Objective lens size

[Joeryan]

Always fighting eyesight issues, so was wondering if a larger objective ( now have a utg 3x9x40 ) say 50mm would give me a substantially larger field of view ? This strictly a hunting gun, and I keep it set at 6x. Is it worth buying a new scope? I'm happy with what I have quality wise, just looking for any edge I can get.

[Motorhead]

A big OB glass does not necessarily equal a wide FOV ... but more of BRIGHTNESS gathering more light.

You want a WIDE FOV buy a scope that has in the description being a WIDE ANGLE FOV,

The HAWKE Panorama  EV / AO is one such scope & a most excellent one at that 

[vinenator]

Well said Scott.

I'll only add that you can compare the brightness of a  scope (or any other optics for that matter) by dividing the objective size by the magnification and then squaring it.

so, a 42mm scope at 10x has a brightness of  17.6
but a 56mm scope at 10x is 31.4, almost twice as bright.
the same 56mm scope at 20x is 7.8 or less than 1/2 as bright as the 42mm at 10x.

keep in mind, the brightness is only a comparative value and means absolutely nothing on its own.

another example, a pair of 50mm binoculars at 10x is 25, but at 7x it is 51!

this is why the image looks dimmer at higher magnifications.

through which scope would the image look brightest, a pair of 50mm binos at 10x or an 8" (203mm) telescope at 40x?

answer, almost identical.

[rsterne]

The "brightness" number is really only valid up to a number of 50 or so, after that it doesn't matter as you can't cram the extra light into the pupil of your eye, even when fully dialated.... What it is, is the square of the exit pupil in mm, which is the objective diameter (in mm) divided by the magnification.... The exit pupil is the diameter of the beam of light exiting the eyepiece.... Since your eye can't open larger than about 7mm (and 7x7=49) any exit pupil larger than that is in effect "wasting" light as it can't enter your eye anyway....

I agree with Scott, the diameter of the objective lense has little to do with the field of view, and in fact that is more a function of the lense (and lense stop or "theater") in the eyepiece....Some scopes are designed to have a wider field of view, and generally advertise that as a feature....

Bob

[Joeryan]

Ok then, as Scott said, I'd have to go for a wide FOV scope like the Hawke EV to do any good. So, I wonder if it's worth the $240 to gain 10mm on the OL. Well, it's either that or turn down the magnification to 4x. .. Thanks guys !

[Motorhead]

Ok then, as Scott said, I'd have to go for a wide FOV scope like the Hawke EV to do any good. So, I wonder if it's worth the $240 to gain 10mm on the OL. Well, it's either that or turn down the magnification to 4x. .. Thanks guys !

Get the HAWKE model # your shopping for off Hawkes  site ... then E-mail WYVERN CREATIONS for a price quote 
You WILL BE buying a scope threw them if your a serious buyer 

[Joeryan]

Ok Scott, thanks !

[D14Jeff]

if you want a wider field of view why not just reduce the scopes power down to 5x or 6x ?
FWIU if you have a 1 inch tube going to a 30mm tube can help if the glass quality is similar ..... don't know that from experience though

[jenora]

Check out pyramid air's recent review of the scout style scope.

[vinenator]

Again, comparing FOV only works if you are comparing scopes at the same magnification.

With telescopes, we change eyepieces (the lens closest to the eye) to change the magnification, but not all eyepieces are equal. Each has an "apparent field of view" and the bigger the value, the bigger the true field of view will be. the down side is, the eyepieces with a wider apparent field of view (68, 82 degrees, for example) are a lot more expensive then the ones with a standard (50 or so).

that is why they can charge more for a wide FOV scope over the standard one.

the formula is:

True Field = Apparent Field ÷ Magnification

[Joeryan]

Ok, made a decision to back to OU to finish, and get my physics degree, but only if Bob can sponsor me

[Joeryan]

Let's see, my last class was an English lit exam in June of 72. Think it'll transfer ?

[rsterne]

vinenator.... Your comments are bang on regarding FOV.... it's the eyepiece that is critical, I also am into Astronomy.... The diameter of the "field stop" in the eyepiece is what shows up as the sharply defined circle when you look through any 'scope, rifle or otherwise.... In an expensive, wide-view eyepiece the lenses are designed to be sharp right to the edges of a larger diameter field stop.... You are also correct that you can only compare the actual field of view if the magnification is the same....

D14Jeff.... A 30mm tube will not, by itself, give you a wider field of view, nor a brighter image.... It WILL allow for more MOA of adjustment within the scope itself.... It MAY allow a larger "zoom tube", with larger lenses, and that may give the ability to use an eyepiece with a larger field stop and a wider field of view....

Bob

[QVTom]

A good post from skylar of SWFA.  Unfortunately the picture links are broken.......
http://www.gatewaytoairguns.org/GTA/index.php?topic=53829.msg513252#msg513252


From the same post.......

Field of View:
This important term describes the actual width of your scope's sight picture at a specific distance.  Field-of-view is a function of magnification and the focal lengths of the objective and eyepiece lenses. But remember this: The higher the magnification, the narrower the field-of-view. Field of view is determined by the ocular lenses in the eye piece.  Different factories and brands will vary in design and stats.  Decreasing the eye relief in a scope will widen the field of view.  So its a trade off one way or the other.
 

Tom