TargetTalk

Hi,

I've been shooting for a while but it's always been in a University club where the technical information is dilute at best...
I have variable iris' on front and rear sights of my rifle and was wondering which size to go with for 50m prone shooting

my rear sight has 0.5-3.0 and my foresight has 3.0-5.0

Thanks in advance :-)

What is your sight radius and do you use an eagle eye, what power if so?
Ed

Hi Ed,

Sight radius is approx. 30.5"/77cm
Currently not using an eagle eye

Xavier

For Prone I'd say 1.2mm at the rear, and 3.8mm at the front.

The front should not be too tight around the target. The inner edge of the aperture looks very sharp, but it's actually blurred by light refracting off the edge. It's good to keep this well away from the target, to avoid overlapping the target. The blurred edge means you still see light, even when the ring overlaps the target. If the foresight is a tight fit, you may not notice that it's overlapping. Some very good shooters use a tight foresight, but they have a very steady hold.

Depending on your sight radius, and personal taste you may find an aperture between 3.6mm and 4.2mm works. This may change with light conditions, as brighter light makes the target appear smaller, and vice versa. I also find the thickness of the foresight ring plays a part. To my eyes, a thinner ring suits a slightly smaller aperture, and a thicker ring a larger one.

The rear aperture shouldn't be too small. Although a smaller aperture increases your depth of focus, the sight picture will become dark, which strains your eye. A prescription lens for shooting will a clear sight picture, so you don't need a super tight aperture. Again it may change according to the ambient light; open it up a little in very overcast conditions or on gloomy indoor ranges.

Good info from Tim.
Try different setups till you find the one that works for you but 4.0 front and 1.2 rear are good starting points.

Ed

Thank you both for the help- really appreciate it!

I suggest you take a look at this article. Lots of good information here:

https://www.usashooting.org/library/Ins ... b_2011.pdf

Very good article, thanks

In addition to the excellent advice above :

I believe that the size of the rear iris is somewhat dependent on the nature of your eye - a small aperture will give better depth of field allowing the foresight and target to both appear sharper BUT if your eyes are less than perfect you will get greater optical distortion.

With a small aperture, light passing through the Rearsight only intersects with a small area of your cornea/lens and any imperfections will be exaggerated compared to a larger aperture where the distortion get "averaged out" over a larger area. A 1.5 aperture is nearly double the area of a 1.1 aperture.
With the larger aperture you lose some depth of field but with an appropriate corrective lens (search for Art's posts on Hyperfocal Distance) you can mitigate that to a large degree.

So, Rearsight aperture is a compromise based on your eyes. Personally I'm sometimes up at 1.6, others I know are on 0.9 or less.

K.

For me rear aperture varies wildly with light, on a sunny day I go down to 1.0-1.2 but at night its 2.2

...and then we are onto the subject of eye relief, ambient light levels and the resulting dilation of your pupil.

Eyes are tricky little things.