Hey guys, question. A lot of people say that running an ARD (killflash) helps with the dot shape and size if you have an astigmatism. They often point out that it works the same as using the backup iron sight with the dot, but here’s my question- are they talking about a REAR killflash? Because if the killflash is on the front, you’re not looking through it as you are with an iron sight. It’s in front of the dot and lenses, not between your eye and the dot, so I don’t understand how that would help anything at all.
Iv heard the same thing, I don’t understand how the killflash Infront of the dot would work like that.
I’d be very interested in that if it did. Red dots look like a nice glowing glob to me.
The killflash doesn’t do anything for dot shape.
Flipping up the rear sight will generally help though.
What RDS are you using now? What does the dot look like to you?
I’m using an ML3. The dot isn’t bad but is slightly “comet shaped” with my contacts in; it’s still very usable. When I run out of these contacts next month I will probably get fitted for torus lenses. I’m really asking more out of curiosity than concern, and figured I’d strike up a thread on it to potentially save people $40+ of they are considering buying an ARD just to overcome an astigmatism issue.
my 2 cents: Killflash - no change. Rear BUIS give about a 50% improvement for me.
On a side note, I have an Aimpoint Comp M and the dot on high settings looks very oblong and distorted. I also have a Primary Arms micro and the dot looks much more like an actual dot to me without the use of irons. No idea why.
I’ve looked through a few Aimpoints with a killflash on the front and I never noticed it making any difference with my astigmatism.
If your ML3 is a 2 MOA dot, try to look through a Micro with the standard 3.6 MOA dot - preferably at the range in bright sun. I have significantly less flare with the Aimpoint Micro for some reason.
M4S w/ARD
I have VERY mild issues. If I turn the dot to the appropriate brightness, I see a VERY faint oval shape to it. I can still shoot ragged 1-hole groups with it at 25 yards, but to be technical, it is not PERFECTLY round.
The ARD makes ZERO difference.
Turning the dot to where it is the correct brightness for ambient lighting the dot works very well for me. No star-fish or lines or anything, just a very faint oval shape to it if I stare REAL hard at it, and the rear BUIS will result in a 100% perfect dot.
Correct. A killflash is on the wrong side of the dot to do anything for the shooter, who is observing it on the back end.
Avid/professional photographers are far more able to describe this in detail, but the wavetops of it are as follows:
The f-stop setting on a camera affects how open/closed the iris of said camera is, i.e., a wider or narrower opening. The primary function of this is to affect how much light is transmiting into the camera. Narrower = less light, wider = more light, but there are other effects.
To wit: the narrower an opening, the greater the depth of field of that focal plane. What does that mean?
Ya set the camera to “auto,” focus on a subject, snap the shot. The subject is in focus, but stuff in the foreground and background are less focused if not outright blurry.
Ya take the camera off focus, narrow down the f-stop (close the iris further), but increase the shutter speed to allow the film to be exposed to the light from the scene for a longer period, snap the photo. Subject is in focus, items in the foreground/background are either also in focus, or at least more sharply focused than in the “auto” shot of the same scene, where the camera’s brain-box is splitting the difference between a few hundred variables.
As I said, that’s a thumbnail; I have no doubts that a photog would nickle-and-dime me to death, but since this is a metaphor and since we’re not talking about taking a photograph…oh gawd please don’t!
The point is, if you view the dot through an aperture instead of just your bare eye, it can help tighten up the dot enormously for many folks, as will dialing down dot intensity (as mentioned above) to the point that it can still be seen/used, but so that the blooming that naturally occurs is reduced.
I was having a hard time zeroing at 50 yards with a magnifier. Sometimes the dot looked like a slash, sometimes like a cluster of grapes, and sometimes like a figure eight. My groups were horrible.
I put duct tape on the end of the magnifier where you look through and poked a tiny hole with a pen. Well to my surprise, I saw a perfect dot and was finally able to zero correctly.
Unless you shoot with that duct tape all the time I don’t know if i’d zero that way because of the possibility of perceived POI shift when you aren’t using it.
I have a little astigmatism also. With shooting glasses it becomes more noticeable than without. I’ll be looking to upgrade those again this year. I’ve tried a few. Even if the glass isn’t distorted it still increases the issue when I have a good cheek weld. Good tip using the rear buis to help eliminate the issue. Using an Aimpoint Pro.
I find that paying more attention to the target instead of the dot helps. I can zero better that way. Glasses fix it, but when you start to sweat they het in the way! I was taught that your natural hand eye will line you up all the time. It’s just getting use to it that’s hard to do.
No. An aperture isn’t a medium. All it does is alter the length of the focal plane, not bend/refract light like another layer of glass would. His aperture is simply one of tape, instead of a peep sight.
An aperture will certainly help with astigmatism and “old eye” focus issues. Of course anything like this will slow target acquisition accordingly… Ron
With a SR-15E3, I shot a group with irons at 50 yards, then with a T-1 at 50 yards.
I just flipped up the rear sight, and the dot was very nice and round, but the POI was about 3" low and 2" left.
Would this be more of a parallax issue as the dot was used in the bottom 1/3 of the T-1 or related to using it with the aperture of the rear sight? The rear sight is a KAC 600m.
Without a doubt a big POI shift. Shot it w/o the rear sight flipped up and like magic went right back to zero.
Damn, that’s a bit of a puzzler…THAT great a shift at that distance is outside the trend I’m used to seeing.
On the surface, it’s in the same vein as how putting tape or the like over the FO on an ACOG keeps the lit portion of the *insert reticle shape, here" from blooming. A group shot with the pre-tape reticle will differ from that of a tighter, more defined post-tape reticle shot group because blooming can and does make the apparent position of a reticle differ from that of the actual, non-bloomed shape of the reticle on the target.
We’re not talking about ACOGs, of course, but it’s still a lit reticle and the principle applies. Given that some folks are seeing bunch-of-grapes shapes, slashes, etc., it adds a variable that somewhat fits what you’re describing…with a shift that great being what prompts me to make s Scooby-Doo interrogative noise… under the same principle, BUT (of course, there’s a “but…!”)…
I’m not an eye doctor, and gynecology’s only a hobby. There’s nothing in my head that tells me an aperture would or should create the effect you’re describing, and it’s telling me that I need to dig deeper into how/whether parallax can be induced by something other than passage through a medium.
And, we’ve still got the individual eye behind the sight to account for…
That’s a long way of saying what amounts to “I got nuthin’,” innit? 
I didn’t have that much time to test it after I noticed that much of a shift.
Next range trip I’ll verify everything is on zero and try it again, and have another shooter give it a try.
The group with the shift was tighter than the group w/o the rear flipped up, all shots at 50y (there was only five per group) were touching but strung vertically. No other group I shot that day was strung vertically, so that was a bit odd as well.
The T-1 mount is a lower 1/3 Larue mount. I’m wondering if the results would be different with a absolute co-witness.