JTEC

Excellent, vibrant, informative, good-humoured forum! But, just on the nerd thing, there needs to be a special subcategory for people who talk about the Svbony 8-3 zoom all the time

Bill Paolini, in his comparative test of diagonals had this to say about thermal settling: ‘ Diagonals absolutely require thermal acclimation time for best planetary performance! Going from a 70ºF inside temperature to a 30ºF outside temperature took a toll on the diagonals, particularly the 2" non-Prisms as they showed astigmatism even directly on-axis. The prisms did not show astigmatism, but did show a less sharp view until thermal equilibrium was achieved. Generally 15-30 minutes was required for optimal high magnification performance.’ Diagonals not eyepieces, but it seems reasonable to think that a chunky, multi-element eyepiece is going to need at least similar consideration. I don’t think it’s just about the behaviour of air in the tube and above the mirror surface, though of course those are always an issue. It makes sense, I think, that an eyepiece, especially one that is physically big and contains numerous lumps of glass with different thicknesses, figures and refractive indices, all supposedly ‘finely tuned’ to work together, stacked usually in a metal housing, is going to be subject to differential heating/cooling through its body - and it won’t perform as designed and intended until everything has settled down. FWIW, I expect to have to allow for this, especially when using big or complex eyepieces or the binoviewer with its GPCs, whenever I’m trying to get the best out of my frac.

Alan, I have the 22mm T4 and it’s one of my all-time favourite eyepieces both in my current refractors and in the 12 and 14” Dobs I used to have. Friends seem to like it too, including some who don’t spend much time looking through telescopes. Really just to say that, imv, it’s a super eyepiece and you couldn’t go wrong with it in terms of quality and performance. Expensive though. I suspect you knew all that already 🙂. I’ve not used the SL, so can’t, I’m afraid, offer any comparisons.

Done, and thank you @laser_jock99 for bringing this to our attention.

Always assuming the light path doesn’t raise issues with focus in your scope, the advantages are all with the 2” I think. First, as Stu and Louis say. And you’d regret getting rid of your favourite eyepiece - why would you do that? I did that once - it was a 22mm Nagler - regretted it and eventually bought it again. I’m struggling to think of any disadvantages of the 2” over the 1.25”. A bit heavier, which really shouldn’t matter. The 2” gives you options. I have had both but only use 2” prisms and mirrors in my scopes now. Those are the Baader prism and the Baader BBHS mirror diagonal, which are, admittedly, high end models - there is no visible performance difference that I can see compared with the 1.25” versions. I like the robustness of the larger model overall and also at the points where it interfaces with the scope and with the eyepiece.

Mark, may I pass on to you a fable that has been of value to me over the years when making choices in a multifarious field? Long ago I was playing around with big cameras, the sort where you put a cloth over your head to view the image on a ground-glass screen, amusing myself doing landscapes. I fancied that I needed another lens and went into a store that sold high end photo kit. Behind the counter stood a pasty youth with - sign of the times - plentiful gel on his hair. This could be a waste of time, I thought. ‘I’m looking for another lens’, I said, ‘but I’m not sure which one to go for.’ ‘Well sir’, replied the pasty one, ‘it depends entirely on what you want to achieve.’ I draw on his unexpectedly wise words to this day and always when buying a lens, an eyepiece, etc - the choices in our hobby are vast and so are the lures and temptations. Reading your posts - and please don’t take this the wrong way - I feel that you still need to clarify and simplify. Exactly what is it you want to achieve? Planetary imaging? DSO imaging? Wide-field or other? General visual observing? All of the above? To quote another even more ancient proverb: no one type of scope is best for everything and all have limitations. Opinions differ as to what scope for what. The best steer, imv, is to look at what the best practitioners are using. I know that fine planetary images are being produced with Newtonians but Damien Peach, by common consent the best planetary imager in the world, has always used SCTs. Fabulous wide-field images are being produced with small refractors - and, having done lots of it, imv, that’s the best place to start with this kind of imaging - the longer focal length stuff is more demanding in every respect. However, a small or even a middle sized refractor is not the best choice for planetary or lunar imaging because, at the sizes we can afford, such a scope won’t have the aperture to resolve the available detail and, usually, the image scale will be too small. For general visual, a small refractor (which I think you already have) for wide field views plus a medium sized (8-12”) Dob. Having owned big Newts and several EQ6 mounts, I think a big Newtonian OTA on one would be a bit of a handful, not just to manhandle but, more importantly, to get to perform optimally - too much to wobble about. Not impossible to achieve, but requiring a heck of a lot of attention to detail and offering lots of things to frustrate and go wrong. Please heed the words of Confucius from the camera store … 🙂 Good luck!

@Flame Nebula Hi, yes, I was satisfied with the views visually. Both scopes were good with the binoviewer, which, fwiw, is my preferred way of viewing Moon and planets. The views, of Jupiter and Mars, for example, were not ‘mushy’ and showed good clarity, colour rendition and detail. The MTF curves I’ve seen would suggest that the SCT might have slight advantage over equivalent unobstructed aperture with high frequency detail but be slightly disadvantaged in the mid range, which, other things being equal, might make it a better choice for some sorts of target than others. The 140 apo image is subjectively nicer to look at and probably samples the available UK seeing almost all the time. When I decided to ‘rationalise’ my kit recently, it was the SCT that went - the apo wasn’t going anywhere. I’ll PM you about the bench test, because a third party is involved - suffice to say, it was done for me by someone whose name most users of the forum would recognise as highly expert and who is a friend. As far as I know, there is no option available to test SCTs before purchase. I had it tested purely out of interest. Please bear in mind that while the SCTs I owned turned out to be good - I’ve heard that quality is more consistent these days - there might still be some ‘less thans’ out there. My feeling is that if you have doubts, it would be better to look elsewhere and many helpful suggestions have been made 🙂.

I’ve owned the 9.25 and the 11 and was pleased with both. I’m a fussy observer and have a TEC140 to compare them with. While the character of views through the apo was (and is) uniquely attractive - there’s no disputing that high quality apos render sweet views - both the SCTs resolved and showed finer detail on, for example, the Moon - not surprising, given their substantial aperture advantage. Both SCTS were good scopes optically and mechanically and this was confirmed for the 9.25 by an expert independent bench test. I’ve had, from memory, 9 Newtonians over the years, from 6 to 14”, including examples with optics by Hinds, Hysom and Grubb Parsons, and would not say that, aperture for aperture, the optically very good Newts generically outperformed the SCTs. There are so many contributory factors, some intrinsic to the design, some to do with the way different sorts of scopes need to be managed in order to perform at their best. And, of course, there’s sky quality to contend with, which doesn’t affect SCTs more or less than any other sort of scope. I liked both of my SCTs. Perhaps I got lucky. Both were rewarding scopes that gave good images and provided decent aperture in a compact package that wasn’t unduly demanding to mount. The AZEQ6 was a good match, incidentally, as was the AZ100.

I’m happy with my TEC which is why, several decades and tens of scopes later, it’s one of two I still have. I’ve always wondered about a Mewlon though, I like the sound of those - optical quality, etc, etc, and, of course, its first name begins with ‘T’ 🙄

Following a recent cull of scopes that didn't get much use, just 2. I call this ‘rationalisation’ but deep down I know it’s just clearing the decks to speculate about what I might get next. For now it’s: TEC140 apo and Stellalyra 90mm apo. Gone for now are the SCTs and big Dobs, but I know they’re all still out there, waiting …

Just on this point. I’ve owned this combo and would advise against it. The Evo is a nice mount but overstretched with the 9.25 OTA. The C9.25 OTA was excellent but putting it on that mount was definitely imv a step too far. As you say, there are problems with clearance at higher elevations, especially with, for example, a 2” diagonal in place. This makes binoviewers and other attachments at the eyepiece end more or less out of the question unless you’re content to observe only at modest elevations. On top of that, high power viewing that was well within the capabilities of the very good OTA was badly affected by the wobbliness of the combination - Celestron should have stopped at the 8.

Bill Paolini’s comparison might be of interest with regard to choosing between the 24mm Pan and the ES68: https://www.cloudynights.com/articles/cat/user-reviews/24-26-mm-eyepiece-comparison-r2651 I have the 24mm 68, my only ES eyepiece, and like it. I really wouldn’t describe it as ‘heavy’. 🙂

Has anyone layered rainfall and other meteo metrics onto a map of UK Bortle data?

The skies where I live in Surrey can vary from a (very rare and marginal) 4.5 to a pretty bad 6. So, I think the Bortle Scale has to be viewed as a somewhat useful but very broad brush indicator. Some of the criteria do seem rather arbitrary and situation dependent - the detectability of the Zodiacal Light, for example - and some of the visual tests seem substantially dependent on the characteristics of the observer. Dark Sky maps have some limitations as well because most show light shining upwards and not the appearance of the sky when viewed from the ground with light domes from adjacent towns, etc - though it’s perhaps reasonable to assume that there’s a useful correlation. A simpler way of finding darker skies is to identify population centres and where people live and get as far away from them as possible. Applying this in the UK will take you to places where you usually can’t observe anyway because it will be raining. 🤣

13mm Ethos, 10mm Delos and 9mm Tak ortho pair in the bino (if that’s allowed). That said, I don’t remember a session when I only used 3 eyepieces.