TargetTalk

My rifle, a FWB 300S, has the FWB rear target sight fitted. Having grown a little older now ( :-) ) my eyesight has deteriorated and I now have a shooting frame for my pistol shooting, this has a 41mm lens and is perfect for 10 metre.
I have recently taken up Bell Target shooting and having looked around at a few solutions to the eyesight issue I was thinking this would work:
http://www.intershoot.co.uk/acatalog/Ge ... 0-744.html

I have absolutely NO experience of any type of Iris other than the bog standard Iris that comes with most basic target sights so I am looking for some guidance here. Any and all suggestions gratefully received.

That iris will certainly thread right into your FWB rear sight with no trouble. And it has all the adjustments you could possibly want, including diopter. Just make sure that your rules allow optical correction to be mounted in the sight. If they don't allow it, consider getting another pair of shooting glasses for rifle.

That aperture will certainly fix your eyesight, but OY! the price!

In reality, there are much less expensive solutions out there - mine!

The issue is that no one has ever worked the optical math to figure out what lens strength you need, so the solution is these expensive variable lenses. Well, I studied photography and optics, and I shoot, so I understand the problem, and I'm over 40, so my vision has gone and I can empathise.

Here's the easy version of the math:

1. The distance at which your depth of field is evenly split between the front sight and the target is called the hyperfocal distance of the front sight. It is an oft used photography concept. Google it for more details.

2. THis distance to focus at to achieve this focal point is exactly 2x the distance from your eye to the front sight.

3. Since lens strength is a measure of focal length, inverted, in meters, you can easily calculate the lens strength you need to shift your eye's focal point from infinity (distance vision) to this hyperfocal distance. A 2 diopter lens will focus you at 1/2 meter. A 3 diopter will focus at 1/3 meter. A 1/2 diopter focuses at 2 meters, and so on. So measure the distance from your eye to the front sight, double it, convert it to meters, invert it, and PRESTO! that is the lens you need to focus at your front sight hyperfocal distance.

There are some simplifying rules, and lenses are only available typically in 1/4 diopter steps, so the answer reduces to a rifle needs +0.5 diopter (or +0.5 diopter added to your distance vision if you wear glasses). Shorter carbines, AR, and pistol usually need +0.75, or +0.75 added to your distance vision.

Net, I can sell you a lens, and an adaptor/holder for the lens for $75 total. You won't have adjustability, but you don't need it if you calculate the lens strength correctly in the first place.

Regards,

Art

ShootingSight wrote:There are some simplifying rules, and lenses are only available typically in 1/4 diopter steps, so the answer reduces to a rifle needs +0.5 diopter (or +0.5 diopter added to your distance vision if you wear glasses). Shorter carbines, AR, and pistol usually need +0.75, or +0.75 added to your distance vision.

Net, I can sell you a lens, and an adaptor/holder for the lens for $75 total. You won't have adjustability, but you don't need it if you calculate the lens strength correctly in the first place.

Regards,

Art

If I am reading this correctly you are saying in essence that I would need my Prescription plus +0.5 for the correct strength for rifle shooting?
To take that one step further, what you are implying is that all normally sighted people should use a +0.5 diopter for perfect resolution of the sight - or am I missing something here?
I usually am BTW. This seems too simple a solution.