Bushnell Elite 429470 LMSS 8-40x 60 (2 Viewers)

8x-fov 4.76* 250' @ 1000yds - 40x 0.95* 50' straight eyepiece. Close Focus 30'.

Eye Relief: 30mm two click - Waterproof - Length: 12.7” - Weight: 37.1 oz.
Aluminium body. MIJ non reticle version. Available 2013 Since discontinued. Model # 780840

If the zoom/fov progresses at the same pace then 20X/3.38* 3.33ep w/half-way mark 24X 2.855* 2.5ep for highest/brightest.

Anybody know anything about this spotter?

ETA: A mite unusual 5-1 variable starting at 8X to boot. Not sure about the claim of ED Prime, whateavah that may be, glass as in how much/how well corrects CA. Would rather have more fov than 30mm ER, but deems da breaks. Likewise, I'd enjoy a bit more objective although I cannot complain about the weight. Besides those characteristics spotters that magnification starts in the single digits don't exactly grow on trees.

I was hoping to use this freehand at low power acquiring targets then zoom in to frame a larger view. I'm not sure how realistic the idea, yet a notion nonetheless.

I have the Russian Tourist 10-40x60 scope.
Really strange mottled gold finish.
Even I find this to be awful, and I am tolerant of poor scopes.

There is the Russian/Soviet 8-24 x40, which is good, but only 3x zoom.

I had two samples of the cheap, possibly Japanese, 30-120x 80 scope, which I liked because it was very useful on planets at 120x. It had almost no internal blackening and had shiny reflections, also the eyepiece on one was off centre.
Taking it apart and painting it matt black would have made it much better, but I never did this.
I think that they were available in Red, Grey and Blue.

Zooms are not usually linear with FOV. They usually rapidly expand FOV from lowest magnification then slow down.
They are often not parfocal, so that one has to refocus.
Often I would use the zoom for fine focus.

The Bushnell sounds interesting at least for me, but I doubt a 5x zoom is up to 3x or 2.5x zoom standards.
It seems expensive.
But it would be worth trying.

The Russian scopes have very long close focus. Other scopes usually have much better close focus.

Binastro said:

Zooms are not usually linear with FOV. They usually rapidly expand FOV from lowest magnification then slow down.
They are often not parfocal, so that one has to refocus.
Often I would use the zoom for fine focus.

The Bushnell sounds interesting at least for me, but I doubt a 5x zoom is up to 3x or 2.5x zoom standards.
It seems expensive.
But it would be worth trying.

The Russian scopes have very long close focus. Other scopes usually have much better close focus.

Click to expand...

I tried contacting Bushnell about additional focus info to no avail. The 8X & 40X FOV is listed & that's it, so I'm guessing. I had read that zooms tended to be narrow on the bottom progressively wider towards the top end in relationship to FOV/X. Even though the FOV decreased as the magnification went up the top magnification had more FOV on average than the lower power. This was a riflescope being discussed, so even if correct it wouldn't neccessarily apply here. Plus, I can't find that post.

As somewhat of grasping for straws I looked up the M5 20X56 Nikon bin; 3.3* AFOV 59.9* fov 173'. Actually I hope you are correct as I would rather have more FOV on the bottom end, 8-24X. All I did was average the difference in the two given fov spread over the remaining magnification levels 1X at a time. I had serious doubts about that being correct.

It has but one focus ring behind the magnification ring. They advise focusing at 40 & working down. For me I'm thinking 24-30'.

I presume I'm buying a return/demo for clearance price <6 bills TTD & it was the only one available at that price.

I forgot to post the close focus of 30' thanks for jogging the ole noodle.

Basically the optics of a rifle scope with a lens erecting system. AFOV is very narrow like a rifle scope, 38º throughout the zoom range. Since the objective's focal plane falls in front of the erecting lenses its focal ratio would be very low with high aberrations almost guaranteed. Also notice the objective is vignetted to 40mm at 8x.

Sorry, I was unclear.

The AFOV normally rises rapidly from lowest then slows down to highest magnification, but the true FOV is largest at the lowest magnification. But not by much.

Usually they perform best somewhat below highest power. Perhaps 2/3 the way from lowest to highest power.
At the lowest power they usually have tunnel vision.

However, high end glass with 3x or 2.5x times zoom achieve fairly wide fields at all powers.

The Nagler planetary zoom eyepiece that I have is 3mm to 6mm. Only a small ratio and small field. I think the same AFOV throughout. I will have to check.

As an astronomer AFOV is much more important to me than real FOV.
But I think birdwatchers are more concerned with FOV.

With the Russian scopes the closest focus changes and can be very far indeed at highest power.

P.S.
Nikon use ISO values for AFOV (using Tan half angle calculation I think), which may not be the case for other makes that just multiply FOV by magnification.

Makes sense Henry. As always thanks for sharing your expertise.

Not a lot in reviews though I found this clip w/LMSS set at 25X, wonder why?, & Samsung phone at 4X spotting yotes at 800+ yds at Lake Las Vegas 100* temps. That's their claim anyway.

https://www.youtube.com/watch?v=GOxmmtjnEcI

Probably more of me being unclear than you. Anywho, later this week it'll be in & I'll be able to take 'er for a spin. I do fairly well hand-held w/higher power bins. Whether I can convert that to this scope, along w/focusing at varying powers on the fly/maintain consistent ER, remains to be seen. It would be nice if I could run up to 24-28X for brief moments.

Binastro said:

However, high end glass with 3x or 2.5x times zoom achieve fairly wide fields at all powers.

The Nagler planetary zoom eyepiece that I have is 3mm to 6mm. Only a small ratio and small field. I think the same AFOV throughout. I will have to check.

As an astronomer AFOV is much more important to me than real FOV.
But I think birdwatchers are more concerned with FOV.

With the Russian scopes the closest focus changes and can be very far indeed at highest power.

P.S.
Nikon use ISO values for AFOV (using Tan half angle calculation I think), which may not be the case for other makes that just multiply FOV by magnification.

Click to expand...

I'm sure the 2.5-3X variable is the better ticket. The 3X seems to be the most popular format in zoom whether exchangeable eyepiece or permanent/built-in.

The 6-3 Nagler is listed as 50* & basically parafocal as I understand.

The dealio for me is beggars cannot be choosers. None are asking me opinion on a new line of spotter. The traditional 20/23-60/65X is nowhere near what I seek.

I brought up the M5 20x56 3.3*/ 170' for comparison & likewise the Vortex Vulture 15X 4.3*/226'. At 8X/4.76* the LMSS spotter will have precious little more fov than the Vulture at close to half the magnification level. Perhaps the LMSS will make 10/10.5X in 4.3*.

That's OK, has to be, I can hit that & the trade off is the ability, hopefully, of performing a quick zoom into the mid twenties power once I've framed the target at lower power. The M5 shows a nice view, but one must practice to coordinate that narrow beam to moving target in a timely fashion.

I would enjoy a spotter in the 12/14-30/32 X 65/70 range w/removable armour. I do not see that hand-held niche market happening, so I'm severely limited in options.

As is this is it & w/price drop along w/90 day return, new unopened r-i-g-h-t, it's worth a shot.

As always, YMMV ...

The Mirador 30-120x70 Maksutov type scope is rare and brilliant. 4x zoom. It also takes 1.25 inch fit eyepieces. But higher power than wanted.

There is a Bushnell? 15x-60x60 from memory or maybe Swift?

The Opticron stabilised monocular might work with the zoom eyepiece.

It may be that the Russian Tourist 10-40x60 is as Henry described a relay system scope, which may be the reason for excessive CA etc. and poor performance.
So ED glass seems a necessity with this type of scope.

I have a 25x (maybe30x?, but I think 25x) to 125x80 binocular, which actually works well up to 80x. After that it becomes soft.
Amazingly it is well aligned up to the true maximum of 135x.
But I prefer a spotting scope.

Minolta made a 100mm to 500mm camera lens, which I had. It was good. With a 10mm eyepiece monocular converter that is 10x to 50x. But it is big.
Vivitar also made a 100mm to 500mm I think.
There may be 80 t0 400mm camera lenses, but I think even bigger than the Minolta. They would give 8x to 40x.

There are massive T.V. zoom lenses by TTH with about 30x zoom and 25 to 30 elements. This is really why multicoating and tuned multicoating became a necessity.
These are seen on T.V. and the performance is impressive.
Sometimes cameramen zoom up from say a cricket match to the Moon, and the Moon's detail is very good.
Probably £100,000 each lens.
I think there are super zooms that may go beyond 100x zoom.

The Sigma 50-500mm f/4 to f/6.3 lens might be fun with a 10mm monocular converter.
5x to 50x.

The weight is listed as 1.8kg plus, so with the monocular converter about 2.1kg.

Perhaps were I handy. Here's another in 12-40 x60 a Gold Ring Leupold that claims mirrors folding the beam also discontinued being around since at least 2009.

https://www.leupold.com/spotting-scopes/hd-spotting-scopes/gr-12-40x60mm

No reticle either, yet also a front focal plane design. Has about the same fov at 40X, 52', coming up w/168' on 12x 3.2* which I suppose is due in part to the longer focal length. Howevah it does come in w/3.33-1 variable. Might it be safe to presume the sides would be cleaner? Not quite sure how that humpback design would handle, but I've seen them around five bills blemished. Appears to have a ring focus as well.

I've never seen that Leupold before.
Similar to the Yukon folded refractors, but probably better quality.
Cabela's site says Made in USA?

I have the Yukon, From memory 20-50x50?
They are not robust, a secondhand one is faulty. New one O.K.
Yukons generally poor coatings, variable quality and not robust.
Their adverts are over the top.
Also the 6-100x100 folded refractor, which I like, but is fragile. Very low weight. Very useful at 100x.

The folded refractor path Leupold would allow a longer focal length objective for better correction.

An 8 inch aperture folded refractor was doing the rounds in England changing hands. It was compact for a long focus refractor.

P.S.
It is a 20-50x50 wide angle zoom Sibir Optics folded refractor spotting scope. The used one has a faulty focus mechanism.

The Yukon 30x50 folded refractor binocular is one of the most impressive high resolution binoculars that I have seen, maybe unique. It is only let down by poor coatings. very nice star images. I probably got a good example.

I wondered as Bushnell has a similar folded light as the Leupold for around $500 US.

The Humpback Leupold apparently came in two versions, over the years, w/later being HD version. I think. I can appreciate folding light for a more compact scope. Though from what little I've read mirrors are more susceptible to scatter

I read a file on CA/light scatter in diagonals, mirror Vs. prism, aluminium Vs. silver Vs. dielectric, in F/8 Vs. F/6.25:
http://www.baader-planetarium.de/news/mirror-Prism-Dielectric-Diagonal-Comparison_2014-03-06_v2.pdf

The F/6.25 is considered fast where the Celestron Regal spotter is F/5.4. The Bushnell LMSS is listed at 12.6" in overall length w/60mm objective. If 12" of that is focal length the best it will run is about F/5.1.

This does not take into account the actual length of travel through the prism just a rough idea based on overall length. Yet, If I do the same to a Nikon M5 20x56 measuring from occular to objective I end up at F/3.4. Even if I drop an inch on the Bushnell to 11", F/4.65, the Nikon would require focal length of 10.25" for the same.

As refractor telescopes go spotter are fast, yet slow next to bins. Maybe someone will design a 125mm objective low power spotter, modeled after a WWII era bazooka, that could be thrown on the shoulder for support. Two inch eyepiece for wide view w/carbon fibre body to dial back the weight.

UPS dropped off the LMSS yesterday at USPS. A shame they didn't bring it by the house as the temps in the afternoon were in the 70's w/partly coudy skies. No such luck today.

Nikon Fieldscope 13-30x50mm ED Straight-Product 8320- for around 7 bills looks promising. Would prefer larger objective but focus ration 2.3 Angular Field of View (Real) 3 ° @ 13 x - Angular Field of View (Apparent) 40 ° @ 13 x. ER 12.9 coming in under a lb & 1/4. Uses the forward placed knob for focus though close focus of 9.8'. 2.5mm sweet spot coming in at 20X. The LMSS FOV is around 4.17* at 13X. Regardless of aberrations, field curvature &/or soft edges I need the extra fov to help locate targets.

The less expensive Bushnell Elite 60mm Straight View Spotting Scope PC-3 Phase Coated, Waterproof, Rainguard Coated 15-45x w/o ED glass shows 2.4 degrees @15x, 1.25 degrees@45x-Field of View at 1000 Yards 125 Feet @ 15x, 65 Feet @ 45x.

The LMSS should be around 208' at 15X, if linear, but 50' at only 40X. The 'extra' FOV appears to be loaded on the low end. Where the less expensive Elite has 15' more FOV at 5X greater magnification.

My Jaegers objective coated doublet refractor 123mm clear aperture, although sold as 5 1/8inch. 630mm focal length.
With the Kodak 1940s hard coated eyepiece it gives 16x123 with 4.7 degree field.
The Kodak eyepiece is 2.5 inch wide but the scope has a 3 inch drawtube.
Some of these Kodak eyepieces use radioactive glass, but not mine.

I used this scope extensively, using 16x, 2 inch fitting Erfle 20x, 2 inch fitting 6 element EWA 35x, RKE 80x, Ortho 105x, and Swift eyepieces, one thorium glass one not, 145x eyepieces. A Clave 3mm gives 210x but reveals a slightly off centre objective.

It is not folded.
Probably my most used scope.

Thanks for sharing. I'd like to peak at & through that scope.

I checked SN w/Bushnell they confirm production date of 2016. No ocular cover but does have objective cover w/stretch arms, locked into side posts, allowing cover to come out/up/back. Small square cut out of the bottom in case you mounted scope on a rail. This model, w/o reticle, is still in production. At 8x, viewing chainlink gate 100 yds, sharp in focus 85-90% w/40X sharp 95%. CA center low-med/low, some conditions worse than others/some folks more sensitive than others, picking up intensity last 15-10%.[ETA: This morn completely overcast looking up at trees 100 yd away SSW the M5 20x56 handles CA better than the LMSS at 20X. The LMSS at 8.5X handles center CA better than the HG Minox 8.5x52. The LMSS under such extreme CA conditions shows CA faster, before reaching the halfway point to the edge, than I noticed yesterday. Being in exact focus is crucial for controlling CA. Looking through a series of trees at various distance makes it hard to dial in. Again, all that I see is handheld.]

At 30' 8X cardinal perched on feeder bright showing minute water droplets. As I zoom out to 25X I walk forward to 25' to stay in focus[measurements roughly]. I could barely keep the male cardinal in the FOV. I detect no pincushion the globe effect/rolling ball is obvious though nothing is spinning. Centering a large tree trunk too close to focus at 8X in static view the center comes towards me. The globe effect is not as pronounced as it is in the riflescope. Even then in the riflescope it's only full blown, which for me is more of a half-globe/hemisphere rollin', from 3.5X to 8.5X then tapers off by 9X[right eye]. After that power I know it's there though there's no more spinning. More as a ripple. It's possible if the spotter went to a lower power that I would see the same as the riflescope. Perhaps I cannot pick up the spin starting at 8X.

The two-click eyepiece extends around 10mm beyond the ocular. That's an eyeball measurement plus I have to rest the eyepiece on me nose. I see no problem wearing glasses w/eyepiece fully extended. I would've preferred the eyepiece to extend the full 30mm away from the glass so I could rest it against the eye socket.

There were eight male-female attachments at various points for mounting accessories. I unscrewed all of them. Handheld the weight isn't bad in part due to the short overall length. I noticed a checker/diamond cut around the ocular. CCW brings the ocular all the way back/out. At that point close focus drops to 20'. I'm not sure if I can see infinity in focus because of the clouds. Adds/subtracts from the focus ring range as a mini-focus ring though instead of going around on the same plane it moves in or out. Perhaps this is an adjustment for varying strengths of prescription glasses. [ETA: perhaps that adjustment for for a reticle that this model doesn't employ. I'll call Bushnell & inquire.]

The view is slightly wider/significantly brighter, at the 100 yd gate, than the M5 20x56.[Bear in mind I have a mild cataract in me left eye whilst the dominant right sports an aspheric IOL] At 15X nowhere near the width of the Vulture 15x56. I had to drop down to 10X for reasonable facsimile of the Vortex FOV. I had to guesstamate 12x, but it was right there close w/Conquest 12x45. Nowhere near as wide as Conquest 10X40 at 10X. The mag dial is marked 8/10/15/20/25/30/35/40. I didn't try to be that accurate. I'd throw up some bins, look at the woods, then follow w/scope set, according to the dial, to the same power. Evah so roughly.

The eyepiece movement is junk. If you go all the way in it's hard to grab/twist bringing it back out. Not smooth or anywhere near say the Leica Trinovid HD quality that I previously returned. It isn't nearly long enough anyway, so I'll just leave it out. Those are the only complaints to date. Body colour is sand. Looks as a dull medium tan w/hint of green hue to me. [I pulled off the rubber eyepiece from a broken zoom, turned it around making A snug fit w/enough length. It'll take some more work, yet for the time being it's better than the original].

The focus & Mag ring are w/o play, smooth though not silky smooth. No fingertip manipulation. Wrapping index finger w/thumb works well. They may loosen w/time, yet finger w/opposing thumb wrap will surely always be required. Setting the focus at 25-30' worked well from 8X up. Allow me to imitate a white house press secretary or two.

"Look! For the price this is the biggest/brightest view ever. Period!"

Well, perhaps in the moment a mite carried away though overall for the weight/view & 540 clams new TTD 'tis hard for me to find fault. Now all I need are clear skies. That might take a few days.

As always YMMV ...

ETA: I would prefer magnesium body over aluminum for less weight. As well I have no use for eight threaded spots to mount rails or the armour that is formidable. As Mick Jagger yelled in the '60s, "U Kant all-ways get what ya waaaaa-nt".

Howevah, the mag ring turns CW the power of 8-40 is appealing w/25X being brightest/highest/5X over the M5 20x56, it allows me to use the new/improved dominate eye w/o mixing the mild cataract/amber tint eye. It also has a slot behind the tripod mount molded into the body for a shoulder strap bandolero style though a harness could easily be adapted.

Kudos to Bushnell. They list */FOV at both ends of magnification. As I snoop around I see others that list only the lower mag specs. I wonder why? For those bothered by rolling ball note that as magnification goes up/FOV shrinks I do not perceive the same movement. [As edited above under extreme CA conditions the center shrinks considerably to less than halfway to the edge. Yesterday was also completely overcast, yet it was darker overcast. Plus, I haven't mounted the scope to a tripod.]

http://8541tactical.com/images/bushnell/Elite Spotter/spotter_5125_HDR2_1080.jpg

There it is, for all intents & purposes, minus the bottom rail/carrying rail & tripod.

ETA II: Mounted on tripod didn't help. First off there's no secondary pin to maintain alignment & the mount is about an inch back of balance. If anything it should be an inch forward due to the weight of the objective at the end of the barrel. Under harsh conditions it doesn't handle CA any batter than the HG Minox 8.5X52. Anything within 100 yds was hard to focus on the sweet spot. Beyonf 100yds, at 8.5X, the CA was well behaved. As soon as I started to go up the ladder in magnification that polite control went out the window. Even looking towards the north was no improvement. Bright, thin layered full overcast is a CA dream. Making it hard to find the small CA free sweet spot. Not being able to securely mount the scope didn't help though even if it were it could not contribute much to the cause. Four hundred dollars will buy you a Kruger Caldera 8x42 that has no problem under these conditions.

At the original price that these scopes sold for it is ludicrous that this glass is called ED Prime. Unless they ditched that glass for some plain-Jane/cheaper offerings down the road. I still want to try it during a sunny day if nothing else to see how well I adapt to using the zoom on the fly handheld.

Nixterdemus said:

...Nikon Fieldscope 13-30x50mm ED Straight-Product 8320- for around 7 bills looks promising. Would prefer larger objective but focus ration 2.3 Angular Field of View (Real) 3 ° @ 13 x - Angular Field of View (Apparent) 40 ° @ 13 x. ER 12.9 coming in under a lb & 1/4. Uses the forward placed knob for focus though close focus of 9.8'. 2.5mm sweet spot coming in at 20X. The LMSS FOV is around 4.17* at 13X. Regardless of aberrations, field curvature &/or soft edges I need the extra fov to help locate targets...

Click to expand...

If you like those specs and price, then you might really love the Nikon Fieldscope 50ED with 27x fixed eyepiece.
You can get get that combo gray market from Japan via Amazon USA for ~$550.
https://www.amazon.com/Nikon-Fieldscope-Eyepiece-40XWDS-Improt/dp/B0007NXT5S
https://www.amazon.com/Nikon-ED50-A...=1519312963&sr=1-21&keywords=nikon+fieldscope
I can't find the straight version on Amazon USA at the moment, but you might be able to get it from Amazon Japan via Tenso.

The real FOV of the 27x is 2.7 degrees. If you like 20x better, you might be able to find the MC version and you would get a real FOV of 3.6 degrees. Another option, both to save money and increase wide FOV options at intermediate magnifications, would be to adapt astro eyepieces to the ED50 as described in this excellent thread: http://www.birdforum.net/showthread.php?t=322702

The Nikon 50ED has exceedingly little in the way of aberrations, field curvature, or soft edges. You should be able to use the whole FOV for high res viewing.

--AP

Thanks for the tips & links. I was a little vague w/"Regardless of aberrations, field curvature &/or soft edges" statement. At that time I was a couple of hours shy of viewing through the LMSS. I was attempting to express that even if not perfect optically I needed/wanted the wide, for a zoom anyway, FOV in the 20-25X range. W/claim of 'ED Prime' glass by Bushnell I thought CA would be the least of concern.

The compact Nikon 12x36 roof from 1990 not phase coated may be a bit soft, lacking the latest/greatest coatings not as bright as current bins, but it tames CA to extinction. It seems the Bushnell LMSS 8-40X60 does well under mild-medium chromatic abberation conditions, yet when mother nature cranks up the intensity it falls flat on its face.

I spoke to a Bushnell customer service representative yesterday about their ED Prime claim. Once I called BS the once colourful conversation degraded to monochromatic. His advice was to return it for another unto the vendor.

I told him I'd rather ship it to Kansas, so Bushnell could send me one that actually contained ED Prime lens.

Whatevah that may be. Silly me, in this one exception to the rule I didn't realize it stood for extra dispersion.

I'm not surprised to read that CA is high in spite of the use of ED glass. Spherical aberration is also probably high because the focal ratio is likely closer to f/4 than f/6. Remember, according to Bushnell's information this isn't a prismatic scope. It apparently uses a lens erector, like an antique spyglass or rifle scope, which also functions as a zoom when the position of the lenses is shifted. A thing like that adds its own latitudinal CA and other off-axis aberrations. It's probably at least a few inches long and is positioned between the eyepiece and the focal plane of the objective lens, so that the objective focal plane probably falls not far from the midpoint of the scope body. I just don't think you can hope for a really high quality scope from this sort of design.

Thanks Henry for providing an explanation of faster scope due to design that includes a lens erector. I always enjoy your posts. Obtaining technical information from Bushnell, other than std specs, is akin to squeezing blood from a turnip. CS puts you on hold while they look up only the basic information it seems.

I was a little harsh on assesment of CA. I've sinced edited previous post to reflect acceptable control in mild-medium CA conditions. So far I've only had overcast skies either dark or light.

https://www.bushnelloptics.com/bushnell-spotting-scopes-780840.html

According to the Bushnell website:

Bushnell Elite LMSS 8-40x60 Roof Prism Spotting Scope, Tan 780840

There is the 780841H w/reticle

Bushnell Elite Tactical LMSS 8-40x60 Spotting Scope, Tan ED Glass, RGHD, H32 Reticle, Box, Tan 780841H

https://www.bushnelloptics.com/bushnell-spotting-scopes-780841h.html?image=59ebcbee03

Might it be that even sharing the same objective size/zoom range the 780840 is a roof prism where the 780841H w/reticle is not? I'm at a loss because I thought it was a roof prism design.

From eyepiece to objective outside-outside is 12.6", roughly F/5.33 not adding prism length, so even if equiped w/roof prism it is still going to be a fairly fast scope. I thought perhaps that was the trade off for more FOV in the middle of the range. I spent quite a bit of time comparing the 20X FOV against the Nikon M5 20X56 and the LMSS is barely wider. I thought that a feat of sorts.

Anywho, am I missing something? Should I presume the description on the Bushnell site is erroneous?

my information about the scope came from here:

http://bushnell.com/tactical/spotting-scopes/elite-tactical/elite-tactical-(lmss)-8-40x-60mm

Notice "Not Applicable" for the prism glass spec, which I take to mean that there is no prism. Also consistent with lenses used for image erection and zoom function is an apparently fixed focal length eyepiece with a very long 30mm eye relief and a very narrow AFOV of 38º across the entire zoom range. The design appears to be similar to the old Bausch & Lomb Discoverer scope.

If there is a roof prism it could be detected by looking for the roof edge from the front of the scope or more certainly by testing for phase correction by looking through the front of the scope at a computer LED screen while wearing polarizing sunglasses. Rotate the scope and look for color or darkness changes with a sharp line dividing the bright circle in half.