Does this lens back focus?

ecoleman

ecoleman

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Elliott
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I've just received the Sigma 17-70mm and due to some of the reviews about back/front focusing decided to run a couple of tests.

I have downloaded the focus chart and running the test on that suggests that the lens has a serious back focus problem, yet pointing the camera straight on at some text on a notepad it seems to be fine.

Anybody have any comments

This is the test chart. You may not see it at this size, but the greatest focus is around the 30mm mark above the focus point.

focuschart.jpg


This is the notepad with focus being on the "e" in Tel and it look fine to me.

notepad.jpg


Anybody have any thoughts on this?
 
The first test chart pic does indicate back focussing. taking a shot straight on won't help you identify focussing problems as the plane of field is constant across the paper.
 
The 45 degree test chart is somewhat flawed, due to focus points being vertical rather than horizontal! Or at least...I think that's right...

I remember someone mentioned on here, try standing up 3 memory cards in a line, offset by their width (so you have them stepping up in distance from the camera). Focus on the middle one, then if either of the other 2 are in focus, you have a problem.

The notepad test you did suggests all is fine!
 
Hi Everyone,

Thanks for your input. Hopefully this weekend i will get some time to go out and have a play in the real world.

I think the problem is, you read reviews and end up looking for problems which don't actually exist.
 
ecoleman said:
Hi Everyone,

Thanks for your input. Hopefully this weekend i will get some time to go out and have a play in the real world.

I think the problem is, you read reviews and end up looking for problems which don't actually exist.
Click to expand...

That is so true! (y)

The problem I have with so many tests is that they are designed to seek out problems completely out of context and emphasise them, and also (as with that 45deg focus chart) they often veer way off the road to reality in doing so. Bearing in mind nothing is perfect, if you push equipment right to its limits and then a bit further, of course you will find fault. Even the best, most expensive equipment has its shortcomings, if you know where to look for them.

I also much prefer rough science, providing it is relevant and sufficiently accurate (eg cerial packets!) to pseudo-science that is fundamentally flawed and leads you up the garden path.

Rant off/ :D
 
<rant> cereal </rant> ;)

Nice one, Cyril.
 
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