Thanks for all that. All of it was what I already believed and thought I understood, so it's good to have some confirmation.

quote:

The knob usually on the left of the riflescope is a side focus knob though many people call it a parallax adjustment. Even some optics company call it a parallax adjustment knob because they gave up trying to educate the masses. I'm not giving up.

Thank you very much, for the post that quote is pulled from. All that makes so much sense, and really puts that aspect of the discussion to rest. One question though: when you say "low magnification", do you mean beneath a certain power in general, or low in the magnification range of the scope? You said 8x, in your example, but that'd be near the top of a 3-9 scope's range.

I mean absolute magnification, not in relation to the zoom range.

Consider the riflescope I was talking about earlier. How much DOF do you think it has at 80X at 200 yards.

If I am understanding all this correctly, your scope, on 80x at 200 yards, would have a very small depth of field, and very small "eye box". The reason I inquired about the power, relative to the range, was: it seems, to me, that if we're at 8x in a 3-9 scope, we may be still "low", when compared to overall magnifications available in rifle scopes, but we're high enough in that particular scope, that we're eliminating one of the the two contributing factors: the (potentially) parallax-error-inducing large eye box. Or am I wrong in my understanding?

This message has been edited. Last edited by: KSGM,

quote:

Originally posted by KSGM:
the parallax-error-inducing large eye box.

I would not say that a large eye box “induces” parallax error.

My point was that a large eye box means we can be farther off from the center line of the scope and still see a full image through it, and if we’re off center when looking through the scope, that’s when the parallax setting may become important. If we’re shooting for precision results at relatively close distances, for example trying to achieve 1/2 MOA groups at 100 yards, then it’s important that either the parallax is set properly or that we’re in proper position behind the scope.

If we’re shooting from a stable prone or bench position, the eye box size isn’t going to make things worse because then it’s easy enough to do the move your eye test to ensure that the reticle position doesn’t move as well. Plus, we will probably be in a good centered position behind the scope. If anything, a large eye box makes the test easier because we can move our eye farther without losing the image entirely.

In addition, because a large eye box makes it possible to see through the scope if we’re off center, it makes it easier to pick up the image and the reticle rather than seeing no image at all and trying to figure out what we’re doing wrong with our shooting position. When I’m trying to get on target in the prone position while my muscles are screaming at me and I’m on the clock, eye box (vision cone) size makes a difference to me, and that’s why I prefer it to be larger than smaller.

To emphasize, for most of the history of optical sights, the parallax was not adjustable except for certain models that were intended for target work at close distances. And even then, as with my ancient Redfield 20× model 3200, we adjusted for focus; no one told us about parallax.

That doesn’t mean parallax setting is not important in some exacting situations. As I mentioned above, I even went to the trouble of developing my own dial setting aid because I like to be precise whenever possible, and I sometimes do use that scope and its cousins for precise shots at close distances—sometimes at 50 yards. But is it something that must be obsessed over in all situations? I don’t believe so.

quote:

Originally posted by KSGM:
If I am understanding all this correctly, your scope, on 80x at 200 yards, would have a very small depth of field, and very small "eye box". The reason I inquired about the power, relative to the range, was: it seems, to me, that if we're at 8x in a 3-9 scope, we may be still "low", when compared to overall magnifications available in rifle scopes, but we're high enough in that particular scope, that we're eliminating one of the the two contributing factors: the (potentially) parallax-error-inducing large eye box. Or am I wrong in my understanding?

My 8-80X56 has an exit pupil of 56/80= 0.7mm at 80X. Your 3-9X36 scope has an exit pupil of 4.5mm at 8X. See where I'm going with that?

This is why I am so insistent that people give the complete name of the scope when they mention one. You always want to state the diameter of the objective lens, because that's how you know immediately what kind of "eye box" you are dealing with.

The size of the exit pupil is calculated by dividng the diameter of the objective lens by the magnification. But please be aware that really only applies to the mid to high magnification settings in a variable. It can also apply to the low magnifications, but not always as there are technical reasons why that formula does not work for a specific riflescope at its low magnification, not that it really matters because it will be large anyway.

So, in order to get a clear view of the objective at 80X, you have to be positioned perfectly behind the scope, and that eliminates whatever parallax may be present due to incorrect focus. It is much more likely that you may experience parallax when looking through your 3-9X at 8X and not being positioned properly behind it.

Fritz shared this in another thread; it's relevant to the parallax discussion.

Excerpts from an email conversation between me and a Leupold representative:

On parallax adjustment (side focus)...
"Factory Parallax setting is 150 on scopes that do not have that adjustment. If they are using it for longer range and or may experience “thermals” etc between the optic and the target it might be a consideration."

On objective lens size (I inquired as to whether there was any impact on image brightness or FOV)...
"The larger objective will increase eyebox and exit pupil. “Exit pupil” is objective lens diameter (in MM) divided by magnification power. So a 4-12x40mm would have an exit pupil of 3.3mm where a 4-12x50 would be 4.16mm. the human eye generally only dilates to 4.5ish mm in the dark (When we are young) As we age the less our pupil is able to dilate). The caveat is that neither of those make for a "Brighter" image. Light Transmission is just one component of Light Management."

His comments seem in-line with our discussion, for the most part. I know a larger objective is considered an advantage by many, when it comes to brightness; apparently it's not.

Interesting comments by the Leupold rep.
A quick Internet search located several links that state the maximum eye pupil diameter can reach 8 millimeters in some people when fully dilated, which is actually larger than what I remember from long ago when I learned the max was 7mm. Perhaps he was referring to daylight conditions, but I also had a Leupold rep tell me that revealing the thread pitch of a sunshade to fit a particular scope would be a violation of the ITAR; I am therefore sometimes skeptical of what such people tell me.

I’m also not sure what to make about the statement that a larger objective lens does not result in a brighter image. I suppose that might depend upon how we define bright, but more light in can result in more light out. That’s why our pupils dilate and camera lens diaphragms open up to let more light reach the retina or film/sensor.

That said, can is the operative word, and there’s much more involved in a riflescope’s brightness than how much light goes through the objective lens. All that “much more,” such as the type of glass, lens coating, number of lenses, etc., probably has more effect than just the objective lens diameter.

I was watching a review of high quality scopes by the Dark Lord of Optics and he said that his Tangent Theta 5-25×56mm scope (which was his favorite) was “darker” than others that were nominally similar. He went on to say, though, that it had superior color “control” and resolved “micro contrasts” better. Although he didn’t attempt to explain why that was, I suspect that it has something to do with how the manufacturer does something with the system that provides a better image, such as adding lens(es), but which also reduces light transmission.

I must believe, though, that scope manufacturers frequently design higher power sights with larger objective lenses for some reason other than to satisfy the demands of ignorant customers.

Thanks again for something more to consider.

quote:

I am therefore sometimes skeptical of what such people tell me.

Same here.

quote:

design higher power sights with larger objective lenses for some reason

I suppose it is to enable a more comfortable exit pupil diameter; if they didn't put a bigger objective on there, it'd be that much harder to stay in the "eye box". In a hunting context, even in something like 3-9, it'd be a perk to have a generous exit pupil, if your circumstances often require quick mounting and firing of the rifle, perhaps in a less-than-ideal position.

quote:

Originally posted by KSGM:
Excerpts from an email conversation between me and a Leupold representative:

On parallax adjustment (side focus)...
"Factory Parallax setting is 150 on scopes that do not have that adjustment. If they are using it for longer range and or may experience “thermals” etc between the optic and the target it might be a consideration."

On objective lens size (I inquired as to whether there was any impact on image brightness or FOV)...
"The larger objective will increase eyebox and exit pupil. “Exit pupil” is objective lens diameter (in MM) divided by magnification power. So a 4-12x40mm would have an exit pupil of 3.3mm where a 4-12x50 would be 4.16mm. the human eye generally only dilates to 4.5ish mm in the dark (When we are young) As we age the less our pupil is able to dilate). The caveat is that neither of those make for a "Brighter" image. Light Transmission is just one component of Light Management."

His comments seem in-line with our discussion, for the most part. I know a larger objective is considered an advantage by many, when it comes to brightness; apparently it's not.

I think you understand the concepts, but you're not grokking them. (There, I just showed my age; grok was a term when I was in college, 50 years ago. Look it up; it will be a strange adventure.)

You understand the relationship between objective lens diameter and exit pupil diameter, but you're not extending that into light. A bigger exit pupil brings in more resolution of the target, and more light. A bigger exit pupil is brighter that a smaller exit pupil because the amount of light coming in is greater. If you take a 3-9X36 and use it at 9X, your exit pupil is 4mm in diameter. If you take an 8-80X56 and set it at 9X, your exit pupil is 6.2mm in diameter, brighter because of more light. Now the light might be wasted because of the size of the eye's pupil, but it's still there. Now extend this and go for something like a 6.5-20X44 and compare it the same 8-80X56 and place them both at 20X. The first one will have a 2.2mm exit pupil, the second one will have a 4mm exit pupil. Again, more light = brighter.

Now lets' talk about the other aspect of light management in a riflescope; transmission. The transmission of light will not change the diameter of the exit pupil, but what it will do is affect the intensity of the light within that exit pupil. In the olden days before lens coatings, the way to have any kind of use out of high magnification optics was to have BIG objective lenses. This would produce a larger exit pupil, but the intensity of the light would be diminished and since different wavelengths get absorbed differently, the IQ would show a washed-out picture. When coatings are applied the amount of light reflected at glass/air boundaries is a small fraction of what happens without coatings. Multiple coatings are used to address the various wavelengths and preserve color fidelity.

And the guy from Leupold is incorrect. The number is closer to 7 or 8mm for young, healthy people.

I will leave you with a thought. Make sure you stay well hydrated when you shoot a match with optics. A month ago, I didn't stay hydrated and during a match, my vision bbecame blurry. Yesterday, I was drinking a liter of water before each match and my vision was fine. (I did have to take frequent bio-breaks.)

quote:

Originally posted by NikonUser:
[QUOTE]Originally posted by KSGM:


I will leave you with a thought. Make sure you stay well hydrated when you shoot a match with optics. A month ago, I didn't stay hydrated and during a match, my vision bbecame blurry. Yesterday, I was drinking a liter of water before each match and my vision was fine. (I did have to take frequent bio-breaks.)

I am old enough to get the term Grok, and have read that book several times, as well as most of what was written by the author,


and I also always appreciate these type discussions,

I'm a lowly Service Rifle\High Power shooter that is coming back into the sport after an abssence and am struggling (but improving) with the scope on the rifles,

(WOA, , as a sidebar, sells a damn fine SR\HP scope)

the part I quoted is one of the most important bits I have read here,

and bears repeating,


please continue

So, inside one brand, with glass and coatings being of equal quality, is the exit pupil diameter on a given magnification a good way to compare the brightness potential?

quote:

Originally posted by KSGM:
So, inside one brand ...?

Others may know more than I do, but some manufacturers have different “lines” within the same brand, and therefore I wouldn’t use brand alone as a basis of comparison. Some years ago a retired senior NCO from the Combat Applications(?) Group (aka “Delta”) told me that one model/series of a highly-regarded scope brand was “crap,” and yet others were good. I’ve seen references here to how some models of certain brands are made in different countries, and, presumably, use different glass and are manufactured to different standards.

In looking at different scopes within a same line I would expect more valid comparisons. But also keep in mind that even then that may not be completely true. In the Nightforce ATACR line, for example, scopes have magnification ranges of 1:4, 1:5, and 1:8. I don’t know anything about the internal construction of those scopes, but it wouldn’t surprise me if the 1:8 scope had more lenses than the 1:4 scopes, and more lenses reduce the amount of transmitted light even if everything else is exactly the same (and that is probably unlikely as well). And because the amount of light that makes it through the scope also affects brightness, exit pupil size might not be the only determining factor.

If we are really concerned about a scope’s image brightness and quality, the advice that member fritz has offered here more than once is ultimately the best: Compare them yourself. And if that’s not possible, seek out the best reviews you can find. I have referenced the “Dark Lord of Optics,” and I believe he really knows what he’s talking about.
On the other hand, whenever I read something on a gun forum by a random poster that a scope is, “Really bright and clear,” I take that with a huge pinch of salt. How many scopes does he own? Has he compared them (literally) side by side as the DLO does, and under exactly the same conditions? Is his experience limited to a mid-priced Leupold and a $79.95 purchase from Amazon? Has he used them under challenging lighting/viewing conditions and target distances? Etc., etc., etc.?

I did mean in the same "line"; I should have had the wherewithal to be more specific.

quote:

1:8 scope had more lenses than the 1:4 scopes, and more lenses reduce the amount of transmitted light even if everything else is exactly the same

I agree; it seems you're bound to lose some light, even with nice glass and coatings.

A 1:8 or 1:10 riflescope definitely has more lenses than a smaller zoom ratio riflescope or a fixed power model. Also, a wide-angle model also has more lenses than a normal view riflescope.

However, the idea that more lenses reduce the amount of light transmission is simply false when discussing quality products. Let me introduce the concept of coating as it applies to lenses. An uncoated piece of glass will reflect about 4.5% of the incoming light at the air/glass boundary. So, just going through one lens, you lose 4.5% of light coming in, and 4.5% of the remaining 95.5% on the other side. Put in a few lenses and you quickly lose a lot of light. A lens coating is a VERY thin film of material applied to the lens to reduce (virtually eliminate) this reflection of light. However, a coat only works for a specific range of wavelength (color), so multiple coats are required to virtually eliminate the reflection of all wavelengths (colors) and thus present a proper image with color fidelity. The current state of the art in lens coating is so good that the loss in in small fractions of a percent. You cannot look through a properly assembled riflescope with excellent coated glass and discern whether there's more glass or less glass. The overall transmission rates even for the most complex riflescopes is north of 95% and crowding 98 and 99%. For top and even middle tier riflescopes and other optics, light transmission with lots of lenses is simply a non-issue and you should not even take it into account.