John

That looks like a DIY thing coupled with a 2 inch par-focalisation ring on the 2 inch section of the barrel. The disadvantage is that the DIY adapter does not enable the use of 2 inch filters whereas adapters such as the one that @globular links to above, to give you a 2 inch filter thread.

Hi John, It is the Feathertouch Micro Pinion MPA-TAK2.5. I was quite happy with the stock single speed R&P on the scope and had it adjusted quite nicely but then this very lightly used FT unit came up for sale at a good price so I thought it worth giving a try. It took me a few attempts to get the feel of the focuser right (there is plenty of room for adjustment / fine tuning when fitting it) but now I'm pleased with it and feel that it is a nice addition to the scope. I used the full FT focuser on my 130mm triplet as a target to aim for when adjusting the micro unit and have now got thing working in a satisfying manner. The feel is different from the single speed R&P of course but I'm now used to it and would miss it if I had to remove the unit for any reason. I have not tried either the Tak or More Blue units so I don't know how they compare. Hope that helps, John

The T1 Nagler 9mm's seem to come in a number of designs depending on the production run. The very early ones (Japan made) were smooth sided with no eye cup and later ones (Japan first then Taiwan I think) had rubber grips and eyecups added. The barrel fitting has always been the hybrid 2 inch - 1.25 inch type but there were detail changes through the production runs. The one thing that they all have in common is that the hybrid barrel (2 inch and 1.25 inch parts) houses the lower set of lenses so cannot be removed or replaced. I can't find any data on their focal plane / field stop position although the Tele Vue specs page does have some information on these discontinued models at the bottom: Tele Vue Optics: Tele Vue Eyepiece Specifications Here are a Japan made 9mm T1 and a Taiwan made one (neither are mine) from the bottom to compare their barrel design. The Taiwan one (right) seems to have a threaded 2 inch skirt whereas on the Japan one (left) it's unthreaded. Sounds like yours is one of the earlier Japanese ones.

That's great if you use a 2 inch eyepiece holder with that diagonal 🙂 I used to use a very similar arrangement. If you use a 1.25 inch one (as I do now) the risk is there because there is no lip to stop a long eyepiece barrel, at least with the ones I've tried, including my current Baader click stop 1.25 inch holder. I use a T2 extension between the eyepiece holder and the diagonal to remove that risk. My arrangement is this for 1.25 inch eyepieces:

This is with a 2 inch Baader eyepiece holder and a 2" to 1.25" adapter when required ? If the diagonal is used with a 1.25 inch eyepiece fitting eyepiece holder, the risk still exists I think.

Just realised that you are referring to a lip in the 2" to 1.25" adapter rather than in the diagonal itself.

That's interesting - my Baader T2 zeiss prism diagonal does not have that lip. Must be a design change 🤔 So caution is still advised in case you have an older Baader T2 zeiss prism (mine was purchased new in 2016).

It's not really a rule, it's a guideline that I have often seen repeated online and in print applied to the newtonian design. My personal experience of owning newtonian scopes up to 12 inches in aperture suggests that there is some merit in it but maybe it's time for us to come up with something better 🙂 Logic has not always played a strong part in my selection of scopes though, I have to confess 🙄

That scope is not mine - I just used it as an example of the appeal of a large aperture, long refractor. My Istar 6 inch F/12 was still quite a beast though and, once setup, there it stayed for the session. I think the whole setup weighed somewhere around 50kg.

Jupiter rarely seems to benefit from high magnifications. Certainly not as high as can be used on Saturn or the moon. Mostly I use 130x-150x with my 4 inch refractor and similarly with my larger scopes. I've found the seeing here in SW UK quite poor on the last two occasions that I've observed Jupiter, quite probably due to the positioning of the jetstream. Last time out even 112x was pushing it a bit !

I'm sure glad that I did not go for the F/15 version of the Istar 6 inch. There was one available from the same source at the time that I acquired the F/12. I saw the F/15 in it's box and decided that there was no way that I could handle it. I would also have needed to cut a hole in the ceiling to stand the thing on end !

I ended up with an EQ6 mounted on a Meade Giant field tripod with 3 inch steel tubed legs. Even that was not really stable enough. I would have really needed something like an EQ8, a Losmandy G11 or even one of the old Fullerscopes Mk IV's. Probably a massive pillar to put the mount on as well. Putting a 7 foot long 30 lbs optical tube onto a mount head that is over 6 feet off the ground is no joke either. I concluded that scopes like this need to be permanently mounted in observatories. No possibility of that where I am 😒

I found my way to the Ethos eyepieces by way of the Pentax XW's. I loved the neutral tone of the XW's, their sharpness and control of light scatter given their quite complex optical design. But I wanted those optical characteristics with an even wider field of view. The Ethos delivered that so I got hooked on those. An expensive taste to acquire 🙄 And quite different from the Svbony 3-8mm zoom too !

Yes, and I have still not completely ruled out another 6 inch refractor at some point. But it will be an F/7 or F/8 I think. Back then I was smitten with the idea of a long and larger aperture refractor. The Istar Perseus AT150 that I acquired was optically very good but it was a beast of a scope to find a suitable mount for. It rather dwarfed my ED120 and ED102SS: Still, we live and learn 🙂 I still rather like long refractors as my avatar testifies.

Some very interesting and thoughtful responses - many thanks folks 🙂 Taking the refractor design, I find it interesting that the benefits that additional light gasp brings, which is 44% in the case of the step from 100mm to 120mm as an example, seems harder to detect (for me) in terms of the appearance of a deep sky object than the more modest increase in resolution that the larger aperture delivers - around 17% better. I can usually clearly see the larger scope resolving tighter double stars which simply don't split in the smaller aperture scope, for example. I guess this is impacted by the nature of the challenge that these different target types present. In the main, a double star being split or not split is fairly clinical to detect but improved contrast or extension in a target that is already nebulous by it's nature is somewhat harder 🤔

Over the years I've been in the astronomy hobby I've found the best cure for an "itch" is to scratch it. I read a lot of different view points from a lot of different sources but there comes a time when only "seeing for yourself" will do. Occasionally I have regretted that, and the example of the 6 inch F/12 achromat refractor that I acquired, as mentioned by @Stu earlier in the thread is one of those. But I learned from it and it's quite possible that had I not actually tried it, I would still have that itch of curiosity for a really long, large aperture refractor. They do look so alluring 🤩

In my case the answer is "no". My scopes vary between F/5.9 and F/9.2 but I very frequently use eyepieces with focal lengths of 5mm down to 3mm and occasionally 2.5mm.

I was going to post this under an existing thread on whether a poster needed a 5 inch refractor but I thought it might benefit from a thread of it's own, so here it is. As a rule of thumb, it is said that, with newtonian telescopes, to get a really consistent and noticeable increase in visual optical performance, assuming the optical quality is comparable, you need a 4 inch step up in aperture eg: 6 inches to 10 inches, 8 inches to 12 inches etc, etc. I wonder what the equivalent step for a refractor is ? Are schmidt-cassegrain and maksutov-cassegrain step changes closer to refractors or newtonians ? To clarify, this is for a performance gain that is noticeable each time you use the scope, rather than something that has to be teased out or only shows on certain targets or under the best conditions. Personally I get this when I compare the views with my 100mm refractor with my 130mm but it's somewhat less marked between the 100mm and the 120mm. 70mm to 100mm is a significant performance jump as well. With newtonians my experience seems to match the rule of thumb above - the differences between an 8 inch and a 12 inch were consistently clear but somewhat less so between a 10 inch and a 12 inch. I'd be interested to hear others experiences on this, from a visual observing perspective 🙂 On a practical front, the physical size, mounting requirements, and general manageability of telescopes do also seem to take a significant step upwards with the related aperture increase. This needs to be factored into a final decision of course. And then there is the little matter of paying for the thing ...... 🤔

That is a great attitude to take 👍

"whump"................ is the sound of a towel being thrown in 🙄 It is still clear but the seeing is rubbish and the transparency not up to much either. There will be other nights ......

Thanks Ian. Although that is not great news for us it is oddly re-assuring that someone else, not too far away, is having a similar experience. The transparency has got a little better here but the seeing is, as you say, possibly got worse. I can see the two main bands on Jupiter but that's about all. I've just had another look and it is just possible to guess that the GRS has started to transit the disk but it is terribly vague. I'll give it another 30 minutes and see if there is any improvement but I suspect it's going the other way.

It is clear here but there is a blustery wind around and the sky transparency can best be described as milky. The Jetstream seems to be having an influence on the seeing as well and it's not a good influence 🙄 I am under the red/orange bit. Jupiter is not great although there is a pleasant arrangement of the planet and galilean moons currently.

I would not worry about that - I seem to be the only observer in the world who did not get on with the ES 92 degree eyepieces. Everybody else seems to think they are brilliant 🙄

I will be 101 in 2061 so probably won't see it's return. I'm glad that I had a decent 6 inch scope back in 1986 - it was rather dim in binoculars !

Apparently, the ideal position for a lower tube counterweight is on the opposite side of the tube to the focuser. That is not easy to apply though in real-world dob design. I'm surprised that the rather simple Skywatcher tension handles approach is as effective as it is. It does seem to do the job though. I thought the Stellalyra dobs had a tension system on the alt axis ?