Small objective lens

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daisygordoninc
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Small objective lens

Post by daisygordoninc »

What is the purpose of a small objective lens ? Does a small objective lens mean the sight field is smaller ?
I have seen them mounted on some long range rifles, it is something I'm not very knowledgeable about.
What are the advantages or disadvantages. I'm sure articles have been posted on this topic.
Pisgah
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Re: Small objective lens

Post by Pisgah »

Let's look first at why some scopes have such large objective lenses. The threory is that they transmit more light to the shooter's eye. Well, yes and no. In a variable scope they do transmit more light -- but only at the highest power settings. Fact is, though, your eye cannot even use all the light that many small-objective scopes provide. Say you have a 2X20 scope mounted on your brush gun -- 2 power with an objective of 20mm. The exit pupil of that scope -- the size of the circle of light it projects out the back -- is 10mm. They very young human pupil can dilate up to maybe 7mm, and this rapidly diminishes with age. By adulthood, even the healthiest eye pupil can dilate only to about 5mm, and as we age that number continues to shrink. Thus, your eye can probably actually use only half the light your 2X20 scope transmits, let alone what a variable with a 56mm objective can transmit.

Does the smaller objective mean a smaller field of view? There are numerous other factors that determine field of view, but the short answer is -- no.

Why have a small objective diameter? Mainly because they allow the scope to be mounted low, allowing for a more secure and comfortable cheek-weld and faster acquisition of the target.
Pete44ru
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Re: Small objective lens

Post by Pete44ru »

.

+1

And, as a bonus, the usable field of view enlarges as the scope magnification goes down - why straight-tubed 2x or 3x scopes have been the knowledgable scoped hunter's first choice for close-cover shots since the 1940's.

It's also why today's red dot & reflex sights are just as popular. :mrgreen:

This is my 1914 Savage 1899H in .303 Savage with a Tasco Red dot optical sight (not a scope, as it has no magnification).

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Last edited by Pete44ru on Mon Feb 19, 2018 3:38 pm, edited 1 time in total.
daisygordoninc
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Re: Small objective lens

Post by daisygordoninc »

I think in the past I have wrongly thought the small objective lens had to do with
the field of view. Thanks for the information, I'm learning from so many of you.
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Sixgun
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Re: Small objective lens

Post by Sixgun »

Yep...learn something new everyday!

Pisgah just enlightened me on an issue I've been having. At one time and for many years...like 35 ...I used a high quality Bushnell spotting scope and I could see bullet holes in the paper out to 500 meters.....then about 5-7 years ago I noticed I could hardly see holes at 200 meters, unless it was big hole on white paper.....could not see them in the black. Thinking that my spotting scope was going bad I..........

....I spend 1,200 smackers on a Leupold spotting scope. Little to no difference.------6
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Old Savage
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Re: Small objective lens

Post by Old Savage »

Have to say I notice no difference but then almost always shooting in the bright sun.
In the High Desert of Southern Calif. ..."on the cutting edge of going back in time"...

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Nath
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Re: Small objective lens

Post by Nath »

Parallax, you get less parallax error with a small objective lens.

N.
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AJMD429
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Re: Small objective lens

Post by AJMD429 »

Sixgun-BGA-1 wrote: Mon Feb 19, 2018 12:55 pmPisgah just enlightened me on an issue I've been having. At one time and for many years...like 35 ...I used a high quality Bushnell spotting scope and I could see bullet holes in the paper out to 500 meters.....then about 5-7 years ago I noticed I could hardly see holes at 200 meters, unless it was big hole on white paper.....
....that's one more reason I like the bigger bore cartridges as I get older.....! :lol:
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Sixgun
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Re: Small objective lens

Post by Sixgun »

I hear ya Doc! But......I've also noticed that as we age, the small bores are more pleasant to shoot......after 40 years I rediscovered the ,22 rimfire and the 357...to hell with the 22 gr. of 2400 in he mighty 44.
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6pt-sika
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Re: Small objective lens

Post by 6pt-sika »

Sixgun wrote: Tue Feb 20, 2018 12:47 am I hear ya Doc! But......I've also noticed that as we age, the small bores are more pleasant to shoot......after 40 years I rediscovered the ,22 rimfire and the 357...to hell with the 22 gr. of 2400 in he mighty 44.
Without a doubt i enjoy punching paper more with a 222 REM HB bolt gun then about anything else . Might also be why I enjoy skeet more with a 20 or 28 gauge ! The little 6.5 Grendel is also getting a fair bit of use from me for hunting as well , but then a whitetail deer ain't that hard to kill either !
Parkers , Mannlicher Schoenauer’s , 6.5mm's and my family in the Philippines !
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