Page 1 of 2 12 LastLast
Results 1 to 10 of 19

Thread: Fresnel lens

  1. #1

    Join Date
    May 2007
    Location
    20mins north of boston
    Posts
    496

    Lightbulb Fresnel lens

    Does a Fresnel lens really improve focusing for you?
    Lauren MacIntosh

    Whats in back of you is the past and whats in front of you is the future now in the middle you have choices to make for yourself:

  2. #2
    Moderator
    Join Date
    Apr 2009
    Location
    Northern Virginia
    Posts
    5,079

    Re: Fresnel lens

    No, that's not its purpose. A Fresnel gather light and points it back to your eye, so that you can see the whole image from edge to edge with enough brightness to compose the photograph. If anything, most Fresnels make focusing using a loupe more difficult, because the Fresnel pattern is a distraction when magnified. Many camera manufacturers made the Fresnel easily removable for focusing, e.g. Sinar.

    With short, slow lenses, one might require a Fresnel to see enough of the image to even be able to see the edges, but then the Fresnel has to be designed for such short lenses to be completely effective. Lenses much too short for the Fresnel will cause ghosting and other artifacts in the Fresnel that actually undermine its use.

    Rick "noting the Fresnels that one can focus through easily are expensive" Denney

  3. #3

    Join Date
    Dec 2005
    Location
    Los Angeles, CA
    Posts
    4,427

    Re: Fresnel lens

    When using a loupe, no.

    When not using a loupe, yes.

  4. #4
    IanG's Avatar
    Join Date
    Jan 2007
    Location
    Aegean (Turkey & UK)
    Posts
    4,122

    Re: Fresnel lens

    Yes a fresnel lens in combination with a good ground glass screen can help enormously with focussing by increasing the brightness substantially.

    About 4 yeras ago I realised that my Crown Graphic was substantially harder to focus than my Wista putting the two side by side there was over 3 stops difference in overall brightness despite the fact that the Crown had an f4.5 lens and the Wista f5.6 (both 150mm at full aperture). The Wista has a combination screen'fresnel.

    I measured the differences in brightness (using a Spotmeter) and also stopped the Wista's lens down until they matched in brightness (the differences matched) and it was 3 and 1/3 stops, admiottedly the Crown had it's original screen.

    Changing the Crown's screen for a Steve Hopf one increased brightness by about a stop, adding a fresnel took it closer to the Wista's combination screen/fresnel and about 2 stops brighter than it had been. That improvement means it's new very much easier to focus particularly when used hand held, the focus hood is fine on it's own.

    Since then I've fitted new screens to all my other LF cameras, it made the a big difference to my German pre-WWII 9x12 cameras (Orion Werks, Rodenstock, KW Patent Etui's etc) these can now be focussed easily even in quite low light. If I could find the right fresnels I'd fit then as well).

    Ian

  5. #5
    Deardorff Sales and service
    Join Date
    Aug 2010
    Location
    Indiana
    Posts
    410

    Re: Fresnel lens

    Fresnel lens..........I hate them. Really truely hate them. You really need different ones for different FL lenses. A really nice fine grind ground glass with the corners cut works just fine. In 40 years of doing this I've seen so many Fresnel lens come and go on the market.....If there was one perfect one it would still be there and this question would not be asked. (I do not blame you at asking it at all, It needs to be asked!!)
    Ken Hough Deardorff Refinisher since 1982
    Deardorff Factory refinisher / remanufacturer 1982-88
    Deardorff Factory Historian 82-88
    Deardorff Cameras on Facebook
    www.deardorffcameras.0catch.com

  6. #6

    Join Date
    May 2007
    Location
    20mins north of boston
    Posts
    496

    Re: Fresnel lens

    Click image for larger version. 

Name:	Hexar-15cm-.jpg 
Views:	30 
Size:	77.2 KB 
ID:	70485Click image for larger version. 

Name:	Hexar lens 15cm.jpg 
Views:	29 
Size:	30.1 KB 
ID:	70486Basically my eye's are getting older , Just was wondering if the Fresnel lens would help me out in focusing I use a lope but some
    times it a hit or miss with me for being on the money with sharpness : thanks all you folks for your answers
    below are two just in last few day as you see one is good the is close but no cigar.
    Lauren MacIntosh

    Whats in back of you is the past and whats in front of you is the future now in the middle you have choices to make for yourself:

  7. #7
    Deardorff Sales and service
    Join Date
    Aug 2010
    Location
    Indiana
    Posts
    410

    Re: Fresnel lens

    You need a loupe that is adjustable to your eyes. The other day I found all my Agfa style loupes that I modified to focus for my eyes. I machine a bit off the bottom edge. Now I need to add a bit!! I finally got a Schneider loupe and love it. I drew a + on the GG and focus on it. Thats it.
    Ken Hough Deardorff Refinisher since 1982
    Deardorff Factory refinisher / remanufacturer 1982-88
    Deardorff Factory Historian 82-88
    Deardorff Cameras on Facebook
    www.deardorffcameras.0catch.com

  8. #8

    Join Date
    Sep 1998
    Posts
    10,341

    Re: Fresnel lens

    I hope you are drawing that + on the grain side of the gg and not the non-imaging forming side of the gg.

  9. #9
    IanG's Avatar
    Join Date
    Jan 2007
    Location
    Aegean (Turkey & UK)
    Posts
    4,122

    Re: Fresnel lens

    Quote Originally Posted by seawolf66 View Post
    ]Basically my eye's are getting older , Just was wondering if the Fresnel lens would help me out in focusing I use a lope but some
    times it a hit or miss with me for being on the money with sharpness : thanks all you folks for your answers
    below are two just in last few day as you see one is good the is close but no cigar.
    You need to try one and see. There is some variation in fresnels and some people swear by the more expensive Maxwell or Beattie screens.

    While I can see where Ken's coming from not liking Fresnels there's a good reasons for using them as well which is why many cameras are sold with them fitted. Many of us find they make focussing very much easier and I very rarely need to use a loupe.

    Ian

  10. #10

    Join Date
    Feb 2006
    Posts
    3,116

    Re: Fresnel lens

    Quote Originally Posted by seawolf66 View Post
    Does a Fresnel lens really improve focusing for you?
    No.
    One man's Mede is another man's Persian.

Similar Threads

  1. fresnel lens
    By joe zarick in forum Cameras & Camera Accessories
    Replies: 22
    Last Post: 15-Jun-2012, 10:19
  2. What is a fresnel lens?
    By lmlmlm in forum Lenses & Lens Accessories
    Replies: 12
    Last Post: 14-Jun-2012, 09:04
  3. Fresnel lens
    By Thompsonr in forum Cameras & Camera Accessories
    Replies: 3
    Last Post: 15-Jul-2007, 08:12
  4. Replies: 3
    Last Post: 7-Feb-2005, 17:21

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
  •