On Sat, 22 May 2004 07:56:52 +0200, you wrote: >JM> I used Rob's excel spreadsheet to calculate lpmm for three lenses at >JM> available apertures f2-f8: the M85/2, FA 100/2.8 Macro, and a manual >JM> focus Vivitar VS1 28-105/2.8-4 (fairly new cheap lens, not some old >JM> cult classic). > >John, you said we can flame away as we like ;-) > >So take on your azbesthos suit: > >lpm doesn't say much about any lens quality. It doesn't take into >account resolution at different contrast levels, nor does it much see >coma. Nor does it sees different gradations each lens has. > >With the high contrast resolution targets, often even cheap zooms will >perform well, but get into low contrast targets, and the lens resolves >only a muddy mush. You would have to have at least resolution targets >with several widely different contrast ratios. > >Either some difficult MTF tests, which are pretty difficult to do meaningully as >well (as always, chosing the right distance, chosing full daylight >spectrum, etc...something they don't do at Photodo), or real world >scenes... You certainly did good at chosing the right distance for >portraits, and your test does tell something about the lenses, and the >digital sensor is different enough that some great lenses can perform >badly on it, but still, you only tested for high contrast resolution. > >So your test is useful, but it doesn't tell the whole picture :) > >I am personally not in favour of lens testing. It's very hard to >evaluate properly, not subjectively, and the results are equally hard >to project into one's photographic needs. > >Best regards, > Frantisek Vlcek
I agree 100% with most all your comments. Lens testing is only one limited data point when learning about a lens, and many data points are needed for a reliable evaluation. But I think personal lens testing has value, especially comparisons between similar focal lengths one already owns. I have owned lenses which time after time disappoint in some subtle manner, the kind which leave nagging doubts about the lens or my technique, when in fact some simple tests showed the lens to be totally incapable of giving decent results compared to other available lenses of similar focal length, so off goes the bad guy to the scrap heap, without regrets. In the case of the M85/2, my little tests provided some data which agreed with what I already knew from actual use: the M85/2 is a keeper, a nice sharp lens which is easily able to perform well in its intended use as a portrait lens. -- John Mustarde www.photolin.com
