40mm vs. 50mm

Discussion in 'Long Range Scopes and Other Optics' started by Nebraska, Aug 23, 2002.

  1. Nebraska

    Nebraska Member

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    I like the idea of having more light gathering ability in a scope but I see many of the long range folks recommending 40mm scopes instead of 50mm scopes. What is the benefit of having a scope capable of fitting in low rings as opposed to one requiring high rings. Please be as specific as you can.
     
  2. PrimeTime

    PrimeTime Well-Known Member

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    Hello-
    I'm no expert but here's my take on it.
    For off hand shooting, I prefer a scope that can be mounted fairly low as it suits the way I shoot. For bench rest shooting, a higher mounted scope works better for me.
    The 50mm probably does gather more light but only if you have a 30mm main tube. I've read several times that with a standard 1 inch tube, a 40mm will allow for maximum light gathering and that a 50mm does nothing but add weight. With a 30mm tube though, the 50mm bell does have added light gathering properties. That's what I've read anyways.
     

  3. Darryl Cassel

    Darryl Cassel Well-Known Member

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    Hello Nebraska

    With a 50MM objective lens scope and a tapored base of .020" to .030" you need high rings so the front bell of the scope does not touch the barrel of the rifle.

    With a 40MM and a tapored base, the rings don't have to be quite as high.

    For off hand shooting a low mounted scope is desirable. Of course an off hand carry rifle does not have or need, a tapored base.

    For longrange shooting from a bench or tripod, I like a 50 mm objective and a tapored base. The scope sits high but, I'm use to it.

    DC
     
  4. rickg

    rickg New Member

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    There is no such thing as "light gathering". There is only light transmission. The objective diameter is governed by the type and magnification of the scope. The goal is to supply the proper exit pupil diameter through out the power range. Just because a scope has a 50 doesn't mean it put more light on your eye, could be the opposite. The criteria I use are coatings and exit pupil.

    The same is true about a 30mm vs 1" tube. You can't ass-ume anything about the quaility of the scope because of the objective or tube size, might be sales gimmicks!

    [ 08-24-2002: Message edited by: rickg ]
     
  5. CatShooter

    CatShooter Well-Known Member

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    rickg... <BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>There is no such thing as "light gathering". There is only light transmission. The objective diameter is governed by the type and magnification of the scope. The goal is to supply the proper exit pupil diameter through out the power range. Just because a scope has a 50 doesn't mean it put more light on your eye, could be the opposite. The criteria I use are coatings and exit pupil.<HR></BLOCKQUOTE>

    Weeell... Not true.
    Ask anyone that uses high powered scopes. The larger objective gathers more light than the smaller one. Whether your eye can use the increased light depends on the magnification the scope is set to, and the time of day (ie, the size of the pupil), that you are using it.

    During the brightest part of a sunny day, the healthy pupil is about 1.5mm. This means that the most light the eye can accept is an exit pupil of 1.5mm... this means that the scopes power limit for full brightness is equal to objective diameter divided by the power, where the answer is equal or greater than 1.5.

    With a 56mm obj, the maximum power is ~36x, but with a 40mm obj, the maximum power is ~26x. With long range shooters, or benchrest shooters, it is not unusual to use powers larger than 26x, and so even under the best conditions (for the eye), the larger objective "gathers" more light. If both were used at 26x, they would appear equally as bright, but if they were both used at 36x, the 40mm scope would appear substantially darker.

    But... on overcast days, the pupil gets larger... typically around 4mm.
    On a day like this, even at 26x, the 56mm scope would look much brighter, until the power was reduced to below 10x, at which point they would both look qually as bright... any magnification above 10x (which is not a lot), the 56mm would always look brighter.

    The purpose of lens coatings is NOT to make the image brighter, but the make the shadows and dark areas appear darker.

    I piece of cellophane only transmits 91% of the light... but it doesn't look dark when you look through it.

    But if a scope has internal reflections from the lenses, (or reflections from internal parts), those bits of stray light cause a haze over the dark areas... and if you are looking for targets that are dark, hiding in the dark shadows, then the haze will mask them.

    CatShooter.

    [ 08-24-2002: Message edited by: CatShooter ]
     
  6. rickg

    rickg New Member

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    If you or your scope can "gather light" you just solved the mystery of warp speed travel Scotty. The original post had to do with light gathering with 40mm or 50mm objective. What I said was valid, you can't gather light and just because you have a 50mm or a 30mm tube doesn't mean it's brighter. And coating due increase light transmission, send your piece of cellophane in and get it coated.

    Quality of the "glass" and coating are the most important thing. You can stack them up in any size, order or distance "see scope length" to achieve whatever pupil size you want.

    [ 08-24-2002: Message edited by: rickg ]

    [ 08-24-2002: Message edited by: rickg ]

    [ 08-24-2002: Message edited by: rickg ]
     
  7. Varmint Hunter

    Varmint Hunter Well-Known Member

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    All else being EQUAL, a larger objective lens will provide a larger exit pupil (more light). A larger exit pupil COULD provide for a brighter image depending on magnification and pupil dilation of the shooter's eye. An additional benefit would be the larger light column visible at the ocular lens, this would allow for easier (quicker) acquisition of the target within the scope.
    Comparing large inexpensive scopes to smaller expensive scopes would be a futile endevour with many ill-conceived conclusions.
    For the vast majority of hunting in daylight, with variable power scopes, the 40mm will do everything that needs to be done. Better to buy quality optics than LARGE optics IMO.
     
  8. daveosok

    daveosok Guest

    Let us not forget field of view at extreme ranges, which a smaller obj will have a smaller FOV. When shooting extreme long range I would expect to see as large of an Obj lens as you could get proportional to the rifle of course.
     
  9. Blaine Fields

    Blaine Fields Well-Known Member

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    rickg:

    The Cat Killer is right in his post, your quibble with the term "light gathering" notwithstanding. There is nothing scientific about the term "light gathering"; everyone understands that the larger the objective, the more light is available to illuminate the object of interest. This concept isn't debatable and is not particularly interesting.

    Nor is it debatable what was posted about "exit pupil." "Exit pupil" is simply a ratio, the mathematical result of dividing the objective diameter by the power - so as the power is increased, the exit pupil is proportionately reduced. Your comment that "You can stack them [i.e., the various lenses] up in any size, order or distance "see scope length" to achieve whatever pupil size you want" is simply wrong if you mean to imply that "exit pupil" is a function of anything other than objective size and power.

    While it is true that good glass and coatings enhance the total amount of light that is transmitted, the size of the objective also effects the amount of light that can enter the scope. In any scope for serious work, one always wants to minimize the light loss; but one may not always want or need the largest objective possible - it very much depends upon the application.

    Read Catshooter's post again. It contains a lot of good information.
     
  10. CatShooter

    CatShooter Well-Known Member

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    Thank you, Blaine...

    You are a scholar and a gentleman... well, a scholar anyway [​IMG] [​IMG]

    CatShooter.
     
  11. Blaine Fields

    Blaine Fields Well-Known Member

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    Nebraska,

    I'm not sure that anyone actually answered your question.

    One consideration in evaluating the size of the objective is how you will shooting your rifle. As you have indicated, if you decide on a large objective, you will of necessity have to use higher rings. If your shooting consists of shooting off a bench, this should present little difficulty. But if you intend to shoot prone, you may find that high rings will not allow a proper cheek weld. I know that for me, my comb-eye distance is subtantially reduced in prone requiring me to elevate the comb of the rifle to obtain a proper eye/scope relationship. So, from the bench high rings may work fine for me; but when I try prone, I have to raise my head to the point that sometimes I will not have any head contact with the rifle at all. Not good. Therefore, I have found that in order for me to shoot prone, it is necessary that I use short rings - and that means that a 50mm objective is out of the question.

    To accommodate my particular needs, I have settled on a USO scope with a 44mm objective. The glass is of good quality, coatings are first rate and enough light is admitted to shot well after sunset. Therefore, the 44mm objective is both practical and adequate for my use.

    You may have other demands that require a larger objective. If so, your scope will necessarily be a little higher. Make sure that this added elevation is compatible with the positions in which you intend to use your rifle.
     
  12. Nebraska

    Nebraska Member

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    Thanks for the info. The gun will be used mainly for hunting deer sized game. In my area we can legally hunt from a 1/2 hour before sunrise to a 1/2 hour after sunset. I'll be using the gun standing, kneeling, sitting, and prone.
     
  13. texas

    texas Well-Known Member

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    Read all the comments on this topic now I curious about the larger objectives like the USO 80mm. Is that considered overkill or what?

    Is bigger really the best way to for wide open spaces or competition shooting? The 80mm seems kinda weird but there must be a place for this type of scope right?
    Where is it?
     
  14. rickg

    rickg New Member

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    Kudo's Varmit Hunter.

    Texas- "IMO" The Bigger The Better with the good stuff.