John

I found quite a few positive reports on the Celestron branded (China made of course) prism diagonal - the one with the part number of 94115-A. They chimed with good experiences I had quite a few years back with the same diagonal which came with a C5 scope that I owned back then. Given that the scope that I wanted it for was F/16 I felt that the risk of 20 quid for the thing was worth taking. It's not in the same league build-wise as my Baader T2 Zeiss prism of course but that cost more than 10x as much ! I probably won't be comparing these two, in case the 20 quid prism performs just as well as the 200 quid one 😉 So far though the cheapie prism has done fine in the undemanding long refractor. I have replaced the chromed set screws with nylon ones to give my eyepiece barrels a chance though 😬

Spotting a bag of tools let go by accident by an astronaut working outside the ISS 🙂 I think that has happened twice now.

Just thought of another one: - Spotting the central star in Messier 57, the Ring Nebula.

Yes - the prism diagonal uses 10-12mm less of the light path of the scope so eyepieces focus that much further outwards / you gain inwards travel.

We have been talking quite a bit lately about a couple of observational astronomy challenges, namely: - Seeing "the Pup Star" Sirius B - Spotting the E & F members of the Trapezium group of stars in Orion I thought it might be useful to start a thread on such challenges which might, over time, build into a useful memory prompt / suggestion box for the visual observers amongst us. I'm intending to stick with challenges for the visual observer rather than for EEVA and similar approaches, which will have their own boundaries I'm sure. To get the ball rolling I'll add a few more to the ones above. Some tougher than others, some more personal challenges rather than "classic" ones, and quite a few of course will have already been achieved by observers on SGL: - Spotting the Encke Gap or Encke Minima in Saturn's A-ring - Spotting Saturn's C-ring or Crepe Ring - Seeing white spots in Jupiter's cloud systems - Spotting the Martian moons Phobos and / or Deimos - Seeing Neptune's moon, Triton - Seeing some of Uranus's 4 brightest moons (all still rather faint !) - Splitting Antares - Spotting quasars - Splitting Zeta Herculis Please feel free to add some more of your own - the more the merrier 🙂

Yes. I recently picked up a cheap Celestron branded 1.25 inch prism diagonal for use with my 75mm F/16 refractor and gained around 10mm-12mm of focuser travel. The optical performance seems quite good too.

Triton should be, on a good, dark night. The moons of Uranus have so far eluded me at apertures less than 12 inches. Even the brightest of those is a magnitude fainter than Triton. Edit: apologies, I realise that I've to some extent repeated what I posted earlier in this thread - I lost track !

Pentax XW's and Baader Morpheus have very good performance, generous eye relief and a wide AFoV. The Svbony 3-8 zoom is very good optically but the eye relief is too short for many glasses wearers I would think (I'm not one).

@Stu is quite right about the seeing being a very important factor in these challenges. Another one, IMHO, is recognising that you are actually seeing something. That might sound an odd way to put it but these tougher challenges don't just pop into clear view when you get the goldilocks aperture / seeing combination. They go from being just beyond the threshold of being seen to just being on the right side of it but still can be very transitory, fleeting, vague and barely sensed rather than a "clean spot". With my 12 inch dob under the right conditions, E & F were so clear you simply could not miss them. With the ED120 under middling conditions, they could be hard to spot, especially F. So as well as "seeing, seeing, seeing" I would add "practice, practice, practice". Your 127 mak is up to these tasks I would think - you just need to keep at it, and at it, and at it ........ Challenging lately with the volumes of cloud and rain that we have experienced in the UK of course 🙄 Plus, the Orion and Sirius "season" is nearly over now of course.

They are not quite equally difficult tasks from my experience. Spotting Sirius B is the tougher one and very much seeing dependant. Of course the further north you observe, the harder Sirius gets.

Lovely drawing Mike, as usual 🙂 👍

Best split tonight with the Elliott 3 inch refractor was Iota Leonis. Here is what the Webb Society's Bob Argyle said back in April 2017 about this uneven brightness pair: Webb Deep-Sky Society: Double Star of the Month: Iota Leonis (webbdeepsky.com) Pleased to get it with the 3 inch tonight at 171x. Secondary was close in but clearly split and more or less due east of the primary. Quite testing for sub-4 inch aperture scopes I reckon.

Quite nice here. A little hazy perhaps but a good double star night, currently.

Class Brass this evening 🙂

That option did go through my mind as well. A few years back the Skywatcher ED100's were the best value ~4 inch ED's by some distance but recent price rises have got them lost amongst better finished and equipped alternatives such as the Starfield 102 ED. I paid £300 for a mint condition ED100 about 20 years ago - nothing could come near that back then 🙄

Twisting the top section of the eyepiece moves that section up and down but does not move the optics in the eyepiece - it's a kind of adjustable eye cup but does not alter the optical focus of either the eyepiece or the scope. Generally with these designs, those who wear glasses when observing use the top section at a lower position, ie: screwed downwards. Those who do not wear glasses when observing will probably find having the top section in a higher position more effective ie: screwed upwards. I'm not sure where you might get a replacement rubber eye cup from. OVL are the main Skywatcher importer so perhaps they could help ?: Stargazing Telescopes, Binoculars, Spotting Scopes, Microscopes by OVL - Optical Vision Ltd

If I was in the market for a third 4 inch ED refractor, the Starfield 102 ED would be very high up my list and if budget was part of the equation, probably right at the top 🙂 I just can't think of a justification for getting another 4 inch frac though - questions would be asked !!! 😬

It looks more like a 5 inch than a 4. The brass focuser reminds me of Sir Patrick Moore's Cooke 5 inch:

I think I'd do the same - move the 130 on to a new owner. The 8" dob and 4" mak make complimentary and contrasting companions I think. Your photo illustrates nicely how an 8" dob is compact for it's performance advantage over the 130 eq mounted newtonian.

Great report ! You make interesting points regarding premium eyepieces and filters. When I've had the opportunity to observe with 20 inch dobsonians, I can remember the amazing views but not which eyepiece or filter was being used at the time 🙂 Star parties are great for getting a taste, even if brief, of a range of other equipment 👍

I think the main drawback is that you are opening the eyepiece up to install the FT ring. It goes between the upper body optical set and the lower set. Except for the 24mm which, as Don says, does not have a lower optical set. I guess it's a fiddly thing to do in the dark and there is always the possibility of dust getting onto the internal lenses of the eyepiece.

Mine as well. Every time I had business in London, somehow my journey home was via Farringdon Road 🙄

For those who remember, I came across this movie on Youtube, Steve Collingwood's channel 🙂

I got suckered out by seeing a clear sky with lots of stars showing. Scope went out. 20 minutes later, clouds rolled back over again. I had just enough time at the eyepiece to see that the seeing was really unsteady, which is a little consolation at least. I've now got my 11x70 binoculars on standby in case there is a sudden clearance again 🙄