Omega 45 d

B

bandeau_rouge

Guest
Hello here is a toot of a question.

When i use the camera properly, and look at things on the ground glass, the ground glass is the standard dark and dreary image except for about 2" circle in the middle.

When I turn the lens to bulb, lock it open with my release cable, and look through the lens and then at the ground glass, i see beautiful, clear, crips, wonderful images on the ground glass.

I have been coming across the idea of either a fresnel sheet or a rick oleson bright screen.

I know the fresnel can alter the focus plane off of the ground glass, but the bright screen, that is supposed to be a complete replacement of ground glass correct?
 
If the fresnel is properly installed, it will not and cannot alter the focus of the camera.
It may alter the focus point of your loupe.
The most common arrangement is to have the ground glass installed with the ground surface facing the lens, with nothing intervening. The fresnel sheet is them installed on the photographer's side, so as to concentrate the image on the ground glass into a narrower cone, which makes the edges seem brighter. As the fresnel sheet has some thickness, it means the loupe is a little further away from the focusing surface.It may need adjusting a little to get the best image.
It's worth mentioning that quite modest magnifications (4x - 6x) are needed for loupes. If you can see the grain of the ground glass, further magnification will resolve no more detail.
Some cameras were designed to have a different arrangement and the two arrangements are not interchangeable. Other members know a good deal more about this.
 
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I make screens regularly, they can be 2 stops brighter than old screens. If the camera didn't have a Fresnel from new then you add it to the rear (eye side) of the GG screen, that way you keep correct focus,

My Crown Graphic came without a fresnel, so I had to add one to the rear, with a new screen as well it was 3 stops brighter and far easier to use, particularly hand held. Some Pacemaker Crown & Speed Graphics came fitted with a fresnel under the GG, the frames were machine to ensure focus was correct. As the casting numbers are the same you need to know which frame you have. Luckily I have both so can easily tell the difference.

Ian
 
the omega view 45D came without a fresnel from factory, but the manual mentions they sold a nifty fresnel lens if you wanted it.
 
bandeau_rouge said:
the omega view 45D came without a fresnel from factory, but the manual mentions they sold a nifty fresnel lens if you wanted it.
Click to expand...

Sinar and other manufacturers offered Fresnels that clipped into the ground glass frame,

Ian
 
Although the makers of fresnels can make huge promises of increased brightness, any old fresnel, like the ones used as a reading aid, will give some improvement and are very much cheaper. You can simply tape it in place if the camera’s back has no special device and they can easily be cut to fit. A specialist screen will obviously be better, but can be much more expensive.
 
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This shows how much overall brightness becomes with a fresnel.

I have cut down cheap fresnels, but the ones I found aren't totally flat so not ideal, but work well. On this particular Crown Graphic (now with a member in Edinburg) adding a new screen and a fresnel increased screen brightness by 2 stops in the centre, and over 3 stops approx an 1¼" from the sides. A huge improvement.

Ian
 
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