seany65
Well-known
I was wondering why the mirrors in TLR's aren't square, and was also wondering if the corners would be brighter if the were?
Anyone got any ideas?
Anyone got any ideas?
pvdhaar
Peter
They're not square because they're sitting at a downward 45 degree angle. Not only does the left to right of the mirror need to cover the image circle, top-down also does.
Retro-Grouch
Well-known
Peter, you're a genius! The answer is self-evident, once you stated it, but I would never have figured that out.
seany65
Well-known
Thanks for the info, Peter.
This is were I show that I only have two braincells. I understand the mirror is at 45 degrees to the focusing screen and that it needs to reflect the entire image up to the focusing screen, but I can't see how the mirror being narrower at the bottom helps.
This is were I show that I only have two braincells. I understand the mirror is at 45 degrees to the focusing screen and that it needs to reflect the entire image up to the focusing screen, but I can't see how the mirror being narrower at the bottom helps.
Retro-Grouch
Well-known
Maybe, since the image circle at the bottom of the mirror is closer to the lens, and thus smaller, the mirror can also be smaller. Maybe? My two brain cells are already getting tired...
Particular
a.k.a. CNNY, disassembler
The lens projects a cone of light that is big enough to cover the square aperture of the film or of the ground glass. It needs to be big at the point of focus (the film or ground glass), but at the lens side it is only the diameter of the lens. The mirror slices this cone at a 45 degree angle. This intersection could result in a unique egg like oval shape, but typical trapezoid was presumably easier to cut in glass.
seany65
Well-known
Thanks for the further replies and info.
Thing is, I've just been looking at a clip that compares an Arax CM to a Hasselblad, which are both 6x6, and BOTH of them have square mirrors that are at 45 degrees. So now, not only do I not know what to think about it all, I don't even know what day it is.
Thing is, I've just been looking at a clip that compares an Arax CM to a Hasselblad, which are both 6x6, and BOTH of them have square mirrors that are at 45 degrees. So now, not only do I not know what to think about it all, I don't even know what day it is.
Retro-Grouch
Well-known
And now I'm equally confused. Let's you and me go have a beer and forget the whole question!
Bill Jones
Contax Lens User
The Arax and Hasselblad are interchangeable lens cameras so they have to accommodate different lens projections. So they must be shaped to reflect longer cones which are closer to square. The square mirror handles this easily and is an easier shape to make. Also since the image is a square the whole cone of light is not used but only a square portion from its center. Normally the used (square or whatever shape you film/sensor is) portion of the cone does not extend to the edges of the cone.