Question: Quality of "Digital Optics" Lenses

Discussion in 'Digital Photography' started by BD, Jul 19, 2005.

  1. BD

    BD Guest

    Hi, all.

    I'm looking at options for my new Rebel 300d.

    I am considering Canon's 75-300 IS lens. I expect it would be a good
    choice.

    I see an inexpensive 2x telephoto out there, from a company called
    Digital Optics. this would give me 900mm effective (yikes!).

    Does anyone know about this crew's lenses? It's certainly a low price
    point ($60 for the 2x), so I am suspicious of the quality. On the other
    hand, it's cheap enough that it might just be worth getting for kicks.

    But some precedent on Digital Optics' quality would be useful.

    Any wisdom out there?

    Thanks!

    DW.
     
    BD, Jul 19, 2005
    #1
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  2. BD

    Nostrobino Guest

    "BD" <> wrote in message
    news:...
    > Hi, all.
    >
    > I'm looking at options for my new Rebel 300d.
    >
    > I am considering Canon's 75-300 IS lens. I expect it would be a good
    > choice.
    >
    > I see an inexpensive 2x telephoto out there, from a company called
    > Digital Optics. this would give me 900mm effective (yikes!).


    "Yikes!" is right, but what on earth would you use a 900mm (equiv.) lens
    for? Do you have any idea of the problems you'd have using such a lens, even
    in the (unlikely) case that such a converter could produce acceptable image
    quality?


    >
    > Does anyone know about this crew's lenses? It's certainly a low price
    > point ($60 for the 2x), so I am suspicious of the quality.


    And rightly so.


    > On the other
    > hand, it's cheap enough that it might just be worth getting for kicks.


    Yes, or you could just put the $60 in a shredder and save yourself the
    bother and wasted time.


    >
    > But some precedent on Digital Optics' quality would be useful.
    >
    > Any wisdom out there?


    No experience with that <ahem> brand myself, but I would be leery of any
    such attachment that's essentially a no-name product. First, would it even
    fit that 75-300mm lens? Most of those kinds of converters are threaded for
    37mm or 52mm attachment. I'd be surprised if any 75-300 has a filter size as
    small as 52mm.

    Here are some comments from others on the "Digital Optics" (aka "Crystal
    Optics") brand attachments:
    http://www.stevesforums.com/forums/view_topic.php?id=50061&forum_id=50

    I strongly suggest you get the 75-300 first and *then* decide if you really
    need or want more focal length. In any case it seems unlikely to me that any
    front-end converter would be suitable for such a lens.

    N.
     
    Nostrobino, Jul 19, 2005
    #2
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  3. BD

    BD Guest

    Yeah, I tend to agree. But I do have a mild 'astral protography' bent,
    and if I could spend $70 more to get some insanely large moon shots
    (who cares about corner/edge problems on a moon shot), That alone might
    be worth the price of admission.

    But yes, I think starting with the 300 would be wise regardless. ;)
     
    BD, Jul 19, 2005
    #3
  4. BD

    wilt Guest

    "2X telephoto...900mm effective" You are quite confused, it sounds.
    In order for 2X to provide 900mm effective, you have to start with
    450mm!!! Put it in front of 80mm, and you end up with something
    similar to a 160mm lens.

    Digital Optics is an example of a way to take a non-interchangeable
    lens and extend its focal length. It mounts on FRONT of the existing
    lens. Since you have an SLR, you don't want that! You want to use a
    'teleconvertor', and most are 2X in effect like the 2X front-mounted
    unit but generally better in quality of result.

    --wilt
     
    wilt, Jul 19, 2005
    #4
  5. BD

    BD Guest

    I will admit to being confused, as I'm only starting to get my head
    around the vernacular. the 900 effective comes from:

    Native lens length = 300
    Teleconverter = 2x => 600mm
    x 1.6 to 'translate' from 35mm to digicam equivalent => ~900mm.

    I'm not intentionally talking out of my arse or being obtuse, I'm just
    at the start of a bit of a learning curve.
     
    BD, Jul 19, 2005
    #5
  6. BD

    BD Guest

    the 1.6 multiplier comes from (I nicked this from another post)
    ...."reduced sensor size results in a 50mm lens
    having the same field of view as an 80mm lens"
     
    BD, Jul 19, 2005
    #6
  7. BD

    Ross Garrett Guest

    "wilt" <> wrote in message
    news:...
    > "2X telephoto...900mm effective" You are quite confused, it sounds.
    > In order for 2X to provide 900mm effective, you have to start with
    > 450mm!!! Put it in front of 80mm, and you end up with something
    > similar to a 160mm lens.


    I think the camera in question was a Rebel-D, so unless Canon has made a
    one-off Rebel-D with full sized sensor the 900mm is quite close. True reach
    would be somewhat greater than 900.

    At the long end of his zoom he'd get 300 x 1.6 = 480. And the 2x would net
    him 960. Admitedly it is probably a very crappy 960, but you were only
    addressing the overall math.....a point on which he was correct.
     
    Ross Garrett, Jul 19, 2005
    #7
  8. BD

    CFB Guest

    In article <>,
    "BD" <> wrote:

    > Hi, all.
    >
    > I'm looking at options for my new Rebel 300d.
    >
    > I am considering Canon's 75-300 IS lens. I expect it would be a good
    > choice.


    It's great. I have one for sale if you are interested.

    >
    > I see an inexpensive 2x telephoto out there, from a company called
    > Digital Optics. this would give me 900mm effective (yikes!).
    >
    > Does anyone know about this crew's lenses? It's certainly a low price
    > point ($60 for the 2x), so I am suspicious of the quality. On the other
    > hand, it's cheap enough that it might just be worth getting for kicks.
    >
    > But some precedent on Digital Optics' quality would be useful.
    >
    > Any wisdom out there?
    >
    > Thanks!
    >
    > DW.


    --

    http://home.nc.rr.com/christianbonanno/
     
    CFB, Jul 19, 2005
    #8
  9. BD

    Nostrobino Guest

    "wilt" <> wrote in message
    news:...
    > "2X telephoto...900mm effective" You are quite confused, it sounds.
    > In order for 2X to provide 900mm effective, you have to start with
    > 450mm!!! Put it in front of 80mm, and you end up with something
    > similar to a 160mm lens.


    Where'd you get that 80mm, though? He's asking about putting the 2x
    converter on a 75-300mm lens. Given the Canon's 1.6x focal length factor,
    that works out to 960mm effective equivalent. Close enough, since these
    numbers are approximations anyway. (The 75-300 is probably a bit less than
    an actual 300mm at the long end, the 1.6x factor is just an approximation,
    and the 2x conversion probably isn't exact either.


    >
    > Digital Optics is an example of a way to take a non-interchangeable
    > lens and extend its focal length. It mounts on FRONT of the existing
    > lens. Since you have an SLR, you don't want that! You want to use a
    > 'teleconvertor', and most are 2X in effect like the 2X front-mounted
    > unit but generally better in quality of result.


    Right, but the problem there is that the rear-mounted 2x tele extender will
    cut his maximum aperture by two stops, at which point his SLR will no longer
    autofocus. I.e., if his 75-300 is f/5.6 at the long end it will be f/11 with
    a 2x extender, too small an aperture for the SLR to autofocus (perhaps even
    too small for it to be readily manually focused).

    That is in fact the one advantage to a front-mounted converter: it won't
    change his maximum aperture, provided it's designed so as to be suitable for
    that particular lens. (Which in this case it almost certainly isn't,
    however.)

    N.
     
    Nostrobino, Jul 19, 2005
    #9
  10. BD

    Guest

    In message <>,
    "BD" <> wrote:

    >Hi, all.
    >
    >I'm looking at options for my new Rebel 300d.
    >
    >I am considering Canon's 75-300 IS lens. I expect it would be a good
    >choice.
    >
    >I see an inexpensive 2x telephoto out there, from a company called
    >Digital Optics. this would give me 900mm effective (yikes!).
    >
    >Does anyone know about this crew's lenses? It's certainly a low price
    >point ($60 for the 2x), so I am suspicious of the quality. On the other
    >hand, it's cheap enough that it might just be worth getting for kicks.
    >
    >But some precedent on Digital Optics' quality would be useful.
    >
    >Any wisdom out there?


    Yeah. Don't get that lens if you want to use a teleconverter. It's not
    sharp enough to get any more detail out of it; it is already pushed to
    its limits without a TC.

    Also. you really should stop multiplying focal lengths by 1.6. That
    zoom with a 2x is 600mm, not 900. It will have about as much detail as
    a really sharp 200mm lens on a full-35mm-frame camera.

    There's no free lunch or magic with teleconverters; they waste light,
    and light isn't worth wasting unless you gain something from it.
    Teleconverters are for sharp, top-end lenses, not budget consumer
    lenses.

    Also, the better TCs start at about $200.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jul 19, 2005
    #10
  11. BD

    Guest

    In message <>,
    "Nostrobino" <> wrote:

    >I strongly suggest you get the 75-300 first and *then* decide if you really
    >need or want more focal length. In any case it seems unlikely to me that any
    >front-end converter would be suitable for such a lens.


    He'd need another lens, really. The 75-300 is only sharp at 300mm
    stopped down, and it is just barely sharp. Magnifying it with a TC will
    only disappoint, unless a person is confused enought to compare by
    small, full-frame, downsampled images.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jul 19, 2005
    #11
  12. BD

    Guest

    In message <>,
    "BD" <> wrote:

    >Yeah, I tend to agree. But I do have a mild 'astral protography' bent,
    >and if I could spend $70 more to get some insanely large moon shots
    >(who cares about corner/edge problems on a moon shot), That alone might
    >be worth the price of admission.


    No, you will get horrible results with a 75-300 and a 2x TC. If it's
    the kind that goes between the lens and the body, the 75-300 doesn't
    have the sharpness to make it worth using; if it's the type that screws
    on like a filter, it will probably be horrible, unless it is made
    specifically for the lens it is mounted on. I have a screw-on 2x for my
    Sony F707; it works wonderfully on the Sony, but is absolutely worthless
    on my 75-300 IS on my Canons.

    >But yes, I think starting with the 300 would be wise regardless. ;)


    Well, that depends on your budget. If price is not an issue, skip the
    75-300, as it will probably become redundant when you decide to get a
    better lens.
    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jul 19, 2005
    #12
  13. BD

    Nostrobino Guest

    "BD" <> wrote in message
    news:...
    >I will admit to being confused, as I'm only starting to get my head
    > around the vernacular. the 900 effective comes from:
    >
    > Native lens length = 300
    > Teleconverter = 2x => 600mm
    > x 1.6 to 'translate' from 35mm to digicam equivalent => ~900mm.


    Yes, close enough. It works out to 960mm of course, but none of these
    numbers are likely to be exactly as advertised anyway.


    >
    > I'm not intentionally talking out of my arse or being obtuse, I'm just
    > at the start of a bit of a learning curve.


    You're doing okay. But I think once you deal with an 480mm equivalent or
    thereabouts, you probably will find that more than enough of a handful.

    I can understand your being interested in photographing the moon. The
    problem there is that the moon's been photographed 18,745,904,320,417 times
    already, with several million of those being done with equipment you cannot
    possibly begin to compete with. I would just buy a book with some good moon
    photographs, of which there must be many. ;-)

    Even a 960mm (equivalent) lens is not going to fill the frame with the moon
    very well. The moon's about 2,000 miles in diameter and what, 238,000 miles
    away? So with a 960mm lens on a 35 the moon image would be 2 / 238 * 960 =
    8.07 mm diameter, or about one-third the height of the frame. If you take a
    long-lens shot and magnify the moon with software you'll probably do about
    as well as you'd do with a cheap 2x converter (if you could even get one on
    that lens in the first place).

    N.
     
    Nostrobino, Jul 19, 2005
    #13
  14. BD

    BD Guest

    Really?! Can you email me offline and let me know what you'd want for
    it? Perhaps also a shipping estimate to the Vancouver area?
     
    BD, Jul 19, 2005
    #14
  15. BD

    Guest

    In message <>,
    "Nostrobino" <> wrote:

    >"wilt" <> wrote in message
    >news:...
    >> "2X telephoto...900mm effective" You are quite confused, it sounds.
    >> In order for 2X to provide 900mm effective, you have to start with
    >> 450mm!!! Put it in front of 80mm, and you end up with something
    >> similar to a 160mm lens.

    >
    >Where'd you get that 80mm, though? He's asking about putting the 2x
    >converter on a 75-300mm lens. Given the Canon's 1.6x focal length factor,
    >that works out to 960mm effective equivalent.


    .... but what does that mean, in practical terms? Nothing, because a
    sharp 300mm lens will capture more subject detail from the same distance
    as this combo will.

    --

    <>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
    John P Sheehy <>
    ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
     
    , Jul 19, 2005
    #15
  16. BD

    BD Guest

    The one I was looking at is front-mounted.
     
    BD, Jul 19, 2005
    #16
  17. BD

    wilt Guest

    <<Where'd you get that 80mm, though? He's asking about putting the 2x
    converter on a 75-300mm lens. Given the Canon's 1.6x focal length
    factor,
    that works out to 960mm effective equivalent.>>

    The original post did not say '960mm equivalent field of view'...it
    simply said 2X on 300mm, and that is 600mm according to how I was
    taught multiplication.

    --Wilt
     
    wilt, Jul 19, 2005
    #17
  18. BD

    Bill Funk Guest

    On 19 Jul 2005 11:41:58 -0700, "BD" <> wrote:

    >Hi, all.
    >
    >I'm looking at options for my new Rebel 300d.
    >
    >I am considering Canon's 75-300 IS lens. I expect it would be a good
    >choice.
    >
    >I see an inexpensive 2x telephoto out there, from a company called
    >Digital Optics. this would give me 900mm effective (yikes!).
    >
    >Does anyone know about this crew's lenses? It's certainly a low price
    >point ($60 for the 2x), so I am suspicious of the quality. On the other
    >hand, it's cheap enough that it might just be worth getting for kicks.
    >
    >But some precedent on Digital Optics' quality would be useful.
    >
    >Any wisdom out there?
    >
    >Thanks!
    >
    >DW.


    If you mean this:
    http://www.buydig.com/shop/product.aspx?sku=SAKDO2X37
    don't bother.
    It's designed to be mounted in front of a video camera, and the optics
    reflect that. IOW, it sucks for digital still photography. It's not
    even good for a digital video camera.
    On top of that, there's no practical way to mount this on your DSLR
    lens.
    It's just not what you're looking for. What you need, if you want to
    go this way, is a Canon mount 2x teleconverter, something like this:
    http://www.bhphotovideo.com/bnh/con...t&shs=canon teleconverter&image.x=7&image.y=7
    or:
    http://tinyurl.com/cbmzt


    --
    Bill Funk
    replace "g" with "a"
    funktionality.blogspot.com
     
    Bill Funk, Jul 19, 2005
    #18
  19. BD

    Zed Pobre Guest

    <> wrote:
    >
    > Well, that depends on your budget. If price is not an issue, skip the
    > 75-300, as it will probably become redundant when you decide to get a
    > better lens.


    .... unless you go on long (multi-day) hikes, in which case you'll want
    the lightest telephoto lens you can find, and the 75-300 is it.

    I'm still looking at the Sigma 80-400 to replace my 75-300 for primary
    telephoto use, but I'd never try to drag that much weight into the
    mountains.

    --
    Zed Pobre <> a.k.a. Zed Pobre <>
    PGP key and fingerprint available on finger; encrypted mail welcomed.
     
    Zed Pobre, Jul 20, 2005
    #19
  20. BD

    ASAAR Guest

    On 19 Jul 2005 13:30:53 -0700, BD wrote:

    > But I do have a mild 'astral protography' bent,
    > and if I could spend $70 more to get some insanely large moon shots
    > (who cares about corner/edge problems on a moon shot), That alone might
    > be worth the price of admission.


    The only good thing about using such a 2x converter for moon shots
    is that even if it introduces severe corner vignetting, it wouldn't
    be as much of a problem with bright round objects. :) On the other
    hand it might make focusing more difficult and inaccurate. I'd
    guess that blowing up the image 2x on your computer would give you
    more consistent, satisfactory results. The 2x teleconverter would
    be good for one thing though. You'd more easily see the effect of
    not having rock solid stability, and might decide to use a decent
    tripod if you weren't already doing so. I'd think the moon would be
    bright enough to allow reasonably quick shutter speeds, but the
    longer focal length would require longer exposures.
     
    ASAAR, Jul 20, 2005
    #20
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