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11-02-2013, 11:15 AM   #1
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Full frame design issues.

Will the Pentax FF body have a small mirror, compared to the Canon and Nikon FF offerings? My SF1 film body has a much smaller mirror then my Canon 5D FF. The reason for the smaller mirror is the extra long diaphragm lever (11.5mm). A smaller mirror means a dimmer view finder, but possible higher burst speeds due to lighter mirror. They could clip the outer corners of the mirror to clear the lever linkage. An entirely new all electrical mount would solve the issue, but orphan all of the F and FA lenses. So its not likely. A fixed translucent mirror as used on the circa 1970 Canon Pelix SLR and some Sony FFs today would work and give higher burst speeds, but finder brightness would suffer. The effective aperture of any lens used would be at least one stop slower also. I hope that Pentax follows Nikon FFs by automatically taking cropped images when a DX lens is mounted, unlike Canon were Crop lenses wont even fit a FF body. What do you think the final configuration will be like?

11-02-2013, 12:06 PM   #2
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Mirror size (length actually) has little to do with viewfinder brightness and much to do with viewfinder image "clipping" with longer lenses. This was a frequently-noted issue for 35mm SLR reviews back in the old days. Longer is better and most (all?) makers eventually moved to an articulated mirror mechanism rather than a simple hinge* to work around things like protruding rear elements. (I am not sure what you mean by long diaphragm lever. The aperture actuator linkage on all my K-mount cameras is well outside the boundaries of the mirror box proper and the mirror travel.)

Size vs. brightness is only a consideration when the mirror gathers light as with a reflecting telescope.

I don't know that mirror size is more of a design issue with digital FF than it was with 35mm film.


Steve

* All of my M42 film bodies as well as my KX have a simple hinge. My Minolta SRT-101 (ca 1969) has a huge mirror and articulated travel. The same is true for my XR Ricoh bodies (early 1980s) and Pentax Super Program.
11-02-2013, 12:29 PM   #3
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QuoteOriginally posted by Big Dave Quote
Will the Pentax FF body have a small mirror, compared to the Canon and Nikon FF offerings? My SF1 film body has a much smaller mirror then my Canon 5D FF. The reason for the smaller mirror is the extra long diaphragm lever (11.5mm). A smaller mirror means a dimmer view finder, but possible higher burst speeds due to lighter mirror. They could clip the outer corners of the mirror to clear the lever linkage. An entirely new all electrical mount would solve the issue, but orphan all of the F and FA lenses. So its not likely. A fixed translucent mirror as used on the circa 1970 Canon Pelix SLR and some Sony FFs today would work and give higher burst speeds, but finder brightness would suffer. The effective aperture of any lens used would be at least one stop slower also. I hope that Pentax follows Nikon FFs by automatically taking cropped images when a DX lens is mounted, unlike Canon were Crop lenses wont even fit a FF body. What do you think the final configuration will be like?

I believe Pentax has already made millions of full frame cameras with more linkages to the lenses than are required now.
11-02-2013, 01:21 PM   #4
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I think that for them the main design issue is to have an effective SR mechanism on a larger - thus heavyer - sensor, in a compact body. Apparently they couldn't solve the issue with the 645 D as they have introduced in lens image stabilisation for the last tele lens (100 Macro if my memory is OK) they designed.

11-02-2013, 02:24 PM   #5
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QuoteOriginally posted by stevebrot Quote
Mirror size (length actually) has little to do with viewfinder brightness and much to do with viewfinder image "clipping" with longer lenses. This was a frequently-noted issue for 35mm SLR reviews back in the old days. Longer is better and most (all?) makers eventually moved to an articulated mirror mechanism rather than a simple hinge* to work around things like protruding rear elements. (I am not sure what you mean by long diaphragm lever. The aperture actuator linkage on all my K-mount cameras is well outside the boundaries of the mirror box proper and the mirror travel.)

Size vs. brightness is only a consideration when the mirror gathers light as with a reflecting telescope.

I don't know that mirror size is more of a design issue with digital FF than it was with 35mm film.


Steve

.
The aperture or diaphragm lever is longer then any other current brand. This does result in a narrower mirror. Corner fall off in brightness is an issue in FF digital dslrs. This may be due to some of the light being passed through to the auto focus system. Canon uses a larger mirror in their FF dslrs then older film models. The bigger mirror presents clearance issues when other brand lenses are adapted to Canon FF bodies. I use most of the popular brand manual lenses on my 5D, such a Nikon,Olympus and Zeiss,but my pentax lenses can't be fitted to my 5D without removing the lever. I don't think that Pentax is going to release a FF anyway.
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