Rifle Scopes Field Of View calculation formula

[Mike Lake]

I have an S&B PMII 5-25 x 56 with quoted field of views of:

5.3m at 5x magnification
1.5m at 25x magnification

Given that 25x is five times more magnification than 5x I don't understand why the field of view is not 5 times less.

A simple formula (for an idiot like me) to go from 5x to 25x would be:

5.3m / 5 = 1.06m

But that does not give the 1.5m quoted in the scope specification.

Does anyone know the right formula to calculate FOV at different magnifications given FOV at one magnification?

BTW: does everyone know that S&B illuminated scopes are no good for left hand bolt? The illumination knob on the left fouls the bolt. S&B were good enough to remove the knob on my scope and replace it with a blanking plate.

Best regard

Trusley_Mike

 

[brand692]

Re: Field Of View calculation formula

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: trusley_mike</div><div class="ubbcode-body">I have an S&B PMII 5-25 x 56 with quoted field of views of:

5.3m at 5x magnification
1.5m at 25x magnification

Given that 25x is five times more magnification than 5x I don't understand why the field of view is not 5 times less.

A simple formula (for an idiot like me) to go from 5x to 25x would be:

5.3m / 5 = 1.06m

But that does not give the 1.5m quoted in the scope specification.

Does anyone know the right formula to calculate FOV at different magnifications given FOV at one magnification? </div></div>

This is due to the tunneling. Tunneling is the effect that you get when you turn down the power and at some point the FOV quits getting bigger. I had MANY questions about this. It annoyed me big time on the optics I was using at the time. Then I got a PH 3-15. It on the other hand, was phenomenal. The FOV continued to get bigger all the way down.

I don't know of a formula that takes in the tunneling effect as it happens to almost all FFP scopes. Honestly, the only one I found that doesn't tunnel is the PH.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: trusley_mike</div><div class="ubbcode-body">BTW: does everyone know that S&B illuminated scopes are no good for left hand bolt? The illumination knob on the left fouls the bolt. S&B were good enough to remove the knob on my scope and replace it with a blanking plate.

Best regard

Trusley_Mike
</div></div>

There is more than lefty that has been greatly disappointed after mounting their S&B on a left handed bolt rifle. Sorry you didn't know that ahead of time. If the quality of S&B is what you are going after with illumination, I again have to say the PH is the way to go.

BTW, Welcome to the hide.

 

[sniperaviator]

Re: Field Of View calculation formula

I dunno. I can tell you this much. I have a Nightforce 5.5x22-56 and when set at 5.5 it is not 1/4 the magnification. I can tell that because it is not FFP and the moa tic marks don't indicate 4 times the length. If I take Nightforces figures for field of view and divide the large by the small, I get 3.72 which is about what the magnifcation difference is also.