Louis D

Under our generally steady Texas skies, aperture rules. The only time they're unsteady while clear is in the first 24 hours after a front passes through. This is because we're generally well south of the Jet Stream. With my 15" Tectron Dob, I could regularly use 350x to 400x with ease when I still able to hoist its 65 pound mirror box. I need to swap it for one of the newer lightweight models or build a permanent outdoor enclosure for it. I don't know if trying to haul out and setup the 185 APO and mount would be any easier. I have a hard enough time trying to get my KUO 152 achromat onto my alt-az mount's dovetail mount due to the height of the mount and ungainly bulk of the OTA. The only thing high on the Dob to be assembled is the secondary cage which isn't all that heavy.

They might also be 8-32 x 1/2”, 10-24 x 1/2” or even 10-32 x 1/2” screws. I believe the first would be closest to an M4.

Yes, but if you're going to go visual for that money plus the cost of a mount, I'd go with a 12.5" Obsession Dob or similar.

How about 1/4-20, the same as camera tripod threads? That is a pretty common size for mounting screws. See if the screw to mount a camera to a tripod head will thread into the hole as a confirmation.

No, the reply was talking about a 33% increase in light gathering due to the larger aperture when squared to account for area increase. More importantly in experience, the linear increase in aperture from 130mm to 150mm is insignificant when it comes increasing resolution. That's only a 15% increase in linear aperture which determines resolving power, thus the comment about only being able to go 15% higher in magnification. If you want a significant increase in linear resolving power for planetary observing, you'll need at least a 50% increase in linear aperture which would be 195mm (200mm) or 8" as suggested above several times. Thus, the recommendation of the 8SE over the 6SE. Also, keep in mind that the half as fast f-ratio (f/10 versus f/5) of SE line versus the 130p means you will not be able to easily get to large exit pupils when using narrowband nebula filters. It takes a 56mm Plossl to yield even a 5.6mm exit pupil. It also means you'll be giving up lower powers and wider true fields of view relative to an f/5 or f/4 Newtonian. In my experience, an 8" Newtonian with a well figured primary yields a higher contrast and sharper planetary image than an 8" SCT. The only exception to this I've found is the 8" Celestron EdgeHD which puts up images rivaling Newtonians with well figured primaries. Of course, if you're doing image stacking, it tends to be able to resolve more detail than the human eye can see, so it may not matter if you're not a visual observer.

I may have found the Holy Grail of dyed filters for blocking both violet and red fringing in fast achromats. I knew the color would have to be somewhere in the yellow-green part of the "filter spectrum", but all the ones I had tried up to now were not blocking violet (and quite often red) sufficiently, and some were just too strong a green color resulting in low transmission of all wavelengths. I have been experimenting with older 48mm camera filters from the photographic age of filtering during image capture because they're cheap and come in a huge variety of color variations. I bought a 4000K LED lighting panel to approximate balanced sunlight to photograph them so you all can see what I see when holding them up to a light. Its spectrum is rather weak in the blue/teal blue region because it uses a violet LED to excite yellow-orange phosphors. I manually color balanced my camera on the blank light before taking images. I then normalize all images to have a white background with RGB values equaling ~248 for all because that results in an image brightness on the screen approximating what I see with my eyes. Experimenting with various combinations of these filters and with unmounted industrial filters mounted in empty 48mm frames, I tried various combinations in both by 80mm f/5 and 152 f/5.9 achromatic refractors by holding them between the eyepiece and my eye. As I've stated over in the TS-152 F5.9 thread, having sharp cutoffs at 470nm for violet and 625nm for red is just about perfect to eliminate all perceptible unfocused violet and red while leaving as much of the spectrum for visual work as possible. The result is a light yellow-green image tint for this and similar filters. Below is an image I captured showing some of the contenders, annotated with what each is. Long story short, the very new to me Vivitar Light Green #11 (X1) from Japan in the center, dating from somewhere in the 70s or possibly 80s, is just about perfect for blocking violet and red color fringing on bright solar system objects in fast achromats. The LP470+SP625 combination above it has slightly higher transmission and sharper cutoffs at each end, but yields just about the same visual color tint and intensity as well as suppression of color fringing. I also verified their spectra are quite similar on the blue end while the Vivitar tails off on the red end rather than having a sharp cut off like the industrial combo. It looks like the latter is more yellow than yellow-green, but the SP625 is an interference type filter that reflects red and doesn't photograph well with this reflectively backed LED light panel. I had to elevate it 3 inches off the surface to get any blue-green tint at all. The Hirsch Light Yellow #12A is there for reference in that it has almost exactly the same passband (yellow tint and saturation) as the industrial LP470, just with a more gradual cut off. It demonstrates that there is a slight blue-green tinge to the LP470+SP625 combination, yet it is slightly stronger than shown when used in a telescope and viewed with eyes rather than a camera sensor. For background, I already had the following filters also shown above: Hirsch Light Green #11 - Doesn't cut violet or red very well at all. Very disappointing filter for this purpose. Panagor Yellow-Green X0 - Slightly better at cutting both ends of the spectrum than the Hirsch. Rokunar Green X1 (#11) - Best green I've found, cuts all violet and red fringing while passing the rest of the spectrum, but has maybe 60% transmission and a strong green tint. Meade Green #56 - Doesn't cut violet very well, good otherwise if stacked with a light yellow filter such as the Hirsch. Cheap Green - Very close to pure chromatic green with decent transmission compared to most green astronomy filters. Cuts all violet, but leaves H-beta line. Strongly attenuates yellow, orange, and red, so some signal is lost in those bands. I swapped back and forth between these and other filters, narrowing down my favorites. The Vivitar Light Green was a surprise winner. I thought it would be the same as either the Panagor X0 or Rokunar X1, but it isn't. It's somewhere in between as you can see above. Truly a Goldilocks of Yellow-Green filters for fast achromat users. I could not discern a significant enough difference between it and the industrial LP470-SP625 combination on the moon and Jupiter to recommend the much more expensive latter combination on bright objects. The fact that I got the Vivitar as part of a $30 lot of 12 used filters is all the more remarkable. I had bought the lot to scavenge 48mm frames, not paying much attention to the Vivitar thinking it would just be a duplicate yellow-green filter. I'll try some other Light (Yellow) Green X1/#11 filters such as those from Hoya and Tiffen if I come across them for a good price in good condition. I'll also look into buying some astronomy targeted 1.25" yellow-green filters such as vintage Meade 4000 and GSO relabels to see how they stack up to the above lineup. I need to find a good 1.25" yellow-green filter for the ST80 because it has a 1.25" focuser. The Hirsch Light Yellow #12A stacked with an industrial 27mm SP650 mounted in a 1.25" frame is pretty decent, but still leaks some red fringing. I haven't been able to locate a 27mm unmounted SP625 so far. When the Hirsch Light Yellow is stacked with a Hirsch Light Blue #82B (really a cyan color), it cuts all red fringing, but yields a strong yellow-cyan color as seen in the image in this post. I need to update that picture sometime with images through some of the newer yellow-green filters and combinations. For reference, the Vivitar Light Green #11 (X1) shows up in 48mm size on ebay in the US quite often for under $15 shipped. Make sure to get the Japan version (labeled on the filter as such). Later versions made elsewhere might not be the same tint. I've seen this with the Meade Yellow #8 filters. Some are lighter and some are more saturated, depending on the vintage.

Are you taking images using eyepiece projection rather than afocal projection? It looks like you may be running into issues with a curved projected focal plane from the eyepiece. Try using afocal projection with a 50mm prime lens on the DSLR, coupling the eyepiece to the lens's filter threads with step rings, to see if you get better results across the field of view. Make sure to leave the lens aperture wide open to avoid vignetting. You can pick up a used Olympus Zuiko 50mm f/1.8 with an OM T-adapter for a reasonable price these days. I use them for this and other afocal photography duties on Canon DSLRs.

I did the 22mm Astro-Tech AF70 vs 22mm Nagler T4 comparison multiple times, and it was close. The former won out on eye relief, lighter weight, and freedom from any SAEP, but the Nagler won out on wider AFOV and being sharp to the edge. The AF70 goes astigmatic in the last 5% to 10% of the field near the edge. I ended up retiring the AF70 to the B-Team case with the 12mm and 17mm NT4s that were retired in favor of the 12mm and 17mm ES-92s. I figure my daughter might want to move up to that case at some point, so I hold onto them.

Look for a used set of Meade HD-60 eyepieces. I compared them to Paradigm/Starguider line and preferred the HD-60s pretty much across the entire lines. Here's my comparison: I've loaned both sets to my 29 year old daughter to use with her scope.

If you want to push your ST80 as far as it can go with a good high power zoom, pick up a Svbony 3-8mm zoom. I reviewed it in the following thread:

The pre-Max ones are fine. I've been flying in them for almost 4 decades now, and have rarely heard of any issues with them. Read up on Boeing. Apparently, their quality control has slipped a lot of late and many companies and countries have taken notice. Most pundits blame it on trying to maximize short term shareholder return at the expense of everything else.

I have an ST80, and it is probably my worst scope for high power planetary viewing due to its short focal length, limiting 80mm aperture, chromatic aberrations, and spherical aberration. Magnifying a marginal image more isn't going to resolve more detail. I would recommend using a Green #56 or Yellow-Green #11 filter to cut some of the poorly focused and spherically aberrated red and blue ends of the spectrum to maximize the central green region of the spectrum for which these scopes are optimized. If you really want to "zoom in on" the planets; that is, magnify them more to see more actual detail, I recommend getting a 6 to 8 inch Newtonian (perhaps as a Dob if you have a lightweight mount) to see much more detail without breaking the bank.

Unless you're trying to keep costs down, you might look into getting either a 6" f/5 or 8" f/4 solid tube Newt with dual speed 2" focuser. You'd need to upgrade to a alt-az mount on a tripod, but having access to 2" eyepieces for much wider fields of view would be "eye opening". That, and the convenience of a dual speed focuser that doesn't rotate the eyepiece to focus can't be overstated.

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."