Louis D

Very good. The Speers-Waler 5-8mm varifocal compares favorably with Pentax XW and XL eyepieces at matching focal lengths, just wider. However, eye relief is tight compared to actual long eye relief eyepieces like the XLs and XWs, so not so good for eyeglass wearers with strong astigmatism. Focal length for focal length, I preferred it to the Svbony 3-8mm zoom over the 5mm to 8mm range mainly because of the vastly increased dwell time between nudges, and more usable eye relief when not wearing eyeglasses at small exit pupils. The main things the Svbony excelled at were small size and near pafocality across its range. You can look at this review for comparison ruler images of the Speers-Waler and others in its range:

Yep, more or less. Just substitute a GSO ED 2x Barlow with TV PBI for the Paracorr so there is one more layer of thumbscrews. And it does indeed become unwieldy trying to locate the right one(s) in the dark.

Why stop there? Plug the assembly into a coma corrector next. I've done that. It becomes hard to reach the Dob tube to move it because I'm sitting so far back from the side of the scope. 😄

I picked up a Svbony UHC which has passbands similar to a traditional LP filter. It works nearly as well as my Lumicon UHC filter from the 90s, so I can't complain for the less than $20 I spent on it. Being in the US with more lenient laser pointer laws, I mostly use a green laser sight to aim my telescopes because I can't contort my neck and back around anymore to use a QuikFinder or Telrad all that much anymore. I also have a RACI, but it doesn't help all that much either aiming or finding targets. It's mostly useful on long focal length scopes like Maks and SCTs to provide a wide angle view for centering purposes. DSCs or planetarium software like SkEye or StarSense are really helpful in light polluted skies.

I looked a the GSO 8" f/4 available from Agena here in the states, but it puts the focuser in an awkward position for proper balancing: I ended up choosing the 6" f/5 for size, weight, mount compatibility (DSV-2B), and price ($300 used with GSO CC, laser collimator, 50mm finder scope, etc.). Either way, it's way better than the KUO 152 achromat in every way I've checked. It's like night and day comparing them side by side on the dual mount. The Newt just puts up a perfectly sharp and color free image while the frac puts up a mushy, chromatically aberrated image. That, and the KUO was almost 3 times as expensive as the GSO. Literally the best thing about the KUO is the V1 focuser. It's a beast. It just exudes quality machining and internals. It's the only Chinese made refractor focuser I own that is buttery smooth, has ample inertia due to heavy focus knobs, is exceptionally well preloaded to handle heavy loads, doesn't slip or unwind with any load at zenith despite lacking a R&P, and has zero backlash, mushiness, or notchiness in the fine focus motion. It feels heavier when focusing than the 2.5" focuser on my TS-Optics 90mm triplet APO. That, and the latter unwinds under heavy load at zenith, has backlash when lifting a heavy load, and has a mushy feel in the fine focus knob.

It would hardly be noticeable to the human eye: It appears to cut on at 420nm and cut off at 680nm. Everything below 460nm is bright violet, so it wouldn't be doing very much. That, and the human eye can barely see down to 420nm, so the violet clipping would be imperceptible. The human eye can barely see above 650nm, so having a cutoff clipping red 30nm above that is also going to be imperceptible. I can barely detect the clipping at 650nm with my SP650 filter. It's really the red from 620nm to 660nm that is problematic to the human eye with fast achromats. Pretty much all of these luminance filters cater to imaging with fairly well corrected objectives. Push the left edge to the right about 50nm and pull the right edge to the left about 50nm, and you'd be in the ballpark of where it needs to be for a fast achromat filter to reject 95% of the poorly focused light. Are you listening Astronomik?

I meant deconvolve the line images. I guess you could take it further and capture more than just three lines to fill in your graph better.

I wonder if you used line filters in the red, green, and blue, could you then get sharper images to be combined into a single RGB image? I also wonder if you deconvolved the component images in software to reduce the appearance of SA could you then get sharper images? Certainly, starting with a better image gives better results, but this might make for an interesting challenge to revisit the pre-achromatic era of telescopes and see if modern imaging technology (hardware and software) could improve their images.

It's been pretty much clear the last few nights here in Texas. That's supposed to change with an Arctic front moving in on Sunday that could bring us sub-freezing temps and frozen precipitation.

I just wrap a heavy duty shipping blanket around my upright Dob and then bungee it to the side near the back of my Chevy Astro van when transporting it. Collimation doesn't shift all that much. Of course, I remove all attachments, so they don't get snapped off by something else being transported as it's being loaded or unloaded. You can put one of those foam cushion squares for long term standing under it if you want to take out some of the shocks to the scope from rough roads. You can then use it to stand on wherever you end up observing from.

I just confirmed this morning upon observing Venus using my ST80 (which has about the same color correction as the KUO 152) that the LP470 cuts all violet fringing while being slightly less yellow than the Yellow K2 filter. In comparison, the Hirsch Light Yellow #12A does leak a tiny bit of violet, but you really have to look for it. Either it or the LP470 make an excellent minus violet filter by keeping as much blue as possible. At the red end of the spectrum, I confirmed that the SP650 helps cut spurious red a little bit while the SP625 cuts nearly all spurious red. Whatever red fringing was left was nearly undetectable. The resulting color of combining the LP470 and SP625 is a light yellow with slight blue-green tones. It's obvious, but not horribly distracting. Now, how to convince a commercial company to market a dielectric 470nm to 625nm passband filter for fast achromats? It won't turn them into semi-APO EDs, but it will sharpen them up enough to use as acceptable planetary scopes while still passing as much of the well focused spectrum as possible.

But quickly enough, you learn what works and what doesn't. It's sort of how SpaceX was run at the outset. They didn't know what they were doing to start with, and look at them now. Trial and error hopefully leads to success eventually. As Edison (sort of) said about his light bulb failures, "I have not failed, but found 1000 ways to not make a light bulb."

I've been investigating ways to mitigate this with various filters in several other threads, but the short answer is that a #8 Light Yellow or #11 Yellow/Green filter can help reduce these chromatic aberrations for not a lot of cash outlay for when greater image sharpness is needed. A #56 Green can go even further to really sharpen up the image on bright objects.

Tinkering with optics is a lot of fun, isn't it? I've got several finderscope projects in various levels of completion myself.

Entry level binoviewers with 21mm to 22mm of clear aperture aren't all that expensive. The main difference between them and the more expensive models are clear aperture, eyepiece holder quality, attachment flexibility, and dedicated accessories. I use the linked Arcturus BVs with the nosepiece from a Meade 140 2x Barlow to reach focus in my Dob. Operating at f/18, I've found cheap, lightweight eyepieces such as SVBONY 68° Ultra Wide Angle 20mm eyepieces work very well in BVs.

Not bad looking for a first effort. It might also work well in a Mak with a 2" visual back to get to a large exit pupil for use with a nebula line filter.

Please post a pic of what you came up with. I'm curious now.

There's a person over on CN, Martin Pond, that at least used to post quite a bit about his tinkerings with various home brew eyepiece designs made mainly from surplus binocular optics. There are several more folks tinkering and sharing ideas there as well. They also mention a Facebook group as well for homemade eyepieces. Hunt around a bit, you might find some fellow eyepiece builders out there to share ideas with. It's a subject that indeed comes up rarely on SGL, but a search here might be worthwhile as well.

To add to the excellent suggestions already: The phases of Venus over time The double-double in Lyra (i.e., Epsilon Lyrae) Trying to pick out Mercury near the horizon naked eye is always rewarding Collinder 70 (Orion's Belt) in binoculars The star cluster rich area near the Double Cluster and Perseus (sorry, don't exactly know the name, but it is beautiful to scan around) The summer Milky Way from Sagittarius to at least Cygnus. It's loaded with bright nebula and star clusters. Again, scanning along it is rewarding. Galilean moon transits/occultations of/by Jupiter and their shadows on Jupiter are fun to watch in real time With a fast achromatic refractor such as yours, you may need to sometimes add some filtration to see fine planetary detail through the violet/red fringing.

Yep, T-thread/mount for camera adapters. It's M42x0.75. Not to be confused with the M42 mount which is M42x1mm and was also used for camera lenses.

Actually, its the distance to the focal plane of the eyepiece that matters, not the location of the lower lens. This is particularly true for eyepieces with internal field stops due to the use of a Smyth lens group.

Check my recent post to the TS 152 thread: I've been chasing the same goal of getting rid of spurious color in fast achromats. I've come to the conclusion I'd rather live with a bit of yellow-green tint and give up H-alpha for non-nebula observing. As such, a nice high transmission, sharp cut-off 470nm long pass filter gets rid of all the violet fringing while leaving almost all blue. This is fine for DSO observing. However, for solar system observing, adding a high transmission, sharp cut-off 625nm short pass is a must to cut red fringing. The color cast goes a bit more yellow-cyan than yellow-green with it. It's certainly possible to then stack whatever nebula, pollution, or Neodymium filters suit your tastes. Can you post the XLCR-1 curve as a point of reference?

The reviewer totally missed that the residual false color with the minus-violet filter was coming from the red end of the spectrum. That was what was causing some issues with planetary observing. Literally no commercial false color filters include far red filtering for unknown reasons. Sure, it's not obvious with no filtering, but once the violet fringing is minimized with a minus-violet filter, it is blatantly obvious as a bright red rim around every bright to dark edge on bright objects. It's not very obvious with scotopic vision due to the response curve of the rods in our eyes, so DSO observing is generally not impacted all that much by it. In my experience, it's the red light above 625nm that really contributes to red flaring in achromats, and scotopic vision pretty much doesn't pick up anything above 600nm as shown below: Thus, little to no red flaring on dim objects once dark adapted. However, photopic vision really picks up on red above 600nm on bright objects like planets and the moon, so some sort of short pass filtering is needed for fast achromats when observing such objects. Weirdly enough, no astro vendors sell such a useful, even necessary, filter. I've had to retask industrial and photographic filters for astronomy use as a result. The closest astro filter is the long out of production Hirsch Light Blue #82B which is really a light cyan with a gradual short pass cutoff around 625nm and fairly high transmission. I happened to find one on ebay last year. I'd never heard of it until then.

Not sure who you're addressing, but I also have a 6" f/5 GSO Newtonian that makes for a fine, sharp wide field scope with no false color, cool down, or dewing issues. I think I picked up my lightly used copy with the GSO Linear Focuser, GSO coma corrector, 8x50 finder, and laser collimator for about $300 shipped. At 13 pounds, it's also considerably lighter than the KUO 152 refractor. The spider vane diffraction spikes don't bother me at all. I also like having the eyepiece up nice and high so I don't have to extend the tripod's legs, leading to a more stable mount. While the Schmidt-Newt and Mak-Newt sound interesting, I'll stick with the simplicity of a pure Newt for now.

One more update on the KUO 152 and filtering. Santa brought me high transmissivity SP625, SP650, and LP470 filters, where SP means Short Pass (cyan in this case) and LP means Long Pass (yellow in this case). The LP470 exactly removes all violet fringing, unlike my Hirsch Light Yellow #12A which has roughly the same cutoff frequency, but trails off a bit, allowing some dim violet to get through. The SP650 helps some with cutting unfocused red light while causing very little color shift. The SP625 almost completely eliminates unfocused red without causing a drastic cyan color like my SP600. So, I spent some time last night on Jupiter, the Orion Nebula, and Orion's Belt (Collinder 70) with the LP470 ahead of the diagonal and swapping in the SP625 and SP650. For dim objects, the SP650 combination was good enough, but for bright objects, the SP625 was noticeably better. With the LP470/SP625 combination, I could sharply see Io approaching Jupiter and then merging with it. I still couldn't make out that it was in front of it, though. Without the filter combo, Io was lost in the unfocused light flares. I then added the Zhumell Urban Sky (Moon & Skyglow) filter (roughly the same as the Baader Neodymium), but I didn't see any appreciable new details, although it did slightly dim Jupiter making it a bit easier to view. Before coming in for the night, I removed the LP470 from the diagonal and moved it in and out of the FOV above the eyepiece. Even combined with the SP filters, there was no appreciable dimming of the Orion Nebula with the filters thanks to their 95%+ transmission each. However, the Trapezium was easier to resolve at low powers with the filters than without again because of their suppression of unfocused light flares. I even compared the various LP/SP/M&SG combinations to the Baader SemiAPO filter. It was no contest. The BSAPO was doing almost nothing to sharpen up the image compared to the various LP/SP combinations. Adding the M&SG to mimic the BSAPO frequency notches due to its Neodymium substrate didn't really add anything to the LP/SP combinations. I think Baader did that just to remove some excess yellow to compensate for the violet suppression. If Baader were actually serious about their BSAPO mimicking an ED scope, they need to suppress unfocused red light along with the unfocused violet light, but they don't. For the LP470/SP650 combination, the M&SG does result in a more neutral color for Jupiter. However, with the LP470/SP625 combination, it simply shifted the color more cyan than the yellow-green it already was. I preferred the yellow-green cast to the cyan cast. Overall, with the LP470 and SP625 in place, the KUO 152 was much more satisfying to use than without. The light yellow-green color cast was hardly noticeable after a while. I actually began to enjoy sweeping the star rich regions of the Orion constellation with it. Once the moon is back in evening skies, I'll have to try out the new filters on it as well.