[Tam]

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Hello everyone,

I recently found a ISCO Schneider Westrogon 24mm f4 for a decent enough price. Fotodiox have a reasonably priced adapter for K-Mount as well. However, whilst researching the lens I came across this review from all photo lenses stating that it cannot be adpated to full frame DSLR. Is this actually an issue? If so, is it just the make/model or any Exakta mounted lenses? Can anyone advise about this?

[stevebrot]

I own several Exakta-mount lenses and can affirm that they cannot be adapted to Pentax-K or M42 without an adapter having an extra glass element. The registration distance for Exakta is shorter than for Pentax and there are physical constraints as well. Conventional wisdom is that the extra glass in an adapter will significantly degrade performance.

Edit: In theory, the small difference in registration might be offset by clever design since the Exakta mount diameter is narrow. Unfortunately, the Exakta mount tangs are fairly deep behind the body flange, creating a clearance problem with the mirror on Pentax cameras. The Fotodiox adapter has additional thickness to allow for the deep reach of Exakta, but then must also have extra glass.


Steve

[boriscleto]

RioRico had a way of adapting them...

ANNOUNCING: Easy cheap non-destructive Exakta-Pentax adapter

As for the review...I see no reason why an Exakta lens can't be adapted to a Canon FF DSLR...

Amazon.com : Fotasy EFEX Exakta Lens to Canon EOS Camera Copper Adapter (Silver) : Camera & Photo

[Tam]

Thanks Steve for the prompt response. I have an adapted PK6 mount 180mm Sonnar CZJ with no glass and a Cannon 50mm FD with glass in its respective adapter. The Sonnar is scalpel sharp, but the Cannon is so-so on resolution. It does create a funky water-color/soft focus effect if you open up the adapter that's actually cool depending on the composition.

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Last edited by Tam; 08-24-2018 at 03:41 PM.

[stevebrot]

RioRico had a way of adapting them...

That is what I meant by "clever design". The main issue on FF dSLRs is mirror clearance. There is an additional issue with RioRico's solution in that the shutter release arm on most Exakta-mount lenses may create issues for a clean mount* as well as being tragically in the way of attachment for most Pentax dSLR bodies unless positioned far clockwise. Two of my Exakta-mount lenses have lens flange wider than M42.

Steve

(...been over most of this ground with my first Exakta purchase...)

*My CZJ lenses have this arm flush with the mount face.

[boriscleto]

That is what I meant by "clever design". The main issue on FF dSLRs is mirror clearance. There is an additional issue with RioRico's solution in that the shutter release arm on most Exakta-mount lenses may create issues for a clean mount* as well as being tragically in the way of attachment for most Pentax dSLR bodies unless positioned far clockwise. Two of my Exakta-mount lenses have lens flange wider than M42.

Steve

(...been over most of this ground with my first Exakta purchase...)

*My CZJ lenses have this arm flush with the mount face.

Well I'm pretty sure RioRico was only going to be using pre-set lenses without the shutter release / stop down arm The more aperture blades the better...

[PJ1]

I was under the impression that you could screw off the Exacta bayonet mount and replace it with an M42 mount. But you would need that actual replacement part. The Exacta/Topcon bayonet has a registration distance of 44mm. K Mount is 45.46mm. There is this adapter on offer:
Exakta EXA Camera lens to M42 Ring Adapter 5990708703547 | eBay
If you look carefully at the images relating to the item, they show the M42 adapter fitting over the Exacta bayonet. The Exacta bayonet has a smaller throat. But the Exacta mount also projects back further than the M42 mount which cause a problem by fouling the mirror on a DSLR. The good news is that the rear projecting section is just empty space. The rear element is much further forward. This is why Zeiss could produce both Exacta bayonet and M42 mounts on the same lens. If you are into experimentation, the solution, as I see it would be to either cannibalise a Zeiss M42 mount from a broken lens and use it to replace the Exacta bayonet mount, or to remove the Exacta bayonet mount, cut off the actual bayonet part (the part that projects) and fit one of these M42 adapters to the lens.

[stevebrot]

I was under the impression that you could screw off the Exacta bayonet mount and replace it with an M42 mount.

That might be possible with some lenses, but probably not with CJZ. I have several 50s that I would like to rebuild and switch over, but the Exakta versions have dissimilar body construction to the M42.

There is this adapter on offer:

Yes, I saw these (there is more than one vendor) early in my search for a way to use my Exakta lenses on a Pentax. I did not order because it appears that the grub screws are not long enough to engage the lens barrel, the thread lens will still take its registration from the flange on an M42 body and from either the body or adapter when adapted further to K-mount. In other words, no infinity focus. Here is a link to the same item from a different vendor with somewhat better photos.

https://www.ebay.com/itm/Pixco-Detachable-3-bit-Lens-Adapter-Ring-For-Exakta...P/273220195234

The good news is that the rear projecting section is just empty space.

Not true for my Pancolar 50/2s or Flektogon 35/2.8 (Vivitar 28/2.8 either). Again, while both CZJ lenses share optics with the same lens in other mounts (M42 and Praktica-B), the lens bodies are often not shared and of course, there is still the hurdle of finding a donor M42 body. Sorry to be so pessimistic, but having taken a Pancolar 50/2 apart, I can assure you that swapping a new rear is something I quickly dismissed.

In my opinion, mirrorless is the best option for adapting Exakta glass to a modern camera.


Steve

[D1N0]

It probably would be easier to change the mount with longer focal length where the rear element is further from the mirror.