Nikon Z 35/1.8 S - hard to find a well centered copy?

Started 4 months ago | Discussions thread
rokoko
rokoko Senior Member • Posts: 2,066
Re: Short exposures and atmospheric disturbances

kenw wrote:

Rhaegar wrote:

might have missed it, but is there any shorter, quicker version of these numerous tests one can do indoors to just be assured you didn't get a lemon?

some of these tests described are so far out of the reach of what your standard hobbyist is going to attempt

Jim Kasson's test is actually really easy for any hobbyist to do with the only real constraint being having enough distance between the camera and the target which usually forces you outdoors. But that's a pretty low burden all things considered for a test which is very difficult to get wrong. If you live above the Arctic circle I'm sure the burden is quite a bit worse...

For Jim's test you don't actually need to use a big Siemens star target either though he recommends it for good reasons. Really anything with high contrast detail will work that is large enough will work. If you have a small printer you can just tape together a larger target on a piece of cardboard. The exact details of the target really aren't critical for seeing if you've got a "lemon" or not.

The theory of the test and the execution are really simple:

https://blog.kasson.com/lens-screening-testing/theory-of-the-test/

Basically just look up on Jim's plots the minimum distance your target needs to be for a particular focal length and aperture and then shoot away. Again, the distance is just a rough minimum and so there is no need to be precise at all in the exact distance you set the target from the camera. And by design Jim's test requires no careful alignment of the test target to the focal plane.

Indoor tests often end up shot with test charts or targets that are small enough and shot at distances close enough that aligning the focal plane and the target to be parallel is critical and this is what most people mess up. If you really want to shoot indoors use as large a test target as possible shot from as far away as possible and use whatever tools and understanding of geometry you can to ensure the target and the focal plane are parallel.

For any indoor testing the alignment of camera with target is critical and challenging. I am still using a modified Siemens stars chart like this:

By viewing it from a 40+ inch 4K TV, perform a defocus test. Again to fill that chart on your camera screen/EVF perfectly is challenging.

A field test I performed for more than a decade, which never failed me is like this:

I think it's similar to this:

https://www.dpreview.com/opinion/4042117089/roger-cicala-why-i-dont-use-an-mtf-bench-to-test-my-own-lenses

By such alike test I noticed an after-repair 14-24 af-s G had a weaker corner performance than the original one, as well as the replacement for that lemon.

The way I like how Reikan Focal does the job is its min target distance requirement and system error control. For 500mm lens it's 10m, and I can do that in my flat. Also it can tell you how good is your chart positioned:

Newer version supports multiple AF points, which I haven't played with fully.

I will perform some outdoors test once I find a good location. I am interested to see how accurate the prediction of the software is, by just analyzing the central AF point data.

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