Page 9 of 11 FirstFirst ... 7891011 LastLast
Results 81 to 90 of 105

Thread: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

  1. #81
    Corran's Avatar
    Join Date
    Apr 2011
    Location
    North GA Mountains
    Posts
    8,924

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Quote Originally Posted by Alan Klein View Post
    1) Why don't 35mm lenses have that falloff? Why are their designs different?
    2) If it's a simple formula, why do different people say the falloff varies? There seem to be arguments on this point.
    3) Why is the falloff more noticeable with chrome film as some people claim?
    1. Retrofocus design (SLR, due to mirror constraint) vs. non-retro ~symmetrical design (RF / LF) PS: they do have fall-off that is corrected by stopping down, due to mechanical vignetting, just like LF lenses but there's still the inherent fall-off from traditional designs that isn't corrected.
    2. As mentioned above, designs vary, and also consider that image circle may affect this (if you are closer to the edge of the IC, more fall-off).
    3. Less dynamic range available - 2 stops underexposed means you are dangerously close to just having nothing usable on the film.
    Bryan | Blog | YouTube | Instagram | Portfolio
    All comments and thoughtful critique welcome

  2. #82

    Join Date
    Nov 2017
    Posts
    654

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Quote Originally Posted by Kiwi7475 View Post
    The fall off follows a cos^4, no need to waste a negative to confirm that IMO. All you need to know is the angular FOV of your lens, diagonally.
    From what I find in the documentation of filters is that wideangle lenses follow cosł. The cos⁴ and cos (no power) is more for "contactcopy machines with point source light" and large format copy machines.
    Expert in non-working solutions.

  3. #83

    Join Date
    Jan 2019
    Posts
    776

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Quote Originally Posted by Havoc View Post
    From what I find in the documentation of filters is that wideangle lenses follow cosł. The cos⁴ and cos (no power) is more for "contactcopy machines with point source light" and large format copy machines.
    Now that we get into the the weeds, let me repeat here what has already been discussed in this very forum a few times before:

    “cos^4 is the basic limiting physics, cos^2 from inverse distance squared fall off, another cos factor from the incident angle of light on the film surface, and the final factor of cos from the apparent ellipticity of the aperture off axis. There are two ways that real lenses differ from this theoretical rule. First, the apex of the off-axis angle can be moved forward using a retrofocus design. Second, some superwide designs mitigate one cos factor somewhat by using the trick of tilting the enterance and exit pupils. This mostly eliminates the ellipticity of the off-axis aperture, leaving only three factors of cosine theta and an improved fall off of the off-axis illumination.

    You can determine whether a particular lens uses this trick by looking at it from various angles. Stop the lens down a couple of stops and look at the front straight on -- both the outside barrel of the lens and the diaphragm will be circular. Next, keep looking at the center of the lens and slowly rotate the lens so that your eye is no longer on the optical axis. On most lenses both the outside of the barrel and the aperture diaphragm will become elliptical. On lenses using the tilting pupil principle, the diaphragm will remain almost circular as you tilt the lens.”

  4. #84

    Join Date
    Sep 2014
    Location
    Montreal, Canada
    Posts
    1,993

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Sorry I'm not sure if you mean Biogon "design" or a specific lens. I thought most of the modern short focal length lenses used this "trick". For example here is what Rodenstock said about the Grandagon-N range:


    "...light fall-off at the edge has been greatly reduced thanks to an optical trick (“pupil distortion” = the entrance pupil diameter
    increases when viewing at an angle)..."


    Quote Originally Posted by Dan Fromm View Post
    You're probably thinking of f/4.5 Biogons. One, the 75/4.5, covers 4x5. Big heavy expensive lens.

  5. #85

    Join Date
    Dec 2001
    Location
    NJ
    Posts
    8,470

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Quote Originally Posted by Michael R View Post
    Sorry I'm not sure if you mean Biogon "design" or a specific lens. I thought most of the modern short focal length lenses used this "trick". For example here is what Rodenstock said about the Grandagon-N range:


    "...light fall-off at the edge has been greatly reduced thanks to an optical trick (“pupil distortion” = the entrance pupil diameter
    increases when viewing at an angle)..."
    I meant specific lenses. 35/4.5, 45/4.5, 53/4.5 and 75/4.5 Biogons for, respectively, 6x6, 6x7, 6x9 and 4x5.

    Your R'stock quote is marketing fluff. I just looked at the "relative light fall of at ratio 0.03x" curves for Grandagon-Ns. It is worse that cos^4 at all apertures larger than f/16, marginally, as in practically speaking not at all, better at f/16.

    Bob look at the charts before jumping in to tell us that R'stock is always right.

    Kiwi, there's no profit in wrangling with people who think they're right.

  6. #86

    Join Date
    Sep 2014
    Location
    Montreal, Canada
    Posts
    1,993

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    I don't think anyone is wrangling regarding the laws of physics. I posted the Rodenstock quote for reference/comment. It's not my quote. I didn't work there.

  7. #87

    Join Date
    Dec 2001
    Location
    NJ
    Posts
    8,470

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Quote Originally Posted by Michael R View Post
    I don't think anyone is wrangling regarding the laws of physics. I posted the Rodenstock quote for reference/comment. It's not my quote. I didn't work there.
    You're not wrangling about the physics and I didn't blame the quote on you. I blamed Rodenstock's marketers.

  8. #88
    Drew Wiley
    Join Date
    Sep 2008
    Location
    SF Bay area, CA
    Posts
    18,338

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    35mm wide angle lenses do have equivalent falloff, Alan. I personally hate that Natl Geographicky look. Falloff is more noticeable with chrome film simply because chrome film has more native contrast to begin with than negative film.

  9. #89
    Corran's Avatar
    Join Date
    Apr 2011
    Location
    North GA Mountains
    Posts
    8,924

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Quote Originally Posted by Drew Wiley View Post
    35mm wide angle lenses do have equivalent falloff, Alan.
    No they don't, if we are talking about modern retrofocus designs. Sure, the 21mm Biogon for Contax 35mm rangefinder has the same basic fall-off characteristics of the 75mm Biogon on 4x5, but the retrofocus Nikon 14-24mm for 35mm / DSLR, when stopped down a bit, has very little fall-off comparatively.
    Bryan | Blog | YouTube | Instagram | Portfolio
    All comments and thoughtful critique welcome

  10. #90
    Drew Wiley
    Join Date
    Sep 2008
    Location
    SF Bay area, CA
    Posts
    18,338

    Re: Best 75mm / 90mm lens?......totally kidding, but not really...read on pls

    Retrofocus would apply mainly to SLR's. But if the lens design is similar, apples to apples, the format size won't make much difference relative to angle of view unless image circle movements are in play. But I'd hypothetically be interested in actual factory bench test results rather than general impressions, that is, if I was even in the market for something 35mm wide-angle, but I'm not.

Similar Threads

  1. Lens Reputations- Are We Kidding Ourselves?
    By Brian Vuillemenot in forum Lenses & Lens Accessories
    Replies: 42
    Last Post: 22-Jan-2007, 09:57
  2. 72/75mm lens vs. 90mm
    By Gary Smith in forum Lenses & Lens Accessories
    Replies: 7
    Last Post: 30-Jan-2006, 05:51
  3. Lee Lens Hoods on 4x5 - Standard or Wide Angle for down to 75mm and 90mm?
    By Leslie Gordon in forum Lenses & Lens Accessories
    Replies: 6
    Last Post: 25-Sep-2004, 11:30

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
  •