This thread discusses cheap methods for fresnels. You can buy page magnfiers at office supply stores.. supposedly they work. Certainly something to consider.
I've thought about that too. What about something like these?
Originally Posted by holmburgers
Not really inexpensive, unless compared to those screens purchased directly from camera manufacturers. Certainly costlier than a simple page magnifier, but probably much higher quality. And no central focusing spot like the Yanke (and Wista 4x5, I have one of those) screens. They would also likely need to be custom trimmed to fit specific cameras.
"Some photographers are the poets of purple mountains' majesty. Some are the poets of the placid suburbs. Weegee is the poet of small-timers who died face down on a city pavement at 3 a.m. in a pool of their own blood."
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These look good, but like you said, they are entering the expensive range. A Beattie or Maxwell might be a comparable investment. How about old 3M overhead projector fresnels? There are several on eBay, perhaps they're good quality.
There are many office-grade page magnifiers, solar fire-starters, rear-window back-up aids, (those types of things), on eBay.
The one thing that is stopping me from buying a cheap fresnel today is the focal length decision. There are many options and so far, a couple different opinions.
Near the bottom a guy says that the FL doesn't matter http://photo.net/large-format-photography-forum/00T94L I'm inclined to believe this, since it's going to be flush against the GG anyways, and none of the focal lengths are anything less than 100mm or so. Another guy claims that they should match the FL of the lens.. Post #8 -> http://www.largeformatphotography.in...ad.php?t=50344
It'd be nice to get a definitive answer on this, but in the meantime, a cheap page magnifier is so cheap, it's worth testing. I've yet to see a focal-length mentioned for GG dedicated fresnels. Maybe they're trying to keep that hush-hush?
Oh, and lastly, apparently there are negative and positive fresnels. (converging and diverging I'd assume?)
Let's get to the bottom of this!
Here's info about the beattie screens http://www.camerascreens.com/LFormat...rge_Format.htm
I did buy one from china.
It is 2/3 stop brighter than my old bosscreen when camera is positioned at a gray card spotmeter: bos 6 2/3, china 7 1/3.
The fresnel is plastic, which can be scratched more easily than glass i assume.
This listing gives us some clues for what type of fresnel to look for... thickness .075 inch. Focal length about 6 inches.
I'm gonna pull the trigger and get a cheap fresnel at some point; will report back.
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Cheap magnifiers as a fresnel lens
I have had great luck using "cheap" office supply magnifiers as a camera fresnel lens. I have used them in my first homemade 4x5 for more than 15 years, in a Cambo SC 4x5 and in a 2x3 Graphic and several 9x12 folders. I also am using the Shen Hao fresnels in a Shen Hao 4x5 and a Burk & James 5x7 I converted to 4x5.
I believe that all work very well and do add several stops of light to the viewing screen. The primary advantage of a fresnel is that it makes the illumination across the ground glass even and makes seeing the entire groundglass at once possible, especially with small maximum aperture lenses and when using significant movements. In theory the fresnel, by making the illumination more even, does slightly reduce the contrast of the ground glass and can make exact focusing a little mure tricky, but this is really not very noticeable. In pure theory the frenel focal lenght should be chosen based on the lenses being used but I find that in large format practical use this is not critical (it is more so for 35mm)
The secret to using the magnifier is to buy one larger than your ground glass and to select only the central area of the magnifier. The center of the magnifier has to be exactly centered with the center of the ground glass. The fresnel should be installed on the lens side of the ground glass with the grooved surface in contact with the ground surface of the glass (many will argue otherwise, but this gives the best results and makes more sense from a physics perspective). I then measure the lens side of the ground glass frame and cut the fresnel to this size. Then one must figure out how to hold the fresnel in place and depending on how floppy it is, keep it from sagging. For short term use even adhesive tape will work, otherwise I glue shims of wood to hold it. Some camera backs already have a built in ledge for the fresnel, in that case I use it.
When focusing with a fresnel in place it is very important to focus on the image formed on the ground surface of the ground glass and not on the weaker image formed on the surgace of the grooves of the lens. So I recommend a focusing loupe. Maybe this is why some people don't like fresnels.
Wow, great write up and great timing. Last night at 'Michael's' I bought one on a whim and was planning to try it out soon.
Good luck holmburgers. Now, if only I could find one large enough for my 8x10...
Hey, mine's only about a half inch & a quarter inch short for 8x10" (respectively), so there's hope!