Archived posting to the Leica Users Group, 2001/02/26
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> 1) Make sure that the resolution and MTF tests are made not only > in the center and edges of the frame, but also 1/3rd, and 2/3rds > out from the center > of the image, and at the corners. That is in the plan. > 2) If time permits you should make all of the above readings > both tangentially and sagitally. Why? I know typically MTF data does include both, but why would that matter in this case? > 3) Test the lens at the most widely used apertures. (Wide open, > two stops down, minimum aperture - your choice, it's your test.) I planned at testing only wide open. I am going to assume degradation will track, but it is a going point, I probably should test at some 'other' aperture...just to show that they track. > 4) Make sure that the operator of the test is accurately making > your measurements within the 24x36 or 6x6 image circle. The > image circles thrown by > the lens will be much greater than their respective camera format. Yes. > 5) Critical focusing of the aerial image is vital. Look through > it yourself to make sure the operator and you agree on the testing plane. No idea, I will ask about that. > 6) What focusing distance are you doing your test at? (infinity, > 20', 10', 5', 1' ?) 3' was the number I was shooting for. > 7) If it was me, I would use the Hasselblad adjustable lens > shade (extended to the maximum amount before vignetting) on each > lens to make absolutely > sure there was no extraneous light hitting the front element or > filter. I would even bring black cards to hold up as gobos for > the front element if > needed. Shade is probably a good idea, I will bring the appropriate shade. I do not have the pro shade, just the fixed shades. > 8) I would also do a test with a light purposefully shining on > the front element and on the filter to gauge the effect a backlit > scene will have on > lens performance - with and without the filter in place. I was thinking about that, but I do not want to be overly aggressive with this first set of tests. I would like to run this type of test though, but not necessarily now. > Somewhere, I have the resolution and MTF data on your 110 Zeiss, > that Zeiss published in the 80's. It might be an interesting > comparison to see if > your results are comparable (provided you can use similar test > parameters). My 110 was made in the 80's ;-) > Good Luck and I may be in the minority, but I too find the test > interesting. Thank you! > Do you think you can test both lenses in one hour ($175.00)? > It's a lot of work. I'm there for two hours, should be no problem. Thanks Rob, your CONSTRUCTIVE input is greatly appreciated. I will also not only document the test setup including equipment etc., but take pictures as well.