except for the tip of their nose perhaps is out of focus. If I focus on their ear it's clearer. This is a fault. A malfunction.

You're telling me that I can't use AF @ 2.8 and I shouldn't worry about it?

I'm hopping mad about it.

[Bluedog]

Take it back and hopefully you can get a copy to satisfy your wants. Its not uncommon to see these kinda results but it is ashame the buyer has to deal with it.

[TheObiJuan]

I'm afraid I don't really buy your logic.

I take a picture of someone's face, focussing on their forehead and their entire face, except for the tip of their nose perhaps is out of focus. If I focus on their ear it's clearer. This is a fault. A malfunction.

You're telling me that I can't use AF @ 2.8 and I shouldn't worry about it?

I'm hopping mad about it.

Feel free to use f/2.8 but understand that it equals a shallow depth of field. If you move the camera slightly after locking focus, you will cause a blurry or soft image. This happens a lot with the 135 f/2 at f/2. If I breath after focusing on a nose or eye, and I snap the pic, it will be a little soft. The best way for me to get sharp pics is to use a wider plane. I shoot portraits at f/4- f/5.6, and you really still get good background blur. F/2.8 and f/2 are for very low light. If I am shootin' at f/2.8, ISO 100, 1/2000 then there is a huge problem. Just because the camera is a f/2.8 lens doesn't mean you always have to use it at that.

[aparmley]

I don't think I can offer up much advice here - however, I think what we have happening here is a mixture perhaps of both, the very shallow DOF 2.8 allows and perhaps maybe a slightly malfunctioning lens. To decide once in for all if it is the lens or just a function of Obijuans excellent description of how sensitive the very small band of focus at 2.8 can be do some test shots on a tripod. Then hand hold the camera for the same sequence and compare the results. I find it very hard to get sharp portraits and other pictures at 1.8-2.8 on my 50mm F1.8 lens hand holding it simple because of what obijuan described, you move just slighty with the pressing of the shutter button and what was just sharply in focus goes soft...

[TheObiJuan]

with usm lenses, they focus super fast, so I don't hesitate to use ai servo to take pics at f/1.8- f/2.8. Any movement is automatically adjusted for.

[fudgeworth]

Thanks for all the feedback. Unfortunately, it's not human error. It was sitting on a tripod and set off with the timer. I've since tested it more scientifically.

At a distance of 1000 mm, at f/2.8 it focuses about 14-20 mm forward, with the centre point being fuzzy - outside the depth of field. It doesn't really capture the mark comfortably until about f/8.

In the real world that means from only about five metres away, it's out by the size of a large bird.

Fudge

[ReValveiT]

Where did you get that focus chart? Can that be d-loaded from somewhere?

Thanks for any info you may have...

[fudgeworth]

Focus chart here:

http://md.co.za/d70/chart.html

[ReValveiT]

Ah! Thankin' you very much!

[fudgeworth]

I sent the charts off to the dealer who sold me the camera and he's exchanging it for a new one!

I'll post again with the results from it.

Fudge