Back focus distance for Rodenstock Apo- Gerogon 210mm f/9 barrel

[gzinsel]

O.K. I looked,as well as I can, on the internet and "other web-sites" but I can not find any spec's on the Rodenstock Apo-gerogon lenses! Maybe someone out there on APUG can help me out? I need the distance from back of flange to Ground glass focused at infinity, for this lens. you would think it would be 210MM but some lenses are not exactly "positioned" that way or their lens is not exactly "such and such"i.e 210mm . (background: I am making a "point and shoot" L.F. camera with no ground glass and with use of a packard shutter.

thank you in advanced, AND
yours truely, cheers!!!

Greg

 

[Dan Fromm]

O.K. I looked,as well as I can, on the internet and "other web-sites" but I can not find any spec's on the Rodenstock Apo-gerogon lenses! Maybe someone out there on APUG can help me out? I need the distance from back of flange to Ground glass focused at infinity, for this lens. you would think it would be 210MM but some lenses are not exactly "positioned" that way or their lens is not exactly "such and such"i.e 210mm . (background: I am making a "point and shoot" L.F. camera with no ground glass and with use of a packard shutter.

thank you in advanced, AND
yours truely, cheers!!!

Greg

The conventional definitions are:

back focus, distance from the vertex of the lens' rear element to the film plane when the lens is focused at infinity.

flange-focal-distance, which is what you want, is the distance from the front of the lens board (= rear of shutter or step in the lens' barrel that rests against the board) to the film plane when the lens is focused at infinity.

This link http://sdrv.ms/1i4czGa will take you to a page of links to information on lenses. One of them will take you to Rodenstock process lens datasheets. The answer to your question is there.

 

[gzinsel]

Thanks dan for all the suggestions and terminology! However, when I got to the rodenstock process lens page, the geronars are missing from them. I looked through all the others, but to no avail could not find any other info. The thought came to me that maybe I was not looking in the right place. so . . . . . if a mindful chap could lend me a hand, so to speak//
thanks
greg

 

[ic-racer]

Hold off building the camera until you get the lens, then just measure the distance. I'd make the camera just a little 'short' and then shim the lens outward to perfect focus as needed.

 

[pdeeh]

I am engaged in a similar pursuit at the moment. You might find some of the posts and advice in this thread helpful: (there was a url link here which no longer exists)

 

[Dan Fromm]

Thanks dan for all the suggestions and terminology! However, when I got to the rodenstock process lens page, the geronars are missing from them. I looked through all the others, but to no avail could not find any other info. The thought came to me that maybe I was not looking in the right place. so . . . . . if a mindful chap could lend me a hand, so to speak//
thanks
greg

Follow the skydrive link and look for gerogon not geronar. I just checked, it works and the files are there.

 

[gzinsel]

Yes, Dan - you are completely right!!!! thank you so much. I appreciate your follow up. Thanks again greg