Advice: more aperture

[Basementboy]

16 hours ago, happy-kat said:

What tripod do you currently use your ED triplet on? 

Sky-Watcher steel 3/8" – https://www.firstlightoptics.com/tripods/sky-watcher-38-stainless-steel-tripod.html

[Basementboy]

16 hours ago, ollypenrice said:

Running an astronomy gite for nearly 20 years, I have some experience of trying to impress the non-astronomer. On the planets, it's easy, in almost anything.  On the deep sky, it's almost impossible - even with a 20 inch.  And... I live at a very, very dark site. I recently introduced some absolute beginners to the deep sky with a 14 inch and found some objects which I think they really enjoyed, but they were seriously interested and had booked an astronomy holiday. For many, most things remain faint fuzzy blobs. M42 is a common exception, as is M31, but that's a winner in binoculars guided by a laser pointer (not in London!)

So, as already suggested, I would concentrate on yourself.

The SCT is compact but the long focal length, in many cases, defeats the object of the exercise by cramping the field of view and excluding many targets you might enjoy. (Rosette, Veil and many, many more.) Personally I'd go for a  collapsible Dob as big as possible.

Olly

Hi Olly, thanks for this - I've always appreciated your advice, on my own questions as well those of other posters.

I had the same concern about the SCT. (Also my father owns a 1980s Meade 8" that I am able to use when I visit Canada so might as well try something different.) Ditto a Mak: I can smash the planets out with the triplet at high mag, which it does well (when properly cooled and under the right conditions obv). The frac actually gets a lot of use; it's just such a beautiful object to use. What doesn't get much love any more is the Newtonian. So I think you're right that the best upgrade is Mr Dobson's.

Do you have any sense of where the sweet spot is for Dobs when balancing bulk versus aperture versus cost? These are Sky-Watcher's flex-tube goto Dobs for full price at FLO:

200P – £1k
250P - £1200
300P - £1800
350P - £2400

Sorry, I know this isn't really your job

And lastly ....... as for sharing with others ... I think I'll get a Goto mount, set about lowering expectations, encourage friends to focus on the social aspect with a side order of cosmos (rather than the other way round), bring a few pairs of binoculars for group fun... and make sure there's plenty of beer.

C.

PS. I'd love to do an astronomy holiday some time: I've never looked through a really large telescope in proper dark sky, in part because London but also because I got into astronomy during lockdown and have never been to a star party

[ollypenrice]

The flex tube dobs are reasonably compact but they are heavy. I don't know how you feel about price but, if only for the fun of it, I'd have a look at David Lukehusrt's website. https://www.dobsonians.co.uk/  He also makes equatorial platforms which allow a period of motorized tracking which is both relaxing and a great practical boon if sharing the view with others. His compact Dobsonians really are very portable for their aperture.

There is no one point at which a fundamental change in the view suddenly occurs in rising aperture. Not for me, anyway. However, I would be unlikely to go for anything less than 12 inches if I had the means of using one.

Olly

[globular]

17 hours ago, ollypenrice said:

The SCT is compact but the long focal length, in many cases, defeats the object of the exercise by cramping the field of view and excluding many targets you might enjoy. (Rosette, Veil and many, many more.) Personally I'd go for a  collapsible Dob as big as possible.

Olly, I'd like to understand your point here.  (Sorry to OP if this is taking it off topic).

I have an 8" f/10.5 SCT and get about 1.0 to 1.25 degrees with exit pupils from 3.0 to 5.5mm.  

What configuration of a big Dob can significantly better that from a FOV perspective?

A 20" f/4 Dob would give 0.6 degrees with a 3.0mm exit pupil (with ES92/12) and 0.9 degrees at 5.5mm exit pupil (Nagler T4 22).

Clearly a big Dob can do high magnification (small FOV) with much brighter/larger exit pupils... but not sure I understand how it can do wider FOV?

[niallk]

On 25/07/2022 at 13:17, Basementboy said:

Whoa. Taurus and Nadirus! Never heard of them. Love the wooden styling ... Are they well-regarded scopes?

Yeah I mean I'd love these but I'm not sure they'd fit in my Fiat 500 even when collapsed. 

Do you know if they're easy to collapse and reassamble? Or it is a pain?

The reports for Taurus and Geoptik which I've read have been positive.   I'd expect similar set up as my 15" Obsession- ie pretty convenient and no fuss.  For the ES, there are several videos on YouTube doing reviews, assembly,  collimation. 

You'd have to look at the dimensions and your car to figure out if feasible.   I stacked two couch cushions which approximated the size of my 15" mirror box, and used to check if I could get through the doors, and onto the back seat of my Avensis!

Edited July 26, 2022 by niallk

[ollypenrice]

4 hours ago, globular said:

Olly, I'd like to understand your point here.  (Sorry to OP if this is taking it off topic).

I have an 8" f/10.5 SCT and get about 1.0 to 1.25 degrees with exit pupils from 3.0 to 5.5mm.  

What configuration of a big Dob can significantly better that from a FOV perspective?

A 20" f/4 Dob would give 0.6 degrees with a 3.0mm exit pupil (with ES92/12) and 0.9 degrees at 5.5mm exit pupil (Nagler T4 22).

Clearly a big Dob can do high magnification (small FOV) with much brighter/larger exit pupils... but not sure I understand how it can do wider FOV?

Well, I had a 20 inch F4 and could see large swathes of the Veil with with a 26 Nagler. Now, with a 14 inch SCT, I'm too boxed in by that  3.5 metre FL to be able to do that.  Surely it's a simple matter of focal length?

Olly

[Basementboy]

5 hours ago, ollypenrice said:

The flex tube dobs are reasonably compact but they are heavy. I don't know how you feel about price but, if only for the fun of it, I'd have a look at David Lukehusrt's website. https://www.dobsonians.co.uk/  He also makes equatorial platforms which allow a period of motorized tracking which is both relaxing and a great practical boon if sharing the view with others. His compact Dobsonians really are very portable for their aperture.

There is no one point at which a fundamental change in the view suddenly occurs in rising aperture. Not for me, anyway. However, I would be unlikely to go for anything less than 12 inches if I had the means of using one.

Olly

That's incredible, he builds them himself? What a legend.

Price slightly out of my range, although this Explore Scientific 12" isn't – and still seems relatively portable:

https://www.rothervalleyoptics.co.uk/explore-scientific-ultra-light-12-dobsonian-telescope.html

[Basementboy]

4 hours ago, niallk said:

The reports for Taurus and Geoptik which I've read have been positive.   I'd expect similar set up as my 15" Obsession- ie pretty convenient and no fuss.  For the ES, there are several videos on YouTube doing reviews, assembly,  collimation. 

You'd have to look at the dimensions and your car to figure out if feasible.   I stacked two couch cushions which approximated the size of my 15" mirror box, and used to check if I could get through the doors, and onto the back seat of my Avensis!

Car tetris! 

[globular]

28 minutes ago, ollypenrice said:

Well, I had a 20 inch F4 and could see large swathes of the Veil with with a 26 Nagler. Now, with a 14 inch SCT, I'm too boxed in by that  3.5 metre FL to be able to do that.  Surely it's a simple matter of focal length?

Olly

OK you're comparing with a 3.5m 14" SCT.  Agreed that is narrower (and very very heavy and not something the OP was considering).

[Mike JW]

With the various Dobs that I have owned I always reckon to choose a low power eyepiece that will give around the 1 degree fov.  That covers most star clusters and does well on many large nebulae but there will always be a compromise between increasing aperture and consequent reduction in fov.

I started with an 8" which was blown out of the water by the 12", which in turn easily out done by a quality 15", then my 20" made the 15 look pathetic. Finally a mates 24" made the 20" look a bit pedestrian. Scopes up to 18" are reasonably portable. Beyond that it gets problematic. The ultralight versions of the Dob design are very prone to condensation in this climate so I stayed away from them.

If you can fit a 12" into your car then that is what I would suggest. Quality will always win out both for scope and eyepieces.

Mike

 

[ollypenrice]

1 hour ago, globular said:

OK you're comparing with a 3.5m 14" SCT.  Agreed that is narrower (and very very heavy and not something the OP was considering).

I'm comparing any scopes of different focal length, I think. Long FL scopes have smaller FOV's than larger. My point was that this is the downside of the SCT. There are a great many excellent objects which require a short focal length, after all.

Olly