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03-20-2012, 11:03 AM   #1
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Pentax AL 75mm F2.8 optical diagram

Hi

Does anyone might have an optical diagram for the Pentax 75mm F2.8 AL lens for Pentax 67??

Thanks

03-20-2012, 07:11 PM   #2
Ole
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Let me know if you find it, I have been looking all over for it!
03-21-2012, 11:24 AM   #3
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well if i find it, I will surely post it here, but so far no success, thats why I opened this thread
maybe some one will do us both a favor and post it
03-22-2012, 01:28 PM   #4
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I have never seen a cross section of the 75 AL. The other lens that came out at the same time was the 90-180 zoom. I have never seen a cross section on that one either. Possibly, Pentax decided not to release the design of these recent lenses? As an optics geek, I can guess what they both look like.

03-22-2012, 01:47 PM   #5
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i supose thats probably the case, cause i had spent too much time looking for it than i wanted to.
oh well, maybe some day, who knows.

thanks folks
03-23-2012, 05:05 PM   #6
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My guess as to what its cross section is; based somewhat on their 55mm latest.
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12-17-2016, 07:46 AM - 1 Like   #7
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mystery revealed..

I found this on a German website some years ago
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12-17-2016, 07:59 AM   #8
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QuoteOriginally posted by Lennart Quote
I found this on a German website some years ago
Good stuff, thanks for posting and welcome to the forum!

Phil.

12-17-2016, 11:19 AM   #9
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That's different from what I was expecting. It is not similar to any Pentax medium format design. It does look similar to the FA 35mm AL f/2.0.
12-17-2016, 02:04 PM   #10
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Information about this lens, including a small optical construction diagram, is included in the "owners manual" packaged with the lens when new.
Mine came with this little manual, but God knows what happened to it and the silver box when we shifted house. Besides which though, schematics don't interest me. But performance certainly does. Viewing a few landscape and scenic pics made by colleagues had me literally swinging from the treetops in search of one! This lens is the very, very best one I have ever plundered more than a thousand dollars on.

Last edited by Silent Street; 12-17-2016 at 06:15 PM.
12-18-2016, 08:43 PM   #11
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QuoteOriginally posted by desertscape Quote
That's different from what I was expecting. It is not similar to any Pentax medium format design. It does look similar to the FA 35mm AL f/2.0.
Yup, looks similar (but not identical) to the 35/2 AL.

Also looks similar-ish to the Zeiss Distagon 40mm f/4.



And here's the Distagon 50mm f/4 FLE CF:



Can't find a diagram of the Pentax 67 55/4 late lens, but since it's a Distagon type it may be similar to that. Or maybe not, some of the distagon versions were fairly different and those may be the ones the 55/4 is based on.

It's not real surprising that the 75/2.8 AL is so different, the 6x7 lineup was very straightforward in most ways. The lenses are mostly just standard designs (105/2.4 Planar type, 150/2.8 double-gauss type, etc) and largely consists of scaled-up designs from the 35mm lineup (which isn't to knock it in any way - it's actually a "greatest hits" collection of their vaunted K-series lineup). Apart from the zooms and the EDIF telephoto lineup everything is pretty conventional 70s-vintage lenses, so a modern aspheric lens is a departure from the rest of the line.
12-19-2016, 09:56 AM   #12
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The cross section for the 55 latest for the 67 can be found in the lens booklets of 1986 through 1988. The Zeiss 50 Distagon above is quite similar to the second version Pentax 55mm (their 1st f/4).
Scaling up designs from the 35mm world caused problems and so designers had to modify them. An achromatic Double Gauss 50mm for a 35mm camera did not have color correction problems but scaling that up to a 165mm, color correction now becomes more of an issue. One can be quite sure that different glass types were used in the scaled up versions for the 67 to prevent tertiary spectrum and lateral color.
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