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| p.2 #6 · Lens Adapters: There Is No Free Lunch |
Roger, there's something about this report/article that just doesn't gel.
I think the data that you present as 'proof' is too vague, specifically that there isn't an explanation for the 'triggers' where readings change direction abruptly and head south. You explained it as per below, but that just says that the data is being manipulated (in a ‘black box’ kind of way) for a certain end but it doesn't really explain what is happening.
"The settings on the optical bench we used for this series make it look much worse than it really is. While the graph makes it look like the...Show more →
John, I don't disagree. This wasn't meant to be an exhaustive report, it was basically a report of me going 'I thought out of 20 adapters I'd find one that didn't make significant changes to measurements on an optical bench and I didn't". It's interesting enough that I'll repeat it on Imatest since that gives us a full 2-D image of the lens, rather an series of liniear cuts across the lens like an optical bench does. That will also give a different distance result since the bench is working at infinity focus and Imatest will be in the 8 to 15 foot range.
I didn't take it further than +/- 40 microns of focusing because anything more than that meant it wouldn't work for me (what appears to be off the chart on the print is simply inability to focus within 40 microns of the center OR inability to get an MTF reading in either tangential or sagittal plane OR too much light fall off to read. Not sufficient for what's happening type investigation, simply sufficient (in my mind) to say "alteration from baseline sufficient to make it unsuitable for testing'.
Similarly, to determine accurately what planes are worsened I'll need to repeat each lens every 30 degrees for 180 degrees (standard is simply 0 and 90 degrees).
I was quite surprised, actually. My expectation was some would be off a bit, but some would be fine and I'd use those for testing. That none were fine surprised me a lot.