whats anything ?
July 16, 2023
63
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Right left differences sounds like an alignment issue with the elements. I would expect zoom lenses will be more prone to that because of more elements and more moving elements. Zooms often fall apart at the long end. If your 23 and 33 are "fine" I would look to issues with the two zooms. In reality 40 MP is not too much. However, it will pick up issues with lenses that a 26 MP might not.
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One advantage to using a standard target is to be able to compare your results with other people’s results. There are many examples on my website. You could compare your results to those. Now that I’ve done it a few times,I can test a lens in 20 minutes.
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I love the last paragraph 😉
It's like someone that crops in 500% to see the flaws. Answer is a simple one, don't crop in then.
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The purpose of lens screening is not to see if there are flaws. There are always flaws. The purpose of lens screening is to reliably assess the flaws and determine whether the lens is acceptable or not. The reliability of the test is key. I think that most of the lenses returned as defective are actually fine for most photography.
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In answer to the bolded question, I would add:
A 40MP 24x16mm sensor has a pixel pitch of 3.1 um. That's about 160 lp/mm geometric resolution. Even at say 100 lp/mm actual resolution that should be enough to "pick up inherent faults" in most lenses, I reckon.
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stand back from the subject 10 or 20 feet and do the spin the camera upside down. its very simple and the results are instant , ive had 3 zooms decentred. then try the same test with a prime.n just use center small focus point and aim for the same place on all shots.
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I am no expert; but... I wonder about the usefulness of a brick wall as a test piece in this case. Brick walls are traditionally used by some to determine barrel and pincushion distortions, but it seems to me that they are not suitable for Alan’s needs, as they are highly textured and, in contrast to a flat image, such as those used by Jim’s method, I find it hard to tell which bits are sharp. Even the side of a packet of Cornflakes stuck on the wall would perhaps give more visual information of sharpness. I exagerate, but I am sure the point is made. 😀
David
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Maybe Alan needs better brick wall www.lensrentals.com/blog/2021/04/selecting-the-proper-brick-wall-for-photographic-tests/
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The problem with the brick wall test is that you have to be exactly normal to the wall, ie not tilted in nay direction, especially if you're using a long lens wide open giving a shallow depth of field. If you're not you bias the test.
A quick dirty and easier test is to focus (use MF) with the lens wide open in a distant object with the object in the centre of the frame, take a shot, then repeat for each corner (and half way along the left, right, bottom and top edges of the frame if you want) and without refocussing. Then repeat with the lens at apertures you actually use (I always stop my 100-400 down a little). What sort of distant object? I use the cross atop Salisbury cathedral which is probably a bit far away from you :-) but pretty much anything similar will do.
If you lens is still under warranty then Fuji UK will fix it for you - I've had very good service from them.
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The problem with using a really distant target, particularly with long lenses, is atmospheric instability. This can create false positives.
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That eliminates the incorrect angle problem, as the angle won't matter with the same subject at the same distance at middle, right and left. Another approach would be to shoot a textured ground in front of you from eye level, far enough away that the hyperfocal range does not cover the frame, and look at the sharpest part of the hyperfocal range at various points from left to right. It won't matter what you focused on, because the center of the focal plane runs through the image.
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Update.
The Tamron has gone back. The shop agreed that it was probably a lens alignment issue.
The Fuji is still with me. It's only apparent that there is something amiss at 300mm. So, I will do some more tests and see what it looks like.I think my bricks work fine for what I need in testing lens sharpness (or softness). But thank you all for your comments and ideas.
Alan
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This is known for ages to be a very crude and non-reliable way of testing, and it doesn't allow to select the best lens sample among three.
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That is how I understand it, but could you briefly explain why it is non-reliable and what is a better way? Thanks!
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It's non-reliable because without expensive specialized equipment it is, at the very least, non-repeatable. One can try, taking a dozen of shots, and see the results - they are conclusive only if a crude defect is present, and shots are taken with great care. More, some defects can't be diagnosed this way, while some can't be attributed.
A better way is to rely on aliasing, producing a "field", "rainbow" picture, as Jim explained. Results are fast and conclusive, no need in specialized equipment, and such test also allows to monitor lens and camera mount health - which is important for me in travels.
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Rightly or wrongly, I find it useful in such matters to do edge detection in the image which can bring out the in-focus versus the out-of-focus parts and can show a "field" quite clearly.
For example: www.dpreview.com/forums/post/67137656
