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Cheap Plastic Fresnel "Page Magnifiers" on Ground Glass - Try it, you'll like it!
The topic of using cheap Fresnel lenses on one's ground glass comes up often and here is some photographic proof that it does in fact WORK!
All I had to do was cut it to size and put it between the g.g. & the lens, ridges facing the lens. However, ridges facing the g.g. didn't make any noticable difference.
As you can see it makes a big difference, and it would be much more apparent if I had used a more evenly lit subject. Notice that a lot of the apparent vignetting is actually due to the subject.
The biggest improvement was not in brightness per se, but in off-axis viewing.
No special mounting or adhesive was necessary, the flimsy page magnifier is rigid enough to sit nicely in place and not buckle. Also, I haven't measured it with a pair of calipers but the thickness is no more than a credit card, probably considerably less. Let's say it's between 10 and 30 mils; do the math and see if that would affect your focus plane appreciably.
For less than $5 you can considerably improve your ground glass viewing. My next goal is to find a cheap method to add an anti-reflective film to reduce reflections from the viewing side. Any ideas?
From the film shooters will rise a well developed practice of the alternative processes that, in time, will be adopted in the age of the digital image to free it from the extreme boringness of pressing print.
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It also has a focal length, so it will affect your focus. Put it behind the ground glass and you will get the same benefits, but no focus shift.
My Chamonix came with the fresnel incorrectly mounted. It wasn't readily apparent that the focus was off for most shots since I had stopped down to f/22 or more, but all shots were softer than they should have been upon very close examination.
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On other fresnel screen installation instructions that I've seen some say behind, some say in front, depending on the camera. Why would that be?
I didn't notice any focus shift at f/4.7 and close range with this setup however. But thanks for the heads up; it's definitely worth inspecting closer.
From the film shooters will rise a well developed practice of the alternative processes that, in time, will be adopted in the age of the digital image to free it from the extreme boringness of pressing print.
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I picked up a couple of these sheets last year, but have held off for the time being. There was quite a long (and sometimes bitter) debate on LFinfo regarding the supposed focusing problems with the Chamonix fresnel. Have you noticed any difference in the sharpness of your images?
(While I was typing, my question was asked and answered... oh well...  )
Cheers,
Tom, on Point Pelee, Canada
Ansel Adams had the Zone System... I'm working on the points system. First I points it here, and then I points it there...
http://tom-overton-images.weebly.com
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putting the magnifier in front of the ground glass will change the focus point 'in theory'. however remember that as you stop down the "depth of focus" at the film plane also increases, so that should make up for the slight distance change. Beyond that, any degradation of the ground glass image would probably be due to the optical quality of the magnifier. At the prices of these sheet magnifiers you can count on marginal optical quality, at least as it relates to photographic optics.
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Behind the GG for me. This one is pretty thick plastic. Acts as a GG protector also 
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I've been using them on my cameras for several years. They work wonders. There's a guy that's been selling these as 8x10 fresnels on ebay for quite some time. Cut to fit your camera for about $60 more than the version you get at staples. Quite a racket.
www.vinnywalsh.com
I know what I want but I just don't know how to go about gettin' it.-Hendrix
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 Originally Posted by holmburgers
On other fresnel screen installation instructions that I've seen some say behind, some say in front, depending on the camera. Why would that be?
I didn't notice any focus shift at f/4.7 and close range with this setup however. But thanks for the heads up; it's definitely worth inspecting closer.
If the camera is designed for a fresnel it will have the GG in a different plane than one designed to not use one. So the directions will depend on the camera design.
When i was testing my Chamonix I first tested close up and didn't notice a shift with a few casual shots. However further experimentation proved I was wrong.
If you do move the fresnel to behind the glass you may want to protect it from scratches. I use a sheet of mylar and hold it and the fresnel on with scotch tape. Looks sloppy, but works fine and is as bright as when it was in front of the glass.
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Ok, so the answer is....? Put in between your eyeball and the groundglass side nearest your eyeball for no focus shift?
thanks!
Robert N.
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That's what L Gebhardt is saying and it seems like that would be a safe bet. But I'll say, in my limited testing, the difference appears to be nominal.
I'd really like to tackle the calculation, but I'm not sure if I'm up to it at the moment... still sipping my coffee.
Let's imagine we have a 135mm lens at f/4.7 (Raptar, Optar, Graftar) and our subject is only 2 feet from the lens (a fairly critical circumstance I would suspect). What difference in the subject distance would be necessitated by a .003" change at the plane of focus; again, 3 mils being a liberal estimate of the fresnel thickness.
From the film shooters will rise a well developed practice of the alternative processes that, in time, will be adopted in the age of the digital image to free it from the extreme boringness of pressing print.
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