Results 1 to 10 of 10

Thread: fresnel lens, cheap and fast

  1. #1

    Join Date
    Apr 2007
    Location
    Vienna
    Posts
    116

    fresnel lens, cheap and fast

    Dear colleagues,

    my 8x10 has arrived, and I need a fresnel. I found out that the Linhof 8x10 fresnel costs about 400 $, and the Beattie about 400 Ä, and here: http://www.3dlens.com/shop/largefresnellens.php ---- fifteen dollars!
    Tell me why not. 5 grooves per millimeter is not overwhelming, sure, but -- it`s free!
    What would be the appropriate focal length? Does this depend on the lenses I use? (Mine are 150 & 240mm.)

    Thanks
    Michael

  2. #2

    Re: fresnel lens, cheap and fast

    Sounds good to me.

    For a different purpose, I am interested to find which is the highest resolution Fresnel lens 8X10 or 4X5 available today.

    Todor

  3. #3

    Join Date
    Nov 2007
    Location
    Nuremberg Germany
    Posts
    1,049

    Re: fresnel lens, cheap and fast

    Fresnel-lenses for focussing screens are special ones. This lenses have two different focal-lenghts combined by a special ring pattern. Also the groove pitch is 0.1mm (254 grooves per inch).

    Peter K

  4. #4

    Join Date
    Jun 2004
    Location
    Montana
    Posts
    603

    Re: fresnel lens, cheap and fast

    I have tried various fresnels that were not specifically designed for photography work and I have found, they really don't work very well, you have to understand a fresnel is a lens in itself and is specifically made for certain focal lengths, to get the maximum amount of light intensification...I have several 8.5 x 11 page magnifiers around here that I have tested and for the most part, in a photographic application, they are pretty much useless.

    Dave

  5. #5

    Re: fresnel lens, cheap and fast

    Tracy Storer recently posted some info about a new fresnel source. He also uses them and would have a lot of advice.

  6. #6

    Join Date
    Aug 2007
    Location
    Indianapolis, Ind.
    Posts
    588

    Re: fresnel lens, cheap and fast

    I have a little experience with selecting an inexpensive fresnel for photographic use and think that with care you can select one that will be useful. It is my experience that 5 grooves per millimeter would be plenty fine.

    You can calculate the required focal length using the lens equation:

    1/(focal length) = 1/(image distance) + 1/(object distance)

    Some interpretation is necessary. Assuming you are trying to collect the light originating at the rear nodal point of the taking lens and direct it to your cornea, then the image distance is the focal length of your taking lens and the object distance is the distance of your eye behind the ground glass. For your 240mm lens, if your eye point is 240mm behind the ground glass (achieved either through young, strong vision of by use of eyeglasses) then the formula yields 120mm for the focal length of the fresnel. This will give you something of a sweet spot centered behind the ground glass.

    Alternately if the fresnel focal length is equal to that of the taking lens, the eye distance becomes infinite, meaning that the light from the ground glass will directed (only generally) straight back. Then there will no sweet spot for your eye, but the portion of the screen directly in front of your eye will always be brightest. Note also that with a view camera, the location of the rear nodal point of the taking lens is variable in all three dimensions so expecting mathematical perfection in the real world is a mistake.

    A good comprise for you might be to take the fresnel focal length to be equal to the shorter taking lens (150mm), giving the infinite eye distance behavior with that lens and something of a sweet spot (albeit at 400mm or 15.75 inches) behavior with your 240mm lens.

    Don't be very concerned about the precision of these calculations. Remember that you have a ground glass in the light path that will spread the light quite broadly around the calculated nominal eye point. You will notice that it is not the usual practice to change the fresnel every time you change taking lenses.

  7. #7

    Join Date
    Apr 2007
    Location
    Vienna
    Posts
    116

    Re: fresnel lens, cheap and fast

    Thanks for that in-depth-answer. I`ll let you know how the story will end, if it ever will.

  8. #8

    Re: fresnel lens, cheap and fast

    I use to have an ultra cheap fresnel over the ground glass on my 4x5. Barnes & Noble bookstores have these page reader magnifiers made from plastic, and with a little trimming matches nicely over the ground glass. The downside is when you place a loupe over this for closer focus, the lines intrude a bit on getting the focus dialed in. Now I have a Satin Snow on my 4x5, which is just as bright (if not more so) and much more evenly illuminated.

    Ciao!

    Gordon Moat Photography

  9. #9

    Join Date
    Dec 2007
    Location
    klamath falls, oregon
    Posts
    1,202

    Re: fresnel lens, cheap and fast

    I have some related questions. I am new to LF and just bought a used Osaka. I understand that it is essentially the same as a Tachihara, and that the newer Tachiharas have Fresnel lenses standard. So here are my questions:

    1. How can I tell if my camera has a Fresnel lens?

    2. When I look at the ground glass from the back it looks like there is a thin piece of clear glass with square corners, and something frosted with clipped corners in front of that. What am I seeing?

    3. Am I to understand from the Satin Snow web site that I could get their 4x5 ground glass for $17 including shipping? That's not much to pay if it would give me more light for focusing...

    I'm just looking to give myself every advantage (without breaking the bank!) when I start using the camera, any suggestions are welcome!

    By the way, I see right now a Tecnikardan Fresnel gg on e-bay. Current bids are not too high. I'm not ready to make a decision in the time left for bidding, but maybe someone else is.

    Gregg

  10. #10

    Join Date
    Sep 2007
    Location
    California
    Posts
    18

    Re: fresnel lens, cheap and fast

    "How can I tell if my camera has a Fresnel lens?"

    If you have to squint or use dark cloth to see the image, then you do not have fresnel. the fresnel looks like a acrylic page magnifier.

Similar Threads

  1. Fast shooting with 4x5 and 5x7...help me decide.
    By Gene McCluney in forum Cameras & Camera Accessories
    Replies: 20
    Last Post: 18-Jun-2007, 09:48
  2. Schneider APO Tele Xenar 600/800mm Convertible
    By Eric Leppanen in forum Cameras & Camera Accessories
    Replies: 6
    Last Post: 6-Nov-2005, 22:43
  3. 8x10 cheap studio lens ???
    By Calamity Jane in forum Lenses & Lens Accessories
    Replies: 27
    Last Post: 4-Apr-2005, 03:12
  4. Date of manufacture and quality of Carl Zeiss Jena Tessar 4.5/300
    By Gregory Popovitch in forum Cameras & Camera Accessories
    Replies: 20
    Last Post: 19-Apr-2004, 15:26
  5. APO Grandagon bad lens cups
    By Steve Grimes. in forum Lenses & Lens Accessories
    Replies: 12
    Last Post: 25-Nov-2001, 11:08

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •