Revelation 16" Dobsonian

[estwing]

i have seen single tuss dobs..but smaller app of coarse

[John]

Given that the poles are captive and they, plus the associated fixings, are heavy, three poles is the minimum number for a rigid structure that minimizes weight.

Russell

I don't know how much a 16" solid tube would weigh but the smaller sized commercial truss tubed scopes (Skywatcher Flextube, Meade Lightbridge) seem to weigh a bit more than a solid tube dob of the same aperture.

[russ.will]

Personally I don't see the point in captive poles on a scope of this size. You want the scope to disassemble into manageable parts not be left with an enormous OTA that is hard to lift onto the rocker.

I just don't get it.

I don't know how much a 16" solid tube would weigh but the smaller sized commercial truss tubed scopes (Skywatcher Flextube, Meade Lightbridge) seem to weigh a bit more than a solid tube dob of the same aperture.

I wholeheartedly agree. I have a Ford Kuga (for the next month, at least) and it's not exactly short of headroom. The 300p Flextube OTA only just fits stood up on the rear seat and jammed against the roof lining. The only advantage the captive pole design seems to deliver, is speed of setup as it doesn't markedly improve portability.

Add to that, the base which is over two foot tall and wide, doesn't break down, so I have to fold the wider of the two rear seats down to fit it into the car. That's two seats gone and we're a family of three. If we want to go camping, either the Dob stays at home, or we have to take two cars. Hardly the point of what is, after all, only a middling sized Dob.

Russell

[Bart]

A word of caution here. When I was shopping around for a 16" it was between the LB and the GSO, which looks identical to this Revelation. I love my GSO 10" and its excellent alt and az movement so was leaning toward the GSO. One of the gentlemen at TS stated they were no longer stocking this truss design as it was not the best at holding Collimation. Worth noting possibly

Barry

[swamp thing]

That's what I'd heard Barry. I thought it was discontinued as the truss system wasn't stiff enough (there was too much flex in the Flextube )

Perhaps this issue has been addressed. One would like to hope so.

[Stargazer_00]

There's going to be one of these on Telescope House's display at IAS next weekend. I'll have a good look at it then.

[John]

There's going to be one of these on Telescope House's display at IAS next weekend. I'll have a good look at it then.

Ask them if the issue with the truss design holding collimation has been addressed and how it's been done

You could also ask if the 1/12 wave figure is RMS or Peak to Valley as well, while you are at it. If it's PV and guaranteed as such then the scope is a bargain - Orion Optics charge nearly £2,500 for just a 16" mirror set at that accuracy.

[Mark at Beaufort]

Ask them if the issue with the truss design holding collimation has been addressed and how it's been done

You could also ask if the 1/12 wave figure is RMS or Peak to Valley as well, while you are at it. If it's PV and guaranteed as such then the scope is a bargain - Orion Optics charge nearly £2,500 for just a 16" mirror set at that accuracy.

John I am going to the show as well on the 18th so if I get the chance I will ask these questions.

Mark

[Stargazer_00]

I asked the guy on the phone this moring and he said its RMS. I said I expected the mirror to be around 1/4 PV and he agreed it probably was or possible a bit more (sales pitch I guessed).

He said GSO has come a long way in producing consistant quality the last few years. Didn't once indicated this was a relaunch of an old design.

I asked about shrouds enchroaching on the light patch and he said he didn't know. Only that there wasn't one on the market designed for this scope 'yet'.

anyway, I'll give it a poke and a push on the 18th, get some photos probably.

bit miffed that I phoned most of the major suppliers and not one of them is bringing a 350p flextube. It's like this scope doesn't exist, i swear. no one is interested in bringing it, even Skywatcher themselves aren't taking one. It's hilarious. It should be called "the dodo scope"

[John]

I doubt they know what the strehl ratio is, which is a better way of measuring mirror accuracy I believe.

.....bit miffed that I phoned most of the major suppliers and not one of them is bringing a 350p flextube. It's like this scope doesn't exist, i swear. no one is interested in bringing it, even Skywatcher themselves aren't taking one. It's hilarious. It should be called "the dodo scope"....

The FLO folks bought one to the last couple of SGL star parties and the SW Astro Fair at Sidmouth so they do exist

[John]

I asked the guy on the phone this moring and he said its RMS. I said I expected the mirror to be around 1/4 PV and he agreed it probably was or possible a bit more (sales pitch I guessed)....

I think 1/4 wave PV is around 1/14 wave RMS.

[Mark at Beaufort]

I am not an expert on the physics of P-V and RMS but I thought they had a 1 to 3.5 ratio. If that is the case a 1/12th wave RMS is about 1/3.5 P-V which is not very good. I have got my judgement wrong?

Mark

[John]

I am not an expert on the physics of P-V and RMS but I thought they had a 1 to 3.5 ratio. If that is the case a 1/12th wave RMS is about 1/3.5 P-V which is not very good. I have got my judgement wrong?

Mark

I find this web page useful and it more or less confirms your conversion Mark:

http://www.rfroyce.com/standards.htm

[Damo636]

Following a recent thread on Cloudy Nights,

I had a conversation via pm with a very well known and respected mirror maker in the USA (Think of a big nightime bird!) He had commented in the thread that almost all the mirrors he refigured were churned out by the same manufacturer, but because of vendor rules, he couldn't state it on the open forum. Anyways, curiosity got the better of me so I contacted him via pm and asked him out straight who the culprit was, this was his response...

GSO is consistantly not good. Almost all of the mirrors I refigure are GSO and almost none of the mirrors I refigure are Synta.Quote:

Food for thought folks!

Edit: Here's the thread in case anyone interested..

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5714805/page/0/view/collapsed/sb/5/o/all/fpart/1/vc/1

[John]

Very interesting Damo. I followed that thread too and saw the post but did not have the nerve to ask what the brand was !

[Damo636]

Interesting and shocking John! I for one was very surprised, as I was, and still am convinced I got an excellent example. In saying that though, I don't possess the skills to accurately analyse a mirrors figure, and have never looked through a scope with premium optics, but for less than £700, a scope that can show me the central star in M57, Sirius B and craterlets in Plato, it can't be all that bad :-)

[estwing]

Double agent Damo...armed only with a tin of beans!! thats also why i held back and bought a custom ground mirror,cost a lot but quality is almost guaranteed

[Stargazer_00]

What is the refiguring process? Can any mirror be refigured? Who does that in the UK?

[Damo636]

Double agent Damo...armed only with a tin of beans!! thats also why i held back and bought a custom ground mirror,cost a lot but quality is almost guaranteed

Ah, but in the right hands, those beans have the potential to clear a room with one shot :-)

[John]

I'm sure you do have a good one Damo - those are tough challenges for a scope.

[estwing]

Ah, but in the right hands, those beans have the potential to clear a room with one shot :-)

...err don't like the smell/sound of that!

[Damo636]

What is the refiguring process? Can any mirror be refigured? Who does that in the UK?

John Nichol does it and will test the mirror free beforehand...

http://www.nicholoptical.co.uk/free%20testing.htm

[estwing]

he did a mirror grinding demo at last years PSP.

[cs1cjc]

There are independent reports on a few GSO Newtonian mirrors.

Two GSO 16": http://translate.googleusercontent.com/translate_c?depth=1&hl=en&ie=UTF8&prev=_t&rurl=translate.google.com&sl=de&tl=en&u=http://www.astro-foren.de/showthread.php%3F10026-Zwei-GSO-Spiegel-im-Vergleich%26p%3D37905&usg=ALkJrhgwfjZ1AZq1QW-fsxqAGs6cA2NKwg#post37905

Meade 12" (GSO made?): http://www.airylab.fr/contenu/mesures/astro/rapport%202010-47001.pdf

[vlebo]

I asked the guy on the phone this moring and he said its RMS. I said I expected the mirror to be around 1/4 PV and he agreed it probably was or possible a bit more (sales pitch I guessed).

He said GSO has come a long way in producing consistant quality the last few years. Didn't once indicated this was a relaunch of an old design.

I asked about shrouds enchroaching on the light patch and he said he didn't know. Only that there wasn't one on the market designed for this scope 'yet'.

anyway, I'll give it a poke and a push on the 18th, get some photos probably.

bit miffed that I phoned most of the major suppliers and not one of them is bringing a 350p flextube. It's like this scope doesn't exist, i swear. no one is interested in bringing it, even Skywatcher themselves aren't taking one. It's hilarious. It should be called "the dodo scope"

I agree . I have been trying to look at one for ages .Considering the Dob is probably Skywathers biggest selling scope in the UK I am surprised they are not trying to push the larger aperture versions more.