An optical adventure in a new arena

I recently had a nice opportunity to apply the insight into optical principles I have developed during my work in photography to a wholly different field. I thought I'd share it with my colleagues here.

A while ago, I was contacted by Robert Burdge, like me an electrical engineer, but also an avid precision target shooter. He told me that he had noticed an unexpected effect in the behavior of a certain common type of rifle sight. He was looking for an explanation in terms of optical theory, had seen some of my writings in that field in the context of photography, and asked if I could help him determine what was going on.

I was able to do that, and we jointly wrote an article that explains the phenomenon, the optical principles that bring it about, and its implications on rifle sighting practice, which are quite startling.

You might find this interesting. The article is available on my technical information site, The Pumpkin, here:

http://doug.kerr.home.att.net/pumpkin/index.htm#ApertureSight

Hi Doug:

It's why a real target front sight also has an aperture and not just a post. In fact, most will have front tubes that allow you to interchange disks with a selection of different posts. In this fashion, you essentially center a front circle inside a very closely fitting rear circular aperture -- the rear apertures on any good target sight are also changeable to help match the relative sizes between the two and/or adjust for lighting changes -- and then the post or pin disk you inserted in the front is already centered. The Lyman 17A is a very basic version using this principle: http://www.outdoorsuperstore.com/product.asp?manufacturer=LYMAN&model=17A+TARGET+FRONT+SIGHT


Secondly, in a conventional peep sight set-up with just a post or hooded post up front, you want the rear aperture not too close to the eye. In this way, you mitigate the effects of parallax between your eye and the rear peep, which in turn improves parallax and alignment between the rear peep and front post.

(In a prior life, I was a competitive target shooter...)

Cheers,

Hi, Jack,

Jack_Flesher said:

In this way, you mitigate the effects of parallax between your eye and the rear peep, which in turn improves parallax and alignment between the rear peep and front post.

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Yes, except in reality that parallax doesn't really happen (the point of our article)!

We now have a credible report of this being verified many years ago in live fire experiments by two military precision firing teams. But none of the "brass" were interested in its implications.

Thanks for your input.

Best regards,

Doug

Doug Kerr said:

Yes, except in reality that parallax doesn't really happen (the point of our article)!

Click to expand...

Parallax with iron target sights does happen -- However, depending on how close to the shooter's eye the rear aperture is, and how well the shooter repeats their "cheek" to the stock, it may not be significant.

The average target rifle is probably capable of 1/2 - 1 MOA accuracy in a perfect environment. If the effects of parallax are 1/4 MOA (significant for parallax) they still impart very little net effect on the system's overall accuracy. When the sight system is optimised, and the shooter uses perfect form, the effects of parallax are mitigated to probably 1/8 - 1/16 MOA and thus all but irrelevant for a shooter using otherwise proper technique.

Hi, Jack,

Jack_Flesher said:

Parallax with iron target sights does happen . . .

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If by "iron sights" you mean the type in which the rear sight does not have a small aperture, then indeed parallax shift will occur.

Situation "A" in my ray tracing Appendix essentially shows this (even thought I don't mention the connection).

Best regards,

Doug

Doug Kerr said:

If by "iron sights" you mean the type in which the rear sight does not have a small aperture, then indeed parallax shift will occur.

Click to expand...

No, I actually meant the aperture set... No matter, this is a photography forum and not a target shooter's forum

Best,

Doug,

What is the take home lesson for photography, say with a Graflex and a target for and after set of rings and squares to compose?

Asher