Help me understand FOV and Objective

M

Max-4

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Hey guys, I am in the market for a good quality scope to go on a "bush" hunting rifle for deer and moose in Ontario. It will be going on top of a Remington 7600 in 30-06 and will be used in the woods and thicker bush. Im not saying there isn't the possibility of maybe a 150 yard shot at a deer on a farm but mainly in hardwood and thicker spruce swamps. Shots where we hunt by north bay are usually under 80 yards for moose and the deer are often running.

I was thinking about a good quality low power scope like the Leupold VXII 1-4x20 or similar. I want to be able to mount the gun and find my target very quickly weither its 10 yards away or running at 20 mph. I am looking at the field of view (FOV) numbers on some scopes and see that the Leupold above has roughly 74 feet at 100 yards on low power. If I look at a Leupold VXI 2-7x33 the FOV is roughly 44 ft at 100 yards. Does this mean when I look thru these scopes on LOW power at 100 yards that's how much horizontal area I can see? What should I be looking for in an Ontario hunting scope for big game?

The other is objective size, there is 20mm, 33mm, 40mm and 50mm on most standard manufacturing companies scopes. How does this differ from FOV and when I look thru the 20mm tube is it going to look small and hard to spot a moving animal? Does Objective size just mean the basic size of the circle or picture you see, and power or zoom decides your FOV at 100 yards?

What should I be looking for in a good scope for hunting big game in Central to southern Ontario? Thanks
 
In practical terms, objective lens size has no bearing on field of view. Objective lens size does have a bearing on how much light reaches the eye. Larger objective means a brighter sight picture (with lot of caveats). Lower power scopes have smaller objective lenses because the human eye can only utilize so much light. If you divide the objective lens size by the magnification, it will give you the size of the exit pupil (the amount of light reaching the eye) For most people anything greater than 5mm is a waste. So a 4x with 20mm objective will give you a 5mm exit pupil.
 
Max-4 said:
... the Leupold VXII 1-4x20 ...
I am looking at the field of view (FOV) numbers on some scopes and see that the Leupold above has roughly 74 feet at 100 yards on low power. If I look at a Leupold VXI 2-7x33 the FOV is roughly 44 ft at 100 yards. Does this mean when I look thru these scopes on LOW power at 100 yards that's how much horizontal area I can see? ...
Click to expand...

Yes.
 
Objective lens size does have a little to do with it, but the difference between e.g. a 40mm diameter and a 50 mm diameter matters much, much less than the power of magnification of being applied and distance from the observer to the area being observed. Think of a cone, it's base being overlaid on the area being observed and the point being at the observer. As the distance is reduced or increased, whether by actual physical movement or by the change in magnification, the diameter of the cone (the FOV) gets smaller or larger. You can model it by shining a flashlight at a wall and moving toward and away from the wall. The effect of changing magnification would be like being able to change the focus of the flashlight from a floodlight to a spotlight.
 
Go online, and compare the same model scope, with the same magnification, but a different sized objective lens, and there is a good chance, that the FOV will be identical.
 
Another VERY GENERAL example, on top of the ones already mentioned.

If you make a 1" diameter tube with a sheet of 8 X 11 paper on the 11" side, your FOV will be
less than if you made it with the 8" side.

Generally..........
A shorter tube will increase the FOV.
A larger diameter tube will also increase the FOV.

A scope is hard pressed to show you a view larger then what's available
down the tube. There are exceptions, of course, let's stick to the basics.

A larger objective will help gather more light and clear up the subject,
again, there are many exceptions. Glass quality/coatings is at the top.

The occular lens (the part you look in) is also very important, it presents the image to the eye.
If you wear glasses, make sure the occular lens is adjustable (-1....+1)
Most people think of the occular as a focus, maybe, but what you should really do
is look at a bright subject, like the sky, and adjust the focus of the occular lens to make
sure the reticle is perfectly sharp, then lock it.
When you focus the scope, the subject (target) is focused onto the reticle, if your reticle is sharp,
it will appear sharp on the subject.

If anyone out there has a better understanding of this, please cut in !!!!!!!!!
 
Benito said:
I know objective does not determine FOV.
But what does determine FOV?
Click to expand...

Engineering in the eyepiece. This is one of the main areas of improvement in new gen scopes. The goal with variable scopes is to have wide field of view, wide "sweet spot" for easy viewing, long and constant eye relief, limited edge distortion and other colour aberations, quick focus instead of turning the entire eyepiece to gain reticle focus, etc.

FOV - area of landscape you see
Objective diameter - diameter of the lense at the front of the scope NOT the diameter of the scope

Hope this helps.

Jerry

Jerry
 
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