rbiemer
Unabashed Amateur
I've been thinking I want to add a fresnel lens to my focus screen for my 4x5 camera but after reading around the web, I keep seeing conflicting info about this.
My desire is to brighten the screen, the camera and my lens focus fine it is just a little dark. And I don't want to spend a ton of $ for this--it's about convenience not necessity.
Initially, I figured to just find some inexpensive fresnel and put it on the back/out side of the screen, the side facing away from the lens. This, I think, wouldn't change where the image is formed for focus and would, I thought, just increase apparent brightness.
However , after spending this morning reading about this, I am seeing lots of disagreement about the correct way to do this.
I'm a little interested in the theory about this but am much more interested in empirical/practical application.
So, who's got the straight poop on this?
Thanks!
Rob
My desire is to brighten the screen, the camera and my lens focus fine it is just a little dark. And I don't want to spend a ton of $ for this--it's about convenience not necessity.
Initially, I figured to just find some inexpensive fresnel and put it on the back/out side of the screen, the side facing away from the lens. This, I think, wouldn't change where the image is formed for focus and would, I thought, just increase apparent brightness.
However , after spending this morning reading about this, I am seeing lots of disagreement about the correct way to do this.
I'm a little interested in the theory about this but am much more interested in empirical/practical application.
So, who's got the straight poop on this?
Thanks!
Rob
sevo
Fokutorendaburando
Plug-in rear fresnel frames, as popularised by sinar, are excellent for composition and simply pop out for focusing. I am no great friend of permanently mounted rear fresnel lenses, as they interfere with magnifier focusing. And I strictly avoid lens side fresnels - these can screw with focusing (manufacturer mounted ones won't, but after a few decades of after-market repairs many frames are mis-calibrated) and work best within a rather limited range of focal lengths (fresnel/gg stacks suitable for ultra wide angle lenses tend to be rare to non-existent, at least in Germany).
mooge
Well-known
I have a fresnel lens on the back of my Sinar F2, behind the ground glass and held in by the tabs that hold the ground glass in. The GG is still in the same place as it was originally, so focus is not affected (I'm pretty sure anyways). The fresnel lens was bought for cheap off of ebay, it's like a page sized magnifier that I cut down to 4x5.
I'm assuming I liked it, because it's still there (as opposed to my Rolleiflex, where I went back to the original screen over a Rick Oleson screen), but honestly I don't remember how dark the corners were before I put it in. I don't have any issues focusing.
I'm assuming I liked it, because it's still there (as opposed to my Rolleiflex, where I went back to the original screen over a Rick Oleson screen), but honestly I don't remember how dark the corners were before I put it in. I don't have any issues focusing.
Jack Conrad
Well-known
My Crown Graphic Special 4x5 has a fresnel screen that sits between the
lens and the ground glass. I haven't shot with it yet, though it appears to focus
ok. I'm probably going to sell it here before too long.
lens and the ground glass. I haven't shot with it yet, though it appears to focus
ok. I'm probably going to sell it here before too long.
Rangefinder 35
Well-known
When I think about it, the ground glass catches focused light rays on the matte side. If you put the fresnel lens between the ground glass and the lens, it will project the fpcused light on the matte side of the GG. I added fresnel lens to my Technika IV, because GG was very dark, especially with my 90mm /6.8 Rodenstock Grandagon. It improved the image-taking tremendously, as D. Trump would say...
Corran
Well-known
It depends on the camera!
x-ray
Mentor
I bought my Sinar Norma new in 1969 and purchased the mounting frame with the external fresnel and also bought the internal fresnel that goes between the lens and GG. I tried both and ditched the external fresnel but kept the frame to mount roll film masks. The internal fresnel is cut such to compensate for focus shift.
I've had several Linhof cameras with external fresnels and don't like that system nearly as well. I find finedocus is much more difficult when viewing through the fresnel.
On my 5x7 and 8x10 Deardorffs I have really high quality GG and prefer no fresnel with the exception of using wide lenses. Even then with a bright GG it's still possible to view with minimum issues.
I've had several Linhof cameras with external fresnels and don't like that system nearly as well. I find finedocus is much more difficult when viewing through the fresnel.
On my 5x7 and 8x10 Deardorffs I have really high quality GG and prefer no fresnel with the exception of using wide lenses. Even then with a bright GG it's still possible to view with minimum issues.