John

53 minutes ago, MartianHill said:

That Istar is really impressive John, you must have needed an equally impressive mount  ?

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 ! 

1 hour ago, johnturley said:

There are several excellent 6 in f7ish Refractors on the market now though, and which will probably give better results than that f12 Achromat

John 

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 ...... 🤔

36 minutes ago, GrumpiusMaximus said:

..... I'm making a point of going out every night there's even a vague chance of seeing anything to get myself into the habit.

....  Still great to get a telescope out ......

That is a great attitude to take 👍

45 minutes ago, John said:

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.

 

"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 ......

13 minutes ago, lunator said:

John I am not that far from you and seeing is going from average to poor. Jupiter is showing some detail but nowhere near as good as the last session.

Cheers

Ian

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. 

5 hours ago, bosun21 said:

I'll be the odd one out here. I didn't get on with the Svbony 3-8 zoom eyepiece. I don't fault it optically at all and found the views to be clear and sharp. I just can't observe comfortably with relatively short eye relief and small eye lenses anymore. I think I have just got too comfortable with both of these attributes being larger. That's why I sold all my orthos and short focal length plossl's

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 ?

Dobs get increasingly nose heavy as the altitude they are pointed at gets lower. So a system that is easily adjustable is needed to compensate for that. 

3 minutes ago, DAT said:

Did that strip have to be screwed on? Looks nice!

It was a magnetic knife rack and held on to the scope tube using very strong double sided sticky pads. I could have bolted it on but didn't need to.

The tube of the scope (an Orion Optics) is aluminium so I could not stick magnetic weights straight on to it.

1 hour ago, bosun21 said:

I just removed the primary mirror on my new scope which is necessary to replace the primary collimation springs. Once I had the mirror out of the cell I discovered that the existing primary springs were actually heavier gauge and stronger than the springs I was intending to upgrade with! I’m pleased to see this now in production dobsonians. The Stella Lyra(12”) i have previously owned had really weak springs which allowed the mirror to shift. It was easier to replace them on the SL though as you could do it with the mirror in place on the scope. Also fitted Bobs knobs on the secondary.

GSO made scopes seem to have been supplied with weak springs for more than a decade now, despite it being a much discussed issue on forums like this. Pity nobody at GSO has picked up on that and improved the springs. Once of the main issues for folks contemplating a newtonian scope is collimation so having a decent primary cell with decently robust springs would be a priority for a manufacturer, one would think 🤔

I used a sliding weight system on my old 12 inch dob. I had a couple of weights (.75kg and 1.5kg I seem to recall) and I could vary their positioning along a magnetic strip and combining the weights for the really heavy eyepieces eg: the 17mm ES 92 degree monster which is the heaviest that I've owned.

My current dob is a Skywatcher 200P classic and that manages to handle my Nagler 31mm and Ethos 21mm without needing a counterweight - the tension control is enough.

Here is my 12 inch dob system:

36 minutes ago, Sunshine said:

It’s HUGE! compared to my 102, it’s big bertha! The behemoth in your avatar looks the business lol

My avatar is a 5 inch F/12 Cooke refractor owned by Sir Patrick Moore. 

My 130mm F/9.2 is a LOT bigger than my ED120mm. When a true 5 inches is reached refractors seem to get bigger rapidly 😲

That looks the business 😁👍

10 minutes ago, bosun21 said:

Some lovely pieces of glass in those cases. I’m too frightened to try an Ethos incase I fall under their spell.

Thanks. I collected most of the Ethos before there were other really good alternatives. If I was looking for 100 degree eyepieces today I would be looking carefully at the APM XWA's which are very, very close to the Ethos in performance. 

Mine are not as neat as @Mr Spock and @bosun21's cases but they have been with me for a while and have seen quite a lot of "coming and going" over the years 🙄

Not so much change lately though although I have managed to whittle things down to 2 cases. I won't say that I'm done though - that's asking for trouble plus a certain amount of disbelief from long standing members on here 😉

10 minutes ago, Stu said:

Clear again, another Quick Look. The seeing remains very average so detail wasn’t amazing. There appears to be a nice barge on the SEB (assuming I got that right, not used to upside down newt views so much 🤪)

I'm clouded out now but I think I could just about make out that dark, elongated feature before I gave up the unequal struggle with seeing, wind gusts and clouds. 

I've just managed to get a scope out but I'm wondering why I bothered. The seeing is really not very good and the wind blustery. Can't see this being a long session unless things improve rapidly 🙄

I'm pleased that the availability of these zooms is still plentiful. I was a little concerned that the supply of them would dry up after the initial production run had sold out.