i'm accessorizing. do i go for a real fresnel lens or will a cheap immitation workgreenspun.com : LUSENET : Large format photography : One Thread
i am poor, and i need a fresnel lens for my 4x5 view camera. i'm not having much 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 well (cut to fit). is this true? also, anyone got a lead on a used fresnel lens?
-- leslie schwab (email@example.com), June 12, 2000
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.
-- Paul Mongillo (firstname.lastname@example.org), June 12, 2000.
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
-- Carl Weese (email@example.com), June 12, 2000.
I hate them too.
-- William Marderness (firstname.lastname@example.org), June 12, 2000.
Edmund Scientific offers a bunch of fresnel in different focal lengths.
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.
-- Bruce Gavin (email@example.com), June 12, 2000.
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.
-- Sean yates (firstname.lastname@example.org), June 12, 2000.
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.
-- Bruce Gavin (email@example.com), June 13, 2000.
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.
-- John Laragh (firstname.lastname@example.org), June 13, 2000.
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.
-- John H. Henderson (email@example.com), June 14, 2000.
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.
-- William Marderness (firstname.lastname@example.org), June 14, 2000.
There is no universal rule as to the placement of fresnel lenses in front of or behind the ground glass. It depends on the design of the camera. For example, from memory and without checking, Linhof Tech IIIs were designed for a fresnel to be placed outside the ground glass, Tech IVs and later are designed for the fresnel to be placed inside the ground glass. You need to check with the manufacturer or some other reliable source to see which way your camera is designed before trying to install a fresnel. Actually, IMHO, the Bosscreen sold by Bromwell Marketing and probably other sources is perhaps the best compromise. It replaces the ground glass. It isn't technically a "bright screen" but it does spread the light evenly around the ground glass so that it's easier to compose. More importantly, it doesn't involve use of a fresnel lens so it's actually easier to focus. They are farily expensive - around $150 - but I think they're worth it.
-- Brian Ellis (email@example.com), June 15, 2000.
I have about 6 Fresnel lens for my 8x10 and probly as many or more for my 4x5. Some work some don,t. Some were very expence and some were cheap. Most of the time I end up useing plain old groung glass. The ground glass I use has fine acid edching and I wash it with dish to keep it clean. An eye lope helps.
-- Richard Ritter (firstname.lastname@example.org), June 20, 2000.
"Tech IVs and later are designed for the fresnel to be placed inside the ground glass"
Not for over 2 decades has this been true!
Linhof's come with fresnel clips to place the fresnel on the OUTSIDE -THE SIDE NEAREST THE EYE, very, very old Linhofs had the fresnel inside closest to the lens.
If one follows your advise with Linhofs made in the last 2 to 3 decaades, at least, then they will create a focus shift eaual to the thickness of the fresnel.
-- Bob Salomon (email@example.com), June 20, 2000.