Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,228   Posts: 1,532,774   Online: 843
      
Page 1 of 10 1234567 ... LastLast
Results 1 to 10 of 96
  1. #1
    DBP
    DBP is offline

    Join Date
    Mar 2006
    Location
    Alexandria, VA
    Shooter
    Multi Format
    Posts
    1,883
    Images
    34

    Lens hood length - avoiding vignetting

    I'm looking for a lens hood for my 180mm Sonnar (P6 mount). It takes an 86mm thread, so options are a bit limited. The one I am currently considering is 73mm deep and I wonder whether it will vignet. Does anyone know, or have a method for figuring it out?

  2. #2
    Dave Parker's Avatar
    Join Date
    Aug 2004
    Shooter
    Multi Format
    Posts
    4,049
    Cut a simular size piece of stiff cardboard and make a hood of approx the same dimentions and then you can hold on the end of the lens and should be able to see if it would vignette, you could also lightly tape to the end of the lens and take a few test shots and have them developed..

    Dave

  3. #3
    DBP
    DBP is offline

    Join Date
    Mar 2006
    Location
    Alexandria, VA
    Shooter
    Multi Format
    Posts
    1,883
    Images
    34
    I'm feeling stupid now, should have thought of that myself. Thanks.

  4. #4

    Join Date
    Sep 2002
    Posts
    137
    If you want, let me know the diameter of the front glass, the film format in use and I will give you the lens shade's size for different shading efficiency.

  5. #5
    Dave Parker's Avatar
    Join Date
    Aug 2004
    Shooter
    Multi Format
    Posts
    4,049
    Also, forgot to point this website out, they have downloadable templates in .pdf format to make your own lenshoods for many lenses as well as a custom design template, it could be helpful if you have to design your own.

    http://www.lenshoods.co.uk/

    Dave

  6. #6
    DBP
    DBP is offline

    Join Date
    Mar 2006
    Location
    Alexandria, VA
    Shooter
    Multi Format
    Posts
    1,883
    Images
    34
    Quote Originally Posted by George View Post
    If you want, let me know the diameter of the front glass, the film format in use and I will give you the lens shade's size for different shading efficiency.
    Approximately 82mm diameter and 6x6.

  7. #7

    Join Date
    Sep 2002
    Posts
    137
    For your 180mm focal length lens, 82mm diameter of the front lens and 6x6 film format, you can use a lens hood:
    1) 74mm long, 76x76mm opening - medium efficiency, but better what you find on the market;
    2) 98mm long, 81x 81mm opening - very good efficiency;
    3) 118mm long, 86x86mm opening - better than very good efficiency;
    4) 138mm long, 91x91mm opening - excellent efficiency.

    In case the 82mm front lens diameter was underestimated you would need to contact me again. The length of the lens shade is measured strictly from the front lens appex. If you screw the lens shade on the filter thread you have to lessen the length with the proper number of mm.

  8. #8
    DBP
    DBP is offline

    Join Date
    Mar 2006
    Location
    Alexandria, VA
    Shooter
    Multi Format
    Posts
    1,883
    Images
    34
    Thanks.

  9. #9
    Helen B's Avatar
    Join Date
    Jul 2004
    Location
    Hell's Kitchen, New York, USA
    Shooter
    Multi Format
    Posts
    1,557
    Images
    27
    George,

    I'm a bit puzzled by your lens hood calculations. Could you explain how you did them? Your opening sizes seem to be rather small, unless I've misunderstood what you meant by 'apex' - I assumed the front vertex. If you meant the entrance pupil, wouldn't you need to know the lens' aperture?

    Puzzled,
    Helen
    Last edited by Helen B; 11-10-2006 at 03:37 PM. Click to view previous post history.

  10. #10

    Join Date
    Sep 2002
    Posts
    137
    Opening sizes rather small? They are the smallest usable for the given lens shade length, the film format and the front diameter. Anything smaller and you would have the beginning of vignetting. Anything biggger and you loose the efficiency. The longer the lens shade, the better the efficiency, but it's not a linear function. After a certain moment you would gain very little with a huge increase of the shade's length. The apex means indeed the front vertex. The calculation is for the maximum aperture - so that you are not limited with your choice of working apertures. To explain the calculation would be simply too long. I build my own lens shades for all my lenses - I did so for the last 15 years.

Page 1 of 10 1234567 ... LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin