Hcompton79
Established
I found a lot of random lens components on Ebay, and saw these objects in one of the photos. They looked like parts of Ektra lenses to me, so I took a chance on them.
Turns out I was right. There were two lens mounts for the Ektra Ektar 50mm f/1.9 lens. The lens capsules themselves were long gone, but other than that they were complete save for a couple of screws. I cleaned them up and lubed them, and they work quite well now.
Now I'm questioning what to do with them. I would obviously be interested in finding an original lens capsule and make a complete lens, but given their scarcity, I am not holding my breath.
My other initial thought was to try adapting something like a Jupiter-8 so I could have a Sonnar type lens in a Ektra mount. However, I think the backfocus distance of a Sonnar type lens would be too small for these lens mounts, as I would not be able to mount the lens capsule far back enough to achieve correct focus at infinity.
Turns out I was right. There were two lens mounts for the Ektra Ektar 50mm f/1.9 lens. The lens capsules themselves were long gone, but other than that they were complete save for a couple of screws. I cleaned them up and lubed them, and they work quite well now.
Now I'm questioning what to do with them. I would obviously be interested in finding an original lens capsule and make a complete lens, but given their scarcity, I am not holding my breath.
My other initial thought was to try adapting something like a Jupiter-8 so I could have a Sonnar type lens in a Ektra mount. However, I think the backfocus distance of a Sonnar type lens would be too small for these lens mounts, as I would not be able to mount the lens capsule far back enough to achieve correct focus at infinity.
santino
FSU gear head
Excellent idea with the J8! I think someone more knowledgeable in that field than me will tell you whether it is possible or not.
What is the inner diameter of the focus mount?
The camera has a focal plane shutter- so it is a question of the barrel fitting deep enough into the focus mount. Once out of the mount, the 5cm F2 collapsible Sonnar has the best chance of slipping deeper into a mount.
The camera has a focal plane shutter- so it is a question of the barrel fitting deep enough into the focus mount. Once out of the mount, the 5cm F2 collapsible Sonnar has the best chance of slipping deeper into a mount.
Hcompton79
Established
Inner diameter of the focus mount is 1.260".
The mount then has a flange at the front where it widens, but the front bell of the donor lens would still need to clear the front focusing ring, which is 1.775" internal diameter.
The aperture ring would need to sit forward of the focus ring, which is 0.305" forward of the flange when the lens helical is furthest back at infinity. Otherwise it would need to be modified.
The flange is 2.375" forward of the focal plane when the mount is attached to a body.
So basically the rear of the aperture ring of the donor lens would need to sit 2.675" from the film plane, which seems like a far distance for a Sonnar design, which has the shorter backfocus distance than the double gauss lens this mount was designed for.
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2.375", "ABOUT" 60mm- to great of a distance for the Sonnar formula 50mm lenses. A Tessar has a much better change of working.
furcafe
Mentor
This is outside my area of expertise, but could 1 of them, plus the mount from a non-functioning body, serve as a model for someone to make a decent Ektra mount adapter for Sony E or other mirrorless bodies?
As far as lenses for the Ektra, the biggest gap would seem to be wides, so perhaps a retrofocus 28 or 35 from an SLR?
Hcompton79
Established
I think I've seen at least one Ektra mount adapter for mirrorless. I don't know why you would need the actual focusing mount component of the interchangeable lens if your intention is to make a adapter, as you would be putting complete lenses on the front of the adapter. You would just need the body side of the lens mount. This could be salvaged from an Ektra, but I wouldn't want to dismantle a complete camera to get one. You could probably machine the thing fairly easily. It's just a circular tube with a bit of internal threading and two machined bosses for orientation.
I do have a few other Ektra lenses 50mm 3.5, 35mm 3.3, 135mm 3.8 and I just picked up a 90mm 3.5 as well. So I'm okay in my selection of other focal lengths, but I do lack a fast prime and haven't thus far been able find a 50mm 1.9 within my budget. Hence I wanted to experiment with something faster in the 50mm focal length.
The other consideration is that the distance scale, focusing helical and rangefinder cam are all built into these lens mounts, so if you want these to function properly on the body, you can't really stray too far from the 50mm focal length.
Hcompton79
Established
To clarify, while I was using the term flange earlier (which is correct for the structure involved), I was not referring to the flange focal distance or back focus distance. With some measurements, I suspect the actual rear lens element of the donor would need to sit at around 38-48mm from the film plane. The main limiting factor in seating the lens further rearward would be the aperture ring or front bell of the lens hitting the "flange" where the mount steps down from 1.775" to 1.260".
What is the distance between the film plane and rear element for a Sonnar 50mm at infinity anyway?
The rear element sits about 1" from the film plane, just inside the LTM mount.
Hcompton79
Established
Got it. Thanks.
furcafe
Mentor
Understood. I actually purchased 1 of the cheap Ektra-Sony adapters off eBay to see how they work, & the problem is that it just uses screws to clamp onto the Ektra lens & doesn't use the threading of the lens mount at all, so not exactly a secure or precise fit. I was just idly thinking that 1 of your glass-less "lenses" could be used to test the threading of a replicated Ektra lens mount on a hypothetical high-quality adapter. Using an actual lens would probably be easier, but I thought perhaps the lack of glass might actually help see how the parts fit together. Yes, the receiving mount on the adapter itself would need to be reverse-engineered or salvaged (without the unneeded toothed RF cam interface) from a suitable body.
If you're just looking for a 50/1.9 Ektar, I may have a spare that fits your budget.
homebrandcrumpet
Newbie
In theory, could an Ektra mount be used to create an LTM or M49 adapter to use on an Ektra body? Or would the flange distance be off?
Hcompton79
Established
The flange distance for M39 is 28.8mm, while the Ektra flange distance is 28.29mm or 1.114". This is close enough to not matter, as the difference could be taken up in the adapter tolerances. There also would be ample room for any LTM lens, as the Ektra uses a gargantuan lens mount that is around 62mm in diameter.
My concerns with it would be that it would be extremely difficult to get the LTM lens to couple to the rangefinder. You would basically need to create a double jointed or spring loaded bar that would transfer the back and forth motion on the back of the LTM lens up to the edge of the Ektra mount where the rangefinder cam is located.
I think it would also be easier to start with a new piece of brass or aluminum than try to use the base of an Ektra mount, as it is composed of several co-rotational elements nested inside of each other like russian dolls.
Hcompton79
Established
Thinking about what you were saying about an Ektra mount to mirrorless adapter, it occurred to me that the Kodak Precision enlarger could accept Ektra lenses directly. I believe it is bellows unit A for the precision enlarger that has the Ektra Breech mount built into it.
Hcompton79
Established
Interesting observation I failed to mention earlier. One of these two mounts has three holes machined in the surface of the rangefinder cam track. The work seems to be of high quality, but I'm at a loss as to why. It does cause a bit of a "blip" in the rangefinder in use, but it doesn't impair its function.
I'm open to speculation if anyone has any guesses.
I'm open to speculation if anyone has any guesses.
Maybe done to give a visual indication in the viewfinder for zone focusing- like near/medium/far.