Thursday, April 19, 2012

Old Eyes and Iron Sights -- Part #6

Rear sight diopters --Testing and selection  


The long lonely bitter winter of 2011/12 is nearly over in Minnesota so I headed to the range to test rear sight lenses today.  I used my Elisio stocked Palma rifle with Phoenix Precision sights.   The front sight is a 22MM with .3 Anschutz lens. But first here is a web site to see a neat lens test kit. Click products and scroll down to see the kit. Pictured below is a single lens. 
There was no shooting was involved, just looking thru lenses.  I set the rifle up in sandbags pointed at a 600 yard target.  The first test was without the Micro Sight from Creedmore or Sinclair.  The quality on my sight picture was about an 8 to 8.5 out of 10 with just a Gehman iris in the rear sight and the .3 lens in the front sight. I then started with the +. 100 lens between my glasses and the rear sight. I went all the way down to -.100 in .25 increments. Nothing improved or changed much that I could see. The front iris around the target was very sharp but the target was a little fuzzy on all 8 lenses.
I then installed the Micro sight and repeated as described above. At +.100 down thru +.25 everything was still fuzzy and unacceptable.  At -.25 thru -.75 the front iris and target were better, back to the 8.5 out of 10 area. At -.100 and below the picture deteriorated rapidly.  Keep in mind I’m NOT an eye doctor and do not play one on TV and thus can’t explain the below phenomenon. I looked thru the sights with the Micro Sight lens taking a few quick looks as if taking a quick shot  then looking away trying to memorize the sight picture.  When putting the negative power lens between glasses and rear sight there was a slight but noticeable improvement. Upon removing the test lens from the sight picture there was a very noticeable reduction in the quality of what I saw. There was much more of a reduction than the improvement seen with the lens in place.  It went down to about a 5 or 6 out of 10.  When again moving the lens into the sight picture there was a slight improvement and a major reduction when removing it. In other words, the original sight picture was not as good as I remembered it to have been prior to looking thru the test lens. This phenomenon was apparent with -.25 thru -.75.  Perhaps it is a focus issue. Maybe it takes a few seconds for the eye to adjust to the change going one way but not the other.  Or not!
A shooting friend/tool designer has designed a neat little device for holding the test lenses in place on the rear iris. It clips on to the rear iris thus eliminating any movement when being held between 2 fingers. See below picture of the prototype. If it works out we may market them at $79.95 at Camp Perry
After this testing I removed the Micro Sight and installed a Gehman 9530 rear iris. This is the model with the adjustable iris and focus built in. The target immediately looked about 3 times bigger but still very slightly fuzzy around the edges.  It was clearly easier to hold on this big target and see very small movements.  With the other lenses I could not see the small movements and I have no idea if this is a good thing or not. 
The maker of these test lenses recommends that the testing be done at the intended shooting distance. I would assume the results seen at 300, 500 and 600 yards or 800, 900 and 1000 would be very similar. If not it will be totally impractical if one needs a different lens for each yard line.  As you might imagine, the zeros change SUBSTANTIALLY when changing lenses in the front or rear. 
After this fun filled day of testing I decided to try more or less the same tests at 100 yards.  The improvements or reductions seen at 100 yards were not nearly as apparent as they were at 600 yards. My conclusion is that the Gehman 9530 is best for me on my Palma rifle. Your mileage may vary. However I may order a -.50 to use in conjunction with the Micro Sight on one of my MRP rifles.
And finally, keep in mind your results and zeros will be different if you use a .37 or .50 front lens.
 So many rifles, so many lenses, so much testing, so little time.
   Capt. Bob Peasley 
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