Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 71,814   Posts: 1,581,607   Online: 814
      
Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 40
  1. #21

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    5,083
    I was simply pointing to light falloff as something that can usually be reduced substantially by stopping down, assuming there is any falloff to begin with. If you're using an 80mm lens for 35mm, falloff is less of an issue than if you were using a shorter focal length. But I raised falloff because it is a different lens property than was being discussed, and an additional reason someone might want to consider stopping down. It is not related to resolution/sharpness. Although regarding sharpness I will back Ralph up on this. Unless you are using a completely corrected, truly diffraction-limited lens, sharpness toward the edges and corners will improve when the lens is stopped down to a degree. It might not be visible in small enlargements, but it is a fact. There are several common abberations which can be reduced by stopping down. Unless you have a perfect lens, there is always an aperture somewhere in the middle of the lens's range that gives you the best balance between the reduction of various abberations, and the increasing effects of diffraction. Even today's most corrected Rodenstock and Schneider enlarging lenses benefit from stopping down 1-2 stops.

    On the other hand if you're pleased with the results you get wide open and everything is working for you, stick to it I guess.

    Quote Originally Posted by Bob Carnie View Post
    I should add that for each format I am using a longer lens.
    ie

    35 - 80mm
    6x6 ,6x7 - 90mm
    6x9 - 105mm
    4x5 -150 and 180mm

    I am still convinced that sharp grain at wide open will not be sharper grain at 2 stops down.

    There are a lot of factors that contribute to edge defects, but if you do all the good things your edges are sharp wide open. At least in my darkroom

  2. #22
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,426
    Images
    148
    Quote Originally Posted by Bob Carnie View Post
    I should add that for each format I am using a longer lens.
    ie

    35 - 80mm
    6x6 ,6x7 - 90mm
    6x9 - 105mm
    4x5 -150 and 180mm

    I am still convinced that sharp grain at wide open will not be sharper grain at 2 stops down.

    There are a lot of factors that contribute to edge defects, but if you do all the good things your edges are sharp wide open. At least in my darkroom

    For many years I'd have agreed with Ralph, and that's how the lenses I used behaved in the 60's and early 70's.

    However at some point I had to use a Rokkor lens wide open for some 20x16 prints and was amazed that the grain was sharp from the edges/corners through to the center. My Schneider Componon's are the same.

    There may be a slight difference but unless you're printing Technical Pan (or similar) it's difficult to spot. Modern enlarger lenses have excellent flat field optimisation so should perform well wide open.

    Ian

  3. #23
    Bob Carnie's Avatar
    Join Date
    Apr 2004
    Location
    Toronto-Ontario
    Shooter
    Med. Format RF
    Posts
    4,705
    Images
    14
    It should be pointed out that I am only referring to grain sharpness within the print. I do understand falloff , abberations at the edge,of large prints can be problematic.

    I too close down the lens, mainly for optimum printing times,

    but if we are talking about focusing on a nose of a subject, being grain sharp then printing wide open, then closing down without refocusing and adjusting time, and then telling me the nose is sharper of a subject on the second print , I will start making the stew of my shorts.

    Its really simple make two prints,

  4. #24
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,380
    Quote Originally Posted by Bob Carnie View Post
    I should add that for each format I am using a longer lens.
    ie
    Yes this holds true by the MTF charts. When looking at the MTF charts, only go out to 50% on the X axis. Same with the light falloff chart; only go out to 50%. Then it is evident that larger apertures will be OK in this case because you are only using the center of the image circle. But, as I indicated earlier you really need to look at the MTF cart of the lens in question rather than making generalizations. For example, the Rogonar-S MTF chart posted earlier shows different characteristics than the Schneider lenses I use.

    Also, a little clarification and explanation of MTF charts. We know from physics that the lens will have the least diffraction wide open. And it can be that the 'Line Pair Per Millimeter' readings on the center of the field will be greatest when wide open. However, the contrast of those line pairs will be suffering. This is one of the reasons for going with the MTF chart as it takes into consideration the contrast. So, that is why we see the center of the Rogonar-S lens produce a better MTF when stopped down but that characteristic should not be applied to all enlarging lenses. (See below).
    Last edited by ic-racer; 09-14-2010 at 02:41 PM. Click to view previous post history.

  5. #25
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,380
    Just to show that you shouldn't generalize comments about enlarging lenses, here is the MTF of a lens I use. It shows the following:
    1) Wicked sharp in the center even when wide open f4 (probably better coated than the Rogonar S and smaller lens elements)
    2) Sharper at the corners at F8 than F5.6 BUT...
    3) If you only use the center of the lens (ie use it for a smaller format negative) it will be better overall at the wider aperture (what Bob is saying).


    The 3 graphs across are F4, F5.6 and F8 in that order.

  6. #26
    Ian Grant's Avatar
    Join Date
    Aug 2004
    Location
    West Midlands, UK, and Turkey
    Shooter
    Multi Format
    Posts
    16,426
    Images
    148
    Quote Originally Posted by ic-racer View Post
    Just to show that you shouldn't generalize comments about enlarging lenses, here is the MTF of a lens I use. It shows the following:
    1) Wicked sharp in the center even when wide open f4 (probably better coated than the Rogonar S and smaller lens elements)
    2) Sharper at the corners at F8 than F5.6 BUT...
    3) If you only use the center of the lens (ie use it for a smaller format negative) it will be better overall at the wider aperture (what Bob is saying).


    The 3 graphs across are F4, F5.6 and F8 in that order.
    It's like the diffraction issue at small apertures.

    Actual reality in final images doesn't match the theory or even tests because the criteria in practice aren't an optical bench.

    That doesn't mean either is wrong rather that it's possible to get great prints or images when theory is chasing it's own tail.

    It's about knowing your own equipment and not going by spurious tests.

    Ian

  7. #27
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,791
    Images
    1
    Quote Originally Posted by ic-racer View Post
    Just to show that you shouldn't generalize comments about enlarging lenses, here is the MTF of a lens I use. It shows the following:
    1) Wicked sharp in the center even when wide open f4 (probably better coated than the Rogonar S and smaller lens elements)
    2) Sharper at the corners at F8 than F5.6 BUT...
    3) If you only use the center of the lens (ie use it for a smaller format negative) it will be better overall at the wider aperture (what Bob is saying).


    The 3 graphs across are F4, F5.6 and F8 in that order.
    I agree with this and your and Bob's comment about using longer lenses (that definitely helps, because you are trimming off the problematic part of the MTF), but I have one question:

    You said, you're using this type of lens. But, this is a f=45mm lens and, therefore, not a 'longer' lens even for 35mm. What 'smaller format negative' are you using this lens for?
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  8. #28
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,380
    Quote Originally Posted by RalphLambrecht View Post
    I agree with this and your and Bob's comment about using longer lenses (that definitely helps, because you are trimming off the problematic part of the MTF), but I have one question:

    You said, you're using this type of lens. But, this is a f=45mm lens and, therefore, not a 'longer' lens even for 35mm. What 'smaller format negative' are you using this lens for?
    Minox and 16mm! In fact I just got a new-to-me Minolta 16 Type I two weekends ago.

    Also, I use that 45mm lens for 16x20s from 35mm negatives as it is easier to center the 35mm frame on my 5x5 enlarger glass carrier, than it is to center the 35mm frame on the 10x10 glass Durst carrier. Even though the 80mm lens I'd use on the Durst 8x10 enlarger has a wide field, it is important to use the exact center if I want to use a wider aperture.
    Last edited by ic-racer; 09-15-2010 at 02:43 PM. Click to view previous post history.

  9. #29
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,380
    Ralph,
    I wish I had the El-Nikkor data.
    Do you have the El-Nikkor brochure at the bottom of this page? http://sites.google.com/site/inexpen...larging-lenses
    It has optimum magnification, mag range, degrees of coverage and lens construction info that is all useful. (but no MTF).

    There are a bunch of El-Nikkor brochures at this site, but I can't get any to download: ftp://savazzi.homeip.net/download/El...lenses%203.pdf

  10. #30
    RalphLambrecht's Avatar
    Join Date
    Sep 2003
    Location
    Central florida,USA
    Shooter
    Multi Format
    Posts
    6,791
    Images
    1
    ic-racer

    Thanks for the links. I did not have the brochure. It's very old (1978) but still valuable. EL Nikkor MTFs seems to be a bit of a mystery.
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

Page 3 of 4 FirstFirst 1234 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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