Results 1 to 12 of 12
  1. #1
    No longer a newbie, moving up!
    Join Date
    Feb 2010
    Posts
    42
    My Gallery
    (0)
    My Photos Are NOT OK to Edit
    Liked
    0 times

    Lense Diameter = Lense resolving power?

    I had an idea today about lense resolution. Coming from a background in astronomy, the larger the front element usually meant it was a better telescope (more light gathering). With lenses we have an f-stop value, so this does not apply to light gathering. However, the large the diameter of the front element also produces a larger lense resolving power, or the potential resolution of the lense.

    Is this true in photography as well? Do lenses with larger front elements have a higher theoretical resolution?



  2. #2
    TPF Junkie!
    Join Date
    Aug 2009
    Location
    West Palm Beach, Fl
    Posts
    2,471
    My Gallery
    (13)
    My Photos Are NOT OK to Edit
    Liked
    29 times
    I think the larger elements are more of a forced issue because of the physical size of the aperture, which is dependent on the focal length. That's why the long lenses with the smaller f-numbers have giant front elements... because they also have giant aperture mechanisms.
    Can't we all just

  3. #3
    TPF Junkie!
    Join Date
    Mar 2009
    Location
    Key West FL
    Posts
    1,261
    My Gallery
    (11)
    My Photos Are NOT OK to Edit
    Liked
    0 times
    The light gathering capability of telescopes generally refers to the effect of diameter, actually area, of the objective on the number of photons collected from a point light source. With diffuse sources, those encountered in conventional photography and when telescopes are used to view/photography diffuse nebulae, it is not the absolute diameter of the objective, but the "focal ratio" (the classic telescope term) that is the controlling factor. Photographers generally refer to a lens' focal ratio as its f/stop, although the lens' spec's engraved on the barrel are traditionally in focal ratio notation (e.g. 1:1.4 instead of f/1.4).

    It is true that Dawe's Limit does impact on photographic optics. As a rule, though, other issues intrude as a result of having to balance the optical performance over a rather wide field and to produce a flat image plane. Still, most camera lenses perform their best at near maximum aperture.
    --------
    Dwig
    happythursday.com

  4. #4
    TPF Junkie!
    Join Date
    Dec 2008
    Location
    Toronto, Ontario, Canada
    Posts
    4,501
    My Gallery
    (0)
    My Photos Are OK to Edit
    Liked
    407 times
    "The ability of a lens to resolve detail is usually determined by the quality of the lens but is ultimately limited by diffraction."

    Wikipedia


    The larger diameter front elements are used for light gathering.

    I have had some large diameter lenses that had poor resolution due to lens aberrations.
    I have had some high resolution lenses with a not so large front lens element.


    Telescopes with high resolution tend not to have lenses ... mirrors are used (which I believe you already know).
    <Dennis>

    Sony Alpha SLT-A57/Minolta Maxxum 9000/Olympus XA/Minolta Autocord/Canon P/Sony NEX-3
    "Shikata ga nai"
    "If you donít know where you are going, every road will get you nowhere.Ē - Henry Kissinger

    My Repair Blog http://oldcam.wordpress.com/

  5. #5
    TPF Junkie!
    Join Date
    Jan 2010
    Location
    Philadelphia
    Posts
    3,667
    My Gallery
    (0)
    My Photos Are NOT OK to Edit
    Liked
    551 times
    What I remember is that the maximum aperture f number for a lens equals the focal length divided by the front element diameter. So, for the same front element size on a longer focal length lens, the f number would be higher. If you double the front element diameter on a given focal length lens, you get four times as much light (area is pi times d/2 squared), which is two stops, or half the f number, e.g., from 2.8 to 1.4.

    I don't know if the element size can also affect resolution, but in any case, resolution is determined also by glass quality and diffraction effects due to the aperture blades. Good glass quality is easier to achieve with smaller lens elements, so sometimes slower lenses are better for that reason.

  6. #6
    Been spending a lot of time on here!
    Join Date
    Nov 2009
    Location
    Orlando, FL
    Posts
    187
    My Gallery
    (0)
    My Photos Are OK to Edit
    Liked
    2 times
    I tent to agree with Robert. I am not saying this is definitely the only reason but I am sure the biggest factor in having larger front element diameter is relative aperture (f ratio).
    I have a 50mm f/1.4 lens. The front element is larger than a typical kit lense but it is not so large. I have also seen 85mm f/1.2 lens and the front element is large!.. for the obvious reason.

    What I remember is that the maximum aperture f number for a lens equals the focal length divided by the front element diameter.
    Relative aperture is focal length divided by the aperture diameter. NOT diameter of the front element. Yes, as the front element diameter gets larger, aperture diameter gets larger. But it is the aperture that controls how much light gets to image sensor/film not the front element. Thus we use aperture diameter in the relative aperture formula.
    Canon T1i 500D with EF-S 18-55mm IS
    Canon EF-S 17-85 IS USM
    Canon EF 50mm USM f/1.4
    Canon Speedlite 430EX II
    Canon A640 with WCDC58N wide converter

  7. #7
    TPF Junkie!
    Join Date
    Nov 2003
    Location
    North New Jersey, United States of America
    Posts
    9,463
    My Gallery
    (0)
    My Photos Are OK to Edit
    Liked
    336 times
    All this talk about the size of the front element, the max aperture, and aperture diameter.... the OP asked specifically about "resolving" characteristics of photographic lenses.

    I can't comment much further as I am not an optics expert but I believe the ability of to gather light is different from the capability to resolve. If I were to take a guess, the ability to gather light is related to the size of the glass BUT the ability to resolve is more a factor of optical design.

    The main example I can think of in the photographic world would be the highly controversial Leica 50mm f/1 Noctilux. In general, the consensus is that the 50mm Noctilux is not a replacement for other 50mm lenses hence why people have two 50s. The Noctilux is the king of low-light... It is a HUGE glass that "gather's light". Meanwhile, the much more compact 50mm lenses (Summilux, Summicron, Summarits) will "out resolve" the Noctilux fairly easily.


    (Ideally, you want both... Big light gatherer that can resolve. But that is a whole different story and complexity)
    Last edited by usayit; 05-28-2010 at 09:54 AM.
    <exits stage left>

  8. #8
    TPF Junkie!
    Join Date
    Aug 2008
    Location
    True North Cold and Freezing
    Posts
    2,135
    My Gallery
    (0)
    My Photos Are OK to Edit
    Liked
    11 times
    Sort of.

    Larg front elements are both the product of a large aperture (which usually indicates a high-quality lens), but also of additional correction of aberrations.
    If you want to judge my credibility as a photographer, don't look at my post count, look at my photography:


    www.eppbphoto.com


    Nikon D7000 | Nikon D200 | Nikon D40 | Tokina 11-16 | 35/1.8 | 50/1.8 | 55-200 VR | 75-150/3.5 Series E | SB-600 | Alienbees Cybersyncs

  9. #9
    has a hat around here somewhere Site Moderator
    TPF Supporter

    Join Date
    May 2008
    Location
    UK - England
    Posts
    19,814
    My Gallery
    (0)
    My Photos Are OK to Edit
    Liked
    2508 times
    Hmm its got to be more than the front element size - my MPE 65mm has a front element that is beyond tiny and yet it has a fantastic resolution of fine details. I know that macro tends to bend a lot of common rules, but certainly that is one lens that does not need a large front element to show high resolution.

  10. #10
    TPF Junkie!
    Join Date
    Nov 2003
    Location
    North New Jersey, United States of America
    Posts
    9,463
    My Gallery
    (0)
    My Photos Are OK to Edit
    Liked
    336 times
    Also, it is indirectly stating that all rangefinder lenses (typically very small elements with a filter sizes such as 39mm 46mm 49mm etc) are "less corrected" than the SLR counterparts which just does not make sense.
    <exits stage left>

  11. #11
    No longer a newbie, moving up!
    Join Date
    Feb 2010
    Posts
    42
    My Gallery
    (0)
    My Photos Are NOT OK to Edit
    Liked
    0 times
    Yea, I am not really inteested in "light gathering" as the F-stop number already measures this directly. I was merely thinking about resolution.....I shoot on a low res D2hs right now (only 4.1 megapixel), but eventually I want to go full frame and I dont want lenses that will be outperformed by a 18 or 21 megapixel sensor!

  12. #12
    I spend too much of my life on TPF!
    Join Date
    Jun 2009
    Location
    San Diego, CA
    Posts
    852
    My Gallery
    (0)
    My Photos Are OK to Edit
    Liked
    6 times
    Here's a pretty technical article about lenses, apertures, and difraction: Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

    essentially, the fstop ratio (reletive diameter) can cause resolving issues the smaller it becomes (regardless of physical diameter).

    The higher the megapixel count, the lower aperture difraction kicks in. Remember though, that this is on a per-pixel level. Someone posted in another thread a great simple example. Let's say you have a high res sensor and a four-pixel row reads BLACK, GRAY, WHITE, WHITE. The grey area is something not perfectly resolved by the by the sensor and acts as a transition between the two. But if you take a sensor half the size, the same space would only be two pixels: BLACK, WHITE. So there's no graying, but there's also a loss half the detail. In the end though, it's only really important if you are printing poster-sized images or cropping to show 75-100% original size. When scaled down, the issue is almost non-existant.
    -Matt
    Canon EOS 7D | Canon EOS 50D
    EF-S 10-22mm f/3.5-4.5 USM | EF-S 17-55mm f/2.8 IS USM | EF 50mm f/1.4 USM | EF 70-200mm f/2.8L IS II USM

 

 

Ads

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Similar Threads

  1. Replies: 0
    Last Post: 04-17-2010, 12:42 PM
  2. Confused over which lense does what... please help buying new camera and lense
    By lbowman920 in forum Photography Beginners' Forum
    Replies: 4
    Last Post: 01-27-2008, 10:36 PM
  3. Lense Diameter/Filter Size Marking
    By fatsheep in forum Photography Beginners' Forum
    Replies: 4
    Last Post: 01-11-2008, 07:48 PM
  4. Vivitar lense vs. Canon FD lense? which one?
    By jermo in forum Photography Equipment & Products
    Replies: 3
    Last Post: 04-01-2007, 04:02 AM
  5. Does cleaning your lense damage the lense?
    By amoki in forum Beyond the Basics
    Replies: 4
    Last Post: 04-21-2005, 08:49 AM

Search tags for this page

diameter of a lense
,
does a larger diameter lense gather more light
,
lens diameter resolution
,
lens resolving power
,

lense diameter

,
resolving power of a lens
,

resolving power of lens

,
resolving power of lenses
,
what is the resolving power of a lens
,

why is a telescope of large diameter said to have a greater resolving power

Click on a term to search for related topics.