TargetTalk

In the prone position, my coach was using 4" as the standard distance from the eye to the rear apperature... but looking at the photos from the recent world championship the distance appears much closer... perhaps 2"... for the coaches in the group how much distance is appropriate as I'm adjusting my LOP... As always, thanks for the help. :)

Do you shoot with shooting glasses?

LOP is more concerned with fit of the rifle to your body. Distance of the sight to eye is usually made by moving the sight forward or backward.

Get into position without the rifle, and get comfortable. Have someone add the rifle to your position, without moving your body, then adjust LOP and handstop. You should start with pressure about the same on your shoulder as on the supporting hand.

Now have your helper slide the sight back toward your eye, and then away. Repeat this, and you will find a spot that is definitely better than other spots for the rear sight.

As mentioned above you need to get the rest of your position sorted and then add in the sights. I seem to recall my coaching notes stating somewhere between 1 and 2.5 inches as (generally) optimal but I don't have my notes to hand, so can't verify that. You do however need to see what works best for you and ideally that would involve you lying in position, with the gun weight taken by a rest and someone sliding the rearsight backwards and forwards on the rail, to find an optimum placing. From that you can then test it properly from the shoulder and see how it goes over a longer course of fire.

Rob.

a good rule of thumb for outdoor shooting is that your apperature will be between .9mm and 1.2-1.3mm depending on light and your eyes. the front sight tube (18mm) should take up about 1/3-1/5 of the sight picture. thats with a standard barrel.
matt

westerngriz wrote:a good rule of thumb for outdoor shooting is that your apperature will be between .9mm and 1.2-1.3mm depending on light and your eyes. the front sight tube (18mm) should take up about 1/3-1/5 of the sight picture. thats with a standard barrel.
matt

Wow -- if I understand correctly, I should see a field of view at the front apperature (front post) 3x my 18mm sight tube or ~36mm... I'm WAY off, as I was attmpting to get a FOV equal to 20 mm... just a sliver of white around the front tube... more of a mechanical alignment....

Really -- 3x-5x FOV -- it will certainly take some adjustment -- I'm shooting tongiht -- any other opinions? :) (thanks!)

you should definitely have a fairly substantial amount of light around the front aperture and, for that matter, around the aiming mark within the front aperture. If you don't, it'll blur out as your eye gets tired and you'll find it much harder to distinguish a good sight picture. If you have plenty of light, the same effect will not be apparent, and you'll find a lot less shots surprise you. I've recently moved to a 22mm foresight and find the extra light it lets in very beneficial for the clarity of the sight picture.

Leo, Hopefully you found the correct distance from your eye for the rear sight. If you have an adjustable rear aperture, the .9 to 1.3 opening is a starting point, but you may need more or less outside depending on ambient light AND how old your eyes are. We need more as we age. Indoor I've gone from 1.5 to 2.1 over the past fifteen years.

Also, we've al been speaking of apertures in the front sight, but it sounds as if you are using a post rather than aperture. If so (are you practicing for high power?) try a post that is equal in width to the black aiming point. Some like narrower (half the width), but I don't k now anyone who uses wider. Our brains "see" geometric patterns that have standard relationships (1/2;1/3;1/4;1/1) easier than other.

Can I insert some science into this discussion? I would like to look at this question from a purely optical and opthalmological perspective.

Here are some facts:

1) the rear sight is totally out of focus. It MUST be so, and must not act as an open window for looking at the front sight. Because if the rear aperture is larger than the diameter of your pupil, you are open to parallax errors. There are studies proving this, and I can give you chapter and verse if you choose not to believe this - and why should you believe it? This is, after all, the Internet! The guy who did the research was Douglas Kerr, and his report is dated May 30, 2007. I have that report. If you need it, I’ll send it.

So it’s important to ensure that your rear aperture is smaller than your pupil. Not easy, since your pupil will dilate and contract according to light levels.

2) if your rear sight is out of focus and its diameter is smaller than your pupil, it will act as a light gate, so if you increase its diameter (while remaining smaller than your pupil) you will simply make the fore sight and the target beyond that seem brighter. You can make it as bright as you like within the limits of the sight, provided that the rear sight diameter stays smaller than the diameter of your pupil. But of course, as you let in more light, your pupil automatically gets smaller… And you just do not know how big your pupil is at any given moment, so dialling in 1.6, 1.7, 1.8 etc is not going to always give you consistent results. It’s a judgment call. Isn’t shooting just great!?

3) the smaller the “entry pupil” as it’s called, which is the smallest diameter aperture in the vicinity of your eye (so that will of course be the rear sight and not your pupil, if you have adjusted it properly to avoid parallax), then the greater will be the field of focus. So if you widen up your rear aperture, and the light levels are low (which may be why you widened up the rear sight in the first place), your entry pupil will be enormous. Well, maybe 2.5mm. At that setting, the things in your field of vision which will be in focus will be those things that are on the focal plane of your optical system. That’s your eyes, by the way, but if you are using enhanced optics, illegal in some disciplines, then that will included those optical systems. You will have, or can arrange to have (MUST arrange to have), the fore sight in focus, although probably nothing else will be.

So, lets say you have opened everything up on the rear sight, and have the fore sight clearly in focus (which is the basic requirement), by using whatever optics you are using or were born with :). So now, if you reduce the aperture of the entry pupil (the rear sight) you will find that the other items in view, ie. the target, will become more in focus than they were. Darker too, of course, which sucks, but there you are. This extension of the field of focus is excellent! But if you go too far, the picture gets too dark, so as with everything in shooting, you have to compromise.

4) If you were to drill a hole in a door, say 1/2” diameter, and then you wanted to look through that hole, you would see more of the outside world if you got closer to the hole. That’s because your entry pupil, which is in this case your real pupil, is very much smaller than the hole, and so if you get up real close you can squint through lots of angles at the scenery beyond, up, down, left, right. But the rear aperture in a target rifle is absolutely not like that. Its pupil, as we have already hopefully agreed, is smaller than your pupil, so squinting sideways is just not an option. So that tells you that getting closer to the hole will get you nowhere.

So to answer the original question, “how much eye relief should I have with a peep sight?” (that was the original question, right?) the answer is, if you have your peep sight adjusted correctly, it doesn’t matter.

I disagree with the "it doesn't matter" statement. It does.

The further you get from your rear iris, the smaller the ring of white gets around your front sight. The smaller the ring of white, the easier it is to keep your sights aligned properly.

The closer you get to your rear iris, the more things you can see around your rear sight...like wind flags and your number board. But, it is harder to keep your sights aligned.

I personally like to see my wind flags while getting ready to shoot my shot, so I'm closer to the rear iris. Probably in the range of 1-1.5 inches from eyeball to iris.

Eric U

edit:

The closer you get to your rear iris, the more things you can see around your front sight...like wind flags and your number board. But, it is harder to keep your sights aligned.

Eric U

Great discussion -- I hope I can put it all into play as I have my first 50/100m match on Saturday and I've never fired outdoors... and of course the range was closed this evening so I didn't get a change to sense check the new arrangement. The exit pupil discussion was interesting -- but I'll look to keep 1/2 the diameter of my front site 9mm as white spacing total fov = 2x9+18 or 36mm -- lots of things to learn from this team -- thanks for the help. :)

Just a quick comment. You really do not want to play with the rear sight iris too much (at all ?) to adapt to different light conditions, that's not what it's for. You should be correcting those aspects with filters. As per Erics comments, opening up the rear sight iris changes a whole host of other things and hence your sight picture looks totally different. I would suggest the rearsight iris could be changed between about 1.0 and 1.3 mm but any more and the errors will come in. Fixed iris's are almost always set at 1.1mm and there's a reason for that.

Rob.

Waisted,
What I hear you saying sounds reasonable but I use a tube sight, do the same rules apply?

Jeff

The ONLY thing you adjust the rear iris diameter for is to adjust for different light conditions. The change in sight picture from adjusting the iris diameter is barely perceptible. That is not what the original question was about. Eye relief, or the distance from the eye to the sight does change the sight picture. At no time in my previous post did I say anything about adjusting iris diameter.

Eric U

A reasonable rear iris setting method is to close it down (slowly, to give your pupil time to react) until the sight picture just perceptibly darkens. Slightly to the periphery of the topic - for the rest, read Waisted.

Anonymous wrote:Waisted,
What I hear you saying sounds reasonable but I use a tube sight, do the same rules apply?

Jeff

I'm not familiar with tube sights but I looked them up. Looks like they are aperture sights, so yes, the above would apply.

Once upon a long time ago I had an FWB 300S, the rifle with the sliding action that absorbed the recoil by moving back on rails. As a newbie I thought my eye should go right up against the rubber eye cup.

After the first shot I had a black eye (from the rubber, not a bruise)! So there was a minimum distance I should have observed. ;-)

Eric U wrote:The ONLY thing you adjust the rear iris diameter for is to adjust for different light conditions. The change in sight picture from adjusting the iris diameter is barely perceptible. That is not what the original question was about. Eye relief, or the distance from the eye to the sight does change the sight picture. At no time in my previous post did I say anything about adjusting iris diameter.

Eric U

Apologies Eric, I was missquoting you. I'm not however convinced you should be adjusting the iris for light conditions, as I said previously, that is the job of filters, but as before, I need to dig out my coaching notes to see what our coach trainer states.

Rob.

With the experience Eric has, and the coaching that's available to him, I think I'll take what he says as right. Colin