Toby said:
Because I had the devil in me today I looked up standard lenses on
www.photodo.com in MTF terms the summicron is second only to the Planar 45/2 the zm 50/2 is not tested. But I noticed that the canon fd 50/1.8got a very good score (4.4). You could buy that lens and a decent body to go with it for less than £100! The pentax smc 50/1.4 f got 4.6 -the same as the summicron and is 1 stop wider -does anyone know how much this costs?
Hi, Toby -
I think that your reference to photo.do is actually quite useful. It's just necessary to look a little beyond the summary score.
Photo.do begins with the assumption that measurements at f/4 & f/8 are the most relevant to photographers to assess lens quality, so their lens scores are an average of the measurements at these 2 aperture settings. In these days of flash photography & zoom lenses, that is probably a fair assumption.
However, it is not the most relevant information for RF photographers who are shooting with available light. We are at least as interested in how the lens performs wide open as we are in how it does when stopped down. Fortunately, photo.do also provides this informaton. Below I've listed the "average weighted MTF" scores from photo.do for 4 apertures : wide open (f/1.8 or f/2), f/2.8, f/4, & f/8:
Contax G 45/2 - 71, 83, 88, 87
Hexanon 50/2 - 74, 78, 84, 87
Summicron 50/2 - 78, 81, 85, 87
These are the only 3 lenses that I've seen at photo.do that score above 70 at f/2. They are all outstanding lenses. The Summicron has the highest score wide open, the Contax G at f/2.8, but the differences between even the best & the worst at these two apertures are small. At f/4 & f/8, there's not a dime's worth of difference among the three. Photo.do did not test the ZM 50/2, but judging by its MTF, by its lens design & by the Zeiss designed Contax G 45/2, my guess is that its numbers would be very similar to these three.
Let me contrast these ratings with those of 3 SLR AF lenses at the same apertures:
Canon 50/1.8 - 67, 77, 81, 85
Nikon 50/1.8 - 62, 78, 83, 86
Pentax 43/1.9 - 56, 72, 75, 81
All of these are lower than the RF lenses wide open. Does this mean that the RF lenses are better lenses? I would respond by asking: better for what? If you are using flash & rarely if ever use f/2, then the SLR lense are probably just as good for your purposes. But if you shoot available light & rely on f/2 & f/2.8 fairly often, then the RF lenses are decidedly better.
It might be asked whether Leica & its recent competitors are just making better glass. Consider the Leica R 50/2 Summicron, made for SLR use:
Leica R 50/2 - 68, 79, 87, 85
Very similar to the Canon. It sems that the intended use is more significant than the manufacturer. They just don't seem to take the design stage to the same level for SLR lenses that they do for RF lenses atthe widest apertures.
The Canon lens that you used for comparison was actually an earlier MF design:
Canon MF 50/1.8 - 55, 77, 84, 85
The newer AF design is actually improved at the widest aperture, so it's not a matter of modern design & manufacturing cutting corners. The same can be seen in the development of lens design at Nikon where the AF MTF at f/1.8 of 62 is an improvement over the old MF design:
Nikon MF 50/1.8 - 57, 72, 78, 85
You also asked about the Pentax SMC AF 50/1.4. It is similarly weak at the widest apertures. It's numbers are listed below with the first number being the average weighted MTF at f/1.4 and the succeeding numbers for f/2, f/2.8, f/4, & f/8:
Pentax 50/1.4 - 50, 66, 75, 82, 84
While these tests are often disparaged, I find them useful as additional data. They have their limits. They tell us nothing about flare resistance or bokeh, the latter having increased importance with wider apertures & reduced depth of field.
It's also important to note that the scores are averaged & center weighted. The average is a composite of about 48 different readings at various points in the field. Although everyone would probably agree that the center of the field is the most important & summary ratings should be weighted in its favor, it is also important to note that these numbers will never capture the character of a lens, its fingerprint. If someone falls in love with a Zeiss Sonnar, it is important to keep in mind that its reputation is sharp in the center with increasing unsharpness in the field. Many have valued its look for portraiture. However, its score - not available from photo.do - might not be as high as some other lenses because of lower scores as it is measured off center & into the corners. In contrast, someone wanting to use a lens for shooting landscapes might really care about a flat field with sharpness as evenly distributed across the field as possible. For such a use, a center weighted score might not be desirable at all. In terms of lens testing, lens performancefor this use can best be understood by looking at the MTF curves across the field & at different apertures.
I hope this is helpful.
🙂
