I just read this in a book written by a long range shooting instructor who was discussing the magnification used for different disciplines:
“[T]he [magnification] tradeoff is less elevation adjustment. … More magnification usually limits your total travel.”

I will add this here for further clarification:
“Most field shooters stick to scopes that hover around 25× or less. Many are shooting them below 18×, enjoying the increased elevation adjustment.” [Emphasis added.]

At first I wondered if he was referring to the amount of the reticle that can be seen for hold-offs with a first focal plane sight, but when I reread it, he is obviously claiming that magnification affects how much elevation can be dialed to engage long distance targets.

My question therefore is: Is that true? Does higher magnification reduce the mechanical amount that the elevation of a scopesight can be adjusted? If I have 50 MOA at 10 power, might that be reduced to 40 MOA at 15×? It’s not a claim I’ve ever seen before and it doesn’t appear in any factory scope specifications I’ve read, so I’ve been trying to figure out why that might be true, but have had no luck thus far.

I am faaaaaaaaar from an expert on this, but I'll play. I've never noticed any decrease in adjustment based on my mag.

Was he perhaps talking about construction? E.g. if you make a scope that is 4-32 it will have mechanically lest available adjustment than a 4-16 scope all things being equal? Just throwing a dart at this, I have no idea if that's how it works or not.

Good question that I didn’t think of. I believe, however, he’s talking about losing adjustment range with the same scope when it’s set at a higher power. A further quotation:

“Most field shooters stick to scopes that hover around 25× or less. Many are shooting them below 18×, enjoying the increased elevation adjustment.” [Emphasis added.]

Some FFP scopes have enough magnification adjustment that you can lose part of the bottom of your reticle for holding over if you zoom in above a certain magnification.

For example, the Vortex PST Gen2 3-15 FFP when adjusted to 15x shows the entirety of the reticle.

The 5-25x version of that same optic will zoom in sufficiently that you lose the bottom part of the reticle.


This is only relevant if you are holding over though, not if you are dialing.

His statement seems strange and I don't think he is correct, but I could be wrong.

Total travel of elevation has more to do with the turret mechanism and the scope body diameter than magnification, as far as I know. In fact I don't think total magnification has anything to do with it, beyond it being more difficult to make good optics with a wider elevation range. Just because of optical challenges.

The travel is dedicated to the tube, line of sight, and glass inside the tube. Typically, FFP scopes have less travel than SFP when comparing the same tube, objective, etc (example is Vortx PST 5-25x50, the FFP has 20 MRAD which is approximately 68 MOA, while the SFP has a stated 75 MOA).

If you choose the same main tube, as your range reduces (same multiple magnification such as 3-15, 4-20 and 5-25), you require a smaller objective, and can still get a greater MOA adjustment. This was part of the reason Weaver 10x were so popular during Vietnam - they had a lot of adjustment.

To get back to it, with the same main tube, and same objective, the greater the magnification range, the smaller your adjustment will be. This is why objectives increase with magnification, and high magnification glass has started to use 34MM tubes as opposed to 30mm.

The Vortex Razor G2 4.5-27 x 56 has an amazing 96 MOA vertical, where as the same tube and a 50MM objective can only produce 75MOA.

Additionally the Razor G1 (5-25x50) has 125 MOA with a 35MM main tube, yet the 5-25x50 PST has a 30MM main tube and only has 75MOA.

To answer the question, I think he is wrong. Within the scope, you don't loose ability to adjust at higher magnification. IT is possible to limit sight view with FFP, but not actual vertical adjustments. Body to body (same tube, objective) with more magnification you will lose adjustment if you were to compare a 4-16x50 with a 30mm main tube to a 6-24x50. If that were the case, you would need to have a moving piece of the optic at the adjustment point that would physically increase the tube to be adjusted, limiting the amount of space.

quote:

Originally posted by 280nosler:
To answer the question, I think he is wrong.

As I say, I couldn’t think of a way that it would be right, but I am curious about what others think. Thanks.

I have no expertise in this. But one would think if it actually made a substantial issue then the mfg of scopes would say things like 30MRAD elevation at 15x or some such qualifier. And they don't.

There is a trade-off between magnification and adjustment range, but it is not anything to do with the magnification changes due to the zoom mechanism as is stated in the quotes in the OP.

While I totally understand that a riflescope is an afocal device, it helps my feeble mind to think of the riflescope had dealing with the image in 3 distinct areas: the objective bell to the start of the erector tube; the erector tube and its zoom lenses; the eyepiece.

The objective bell presents an image to the erector tube. The erector tube looks at a section of that image, flips it upside down and zooms in on what it sees, it also adds in the reticle, before the zoom lenses (FFP) or after the zoom lenses (SFP). The eyepiece looks at the image that the erector tube produces.

After working with March designing the reticles for their upcoming scope, I gathered some further understanding on field of view, adjustment range and their relationship to the actual riflescope.

Designing a reticle is one thing, bringing it to production is something else. Each reticle design costs money and it's not something that you do at the drop of a hat. For one thing, you try to maximize the effort by making the reticle fit a number of riflescopes. I can talk about that a lot more at another time, but for our purposes here, the main driving feature of the reusability of a reticle is the design of the objective bell.

As we all know, the magnification of an optics is the measure in focal length; that is the length of the lens to the focus point. The longer the length, the greater the magnification. In photography parlance, for a 35mm sensor (remember the film in yellow cylinders?) a focal length of 50mm was considered "normal" in other words, no magnification. Then you have telephotos and they are all expressed in focal length: 100mm, 135mm (very popular in the day), 200mm, 300mm, and so on. As the mm went up, the lens was growing in length at the exact same rate. A 500mm lens is close to 2 feet long and can barely be hand held. A 1000mm lens comes with its own tripod mount built in. But a 1000mm lens, at over three feet long, is only a 20X magnification for a 35mm sensor.

So, how do we stuff a 40X or 80X magnification capability in a riflescope that's less than 2 feet long?

We cheat. We start with an image which is produced by the objective bell with some low magnification and then we zoom in on that image with the erector tube. The eyepiece zooms into that image further.

The objective bell is really the only place where we actually take the image coming into the riflescope and enlarge it completely. The remainder of the scope is just concerned with an ever smaller section of that complete image.

For an FFP reticle to relate to that first image, it has to be designed with the focal length of that objective bell in mind. The design and size of the reticle are intimately related to that first focal length. Once that image is formed at that focal point, the rest of the riflescope can do whatever it wants to it, it will not change the relationship between reticle and image.

The objective bell will produce an image that is at a specific X magnification and will be 26mm in diameter inside a 30mm scope. That's the sensor size, 26mm in diameter. Now comes the adjustment part. The erector tube located inside the main tube is looking only at a smaller part of that 26mm image. I do not have the specifics on this but my guess is that it's probably about 18mm in internal diameter, maybe less. So you now have a tube that 18mm in diameter looking over an image that's 26mm in diameter. As you move the tube up and down and side to side, that movement is the adjustment range of the erector tube inside the main tube. If the image it is looking at is normal size (1X) its movement covers quite a bit of apparent range. But if the image it is looking at is (2x), the exact same movement now only covers 1/2 of the apparent range. If the image is 3X, then the movement of the erector tube is 1/3 the range and so on.

As you can see, the dimensions of the FFP reticle have to be matched to the focal length of the objective bell.

There are three ways to gain adjustment range on a riflescope: larger main tube, smaller erector tube and shorter focal length at the objective lens.

Larger main tube: This makes the scope bigger and heavier.

Smaller erector tube: This makes the many internal lenses even smaller and that is bad from a view of amount of light and resolution.

Shorter focal length: With the same objective size needed to provide enough light for high magnification use, this bends the light more and will create chromatic aberration that must be addressed with ED and Super-ED lenses. So more costly or crappier IQ.

I hope I've explained this well enough. I left out the eyepiece part which is extremely critical and presents opportunities. I'll be adding this to my stickied thread at some point.

All right: As I understand everyone’s comments, no one (yet) agrees with the man I quoted that a scope’s magnification changes its available adjustment range.

And thanks to you in particular, NikonUser, for all that. The guy who made the comment about adjustment range and magnification also states that the erectors in 30mm and 34mm maintubes are the same and that sunlight can degrade lens coatings (some? cheap ones?). I don’t (currently) know if either or both are correct, but although the author seems very knowledgeable in some ways with his references to Abbe numbers for lens design and other issues, I am obviously skeptical about some of what he tells his readers.

it's entirely possible that the erector tubes for 1inch, 30mm, 34/35mm and perhaps even 40mm, are all the same size.

It's easy to figure out by looking at the specifications and seeing what the adjustment ranges are for the various size tubes.

For March scopes, the difference between 30 and 34mm tubes is the actual thickness of the tube wall. The 34mm tube goes from 2mm thick to 4mm think making the March 34mm tubed riflescopes immensely strong. Other companies use the additional ID to provide for greater adjustment range.

As for sunlight degrading lens coating; I'm sure that's possible but I have not heard of it being an issues for quality optics.

Abbe number, Dawes limit. The quality of riflescopes are making these things relevant now. We live in great and interesting times.

quote:

Originally posted by NikonUser:
We live in great and interesting times.

Even without being a highly dedicated precision shooter, that is so obvious to me as I think back about the evolution of scopesights. Although I am vague about the specific details of the most modern sights, I remember my own experiences and have read everything I can find about the history of military snipers and their equipment.

Another observation I found interesting from the author I referenced above was, “It used to be that the top-of-the-line Leupold Mk4 cost $1,250; now that is a low-end scope [in terms of] money spent.” He then goes on to say that his jump from there was an S&B at $2,000 and which now retails for as much as $3,800 or more.

And of course it’s not only the sights today but also the rifles and ammunition. It demonstrates what industry can do with the right incentives from buyers who are willing to pay for improvements.