Originally posted by Adam You're probably not going to be able to tell the difference (especially on film) unless you plan to leverage the faster F stop for bokeh.
Just to be sure, this especially applies more to digital. More importantly you have to know what tests are being conducted, how they are conducted and how the results are to be evaluated. With film there is that additional step on how to extract the information from it.
I test all my lenses since I do buy a lot of used equipment as I wouldn't really know if they are up to original factory specs nor do I know wha those faactory specs are. I like to weed them out so that if I need to count on them, I will know what can be expected. Below are the results of testing my Pentax 50mm lenses using a 2X2 arrangement of the ISO12233 chart, properly lit, tripod mount with my
14.6MP Pentax K20D.
Lenses
Results
Full res version ->
Pentax 50mm Lenses
Using the K20D, I can establish a baseline by comparing it to results from others like DPREVIEW showing the 14.6MP K20D ideally attains about
24 ->
Pentax K20D Review: Digital Photography Review
Since I do use film, I also conducted this test but this time with a 4X4 arrangement of the ISO12233 chart, properly lit, tripod mount using my K20D with a known baseline but also this time on Kodak Techpan @ ISO25 processed in Technidol and then scanned 4000dpi on Coolscan.
As shown below, this combination achieves much higher results of about 30~36 with the Pentax SMC Macro 50mm F4 on my Pentax LX[B].
Taking it further, I used the Pentax Autobellows to take a peek at the frame of film at about 4.5X magnification and as you can see from the far right blowup, this lens+film combination actually achieves an even higher
52. Like I said, the challenge with scanning is being able to resolve all the detail that is captured on the film.
Full res version ->
Pentax SMC Macro 50mm f4 series
Since I don't really know how these lenses are supposed to perform brand new, I still don't know what is the limiting factor in these tests. However, I do know that the lenses are not the bottleneck at least when it comes to resolution.
BTW, I have now had considerable experience shooting the 50mm f1.2 on my film bodies as well as the K20D and I can tell you that a handheld shot with the K20D's tiny viewfinder - compared to the giant viewfinders in the film bodies, yields very poor results in achieving critical focus. Even in bright scenes, I am lucky to get a sharp wide open shot with the K20D in 5 or more attempts but have no problem nailing each with my MX or LX.