mikeDnight

I use a Baader/Zeiss BBHS prism with my FC100DZ and can tell you with hand on heart, there is zero visible CA. With mirrors you'll always have light scatter, but not so with a prism. At 500X star images are textbook perfect and set against black velvet, with no light halo due to scatter. The downside is that you pay all that money and end up with a colour free view, like black and white tv from the 60's, but in HD.

An experience I had some time back may be of interest. I'd been loaned a lovely 8" SW Dob from paulastro to use alongside my then SW 120ED Equinox. I'd set both scopes up alongside eachother around 3pm on a spring afternoon so as to let each acclimatise. Around 6pm, another friend paid me a visit, and we just sat chatting for about three hours. As my friend got up to leave, I suggested we both have a look at the Moon and Saturn, both of which were high in the sky. I aimed the 8" Dob at the Moon and was in awe at the superb view of a detailed lunar landscape that was as steady as can be imagined. It was a terrific view, and in my mind I thought the 120ED had no chance of coming close to replicating such a view. When I aimed the ED at the Moon, I was again stunned, not by greater detail, but by the sharpness of the view. The superior sharpness of the 120 ED more than compensated for the greater resolution of the Dob. Neither of us could believe the difference would be so obvious or that the scales would tip so greatly in favour of the refractor. Next it was the turn of Saturn, and again the 8" Dob gave a view that was nothing short of spectacular. Again I thought to myself that the ED wouldn't stand a chance of matching, let alone beating the view through the 8". And again I was utterly stunned by the 120ED's planetary punch. In the 8" Saturn was rock steady, showing all the major ring components with ease, so that the A ring, Cassini division, B ring and Crepe ring were all immediately obvious. The globe too showed the EQ and temperate belt along with dark polar hood easily. The 120ED again delivered a significantly sharper view, which became most obvious when comparing the ring detail. The refractor hinted quite forcefully at fine grooves in the B ring that were not visible in the 8" Dob. The A ring easily showed the Enke minima and even hinted at a razor thin dark Enke gap close to the outer edge of the A ring. Cassini's division also showed a soft outer edge that almost bled into the A ring. Radial spokes were seen in the refractor but not in the Dob, which is another indication of the better definition of the refractor. The 8" Dob was a superb scope, but the 120ED had the edge on definition.

That's a good video! From my understanding though, the only light loss with a prism occurs at the prism surface, and that 100% of the light that enters the prism also leaves the prism. Obviously with multiple prisms there will be losses at each air to glass entrance, but otherwise I find the views virtually as bright with as without when it comes to Moon & planets. Whatever the reasons, looking back at my observational sketches I made while using my FS128 and single eyepiece, and comparing what I see through my FC100D, I see significantly greater detail through the binoviewer & 100mm scope.

I think a 5" refractor hits a real sweet spot for planetary. But there are a couple of things to seriously consider before taking the plunge. The bigger the scope the more effort will be needed to set up and strip down. That can at times be a negative when you're frozen to the bone and your scope and mount is caked in ice, even though the scope is good. A 5" refractor needs a strong mount if its being used for planetary observing, as tremor will wash out finer detail, and unless its being mounted in an observatory the scope will be subjected to strong breezes and wind's at times. A lot of people underestimate the ability of a good 4" refractor to cut through the seeing and pull out impressive planetary detail. It's not all about aperture or exotic glass types. The quality of the figure is massively important, so although aperture is often said to be "king", quality is "queen", and as in chess the queen is of far greater importance. And, although an 8" or 10" reflector will show good planetary views some of the time, a good 4" refractor will show good planetary views most of the time. Plus the refractor will give a clearer, cleaner, sharper view that often outweighs the softer views that most other scope designs show. For visual planetary observing a quality doublet can be preferable to a triplet simply because it will acclimate more rapidly. You can also get even more impressive views by using a binoviewer and a pair of cheap orthoscopic's rather than hugely expensive multi element designs. Below are a few pencil sketches that illustrate the visual appearance of some planets through a 4" refractor. (The lunar sketches are very basic and the actual view through the telescope was vastly more detailed). (( Note also the first two Mars sketches. The top sketch was made using an 8" F6 Newtonian, while the lower was made using a 100mm F8 apo refractor)).

I have no experience with this 90/660 scope, but I'm pretty sure it will be a good rich field refractor. I'm basing this on the fact that I've used the Star Travel F5 refractors in all their apertures extensively over the years, and given they are specialist wide field instruments, I think they are terrific scopes in the right hands. I found the CA in the Star Travel's is really very good all things considered. Similarly, the 90/660 is a specialist scope that should perform admirably on targets its intended for. But its aperture may actually work to its advantage, in that CA may not be too detrimental to a lunar or planetary view, making it a reasonably good all round grab & go. With a barlow, it could be quite good for moon & planets.

Looking good so far. Can't wait for your thought's on it's performance, especially as we'll have a spectacular high Moon in the evening sky until May.

Thanks for your detailed and insightful reply Don. It's much appreciated.

It's a strange thing. I used to observe from a friend's run-off roof observatory which was actually little more than a garden shed, except I wasntballowed to call it a shed. It stank of creosote, as did I after a night's observing, but it was also full of spiders, moth's and the occasional woodlouse. When i built my 8' by 7' roll off roof observatory in 2011, I expected that before long it too would have plenty of unwanted wickies move in. For some strange reason it didn't happen. I'm not sure if its because the structure is built from 3/4" ply glued and screwed, then clad externally with white tongue and groove plastic cladding, hence there are very few gaps through which to gain access. Or, if its because I've lined the internal floor and walls with interlocking exercise matting. The matting had a rubber odour initially and may be it still does and i just dont notice it? But perhaps these qualities are the reasons i seem to get very few unwanted visitors. You could try sealing up any gaps and cladding the floor and walls with the exercise matting to see if it keeps your little pets away. This pic is from about four or five years ago, but the observatory looks just as good today.

Beautiful! Very Nasmyth!!

What size bracket do you have, a 30mm or 50mm?

It doesn't seem to make sense does it. Yet it never ceases to amaze me!

I agree that the telrad's are ugly, but they are excellent finders. I could quite happily rough it owning a TSA with a Telrad attached. You never know, a Tak finder may slip under the radar sometime in the future.

That's interesting! I'd consider the binoviewer and cheap orthoscopics to outstrip any mono eyepiece view I've ever seen as far as lunar observing goes. I've just spent an hour observing the Moon just playing around with my eyepieces, and the bino view was in a whole different league I felt.

Just a little thicker felt would do it, but it might not need much.

Personally I'd use the Tak focuser rather than the moonlight, but I dislike Crayfords and love the classic look of the Tak rack and pinion. With my DZ though, I use a Baader BBHS prism with helical micro focuser. The reason is that the rediculous high powers the scope takes, particularly when looking at double stars, does require a very fine touch. You have a truly fantastic scope!!

I felt my Tak Barlow was more trouble than it was worth and sold it not long after buying it. It did come to focus on my DC with Tak prism though. In side by side comparisons I found the Skywatcher Delux barlow gave an image that was just as good, and that fit post diagonal. However, the nose of the Barlow can touch the prism surface, so a spacer ring or a couple of rubber O rings can be fit over the barlow's nose to prevent contact.

Very nice shot Paul. "Cup handle", I've never heard that one before. It sounds much more romantic the Bay of Rainbows, but I like it!

I did read somewhere, probably on CN, that Takahashi used their influence to stem the flow of this five element Masuyama design from Japanese manufacturers to such companies as Celestron, so as to keep it for themselves. Have you any idea if there's any truth in this Don? Having said that, I think the 25mm Parks Gold and 35mm Ultima are leaps and bounds better than the 25 & 30mm Tak LE's.

Thankyou Nicola! It's worth mentioning that the sketches really represent what I saw over time. So for example the nebulosity enmeshing the Pleiades took me 30 minutes, Orion nebula 20 mins, and similarly with the Dumbbell and Ring nebula. With the Orion nebula, the longer you spend studying it the more three dimensional it appears to be, and the more obvious and impressive the layers of black nebulosity become, adding depth. The green colour also becomes very evident.

Thanks for that info Louis. It is very sad. I remember looking longingly at the Parks scopes when they advertised in Sky & Telescope back in the early 80's. I could only just afford the magazine back then, so a telescope from Parks was just a dream.

I've had most of the TV plossl's but can't remember all the various focal lengths. I know they go down to 8mm but feel 10mm is more comfortable. If you're using a barlow on the nose of your binoviewer then 18mm to 15mm would give some superb lunar and planetary views. Your 25mm Halloween's will be excellent! I love the 35mm Eudiascopic and Ultima, and yes I use them as a matched pair in my binoviewer. They are identical in optical performance and pair up perfectly.

I think it looks like a very nice telescope, and definitely an improvement on the star travel. It isn't FPL53 (probably FPL51 or similar) and so will have some residual CA, but not on the level of the Star Travel. I'm sure it will perform admirably as an all round scope.

DSO's in a 4" F7 can be quite impressive, especially if you block out surrounding light by using a blackout blanket or hood over your head and eyepiece. Also, with the beautiful wide field your scope will be a great comet seeker too!

A weather balloon can be very high, and although I wondered about the angle relative to the Sun, I've seen the typical intermittant orange reflection many times before. In a telescope you'd almost certainly detect its form as they tend to look like long deflated balloons. When they cross the Moon they can give you quite a thrill momentarily. Whether the Moon itself would reflect off the silver balloon I'm not sure, but as it was orange in colour I'd imagine it was catching sunlight as it refracted through the earths atmosphere. Of course I could be completely wrong! 🛸

Thanks Heather! I'd have grumbled on for years if you hadn't pointed that out, but thankfully I wouldn't have been the only one it seems. I never think to look at SGL updates, its too much like reading instruction manuals, which are always an absolute last resort.