Spotting Scope Resolution at 1000 Yards (in Ideal Conditions)
While attending the CA Long Range Championship a while back, we had the opportunity to test the performance of a high-magnification (63X) spotting scope in near-ideal conditions (maybe the best I’ve ever witnessed). On the event’s last day we arrived at 5:45 am, literally as the sun was cresting the horizon. I quickly deployed our Pentax PF-100ED spotting scope, fitted with a Pentax SMC-XW 10mm fixed-power eyepiece. When used with the 100mm Pentax scope, this 10mm eyepiece yields 63X magnification. Befitting its $359.00 price, this eyepiece is extremely clear and sharp.
At the crack of dawn, viewing conditions were ideal. No mist, no mirage, no wind. The first thing this Editor noticed was that I could see metal nail heads on the target boards. That was astonishing. As soon as the first practice targets went up, to my surprise, I could see 6.5mm, 7mm, and 30-caliber bullet holes in the white at 1000 yards.
That’s right, I could see bullet holes at 1000. I know many of you folks may not believe that, but there was no mistaking when I saw a 7mm bullet cut the white line separating the Nine Ring and Eight Ring on the target in view. (I was watching that target as the shot was fired and saw the shot-hole form). And when I looked at the 30-cal targets, the bullet holes in the white were quite visible. In these perfect conditions I could also make out 3/8″ bolt heads on the target frames.
The Human Factor
When viewing the bullet holes, I was using my left naked eye (no safety glasses or magnification). I also had a contact lens in my right eye (needed for distance vision). To my surprise, while I could see the bullet holes without much difficulty with my left eye, things were fuzzier and slightly more blurry with the right eye, even when I re-focused the scope.
Then I invited 3 or 4 shooters to look through the scope. One younger guy, with good eyes, said immediately: “Yeah, I can see the holes — right there at 4 o’clock and seven o’clock. Wow.” Some older guys, who were wearing glasses, could not see the holes at all, no matter what we did to the scope’s main focus and diopter adjustment.
The lesson here — if you have to wear glasses or corrective contact lenses, just that extra bit of optical interference may make a difference in what you can see through the scope. Basically anything that goes between the scope eyepiece and your eyeball can degrade the image somewhat. So… you may be better off removing your glasses if you can still obtain good focus sharpness using the diopter adjustment and focus ring. I did the left vs. right eye test a half dozen times, and I could definitely see small features at 1000 yards with my naked eye that I could not see with my right eye fitted with a contact lens. (I did have to re-focus the scope for each eye, since one had a corrective lens while the other did not.)
Mirage Degrades Image Sharpness and Resolution
The “magic light” prevailed for only an hour or so, and then we started to get some mirage. As soon as the mirage appeared I was no longer able to see raw bullet holes, though I could still easily see black pasters on the black bulls. When the mirage started, the sharpness of the visible image degraded a huge amount. Where I could see bullet holes at dawn, by mid-morning I could barely read the numbers on the scoring rings. Lesson: If you want to test the ulimate resolution of your optics, you need perfect conditions.
Chromatic Aberration Revealed
As the light got brighter and the mirage increased I started to see blue and red fringing at the edges of the spotting disk and the large numerals. This was quite noticeable. On one side of the bright, white spotting disc you could see a dark red edge, while on the other side there was a blue edge (harder to see but still present).
The photo below was taken through the Pentax spotter lens using a point and shoot camera held up to the eyepiece. The sharpness of the Pentax was actually much better than this photo shows, but the through-the-lens image does clearly reveal the red and blue fringing. This fringing is caused by chromatic aberration — the failure of a lens to focus all colors to the same point. Chromatic aberration, most visible at high magnification, causes different wavelengths of light to have differing focal lengths (see diagram). Chromatic aberration manifests itself as “fringes” of color along boundaries that separate dark and bright parts of the image, because each color in the optical spectrum cannot be focused at a single common point on the optical axis. Keep in mind that the Pentax does have “ED” or low-dispersion glass, so the effect would be even more dramatic with a cheaper spotting scope.
  CLICK HERE to view LARGE PHOTO that shows aberration more clearly. |
If you wonder why top-of-the-line spotting scopes (such as the $3900 Leica APO-Televid 82) cost so much, the answer is that they will deliver even LESS chromatic aberration at long range and high magnification. With their exotic apochromatic (APO), ultra-low-dispersion glass, a few ultra-high-end spotting scopes can deliver an image without the color edging you see in the photo above.
The Pentax PF-100ED is a heck of a spotting scope. Any scope that can resolve bullet holes at 1000 yards is impressive. But if you want the ultimate in optical performance, with minimal chromatic aberration, you may need to step up to something like the 88mm Kowa Prominar TSN-883 with Flourite Crystal lenses ($2450.00 body only), or the 82mm Leica APO ($3899.00 with 25-50X eyepiece).
EDITOR’s NOTE: The purpose of this report is to show what is possible… in IDEAL conditions. With this Pentax 100mm, as well as a Swarovski 80mm, we have often been able to resolve 6mm bullet holes at 600 yards. But again, that performance requires really good viewing conditions. By 10:00 am at my range, even with the 100mm Pentax at 75 power, seeing 6mm bullet holes is “iffy” at best. So don’t go out and mortgage the house to buy a $4000 optic with the hope that you’ll be able to spot your shots at 1000 yards. If conditions are anything less than perfect, you’ll be lucky to see bullet holes at 500 yards. The real solution for very long-range spotting is to set up a remote target cam that broadcasts a video picture to a screen at your shooting station.
Similar Posts:
- Seeing Bullet Holes at 1000 Yards — the Ultimate Optics Challenge
- Seeing Bullet Holes at 1000 Yards? Yes It IS Possible…
- Bullet Holes at 1000 Yards — The Ultimate Optics Challenge
- Seeing Bullet Holes at 1000 Yards — Yes It IS Possible
- Big Pentax Spotter on eBay Cheap
Share the post "Spotting Scope Resolution at 1000 Yards (in Ideal Conditions)"
Tags: Chromatic Aberration, Mirage, Pentax, Resolution, Spotting Scope
I have not seen this Pentax yet. But I can tell you that the new Kowa 883 88 mm has to be the clearest scope I have ever used. You have got to try it to believe the difference between this and other Kowas. Seated next to my 821 Kowa there is no comparsion at 1000 yards. I would love to try this new Pentax next to it.
Eric,
The Pentax PF100ED has been around for a few years. We’ve tested it side by side with a Swarovski 80mm HD and the Swaro is maybe a little bit sharper with both scopes fitted with zoom eyepieces. With the 63X 10mm on the Pentax, it is virtually as sharp as the Swaro, and the Pentax’s light gathering is better in early morning. The Swaro is much more compact, making it more stable on a tripod. Also we prefer the large focusing ring on the Swaro to the small diameter single knob on the Pentax. The Pentax PF100ED is a very long scope. We note that more modern designs have used computer-aided design to achieve high magnification in a shorter length. That’s a good thing.
We’d love to test the Kowa TSN-883 Prominar, the Swaro, and the Big Pentax together.
Nice report. It would be interesting to see how the xw 7 – (90 power) and xw 5 (125 power) eyepieces would perform on your Pentax 100 vs bullet holes at 1000 yards.
This might be the Zeiss 60 spotter referrred to above.
http://hudisco.com/spotter_60.htm
Price tag is just under 5 grand. Where will this price madness in a depressed economy end?
Same in Australia. We have seen 30 cal bullet holes in the white with the Leica spotting scope and with the March 80x scope.
But the conditions have to be perfect and the window for this to happen when a match is on is very small.
It is all about the conditions once you have good glass. Try shooting down here in South La. in the middle of summer. Even at 400-600 yards a 4″ shoot-n-see black dot dances around in the mirage like crazy. If the climate and atmosphere between you and the object you are viewing is not ideal you can have the best glass you can find and still not see what you are looking for. Think they are expensive scopes now wait till they figure out how to removed the motion from mirage and wind lol.
BTW, the Pentax PF100ED has been discontinued.
EDITOR: Geoff, you are correct. Fortunately, the wonderful Pentax eyepieces fit other still-produced spotting scopes in the Pentax line-up as well as spotters that take standard astronomy-type eyepieces.
30 years ago at camp blanding fl I could see 30 cal holes in the white at 600 with a 25x bushnell spacemaster jut about anytime I wanted to.
A few years ago a fellow had a Pentax ‘scope out at a 600 range I was at, we could see 6mm holes in the white that day.
Last Monday at Lodi WI around 1 PM at 1,000 yards I could barely see the AIMING BLACK thru my Palma sights because of the mirage present.
It’s ALL about CONDITIONS when it comes to seeing stuff that’s “way, WAY out there” no matter what’s aiding your eyes…
For NRA highpower, seeing bullet holes beyond 300yd is of little value. What is important is to see mirage as early as possible to ‘see’ the wind. If you want to see bullet holes, buy a camera system which is much cheaper than a high-end scope.
Steve: These are all good points. We agree 100% that a camera system is the best way to see bullet holes at long range. However, target cams are not legal at this time in High Power, F-Class, or long-range benchrest (where shots are not marked on the target).
Some of the high end scope mfg-ers should pay attention to CA and color seperation. Despite the claims of HD and ED glass, the fringing and CA is through the roof on high contrast items, on par with some $50 scopes.