Clearing up some scope questions

by B.B. Pelletier

We had a LOT of questions about UTG Tactedge 4×40 scope and we got an important question about the Rex 10-40x scope that is directly related to the UTG questions, so today I thought I’d spend more time on my explanations.

Lack of AO
One person asked why I didn’t mention that the 4×40 scope lacked an AO feature, and someone else asked whether or not it has AO. I actually DID address this point when I mentioned that the parallax is fixed at 35 yards. That means it isn’t adjustable – no AO! I felt that was good enough, but the questions say otherwise. So, why didn’t I mention the lack of an AO specifically?

I didn’t mention the lack of an adjustable objective (for parallax correction) for the same reason that I don’t expect a Porsche Boxster sportscar to come with a class IV trailer hitch. It’s not appropriate. To use the adjustable objective, you must be able to see very small details, so you can tell when they come into sharp focus. Things as small as sugar ants. A 4x telescope can do that to about 5-7 yards. Beyond that, it’s a guess. AO on a 4x scope would not be be useful at any great distance, and that is what AO is most used for by airgunners – determining distance!

In the post, I went on to say that everything seen through this scope from 7 yards to infinity appears to be in sharp focus. There’s another clue that AO would not work. You need to be able to determine any change of focus through the scope, which is how AO works.

This situation doesn’t just pertain to this scope, but to ALL scopes of low power! As magnification increases, the distance at which the AO can be used for rangefinding increases proportionately. A 6-18x can determine range out to about 25 yards but not beyond. A 6-24x can go out to maybe 35 yards. An 8-32x can go out to 50 yards if the optics are bright enough to see anything, which is where a lot of scopes fail. They will magnify as much as advertised, but you will only be able to see small details when the bright sun is coming from behind your position. That’s where bright, clear optics pay off.

MCA just asked me to relate the 4×40 to the Bug Buster 4x scope. Okay, the Bug Buster, which has AO, will focus as close as 3 yards. That’s nine feet. Even though the magnification won’t allow you to rangefind out to great distances, the Bug Buster works in the region where 4x can actually be used to determine range. The parallax at three yards is many times greater than it is at 20 yards, so this feature is a good one. With the 4×40 UTG, you have no AO, so you have to guess the range and learn the trajectory of your pellet at very close ranges, which is exactly where pellets vary wildly with every yard they advance.

When I said AO is not appropriate for 4x scopes, I was referring to conventional AO that starts at 10 yards. With the Bug Buster, we have a special situation in which the AO minimum focus range has been brought close enough to give us a great feature that no other scope on the market has. At 25 yards, the Bug Buster isn’t useful for rangefinding, either, but it can focus close enough that we can take those impossibly close shots.

Also, the Bug Buster is a mini scope, while the 4×40 Tactedge is of normal length. That will make a difference when you mount the scope. Compacts are more difficult to position correctly for your eye – especially when a scope stop is involved.

Relating to the Rex 10-40×50 scope
Why is the big Rex scope with high magnification not good for field target? Simple – it doesn’t adjust down to 10 yards. Don’t get confused because I said the scope is clear and sharp at 10 yards at 10x – that’s not the same thing. If you crank the power higher, things will start becoming blurry, meaning that it really isn’t in exact focus – it just looks like it is at 10x. There isn’t enough adjustment in the parallax wheel to focus as close as 10 yards, so at higher power you will be stymied. You can still see your targets clearly and will be able to shoot at that distance – just not rangefind.

Joe in MD mentioned that people adjust their objective lenses to compensate for this, and he’s right. But I don’t want any of you doing that. I already answer enough comments about how to put this or that airgun back together – I certainly don’t want to start on scopes! Until Rex changes the AO on this scope so that it focuses down to 10 yards out of the box I cannot recommend this scope for field target. But for long-range shooting of any kind, this one is a dream!

I think rangefinding with a scope is overrated
Just because the UTG 4×40 scope doesn’t have AO is not a problem. I almost NEVER trust a scope to determine the range to a target. Because I’m out in all kinds of weather and the AO on scopes only works properly in a narrow temperature range, I find rangefinding to be overrated, cumbersome and a bother.

I once sat next to another field target shooter who missed two easy shots because he trusted his scope for the range. I could see that the target was less than 20 yards away, but his scope said 25 yards. That’s right at the spot where pellet trajectories play tricks – all shots closer than 20 yards. I even told him the target was about 18 yards in my estimation, but he wouldn’t hear it. He had a $475 Leupold scope with another $300 worth of modifications on it and, by golly, he was going to put his trust in the equipment! So, he missed two shots on a dead-easy one-inch kill zone.

There you have it. I hope I was clear enough this time, but you’ll tell me by your questions.

30 thoughts on “Clearing up some scope questions”

  1. Hi BB

    You said that parralax at 3 yrds is greater than at 20 yards. Does this mean that the farther you go out the less parralax you can experience?

    Thanks, Kyle

  2. Quick question, say someone has a large amount of skill and the scope (you posted yesterday) mounted on a Airforce Condor. Say the conditions are perfect, everything. What would be the max range of accuracy / power? I hear people hitting targets at 60 yards, but can this thing pass 120?


  3. BB I saw that you said the parallax was fixed at 35 yards but became confused when you said it was good at 10 yards. I didn’t understand. thanks for explaining

  4. B.B. wrote, “As magnification increases, the distance at which the AO can be used for rangefinding increases proportionately.”

    Wowzer! Thanks for sharing your opinions, about the useful range estimation maximums of variable power scopes. That’s a real eye opener!

    Now I truly understand trying to use my old Bushnell Sportview 4×32 AO scope, for range finding, is an exercise in frustration. It’s just a good short range hunting & plinking scope which has a close focus of ~7.5 meters (~8.2 yards).

    I had all the facts about variables like temperature, magnification, optical clarity & brightness, but I just never made the leap to understanding. Thanks for handing it all to me on a silver platter!

    “Ohwha tafoo liam!”


  5. Is an AO scope in lower magnification still useful for parallex correction at longer ranges, even though you can’t rely on its range estimation? That is, using the technique of viewing a point through the scope, moving your head side to side, seeing if the point moves, etc.? I realize this may take some experimenting with just where to set the distance on the scope, if focusing can’t be relied on.

  6. Yes! Remember that AO was NEVER intended to be a range-estimating tool. It was always only to correct parallax at a given range. Airgunners stumbled on the other use while shooting field target, which happens to coincide with the optimum distances at which rangefinding can be done.

    That’s one BIG reason why the magnification of airgun scopes is so great – to see small details farther and be able to see when they come into sharp focus.


  7. GadgetHead,

    You inspire me to write a blog about mistaken perceptions.

    Back in the 1960s when the musclecar dominated the automobile scene, cars had speedometers that went to 120 m.p.h. It didn’t matter that the cars they were in could only go 95, or that the tires they rode on were only rated to 90 – 120 m.p.h. was the magic number that had to be on every speedometer to sell cars.

    Guess what the magic airgun number is?

    In fact, how many airgun-related urban legends can you guys come up with?


  8. does the parallax free range change as the power goes up, or does it stay the same for all powers? also, how much would it be to have a pro adjust the scope down to closer ranges? would you lose any thing from doing it?

  9. B.B. wrote, “Guess what the magic airgun number is?”

    Well, one magic number is “671 fps,” but that’s not the one you’re looking for, I bet.

    Muscle Cars vs Magnum Airguns, huh? May be the number you mean is “1100 fps” muzzle velocity.

    But, you’re pretty tricky, and your regular readers know how you feel about *that* number, so… I don’t know.


  10. B.B.,
    I’ve read your comments on both Peep sights and Red/Green dots. I’m considering adding one or the other to a
    Benjamin 392 Limited Edition (3/8 dovetail) and was curious to know if you’ve done any testing to compare peep vs dot accuracy. Ideally on the same rifle.

  11. Jay,

    Peeps and dot sights are roughly comparable. What makes it so rough is that some dot sights are forgiving of head placement and they allow a lot of parallax. So head placement is critical.

    A good target peep will take care of parallax with a tiny peep hole, but if the hole is larger, as it is on a sporting Williams peep, you can have some parallax there, as well.

    Head placement turns out to be the critical factor. With good placement, dots and peeps are about the same.


  12. BB

    If it is permitable on your gun, is it better to get a scope with a larger objective lense (say 50 mm) compared to a smaller objective (32-40 mm), or is this just a money waster. And by “better” I mean a brighter, clearer image. I’ve been wavering between a leapers 3-9X40ao and a 3-9X50ao.

    Thanks Kyle.

  13. Kyle,

    I usually go for scope with the largest objective lenses that will fit on my rifle. They are brighter, and light transmission means everything when it comes to pinpoint accuracy.

    However, you will only need the extra brightness in 5 to perhaps 20 percent of the shots you make, depending on what sort of shooting you do. So the real answer is to decide whether a brighter scope is for you.


  14. Hi, I’m hoping you can take a minute to answer a dumb question for me. I’m in the process of buying a scope for a Gamo and a BAM airgun and I’m still confused by the the 11mm vs. 3/8″ scope mounts? Are they interchangeable, or do I need to make sure I buy the correct size?


  15. As I explained a few weeks ago, 11mm isn’t the rigid standard it’s purported to be. Mounts of that size actually may span 9.5 to 13.5 dovetails.

    Mount makers believe they are doing you a favor by saying their mounts also fit 3/8″, but most 3/8″ mounts are very cheap, where most 11mm airgun mounts are higher quality.

    If you are talking about a Leapers mount and it fits both, it can be used on an airgun with no problem.

    Since .22 rimfire rifle recoil so little, almost any metal clamp will work on them, which is why purpose-built 3/8″ mounts are usually so cheap.


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