Question on MOA changes with magnification

T

tpcollins

New member
I have a Swarovski AV 3-9x36mm (previous model to the Z3) with a 4A reticle. I found the reticle's specs online for the distance between the heavy horizontal lines at 100 yards as 16.6" on 9X and 50.4" on 3X.

If the magnification is on a linear taper, the distance for 6X would be in the middle at 33.8". But in reality should the distances change based a linear taper or more of a parabolic taper? Thanks.
 
I'm not sure I know what you are talking about. But, why would you even consider a parabolic taper?

Seems to me that if you're talking about ranges, its simply a matter of triangular proportions?

Bob Wright
 
But, why would you even consider a parabolic taper?
Click to expand...

I was trying to think of the opposite of a linear taper and parabolic is all I could come up with.

I'll ask the question this way - on my 3-9 scope, does the magnification increase evenly throughout the power range?
 
I may be wrong 'cause my brain don't always think too good and I haven't been in a math class in over a decade, but to use your graphing descriptions I don't think it would be a straight line because that would mean you could magnifying something until your field of view was absolutely zero inches. It would be some kind of exponential decay graph? I haven't though about algebra in a long time.

So it sounds like the field of view you're measuring would be around 150.3 inches at 1x magnificaton. So at 6x magnification this FOV would be around 25.05 inches?

This is why I buy fixed power scopes. mostly:)

I could be completely wrong and someone far more qualified will hopefully come along and correct my ramblings. good luck.
 
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The manufacturer determines how magnification changes as you rotate the "power ring". It is basically a cam/pin affair that moves the lens group forward/back as you rotate.

If you look at the power markings on the ring, you can measure the difference between 3X, 6X, 9X and see how linear it is for that model scope.

I would not be a bit surprised to find out that there is no "standard" for how this is done between different manufacturers.

However, as to your question, regardless of how much you have to move the power ring, the height subtended by two lines (or the ends of two bars) in a reticle in the 2nd focal plane is a function of the magnification, for a constant target distance.

To confirm this, stick up a tape measure at a relatively close range and check the subtension at different powers.

Here's a link -

http://www.premierreticles.com/pdfs/2009-HowToFFP-SFP.pdf
 
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Just a guess, but could it be that with the reticle being constant and the targets size changing with magnification the apparent distance between lines must increase with a reduction in magnification.
Or was that even part of the question?
 
Just a guess, but could it be that with the reticle being constant and the targets size changing with magnification the apparent distance between lines must increase with a reduction in magnification.
Or was that even part of the question?
Click to expand...

Not even close. I appologize in my OP that I didn't explain it well enough. But DMAZUR got me thinking so I went and looked at my scope. The 3-9 markings are 180 degrees apart on the ring. However, the spacing between 8 & 9 are much closer together than the 3 & 4.

Since the FoV for this 3-9 scope is 39' - 13.5' at 100 yards, I would assume due to theway the numbers are spaced that the FoV for 6X should be in the exact middle at 26.25'.
 
I'm not certain why you're concerned about this. Most SFP scopes have the subtensions calibarated at the highest magnification. I use a FFP scope for all my longrange shooting. On a FFP the heavy crosshairs will disappear at highest magnification.

I have never even used a Swaro scope, so I can't say diffinitively, what your field of veiw is at any range. I doesn't matter as far as using the subtends for rangeing. In a Milrad scope 1 milrad equals 3.6" at 100yds. In MOa's one MOA subtend is equal to about 1". You can then extrapolate, from the mumber of subtends, the size and distance to your target. I use milrad, FFP, and find it easier to figure, cause there are fewer subtends to count.

Swaro scopes are supposed to be top of the heap, I can't imagine that they would fail to help you if you were to call them.
 
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The reason I asked was since Swarovski's spec at 9X is 16.6" from heavy edge to heavy edge on the horizonatl line, it's also 8.3' from the crosshair down to heavy edge of the verticle. At 6X that distance extrapolates to 16.9". The drop at 200 yards on my ML is about 9". If I "frame" a deer's body )about 18") at 200 yards with the center of the crosshair and the bottom edge of the heavy line which is 17", I can use that instead of "hold over" of the center of the crosshairs.

That's the long story. The short story which I asked was whether these numbers (or the FoV) was on a liner taper throughout the magnification range. Since the graduations on the scopes dial is not equidistant, I have to assume Swarovski placed the numbers on the dial to coincide with the true magnification.

I'll check it when I go to the range, I just wanted to know ahead of time.
 
Some numbers are rounded.
9/6=1.5
1.5 x 8.3 = 12.45
9/4.4 = 2.05
2.05 x 8.3 = 17
Somewhere around 4.4X on your scope should give you 17" between the top of the post and the horizontal crosshair.
 
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