Telescope eye relief question

[JimGnitecki]

At my last range session with my Pedersoli 45-70 buffalo rifle with its Leatherwood Hi-Lux Malcolm type full barell length scope, I realized that I was needing to hunch forward some distance, beyond what I would call the "natural" head position, to see the image in the scope with minimized black perimeter outline and maximized brightness.

So, I set up my iPhone on time delay to catch a photo of me, instead, in what felt like the most comfortable and lowest muscle effort position.

Viewing the photo afterward, and blowing it up on my computer screen immensely to be able to accurately measure my eye relief at this "ideal" position, I found that I was positioned at 5.6 inches of eye relief. The scope states that eye relief is 4 inches. So, no wonder I felt a bit uncomfortable getting to the 4 inches. Here's the photo before zooming in:



Fortunately, this scope, with its external adjustments and "slide during recoil" feature (to eliminate the heavy 45-70 recoil effects on the scope) allows a shooter to change its overall length via different sunshade lengths for the front of the scope that fasten it to the front barrel mount. I simply changed from the 5 inch "standard" sunshade length to a 7" sunshade length, by unscrewing the original shade and screwing in the new one. Because the front mount remains in the same place on the rifle barrel, that moved the REAR of the scope rearward 2 inches. That got the eye relief down from 5.6" to 3.6". And now, the scope's posiiton relative to the rifle looks like this:



This change obviously will make the rifle more comfortable for me to shoot, and may even as a result improve my group size a tiny bit due to less fatigue during a firing string. It will also brighten the image in the scope (I had already noticed before I made the change that the image brightened noticeably when I leaned forward, and I had never tried to get as far forward as I would have liked, because moving my head forward more was uncomfortable and also affected my cheek weld to the stock.)

But, I got to wondering what other effects a change like this might have.

I don't think the scope zero will be affected much if any, as the distance between the front and rear mounts, which controls how much change occurs when I change elevation by raising ir lowering the rear vernier mount position, remains the same. The actual optics of the scope have been moved rearward, as one fixed assembly, by the swap to the longer sunshade (which is just an empty steel tube). However, since the scope's optics's fore-aft position has been slid rearward, I suppose there might be a tiny change in elevation, because the end of the barrel now extends 2" further forward from the scope, although at he same slight angle as before?

I also think that any error created when the shooter's eye is not perfectly centered relative to the scope is unaffected, as I am still at the same original eye relief. With the scope's "sliding" freedom to stay in place while the rifle below it recoils, I COULD actually move closer than the published 4" eye relief distance without getting a black eye on recoil, but would doing so get me any optical benefit?

I guess I am just wondering if this change will affect anyhting else beyond my improved comfort and posture.

Jim G

 

[Ks5shooter]

Have fun checking zero and enjoy a nice rifle.

 

[Hugger-4641]

Zero may or may not be affected, but changing your distance from the scope may or may not affect poi.
You may not even notice from 150yds or less, but parallax error is real. Unless you are still positioning your eye in the exact center of the optic, you will get some parallax error. How much? IDK, but if you're not shooting 1moa groups it may not be enough for you to notice anyway.

 

[Dave DeLaurant]

I think the answer is maybe, probably but only slightly, or some variation. I'm in the shoot-it-awhile-and-see camp though -- safe experimentation is far more fun than trying to solve via theory.

Nice rig, BTW!

 

[JimGnitecki]

On the parallax thing: I was told that to eliminate, or at least greatly minimize parallax, I should hold my head at the distance from the scope that leaves a very thin black circumference around the scope image.

This is achieved by starting "too far rearward" (i.e. longer eye relief than the scope specifies), noting the black ring that appears when you do this, and moving your head forward until the black ring ALMOST disappears. If the black ring is the exact same thickness all the way around, you are centered and parallax is eliminate or at least minimized.

Jim G

 

[.45Coltguy]

Very nice set-up you have there. I'm following this to see the end result. Scope looks perfect for that rifle.
BTW, that range reminds me very much of the one in Rexburg, Id. Anyways, enjoy that set-up.

 

[JDGray]

Title should read…
“Telescope eye relief question” lol!
Very nice setup! My FFL has an unertl scope on his target 22lr, worth more then the rifle he jokes!