i am poor, and i need a fresnel lens for my 4x5 view camera. i'm not having muc h luck finding a used one, and a kid at the campus camera shop told me that one of the plastic lenses you see in the rear window of an R.V. would work just as w ell (cut to fit). is this true? also, anyone got a lead on a used fresnel lens ?
Try Glassers (or is it Glazers) in Seattle. Although I have never purchased a used one I believe they sell them when they have them. Ask for someone in the Large Format Department 1-888-531-3232.
Leslie,
Why do you think you need a fresnel lens for your 4x5 camera? I can't stand the things. If you're on a budget you'd be much better off investing in film.---Carl
I hate them too.
Edmund Scientific offers a bunch of fresnel in different focal lengths.
http://www.edmundscientific.com/Products/Search.cfm?query=fresnel
None will accurately replace the fresnel in a Crown Graphic, but if you are placing it behind the ground glass (farther away from the lens) it won't affect your groundglass focal plane.
I have used a map page magnifier cut to fit my 8 X 10 for the past 4 years. I think it's 4 years, it could be five now.... I used one on my 5 X 7 before that.
Leave the g.g. in place, cut the fresnel to fit the inside and tape it in place. Test for focusing accuracy by focusing on a crisp dollar bill or a newspaper page and then exposing with the aperture wide open. I'm sure others will additional thoughts on the subject.
They do leave something to be desired when used with wide lenses. A very finely ground g.g. might actually solve your problems though.
The difference between the Edmund Scientific fresnel lenses and the one that Calumet wants to sell you is one of fit and quality. I bought an Edmund as an experiment. You were correct stating it to be like the ones they stick in car windows. This one was for a fish aquarium. Fortunately, it arrived damaged, so I got to see how it would not suit my needs, and was able to return it.
Fresnel lenses can be mounted either between the lens and ground glass, or behind the ground glass. If between the lens and gg, it is out of the way and less subject to physical damage. They are just pieces of plastic and will eventually get trashed and scratched. However, it is claimed the fresnel itself has a focal length that can interact with the accurate focus on the gg itself. My Crown Graphic fresnel is mounted in this manner. But the back is specifically engineered to keep the gg focal plane located correctly to the film holder.
If you put the fresnel behind the gg, it will be more exposed to scratching, but can also be easily removed when you figure out how much it really sucks, plus it won't interfere with the location of your gg focusing plane.
Using a fresnel is a personal choice thing. I have them on my Crowns, and do not have them on my Sinar. Personally, I prefer not having a fresnel. The screen is indeed brighter and more uniformly illuminated (with standard lenses), but is harder to focus.
Each fresnel lens has a specific focal length. Hold it up to light and focus it like you would a magnifying glass. This is the approximate focal length. It appears the fresnel focal length should match that of the lens being used. This is speculation on my part, as the Crown Graphic fresnel lenses have a 135mm focal length which is the same as its standard lens. The fresnel doesn't do much good on wide angles such as my Nikkor-SW 75 on the Crown. It still has a hot spot in the center and very dark at the edges. This is life with a wide angle, so you deal with it.
Get a Linhoff Super Screen. It is a plastic screen that replaces the GG. I have one and it works well. Wide open I can see corner to corner. It takes a liitle more care in focusing than the GG, but is worth it to see whole image. They cost around $75.00 and you can get one from B&H in New York.
I didn't hate the fresnel on my Toyo 45A until I recently got a 90mm Super Angulon. Ugh. Can't see the edges and corners of the images at all. I would like to try without it, but I understand is designed into the Toyo, and I would have to shim the ground glass if I removed it (It is in front of the glass) to maintain proper focusing.
Fresnels should not be placed between the lens and ground glass. A fresnel displaces light about 1/3 the thickness of the fresnel. True, the ground glass can be adjusted to compensate for the fresnel, but there is still a problem. Light from a lens projects at different angles. When light passes through the fresnel at a steep angle, such as with a wide angle lens, the light passes through a greater thickness of the fresnel. This creates a curvature of field. To compensate for a fresnel placed between the lens and ground glass, the ground glass needs to be more than just moved. It needs to be curved, and the amount of curvature would need to be adjusted for each lens used, and even for the movements used with any particular lens. A curved ground glass is, of course, ridiculous. My point is, putting a fresnel between the lens and ground glass can be done for convenience sake with reasonable results, but if you want to be able to focus precisely, do not place a fresnel between the lens and ground glass.
Posting Permissions
Reply With Quote
Bookmarks