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09-05-2010, 08:23 PM   #1
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Option to mount large rear diameter lens

I have some a bit larger in diameter M42 thread lenses that won't fit K100D or even K-x..... Not sure why Pentax did not designed their cameras similar to Canon or Olympus where there's more room for larger lenses, like older M42 or mirror lenses.

So, is there any possible way to mount them? or is Teleconverters are my only option? I really don't want to use Teleconverters for obvious reasons.

09-05-2010, 08:49 PM   #2
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M42 lenses have a narrower mount that regular K-mount lenses, and can therefore be mounted without a problem with just a small adapter. Can't believe you missed this!

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-manua...7-k-x-etc.html

P.S. if you really want to mount larger diameter lenses, check these out:
- Pentax-K Adapter for 645 Lens Reviews - Pentax Lens Review Database
- Pentax Adapter K for 67 Lens Reviews - Pentax Lens Review Database

Adam
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09-05-2010, 09:10 PM   #3
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I know about adapter to fit the M42 thread, that is not what I meant.

I have Soviet Helios 40 lens that is M42 and it's practically touching the flash housing on K100D. Any larger lens and it won't fit. On Canon there's plenty of clearance.

Really don't want to buy a different camera brand but I might have to.
09-05-2010, 10:36 PM   #4
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QuoteOriginally posted by fiveseven Quote
I have some a bit larger in diameter M42 thread lenses that won't fit K100D or even K-x..... Not sure why Pentax did not designed their cameras similar to Canon or Olympus where there's more room for larger lenses, like older M42 or mirror lenses.
AFAIK, only mirror lenses have large diameter right from the back and there are not a lot of mirror lenses exist. Also a majority of those few mirror lenses can be mounted on Pentax bodies. So this problem is very specific so I don't think you can just blame Pentax engineers for this. BTW, how about Nikon and Sony, did they design their cameras to fit your random spec?


I don't know but I can not imagine the Canon and Olympus engineers have actually extensively studied hundreds of lenses from foreign countries when they designed the camera bodies. I also can not imagine the Pentax engineers have really carefully designed the Pentax bayonet mount so that the Nikon lenses could fit if put on certain angles. I also can not imagine the Canon engineers have thoughtfully designed the 5D mirrors so it would hit rear element of old popular lenses made by rival companies. There is also the famous Ricoh pin issue, is the Pentax engineers to be blame for this?

My guess is they're all pure co-incidence / bad luck.

To answer you question, if you really dedicated to those lenses maybe you can try to re-assemble them (no idea if this is even possible, though). Anyhow, you might find this thread handy: https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/64271-impossible-lens-club.html .


Last edited by sajah; 09-05-2010 at 10:53 PM.
09-06-2010, 12:19 AM   #5
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QuoteOriginally posted by fiveseven Quote
I know about adapter to fit the M42 thread, that is not what I meant.

I have Soviet Helios 40 lens that is M42 and it's practically touching the flash housing on K100D. Any larger lens and it won't fit. On Canon there's plenty of clearance.

Really don't want to buy a different camera brand but I might have to.
Helios 40 in m42 mount? Looks like a non-issue to me. Helios 40-2 85mm f/1.5 (M42 to Pentax) - Review / Test Report

I am sorry man, but thinking of switching brands because of another fat lens that you do not have yet, which may or may not mount on a Pentax DSLR, is about as trivial as it can get. Good luck with your new Canon.
09-06-2010, 07:51 AM   #6
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That photo (from the link ) does not show how tight the back of the lens actually is up against the flash housing.
Yes, I'm much into big fat old manual lenses..... so much so that I look at the lens before I look at the camera. Here's a quick snap shot of Helios 40-2 on K100D S and look at the tolerances from rear lens diameter to the body. There is none.




Yes, I'm very interested in another lens and since it's bigger diameter (compared to Helios 40) I have a feeling it won't fit even on K-x. I'll buy it anyway but might buy another camera since I was hunting this lens down for a very long time.
09-06-2010, 10:54 AM   #7
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Interesting. Looks a design flaw of that particular lens - why on earth does that rear diameter need to be that large and that close to the mount? Surely there isn't glass out there - glass that far the center at the rear of a lens couldn't possibly be functional. That's why this issue normally comes up only with respect to mirror lenses, where there actually is a large (reflective) element toward the back.

But I'm confused - this is a case of a lens that *does* fit, albeit barely. You said you have some that *don't*. Which are they? In the five years I've been with Pentax and participating in online forums, I can't that I recall this having come up before. A couple of times where, like your example here, it's close.

Not saying it's impossible that one or two don't exist somewhere in the world, but changing systems over the possibility of not fitting one or two very obscure lenses does seem odd to me. After all, in changing your systems (in any direction), you're basically throwing away compatibility with *hundreds* or even perhaps *thousands* of lenses that fit your former camera - just to gain compatibility with those one or two. Those had better be some incredibly awesome/unique lenses!

But FWIW, the size and shape of the that front piece does vary between different Pentax cameras. Even if you found some lens that was so oddly designed that didn't fit your K100D or K-x, chances are pretty good it would fit a larger Pentax body.
09-06-2010, 11:34 AM   #8
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The lens I'm very much interested in is Jupiter-6 (I know it's not everyone's cup of tea, but I have my reasons).
After looking at many photographs in comparison to Helios 40's and it being mounted on other SLR's I have my doubts although it's not a guarantee.

I just though maybe there's some alternative out there that is less disruptive then magnifying converters.
Just to clarify, I'm not disatisfied with Pentax, if anything I chose them over other brand and so far Ive been satisfied.

09-06-2010, 03:03 PM   #9
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The obvious alternative is a (short) macro ring. Depending on how far away you want to be able to focus it may be no problem.

It's also quite possible that there isn't anything important in that part of the camera, making it possible to shave some of it off. But I don't think it's a good idea.
09-06-2010, 05:58 PM   #10
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Jupiter 6, is it this one? JUPITER-6-2 2.8/180mm BLACK M42 Zenit SLR cameras, EXC! on eBay.ca (item 130426656491 end time 07-Sep-10 05:00:40 EDT)
That is quite fat around the base but is it any fatter than the base of the P645-PK adapter mount? You must have a very good reason for wanting this lens but I would get the CZ Jena Sonnar 180mm f2.8 in Pentacon 6 mount and find the appropriate Pentacon 6 - PK adapter mount, which coincidentally is sold by the same vendor that's selling the above lens.

Thanks,
09-07-2010, 02:40 PM   #11
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Most people complain that their FSU M42 lenses (e.g. LZOS Jupiter-9) have too narrow a base such that the lens "rocks" on the mount. As for the Helios 40-2, I have never heard of a problem mounting that lens to Pentax despite there being several forum users that own one.

Looking at the eBay photos of the J-6, I see the source of your concern. The base diameter is at least 80mm and may be a tight fit on ANY dSLR model with a built in flash. If it is any consolation, there are several FSU lenses that have fit issues with other than the cameras they were intended to mount to. The Helios 44-3 58/2 comes to mind. About half of them have an aperture ring that only has adequate clearance for the body flange on a Zenit camera. Yes, the ring seats AROUND the mount. Go figure...


Steve
09-07-2010, 07:01 PM   #12
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Well, since I bought K100D just so I can use it for manual lenses, I might do what other member suggested, I'll see if it's possible to shave off some material with a hot knife.
I'm guessing, up to 5mm can be taken off safely.
09-08-2010, 01:16 AM   #13
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QuoteOriginally posted by fiveseven Quote
Well, since I bought K100D just so I can use it for manual lenses, I might do what other member suggested, I'll see if it's possible to shave off some material with a hot knife.
I'm guessing, up to 5mm can be taken off safely.
Hello 5-7, please let us know the outcome! I am willing to do this on a K100D too. I would take off the whole pop-up-flash unit too (replacing it with a nice 'Asahi Optical' housing .-).
Good luck,
Georg
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