Louis D

Speaking of high end spotting scope eyepieces popular with amateur astronomers, there is also the discontinued ZEISS DiaScope Vario 15-56x/20-75x (6.9mm to 25.1mm) which is popular for its extended zoom range.

I use a GSO CC in my GSO 150mm f/5 Newt. It gets the job done with wide field eyepieces. For Orthos and Plossls, the difference might not matter much to most observers. Because it imparts some spherical aberration on axis, I remove it for high power viewing of planets to get the sharpest image possible.

I bought a few 48mm vintage camera lens color filters to try since they can be directly threaded onto 2" eyepieces. First up is a Rokunar Yellow K2 - #8 which appears to be very close to the original Wratten spec for a Yellow #8 with a 19% cut-on around 480nm. In fact, the Hirsch Yellow #12A appears to be very similar to the Wratten #4 spec with a 42% cut-on around 470nm. The Meade Yellow #8 seems paler than even the Wratten #3 spec which specifies a 38% cut-on at 460nm. I've run the Rokunar Yellow K2 through my spectrograph and found it to be about midway between my (GSO) Yellow #12 and Hirsch Yellow #12A. On Venus, Jupiter, and the moon, it performs more similarly to the #12A than to the #12. It cuts all violet while imparting only a slightly deeper yellow cast to the image than the #12A. The #12 imparts a noticeably yellower cast to the image than either of the other two. Here's the lineup of my various yellow filters as seen through the spectrograph: Next up is a Rokunar Green X1 -#11 which appears to be very close to the original Wratten spec for a Yellow-Green #11 with a 26% cut-on around 480nm, a peak of 50% or better from 500nm to 550nm, and a 19% cut-off around 610nm. This is almost exactly where achromats are best corrected. It is almost identical to the R89 Moss Green in appearance, spectrographic analysis, and in use on Venus, Jupiter, and the moon. Here's the lineup of my various green filters that I've found useful with a fast achromat as seen through the spectrograph:

From what I've read online, it has a T2 thread on top if it is the 1.25" version. The Maxview II version seems to have a 58mm thread on top. You weren't specific about which version you bought. I think both are hidden by the thread-on eye cup adapter. You would need to find the appropriate step rings to get from there to whatever lens thread exists on your camera lens.

Except at very high powers where the new Svbony 3-8mm zoom excels, I find myself jumping in 3x increments generally. Thus, a 3x zoom like an 8-24mm works out to 1 to 2 useful focal lengths for me. I tend to start at 40mm with a 2" eyepiece, then I jump up to a 12mm to 17mm eyepiece to get a closer look, if it comfortably fits in the field of view. From there, I generally jump up to a 5mm to 7mm eyepiece if it is a small object or has some fine details I want to examine more closely. Thus, most 3x zooms only cover the middle range and miss at both ends. I'd need a 2", 8x zoom (5-40mm) with a 70 degree AFOV to be really useful for my style of observing. If it was well corrected like XWs and Deloses with 18mm of usable eye relief, I'd easily pay $1000+ for one just for the convenience. However, I've never heard of anyone seriously considering bringing such a zoom to market.

You're going to be starting off at a small exit pupil at 8mm (8/10=0.8mm) progressing to a very tiny exit pupil by the time you get to 3mm (really 3.5mm, so 3.5/10=0.35mm). If floaters are not an issue with your eyes, and you have really good seeing conditions (going from 2032/8 = 254x at 8mm to 2032/3.5 = 581x at 3mm/3.5mm), you might make good use of it to probe the limits of your scope, seeing, and eyes. Have you tried experimenting with these high powers using your existing eyepieces and a 2x or 3x Barlow already? Also, your collimation will need to be spot on for best results at these powers.

As did I after I wrote this initial report. I didn't see any noticeable degradation going from f/6 to f/5.

Agreed on all but the 3.5mm. Did you see chromatic aberration at the edge in your 3.5mm XW? My 5.2mm XL is also free of color to the edge. After seeing the chroma at the edge of the 7mm, I decided to keep the 5.2mm rather than "upgrade".

Has anyone ever come up with a binocular collimation methodology or technique that doesn't rely on an expensive, precision optical test bench?

No, just the Svbony 3-8mm zoom at 3mm which actual 3.5mm. The XW stomps all over it in eye relief, field of view, sharpness, and control of chromatic aberrations. This should surprise no one. I don't spend a lot of time at tiny exit pupils. The only reason I picked up the XW was because Amazon dropped the price to $216 years ago, so it was too tempting to pass up.

When viewing Venus at low elevations, I found my Meade Green interference filter worked best in my achromat by squashing all spurious red and blue, both from the scope and the atmosphere. I then tried it in my 72ED, and it did the same for atmospheric smearing, leaving a nice and sharp view of the planet in brilliant green.

The 3.5mm XW is probably the finest of the XW line. No edge astigmatism, chromatism, or field curvature at f/5 to f/6 in my scopes. It is sharp and contrasty across the field of view. The problem for me is with the resultant tiny exit pupil and my floaters getting in the way of enjoying the view. Eye relief is excellent for relaxed, extended viewing.

I went ahead and added the Meade Yellow #8 spectrograph image to the rest of the minus violet spectrograph images above. The Yellow #8 cuts just the tiniest bit more violet than the Minus Violet. I have no idea why they strayed so far from the Wratten Yellow #8 spec, which is much closer to the Cheap Yellow or Yellow #12A below. I've got a vintage 48mm Yellow #8 (also known as Y, K2, Y48, or 022 by other filter specs) camera filter on the way to use on 2" eyepieces. I'll run it through the spectrograph once I have it to see where it falls on the "spectrum" of minus violet (yellow) filters. I'm really curious because it looks way more yellow than the Meade #8 Yellow in its photos.

Since I have such strong astigmatism in my eyes (2.0+ diopters), I need to wear eyeglasses even at 1mm exit pupils, so that rules out short focal length orthoscopics. I did buy a 25mm Edscorp Abbe orthoscopic (volcano top) just to what they're like. I didn't care for it at all. It has terrible correction across the field in my fast scopes. I even disassembled it, clean everything (not that hard, just a singlet and a triplet), and tried every combination of flipping each of the two elements (there's just 4 possibilities), but the way it was delivered yielded the best images, so it's just the design itself that can't handle fast scopes. It does better in my 127 Mak at f/12, but that's a pretty limited application. I prefer my Pentax XLs and XWs for short focal lengths. Nice and sharp across the field with excellent contrast. For critical planetary observing, I use my binoviewer with a pair of vintage microscope eyepieces adapted to 1.25" or a pair of Svbony UWA 20mm eyepieces. I use the nosepiece of a vintage Meade 140 2x Barlow to reach focus, boost power by 3x, and to slow down the light cone to f/15 to f/18 so the eyepieces perform at their best. I also have a pair of Celestron Regal 8-24mm zooms that I sometimes use, but they tend to make my BV rig quite heavy requiring rebalancing. For long focal lengths at lower powers, I prefer 2" eyepieces. My favorites are my 40mm Meade 5000 SWA decloaked, 30mm APM UFF, and 22mm Nagler Type 4. In the mid range, I prefer my 17mm and 12mm Explore Scientific 92 degree eyepieces. At high-mid power, I really like my 10mm Delos and 9mm Morpheus. If I'm using 1.25" eyepieces only, I'll substitute my 12.5mm APM Hi-FW for the 12mm ES-92, 14mm Morpheus or Pentax XL for the 17mm ES-92, and 24mm APM UFF for the 22mm NT4.

That's just a small sample of my eyepiece collection. Check this thread for more: I've added couple more since this photo was taken.

Probably a travel Dob would give the most aperture per kg.

They must have changed the rubber formula, then. The eye cups flip up and down quite easily on my set of 6 of them. Up: Down: If you want to talk about stiff, the eye cups on my Astro-Tech AF70s can't be flipped at all. I have to unscrew and remove them to use them with eyeglasses. The 22mm version is second from the right below while the 18mm HD-60 is on the far left.

Without running your Orion Ultrablock filter through a spectrograph or optical spectrum analyzer, it's hard to say what's wrong with it. My guess based on your latest comparison is that it is left shifted and is only passing H-Beta and no OIII bands where M42 is brightest. My cheap Svbony UHC has a wider passband than my 1990s Lumicon UHC, but the view of M42 is surprisingly similar under Bortle 6/7 skies. M42 has enhanced contrast with both filters without unduly dimming nearby stars. For under $20, the Svbony UHC comes highly recommended for those on a tight budget.

I picked up a Japanese made Meade #8 Yellow for comparison since they are so often recommended as a cheap minus-violet filter. Through my spectrograph, it is nearly indistinguishable from my vintage minus-violet filter shown in my comparison images posted above. It is indeed way off from Kodak's Wratten specification for a #8 Yellow and closer to a Wratten #4 Yellow. The #12A Yellow is closer to the Wratten #8 Yellow specification. It's too bad the closest modern equivalents are the cheap yellow filters coming out of China that show a bit of scatter. Last night I had super clear and steady skies after a front moved through the day before. I compared the various Yellow, Yellow-Green, and Green filters through my ST80 f/5 achromat. I even combined a few of them with the M&SG filter. Venus required the heaviest filtration: The #8 Yellow left noticeable violet flaring ruining the view. No yellow cast could be detected. Venus looked about the same with or without this filter. The #12A Yellow removed all violet fringing leaving a slight yellow hue, but the red fringing then overwhelmed the view. The #12 Yellow left a deep yellow color cast that when combined with the residual red fringing created an orange hue. The Hirsch #11 Light Green needed combined with the #12A to block enough violet to be usable. It still leaked a fair amount red, but it was an improvement. The R89 Moss Green completely eliminated all violet and red fringing while still showing a bit of blue and yellow hues. Venus was a sharply defined disk. The brightness needed cut down a bit, though, for better contrast. The Cheap Green showed a purely green view that was darker and slightly sharper. The Meade Green (interference) showed hints of yellow shades and despite the brighter view due to high transmission still showed excellent contrast. Jupiter required a noticeable step down in filtration: The #8 Yellow left barely noticeable violet flaring. A barely noticeable yellow cast could be detected. Adding the M&SG filter cut most of the yellow cast, leaving an odd color cast (pale magenta?) The #12A Yellow removed all violet fringing leaving a noticeable, but subdued, yellow hue. The red fringing was all but unnoticeable unlike with Venus. Adding the M&SG didn't cut the yellow color cast much at all. The #12 Yellow left a deep yellow color cast that overwhelmed the view. The belts were a bit sharper, though. The Hirsch #11 Light Green did a decent job. Moving it in and out of the light cone, it did cut some of the unfocused red while imparting a light yellow-green hue that was unobtrusive. The R89 Moss Green completely eliminated all violet and red fringing while imparting a blue-green-yellow color cast. It was probably overkill for Jupiter, though. The Cheap Green showed a purely green view that was darker and slightly sharper. It seemed like overkill. The Meade Green (interference) showed excellent contrast, but with a strong green-yellow color cast. The Moon, being a greatly extended, but very bright object, was somewhere between Jupiter and Venus in filtration needs. The #8 Yellow left noticeable violet flaring and a violet wash all gray areas. A barely noticeable yellow cast could be detected. Adding the M&SG filter cut most of the yellow cast, leaving an odd color cast (pale magenta?) The #12A Yellow removed all violet fringing leaving a noticeable, but subdued, yellow hue. The red fringing was unnoticeable unlike with Venus. Adding the M&SG created an odd color cast (pale magenta?) on the gray areas. The #12 Yellow left a deep yellow color cast that overwhelmed the view revealing greenish tints to shadows. The Hirsch #11 Light Green needed combined with the #12A to block enough violet to be usable. It was a slight improvement over the #12A alone. The R89 Moss Green completely eliminated all violet and red fringing while imparting a strong blue-green-yellow color cast. Details were nice and sharp without fringing. The Cheap Green showed a purely green view that was darker, but not any sharper. It seemed like overkill. The Meade Green (interference) showed excellent contrast, but with a strong green-yellow color cast. The Meade Red (interference) showed excellent contrast once refocused for red. It left a strong red-orange color cast. The Meade Blue (interference) revealed strong violet blurring on high contrast details. It needed combined with the #12A to create a teal-blue filter that showed excellent contrast once refocused for blue. I could see using the above Meade color separation filters in a filter wheel with the #12A on the front of the diagonal as a pre-filter to cut violet for the blue filter for all bright objects. The #12A has no effect on the green and red filters (verified with blinking it in and out). That way, the observer could get sharp views in teal-blue, green-yellow, and red-orange after refocusing for each filter's passband. It's just too bad the human mind can't combine RGB channels sequentially in time. I suppose if the filters and focus could be changed rapidly enough it might work. Alternatively, use three achromats filtered in RGB and use relay lenses to send the outputs to a combiner prism and view the result. 3-CCD video cameras do the reverse, so I know it can be done. Orion nebula and star clusters: The #8 Yellow barely helped with bright star fringing. Violet was subdued but still obvious, as was red flaring. The #12A Yellow was a better choice for violet flaring, but left red flaring on bright stars. The Hirsch #11 Light Green was just about the best choice, possibly combined with the #12A Yellow to eliminate the residual violet flaring. Without the #12A, violet and red flaring was still slightly visible, but not too intrusive. Overall, probably the best choice. The nebula was still visible, but contrast wasn't really improved any. The R89 Moss Green gave sharp views with no flaring, but was a bit dark. The faintest component of the Trapezium was all but eliminated. However, the nebula stood out a bit better by squashing some light pollution. The green filters eliminated flaring (good) and the nebula (bad), so not appropriate for this view. It became clear to me that there is no one filter that is best for all objects in an achromat. You want to apply the lightest touch possible to get to a sharp view. The #8 Yellow is barely useful. I think it was useful only on Jupiter, but not much else. The #12A Yellow filter, being halfway between the modern #8 and #12 filters, desperately needs reintroduced as the Goldilocks of minus-violet filters. It cuts all violet fringing on all objects without cutting too heavily into the useful blue spectrum, thereby leaving a light yellow cast instead of a heavy yellow cast as with the #12 Yellow. Until then, either pick up a cheap yellow filter from China or cut your own from Rosco's R11 Light Straw material. There needs to be an interference filter with a similar passband to the R89 Moss Green filter to improve transmission. The blue end needs to cut on at around 570nm to cleanly get H-B emissions at 586nm and cut off at around 610nm to eliminate red flaring while leaving the yellow and orange-red spectrum that focuses fairly closely to green. This filter could act as a jack of all trades to sharpen up achromat views of bright planets, the moon, and bright stars and star clusters while still allowing nebula to be seen in context.

I've done that too, simply sighting along people's scopes that they brought, shooting from the hip, so to speak, to put them on target. If you don't know the sky and the scope doesn't have goto, DSCs, setting circles, or even a decent sighting device, what other choice does one have?

Most professional astronomers request time on large scopes by submitting imaging proposals that are graded and either approved or rejected or perhaps tabled. The imaging request is then added to the telescope's imaging schedule if approved. Sometime in the future, the data is gathered and sent in raw format to the astronomer who then processes it (or possibly sends it to a processing expert). Regardless, the professional astronomer never actually travels to the telescope. Almost no professional astronomers own their own equipment these days.

I only use DSCs when I'm trying to track down unfamiliar targets or moving targets like Uranus and Neptune. Most of the time lately, I've been comparing equipment and experimenting, so I look at mostly showpiece objects that I'm very familiar with. In my younger days, I spent a lot of time using DSCs to track things down. Once I knew where they were on the sky, I needed them less and less. Uranus, Neptune, and comets don't fit that model very well, so I tend to still use DSCs sometimes for them if I'm having difficulty tracking them down. I was able to find C/2022 E3 (ZTF) several times without DSCs thanks to it being fairly bright, high in the sky, and near bright stars/Mars.

Where have you been @John? Miss us?

I've been using a Popular Mechanics plastic toolbox since the late 90s to hold many of my non-eyepiece bits and pieces like collimation tools, solar finder, laser sight, filter wallets, allen wrenches, Rosco gel swatchbook, small counterweights, observing eyeglasses (in a case), various photography adapters, smartphone mount, tri-finder mount, alternate diagonal noses, focal reducers, folded nightsky map, etc. A few things like my filter wheel, spare 2" diagonal, and Herschel wedge still get their own small cases/boxes outside of it.

OMG, my last post on this thread was 6.5 years ago. Apparently, people really do go back through the archives and read these musty old threads.