Ags

Looks like I am going to have to start the Campaign for Real Astronomy 🤣

Rage, rage, against the dying of the light.

I do enjoy my Scout most when stopped down to 43 mm for contrasty surface detail and for imaging, but the full 60 mm is great for viewing prominences in detail.

I think these things are the astronomical equivalent of the Singularity where the hobby evolves into a radical new form I no longer recognize. I feel they replace the visual experience with something that looks better, but which is really just another glowing screen displaying digital content.

I find I can flip left-right when looking at a double, but not when looking in a finder scope. I suppose with the double, I know what I am looking at, but in the finder I am trying to recognize star patterns and flipping and rotation is too much math... So my finder is a RACI but the main scope has a simple prism not an amici. Not a fan by the way of the diffraction spikes caused by an amici, which would be very visible at higher magnification.

Indeed I have a regular prism.

I had another look last night. No time for side by side views with the mirror diagonals, but I got an excellent view of M57 and Albireo. I also confirmed the double split on Epsilon Lyrae and the absence of false color when slightly defocused (versus the strong false color seen with the mirrors). Star fields were very sharp when browsing 2.2° fields.

No, seems to be fixed. Which I like. I can solve this with the right screw heads. Looks nice, I think FLO also sell this under StellaSomething branding.

...they would jog a little faster 🤣

That's appalling! You couldn't get a refund?

I know this is a bit niche, but I wanted to share my rule of thumb for approximating eyepiece field stops: if an eyepiece has about 60° apparent field of view, then the field stop diameter is roughly equal to the eyepiece focal length. It's the same formula as for calculating the field of view of a camera, so this approximation is best for eyepieces with exactly 57.3° apparent FOV 😀 For example, the Delite 3mm has a 3.2mm field stop, and the Delite 5mm has a 5.3mm field stop. As the Nagler 5mm has 82° AFOV vs the 62° of the Delite, you would expect the Nagler to have ⅓ more field stop, and it does with 7mm.

I don't think I am seeing significant collimation issues. All the diagonals put the object within a 4 mm circle, and collimation would show as coma/astigmatism and (in the case of a dielectric) a color change and dimming. But with the TS dielectric I am seeing a softness to the image combined with a rainbow line visible at high powers such as might be produced with a diffraction grating. I wonder if the dielectric layers were not deposited evenly, that might explain it.

I haven't fitted a focusser to my SCT; I just have a fixed visual back and focus with the primary mirror.

I don't have a laser to test the diagonals, but I can test with my SCT on the next clear night - using a camera, collimate the SCT without diagonal, then check collimation with diagonals. Unless I am mistaken, the TS dielectric is uncollimatable. When switching diagonals I did notice some image shift, so I would guess collimation can be a factor.

I have always wanted to get the Tak, and i think I will at some point. With the TS dielectric likely headed to the bin (can't in good conscience sell it) and not really liking the SkyWatcher freebie, I need at least one more diagonal. I went for the Celestron over the Tak as I hear it works better (provides stronger correction) in fast semi apos like the Long Perng 90 f5.6 which I have my eye on as a travel / grab-and-go scope. It certainly seems combine well with the ZS66. If it's clear tonight, I want to continue the testing on some planetary nebulae and colored doubles. Color rendition seemed best with the Celestron prism while looking at white and yellow stars, it will be interesting to see how an orange-blue double like Albireo fares. With the ability to go over 100x with the Celestron prism, some testing on the Moon seems worthwhile too. Another thing I would like to try is the poor unloved C6 with the prism. I have been blaming the C6 for mediocre views, but it looks like the dielectric is the true culprit.

Last night was the first time I felt I could push the scope down to 3mm (129x) and now I am thinking about an SLV 2.5mm as a starsplitter and Mars eyepiece. I can't understand how dielectric is producing the multicolored distortions I see. I went back and forth between the diagonals many times to make sure. The difference was however stark and undeniable. The only issue I had with the Celestron prism was a faint blue halo around Vega; this might be an issue viewing the Moon... I will do more testing on other targets and different conditions.

I have no doubt they are generally good. But the one I have appears to be an exception.

I am sure they are usually very good but perhaps mine slipped past QC.

Today I became the owner of three diagonals after a cheap Celestron 1.25” prism diagonal joined my TS dielectric diagonal and a SkyWatcher starter diagonal that came with a Skymax 102 (both 1.25” diagonals). I researched the Celestron online before buying it, and learnt that it is at least as good as a Zeiss, but it also covers the view in blue chromatic aberration and gives a soft image. It has very little scatter, except when it has ridiculously large amounts of scatter! I got the Celestron unit to see if scatter is possibly lower with a prism, and because of the potentially beneficial refractive properties of prisms. Prisms increase spherical aberration, so if a scope is undercorrected it might benefit from a prism. Also prisms push color error to the blue end, so if a scope is poorly corrected in red, the prism can again offer some improvement. Of course, a perfect telescope can only suffer from these prism aberrations (corrections?), but who has a perfect telescope? Tak owners, put your hands down. I don’t have a clue if my Zenithstar 66 is undercorrected, and I have never seen any color error, but it’s not a very expensive experiment to conduct. I do not like the SkyWatcher diagonal - it disassembles far too easily and the thumbscrews collide with wider eyepieces as they are too near the top of the barrel and the screw heads are the wrong shape. The Celestron is quite similar with the same troublesome thumb screws, but feels a little more solid… maybe it is just heavier. At least it doesn’t disassemble. The coatings on the Celestron’s prism do the job - I needed to use a flashlight to prove to myself it really was a prism and not a mirror diagonal. The TS is chunky and looks and feels like a solid, quality unit. But some of the money spent on the diagonal has gone into styling it like a solid, quality unit… Hopefully most of the cost went towards a spectacularly good mirror? My testing strategy is Lyra, Lra, Lyra. The ZS66 only splits one of the pairs of the Double Double with a 3mm eyepiece and the TS diagonal. Will the Celestron do any better? And will the SkyWatcher do worse.? My money is on no observable differences between all three, and I will probably get the diagonals muddled in the dark anyway. By the way, if my back holds up, and I can reach focus, I will also try the straight-through view too, so there is a baseline of a “100% Strehl diagonal”. Staying with Lyra, I’ll look at the scatter around Vega with my most forensic and least scattery eyepiece, a Vixen SLV 6mm. The Ring Nebula provides a chance to see if faint fuzzy objects appear any different in the SLV 6mm with each diagonal. Finally, can any of the diagonals reveal Polaris B - another double that escapes my ZS66 under my city skies? The B component should be in range of the ZS66 - it’s not that faint - but I have never had more than hints. Clear (but not dark) skies are predicted tonight, so hopefully the answers will soon be in! LATER, MUCH LATER… Well, I have had a surprising and eye-opening night. The first target was the Double Double. Celestron diagonal - both pairs split, the components appeared white or slightly bluish stars and were pinpoints - I immediately feel I haven’t had a view this good in a long time. SkyWatcher diagonal - both pairs split, they however appear blue-green; they are pinpoints with a little bit of scatter. Not bad. So why has this double been double trouble this year? Finally my “fancy” TS diagonal I always use - no sharp focus point, blue-green stars , only one pair splits and a bad split at that, stars are messy, not pinpoint. Who would have thought - my special dielectric bought as a welcome gift for my Zenithstar has been sabotaging views for months? Celestron clear winner. TS fails hard. Vega next… Celestron - clear diffraction rings in 3 mm eyepiece, very diffuse blue haze around the star. Numerous, pinpoint stars in 13.4 mm eyepiece. SkyWatcher diagonal - subdued diffraction rings at 3 mm (129x), red edge to Vega. Strong blue outside focus, strong red inside focus. When seeing is poor, kaleidoscope around star. Spiky stars at 13.4 mm, less numerous than in Celestron. TS diagonal - no diffraction rings around Vega which has linear rainbow effect with a line through the star at 3 mm, good bright stars at 13.4 mm however. Is the dielectric mirror cracked???? In the mirror diagonals the red or blue false color was extremely strong just inside and outside focus, but with the prism, this was not observed. Celestron clear winner. TS fails hard again. Polaris next. However I only used the Celestron prism. With 3mm eyepiece: vividly yellow primary with diffraction rings, very faint but clearly seen secondary. Confirmed in Stelle Doppie and Stellarium. I am smiling ear to ear. Finally splitting the Double Double and resolving Polaris B (mag. 9.1) has seemed impossible at times with the Zenithstar. I had always expected more from it, and it looks like I was being held back by my fancy dielectric diagonal. Moral of the story: don’t always judge equipment by the price tag or the external stylings!

A little Celestron prism. Anti reflection coatings are quite good, at first I wasn't sure it was a prism. Initial impressions are favorable for the price, only real gripe is the thumb screws should be 2mm lower to avoid colliding with the bottom of wider eyepieces.

The charts helped me locate M56 last night, which is almost completely drowned in light pollution where I am. I have been looking for it for years, so that's a big win for the book!

Quick session, work night but can't let good skies go totally to waste. Beta Lyrae, Ring Nebula, down to Albireo, which is showing really strong colors tonight. Inched my way back to Lyra, matching the patterns to star charts and finally located M56 after years of trying - just a slight puff against the milky background. Over to M13 for a quick view.

Dark skies certainly help, and I do treasure my trips to dark skies, but regardless of light pollution levels its fun standing alone outside sharing the quiet darkness with the gently humming mosquitoes, gliding this way and that with a fine telescope. Even if the destination is an averted vision smudge, there is still the fun of chasing it down. I observe with a small refractor in a city, chasing things at the limit of my vision. Give another astronomer a 24" dob and pitch black skies and what do they end up doing? Hunting down obscure ICs and NGCs at the limit of their vision!

I will respectfully reject your counsel of despair. I haven't seen the milky way from my back garden for 12 years, but I still go hunting for DSOs. Maybe my expectations are lower? I'm just happy to find them! The main drawback with the Bortle Scale is it only officially goes to Nine. It must be at least Eleven round these parts 🤣

Thanks all. My own copy of the "final" version arrived today. Clear skies tonight but work tomorrow 🙄