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02-18-2016, 07:51 PM   #16
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With the larger aperture/size viewfinder the scene should be brighter this should make it somewhat easier to focus manually. Can anyone with K1 currently confirm this please or give opinion? I didn't read every post here and now see Monochrome has asked the same question. thanks

02-18-2016, 08:32 PM   #17
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QuoteOriginally posted by gmans Quote
Can anyone with K1 currently confirm this please or give opinion?
You might want to include owners of FF AF film cameras in that request. The manual focus issues are the same for that class of camera as for dSLRs.

QuoteOriginally posted by gmans Quote
With the larger aperture/size viewfinder the scene should be brighter this should make it somewhat easier to focus manually.
Relative aperture (f/stop) is the same amount of light regardless of format. Focus screen design is more important in regards to viewfinder brightness and manual focus "sensitivity". Ironically it is the optimization of screens for brightness that is the root of manual focus deficiencies for auto-focus SLRs. At root is the use of a half-silvered main mirror to provide an image to both the PDAF system and the viewfinder. Less light from the mirror means less light at the focus screen. I cannot provide a detailed explanation of why the brightness optimization degrades the manual focus functionality except to summarize the points where the system is changed or compromised:
  • Apparent screen brightness is the same at f/1.4 as it is at f/4
  • Similarly the apparent DOF is greater than the actual lens aperture
  • The above point has serious implications for focus precision (the ability to reliably attain accurate focus) to the extent that it is difficult to accomplish fine focus with lenses faster than about f/3.5 when using the stock focus screen.
All three of the above points are true for the stock focus screens for most (all?) AF dSLR models across all brands.

In short, I would not expect improved manual focus performance on the K-1 using the stock (Natural Bright III) focus screen. Lacking optional screens similar to those available for Canon and Nikon FF bodies, the user strategies for manual focus remain the same as with the current model APS-C bodies using the stock screen:
  • Viewfinder magnifiers have been reported as helpful
  • Magnified live view with or without focus peaking
With any luck, Pentax will provide a high-performance matte screen similar to the Canon S-type and maybe even a split-image screen as options for the K-1. Note that I did not mention 3rd-party screens. The problem is having a donor screen suitable for modification to the Pentax camera. For a crop-sensor, the solution is to cut down available FF screens from various makers. With FF, it is unclear whether that would be possible to modify an existing screen.

The apparent viewfinder frame size for the K-1 is a little larger than the K-3/K-3ii, but not by much. That may make manual focus easier in much the same way as using a viewfinder magnifier.


Steve

Last edited by stevebrot; 02-18-2016 at 08:48 PM.
02-18-2016, 08:47 PM   #18
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QuoteOriginally posted by stevebrot Quote
You might want to include owners of FF AF film cameras in that request. The manual focus issues are the same for that class of camera as for dSLRs.



Relative aperture (f/stop) is the same amount of light regardless of format. Focus screen design is more important in regards to viewfinder brightness and manual focus "sensitivity". Ironically it is the optimization of screens for brightness that is the root of manual focus deficiencies for auto-focus SLRs. At root is the use of a half-silvered main mirror to provide an image to both the PDAF system and the viewfinder. Less light from the mirror means less light at the focus screen. I cannot provide a detailed explanation of why the brightness optimization degrades the manual focus functionality except to summarize the points where the system is changed or compromised:
  • Apparent screen brightness is the same at f/1.4 as it is at f/4
  • Similarly the apparent DOF is greater than the actual lens aperture
  • The above point has serious implications for focus precision (the ability to reliably attain accurate focus) to the extent that it is difficult to accomplish fine focus with lenses faster than about f/3.5 when using the stock focus screen.
All three of the above points are true for the stock focus screens for all dSLR models across all brands.

In short, I would not expect improved manual focus performance on the K-1 using the stock (Natural Bright III) focus screen. Lacking optional screens similar to those available for Canon and Nikon FF bodies, the user strategies for manual focus remain the same as with the current model APS-C bodies using the stock screen:
  • Viewfinder magnifiers have been reported as helpful
  • Magnified live view with or without focus peaking
With any luck, Pentax will provide a high-performance matte screen similar to the Canon S-type and maybe even a split-image screen as options for the K-1.

The apparent viewfinder frame size for the K-1 is a little larger than the K-3/K-3ii, but not by much. That may make manual focus easier in much the same way as using a viewfinder magnifier.


Steve
Thanks Steve for the explanation, i was more referring to the FF pentaprism size (.75x 100%) versus APSC (.95 x 100%) and probably should not have mentioned aperture. My apologies for wording the question badly. I believe that binoculars perform better with larger aperture lens than versus smaller lens at relative magnification and i thought this would also apply to pentaprism as well.

---------- Post added 02-19-16 at 02:50 PM ----------

I worked out that FF vs APSC is about one stop difference in apparent light, if my math was correct. Have to go now. cheers
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