[yucafrita]

I have a very strange experience using the DOF preview on my MZ-S.

When I put a tele or tele-zoom on it and use a higher aperture, and then engage the DOF preview, I can see that the upper edge of the viewfinder has a more or less pronounced shadow. It's not the same with every lens. E.g., with my M 135 3.5, there is absolutely no shadow, even with F32. With my M 75-150, starting from F8 or so, you see it. I first noticed it, when I put my DA* 300 on the MZ-S because there is a very small shadow even with F4 (thought this might be normal since the lens is usable for FF by "chance"). Then I tested the 75-150 and got puzzled.

On shorter lenses, there is absolutely no shadow seen in the viewfinder.

So I wonder if this is normal with longer lenses or something is weird with either the lenses or the camera's viewfinder. Havent used the DA* 300 yet on film and currently no DSLR in the house, so I cant check. But with the 75-150, I never saw an impact on the picture taken.

I mean, it could be a "feature" of the viewfinder. It is not vignetting! Just in case. I am sure about that.

PS: found that somewhere on the internet: "the mirror not attaching to the top of the light box properly and obscuring some of the light from the image circle cast by the lens"

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Last edited by yucafrita; 11-02-2018 at 11:53 AM.

[TomB_tx]

The top of the viewfinder shows the image from the bottom of the "light box" - as the image is inverted on film. The "shadow" with long lenses is typically due to the length of the mirror reflecting the light up towards the prism. Many SLRs used a mirror adequate for wide to moderate-tele, but would suffer "mirror-cutoff" a bit with very long lenses. Depending on the geometry of the lightbox a mirror long enough to completely avoid this might hit the back element of some shorter lenses, so this was a choice in the design.
The VF cutoff has no effect on the actual picture, just the VF.

[yucafrita]

Thanks a lot, great explanation!

[Alex645]

I concur with TomB_tx and that this vignetting in the viewfinder with DOF preview engaged and will not affect your actual exposure.

[nickthetasmaniac]

The top of the viewfinder shows the image from the bottom of the "light box" - as the image is inverted on film. The "shadow" with long lenses is typically due to the length of the mirror reflecting the light up towards the prism. Many SLRs used a mirror adequate for wide to moderate-tele, but would suffer "mirror-cutoff" a bit with very long lenses. Depending on the geometry of the lightbox a mirror long enough to completely avoid this might hit the back element of some shorter lenses, so this was a choice in the design.
The VF cutoff has no effect on the actual picture, just the VF.

Getting a bit OT, but is this why the later Hasselblad 500 series bodies had a floating mirror assembly?

[TomB_tx]

Getting a bit OT, but is this why the later Hasselblad 500 series bodies had a floating mirror assembly?

Yes, and a few 35mm bodies also used a linkage that moved the mirror back as it moved up to allow a longer mirror.

[stevebrot]

Yes, and a few 35mm bodies also used a linkage that moved the mirror back as it moved up to allow a longer mirror.

My Ricoh XR7 has an articulating mirror as does my Minolta SRT-101.


Steve