[Bruce Clark]

Pardon my ignorance but I have just picked up my old film SLR Ricoh XR-P, slipped a Rikenon 50mm f1.8 lens on it and was blown away by the brightness in the viewfinder. Putting the same lens on the trusty K-7 the resulting view is quite dark. I have read some where reasons for this but my memory fails me. A quick google got me bogged down in all sorts of other arguments of film v digital.


I vaguely recall two arguments. Is it to do with the APS-C format letting less light in or is it some property of the focusing screen which pinches some light to operate the Auto focus system? If it is APS-C is the K-1 much easier to see through?


I understand alternative screens are available, Cats eye was one but I understand they are out of business. Is there any alternative now available? What are the advantages/disadvantages of such screens?

On a slightly separate note I also was re-introduced to the diagonal split screen focusing available in the Ricoh. What a marvelous thing that was, or is. I almost wish I never picked up the XR-P again.

I would appreciate any thoughts, comments or suggestions.

Thanks in advance

[Adam]

I don't think DSLR viewfinders are inherently much darker, but on APS-C cameras, they are certainly smaller, which can give that illusion.

Also, the magnification is lower, because unlike most film cameras, modern DSLR viewfinders give you 100% coverage.

[stevebrot]

The mirror on autofocus SLRs is part-silvered to provide an image to the autofocus sensor in the bottom of the mirror box. This significantly reduces the light to the focus screen and optical viewfinder. Special treatments are applied to the focus screens as a partial remendy to increase the apparent brightness of the viewfinder image. That and lower magnification allow for something close to the bright view available with manual focus SLRs of the 1980s.


Steve

[Jonathan Mac]

The K-7 viewfinder is much smaller, diverts part of it's light to the AF sensor and is not designed for manual focusing, which older film SLR viewfinders are.

[UncleVanya]

I can't recall is the k7 pentaprism or pentamirror? The latter is much darker and was used by some Pentax competitors (and pretax to a lesser degree).

[stevebrot]

I can't recall is the k7 pentaprism or pentamirror?

All flagship model Pentax dSLRs are pentaprism as are all manual focus film SLRs except for the ZX-M. It was with the AF film cameras that viewfinder specifications started to slip.


Steve

[UncleVanya]

All flagship model Pentax dSLRs are pentaprism as are all manual focus film SLRs except for the ZX-M. It was with the AF film cameras that viewfinder specifications started to slip.


Steve

Noted. I forgot that the k7 was a flagship.

[RKKS08]

What you see in the viewfinder of an APS-C camera IS darker.

The illumination per area of the projection to the sensor or screen is the same as with FF (at the same aperture setting).
But the size of the picture (for both sensor and screen) is just half of it.
So you either get a picture as bright as with FF, but half the size, or you optically enlarge it by 2x in the viewfinder path (ocular) and get half the brightness.

Law of physics.

[stevebrot]

So you either get a picture as bright as with FF, but half the size, or you optically enlarge it by 2x in the viewfinder path (ocular) and get half the brightness.

My K-3 has 100% coverage with .95x magnification.
The K-1 has 100% coverage with .70x magnification.

Mathematics says the K-3 has .25x greater magnification.

Luminance flux (perceived as brightness) is measured in terms of light energy per unit of angular measurement, so frame area (crop) is coincidental in regards to measurable brightness.

That leaves magnification and apparent distance relative size of the 3:2 frame (angular view).

Edit: The above line is clumsy and not quite accurate. The apparent viewfinder frame size for the two cameras is very similar with the K-1 appearing a little larger. The K-3 screen may appear somewhat dimmer as a factor of the greater magnification. This subject is deeper than it first appears. It is helpful to consider the focus screen as an array of emitters of set density viewed through a simple lens and go from there.


Steve

(Total light to the screen or sensor is not related to brightness/exposure to either.)

[Bruce Clark]

Thanks for the explanations, much appreciated. So it seems the mirror is a significant contributor to this phenomenon. I think it somewhat ironic that a technology intended to facilitate auto focus, a system that has its own inherent problems, should act to degrade the performance of the tried and true manual focus process. A part of me thinks there must be a better way to achieve autofocus, However I have to accept that folks smarter than me are designing cameras and this is the best way.

I am fixing to sell my XR-P's on Ebay but a tinge of nostalgia is giving me second thoughts.

Thanks again for you input.

[stevebrot]

I am fixing to sell my XR-P's on Ebay but a tinge of nostalgia is giving me second thoughts.

It was that twinge of nostalgia that saw me out shooting with my XR7 after almost two years with a K10D. The freedom of shooting with fast, light/compact kit and a viewfinder that was more like looking out a window rather than peering into the tunnel-like finder of my rather bulky, heavy, and slow dSLR solidified a decision to retain film photography as part of the mix.


Steve