Scope 101 ?

[Slackdaddy]

I'll be honest, even though I have been shooting and hunting for 30+ years, I know little about the inner workings of a scope.
I basically have always bought $50 3-9s for my .22s and $100 Nikon/Bushnell banner 2-7x32s for my slug/muzzle loaders, and an occasional fixed 4x for my Rugers.

Main question:
Objective lens, why do some scopes have a front objective bell and objective lens larger than the tube.
And some scopes (such as 1.5-6 etc) have the objective lens the same size as the tube??

I had assumed the larger objective lens helps with low light ?? So should I avoid straight tube scopes for hunting ??

 

[KRC]

You are correct - light gathering. As magnification increases, more light is needed.

 

[Bountied]

 

[Slowhand]

Rifle Scopes: First Focal Plane vs. Second Focal Plane (Explained in Plain English) - Scopes Field

What’s the difference between the first focal plane and second focal plane in riflescopes? In this guide, I break them both down.

scopesfield.com

"What’s the difference between first focal plane vs second focal plane?

A first focal plane reticle enlarges and shrinks as you adjust the magnification while the second focal plane remains the same size."

More info at the link.

 

[Uncle Duke]

There's a lot of focus on brightness. But it helps to know what light your eyes can (and cannot) actually use.

The Truth About Riflescope Brightness (And How to Pick the Best Hunting Scope for Low Light)

Few things in hunting optics are more hyped and misunderstood than riflescope brightness. Every shooter wants a bright, bright view. And every scope maker promises one.

www.outdoorlife.com

 

[E.Shell]

...Objective lens, why do some scopes have a front objective bell and objective lens larger than the tube.
And some scopes (such as 1.5-6 etc) have the objective lens the same size as the tube??

I had assumed the larger objective lens helps with low light ?? So should I avoid straight tube scopes for hunting ??

As you assume and KRC states, yes, the size of the objective lens is related to light transmission. No scope 'gathers' light, they all transmit the available light through multiple lenses to your eye

If you divide the diameter of the objective lens by the magnification, you will get the size of the 'exit pupil', the diameter of the shaft of light that is presented to your eye. This is essentially why higher-magnification scopes have large objective lenses

Because the average human eye can use up to about a 7mm exit pupil, an exit pupil diameter of less than 7mm is perceived as being a little darker than ambient light.

Straight tube scopes of 1" diameter provide about a 20mm objective. If we divide the 20mm objective by the magnification, we see that anything over about 3x in a straight tube scope will reduce the exit pupil enough to be darker than ambient. a 6x scope with a straight 1" tube will provide an exit pupil of just over 3mm, about half the diameter we can use.

Under bright conditions, this slight darkening is not an issue, but early morning/late evening when levels are lower, this light limitation can make it harder to see unless we reduce the magnification and therefore increase the exit pupil diameter. Going from 6x down to 3x doubles the exit pupil and makes the image brighter.

You will notice that many scopes up to 5-6x can use the 20mm objective lens of a straight 1" tube, but when we get to about a 3-9x scope, objective lenses are increased in size, often to 30 to 40mm.

A 40mm scope at 9x provides an exit pupil diameter of 4.44mm, but as light levels drop off, we can reduce magnification to as low as 3x and the image appears substantially brighter because the exit pupil is now 13.3mm and larger than our eye can use effectively.

Once our exit pupil reaches 7mm, it is hard to see any increase in light as the exit pupil gets bigger, so a 40mm objective lens reaches maximum brightness around 5x.

Years ago, the "European scopes" had what seemed to be extra-large objectives and the reason for this was that so much of their hunting took place at lower light levels.

With the advent of higher magnification tactical/target scopes, objective lenses were forced to be larger to maintain a usable image. Some of these objective lenses are 50 or 60 mm, which can deliver satisfactory image brightness at their higher magnifications, and when light levels drop off, the magnification can be reduced to maintain sufficient light transmission.

Another thing many people wonder about is the 'adjustable objective' and the 'side focus', which are both actually 'parallax' adjustments.

These adjustments are designed to reduce the symptoms of the the reduced 'depth of field' found in higher magnification scopes. As magnification increases, the depth of field, and the related parallax-free zone is reduced and the location of the field (distance to target) becomes more critical.

Under about 10x, the depth of field is great enough to no have parallax or focus issues, and parallax has a reduced effect. For example, a 4x scope allows for a very long depth of field and from about 50 yards to 'infinity', parallax/focus is acceptable and the scope doesn't need an adjustable objective.

Over about 10x, the depth of field is short enough that unless the target is located in the center of the set parallax distance, there will be obvious parallax that can affect your impact point, as well as a distracting 'out of focus' condition. For this reason, we will need to vary the position of the parallax-free area to provide the correct distance to the target. This is why most scopes over about 10x provide an adjustable objective or a side-mounted parallax adjustment.

These adjustments are not truly 'focus' adjustments as many people and even scope makers call them, they are parallax adjustments to put your target on the same focal plane as your reticle. If your reticle is not crisply focused and parallax is set to be minimum, your target will not be focused either.

To set your scope up properly, you first need to set your ocular adjustment to provide a crisp image of the reticle without letting your eye work/strain correct any focus error. Once this is accomplished, when we set our parallax setting for minimum parallax, target focus is also at its best.

 

[Uncle Duke]

This guy's a bit of a live one at times, but he does a pretty good job of touching upon some riflescope highlights in a 10 minute video.

 

[Slackdaddy]

As you assume and KRC states, yes, the size of the objective lens is related to light transmission. No scope 'gathers' light, they all transmit the available light through multiple lenses to your eye

To set your scope up properly, you first need to set your ocular adjustment to provide a crisp image of the reticle without letting your eye work/strain correct any focus error. Once this is accomplished, when we set our parallax setting for minimum parallax, target focus is also at its best.

Thanks for the in depth explanation,, I helps greatly.

So a 1.5-6 x 20mm will have issues at low light while cranked to 6X

 

[Slackdaddy]

This guy's a bit of a live one at times, but he does a pretty good job of touching upon some riflescope highlights in a 10 minute video.

Thanks

 

[E.Shell]

Thanks for the in depth explanation,, I helps greatly.

So a 1.5-6 x 20mm will have issues at low light while cranked to 6X

Yes, if it's low enough. Reducing magnification is useful when light conditions make higher magnifications seem dark. Optimum light transmission in the example you provide will occur at around 2.5x.

 

[trickg]

Scopes are one of those things where I don't really think too hard about the mechanics of what's going on. I generally know that certain brands have better reputations than others, and that more money typically gets you improvements in things like:

Better glass quality/clarity
Better coatings that assist clarity and light
Better features such as side focus/parallax adjustment
Better reliability and durability
Better eye relief and bigger eye box

It's been a general observation that if all you want to spend on optics is $50-$100, you'll pretty much get what you pay for. If you bump your budget to the $200-$300 range, you can get a pretty respectable optic that will give you years of decent service, and let's be real - it's as good as some folks will ever need. Bump your budget to the $500-$800 range and you're hitting the bottom tier of upper end glass. Once your budget goes past $1000, at that point one has to decide what they prefer, and how much more they are willing to spend to eke out the next increments of quality and features.

I have an Arken EP5 on a precision rifle build I did. It's a pretty nice scope - adjustments are good and solid, the glass is clear and bright, and it holds up well when compared against scopes in that upper tier. With that said, I also understand that it's not at that upper level - it just isn't. What it is, is a great value for the money.

 

[E.Shell]

This guy's a bit of a live one at times, but he does a pretty good job of touching upon some riflescope highlights in a 10 minute video.

Decent video.

When he says "build quality" and "lens quality", he really means "coating quality", because lens coatings are the key to reducing reflection (lost light) and internal dispersion (stray light bouncing around inside the scope and causing a hazy/milky look.

 

[Uncle Duke]

Decent video.

When he says "build quality" and "lens quality", he really means "coating quality", because lens coatings are the key to reducing reflection (lost light) and internal dispersion (stray light bouncing around inside the scope and causing a hazy/milky look.

Yes.

An article that elaborates on Ed's point, and also not a small part of what you're paying for at different price points, for those interested.

https://www.shootingtimes.com/editorial/optics_st_lenscoatings_200805/100290

 

[Slackdaddy]

Yes, if it's low enough. Reducing magnification is useful when light conditions make higher magnifications seem dark. Optimum light transmission in the example you provide will occur at around 2.5x.

But after doing the math,, anything over 7mm exit pupil is not going to add benifit as far as light transfer ?

 

[E.Shell]

But after doing the math,, anything over 7mm exit pupil is not going to add benifit as far as light transfer ?

Correct, if YOUR eye is "average". If turning down the magnification continues to show increased light perception and you need it, keep turning it down...

 

[PaFrank]

good scope vs cheap scope example... I went bear hunting in Maine a few years ago.. brought 2 rifles. Both had 3x9x40 scopes.. One was a Leupold the other a Zeiss.
Performance was equal up until the last 8-10 minutes of usable light. With the Leupold i could only see shadows while the Zeiss was still bright.
My hunting partner confirmed this experience with his Zeiss vs I think it was Nikon.

the bottom line, in my opinion, is not brightness, or light gathering, but rather resolution. Resolution is determined by the quality of the glass and the coatings. i.e. coated, fully coated, multi-coated etc..
and I'm sure you all have seen this with spotting scopes.. The shooter with a brand new Chinese or branded (like Winchester, etc) 20-60 zoom spotter that is struggling to see 30 caliber holes at 100 yds, while the guy with a 60 year old Bausch & Lomb 20x can clearly see 22 holes at 100. Thats the best example of resolution I can think of that everyone should be able to relate to or even reproduce..

 

[Uncle Duke]

good scope vs cheap scope example... I went bear hunting in Maine a few years ago.. brought 2 rifles. Both had 3x9x40 scopes.. One was a Leupold the other a Zeiss.
Performance was equal up until the last 8-10 minutes of usable light. With the Leupold i could only see shadows while the Zeiss was still bright.
My hunting partner confirmed this experience with his Zeiss vs I think it was Nikon.

the bottom line, in my opinion, is not brightness, or light gathering, but rather resolution. Resolution is determined by the quality of the glass and the coatings. i.e. coated, fully coated, multi-coated etc..
and I'm sure you all have seen this with spotting scopes.. The shooter with a brand new Chinese or branded (like Winchester, etc) 20-60 zoom spotter that is struggling to see 30 caliber holes at 100 yds, while the guy with a 60 year old Bausch & Lomb 20x can clearly see 22 holes at 100. Thats the best example of resolution I can think of that everyone should be able to relate to or even reproduce..

To add, it's about more than brand name alone. Most manufacturers today make models that vary from low to high (or higher) end. In many instances, the differences will tend to range from significant to astounding.

 

[Slackdaddy]

good scope vs cheap scope example... I went bear hunting in Maine a few years ago.. brought 2 rifles. Both had 3x9x40 scopes.. One was a Leupold the other a Zeiss.
Performance was equal up until the last 8-10 minutes of usable light. With the Leupold i could only see shadows while the Zeiss was still bright.
My hunting partner confirmed this experience with his Zeiss vs I think it was Nikon.

the bottom line, in my opinion, is not brightness, or light gathering, but rather resolution. Resolution is determined by the quality of the glass and the coatings. i.e. coated, fully coated, multi-coated etc..
and I'm sure you all have seen this with spotting scopes.. The shooter with a brand new Chinese or branded (like Winchester, etc) 20-60 zoom spotter that is struggling to see 30 caliber holes at 100 yds, while the guy with a 60 year old Bausch & Lomb 20x can clearly see 22 holes at 100. Thats the best example of resolution I can think of that everyone should be able to relate to or even reproduce..

Well JEEEEZ and thanks a lot,,, I was about to really step up my game and buy a Leupold!

 

[Upperbay]

I would like to add that Leopold customer service is great. Was having issue with scope on muzzleloader several years ago. Point of aim was moving during repeated shots sometimes. Thought it was scope. Talking with service tech while going over gun. Came up with 2 possible issues. Scope going bad or issue with rings. Long story shortened. The scope was slightly touching firearm and when barrel became hot it was causing issue. They sent me a new slightly higher set of rings at no charge. Issue was resolved.

 

[Sticky]

Nothing wrong with a Leupold, I have several, many have served me well for decades. I also have other brands, I hunt with all of them and they all work well for my needs. Yes, you can spend enough money to see the difference in the very high end scopes, but... do you want to spent over $1k on a scope for a 22? Not me. Though I did just spend over $200 for one for a 22, it happens to be a Vortex and I am not disappointed at all.

I had a custom rifle built for my Montana elk hunt last fall and put a Leupold on it. I spent the summer shooting it out to 1000yds, working up loads for it and it did not disappoint when the guide asked me if I could take that bull at 720yds across the canyon. It placed the bullet perfectly. Don't discount them, they are solid and backed by excellent customer service.

My brother had one fail (loose reticle) years ago, sent it back and got a brand new one in return, no questions asked. Vortex also gives a lifetime warranty and are fairly reasonably priced.