View Full Version : New chamonix 45-F1 has dim ground glass

29-Jun-2017, 18:39
Hi all, I'm relatively new to large format but I just bought a chamonix 45-f1 with fresnel and noticed that the ground glass is very dark compared to my previous Toyo 45A. Does anyone know if this is a common problem with chamonix'? Or is the Toyo just known for being bright and I was spoiled by it? I'm not sure if I should trade up to a better GG or just get used to it. Thanks in advance

18-Aug-2017, 04:44
I thought the fresnel was duller too, but it has to do with viewing angle. I used a spot meter and measured the GG light output with and without the fresnel in place. The Fresnel is about 1 stop/EV brighter. You have to look squarely at the GG from a few inches away. I have resorted to using a 4x5 inch mirror at a 45 degree angle to see top and bottom of the image to make sure I am focused and have the elements in the image I want. IF your design is like mine you can remove the fresnel from the GG, it is not permanently attached. You can also try a piece of frosted plexiglass in place of GG to see if it feels brighter to you.

Steve Hamley
20-Aug-2017, 13:02
A certain amount of light hits the ground glass in any given instance, and anything that you put between the GG and the lens decreases the amount of light hitting the GG. Fresnels for LF cameras work by re-distributing the light, making some parts of the GG image brighter and some dimmer. GG/fresnels generally appear dimmer toward the edge because the light rays at the edge of the GG are hitting it at a shallower angle. You can see this because tilting the loupe improves things more with a fresnel than with a plain GG. I've used both setups, and the quality of both the GG and the fresnel matter. Generally if you can find a GG you like without a fresnel, that's a good thing.

Cheers, Steve

20-Aug-2017, 14:35
Can you remove the Fresnel on a Chamonix or is part of the focusing system, what I mean is, is the thickness of the Fresnel taken into account when you focus.

I know the Fresnel is behind the Ground Glass (not lens Side) so I am not quite sure

Steve Hamley
20-Aug-2017, 14:58
If the fresnel lens is behind the ground glass you can safely remove it because removing it does not change the effective focal distance. A lens in front of the GG does change the effective focal distance as does removing it. That's why in general lens attachments go on the front of the lens, not the rear.

Cheers, Steve