Re: 7P Realist

[P3D John Slivon <frogs@xxxxxxxxxx>]

>>Next came the search for suitable lenses. I wanted Leitz Summarons but ran
>>into the $ issue. I settled on a pair of unblemished 35mm 3.5 Rikenon lenses
>>from  two junk Ricoh AF-70 point-and-shoots that I found in a St. Paul
>>camera store for $6. These are very nice lenses based on a highly compressed
>>Tessar design. [...]  > By the way, the picture quality is superb.
>>    John R. Slivon
>    
>Just curious... Couldn't you have left the Realist lenses?  (of a 2.8 Realist?)
>Why change?  Realist did make a couple of 7p 2.8 Realists as we know from
>Wolfgang Sell's article in Stereoscopy. -- George
>
>

You bring up an interesting point. I too have wondered about 
the possibilities of the 2.8 Realist lenses. The 3.5 lenses, being 
Cooke triplets do not have enough coverage to accomodate a 
24 x 30 format. The 2.8 lenses, being basically tessars, and 
I'm assuming not wide-angle tessars, would be right at their 
limit of producing a sharp image over a 24 x 30 format. The 
Cooke triplet has a cone of sharpness of approximately 40 degrees, 
while the tessar's is approx. 52 degrees (Neblette). At a smaller 
aperture the tessar's is probably 56 degrees while the triplet's
remains unchanged. I'm assuming that the actual focal length of the 
Realist lenses is 38mm, not 35. That would give a circle of sharpness 
for the 3.5 of 27.6 mm diameter. The hypotenuse of a 24 x 23 rectangle
is 33.2 mm. This calculation would suggest that there should be some 
unsharpness in the corners of a Realist neg. taken with a 3.5 lens. On 
the other hand, the calculated circle of sharpness for the 2.8 Realist
lens is approx. 37 mm. diameter. The 24 x 30 rectangle requires 
a circle of coverage of 40 mm. This would also suggest
a degree of unsharpness in the corners of a 24 x 30 rectangle at 2.8. 
The coverage proceeds to 100% as you stop down. The 2.8 is more than 
adequate for the 24 x23 format and probably right at the limit for the 
24 x 30 format. The actual picture size of 23 x 28 should be sharp, 
corner to corner at 2.8.

I was unaware that the Realist was made in a 7P format. With the 2.8 
lenses this seems possible. The frame spacing would be a bit goofy
because of the lens separation distance but nothing to worry about.

I wonder what sort of frame regulating system was used for the 1-3 
frame advance on the 7P Realist. In my article I mentioned the gearing 
system that I used was dictated by the availability of gears. I also 
have gear backlash to contend with because of the limitations imposed 
on my craftsmanship by imprecise tools. However, I do have a workable 
solution. My frame size is actually 25.3 mm x 32.2 mm and this stuffs 
an RBT wide(7 1/2 perf) very nicely. 

The conversion of a 2.8 Realist to 7P would be a piece of cake. With 
no lens mounts to remake, and no focal plane adjustments to worry about,
the remaining modifications are relatively easy. I haven't seen many
beat-up 2.8 Realists around, have you? 

Can you point me in the direction of the article by Wolfgang that 
you mentioned? I'd appreciate it.


John R. Slivon


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