Home Forums Hunting & Shooting Ask The Gunwriters Ask John Barsness Questions About "HUNTING SCOPE MAGNIFICATION"

Both side-focus and an adjustable objective essentially correct the focus of the reticle, but the side-focus does it inside the scope, rather than by moving the objective lens. Generally an adjustable objective is considered more precise and perhaps tougher, but side-focus is certainly handier--at least for right-handed shooters!

I don't know why a side-focus scope would be dimmer than an adjustable-objective scope, and haven't noticed it in using a number of side-focus scopes. Is the reticle in your older scope a plain plex-type, and the reticle in the new scope a "ballistic" type? Usually plain plexes are wire, while ballistic reticles are etched. The glass that reticles are etched on is usually uncoated, and can slightly dim the image, though the difference normally isn't vast.

The reticle in the older scope is a Nikoplex, as is the reticle in the newer scope. This scope was unbelievably dim, as in the Bushnell Trophy 3-9x40 that we mounted on his .22 LR and sighted in at the same session was much, much brighter, as was the Nikon Prostaff spotting scope we were using. I didn't say anything because I didn't want to offend the BIL, but I certainly made note of it. I'll check it out again while we're hunting together next weekend to see if it was as bad as I'm certain it was. I'm a big fan of Nikon optics and was disappointed to see how dim that scope was!

That's very interesting. I wonder if something's wrong with it.

I am wondering about this too. I am looking for a scope that has very good low light performance and it seems to me that things appear "farther" in poor light. The natural response is to want to increase magnification, but then you must also increase the objective lens diameter.

Not necessarily, but sometimes. It depends on the magnification and the person's eyes.

The twilight factor formula is an attempt to resolve these factors.

MD,

Do you have the Twilight Factor Formula handy?

TF is the square root of magnification x objective lens diameter (in millimeters).

A small adjustment:

TF is the square root of (magnification x objective lens diameter)

Thanks!

so should I buy a Conquest 3x9x50 or a 3.5 x10x50 for my next 223 caliber deer hunting rifle? No shots are ever over 150 yards but I do like the big image in the 50mm scopes. The 3.5 x 10 is an inch longer and 3 ounces heavier but my eyes are getting weaker.

If I were you, the 3.5-10x50 would be it.

yes that is what I really want, foolish as I know it is.

Man, I just read the article and all the comments for the first time. Learned a lot! Thanks Mr. Barnes!

You're welcome!

I either need to sell a rifle or get another scope. (I like all mine that are to wear a scope ready for use, even those that I may not have shot for quite some time,) My most often used rifle is an accurate, lightweight, .308 topped with a top of the line Zeiss getting on to about 20 years old. Never had any trouble hitting stuff in the "volleyball" out to as much as 500 yards ( which I really do not intend to do again - too much could go wrong.) That should tell me something. This rifle's twin sister is an identical model in .243, wearing a Leupold 3-9 Ultralight EER which I need on a .22LR for the parallax adjustment. My thinking for the .243 is for the Leupold 6x36 as a replacement. I do not see many used ones in this marketplace, so I may have to go new.

John, I appreciate your work. If you have sold out to the industry, you sure hide it well. Thanks for being open and objective. jack

jt402,

Thanks--I think!

Actually 6x36 Leupolds come up for sale fairly regularly on the Campfire Classifieds. Usually they're M8's instead of the new FX-II's, but the M8's were quite bright. I probably have 8 or so I've picked up there.

Mule Deer

Are the FXII's the same line & quality as the VXII's only in fixed powers?

Yep, same adjustments and lens coatings.

Thank-you John

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