Rifle Scopes Why the small objective lenses?

[Stevo3556]

Since I was old enough to buy scopes I have always tried to buy ones with large objective lenses for more light.

Now I am getting interested in 3 gun and noticed that most people have very nice high end scopes but opt for the 24mm objective lenses. Is this because the goal is a light weight rifle and the large lens is adds weight and is not needed for 3 gun which is mostly during the day?

If you shoot 3 gun, what are your priorities for your rifle scope? Weight, field of view, reticle, ???

Sorry for the 3 gun newbie question. Just different than all my years of rifle scope buying....

Thanks for your time,
Steve

 

[flyer]

Exit pupil is determined by objective diameter divided by magnification and after a certain point more exit pupil does not enhance brightness. If the magnification is low, it doesn't make sense to go larger on the objective and also they can keep the focal ratio higher which reduces chromatic aberration.

 

[Stevo3556]

Thanks Flyer. Had not thought about the exit pupil, had read about that in relation to magnification long ago. Most of my scopes are high magnification. Will have to read up on Focal Ratio again....

If you are a 3 gunner, what is your goal for your ideal rifle, weight, ect??

Thank you.

 

[strat81]

If you are new to 3gun, get a Burris RT6 and run it for a season or two. Midway has cosmetic blems for $270. Great scope for newbies and seasoned guys on a budget.

Get experience to learn what you value in a scope. You don't need a Razor 1-6 to win at the club level. With great 3gun shooters, the winners are those who can load their shotgun the fastest and are the most efficient in how they shoot the stage.

 

[jLorenzo]

As far as I can tell a tube is a tube, light will go through it. A larger one wont "gather more light" seems to be all about FOV and size/handiness, possibly weight.

 

[Stevo3556]

Thank you Strat81,

I used my work AR with a Eotech and magnifier. Found the very narrow field of view was a real issue and it is heavier than needed. Noticed that I was the only one with he Eotech.... was planning on getting a low powered scope like the RT6 when I ran across a deal. Bought a lighter used AR and it came with a Vortex Strike Eagle 1-6 scope. Plan to give it a try for a few matches. I am a big fan of Vortex scopes as I have them on my LR rifles.

Practicing reloading with the shotgun.

Thank you very much for the advise and sources! Gotta love a deal.

Steve

 

[Stevo3556]

Thank you jLorenzo,

Steve

 

[koshkin]

Getting true 1x on the low end and keeping the scope compact gets pretty tricky with large objectives, so most scopes used in 3 gun are configured they way they are because of the need for 1x.

Notice that they are all 1-4x or 1-6x or 1-8x, etc. 4x to 6x is usually enough for longer shots, but you typically use the 1x setting a lot more.

With low range variable scopes, my standard recommendations in ascending price order are as follows: Burris RT-6 1-6x24, Steiner P4Xi 1-4x24, Hawke Frontier 1-6x24, Burris XTR II 1-8x24.

ILya

 

[Stevo3556]

Thanks for the explanation Koshkin.

Other than the obvious power differences and pricing, is the main difference of these scopes clarity of the glass? Are the field of view, weight, turrets, ect pretty much the same?

Steve

 

[flyer]

Focal ratio is focal length divided by aperture and a ratio of about 15 or higher controls chromatic aberration well with an achromatic doublet onjective. Faster focal ratios require low dispersion glass or an apochromatic triplet objective.

 

[Stevo3556]

Thank you Flyer.

 

[loveha]

Focal ratio is focal length divided by aperture and a ratio of about 15 or higher controls chromatic aberration well with an achromatic doublet onjective. Faster focal ratios require low dispersion glass or an apochromatic triplet objective.

Is there something I can read so I can understand what the hell you just said...

 

[flyer]

Different wavelengths of light travel at different speeds through glass which is how a prism can separate white light in to a rainbow.

A simple lens will focus different wavelengths of light differently, so if you had a red, green and blue lightbulbs 100 yards away, you could focus on one and the other two would be blurry.

An acromatic doublet uses a pair of lenses either air spaced or cemented together. They are usually different types of glass and ground differently. Since you have two different types of glass you can simultaneously correct for two wavelengths and between those wavelengths, it's close enough as long as you have a very long telescope.

When you try to make a telescope shorter, you reduce the focal length of the objective lens but now the wavelengths between the two corrected spots is enough that you will see color fringing which looks like a violet glow around bright objects.

To get rid of that you can use ED glass which will help some or you can step up to an apochromatic triplet which has three pieces of glass and corrects at three wavelengths simultaneously and again the wavelengths between the corrected spots are close enough.

The thing you'll notice in all of this is that an Apochromatic design costs much more because the lens grinding has to be much more precise and each lens has to match with two others, not just one.

That's why a cheapo 100mm Chinese achromat telescope can cost $200 or less while a quality 100mm Achromat probably costs more than $2,000.

If the cheapo achromat has an objective focal length of 1,500mm (f ratio 15), it should have an image close to as good as the apochromatic.

On the other hand a 100mm apochromat might have a focal length of 600mm or even less so the scope can be much more compact.

 

[Bender]

I can drool on myself. I usually do when looking at nice scopes....

 

[koshkin]

Thanks for the explanation Koshkin.

Other than the obvious power differences and pricing, is the main difference of these scopes clarity of the glass? Are the field of view, weight, turrets, ect pretty much the same?

Steve

There are some differences across the board, not just optical. These are all different and unrelated designs.

With turrets, I prefer scopes of this type to to be in a set and forget mode, so as long as they stay zeroed, turrets do not matter much to me.

With FOV, both the width and the distortion matter, especially on 1x.

Also, reticle illumination makes a difference. You kinda need to define what you are trying to do.

ILya

 

[mdmp5]

I can drool on myself. I usually do when looking at nice scopes....

Or at the motivational pic thread