Microprisms...

[eight08]

Hey guys! I have a Yashica 109MP, it has a microprism focusing thingy... and just wondering, sometimes, when focusing, one of the sections goes black... why is that? and how would it affect the shot?

 

[KmH]

Sounds like something worth looking up in that little book kinda thingy that comes with most cameras.

 

[Derrel]

Hey guys! I have a Yashica 109MP, it has a microprism focusing thingy... and just wondering, sometimes, when focusing, one of the sections goes black... why is that? and how would it affect the shot?

Sounds like you might mean a split-image rangefinder focusing 'thingy', which will go black when the maximum aperture of the lens or lens+ extension tube or lens+ teleconverter drops below roughly f/5.6 or so. It's called "rangefinder black-out" and is/was pretty common with "slow" lenses.

The split-image rangefinder in the center of the viewfinder screen was often surrounded by a microprism circle, often called the microprism doughnut.

 

[eight08]

Hey guys! I have a Yashica 109MP, it has a microprism focusing thingy... and just wondering, sometimes, when focusing, one of the sections goes black... why is that? and how would it affect the shot?

Sounds like you might mean a split-image rangefinder focusing 'thingy', which will go black when the maximum aperture of the lens or lens+ extension tube or lens+ teleconverter drops below roughly f/5.6 or so. It's called "rangefinder black-out" and is/was pretty common with "slow" lenses.

The split-image rangefinder in the center of the viewfinder screen was often surrounded by a microprism circle, often called the microprism doughnut.

Thanks for the reply... i was just wondering, would it affect the shot at any way?

 

[eight08]

Sounds like something worth looking up in that little book kinda thingy that comes with most cameras.

It's not in there...

 

[Dwig]

Hey guys! I have a Yashica 109MP, it has a microprism focusing thingy... and just wondering, sometimes, when focusing, one of the sections goes black... why is that? and how would it affect the shot?

Sounds like you might mean a split-image rangefinder focusing 'thingy', which will go black when the maximum aperture of the lens or lens+ extension tube or lens+ teleconverter drops below roughly f/5.6 or so. It's called "rangefinder black-out" and is/was pretty common with "slow" lenses.

The split-image rangefinder in the center of the viewfinder screen was often surrounded by a microprism circle, often called the microprism doughnut.

Actually, one of the facets in a "split rangefinder prism" or a "microprism array" can black out at wider apertures. When this is happening the cause is that your eye is not well centered in the VF. The blackout Derrel is refering to occurs when the lens' maximum aperture is so slow that no matter where you place your eye one of the RF's prisms is black/dark. When this happens with microprisms, only one or two of the six facets on each of the hundreds of little prisms blacks out. Focusing is not practical, but the dark areas are small and less annoying.