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09-01-2010, 10:48 PM   #1
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OK, so am about to do lens tests on my lenses - tips/pointers/suggestions?

Having been a film boy many moons ago but only recently jumped into digital SLRs recently, ive been getting up to speed with all the recent developments etc.

Ive also picked up a heap of (mostly) used lenses including the FA31 ltd, FA77ltd, FA50/1.4, DFA 100 Macro, DA*16-50, DA*50-135, DA 18-250 & Sigma 10-20.

Coming from a film background, I was never a pixel peeper, but with the new levels of resolution i also want to make sure that all of these lenses are in good nick and doing what they should do, especially with some of the QA issues regularly discussed with the 16-50 and 10-20 as examples.

So Ive downloaded and printed some focus charts and instructions, but does anyone have any other tips about what to look out for or other 'real world' things to put em through their paces? Can any back focus/front focus be adjusted in-body with my K7 if anything is picked up?

I really dont want to do this more than once or have to send anything off for adjustment (especially as they arent in warranty here) - i'd rather just know they work fine and get on with taking photos rather than endlessly analysing the results!

09-01-2010, 10:54 PM   #2
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My feeling is that if you're not already very experienced at performing controlled tests, the chances are great that no amount of advice given here will quickly get you to the point of being able to do them accurately enough to be useful. You're much better off just shooting them normally. If there's a problem worth worrying about - and one that would have been capable of being detected in your tests - it will be obvious enough in real world usage too.
09-01-2010, 10:58 PM   #3
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I'm with Marc on your question. Believe me: the best way to spoil your fun in photography is to conduct lens tests. Suddenly you will see fault in all of your lenses, while in real life, there's no problem at all.

Please save yourself some sleep and don't do it. It just isn't worth it unless you have a lens that in real-world usage is completely soft.
09-01-2010, 11:07 PM   #4
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QuoteOriginally posted by Asahiflex Quote
I'm with Marc on your question. Believe me: the best way to spoil your fun in photography is to conduct lens tests. Suddenly you will see fault in all of your lenses, while in real life, there's no problem at all.

Please save yourself some sleep and don't do it. It just isn't worth it unless you have a lens that in real-world usage is completely soft.

cheers
yep, im definitely more for spontenaity and looking for 'the frame' as i walk around and less for the technical kind of photography - kind of mood-killing for me. i feel i have a pretty good array of lenses (a few only picked up in the last week) and the winter is just giving signs of clearing now, so i can begin cracking them out in sunlight more!

though part of me was always wondering "so why was this up for sale?", hence me considering running a few tests...

09-01-2010, 11:27 PM   #5
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I disagree, You should go as far as doing at least some testing to be sure your glass was assembled correctly. I've checked my used lenses and satisfied my concerns that it is shooting straight. Now I photograph with the knowledge of what my lens and and can't do.

Oh, and yes... found one of my used lenses with signs of being opened and the person left an element loose inside.
09-01-2010, 11:59 PM   #6
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I don't necessarily disagree. I'm saying, if you already *know* how to do a good test, then by all means, do one. But if you don't already know - and asking here kind of suggests that's the case - I'm saying you're unlikely to learn how quickly enough to do anything but confuse and frustrate you.

It's sort of (well, only a little) like saying I want to overhaul the engine in the used car I just bought to make sure it's running at its best - and then asking someone on an Internet forum what's the best way to overhaul an engine. If you're already an experienced mechanic, sure, you might be likely to actually get the car running better. If you're not, there's basically no way that asking for advice on an Internet forum is going to quickly get you to a point where you really have any chance of success. And no, I'm not saying that testing a lens is as hard, or as potentially damaging, as overhauling an engine. But still, it's incredibly easy to conduct flawed tests that provide no useful information and do end up causing you to imagine problems that don't exist or miss problems that do.
09-02-2010, 12:28 AM   #7
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+1 on Marc and Asahiflex's comments.
Many of us have gone through the phase of trying to 'test' our gear to see if it's up to scratch - invariably it's the method and technique that is flawed and not the lens in testing, and hence the apprehension to advise on lens testing for yourself.

If there is a 'fault' in your lens it will indeed be obvious in real world testing - the major ones being front or back focusing (for AF lenses), misaligned lens elements causing wrong parts of the image being in focus amongs other anomalies, and mechanical issues such as stuck aperture levers and zoom problems.
09-02-2010, 04:41 AM   #8
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Thanks all

I figured as much, but thought it couldnt hurt to investigate. Guess I'll just keep an eye on things and get down to the job of 'making images'

09-02-2010, 04:59 AM   #9
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I agree 95% with marc.

There is no amount of testing that can really confirm the lenses are "good copies" or not, that cannot be replaced with going out and shooting with the lenses. Not to pick a fight with MysteryOnion, unless he gives us the specific tests he uses, his statement will do nothing to help you determine a good vs bad lens, and only cause panic and anxiety over testing.

The one test I would recommend, you do make is the following

find a block wall or paved road surface, which is uniformly lit and big enough to occupy the full frame of each lens you own.

systematically select an ISO setting for the lighting conditions that allows you to go through the full range of apertures on each lens, with all camera settings at neutral.

either review with the in camera hystogram, or preferrable use a photo editor to evaluate the histogram of each lens.

A really good editor will allow you to measure the histogram of a selection, not just the whole frame.

The idea here is two fold.

1) you can measure the exposure accuracy of each lens. I have found for example that the Tamron 28-75 F2.8 I own has a slight non linearity in the aperture control, which causes exposure to rise slightly (i.e. greyscale value measured) between F2.8 and fully stopped down, by 1 stop. it is a gradual error, but an error non the less, You should know your lens performance so you don't get caught out when using it.

2) you can measure the central 10% of the frame and compare it to the corners, to evaluate the vignetting of each lens as a function of aperture.


This is the only test I do. sharpness and focus issues, if they exist, can be easily determined by going out and taking photos as easily as measured in a lab, and at the end of the day, no one has sold an image of a focusing chart or resolution test strip. Don't waste your time with these unless yo really think you have a problem.
09-05-2010, 05:44 AM   #10
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I'm a newbie at lens testing, but with a bit of an interest in physics and statistics, I find lens testing to be quite enjoyable, particularly in determining which second hand lens to keep and which to sell again at the same focal lengths. I've done a bit in optics labs in the past, and this is similar in that there is a lot of fine finger feeling required, in terms of patience and care. Comparisons are highly dependent on consistency.

You are always a beginner at something you have never done before, but that is no reason to not try and learn a new trick. However, your results might be inconclusive with your lens testing initially, but once you get used to it, you begin to understand the pitfalls, and eventually you will be able to discern which lens is superior for your intended application.

I wasted a lot of time initially with film testing, and personally think a lot of tests are completely misleading, such as the Takinami tests which are very restricted due to the Takinami's massively subjective determination of satisfactory contrast, grossly wide MTF banding and usage of film. (Given the ease with which we can measure contrast between pixels, a simple add in for GIMP could be written to calcuate the contrast present in an image and therefore cumulative accutance). The only way to test a lens's resolution alone is using a microscope at the back of the lens to measure aerial resolution. Once you start using a sensor, inaccuracies thanks to the sensor and body are introduced. For instance, if the distance from the viewfinder to rear element is not the same as from the sensor to rear element, then your manual focus is wrong. This is a major limitation in all lens testing, but it is what is and as long as you account for it, you're ok. A stinking lens is still going to stand out like a sore thumb, but the real resolution of a 50mm prime of 300lp/mm is not going to be picked up by a digital sensor only capable of 60lp/mm.

For test charts, have a google for ISO_12233. Use a tape measure and a tripod. How the chart is printed is also important, for instance, poor black ink on low reflectivity paper is automatically going to reduce the target contrast, making testing much harder. I'd also google for the Zeiss document on interpreting MTF charts.

A tip from bicycle maintenance would be that at the point you get sufficiently frustrated to decide you need something like a hammer, walk away from the thing for 24 hours! I'd not go into bat with the shop you buy your lens from on the basis of your results from your personal tests for instance.

Don't forget that res charts are only looking at the focal plane, whereas for practical usage you are just as interested in the out of focus areas. To misquote Henri Cartier Bresson, sharpness is not everything. The following guide to informal testing is copied from the excellent book "The lens book" by Hicks and Schultz, David & Charles, 1994.






Last edited by whojammyflip; 09-05-2010 at 06:04 AM.
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