Don Pensack

Easy enough on those to take them apart and blacken lens edges and spacers.

https://www.cloudynights.com/topic/821853-finally-a-killer-zoom-for-binoculars/ Read the whole thread. The review gets more in depth.

https://www.telescope.com/Orion-Premium-Linear-BinoViewer-for-Telescopes/p/130300.uts Reviews: https://www.cloudynights.com/topic/692020-orion-linear-binoviewer-mini-review/ https://www.cloudynights.com/topic/739149-ok-so-i-bought-an-orion-linear-binoviewer/ https://www.cloudynights.com/topic/615344-orion-premium-linear-binoviewers/ https://www.cloudynights.com/topic/643840-orion-binoview-any-opinion-or-actual-usage/

Filters have a lot of coatings and can be easily scratched. I would go with Lumicon's recommendation to never use anything stronger than isopropyl alcohol. Pure ethyl alcohol would work too but it is illegal for sale in many places since it can be consumed. Something strong enough to remove mould, like MEK or a solution of sodium hypochlorite would likely damage the coating.

I have had eyepieces for >20 years that I sold that looked brand new. I clean them by: 1) blow off all debris to avoid scratching. I have an electric blower (no propellant or oil) that blows just about everything off. 2) I add 1-2 drops of fluid to a Q-Tip, and, while the Q-Tip is wet, make a spiral pass of the entire lens surface, starting in the center, then quickly flip the Q-Tip and repeat with the dry end to mop up the residue. 3) I quickly grab a 2nd Q-tip (cotton only, no additives) and, moving from edge of lens to just past the center of the lens, rotate the eyepiece under the Q-Tip until the whole lens has been brushed twice. I then flip that Q-Tip to the clean end and repeat the spiral pass. When done, no streaks, no residue, and a clean lens. One way you know the lens is very clean is that the resistance to the movement of the Q-Tip on the lens disappears during the process, as if the lens is teflon coated.

If cost is no object: TeleVue Panoptic 41mm. You won't find a better eyepiece, optically, in or around that focal length. It has a 46mm field stop.

The StellaLyra is a GSO-made, and a good one. It's a conventional telenegative Barlow. The one in Mike Q's post is made by JOC, the maker of Explore Scientific, Maxvision, et,al. and is a 4 element telecentric Barlow. You can look up "telecentric Barlow" to find posts explaining the difference.

A couple reviews so far, but mostly from daytime users. I think more will have to be in the hands of users to get better information on aberrations and eccentricities.

You cannot simultaneously remove both rectilinear distortion (RD) and Angular Magnification Distortion (AMD). The way to have very small amounts of distortion is to keep the eyepiece apparent fields narrow, since distortion increases with apparent field. If any eyepiece with more than about 40° of AFoV has zero RD, it will have a lot of AMD, and vice versa. In daylight use in spotting scopes, reducing RD to keep straight lines straight seems important. And if this means the magnification at the edge is not the same, it's not a problem, since you can simply move the object viewed to the center. (no RD, let AMD be larger) In astronomy, though, having a different magnification at the edge is a problem (for many reasons I won't go into here), while there are no straight lines to keep straight, so having a more uniform magnification across the field is better (no AMD, let RD be larger) Here are the curves for RD and AMD and you can see how apparent field affects the amount of distortion seen:

What is noted is that reducing the brightness a bit on a planet or the moon can make things easier to see because the image isn't so bright it washes out by dazzling the eye. One easy way to do that is to add a 50% transmission neutral density filter to the eyepiece, or to double the magnification (which reduces brightness by 75%). If you are already at high power, the ND filter makes a lot of sense. One of the reasons my best view of Jupiter ever was with a Paracorr + PowerMate + Ethos eyepiece was the 18 lens elements in the optical train in the focuser. It was also a high magnification (456x, 0.7mm exit pupil). The light loss due to magnification and several inches of glass and innumerable air-to-glass surfaces was just enough to make the image look photographic and not even a bit washed out. Having superb seeing didn't hurt.

Your choice of a 2X Barlow was a good one. With the eyepieces you have (also good ones), you now also have 9mm, 6mm, and 4mm. The jump from 200-300x might seem large, but here is the thing: on the nights when a 200x image is clean and sharp and not scintillating, it is likely 300x will be usable too (Moon, double stars, Mars at opposition, Neptune, Uranus). And on a night where 200x is really pushing the limits imposed by Seeing conditions, even 250x won't be usable. So the 100x jump a the high end is likely to be fine. It's the same reason why, in my 12.5", I have smaller steps to 300x, then jump to 400x and 500x. On the nights when 300x is clean and sharp and still, 400x and 500x are usually usable.

Bill Paolini reports: I just looked on the Tak Japan site and they are NOT discontinuing the TOE. And nice to hear they are developing successor eyepieces!! https://www-takahashijapan-com.translat ... _tr_pto=sc Notice of discontinuation of production of some eyepieces February 16, 2022 We would like to express our sincere gratitude for your continued patronage of our products. We have decided to discontinue the production of his LE and Abbe series of eyepieces and his Erfle 28mm. Sales of each product will end as soon as they are out of stock. We are enthusiastically developing the successor product based on the opinions and requests we received. We apologize for any inconvenience this may cause, and thank you for your understanding. The TOE series will continue to be produced, so if you are considering a short focus eyepiece, we would appreciate it if you could consider it as a candidate. -Bill

A 40mm eyepiece is useful in a long f/ratio scope, to achieve a larger exit pupil and a brighter image--always a good possibility for long f/ratio Maksutovs. But in 0.965", the apparent field will be 32-33°, so that is one narrow eyepiece. Still, likely the true field maximum limit for the scope. A lot of people who owned those scopes added hybrid 0.965--1.25" diagonals to be able to use 1.25" eyepieces. But with a complete set of Japanese-made 0.965" eyepieces, few would bother.

6 elements versus 9 elements. And 82° versus 70°. But, you make a strong argument in favor of the APM. That is one of many reasons I use that eyepiece for my lowest power.

Oof. Bad seeing. The "not sharp at the edge" could be coma, and the eyepiece has a tiny bit of unresolved astigmatism near the edge as well. You don't say whether you are using a coma corrector in the dob or not. Good luck finding the comet. https://en.wikipedia.org/wiki/C/2017_K2_(PanSTARRS)#/media/File:C2017_K2_skypath.png It's a tiny fuzzy star at the moment. Here is the ephemeris: https://in-the-sky.org/ephemeris.php?objtxt=ck17k020 Your best bet is to plot it on an atlas so you can find it easily by star hopping from a nearby naked eye star. If you have a computer atlas, you can print the page where it is and mark it in.

It should work equally as well or poorly in an f/3.3 finder as the typical f/4 as long as the clear aperture is adequate for the fatter light cone.

It works in finders but that's because of the extreme low powers. And, if you really analyzed the finder like you do a telescope, you'd find excessive astigmatism, spherical aberration, chromatic aberration, vignetting, and a darker image than should be the case. So in an f/3.3 scope, you'd not only get a loss of brightness, you'd have excessive lateral chromatic aberration, serious vignetting, a visible line in the field, and likely a poorer quality axial image. In general, prisms of any kind are not recommended below f/8 because the lateral rays enter at too oblique an angle, yielding significant chromatic aberration. And, if the clear aperture is insufficient, vignetting.

If I'd saved every eyepiece I've ever owned, you'd need to shoot the portrait in Panorama Mode. (over 350 at this point). I just unloaded 10 of them, so I'm down to only 12. How long that will be the case, I have no clue.

And one reseller in the US is selling these under the manufacturer's name.

Looks like the one on the left in the bottom photo has a noticeably larger clear aperture.

I don't sell to the UK. Nor do I sell this tool. I merely reported my experience with the tool. something, I believe, an amateur astronomer can report, based on experience and not hearsay? I have used nearly every collimation tool there is over the years, and most have their ups and downs. FLO, BTW, sells an incredibly nice combination Sight tube/Cheshire: https://www.firstlightoptics.com/other-collimation-tools/stellalyra-premium-cheshire-collimating-eyepiece.html Here in the US, there ae several very poorly-designed collimation tools that are sold, but sales don't necessarily equal good design. I try new tools all the time to stay up on collimation trends. As for the Concenter, I've stated my experiences with the tool, which I obtained at retail from the EU. The new one doesn't solve problem G--you won't be able to get the pupil of the tool down to the focal plane of the scope. In the case of the new one, perhaps not down to the apex, even. The new design would seem to solve several of the other issues I saw with the tool, however.

Here are some things I noticed about the Concenter. This is the version I had: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p5506_TS-Optics-Concenter-2--Collimation-Eyepiece-for-Newtonian-Telescopes.html 1) It does agree with other tools once you have collimated with the other tools. Read on as to why the "AFTER" other collimation tools is necessary. 2) However, it suffers from multiple problems: a. it's too short. I couldn't focus on the rings even with reading glasses because they're only ~3" away from the eye. b. I could not adjust the focuser to get even one ring to correspond to the outer edge of the primary mirror OR secondary mirror, even running my focuser from one end to the other. They're spaced wrong for my f/5 setup. c. the rings are very broad and not particularly sharp in execution d. the center hole in the reticle is larger than the hole in the center marker, but smaller than the Hotspot, so it isn't visible at all. It would collimate a mirror with a Sharpie center dot kind of like a collimation cap can, but wasn't useful in my scope for primary adjustment at all. e. but the biggest problem and one that makes the tool completely worthless, is the terrible problem with parallax. The center hole isn't large, but with such a short distance to the rings, they wandered all over the place. I tried to stabilize my head by sitting and putting fingers on tool and cheekbone, but that didn't help at all. The wandering rings problem makes the tool worthless unless following after some normal collimation tools are used. I had no such problem with the Astrosystems LightPipe, even though it has a larger center hole than the Concenter. f. The eye relief of the tool is perhaps 8mm to see all the rings and the outer inside edge of the tool. At that distance, I couldn't focus on the rings at all--they were just a blur. When I put my bifocal reading glasses on and looked through the bifocal section to focus on the rings, I couldn't even see my entire primary mirror. g. When my focuser was nearly all the way in, I was at the apex for my mirror because the pupil of the Concenter sits almost 1.5" above the shoulder of the tool. I couldn't even get the pupil TO the focal plane of my scope, which is 0.75" above the racked in focuser. Just a horrible execution of a decent idea. It needs to be a longer tool--a LOT longer. It needs to move the pupil in to about the top of the focuser so the entire field can be seen. I have no idea how to solve the problem of the invisible center hole in the reticle. Maybe make it a lot smaller or larger? Or make multiple f/ratio versions?

TeleVue is in the process of eliminating all the 0.25 sizes Currently, the quarter diopter sizes are only available in: 0.25, and 2.25 Otherwise, they are now only available in half diopter increments. I suspect the 0.25 diopter one won't stick around, either, as most with that little astigmatism see no need for glasses at the eyepiece.

Flocking will make a huge difference: https://www.cloudynights.com/topic/523747-deadening-a-6-f5-newtonian/?p=6993629

Having bought glasses from 3 on-line merchants, I recommend GlassesUSA.com as their lenses seem to be better and more uniform in optical quality, even single vision.