Mirror Lenses Revisited

Discussion in 'Digital Photography' started by Justin Thyme, Aug 12, 2005.

  1. Justin Thyme

    Justin Thyme Guest

    I'm just wondering, why are mirror lenses so bad? Is it because they are
    poorly made or is it an inherent problem. I would have thought that apart
    from the donut shaped highlights they should be better than traditional
    lenses. In telescopes, Newtonian reflectors are far superior to refractor
    telescopes. A mirror lens is very similar to a Newtonian reflector, while a
    traditional lens is more similar to a refractor telescope. So why is it that
    cameras reverse the conventional wisdom learnt from astronomy?
    Justin Thyme, Aug 12, 2005
    #1
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  2. Justin Thyme

    Deep Reset Guest

    "Justin Thyme" <> wrote in message
    news:lY8Le.514$...
    > I'm just wondering, why are mirror lenses so bad? Is it because they are
    > poorly made or is it an inherent problem. I would have thought that apart
    > from the donut shaped highlights they should be better than traditional
    > lenses. In telescopes, Newtonian reflectors are far superior to refractor
    > telescopes. A mirror lens is very similar to a Newtonian reflector, while
    > a traditional lens is more similar to a refractor telescope. So why is it
    > that cameras reverse the conventional wisdom learnt from astronomy?


    Ha! tres amusant user name.

    Not.

    Camera mirror lenses are hybrids, part refractor part reflector, the front
    element *is* a lens, unlike a true Newtonian..
    Deep Reset, Aug 12, 2005
    #2
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  3. Justin Thyme

    wavelength Guest

    And what exactly is the price difference between those?

    And who want's a donut in their picture of a Booby footed red beaked
    southern woodpecker anyways?

    Not speaking from any technical experience, I believe that the optics
    to get a perfect, high-resolution/clarity mirror are harder to mass
    produce than glass. Which makes them more expensive to produce the
    same/higher qualtity than glass. Just a guess. The net effect being
    that most if not all mirror lenses (at least from what i have learned,
    not experienced) are crap. Seems it was a gimmick to sell some
    lightweight telephoto lenses, but didn't fly with consumers.
    wavelength, Aug 12, 2005
    #3
  4. In article <lY8Le.514$>, Justin Thyme
    <> wrote:

    > I'm just wondering, why are mirror lenses so bad?


    The biggest issue, aside from the donuts, is that the aperture is fixed
    - and it's a small one. With a mirror lens, you're focusing a dim, high
    magnification image (600mm f/8 in the last one I used) and can't stop
    down to cover minor focusing errors.
    Scott Schuckert, Aug 12, 2005
    #4
  5. Justin Thyme

    Nostrobino Guest

    "Justin Thyme" <> wrote in message
    news:lY8Le.514$...
    > I'm just wondering, why are mirror lenses so bad?


    They aren't "so bad" unless you're talking about some inferior mirror lens.
    I've had Minolta 500mm f/8 and 250mm f/5.6 mirror lenses and they were
    superb. (But I think most of the mirror lenses sold were much cheaper than
    those and, I expect, not of nearly the same quality.)

    They do, however, have some inherent problems in use. You can't change the
    aperture and that is generally quite small, and actual light transmission is
    even less than the f-number would lead you to believe. As I recall, my 500mm
    f/8 passed only as much light as you'd expect from about f/11 in a
    conventional lens. That's probably because of the secondary mirror and other
    obstructions in the light path. With the film speeds generally available at
    the time I that lens, especially since I mostly used slide films, that
    pretty much limited it to tripod use.

    N.
    Nostrobino, Aug 13, 2005
    #5
  6. Justin Thyme

    Dirty Harry Guest

    "Justin Thyme" <> wrote in message
    news:lY8Le.514$...
    > I'm just wondering, why are mirror lenses so bad? Is it because they are
    > poorly made or is it an inherent problem. I would have thought that apart
    > from the donut shaped highlights they should be better than traditional
    > lenses. In telescopes, Newtonian reflectors are far superior to refractor
    > telescopes. A mirror lens is very similar to a Newtonian reflector, while

    a
    > traditional lens is more similar to a refractor telescope. So why is it

    that
    > cameras reverse the conventional wisdom learnt from astronomy?


    Could someone please post some large images from one of these things so we
    can actually see what the heck we are dealing with?
    Dirty Harry, Aug 13, 2005
    #6
  7. Justin Thyme

    Charles Guest

    On Sat, 13 Aug 2005 01:36:09 GMT, "Dirty Harry" <>
    wrote:

    >
    >"Justin Thyme" <> wrote in message
    >news:lY8Le.514$...
    >> I'm just wondering, why are mirror lenses so bad? Is it because they are
    >> poorly made or is it an inherent problem. I would have thought that apart
    >> from the donut shaped highlights they should be better than traditional
    >> lenses. In telescopes, Newtonian reflectors are far superior to refractor
    >> telescopes. A mirror lens is very similar to a Newtonian reflector, while

    >a
    >> traditional lens is more similar to a refractor telescope. So why is it

    >that
    >> cameras reverse the conventional wisdom learnt from astronomy?

    >
    >Could someone please post some large images from one of these things so we
    >can actually see what the heck we are dealing with?
    >


    Pick a test group, i'll put one up, full rez from a canon d rebel and
    the vivitar 600. Hope I got it focused close to right.
    Charles, Aug 13, 2005
    #7
  8. Justin Thyme

    Charles Guest

    On Sat, 13 Aug 2005 01:46:38 GMT, Charles <>
    wrote:

    never mind, it's awful. Let me try to get a good shot.
    Charles, Aug 13, 2005
    #8
  9. Justin Thyme

    Charles Guest

    On Sat, 13 Aug 2005 01:36:09 GMT, "Dirty Harry" <>
    wrote:

    >
    >"Justin Thyme" <> wrote in message
    >news:lY8Le.514$...
    >> I'm just wondering, why are mirror lenses so bad? Is it because they are
    >> poorly made or is it an inherent problem. I would have thought that apart
    >> from the donut shaped highlights they should be better than traditional
    >> lenses. In telescopes, Newtonian reflectors are far superior to refractor
    >> telescopes. A mirror lens is very similar to a Newtonian reflector, while

    >a
    >> traditional lens is more similar to a refractor telescope. So why is it

    >that
    >> cameras reverse the conventional wisdom learnt from astronomy?

    >
    >Could someone please post some large images from one of these things so we
    >can actually see what the heck we are dealing with?
    >



    Okay, I have one under exposed, one over exposed. Where do you want
    them?
    Charles, Aug 13, 2005
    #9
  10. Justin Thyme wrote:
    > I'm just wondering, why are mirror lenses so bad? Is it because they are
    > poorly made or is it an inherent problem. I would have thought that apart
    > from the donut shaped highlights they should be better than traditional
    > lenses. In telescopes, Newtonian reflectors are far superior to refractor
    > telescopes. A mirror lens is very similar to a Newtonian reflector, while a
    > traditional lens is more similar to a refractor telescope. So why is it that
    > cameras reverse the conventional wisdom learnt from astronomy?
    >
    >


    Mirror lenses can have wonderful performance.
    Here is a 760 mm f/5 home made telescope/telephoto
    that cost me less than $200 to build:
    http://www.clarkvision.com/newt-tele1
    Performance is sensor limited, not optics limited!

    The problem with small telephotos that you typically see for
    sale as camera telephoto lenses: they are cheaply made.

    The concept that they are fixed f/ratio is bogus. You can add
    a diaphragm that is off-center so as you close down, you
    crop out the central obstruction. There are also optical designs
    that have no central obstruction, but they tend to
    have odd shapes.

    In the super telephoto lens category (600 mm f/4 and up), it is
    my opinion (as someone who has written ray tracing programs, and
    published scientific papers based on ray tracing mirror optical
    systems), that a mirror telephoto would be superior optically
    to a lens system, lighter, and cheaper to make. It is only
    reasonable to do this in the larger apertures because it becomes
    easier for the secondary mirror to field the light cone and deliver
    it to a 35mm size focal plane. If someone would just market
    a focus mechanism that takes a DSLR and attaches it to a telescope
    with autofocus, one could use a number of telescopes for high
    power wildlife photography. I would take a 1016 mm f/4 telephoto
    on my next bird photo expedition if I had autofocus (cost: about
    $1000.).

    With a lens, you have to have multiple elements (10 elements are common),
    each with 2 surfaces. Optical glass is very expensive as it can have
    no bubbles or shear (stress). You must then grind about 20 surfaces,
    but they are typically spherical (with perhaps a couple of spherics,
    and tolerance on the surfaces is about 1/2 wavelength. Then you must
    anti reflection coat all surfaces, and accurately mount all lenses.
    This add to a big expense.

    A mirror system can have as little as 2 surfaces, the glass can have bubbles,
    and you have only 2 mounts and 2 coatings. Optical tolerance is 1/2
    that of a lens, about 1/4 wavelength (or better), but that is easy
    these days. But one is flat (Newtonian), or hyperbolic secondaries,
    and typically parabolic primaries. Still simpler. For a given
    aperture, a mirror system is many times less costly to produce.

    Why no manufacturer has done this is a good question.

    After doing the above (web page) experiments to show I had the optical
    quality, I bought a Canon 500 mm f/4 L IS telephoto because of the
    autofocus capability. It was worth every penny--it is a wonderful
    and versatile lens, and portable too.

    Roger
    Photos at: http://www.clarkvision.com
    Roger N. Clark (change username to rnclark), Aug 13, 2005
    #10
  11. Justin Thyme

    Dirty Harry Guest

    "Charles" <> wrote in message
    news:...
    > On Sat, 13 Aug 2005 01:36:09 GMT, "Dirty Harry" <>
    > wrote:
    >
    > >
    > >"Justin Thyme" <> wrote in message
    > >news:lY8Le.514$...
    > >> I'm just wondering, why are mirror lenses so bad? Is it because they

    are
    > >> poorly made or is it an inherent problem. I would have thought that

    apart
    > >> from the donut shaped highlights they should be better than traditional
    > >> lenses. In telescopes, Newtonian reflectors are far superior to

    refractor
    > >> telescopes. A mirror lens is very similar to a Newtonian reflector,

    while
    > >a
    > >> traditional lens is more similar to a refractor telescope. So why is it

    > >that
    > >> cameras reverse the conventional wisdom learnt from astronomy?

    > >
    > >Could someone please post some large images from one of these things so

    we
    > >can actually see what the heck we are dealing with?
    > >

    >
    >
    > Okay, I have one under exposed, one over exposed. Where do you want
    > them?

    How about a link right here? If you want you could email and I can host
    them.
    --
    www.harryphotos.com
    Dirty Harry, Aug 13, 2005
    #11
  12. Justin Thyme

    Dirty Harry Guest

    "Dirty Harry" <> wrote in message
    news:M4jLe.204222$s54.129933@pd7tw2no...
    >
    > "Charles" <> wrote in message
    > news:...
    > > On Sat, 13 Aug 2005 01:36:09 GMT, "Dirty Harry" <>
    > > wrote:
    > >
    > > >
    > > >"Justin Thyme" <> wrote in message
    > > >news:lY8Le.514$...
    > > >> I'm just wondering, why are mirror lenses so bad? Is it because they

    > are
    > > >> poorly made or is it an inherent problem. I would have thought that

    > apart
    > > >> from the donut shaped highlights they should be better than

    traditional
    > > >> lenses. In telescopes, Newtonian reflectors are far superior to

    > refractor
    > > >> telescopes. A mirror lens is very similar to a Newtonian reflector,

    > while
    > > >a
    > > >> traditional lens is more similar to a refractor telescope. So why is

    it
    > > >that
    > > >> cameras reverse the conventional wisdom learnt from astronomy?
    > > >
    > > >Could someone please post some large images from one of these things so

    > we
    > > >can actually see what the heck we are dealing with?
    > > >

    > >
    > >
    > > Okay, I have one under exposed, one over exposed. Where do you want
    > > them?

    > How about a link right here? If you want you could email and I can host
    > them.
    > --
    > www.harryphotos.com


    And how much was that lens btw? Did you pick it up for shots of the stars
    or something else?
    Dirty Harry, Aug 13, 2005
    #12
  13. Justin Thyme

    Chris Brown Guest

    In article <d8cLe.1843$vj.1781@pd7tw1no>,
    Dirty Harry <> wrote:
    >
    >Could someone please post some large images from one of these things so we
    >can actually see what the heck we are dealing with?


    I didn't keep many of the shots I took with mine, but here's a test shot.
    Full res JPEG, taken on a Canon EOS D30:

    http://homepage.ntlworld.com/narcissus/mirrorlens.jpg

    Notice how it's already struggling to pprovide the sensor with a decently
    sharp image, even though the D30 was only a 3 megapixel camera. Notice also
    the lack of decent contrast. Notice also the utterly vile way it's rendered
    the slightly out-of-focus eyebrows.

    This was a Sigma 600mm f/8 mirror lens.
    Chris Brown, Aug 13, 2005
    #13
  14. Justin Thyme

    richard Guest

    Deep Reset wrote:

    >
    > "Justin Thyme" <> wrote in message
    > news:lY8Le.514$...
    >> I'm just wondering, why are mirror lenses so bad? Is it because they are
    >> poorly made or is it an inherent problem. I would have thought that apart
    >> from the donut shaped highlights they should be better than traditional
    >> lenses. In telescopes, Newtonian reflectors are far superior to refractor
    >> telescopes. A mirror lens is very similar to a Newtonian reflector, while
    >> a traditional lens is more similar to a refractor telescope. So why is it
    >> that cameras reverse the conventional wisdom learnt from astronomy?



    >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>


    The donut highlights you are probably referring to is the out of focus
    background light that passes through the optical path revealing a shadow of
    the secondary mirror in the optical system train. Just as any light with a
    regular lens will show up out of focus as a big light blob. Nothing wrong
    with these in telephoto shots. Mirror lenses are not as bad as you think,
    they may be bulkier in size and weight and the f/ratio is typically pretty
    high. They may also suffer much less achromatic aberration then a typical
    lens that may require many more compound lens groups. They are also cheaper
    to manufacture because of fewer optical surfaces to grind, polish,and
    antiglare coat.

    Richard
    richard, Aug 13, 2005
    #14
  15. In article <>, change username to rnclark
    <> wrote:

    > The concept that they are fixed f/ratio is bogus. You can add
    > a diaphragm that is off-center so as you close down, you
    > crop out the central obstruction.



    Is this theoretical, or are you thinking of a production lens I'm not
    aware of? I've sold and/or owned a lot of mirror lenses over the years,
    and they were all fixed aperture.
    Scott Schuckert, Aug 13, 2005
    #15
  16. Justin Thyme

    redbelly Guest

    Justin Thyme wrote:
    > I'm just wondering, why are mirror lenses so bad? Is it because they are
    > poorly made or is it an inherent problem. I would have thought that apart
    > from the donut shaped highlights they should be better than traditional
    > lenses. In telescopes, Newtonian reflectors are far superior to refractor
    > telescopes. A mirror lens is very similar to a Newtonian reflector, while a
    > traditional lens is more similar to a refractor telescope. So why is it that
    > cameras reverse the conventional wisdom learnt from astronomy?


    Telescopes differ from cameras in that the field of view required is
    very tiny, just a few degrees at most and usually less than 1 degree.

    Compare that to a camera, where the field of view is much larger. With
    a multi-lens system, those many curved surfaces are needed to
    compensate for aberations and the fact that much of the image is not
    being viewed straight-on.

    A mirrored system is limited to just 2 curved surfaces. That's fine
    when most of the image is being viewed from straight ahead, as in
    astronomical work, but for large fields of view needed for cameras,
    photos would be blurred away from the center of the picture.

    Mark
    redbelly, Aug 13, 2005
    #16
  17. Justin Thyme

    Charles Guest

    On Sat, 13 Aug 2005 09:33:37 GMT, "Dirty Harry" <>
    wrote:


    >> > >
    >> >
    >> >
    >> > Okay, I have one under exposed, one over exposed. Where do you want
    >> > them?

    >> How about a link right here? If you want you could email and I can host
    >> them.
    >> --
    >> www.harryphotos.com

    >
    >And how much was that lens btw? Did you pick it up for shots of the stars
    >or something else?
    >


    Okay, I found my good tripod. Let me go out and get some more
    representative pictures today, I'll try to get some donuts in ther as
    well.

    the lens was somewhere between 4 to 6 hunded, this was back in the
    1970's so I don't remember exactly. It filled a need that I have one,
    I didn't have any real use for it beyond just wanting it to make my
    life complete. It didn't do that either. It is the old Vivitar
    Series one cat lens.
    Charles, Aug 13, 2005
    #17
  18. Justin Thyme

    Charles Guest

    On Sat, 13 Aug 2005 11:28:37 GMT, Chris Brown
    <_uce_please.com> wrote:

    >In article <d8cLe.1843$vj.1781@pd7tw1no>,
    >Dirty Harry <> wrote:
    >>
    >>Could someone please post some large images from one of these things so we
    >>can actually see what the heck we are dealing with?

    >
    >I didn't keep many of the shots I took with mine, but here's a test shot.
    >Full res JPEG, taken on a Canon EOS D30:
    >
    >http://homepage.ntlworld.com/narcissus/mirrorlens.jpg
    >
    >Notice how it's already struggling to pprovide the sensor with a decently
    >sharp image, even though the D30 was only a 3 megapixel camera. Notice also
    >the lack of decent contrast. Notice also the utterly vile way it's rendered
    >the slightly out-of-focus eyebrows.
    >
    >This was a Sigma 600mm f/8 mirror lens.


    I notice that it will focus fairly close. Mine won't.
    Charles, Aug 13, 2005
    #18
  19. Justin Thyme

    Charles Guest

    On Sat, 13 Aug 2005 08:25:28 -0400, Scott Schuckert <>
    wrote:

    >In article <>, change username to rnclark
    ><> wrote:
    >
    >> The concept that they are fixed f/ratio is bogus. You can add
    >> a diaphragm that is off-center so as you close down, you
    >> crop out the central obstruction.

    >
    >
    >Is this theoretical, or are you thinking of a production lens I'm not
    >aware of? I've sold and/or owned a lot of mirror lenses over the years,
    >and they were all fixed aperture.



    This is familiar, I've read about it. Take the production lens, put a
    hole in the lens cap, off center, but circular. It reduces the
    effective aperature. Never tried it, though.
    Charles, Aug 13, 2005
    #19
  20. Scott Schuckert wrote:

    > In article <>, change username to rnclark
    > <> wrote:
    >
    >
    >>The concept that they are fixed f/ratio is bogus. You can add
    >>a diaphragm that is off-center so as you close down, you
    >>crop out the central obstruction.

    >
    >
    >
    > Is this theoretical, or are you thinking of a production lens I'm not
    > aware of? I've sold and/or owned a lot of mirror lenses over the years,
    > and they were all fixed aperture.


    I've not seen a production lens with it, but it is not hard.
    I've done it on my telescopes.

    Roger
    Roger N. Clark (change username to rnclark), Aug 13, 2005
    #20
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