[jackh]

i looked through a VX-II 4-12 at bass pro yesterday and it was so freakin nice i loved it. i also looked through a VX-II 6-18 that was like $40 cheaper and didn't like it as much. i asked the guy why the more powerful scope was cheaper, he said the more $$ one was 50mm. i though the bigger the tube, the more light coming in but he told me something about it having a wider FOV.

can someone explain to me what this relates to? i know what it means literally but i used to thing the smaller the FOV was @ 100 yds the better because whatever your aiming at is gonna be big in the scope cuz its so powerfule. i guess im asking if its good to have a wide FOV so you can see more when powered up or what? thanks

 

[paulosantos]

You want as wide of a field of view as possible, especially for tactical purposes and hunting so you can see multiple targets and for the moving targets. For just shooting paper, it doesn't matter that much.

 

[ccoker]

most guys behind the counters are idiots

bigger objectives don't make for a bigger field of view
they allow for more light when at higher magnification

the lower the power, the wider the field of view of course
you really, really need to get scopes out of the store and outside at low light
I have tested scopes that in the daylight they were indistinguishable, yet at dusk, things changed drastically


here's some good info
http://www.opticstalk.com/forum_posts.asp?TID=5023

 

[jackh]

but a 50mm will have a wider FOV than a 40mm right?

 

[paulosantos]

but a 50mm will have a wider FOV than a 40mm right?

If everything else is the same, the 50mm will have the wider field of view. I don't know why, but they do.

This is comparing a Leupold 4.5-14x40 Mark 4 LR/T 30mm Riflescope and a Leupold 4.5-14x50 Mark 4 LR/T 30mm Riflescope.
http://www.swfa.com/pc-3327-297-leupold-45-14x50-mark-4-lrt-30mm-riflescope.aspx
http://www.swfa.com/pc-3410-297-leupold-45-14x40-mark-4-lrt-30mm-riflescope.aspx

 

[ccoker]

I would want to test for myself, sometimes published specs are a little optimistic

same scope say a 3-9x40 vs 3-9x50

 

[J.Boyette]

Ok,

This is what I do understand.

The larger the objective size = crappy glass 9 out of 10 times.

The higher the quality of glass = smaller need in objective size.

If you have a large objective and quality glass [ insert NightForce, US Optics, S&B or PR] you get better light transmission to your eye in low light situations " But you need a reticule you can see also"

Now Field of View.

Ok, so if I made a optic that's a 3-9x I could make the field of view anything I want. By making the field of view smaller I increase the reticules size. at 9x or if its a First focus Plane optic across the whole adjustment range.

The balancing act that quality optic makers have is this.

To have a reticule that is usable from the lowest to highest adjustment setting for the end user wile not killing off my FOV or light transmission to your mark 1-1 eye ball.

Now if I run a 50mm obj, I can then in turn have a lower level of quality of glass, and have a bigger exit pupil for light transmission. But I add alot a parallax issues. Now I need to adjust for that too.

Or I could go with a 42mm have higher quality of glass, with the same level of light transmission as my cheap 50mm obj, less parallax issues.

Or I could go all out and build a optic thats sales 200 units a year and make it killer.

The bottom line is this. You need to buy equipment that fits your needs, not what looks great in a store. The key here is to be honest and get what you need.

Case in point. I went and got a Savage 93 17HMR. I bought a BSA 3-12x40 Sweet 17 Riflescope $90 optic for that gun. Man does it suck or what.

BUT!!!!!!

I do not need a USO or a Leupold on a 17HMR. ON the other hand my GAP 700 sports a IOR 3-18x42FFP with a reticule I did up for them.

The field of view in both optics is what I needed. With the 6 to 1 ratio of the 3-18 IOR I get what I need very wide @ 3x and narrow @ 18x. With the BSA and its 4-1 ratio with crappy glass the FOV is just right, very narrow at all power settings.

Now wrap your head around this idea.

If you have a Leupold 3.5-10 MK-4 the FOV @ 100yds set @ 10x is 11ft or 36.66 Mil wide. IF I would reduce the FOV by 10% I would get a FOV that is now 33 Mils wide. This would make the TMR look 10% larger.

I did just this with a US Optics 3.2-17x50 with a MPR reticule. We sent it back to USO and asked them to insert a shim in the optic that would reduce the FOV by 10%. We now could use the MPR reticule at 4x, when before the lowest that reticule worked was 6.5x.

Just things to think about.

John

 

[Cold]

That was a damn fine read, thanks J.Boyette

 

[jackh]

damn sounds like you know your stuff!! thanks for the info. now, what is parallax adjustment? and what is exit pupil?

 

[paulosantos]

damn sounds like you know your stuff!! thanks for the info. now, what is parallax adjustment? and what is exit pupil?

I think John forgot more about scopes than most of us will ever know about them. :lol: :lol: :lol:

 

[ccoker]

damn sounds like you know your stuff!! thanks for the info. now, what is parallax adjustment? and what is exit pupil?

pointing you here is easier than typing:

http://www.opticstalk.com/forum_posts.asp?TID=5023

 

[J.Boyette]

Guys,

I truly do not know that much about optics. I just understand how to use them to there full advantages and try to pass that down to my students so they are educated in what does what and how.

now, what is parallax adjustment? and what is exit pupil?

Lets talk about what parallax does to a shooter, the info I am about to talk about is a easy way to visualize the issue, but will not be spot on in the mechanical aspect of what happens.

A parallax adjustment knob is found on the left side of most optics. This knob is mistaken as a focus adjustment do to the sight picture the shooter sees going in and out of focus as he / she adjusts the knob back and forth.

What parallax basically is, the image of the reticle, that is adjustable, floating around the object the shooter is aiming at.

Part 1.

Check this out, when you dial with a elevation or windage knob, all you are doing is moving the housing the reticle is built in, up, down, left or right be it, a piece of glass, or wire. So when you do this, your Point Of Aim "POA" is moved. When your POA is moved, so does your Point Of Impact "POI"

If you line up your POA to your POI you have something called a ZERO. Do to ZERO adjustment to get the bullet to hit where you are aiming at.

In the process is getting your POA to move around, you screw with the location your eye is seeing the reticle's image at in the lens of the rifle scope.

Part 2.

Since a lens is curved, if you look in the middle of the lens all is cool, if you look at the 6 o'clock location within the center of the lens you will not have the same clear and crisp picture as if you where looking at the dead center. This is where the parallax adjustment comes in to play.

By adjusting the parallax you clean up the image of the object you want to shoot at, and place the reticle on the same FOCUS PLANE.

TEST

Do this. Get on your rifle, get solid position built and have your reticle aimed at the target. Then lift your head up just enough so you do not have a cheek weld on the stock.

Now move your head around in a small circle. If the reticle moves and dances around the target, your parallax is off do to the target and the reticle not being equal on the same FOCUS PLANE

Once you get your parallax set, you can move your head in a circle and the reticle is dead on the target and does not dance around do to the target and the reticle are now both on the same FOCUS PLANE

Why do I need this parallax crap?

Well its simple, you do not NEED parallax if you do not plan on engaging your target will precise shot placement "with in 4 MOA"

I have seen shooters go from a 5 MOA group @ 100yds to a 1 MOA group by adjusting there parallax and get it set right.

Keep in mind, a correct parallax setting needs to be done per distance you shoot at. So if you are shooting at 100yds then 600yds, you might want to adjust for parallax.

Or if your cheek weld and marksmanship skills are good, you can run with a 300yd parallax setting and be good to go.

Most optic brands have adjustable parallax models of rifle scopes. If I buy lets say a Leupold Vari-III 3.5-10x40mm it has a fixed parallax of 100yds.

Well that sucks I think, I send mine of the the custom shop to get the fixed parallax adjusted to 300yds. A 300yd fixed parallax is a great distance to run in a non-adjustable rifle scope. Due to @ 1000yds I am only floating around with 1.5 MOA of parallax. So for me, thats all good.

John