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12-19-2012, 09:37 PM   #1
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Lens Testing Procedures?

Sorry I have been out away from my computer a lot. I will be out a lot more in the coming days but I have some down time to start a discussion. If I don't reply soon keep on posting and when I get a chance to get online I will read everything

This is not about any specific lens, but rather what is your personal system for testing out a lens?

I have one lens that I have been somewhat enamored with, but I am trying to come up with a systematic way to test said lens so that I can know for myself the characteristics of the lens.

What I did is put my camera on a tripod, focus the lens (its a manual f1.4 50mm), then went every single stop and took an identical picture without moving the camera or refocusing..

The lens has an aperture ring that you have to turn manually so I would just turn it one stop, hit the green button, then snap snap snap.

I did it all in order so I then labeled each jpeg (yes I shot it in jpeg) with the f1.4, f2.0 etc etc label...

I am trying to identify those sweet spots and any other property of the lens.

I am wondering if any of you have any ideas about what exactly to look for and maybe some other options? I did my test indoors with the same lighting. I am trying to isolate the lens and the f stop as the only variable as much as possible.

Last edited by alamo5000; 12-19-2012 at 09:43 PM.
12-19-2012, 11:28 PM   #2
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Some ideas

I just picked up a K-01, and am interested in testing my various old and newly purchased lenses.
One test it for basic sharpness. I found a printable lens test chart (just search, there are tons) and printed it out. I mounted it in an old paper display sleeve to keep it flat, and put a glass frameless frame below it to use dry-erase markers to indicate the lens.

This is a reduced resolution example, just to show what I mean. I do this wide open, fully closed, and a couple stops in the middle. You could certainly burn the bytes to do every stop. I left some background to demonstrate bokeh and eventually DOF.
A similar test would use a large grid (like a good paper cutting mat) shot filling the frame to indicate distortion.

Another good test would be to get a tape measure and run it along a fence. Put your white board in the middle, focus there and start adjusting the aperture. This should readily indicate the DOF at each stop. This is an example of what we're trying to accomplish, but without the technical stuff:

Copyright All rights reserved by Pete A. McLeod

A good still life with bright colors and interesting textures in repeatable lighting can illustrate color saturation, maybe with highlights to check for PF or CA. Something like DPReview does for their reviews.

There are setups you can buy but it should be easy enough to make all this stuff.
12-20-2012, 02:22 AM   #3

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QuoteOriginally posted by alamo5000 Quote
This is not about any specific lens, but rather what is your personal system for testing out a lens?
I just use it the way I plan to use it, and see what the results are.

Since I'm shooting distant subjects a lot of the time,
test charts at a couple of feet don't really help.
12-20-2012, 07:35 AM   #4
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When I get a new lens, I stick the camera on a tripod & aim it as straight as I can at a detailed color magazine page. I take a shot wide open, f8 & f11, and use that for my general sharpness test. For PF, I have a utility pole with a metal hood in my back yard that I shoot wide open & f8. The metal hood, and wire against the blue sky is great for showing up PF.

12-20-2012, 10:46 AM   #5
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QuoteOriginally posted by lytrytyr Quote
Since I'm shooting distant subjects a lot of the time,
test charts at a couple of feet don't really help.
That's a point that I think deserves stressing some more. Lens performance may in fact vary with subject distance, though usually close focus tends to be worse than infinity in such cases. It can be the other way round in macro lenses though (as they'd obviously be optimized for close-focus work).

I usually take a few shots out the window (with a few hundred meters worth of sight) while stopping down in full stops. No conventional tripod possible there, unfortunately, but it usually gives me a decent idea.

Semi-controlled testing with test charts or targets may still be very useful, alerting you to flaws that may not be as obvious in casual shooting and allowing for more accurate comparisons. Some 3D extension of targets is not necessarily a bad thing.

A little trick when working with manual lenses: Meter only once, then choose exposure time manually according to aperture setting. Then you'll always know what setting you used. As full and half-stop steps tend to be most common, set up the camera to use the latter.

A little example: Let's say we have a 50mm f/1.7 lens.
Metering full open may give the minimum of 1/6000 s (for a K-x @ ISO 200 = minimum with highlight extension on) when it's nice and bright outside in summer, so you may have to repeat that stopped down until it gives a longer time. (Shots at minimum exposure time can still be distinguished by brightness.) But ideally, it would look something like this:
f/1.7 - 1/6000 s
f/2.0 - 1/4000 s
f/2.8 - 1/2000 s
f/4.0 - 1/1000 s
f/8.0 - 1/250 s
f/16 - f/60 s

Anything beyond f/16 usually isn't worth it, being entirely diffraction limited. Plus, you really want a 1/f exposure time as a bare minimum when shooting handheld, preferably 1/2f or even 1/4f. Otherwise sharpness may be difficult to assess. Oh, and don't think a tripod will eliminate any and all camera shake. Your first tele lens may well beg to differ.

Focusing can be extremely critical in fast or long lenses. (My first 135mm f/2.8 showed me that even 100m does not quite approximate infinity yet.) It is best carried out in liveview with zoom. Many lenses should be fine when focused wide open, but it is not too uncommon to see some focus shift when stopping down very fast ones, so you may want to recheck an f/1.4 at f/2 or so. It also wouldn't be uncommon to shoot several times with slightly varied focusing (focus bracketing), going through all the aperture settings for each focus setting.

Last edited by 52mm; 12-20-2012 at 10:51 AM.
12-20-2012, 07:31 PM   #6
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QuoteOriginally posted by alamo5000 Quote
This is not about any specific lens, but rather what is your personal system for testing out a lens?
I go out and take pictures of colorful things at a few various apertures and distances (and focal lengths if a zoom).

Then I look at the pictures. If I smile, the lens is good. If I frown, I check to see if it is me or it.

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