I noticed image distortion this weekend with my SWFA 10x scope that I use as a test scope. I was aiming at a black diamond with a smaller orange diamond in the center. The orange diamond looked more like a circle and it was not centered in the black diamond. It was off center in the 5 o’clock direction. Distance was 200 yards and parallax was adjusted as best as I could.

I do believe accuracy suffered as a result.

Anyone else notice this?

Tony.

On second thought:

I could conceive of an increased elevation mount’s having an effect on image distortion if it were necessary to dial down to a significant degree. Rather than looking through the center of the internal lenses, you’d be looking though them closer to the top(?) edge and it’s not uncommon for optical quality to fall off at the edges.

What say the experts?

Let's start with the assumption your pre-20-MOA rail is perfectly parallel to the bore. If it isn't parallel, then the results might be a little different.

Zeroing to 100 yards probably consumes 3-4 MOA of up adjustment on the scope. Dialing up to 200 yards probably consumes another 2 MOA of up adjustment. So now you're at 5-6 MOA of up adjustment in elevation -- above dead center on the scope.

The 20 MOA rail reduces this to 14-15 MOA below center on the scope.

All scopes have better clarity in the center of the scope. I believe yours has over 100 MOA of internal elevation adjustment. Being 5 to 15 MOA on either side of center shouldn't affect clarity. Or at least affect it enough for human eyes to see. But if being only 15 MOA off center on that scope does affect clarity, then the scope has total shit optics -- and it's time for a quick trip to the trash can.

Possible issues include:
- You weren't looking through the center of the optic on the 200 yard shots.
- The 20 MOA scope changed the scope setup enough that you no longer are looking through the center of the optic. The 20 riser does change the optimal eyebox position slightly, but in my opinion most people adapt.
- You cheek welds were inconsistent from one day to the next.
- Our eyes change from day to day. Some days for the better, others not so much.
- Your parallax setting wasn't as good as it could be.
- The scope lenses need cleaning.
- The atmospheric conditions were noticeably different.

Or possibly, a better scope is required.

Looks like the scope has +/- 20 mils so 20 MOA is +5.7 mils. I’ll have to go and check how far it is from the limits.

Sorry for the delay in responding; work is a bear and really gets in the way of important stuff.

What is being described looks like a bad case of CA to me. CA will become more apparent as you move away from the center of the lens, in other words, as you bend the light more.

Also, you are aware that the bottom of Coke bottles are repurposed as lenses for SWFA riflescopes.

Thanks! So I’m not crazy then. Reading up on CA (chromatic aberration), I understand now that the colors can have different focus shifts in vertical and horizontal planes as well as a different focus spot for different wavelengths (colors).

In my case, I had both TCA and LCA which resulted in a blurred and displaced orange diamond while the black diamond was in focus and where it should have been.

I hadn’t noticed this before because I rarely use orange targets. Orange seems to be more distorted with this scope.

Looks like I need to find a better test scope. I’ll have to put it in the budget. I’ve always been partial to Pepsi anyway. Vortex?

Tony.

It's always dangerous to try to diagnose such issues on a discussion forum. I'm simply saying that's what it looks like and I could be wrong.

Vortex PST is good. Tract Toric would be good also. Around $1000 or less.

If you have a price limit let me know.

quote:

Originally posted by benny6:
I hadn’t noticed this before because I rarely use orange targets. Orange seems to be more distorted with this scope.

Regardless of the scope I use, orange targets don't always work the best for me. Orange lines on a white background are good, especially if the lines are just slightly thicker than my reticle. Small orange dots are generally pretty good, both for white and black backgrounds. I have trouble with precisely shooting large & solid orange shapes against black backgrounds, regardless of scope brand or quality. It's probably a limitation of my eyesight. Nobody ever called me "ol' eagle eyes".

Vortex is one option for a test scope. If you're looking at the PST line, make certain it's a Viper PST Gen 2. IMO the Gen 1 models were lacking in optical quality. I have a 2-10x PST Gen 2, and it's a decent scope for the money. I have it on an AR-15, which I find capable out to 500-ish yards. IMO a better Viper PST test scope for client's rifles is the 3-15x or the 5-25x. Of course, if you really want quality optics from Vortex, you should look at their higher-priced products. Razors may be more than you want to spend, but the glass is better than Viper.

There are many scope options on the market. I wouldn't test a client's rifles with an SWFA. Well, at least clients who are interested in accurate rifles.

Start with both a budget and your shooting expectations.

Sounds good! I'll look into the Viper PST.

I've had the SWFA for years and it's probably been on over 50 different rifles in that time. It was good enough for me to see that a rifle was decently accurate before I shipped it out to a customer.

It was good enough for me to say "Hey, it shot good for me before I shipped it to you..."

I don't normally use targets with orange dots or diamonds and now I'm remembering why. Someone gave those to me and I was just using them up.

I normally use SR-1's with a blue or green 3/4" dot in the X-ring, or I use a white or fluorescent green sheet of paper with a black crosshair drawn with a carpenter's level.

Thanks for all the help, friends.

Tony.

The question of test targets is an interesting one to me. Target design does make a difference because of the “aim small, miss small” principle. Using a large solid color circle, for example, makes it difficult to ensure that we’re aiming at the exactly the same place for every shot. That’s especially true when trying to center a black reticle on a black bull’s-eye type target. I’m always a little surprised when I see a YouTube tester of a gun or ammunition use a target like that because it increases the chance that aiming errors will affect the results.

I much prefer Mountain Plains Industries targets for precision and accuracy tests. Their diamond shape targets align with crosshairs; the central dots provide a small, precise aiming point; and the blue color provides good contrast with both the white background of the target and scope reticles.

http://www.precisionplustargets.com/hiviztargets2.htm

quote:

Originally posted by NikonUser:


Also, you are aware that the bottom of Coke bottles are repurposed as lenses for SWFA riflescopes.

Is that the case across their whole range of riflescopes?