Why a 50mm objective ?

Discussion in 'Long Range Scopes and Other Optics' started by POP, Jan 12, 2007.

  1. POP

    POP Well-Known Member

    Messages:
    1,487
    Joined:
    Jul 25, 2001
    Where does a 50mm objective help out over a 40mm?

    Also does an Adjustable Objective make that big of a difference?
     
  2. Varmint Hunter

    Varmint Hunter Well-Known Member

    Messages:
    2,540
    Joined:
    Dec 26, 2001
    Three reasons:

    1. In dim light with the power selector turned up.

    Optimally, you would want about a 6mm exit pupil of light for maximum brightness to your eye in low light conditions. With a 50mm objective lens you could have the power turned up to about 8.5X and still achieve this goal. With a 40mm objective you would have to reduce the magnification to about 6.7X. Is it worth the extra weight, bulk & expense of the 50mm <> Not in my opinion.

    2. For a larger light column which makes for a less critical eye/scope alignment and a more rapid sight picture aquisition.

    It's hard to judge the value of this but I rarely (if ever)take snap shots so it has limited value to me.

    3. Large objective scopes look very impressive to some gun owners.

    Value of this attribute ***** Priceless /ubbthreads/images/graemlins/grin.gif
     
  3. CatShooter

    CatShooter Well-Known Member

    Messages:
    1,063
    Joined:
    May 8, 2001
    [ QUOTE ]
    Value of this attribute ***** Priceless /ubbthreads/images/graemlins/grin.gif

    [/ QUOTE ]

    HA! - I love it.

    99% of the time, that's the only reason to have one. The down side is that they have to be mounted higher, cheek position is compromised, and they are heavier and more awkward.

    .
     
  4. Chrismadrid

    Chrismadrid Well-Known Member

    Messages:
    315
    Joined:
    May 28, 2005
    A 50mm obj picks op more than 50%more light than a 40mm. It's brighter (noticeable in poor light)

    Adj Obj. It CAN make a BIG difference - it just depends what you want to do with the scope. It bocomes more important the CLOSER you intend to shoot and the Higher the magnification.
     
  5. Brown Dog

    Brown Dog Writers Guild

    Messages:
    635
    Joined:
    Sep 26, 2003
    POP,

    Well, I would have said there's far more to it than simply comparing exit pupil diameters.

    Comparing 40 to 50mm is only relevant if you are comparing scopes of the same quality.....one of 'China's Finest' scopes in 50mm will not be as good as a quality 40mm.

    (Once you are comparing scopes of similar quality) do some reading (web search) on 'twilight factor' and resolving power.

    .....and remember that the surface area of the front lens goes up by the square of the radius so (as with Chris's point) small increases in diameter give BIG increases in surface area....hence the often seen military compromise of 42mm. Talking of military, the Brit Army switched to 50mm scopes some time ago; I believe the USMC have done the same.

    All that said, it's only a real issue if you anticipate a requirement for decent magnification when shooting in poor light (in which I would include heavy mountain overcast...not just twilight). If weight's more important to you, you should save a few ounces with the narrower objective.

    ...as regards 'AO', revise the question to 'parallax adjustable' and I would say definitely get it; it makes your scope forgiving of inconsistent head position/ eye alignment. An actual 'Adjustable Objective' is a non-starter for field use (IMHO) because you will have to break position to reach forward to adjust it, side turret parallax adjustment is the only way to go.
     
  6. Varmint Hunter

    Varmint Hunter Well-Known Member

    Messages:
    2,540
    Joined:
    Dec 26, 2001
    [ QUOTE ]
    Well, I would have said there's far more to it than simply comparing exit pupil diameters.


    [/ QUOTE ]

    I've stated the benefits that I'm familiar with. Could you elaborate on the others. Always interested in learning something new.
     
  7. POP

    POP Well-Known Member

    Messages:
    1,487
    Joined:
    Jul 25, 2001
    thanx gents /ubbthreads/images/graemlins/grin.gif
     
  8. Brown Dog

    Brown Dog Writers Guild

    Messages:
    635
    Joined:
    Sep 26, 2003
    [ QUOTE ]
    Could you elaborate on the others.

    [/ QUOTE ] Thought I had?? /ubbthreads/images/graemlins/confused.gif

    [ QUOTE ]
    Comparing 40 to 50mm [ edit: ie by comparing exit pupil diameter ]is only relevant if you are comparing scopes of the same quality.....one of 'China's Finest' scopes in 50mm will not be as good as a quality 40mm.

    (Once you are comparing scopes of similar quality) do some reading (web search) on 'twilight factor' and resolving power.


    [/ QUOTE ]
    This is rather a good summary on twilight Factor (good summary on transmission too) /ubbthreads/images/graemlins/smile.gif : http://www.zeiss.com/de/bino/glossary_e....ReadForm&84
     
  9. tulku

    tulku Well-Known Member

    Messages:
    237
    Joined:
    Dec 9, 2005
    It's been a while since I have been in the Custom Optics ordering business , but here is something interesting to think about . If you want to build nearly equivalent "Quality" Optics , the cost factor does not go up Proportunately , it goes up as the second or third Power . To take a simple example , if I want to go from 30 mm to 60mm , the Cost goes up not twice , but somewhere from 4 to 8 Times ( range takes into account how many compromises are made ) . Therefore the Objective size seriously impacts the scope Price ( if you want to keep resolution , etc . about the same } . It's surprising how Sharp some of the old Scopes are , but it's sometimes like looking into a Black Hole unless you are in bright Sunlight. Since I'm always shooting in bright Sunlight , and since I'm not a fan of ultra-high Scope Mounts , I wonder when this trend toward bigger and bigger Scopes will stop ? /ubbthreads/images/graemlins/confused.gif