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11-23-2018, 05:23 AM - 2 Likes   #1
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On Pentax 6x7

Came across this and just had to share... I put a bid in for a soft focus Mamiya rb67 lens and then I found out that I need diffusion disks for it and that the lens I am bidding on does not have them. Ugh. So here is me digging through the net trying to find them or at least trying to find out if I can make them. And I came across this review of mamiya that had a bit on Pentax 6x7. I just had to share it.

"And there was the*Pentax 6x7, which deserves its own paragraph. The body was physically clumsier - it was a giant pumped-up Pentax Spotmatic, along the lines of the Soviet*Kiev 60*- but had a sierra hotel range of Takumar lenses. Including the standard 105mm f/2.4, which was almost all the lens you needed. Top shutter sync was only 1/30, which was problematic for the very photographers most likely to use it - wedding and portrait shooters, with their standard backlit sunlight / fill-flash shots. But 105mm f/2.4 in 6x7 format, cor.*Diane Arbus used one*towards the end of her life and the Pentax 67 has always had an artier, more tasteful reputation than the relatively agricultural RB67. Walk into a camera club meeting with a Pentax 67 and you'll be treated like a God. Men will respect you, women will disrobe for you. The clouds will part for you. Your clothes will fit you. Nothing stands in your way, when you have a Pentax 67."


Women and Dreams: Mamiya RB67: Heavy Plasma

11-23-2018, 11:15 AM   #2
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That's an entertaining description of the P6x7. About every medium format film camera has strong and weak points relative to other medium format film cameras. Two major catagories of MF cameras include studio and field designs. Each can be used in the domain of the other but typically not as conveniently or to the capacity of the other design.
11-23-2018, 11:22 AM - 1 Like   #3
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If I wasn't happily married I'f be blowing the dust off my 67 right now
11-23-2018, 12:12 PM   #4
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QuoteOriginally posted by IgorZ Quote
... I put a bid in for a soft focus Mamiya rb67 lens and then I found out that I need diffusion disks for it and that the lens I am bidding on does not have them. Ugh. So here is me digging through the net trying to find them or at least trying to find out if I can make them. ...
On the subject of diffusion, the filter and flash company Cokin once manufactured a diffusion filter for portrait work. (Checking my old brochures, there were several of them.) Perhaps Cokin still do manufacture them. Their filter would likely need to be cut down to fit. However, if in your case the filter is part of the optical prescription, as the rear filters are used in the MF fisheye from Arsenal, then thickness times index of refraction would have to be the same. Let me know if you need a Cokin number to hunt it down, as I would have to root a bit to find it.

11-23-2018, 01:21 PM   #5
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QuoteOriginally posted by IgorZ Quote
Came across this and just had to share... I put a bid in for a soft focus Mamiya rb67 lens and then I found out that I need diffusion disks for it and that the lens I am bidding on does not have them. Ugh. So here is me digging through the net trying to find them or at least trying to find out if I can make them. And I came across this review of mamiya that had a bit on Pentax 6x7. I just had to share it.

"And there was the*Pentax 6x7, which deserves its own paragraph. The body was physically clumsier - it was a giant pumped-up Pentax Spotmatic, along the lines of the Soviet*Kiev 60*- but had a sierra hotel range of Takumar lenses. Including the standard 105mm f/2.4, which was almost all the lens you needed. Top shutter sync was only 1/30, which was problematic for the very photographers most likely to use it - wedding and portrait shooters, with their standard backlit sunlight / fill-flash shots. But 105mm f/2.4 in 6x7 format, cor.*Diane Arbus used one*towards the end of her life and the Pentax 67 has always had an artier, more tasteful reputation than the relatively agricultural RB67. Walk into a camera club meeting with a Pentax 67 and you'll be treated like a God. Men will respect you, women will disrobe for you. The clouds will part for you. Your clothes will fit you. Nothing stands in your way, when you have a Pentax 67."


Women and Dreams: Mamiya RB67: Heavy Plasma
Darn It! I went to the wrong meetings! Lol!
11-23-2018, 02:13 PM   #6
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QuoteOriginally posted by kaseki Quote
On the subject of diffusion, the filter and flash company Cokin once manufactured a diffusion filter for portrait work. (Checking my old brochures, there were several of them.) Perhaps Cokin still do manufacture them. Their filter would likely need to be cut down to fit. However, if in your case the filter is part of the optical prescription, as the rear filters are used in the MF fisheye from Arsenal, then thickness times index of refraction would have to be the same. Let me know if you need a Cokin number to hunt it down, as I would have to root a bit to find it.
Thanks for the suggestion, I'll check out Cokin. From what I understand, the disks used with mamiya lenses are just pieces of metal with one big hole in the center and a bunch of small holes around it.
11-23-2018, 03:10 PM   #7
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QuoteOriginally posted by IgorZ Quote
Thanks for the suggestion, I'll check out Cokin. From what I understand, the disks used with mamiya lenses are just pieces of metal with one big hole in the center and a bunch of small holes around it.
Were these disks mounted where lens filters are usually mounted, in front of the objective lens? What a hole pattern would be expected to generate (located at the effective pupil) is a complex diffraction pattern different from the diffraction limited Airy disk pattern that usually results from setting the f/no to a high value. Solving a nightmare of equations would yield the resulting diffraction pattern from an arbitrary hole pattern. I have never seen a paper that described hole patterns that would be good for slightly diffuse portraiture. I also cannot imagine what modulation transfer function would be superior for this task relative to just a low-pass filter. But what I imagine results is the potential for narrow depth of field (from low f/no) plus blur within the DOF that looks different than spherical aberration or whatever. Velly intellesting approach.

I wonder if this is treated to some extent in Introduction to Statistical Optics by Edward L. O'Neill. I see this has become a Dover book, so I'll have to get a copy next time I order some books.

---------- Post added 23rd Nov 2018 at 17:48 ----------

I dug out the Cokin filter. To the casual viewer it would look clear and transparent. Close inspection reveals a random pattern of "microscopic worm tracks" on one side of the plastic. I believe these changes in thickness cause different rays from the same [far field] point to have different random phases at the focal plane that will subtly degrade the image resolution. This might be imagined as tiny amounts of weak narrow-angle forward scattering applied to the image. A multiple hole aperture would also create both image diffraction but also phase effects from the offset holes. I suspect the results are different in how each portrait effect looks macroscopically.

The Cokin filter designation is Diffuser 1 P. 083

Last edited by kaseki; 11-24-2018 at 10:21 PM.
11-23-2018, 05:45 PM - 1 Like   #8
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QuoteOriginally posted by IgorZ Quote
[...]
Top shutter sync was only 1/30, which was problematic for the very photographers most likely to use it - wedding and portrait shooters, with their standard backlit sunlight / fill-flash shots.
This only holds true for amateur users who did not look at the advantages of leaf shutter lenses with flash use within the Pentax 6x7 / 67 lens line-up. For professional users LS lenses were in widespread use irrespective of the 1/8s FP sync speed on the camera side but any speed up to 1/500 on the LS side.

11-24-2018, 05:46 PM - 1 Like   #9
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FYI-- Pentax did make a soft focus 120mm lens for its 67. They are not common and are probably soft due to intentionally uncorrected aberrations (probably spherical).
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