New Tamron 28-75

After a lot of research on this forum i decided to buy the Tamron 28-75 for my 20D, I used it over the weekend out doors in very poor light and the results were not that good, so i decided to do a focus test today and i think it may be slightly front focusing. Is front or back focusing caused by the Camera Body focusing mechanism or the Lens?
any advise please, Quadphoto.

Tamron 28-75 8mm@f2.8 (INVALID EMAIL)

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You have to remember that the red square in the viewfinder is slightly smaller than the actual AF point that the camera use (why this is so, only Canon could enlighten us about). So you might try the same test again with the red square slightly higher than you think it ought to be, to see if the picture is focused then where you think it ought to be. That "focus here" line is fairly thick, so there are lots of potential combinations of alignment which would be within human error margins, such as the top of your red square in the middle of the text.

I'm not sure if Canon or Tamron would look on this as front-focusing or as being within the acceptable margin of error.

Can You send me copy of this chart to test my 28-75, please?
It can be pdf file or any other ..


poczta@dziechciarz.art​.pl

Many thanks

Tomasz here is the link where you can down load the test chart and instructions.
http://md.co.za/d70/ch​art.html

I'm going to test mine too. Thanks

seems to me like you are splitting hairs..

@ 2.8 as close as you were.. think you have a keeper

It could be the angle you were using. That to me doesn't look quiet at 45 degrees. Here's my result done when acquiring my copy:

70mm @ f/2.8

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Gawd some of you guys are fussy. Test charge is fine as far as I'm concerned. More likely the conditions caused any problems in real world shooting.

Looks like a slight front focus to me, but i'd probably stay with it. Shoot the test chart 5 times, focus on infinity between shots, make sure you use a tripod.

Initially I was thinking mine was a tad soft at f/2.8, still may be and Tamron will calibrate if necessary if I don't mind being without for a month. Then got to thinking, just how often do I shoot at f/2.8 with that particuliar lens. That coupled with the fact that others say it looks great, will probably sway me to leaving well enough alone. If not pixel peeking, then I am sure the lens is sharp all the way.

I tend to lean toward user error sometimes with mine @ f/2.8 as well. I've gotten some outstanding results but also have seen a few softer ones too. Not enough to warrant sending it off.

Ya same here,.. I use mine and SOME shots at 2.8 are sharp, some are soft.... ?

It may be the distance away from the object... Its not very sharp at 2.8 when im shooting distance, sometimes ever portrait.

IF YOU WANT TO ENJOY THIS LENS, DONT WIND YOURSELVES UP OVER THIS TEST.
I will not be testing mine as i am pleased with the results. If i find a slight front or back focus error, then it will grind at me. Go out and enjoy the lens, if it looks poor when you get the results home then do the test.

Simon, when i originally posted this thread i was seeking advice concerning the front focusing problem that my new Tamron 28-75 lens was suffering from, and i very much doubt that this test would WIND anyone up that was about to buy or had just bought this lens. I took loads of images before doing this focus test because the front focusing problem existed as far as f5.6 there was clearly problem with this lens and you did not have to be a photographic expert to realise it. When I contacted Tamron UK they openly admitted that there was a focusing issue with the Canon fit 28-75 F2.8 XR Di lens, and they had successfully re-calibrated all the ones returned to them, I returned mine and it now focuses accurate and is pin sharp and i am enjoying it very much, good luck with yours.

seen lots of posts about front / back focusing
could somebody explain (in plain english) what this is all about please