Retina IIa Zeiss lens

[Novembersierra]

I have a Retina IIa that I'm planning to restore, so expect some more questions for me in the next months 🙂

Anyway, while I was tinkering with the Kodak it came to my mind that somewhere I had a Zeiss Triotar 75mm left from a broken Rollei bought as a project and later sold for parts. Some minutes later, the uncoated 1939 triplet from Jena was screwed flawlessly on the Compur shutter.
I already knew that the lens has a huge (6cm? idk) back focal leght, and checking with a ground glass shows a nice blur: focus is way beyond infinity.
So what?
The only solution I can think of is a close up lens to compensate, but then again, how 'strong' and which one? Moreover, I'd have to find a 28,5mm to 32 (or greater) step up ring and quite surely have some troubles with the rangefinder.

Still, I love this kind of stuff and having a portrait lens option in my pocket would be nice!

 

[colyn]

Adding a closeup lens won't work. The difference between the Retina and Rolleiflex register means you would have to add an extension between lens and film. Then you have the problem of a lens that was designed for a larger size negative which translates to a larger circle of confusion. The image would likely be too large for the 24x36..

 

[Novembersierra]

But why not? my thought was that diopters should work the same way as extension tubes, and in this case extension tubes would make up for the incorrect back focal lenght -am I missing something?
Back when I had the shutter I tested the lens on an aps-c camera and the images were very good so on a full 35mm perhaps it could perform even better. What's the 'too large' issue?
Thanks

 

[colyn]

Diopters whether in front of a lens or behind it degrades the overall image. When placed behind the lens such as the adapter to use Minolta MD/MC lens on Minolta/Sony autofocus cameras can only do so much. Trying to magnify a larger distance such as you need simply will not work because of the increased degradation of image quality. I've tried adapting lens like what you want and it did not work.

Also the Triotar is an inferiour lens when compared to the original lens used on the Retina..