Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,553   Posts: 1,544,926   Online: 864
      
Results 1 to 6 of 6
  1. #1

    Join Date
    Jul 2012
    Shooter
    35mm RF
    Posts
    4

    Micromega Critical Focuser

    Bought a Micromega Critical Focuser with blue filter. Did first printing and so far very happy. The only concern is to how the blue filter works. My focuser has integrated switch-blade-filter. From what I found it is recommended to use filter for a better tuning to get sharpest grain. I've read the book by Gene Nocon where he says about Omega focuser being exceptionally good but there is no specification on how to get it work. I don't really see the grain through the blue filter but rather different light tone which in my case doesn't make any difference. Grain comes from using the focuser without a filter. I will really appreciate any given information.

  2. #2

    Join Date
    Jun 2008
    Location
    florida
    Shooter
    Medium Format
    Posts
    1,169
    Images
    2
    I have a grain focuser that also came with a blue filter. During the forty years that I have been using it, I never used the filter. It's best to focus with a piece of the same thickness paper you will be printing on under the focuser. I focus with the lens wide open and then stop down.

    http://www.jeffreyglasser.com/

  3. #3
    clogz's Avatar
    Join Date
    Dec 2002
    Location
    Rotterdam, The Netherlands
    Shooter
    Multi Format
    Posts
    2,837
    Images
    114
    As to the blue filter: see Ctein "Post Exposure" page 76. http://ctein.com/PostExposure2ndIllustrated.pdf
    Digital is best taken with a grain of silver.

  4. #4

    Join Date
    Jul 2012
    Location
    North Yorkshire, England
    Shooter
    35mm
    Posts
    721
    The purpose of the blue filter as explained by the late Canadian Photographer Gene Nocon, is, it is a critical grain focussing aid. It is explained in his book about darkroom printing that the light from an enlarger tends to be towards towards the red end of the spectrum and printing paper is sensitive towards the blue end. If the colour of the light from the enlarger is changed to blue, then the image we see via the eyepiece of the grain focusser should be more accurate than without it.

    In his book he demonstrates how this can be so. Two identical images are printed, one using the blue filter and the other without. The difference although slight is clearly visible.

    I have a similar focussing aid which was sold in UK under the name of 'Peak' I don't have the blue filter, so I dial in blue light using the colour filters from the colour head, and yes it does seem to work. However stopping down the lens from F2.8 to F8 will cover most inconsistencies, but it is nice to get it accurate before you start to print.

    Obviously when printing RA4 the blue filter is not used.

  5. #5

    Join Date
    Sep 2002
    Location
    Oregon and Austria
    Shooter
    4x5 Format
    Posts
    836
    Most modern high-quality enlarging lenses focus blue and near-UV in the same plane as red and green, or at least close enough for enlarging purposes. Older and uncorrected lenses often focus blue (to which your paper is sensitive) in a slightly different plane than red/green (to which your eyes are most sensitive). For these uncorrected lenses, using the blue filter will get you better focus. For anything else, it is superfluous.

    Do a quick test: focus with and without the blue filter, make a couple of test strips/prints and see if the blue filter gives you better results. I doubt it will, especially if you are using VC paper, which is also sensitive way into the green part of the spectrum.

    I've never used my blue filter with my Peak grain focusers, and have no complaints about the sharpness of my prints.

    Best,

    Doremus


    www.DoremusScudder.com

  6. #6

    Join Date
    May 2005
    Location
    Daventry, Northamptonshire, England
    Shooter
    35mm
    Posts
    6,965
    [QUOTE=BMbikerider;1464700]
    In his book he demonstrates how this can be so. Two identical images are printed, one using the blue filter and the other without. The difference although slight is clearly visible.

    QUOTE]

    When I first started printing I got the Gene Nocon book and for the life of me I couldn't see any difference in the two images but put this down to the standard of book reproduction. Then I bought Tim Rudman's book and noted that he was sceptical. I then read around further and looked at comments on forums such as these and must admit that my conclusion is that the jury is still out. If it really was that clear a difference then you'd expect the weight of opinion to favour the blue filter and so far I haven't seen such a weight of opinion

    I remain agnostic

    pentaxuser



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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