I'm a Canon DSLR user that adapts M42 mount lenses to my 5D Mark III. I have 41 M42 lenses. There are people that also adapt them to APS-C and Micro 4/3. That said, I don't think the market is as large as one might think. I spend many hours on Ebay cataloging the 50mm f/1.4 lenses I see and one would be surprised at how many do not sell and get relisted... over and over again. There are people that say they adapt these lenses to get that "film look" in their images. BS. Film and photographic paper gives the "film look", not the lens.
I love my M42 lenses, but I don't believe reviving the old Takumars would be economically viable. As far as paying a premium over modern Canon lenses? Maybe for a scant few lenses, but the reason those "valuable" lenses are priced in the thousands is because they are truly rare. A lot of sellers on Ebay put "rare" in their listings. Very very few lenses are rare.
People buy M42 lenses for a few reasons:
1. Nostalgia
2. They don't have a lot of money and get them instead of the modern lenses.
3. They bought into the idea they give a "film look". What they really mean is that they get horrible flare, slightly out of focus (operator error), images.
4. They like to post their latest thrift store find. "I got this today for $5." So the popularity is because they can be found dirt cheap. Try to sell them now in brand new condition and you are talking big $. I have seen NIB Takumars. They cost thousands. It would not be cheap to make a lens to the build quality of the old Takumars (Think modern Zeiss).
5. They are obsessive compulsive collectors.That's me. I know of more than a few people that have literally hundreds of these old lenses. They scour Ebay for lenses that are under $20 and buy them. It doesn't even matter what the lens is. They just buy it. They even buy them when there's a fungus farm in the lens. They will tell you that they have only used most once (flower pics mostly) or have not used most at all.
6. They also like having a couple dozen adapters.
So while internet forum and Facebook forum groups would give the impression these old lenses could be a new market for new lenses they aren't. They certainly are not wildly popular enough to build new assembly lines, R&D, and hire people to build them. There just are not enough people looking to spend into the high hundreds or thousands for a modern manual focus lens. I'm frankly shocked at what Zeiss gets for their line, but Zeiss is a very old name and serves a very niche market. Somebody is going to say Zeiss is the best there is. Not true. There are modern popular brands that have lenses that beat Zeiss. Zeiss is the equivalent of the middle aged guy that buys a Porsche... because he can. There really is not something extraordinary in a photo taken with a Zeiss lens. You can't look at a photo and tell what lens the photo was taken with. I could take the same photo with 5 different lenses. You would not be able to tell me which one is the Zeiss photo and why it is. You might get lucky, but luck is all it is.
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---------- Post added 10-20-18 at 09:58 AM ----------
Originally posted by GUB Surely the M42 thread is not the driver here - what you are asking for is something like the K mount K 400 5.6. (and presumably others). That is a focus ring and manual aperture ring. Throw in modern coatings and you have a viable alternative for that wonderful old Takumar Glass without the need of an adapter. Describing Canon's heritage is not a good example as far as I can tell. Doesn't their compatibility go back only as far as 1987? K mount goes back to 1975.
There are adapters for M42 to Canon FD. There are adapters for almost everything. Some even have focus confirmation chips.