Lens in Anschutz rubber eyecap

[Humpers]

Are there any disadvantages to putting a correcting lens in an Anschutz rubber eyecup like the one shown below instead of using shooting glasses? Does anyone else use this setup?



I am considering getting the usual Champion/Varga type shooting glasses to improve my sight picture when shooting prone, but as I already use this eyecup I believe inserting a lens into it is an option. I like the idea of this as the lens should be exactly in the right position for my line of sight (provided my head position is correct), and it's a lot cheaper than glasses. I use a blinder attached to my rear sight which I'm happy with, so can't see (sic!) any advantage in having one on shooting glasses (and the latter may make looking down the spotting scope more difficult).

The main disadvantage I can think of is that the lens will be further away from the eye if pushed all the way down to the two "lugs" at the bottom of the eyecup (are they there specifically to support a lens?). As I understand things, lenses work best when as close to the eye as possible, but perhaps it will just affect the prescription I need?

Any insights gratefully received.

Humpers

[David Levene]

Are there any disadvantages to putting a correcting lens in an Anschutz rubber eyecup like the one shown below instead of using shooting glasses?

Not allowed under ISSF rules, but it is allowed under NSRA rules.

[Tim S]

In addition, it's not unknown for those eyecups to be knocked askew while shooting. If you aren't shooting to ISSF rules, but want a cheaper alternative to shooting frames, the lens holders that clamp onto the eyepiece are a better solution than an eyecup

[John Marchant]

The two little lugs inside the eye cup were originally placed there to enable a coloured filter to be fitted, back in the day.
If you fit a lens just inside the eyecup, it will be much nearer to your eye.
However if you have an astigmatism, you will need to ensure that the reference on the lens ends up in the correct place for alignment or you will be seeing oval shaped aiming marks.
A further allowance for correct rotational positioning would need to be made if you shoot with a cant.
And as Tim says, if you knock the eye cup, the lens alignment could easily be disturbed.
I have been using a lens fitted in the eyecup for the last three years and it is certainly very effective.

[Humpers]

Thank you all for your helpful replies. Sadly I'm not (yet!) shooting under ISSF rules, and I only have an almost immeasurably small astimatism which doesn't appear to affect my sight picture at the moment.

Is it possible to use one of the lens holders that clamps to the back of the rear sight at the same time as using an eyecup? I would like to continue using the eyecup as it does seem to cut out extraneous light and distractions.

John, I presume it's useful to have an anti-reflection coating on the lens for use in an eyecup?

Regards,

Humpers

[Tim S]

You could have both at once, but if the eyepiece is (or will be) an adjustable iris type, that rearsight is going to be awfully long at the back, and the eye relief will be too. A visor, hat, or peaked cap (with sideflaps permitted under NSRA rules) would block unwanted light, and unlike an eyecup won't distort the sight picture or lens if knocked.