ED glass, CA and mirage

[paulT]

A great question. My thinking on this is evolved over time. Before I go any further, let me state that I am not a great shooter with a string of medals, awards and so on. I've been doing this a long time but lately, I've encountered challenges with my marksmanship. Age. So please keep that in mind as you read on.

As I've been discussing in this thread, for several years now, I have been of the opinion that ED glass and its betters (for the lack of a better word) allow the user to deal with mirage differently than before. In my mind, the order of glass with increasing resistance to IQ degradation due to mirage is as follows:

Regular optical glass.​

Premium optical glass.​

ED glass.​

Super ED glass​

Pure fluorite crystal glass.​

I used to think that the spotting scope should not have ED or better glass in order to get the full effect on the mirage in image. Since we keep them down to 20-25X and they are not used to aim but to monitor the conditions, good non ED glass was the way to go.

After spending some time with my March-X 10-60X56 HM, (Super ED glass), I found myself using that one to monitor the conditions much more than my Kowa 82-SV. I have a large wheel on the side focus knob that allows for much greater, granular control of the focus and I could snap back and forth to check mirage at different distances and then get back on target to take the shot.

In the 10-60X56 HM, I could make out the faintest mirage and not have the IQ degraded anywhere near what happens with non-ED glass. I found I was not using the 82SV anywhere near as much as I used to because of that. So I recently bought a Kowa 883 Prominar with pure crystal fluorite objective lenses. Reading the mirage with that puppy is amazing. I have just started deploying the 883 in position and in fact, the Nationals is almost the first time when I did that. Now I have to retrain myself to use the spotting scope more when in position.

The Kowa design has a dual focus control, which I like but I am still learning it. Currently at the 1000-yard line, I use the 25X LER eyepiece and I set up the 883 right alongside the scoped rifle. I can look through the 883 and get behind the riflescope very quickly and I'm still developing the setup. I use the fine focus to go back and forth between 500 & 1000 yards. I'm trying to find a set distance at which I would focus and leave it, but that seems to be different every time.

The fluorite lenses allow me to discern the faintest mirage, without messing up the IQ. It's actually a joy to look through. I shot several videos through the 883 using their digiscoping adapter and my Nikon D7500. After I clean up the videos, I will post a link here. The maximum magnification of the wide angle zoom eyepice that I use for digiscoping, is 60X, which is equivalent to my March-X 10-60X56 HM but shy of the March-X 8-80X56 HM WA. I video and different mags to provide a good feel for the mirage.

I also use a spotter scope with my FTR Scope on the Line
An older 82mm model kowa 823m prominar with the 30x wide angle Lens however i have ordered the 27X LER Eyepiece to help with eye relief when switching between rifle scope and spotting scope i also noticed i can observe a tad more fine Mirage detail with the kowa lenses verses an expensive baader zoom telescopic lens which gives bright images at target but just not the same fine detail for reading the finer mirage
A mirage band for dissipating barrel heat a must when also using the rifle scope for reading mirage/targets etc.

 

[Fred Bohl]

A mirage band for dissipating barrel heat a must when also using the rifle scope for reading mirage/targets etc.

During some of testing on a near zero wind and very little mirage day, our optics group found a "cloud" of hot gasses hanging for minutes out in front of the barrel after firing. This appeared as churning "soup" when viewed through the scope making aiming very difficult for the following shot.

Since then for testing we have been using a small fan with rechargeable battery to quickly dissipate the gas cloud. We have also discovered that such a fan will also clear the barrel heat mirage better than the typical "mirage band" attached to the barrel.

Presumably not legal for competition but great for testing and load development.

 

[Appalachian]

Hello Ned, always a pleasure talking with you.

I started this thread about 2.5 years ago, and making the totally unsupported by existing science at the time, that ED glass and more so with Super ED glass, I was observing that the IQ degradation due to the phenomenon we incorrectly call "mirage" was retarted or somewhat contained compared to regular (non ED or Super ED glass.

Early on in this longish thread I was challenged to get confirmation from Deon about this. In post 79, I announced, a year after the prior post, that Deon had indeed confirmed that Super ED was doing a better job with shimmer (mirage) than their ED-glassed scopes. They had no regular glass scopes with which to compare as all non-LPVO riflescopes they make all have ED or in the case of a few models, Super ED glass.

The shimmer protection (mirage retardation) has nothing to do with coatings; it's inherent in ED but mostly Super ED glass.

Higher quality glass does do a better job in mirage compared to lesser quality glass because the resolution of the glass is better and that seems to help retard the degradation a little bit. But it ain't ED and definitely no Super ED glass.

Here is a link to Glass VS ED VS Super ED comparison.

In a proper riflescope design, the manufacturer strives to control the dispersion of one or two specific wavelength(s). ED glass, and especially Super ED glass reduces the dispersion of ALL wavelengths (Super ED more so.) The best dispersion control is with pure crystal fluorite lenses, which are just not found in riflescopes for various reasons. (Cost, fragility, susceptibility to environmental conditions.)

But fluorite glass is available in some camera lenses and spotting scopes. Kowa Prominars (883/884, 99A/S) have that type of glass. I bought a Kowa 883 just for that reason. More on that in time.

Now that DEON had realized that I was correct in my long-term observations that Ed and especially Super ED did in fact retard IQ degradation due to shimmer/mirage, they also discovered a few more things that further enhance this quality in a riflescope and they produced the March-X 8-80X56 HM WA with these qualities in mind.

The result was in the announcement to which I linked a few days ago above.

At the recently concluded US F-Class Nationals LR in Phoenix, Tim Vaught shot the entire LR championship with that riflescope set at 75X-80X, and won. Tim is an awesome shooter and has won numerous events but read the article again to see what he said about his experience with the riflescope.

I shot in the same conditions with my March-X 10-60X56 HM set at 50X all week long. It performed exceedingly well. I also looked through the March-X 8-80X56 HM WA in the same conditions and I was amazed that I could get to 80X with an IQ as good or better than the one in my faithful 10-60X56HM set at 50X.

I wasn’t aware the March 8-80 was available with Super ED glass or that it was a High Master. Do you know the model number?

 

[Ranger188]

Read the article. 8-80x56 HM

Congratulations to Tim Vaught for becoming the US National F-Open Champion for 2022 shooting with our prototype of the new 8-80×56 High Master Wide Angle Scope | March Owners -Shooting, Reviews, Competitions etc. | MARCH Scopes | DEON Optical Design

MARCH Scopes Official Site

marchscopes.com

 

[Turbulent Turtle]

I finally was able to edit a digiscoping video that I made at the Nationals last month. The purpose of the video is to show the mirage distortion at various magnifications through a hign magnification optics with CA controlling glass. In this case, I connected my Nikon D7500 to the back of my Kowa 883 which features pure fluorite crystal glass lenses, via the Kowa PA7A digiscoping adapter. The spotting scope was wearing the Kowa 25-60X Wide Angle eyepiece. The regular eyepiece I use on the line is the 25X LER version, but that cannot be used with the digiscoping adapter.

It took several attempts to get a passable video because this was my first time with this equipment. The D7500 can only be used in manual mode when it is using the digiscoping adapter. I had to hunt around to find a proper exposure setting, first for still, and then for video. Since I do not control the aperture, I had to play with the ISO setting and the shutter speed. That day was kind of windy, but I had brought my "heavy" tripod for that purpose. I did discover that whilst my new tripod head was excellent when using the Kowa by itself, the addition of the big & heavy D7500 to the extreme rear, attached with the PA7A, exceeded the proper payload for my new tripod head. So, adjusting the camera, framing, composition, focus and exposure, caused all manners of shaking and tremblors. I decided to edit those out so as to spare you the seasickness-inducing footage. You're very welcome.

The added dimension to my travails was the actual focusing of the lens. When the camera is connected to the Kowa, I turn on live view and the image is displayed on the back panel. This panel is great for changing settings, and "chimping" while taking pictures, but it's difficult to use to properly fine tune the focus for video in bright sunlight on a tripod. The Kowa has a dual focusing knob; coarse and fine. I was amazed to find out that I had to focus anew at each magnification when digiscoping and it was not just a small amount. I have a hypothesis about this, but that's for another time.

At any rate, I persevered and succeeded in getting some semblance of a video in which the mirage features greatly.

Notice how the aiming black is still round and the rings are plainly visible and distinct even at 60X. I think this is testament to the pure fluorite crystal glass in the Kowa.

Without further ado, here is the video.

https://www.facebook.com/video.php?v=813945403166343

 

[muleystalker]

I finally was able to edit a digiscoping video that I made at the Nationals last month. The purpose of the video is to show the mirage distortion at various magnifications through a hign magnification optics with CA controlling glass. In this case, I connected my Nikon D7500 to the back of my Kowa 883 which features pure fluorite crystal glass lenses, via the Kowa PA7A digiscoping adapter. The spotting scope was wearing the Kowa 25-60X Wide Angle eyepiece. The regular eyepiece I use on the line is the 25X LER version, but that cannot be used with the digiscoping adapter.

It took several attempts to get a passable video because this was my first time with this equipment. The D7500 can only be used in manual mode when it is using the digiscoping adapter. I had to hunt around to find a proper exposure setting, first for still, and then for video. Since I do not control the aperture, I had to play with the ISO setting and the shutter speed. That day was kind of windy, but I had brought my "heavy" tripod for that purpose. I did discover that whilst my new tripod head was excellent when using the Kowa by itself, the addition of the big & heavy D7500 to the extreme rear, attached with the PA7A, exceeded the proper payload for my new tripod head. So, adjusting the camera, framing, composition, focus and exposure, caused all manners of shaking and tremblors. I decided to edit those out so as to spare you the seasickness-inducing footage. You're very welcome.

The added dimension to my travails was the actual focusing of the lens. When the camera is connected to the Kowa, I turn on live view and the image is displayed on the back panel. This panel is great for changing settings, and "chimping" while taking pictures, but it's difficult to use to properly fine tune the focus for video in bright sunlight on a tripod. The Kowa has a dual focusing knob; coarse and fine. I was amazed to find out that I had to focus anew at each magnification when digiscoping and it was not just a small amount. I have a hypothesis about this, but that's for another time.

At any rate, I persevered and succeeded in getting some semblance of a video in which the mirage features greatly.

Notice how the aiming black is still round and the rings are plainly visible and distinct even at 60X. I think this is testament to the pure fluorite crystal glass in the Kowa.

Without further ado, here is the video.

https://www.facebook.com/video.php?v=813945403166343

I don't know if its just me but I can't get the video to play.

 

[Turbulent Turtle]

It looks like it's not just you. It works for me and others, but not for some. This is my first attempt at linking to something I posted on Facebook.

You might want to go see if you can see it there:

Denys Beauchemin

Denys Beauchemin is on Facebook. Join Facebook to connect with Denys Beauchemin and others you may know. Facebook gives people the power to share and makes the world more open and connected.

www.facebook.com

 

[Fred Bohl]

Thanks very much for all your work on the video!

IQ - Absence of color fringing even on targets low contrast rings at all magnifications is outstanding.

FOV - 25x not enough target detail and excessive mirage/wind info; 45x improved target detail but still excessive mirage/wind info; 60x just adequate (for me) target detail good mirage/wind info. Based on my experience I would use 80x if it were available for better target detail and adequate mirage/wind info for my rifle scope but probably your spotter setup at 60x if coaching or with the 25LER for shooter aid.

Focus - good work on getting comparable focus for all three power settings but I'm still dumbfounded by the need to refocus so much with power changes in such a high end eyepiece.

BTW - I'm sure your 25-60X is helping IQ since the Kowa TE-11WZ II "contains 2XD-lenses".

 

[Turbulent Turtle]

Thanks Fred, I appreciate the comments.

The CA is extremely well controlled in the Kowa, a tribute to its fluorite crystal glass lenses.

The focus changes may have to do with the use of the digiscoping adapter as I have not notice anything close to that using my mark 1 eyeball. I will do more digiscoping work now that I have figured out the exposure with my D7500 on manual. This takes me back to the late 60s and 70s with my Nikon and Minolta SLRs.

The XD lenses in the eyepiece will not improve the IQ coming from the objective lens, as you well know, but they do prevent the rather strong lenses in the eyepiece from messing up the image from the objective.

The wide angle eyepiece is really nice on the Kowa, and so is the one on the new March-X 8-80X56 HM. It ushers in a new era in high magnification riflescopes.

 

[Fred Bohl]

TT what was your intended sharp focus distance in those videos? Also do you know what the depth of field was for each power?

 

[Turbulent Turtle]

FB aka @Fred Bohl, I was hoping to focus at 1000 yards. I can do a better job with my riflescope, especially with the big wheel attached to the side focus on my March-X 10-60X56HM. One of the unheralded benefits of aging is a little-known affliction called arthritis. Fine control with my left hand can be problematic at times, the rest of the time it's just downright challenging.

(As a side note, I am so thankful we now have many automated or at least powdered, devices for handloading.)

The large side focus wheel allows me a higher degree of control on focus, and allows me to play a bit to focus a different distances to get a feel for the conditions. However, since I have been using the Kowa 883, I have focused less often on the riflescope. At the last match, I was able to detect the very faintest of mirage during the match and adjust accordingly. This was the equivalent of plugging the trickle before the tsunami hit. The conditions turned very sporting inside of about 3 minutes, and I managed to eke out one of my lowest scores in years. I didn't miss the target or shoot lower than a 7; but a collection of 8s with one or 2 7s will murder your score. I did finish the string with a X. My one solitary X for that string.

As for the DOF, since I do not have the focal length of the Kowa, I can't use a DOF calculator. Or maybe I can guesstimate it. The body is 13 inches. If I guess that the front of the prism is 9 inches from the objective lens group, let's call it 230mm. With an objective diameter of 88mm, that gives me: f-length 230mm; f-number f/2.6. Distances 1000 yards. I'll use a CoC of 0.030 for 25X; 0.020 for 40X and 0.010 for 60X

25X (CoC 0.03): DOF: From 400 yards to infinity.
40X (CoC 0.02): DOF: From 550 yards to infinity.
60X (CoC 0.01): DOF: From 700 yards to 1600yards.

These are extremely rough, back of the tablet, calculations with wild guesses for values. I am certainly open to using radically smaller values for the Circle of Confusion at different magnifications (especially with the digiscoping adapter and the 20MP sensor of the D7500): maybe something like 0.020, 0.015, and 0.010. And my focal length can be off quite a bit as I am not familiar with the exact internal design of the Kowa 883. So, if you, or someone else has better values, by all means, speak up.

 

[Fred Bohl]

Thanks for the rough calculations. I asked in regards to the focusing problems you were having to make the videos. For 1000 yards using a spotting scope I would have probably preset focus on the spotting scope for the hyperfocal distance (I find that experimentally and match mark the scope focus control and body).
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Pause to blow off a little steam - we spend serious money for these scopes and I don't think it would be too much to ask for spotting scopes to have the hyperfocal distance as a marked preset on the focus controls and a specification sheet with the actual clear aperture and focal length.- OK I've avoided a heart attack.
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Back in my competition days, at long range (600 to1000 yards) I would try to set my spotting scope focus on the target with a resulting depth of field from half that distance to infinity. For 1000 yards that was close enough to the hyperfocal distance for the spotting scope I was using back then. For 600 yards I had marked the retracted focal position on the spotting scope body so I wouldn't have to fiddle with it during the match relay. Below 600 yards I did not use a spotter. At 100, 200, and 300 yards the sea of flags was the primary wind indicator and the rifle scope would show enough mirage detail to catch a quick wind shift.

 

[Turbulent Turtle]

Let's talk hyperfocal distance for a minute here. Hyperfocal distance setting is the distance setting at which the optical device produces the greatest DOF. In other words, at which distance setting does the optical device have a DOF that goes from the closest distance to infinity.

Yes, it would be REALLY nice if manufacturers provided aperture and focal length. I have discovered that for riflescopes at least, these values are usually company confidential. Yeah, shocking. I do not know about spotting scopes, but it would not surprise me to learn it's the same there as well. In the photography world, these values are actually part of the name of a lens.

The DOF calculator I use produces the hyperfocal value with the data I provided, it's a well-known formula involving the focal length, the f-number (aperture) and the CoC.

For 230mm, f/2.6:
CoC 0.010 (60X), it's 2,500 yards with near being 1,250yards.
CoC 0.020 (45X), it's 1,300 yards with near being 625 yards.
CoC 0.030 (25X), it's 800 yards with near being 415 yards.

So for the Kowa 883, the hyperfocal distance setting would vary considerably as you increased the zoom in the eyepiece, so I'm not quite sure how there could be presets. As I explained earlier, I link the size of the CoC inversely to the magnifying effect of the zoom setting in the eyepiece. My view is that the CoC needs to be smaller with a greater zoom value.

My numbers agree with your use of hyperfocal distance settings in a spotting scope with a 20-30X magnification (415 yards in the 883, according to my really wild guesstimates.

My head hurts...

 

[Fred Bohl]

TT, I'm sorry to have caused you a head ache. This thread has historically been about ED glass CA and mirage but I diverted it out into the weeds of focusing spotting scopes. Sorry for that diversion so I will step aside and let all get back on point.

 

[JFrank]

It won’t matter you guys are talking way over most of our heads anyway.

 

[Turbulent Turtle]

TT, I'm sorry to have caused you a head ache. This thread has historically been about ED glass CA and mirage but I diverted it out into the weeds of focusing spotting scopes. Sorry for that diversion so I will step aside and let all get back on point.

I was just teasing. You just caused me to think more deeply about this aspect of optics.

Actually, this thread has been about observations and trying to translate empirical data into actual data that can be used by anyone.

For instance, this thread has caused me to reevaluate my understanding of spotting scopes and riflescopes vis-a-vis mirage. A few years back, I was of the opinion that you did not need, or want CA-suppression glass in your spotting scope so you could detect the mirage better. The accompanying opinion, is that you wanted the best CA-suppression glass in your riflescope to retard the IQ degradation due to mirage. As we can see, I have changed the first opinion because of these observations and ensuing discussion. You want the best CA-suppression glass possible for your spotting scope BECAUSE you can more easily detect the mirage, without having your IQ scrambled. I have found that my Kowa 883 shows me the very faintest of mirage quite nicely, something my 820SV could not do. I will try to determine the hyperfocal distance of the Kowa 883 using the CoC that will fit the LER eyepiece, probably .025 to 0.030 and set the distance to that value to provide the broadest DOF to catch as much conditions as possible.

I think my hypothesis about Super-ED glass doing a great job retarding the IQ degradation due to mirage has been, if not confirmed at least made viable (for now) and the follow-on riflescope with Super ED and other tweaks seems to be performing well at even higher magnification. I will be testing it more going forward.

Optics is optics, and conditions is conditions, and they mess with the optics. I should think the more we observe and try to explain, and then try tp figure how to take advantage of this new knowledge, is something that benefits everyone.