Iskra I rangfinder coupling... Custom 75mm lens on compact 66 or 67 RF camera.

[bwright]

I am looking into getting an ISKRA folder and swapping out the lens for another 75mm. I know this will require some extensive modification but The 75mm lens I have I would love to have on a compact 120 camera.

Does anyone know how the rangefinder is coupled to the focussing of this camera? Is it a shaft the connects to the lens when it moves forward and back? Or is it somehow otherwise connected to the helicoid when it turns? This will affect whether I will need to keep the helicoid or if I can remove the entire lens standard and replace with my own design.

I am open to other camera options as well. Preferably a 66 or 67 rangefinder with a 75mm lens coupled to the rangefinder with bellows focussing.

 

[bwright]

I was drawn to the ISKRA for its wide RF baseplate and the lens focuses traditionally by moving all the cells forward and back while coupled to the rangefinder.

 

[GaryLH]

Bessa 2 is 6x9 and Bessa 3 (gf670) is 6x6 or 6x7... And are not front cell focusing mechanisms. Why would u want to replace the existing lens. I have one, it is pretty good.

Gary

 

[Moto-Uno]

I too have an Iskra 1 (not to mention a Mamiya 7 with a 50,80&150,plus a Kodak Medalist,along with some Bronica ETR lens) and from my limited experience , you'll be hard pressed to improve upon that Iskra lens. But having said that ,my Iskra has an adjustable bar near the bottom of the lens and that pushes on another arm near the back of the bellows which connects to a pivot near the top of the camera (all on the left hand side as you hold the camera to take a picture)
Peter

 

[bwright]

Peter, Does the bar at the bottom of the lens move the same distance as the lens when focussing or is it different? If it moves the same as the lens when focussing I won't have to keep the same helicoid when replacing the lens board which would make things easier on me.

I have a super fast f2 75mm I'm wanting to use for hand held street shooting. I could pure it on a press camera with a kalart rf pretty easy but I'm looking for small and easy to shoot. 😉

And ain't no way am I going to mess with a GF670! That would be a pretty expensive project camera. 🙂

 

[Moto-Uno]

Sorry for not getting back sooner,but it seems the bar moves in direct relationship to the lens assembly(the bar and lens are in lockstep)
Peter

 

[Ernst Dinkla]

Sorry for not getting back sooner,but it seems the bar moves in direct relationship to the lens assembly(the bar and lens are in lockstep)
Peter

My observation too.

It will be difficult to get a faster lens + shutter + helicoid between the folder struts though. If it still has to fold. Otherwise you can not discuss it in this forum 🙂

Ernst

 

[bwright]

Haha. True! So I am looking to possibly take the fold out of a folder? Is that a sin? Thanks!

 

[citizen99]

... It will be difficult to get a faster lens + shutter + helicoid between the folder struts though. If it still has to fold. ...

+1

... I have a super fast f2 75mm I'm wanting to use for hand held street shooting. ...

Can you tell us / describe what is the lens, and is it in its own shutter? If it's shuttered, are the shutter mounting and release lever etc compatible? and if not, are the lens cell assembly and dimensions compatible with the Iskra shutter?

I don't have an Iskra, but I have done a few lens/lens+shutter 'transplantations' on other folders, like this, but I would expect an f2 lens to be quite a bit more bulky.

 

[t6un]

As far as I know there is no way of adjusting the RF "gain" on an Iskra. Your f/2 lens focal length has to match the "gain" precisely,in fact more precisely than that of the stock lens.

 

[citizen99]

... Your f/2 lens focal length has to match the "gain" precisely,in fact more precisely than that of the stock lens.

Good point.

And, if you (the OP) were able to successfully meet all the other constraints mentioned by previous posters, you might still need to adjust the distance of the lens/shutter assembly from the film plane.
Shimming out at the shutter mounting to the body might be possible if it's too close.
If, on the other hand, it's too far away you would have, if possible (it may well not be, due to whatever is the f2 lens construction), to treat it as a 'pre-set cell focussed' lens if you can adjust the distance between the front cell elements. The likes of Zeiss, and many others, considered front cell focussing to be good enough on their triplet and Tessar type lensed folders. However, I'm not aware of any of these being found at apertures greater than f2.8, and I would expect your f2 lens to be of more complex multi-glass construction.