Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,697   Posts: 1,549,085   Online: 1095
      
Page 3 of 3 FirstFirst 123
Results 21 to 29 of 29
  1. #21
    keithwms's Avatar
    Join Date
    Oct 2006
    Location
    Charlottesville, Virginia
    Shooter
    Multi Format
    Posts
    6,079
    Blog Entries
    20
    Images
    129
    Cotdt there are non-apo RB (KL) lenses that use some ED glass, and then there are apo lenses that are more rigorously corrected across the spectrum as described above. They are two different sets of lenses in the lineup, that's where the original question came from.

    Regarding process lenses, a small caution: my understanding is that "apo" in this case means quite specifically that these lenses have no refocus in the near UV where the film would be predominantly exposed. So there's no guarantee that an apo process lens is really all that apo through the reds! (Nevertheless, I have found my apo process lenses to be useful right from near UV to near IR, with little or no refocus. Go figure.)

    What people look for in "apo" has changed somewhat - nowawdays, because of quite noticeable fringing issues with reduced-frame Bayer sensors that require interpolation, apo takes on a quite different value. This issue if far less extreme with film... or foveon-type sensors.
    Last edited by keithwms; 05-16-2008 at 01:09 PM. Click to view previous post history.
    "Only dead fish follow the stream"

    [APUG Portfolio] [APUG Blog] [Website]

  2. #22

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    Quote Originally Posted by Lee L View Post
    Reflector/mirror optics with a corrector plate, right? There's no inherent chromatic aberration with reflector/mirror optics because [...] You can make a rainbow with a prism, but not with a front surface mirror.
    True. But alas, the "corrector plate" is a refractive device.

    Most, if not all photographic mirror lenses do have indeed lenses (more than just the one, the corrector plate) as well as mirrors.
    So no reprieve: chromatic aberrations are still there.

  3. #23
    DJGainer's Avatar
    Join Date
    May 2006
    Shooter
    Medium Format
    Posts
    151
    Images
    25
    Is this discussion focusing too much on the abstract? I mean, unless you are shooting extreme macro, won't the depth of field usually include all the wavelengths of the general subject area?

  4. #24

    Join Date
    Jul 2007
    Location
    Netherlands
    Shooter
    Medium Format
    Posts
    5,686
    Quote Originally Posted by DJGainer View Post
    Is this discussion focusing too much on the abstract? I mean, unless you are shooting extreme macro, won't the depth of field usually include all the wavelengths of the general subject area?
    Yes, and no. Depth of field would be different for different colours of the spectrum...

  5. #25
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,244
    Quote Originally Posted by Q.G. View Post
    True. But alas, the "corrector plate" is a refractive device.

    Most, if not all photographic mirror lenses do have indeed lenses (more than just the one, the corrector plate) as well as mirrors.
    So no reprieve: chromatic aberrations are still there.
    You are correct. The refractive glass element is used to correct other aberrations commonly found in "folded" or fast mirror systems. However, corrector plates tend to have a much lower differential between front and rear surface curves than achromatic refractor lenses and camera objectives, so they tend to introduce less chromatic aberration than compound refractor optics.

    I'm more connected to the astronomical world than the photographic world when it comes to reflectors, so I tend to think of the classical Cassegrain and Newtonian reflectors. I'm not a big fan of and don't normally use Maksutovs, Schmidt-Cass, Schmidt-Newt, or other corrector-plate + mirror arrangements. However, I'll readily admit that they are extremely popular because of their form factors and economical production. (Questar isn't run of the mill on that front.) I'd much rather use a well made straight refractor or Newtonian, depending on the object. The corrector-plate + mirror designs almost always feel like a compromise to me.

    Lee

  6. #26
    DJGainer's Avatar
    Join Date
    May 2006
    Shooter
    Medium Format
    Posts
    151
    Images
    25
    Quote Originally Posted by Q.G. View Post
    Yes, and no. Depth of field would be different for different colours of the spectrum...
    Yes, yes, yes; but not that much different to be outside the zone of focus. There are likely to be several inches in front of and behind your main subject that would be in focus at least, so colors on the subject itself would be in focus. No?

  7. #27

    Join Date
    Mar 2005
    Shooter
    Multi Format
    Posts
    3,427
    Will someone please put the OP out of his misery by telling him which of the lenses he asked about he should buy?

  8. #28
    DJGainer's Avatar
    Join Date
    May 2006
    Shooter
    Medium Format
    Posts
    151
    Images
    25
    Quote Originally Posted by Dan Fromm View Post
    Will someone please put the OP out of his misery by telling him which of the lenses he asked about he should buy?
    Fine.

    xtolsniffer, I used the RB system for 2 years with the C lenses. The colors produced by those lenses were beautiful. KL is supposedly the new and improved version of the lenses for the RB so I am sure you won't go wrong with either.

    From what you are saying, you need only to separate the foreground from the background, and it does not sound like you are doing macro, so all this APO talk is likely abstract as it pertains to you.

    Something that is far more important is the minimum focusing distance. Without extension tubes, you need at least 6' for the 250mm you mention and 11' for the 350mm. I'd opt for the 6' because I can imagine far more situations where I would want to get closer to the flowers than further away due to space constraints.

    So there you have it, 250mm non-APO; that's my advice.

    -Dave

  9. #29

    Join Date
    Mar 2008
    Location
    Yorkshire, UK
    Shooter
    Multi Format
    Posts
    331
    Thanks all, I have followed the discussion with great interest, all very useful!

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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