Don Pensack

Orion's official name is "Sky Glow Ultrablock" filter. That's confusing, because they also have a Sky Glow Broadband filter. So everyone just refers to it as an "Ultrablock". It is Orion's narrowband "UHC-type" filter and is comparable to other "UHC-type" filters. Someone may just call it a "UHC" to avoid confusion with broader filters. That's not a bad thing--good for the seller. It will be used at powers from 10x/inch and lower, so if your low power eyepieces are 2", get a 2" filter. A 2" filter will fit the bottom of many 1.25" adapters for a 2" focuser, and also thread on to the front of a 2" star diagonal, so 2" is the universal size if the scope has a 2" focuser. If the scope is 1.25" all the way through, including the focuser, then 1.25" filters are appropriate, of course.

The William Optics is a re-packaged Norin binoviewer. As such, it has the disadvantages of a low end unit: --small clear aperture (20mm) --The WO OCA has significant chromatic aberration and spherical aberration. Use another brand if you can. It's probably a good "gateway" to see if you like binoviewers. If you like binoviewing, it won't be your last binoviewer, though.

This may end up in a grey area, but I have found that apparent fields wider than about 68° do not work well in a binoviewer. Why? Well, in a mono-viewing situation, if you want to look at the edge of the field with direct vision and the field is 70+°, you slightly roll your head over to look since you need to keep the pupil of your eye at the exit pupil of the eyepiece. It's no problem at all to do so. You can't just simply move the eye to look directly at the edge with foveal vision because that moves the pupil of your eye away from the exit pupil of the eyepiece. The head movement is so slight, most people don't even notice the movement. Therein lies the issue with ultrawide fields and binoviewers. You need to roll the head slightly to look directly at the right and left hand edges of the field. If you do so, one eye gets lifted away from the exit pupil and that side goes dark. You can simply ignore the edge and only focus on the center, but that means you cannot follow and object across the field from edge to edge in an untracking scope. But if you stick to 68° and smaller in binoviewers, you can see right and left edges of the field by merely moving your eyes and you can track the object from edge to edge. This is the main reason, I believe, that it is a very rare binocular that has an apparent field in excess of 65°. So how wide an apparent field can you use? Therein lies the grey area. If you don't care about looking at the right or left edge of the field with direct vision, then the only limit is your IPD and the scope's focuser's ability to handle the weight. If you do care about seeing the entire field with direct vision, then smaller eyepieces of up to 68° will work best. 60° eyepieces are almost universally bino-friendly, and because they are modest in price, having dual copies of each will likely not be much of an economic hardship. And many of them are quite good.

TeleVue still offers the Naglers for sale in 31mmT5, 22mmT4, 16mmT5, 13mmT6, 9mmT6, 7mmT6, 5mmT6, 3.5mmT6 In the last few years, , the 26mmT5, 20mmT5, 17mmT4, 12mmT4, 11mmT6, and 2.5mmT6 were discontinued, to joint the originals, and type 2s in history.

The 'evidence' I've seen is almost completely anecdotal, as an endlessly-repeated comment from Vernonscope about Brandon eyepieces and why they have single layer anti-reflection coatings. The coatings explained: https://www.edmundoptics.com/knowledge-center/application-notes/lasers/anti-reflection-coatings/ https://www.edmundoptics.eu/knowledge-center/application-notes/lasers/an-introduction-to-optical-coatings/ I've read over a hundred studies about this, and the conclusions investigators come to are that the scatter is almost totally dependent on the smoothness of the surface the coatings are put on, not the coatings themselves. When you stop and think about it, if the surface reflects LESS light, how could scatter be MORE unless the surface becomes rougher with each layer? I guess I could see that a rough lens surface will scatter more light, but it's hard to see how a multi-layer coating will scatter more light unless the multicoating adds to the roughness of the coated surface. That is possible, but comparing a cheap eyepiece with multi-coatings to an expensive eyepiece is likely comparing surface smoothness more than it is the coatings. Brandon eyepieces have low scatter because of a higher end lens surface roughness figure. And Zeiss uses multi-coatings but has superior lens surface polish. This explains the main rating used for surface smoothness: https://www.advancedoptics.com/scratch-dig-specifications.pdf

Synta Maksutovs (90mm, 105mm, 127mm, 152mm, 180mm) are sold under many labels in the world. I have seen the whole line sold under the SkyWatcher brand in many countries. Most of them have a V-sized dovetail.

JOC was a supplier of Meade from the late '90s to 2011, but they never owned Meade. Meade was owned by Sunny until the recent lawsuit. Meade is now owned by Orion in the US. They do own Explore Scientific, however, and are a supplier for Bresser. How Bresser and JOC relate in the financial sense other than for purchases, I don't know. The UK has a couple sellers who import from JOC.

Not, I suppose, a giveaway bargain, but £83 is a pretty inexpensive eyepiece. It's a nice Japanese eyepiece for the price of a Chinese eyepiece. FLO has a lower price than many of the EU dealers.

Brightness is directly related to the area of the exit pupils. The brightness ratio would be the ratio of radiuses squared, i.e. r²(1) / r²(2) where 1 and 2 are the compared exit pupils. So a 5mm exit pupil, compared to a 3mm exit pupil has a brightness comparison of 6.25/2.25 = 2.78x, so the 5mm exit pupil is 2.78x as bright as a 3mm exit pupil. Pretty much, a 0.5 magnitude difference becomes a minimally different brightness difference. That is an increase of exit pupil area by 1.58x, so if you start with an exit pupil of 6mm at the large side, the next exit pupil would be 4.8mm and the next would be 3.8mm, etc. At the low end, that would probably yield magnifications that are too close together, but it would result in a visible change in field brightness. A typical narrowband with a narrow bandwidth will increase contrast for the nebula by about 2.4-2.5 magnitudes. A narrow 2-line O-III filter will increase contrast for a O-III emission nebula by about 2.9 magnitudes. Those increases in contrast are why the nebulae become more visible, because nebula filters do not make them brighter at all. It just seems like they do. Contrast diminishes sharply above about a 10x/inch magnification (2.5mm exit pupil), so nebula filters are low power accessories. If you like to look at small planetaries at 500x, you won't be using a filter.

List of H-ß targets. https://www.cloudynights.com/topic/477453-h-beta-filter-is-it-any-good/?p=6232667

Where they are made is a big part of the price, as well as the polish on the lenses. Double the lens polishing time for a 3% improvement, and production costs increase 100%. Coating the lenses is just a small part of production costs. When I was referring to high-end, I was referring to Zeiss ZAO, Pentax XO, Astrophysics SPL, TMB Supermonos, etc., not the innumerable labels for the Ohi Optics orthoscopics and the like at the lower price points.

The argument for single layer coatings has to do with axial light scatter, not transmission. Transmission with single layer coatings is likely to be ~93-94% at best. With multicoatings on all surfaces, it could be ~97-98%. The biggest difference is in the UV-deep violet, where the difference is larger. That difference is completely unimportant unless the greater internal reflection causes ghost images. Otherwise, a 4% difference is in the low hundredths of a magnitude, especially unimportant for lunar/planetary usage. Note, however, all the ultra high-end planetary eyepieces have been multi-coated, so a single layer coating is more likely to be a cost-cutting decision.

An inexpensive Twist-Lock adapter will work just as well, and works well with undercut barrels. No snag going in or out.

Yes, the 12.5". I find the H-ß filter does work in my 4", but that scope is rarely used in darker skies, and even then a large exit pupil is such a low power in that scope the view isn't very good. A 5mm exit pupil in my 4" is only 20x, whereas in the 12.5", it's 63x. So, at equal brightness, the 12.5" image is over 9x as large.

That is the page I went to using a Google search: https://www.baader-planetarium.com/en/baader-2"-clicklock-eyepiece-clamps.html When going to the Baader site and searching, I came up with this page: https://www.baader-planetarium.com/en/baader-2"-clicklock-eyepiece-clamps.html Same page. The link leads a different place. try typing in click lock in the search box on the Baader site and choosing Baader 2" ClickLock eyepiece clamps (from T-2 to 4,1") Oddly, that leads to the same page as the other links.

All: 2.5mm and larger, though I will use 2.4mm on some brighter objects for a narrowband/UHC.. H-ß is usually more effective for me above 3.8mm, though I think that depends on the target and how dark the sky is. Effectiveness reduces when the sky becomes darker with magnification and the object dims.

The Pleiades benefits from a 2.5-3° field: https://science.nasa.gov/pleiades-seven-sisters-star-cluster The "dipper" shape is only about the center 50° of the cluster. Best view ever: 80mm refractor at 15x. Nebulosity everywhere, even way outside the cluster. Though, if you are looking for details in, say, the Merope nebula (near star 23), that magnification is great.

Rectilinear distortion illustrated: http://m43photo.blogspot.com/2013/01/geometric-distortion-correction.html You might find this illuminating: https://www.cloudynights.com/topic/420879-what-does-amd-look-like/ That was back in 2013, where I was just exploring the effects of distortion on telescope images. Star images in focus do not seem to be affected, which is why we have eyepieces with barrel distortion and pincushion distortion existing in the market side by side. One thing I would note, however, is that lunar viewing in an undriven scope is better in eyepieces of 65° and narrower because of edge of field distortion. And quick panning of the sky, as in a comet seeking use, would be better with reduced RD and reduced AMD, or a combination of both. Rolling ball (globe) distortion is obnoxious in that case, as is serious RD of either sign. In such a case, it would also seem that a tight control of astigmatism would be beneficial. It makes it easy to understand why planet observers like orthoscopic eyepieces (narrow field with near-zero distortion) if the scopes don't track. Planet images would stay a constant shape.

All Baader Click Lock attachments have a series of very tiny screws that allow you to rotate the ClickLock to place the pin in the most convenient place. You can see them in this picture: https://www.baader-planetarium.com/en/baader-2"-clicklock-eyepiece-clamps.html

It should be noted that angular magnification distortion and rectilinear distortion do not have exactly the same effects. Angular magnification distortion expands or shrinks the image in all directions. Think of it as expanding or compressing the area in the field. The effect increases with apparent field width. Rectilinear distortion (pincushion, barrel) is a radial distortion and expands (pincushion) or shrinks (barrel) the image along radial but not circumferential lines. The effect increases with apparent field width. The image of a circle with AMD will become somewhat egg shaped as the image nears the edge, with the edge either being smaller (usual) or larger than the circle closer to center. The image of a circle with RD will become oval radially (pincushion, due to expansion) or circumferentially (barrel, due to compression). Describing the image at the edge as a function of magnification, or a change in focal length, doesn't really describe what's going on. It implies the image is larger or smaller, but doesn't really describe the distortion in the image that takes place. We cannot escape distortion--the wider the apparent field, the more there is. The designer does have the ability to determine what the expression of distortion is, however, i.e. the type of edge distortion we see, but not whether we see it or not. Here is a chart showing the two forms of distortion in the optical image with apparent field.

7mm APM XWA

Here is the spec sheet from Vixen Japan:

I have 14 eyepieces in my kit box and one coma corrector. The 2" adapter for that CC, and the 3 eyepieces with undercuts all got the treatment with copper tape to fill in the undercuts, and now slide right in and out. The copper tape technique works quite well.

They've been around for several years, so many on-line reviews if you search.

I think 3 companies have had 4 element telecentric Barlows: Tele Vue Optics, Harry Siebert Optics, and Jing Hua Optical( sold as Meade, Explore Scientific, Altair, and others). There may have been others, but I am not aware of them.