Problems with "Film" Lenses on DSLRs?
Without getting sidetracked into something that is actually a very large issue, there are two important problems with legacy lenses. One is that film doesn’t care how oblique an angle the light rays from a lens strike it. Digital sensors do. With normal to wide lenses the angle of the light rays can be really oblique, and this can cause a lens that was very good at laying an image down on film to be a poor performer on a digital camera. When SLR cameras were introduced, “retrofocus” wide angle lens designs had to be invented. This is a lens that is physically farther from the film than its effective focal length, necessary to get the lens out of the way of the SLR mirror. A similar maneuver is needed to make normal and wide lenses for dSLRs deliver their light rays nearly perpendicular to the sensor.The second legacy lens problem (there are more than two but these are the ones we can actually see and deal with as consumers) has to do with the highly reflective glass that covers the digital sensor. It bounces a lot of light back to the rear element of the lens, far more than film. This means that a lens meant for digital capture needs just about as much attention to anti-reflective protection for light coming back from inside the camera as it does for the imaging light coming in from the scene being photographed. I’ve used designed-for-digital lenses for all of my work with dSLR cameras over the past three years, but recently I tested a 28mm legacy lens that clearly showed both these problems. Definition wasn’t great anywhere, but got worse at the edges, even though this is not a wide angle lens in context, but a nearly perfect normal (format diagonal) length for the sensor. Worse, the internal reflection problem was, well, glaring. In any picture with bright highlights, the capture showed a highlight-colored overall haze of non-image fog/flare density. Nasty.
I do not know what Mr. Weese’s qualifications may be, but he certainly sounds authoritative. What are we to make of his claims about older lenses designed for use with film? Does this old glass lack “great” definition? Do film lenses suffer from a “glaring” internal reflection problems? Do images taken with such glass show a “highlight-colored overall haze of non-image fog/flare density”? In short, are lenses that not “designed for digital” just plain “nasty”?
Mr. Weese refers to what he calls a “28mm legacy lens.” Unfortunately, he doesn’t specify which 28mm legacy lens experienced the problems he indicates. I have two 28mm “legacy” lenses, and have not experienced any such issues. The old Pentax M 28/2.8, which is quite ubiquitous on ebay, hardly suffers from these issues. It handles a prolonged exposure (over two minutes) against the sun with ease in this photo:
I have an even older 28mm lens, the Pentax K 28/3.5. Again, I can point this lens toward a bright highlight (e.g., the sun) without significant issues:
While there are “flare” streaks in the second photo, they’re of just the sort one would find in lenses designed specifically for digital cameras, as in the following photo taken with the Pentax DA 12-24:
It’s not just the legacy 28mm lenses that do fine: but legacy lenses of all sorts and types. Consider the Pentax M 20/4:
Now although there is some flare in the last M 20/4 shot, it’s hardly “nasty”; nor does it have any affect on the color or contrast of the image.
Next, consider the Pentax K 35/3.5:
Or the Pentax K 50/1.2:
While the second shot may not be much of a photograph, it does illustrate is an old lens from the mid-seventies handling some very bright light at f1.2 without serious issues. I would also note that that old ultra-fast 50mm lens is the best lens I own, better even then my Pentax DFA 100 f2.8 macro, which is a heck of a lens in its own right and designed for digital, yet no match for the K 50/1.2.
Here’s a sample from the Pentax K 200/4:
Older zoom lenses are potentially more problematic because they have more elements. But even the old Pentax A 35-105/3.5 suffers any major issues that might not afflict a “digital” zoom:
What about Mr. Weese’s claim about resolution? Anything to that?
Again, I find nothing to substantiate such claims in my own experience. Definition is not only very good in all most of my older lenses, it’s often outstanding, even in the corners. Consider the corner of M 20/4 in following 100% crop:
The Pentax M 20/4 is hardly known for being a great resolution, nor for having high definition corners; yet it performs splendidly on a digital camera. The K 50/1.2’s corners are even sharper, as this 100% crop attests:
What, then, is Mr. Weese complaining about? The older lenses perform fine. Indeed, most people could not distinguish an image taken with an old “film” lens from a digital lens. If you have any doubts on this score, try to determine which of the following images were taken with lens designed for digital cameras and which were taken from lenses designed for film cameras:
Which are taken with film lenses? Answer: B, C, E, G, J, M and P.
Now is it possible that the reason why these old legacy film lenses performed so well is that they are Pentax lenses? Perhaps the problem is that Mr. Weese was using an old third party lens. Since Mr. Weese doesn’t reveal the identity of his legacy 28mm lens, his statement cannot be evaluated. In any case, there are plenty of reports (with images to go with them) of people getting great results out of old Nikon and Zeiss glass. And as more people begin using old Canon and Minolta lenses on mirrorless ILCs, we’re likely to get positive results from those old lenses as well. Moreover, both Canon and Nikon still keep some old film lenses among their current lenses, like their old 35 f2 glass. Why would these two companies, which dominate in the DSLR market, do such a thing if the lenses were downright “nasty” on DSLRs?
One more thing to note: the lead image at the top of the page of the Egret flying was taken with a real old lens: the Tele-Takumar 300/6.3, a preset lens from the early sixties. This is a lens without multi-coatings and as primitive as one can imagine, yet still capable, despite what Mr. Weese might think or say, of taking very nice photos.