50mm vs 40mm Objective +/-

Discussion in 'Long Range Scopes and Other Optics' started by bookworm, Sep 26, 2009.

  1. bookworm

    bookworm Well-Known Member

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    Can someone outline for me the advantages/disadvantages when deciding between objective lens diameter?

    As far as I can tell the main advantage of 50mm is light transmission, with the main disadvantage being size/weight/cost.

    What other important considerations are there?
     
  2. royinidaho

    royinidaho Writers Guild

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    If given the choice between a 40 and a 50 I'd always go for the 50 for the reason you stated.

    The 50 compared to the 40/42/44 seems to not be much more bulky feeling.

    The jump to 56 mm appears to cross the bulky bump into stuff barrier....
     

  3. phorwath

    phorwath Well-Known Member

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    Agree. I would go with the 50mm too. You'll have a larger exit pupil of light which can make it a little easier for your eye to catch the field of view. 56mm just seems to bulky to me - my opinion. If weight is a primary concern, the larger objectives will also add a couple oz in weight.
     
  4. Nvhunter

    Nvhunter Well-Known Member

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    I went through this same process this last spring. What I found, for me, is that all this book theoretical data is enjoyable to read...but left me overthinking the process. Light transmission, clarity, parallax, bullet compensation, etc...

    The one overriding thing that made me decide upon my 40mm instead of a 50mm was Fit...Cheek weld and eye relief. Two things that are not often discussed when speaking of the technical merits of a scope.

    Now that I am getting into MOA adjustments, instead of windage holdover, My perfect scope would be a Swarovski, fine crosshair, 40mm. Recticle is in the first optical plane, means that rectile placement on the target does not change with different power settings. It is really good glass. Fine crosshairs do not mask as much of the target at longer distances.

    For a field report: I did side by side comparison between a Leupold VX-II 50mm and my VX-III 40mm after sunset. Astounding, my VX-III 40mm was more clear, brighter and showed better color than the 50mm....I did not have my light meter with me, but It seemed 30% better on all counts to me - and my friends.

    I think glass quality is paramount. No book I ever read said that a 40mm could out perform a 50mm.

    Get the best quality glass you can afford, and make sure of the fit.

    Perhaps a local shop would let you place a few 40s and 50s on your rifle and see what fits you best.
     
  5. phorwath

    phorwath Well-Known Member

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    No one said the quality of the glass wasn't important. Or that Swaro glass isn't better than Tasco. Once the price and glass quality of scope has been selected, a 50mm will have some benefits over a 40mm, without a huge increase in price.

    You're right, if a 50mm won't let you rest your cheek on your stock but a 40mm will, due to the lower mount on the receiver, a person ought to go with the 40mm. A 50mm will require the scope to be mounted a minimum 0.2" higher for the objective bell to clear the barrel. I've not had problems with 50mm objectives so far. Doesn't mean it isn't a valid consideration though.

    I agree the quality of the glass and the glass coatings is one of the most important decisions in a scope purchase. Right up there with the mechanical reliability of the scope and turrets, and hardiness of the scope to withstand recoil without busting a gut.

    But once the scope manufacturer and grade of scope has been selected, I'd recommend 50 over 40. The quality of the glass should be identical and the exit pupil will be 20% larger on the 50mm than on the 40mm. And 50mm are generally funtional for the average shooter with respect to planting the cheek on the stock. That's what I thought the question was (40 vs 50mm objectives - all other components being equal) and that's what my response addressed.

    There is no one-size-fits-all answer. It would be best to be able to compare the scopes on one's rifle, but that can get pretty expensive. Thus this Forum and a collection of opinions to help with the 'better' selection on the first purchase.
     
  6. Nvhunter

    Nvhunter Well-Known Member

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    I agree. All things being equal 50 will gather more light than 40. What I have found, is that I have to find the equipment not that is best, but that is best for me.

    I placed Near.mfg 20 MOA scope rail and alpha rings with a VX-III 40mm on my Sako 75 7MM STW. (shots like a dream - Knocking out bullseyes at 500 yds)...Anyway, my cheek weld is too high. I'll need a comb elevator. For my purpose a 50 would really be too high.

    There is a Bass Pro near here. These guys will let you bring in your rifle and try different scopes. I bet cabellas, gander mountain, etc are normally just as friendly..if you have one within driving distance.
     
  7. mo

    mo Well-Known Member

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    I agree that 50 mm gathers more light vs the 40mm. The question is does your eyes know the difference? Mine do not as long as both have quality glass. If your eyes can tell the difference then you need to buy the 50mm.
     
    Last edited: Sep 27, 2009
  8. bookworm

    bookworm Well-Known Member

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    Good points by all. I'm going to mount a 50 and 40 on my stock and see which one feels and fits best.

    Thanks everyone.