Revelation 16inch Dobsonian

[Astronolee]

.......carrying on from the PM's. you did well to hold off on that 12" offer ? There will be lots of offers like that popping up, but just take your time. You`ll make several folk envious when the 16" eventually arrives ?

Yes I did hold off getting the 12" today...thanks for your advice...Best advice I guess "take your time" :-)

[swamp thing]

You'll find big Dob owners are like moths to a flame on threads like this.

There aren't so many threads on big Dobs for us all to chin wag on

Just remember don't rush in, take your time. Plan your big scope well and your relationship with it will be a happy one.

[Dude_with_the_tube]

We'd all like a Zambuto mirrror in our Dobs but you can't pay the postage from Carl's workshop to the UK for the price the OP is talking about!

Let's remind ourselves of John Dobson. Was he a prima donna scope fetishist for whom only a tenth wave mirror would do? He was not. He was a great man who wanted to bring faraway galaxies to the public on a budget. The big cheap Dob is an astronomical institution and rightly so. The question is, what can you get away with?

Olly

i agree with what you are saying Olly and obviously I would love to have Zambuto mirror,however,there are a few very good quality mirror producers here in UK .Even a good figured 1/4th wave mirror will show a lot,but bad 1/4th will show very little.i think that was the point i was trying to bring across.

Btw,i have sent my Skywatcher mirror off to Orion optics for test.Should have the test results on monday.Will be interesting to see them... or not? ...

[russ.will]

I went from a SW 200p to a SW 300p, back down to a Orion UK VX8L 1/10th Wave and back up to a ES 305 Dob. Okay, that's only an 8 to 12" swing (twice) but one of those 8" scopes had not only had one of the highest quality mirrors available in the UK, it was also F6, making it supremely eyepiece friendly.

Off the back of that experience and given that portability issues seem to be covered, I'd say buy the biggest mirror you can afford, without a shadow of a doubt. I'll qualify that.

I'm not in a dark sky location for most of my use (but it ain't exactly LP hell either), but I've dragged most of my scopes up to the Norfolk coast sooner or later. Occasionally, the atmosphere has conspired to deliver great conditions at home or away. This factor is important, because regardless of how dark, or crystal clear the night looks, atmospheric stability has been the limiting factor on how high you can push magnification, which really only affects planetary viewing. Planets are so bright, they basically couldn't care about light pollution anyway - Heck, I've had some really nice views of Jupiter at 10am!

No, my point is that these really high magnification nights have happened in my three years of astronomy maybe four or five times. That's five nights in three years where conditions conspired to let the benefit of a high grade mirror stretch it's legs and a dark sky site would not have helped.

Now, when it comes to DSO fuzzies and sub 150x magnifications, the situation is entirely reversed. The 1/10th wave OOUK never showed me the structure, the extent, the detail in galaxies, globular clusters and nebula that the 300p did and that was a scope I was never that happy with, for reasons both functional and optical. Having off-loaded the 300p, I had high hopes the first time I swung the OOUK on to M42 as a no-brainer first time target, expecting it to 'pop' in some new and unexpected way. It didn't. Even on this, the easiest and brightest of DSO targets, it was half the size and far less three dimensional than the 300p had shown it. Gutted. Even the relatively higher magnification globs which should favour the better figured mirror didn't sparkle the way the notionally less superior, but larger 300p had portrayed them.

I'm now back with a 12" mirror of vaguely 1/4 wave quality - It may be GSO, or some such, but I don't care. The first time I swung it onto a globular cluster, it felt like slipping on an old, comfy slipper. The faint, flat circle of stars the 8" had shown, now became the glittering ball of pin [removed word] stars so numerous, it re-elevated the genre back to wow!

I'm sorry, there are lots of arguments for superbly figured mirrors, but in the UK there are greater arguments in favour of a larger mirror as being more advantageous more of the time. Sure, the structure of the scope is a also factor, but as a budget Dob owner, the extra aperture can be off-set with a bit of patience as a foil to the short comings.

Russell

[Paul73]

Russell

Thanks for keeping the apature fever alive.

Nice to see the OP has remained strong!

Paul

[vlebo]

I think the often overlooked Flextube 350p http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-350p-flextube-dobsonian.html  is a good compromise . With large aperture and a collapsible base it offers easier portability and at £1269 the price is comparable to the Revelation but with Skywatchers more proven build quality.

[Astronolee]

I think the often overlooked Flextube 350p http://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-350p-flextube-dobsonian.html is a good compromise . With large aperture and a collapsible base it offers easier portability and at £1269 the price is comparable to the Revelation but with Skywatchers more proven build quality.

That is in fact my 2nd choice after the Revelation 16"...Same price hmmm

[quaoar]

http://www.astromart.com/classifieds/details.asp?classified_id=863985  ....last roll of the dice

[Peter Drew]

"Pick up only", that will bump the price up.  

[John]

"Pick up only", that will bump the price up.  

Yep - the OP is in Essex !

[Scooot]

There s an Essex County in north east New Jersey -

[kirkster501]

These big scopes are heavy and unwieldily.  Do you have somewhere to store it?  Can you manhandle it ok?  if you get to the stage where you cannot be bothered because of the hassle, you bought too big...

[astronymonkey]

This scope was reviewed in the October issue of the S@N magazine last year which showed the usual close ups of some of the details on the scope. One thing I did like the look of was the sllider Alt bearings which allow you to shift the balance of the scope and the cell seemed to be an exact copy of the meade lightbridge one which is well designed and up to the job. I dont like the three pole design though as I dont this would be as ridgid as a trussed system although the flextube is similar and gets good reviews.

At this size though you are going to have to accept some of the compromises which are inevitable in the price versus quality discussion.

So, the compromises are:

•  Size - these scopes are huge and a 16 inch will stand 6ft high and weigh over 10 stone, the are difficult to move about - but when set up the height is an advatage as the viewing position is at standing height unless your are below 20 degrees.
• Chipboard base - damp from the grass will damage the base by expnading the particle board so you need to be careful with this and the base is heavy to move about.
• Price - These art cheap scopes but you are getting a huge mirror for he money. Ok its not a premium mirror but as has already been said , how often is seeing good enough to make full use of a 1/10 wave mirror.
• Time to set up - if you move it in a few pieces (top, truss, bottom, base) then maybe 10 mins from taking out  to viewing, and a similar amount for strip down.
• Coma etc, on a fast mirror this is going to happen and poor eyepieces wont help
• Transportability - you need an estate car, although I have seen a pic of a similar sized scope squeezed into an audi TT.
• Modifications, these ship with a straight through finder whereas a right angle works much better and a red dot finder works as a nice companion to this. A shroud would also help along with some for of secondary dew control.

But with the compromises aside a 16inch dob is a phenominal scope. I would not opt for one as a first scope though as I think the compromises will get in the way of finding your way around the sky (and a 200p would do nicely for this)...... but in the hands of an experienced observer, who knows how to get the most from such an unwieldy beast, nothing will give you a better view on deep sky objects .

I went from using a 6inch scope with a premium mirror for 15 years,  to a 16inch lightbridge , and I have to say I have never looked back.

Cheers

[John]

Here is another review of the same design scope albeit under a different branding (Astro Tech) and from 2008:

http://www.cloudynights.com/page/articles/cat/user-reviews/telescopes/dobsonians-10-40/astro-tech-16-dob-r1753

[russ.will]

Transportability - you need an estate car, although I have seen a pic of a similar sized scope squeezed into an audi TT.

This was my main bug-bear with the 300p. The OTA, even when retracted still takes up a passenger seat and the base wouldn't even fit in the boot of my Ford Kuga. Admittedly, the base of the larger FlexTubes breal down further, but you're still going to have to fit a 2ft+ diametre disk in the car.

The ES 305 basically stacks in a nice compact cube that takes up no more space than the upright sections of the 300p base, leaving no more than a bundle of skinny poles to stash. I can't see why the same wouldn't be true of the ES 406 v a 400p, but it's easy to suggest a more expensive option to side-step virtually any cost based compromise....

On a structural note, I would say the truss based ES is quicker to damp vibration than the 300p Flextube was, despite the obviously longer truss poles - I guess the triangulation, plus the tension they exert against each other, in concert with the far lower mass of the secondary OTA explains this. That said, when moved with care, the 300p was extremely good at holding collimation from one session to the next, as the poles do lock very precisely in place. As long as you were just moving it in and out of the house for instance, you could practically place it where you last used it and hit the ground running, rarely having to resort to the collimator.

This is definitely not true of the ES, but the flip side to the coin is that being able to collimate the primary from the front with the collimation pole, means you can sit down and collimate without having to move more than your arms. Flex/solid tube collimation is relatively athletic pursuit by comparison.

Russell

[Paul73]

It turns out that the optics are considerably better than 1st thought!

See extract from Telescope House website:

"This telescope's heart is its 16" f/4.5 Parabolic primary mirror, which is made from BK7 optical glass, is figured to 1/12 wave to ensure excellent optical performance and is well-supported on an 18-point mirror cell with integral 4.7-inch cooling fan to help reach thermal equilibrium quickly. The in...."

Paul

[quaoar]

Worth a read, comments on glass issues by Mike Lockwood  http://www.loptics.com/intheshop/shop40.html

[John]

It turns out that the optics are considerably better than 1st thought!

See extract from Telescope House website:

"This telescope's heart is its 16" f/4.5 Parabolic primary mirror, which is made from BK7 optical glass, is figured to 1/12 wave to ensure excellent optical performance and is well-supported on an 18-point mirror cell with integral 4.7-inch cooling fan to help reach thermal equilibrium quickly. The in...."

Paul

That's 1/12 wave RMS which is just about 1/4 wave PV ie: just about diffraction limited. Not that that's bad for an economy dob but I do feel that TH's pitch is a bit misleading

They use the same mirrors and mirror cells as the Meade Lightbridge 16".

[Scooot]

That's 1/12 wave RMS which is just about 1/4 wave PV ie: just about diffraction limited. Not that that's bad for an economy dob but I do feel that TH's pitch is a bit misleading

They use the same mirrors and mirror cells as the Meade Lightbridge 16".

Hi John,

I'm sure you're correct but how can you tell whether they're quoting 1/12 RMS as opposed to 1/12 PV, or do you just know this.

[Paul73]

Hi John,

I'm sure you're correct but how can you tell whether they're quoting 1/12 RMS as opposed to 1/12 PV, or do you just know this.

Unless these guys have suddenly revolutionised the mirror making process it can't be PV.

It is more likely that the publicity is written by a marketing agency with even less knowledge of optics than me! If someone knowledgeable wrote this.....

Reputable retailers need to be so careful about copying and pasting marketing guff into their websites. It has made me think twice about availing myself of a new Delos in this weekend's sale. I might give them a ring, and dependent on their response, make a purchase. Or not (the Delos, not the scope).

Paul

[John]

Hi John,

I'm sure you're correct but how can you tell whether they're quoting 1/12 RMS as opposed to 1/12 PV, or do you just know this.

I asked them

Also it's common sense and to some extent, "caveat emptor". Orion Optics in the UK make a 16" mirror figured and tested to 1/10 PV or better. The mirror set (primary and matched secondary) will cost just over £2,000 plus VAT. Galvoptics in the UK charge over £1,000 for a 16" F/5 primary finished to 1/8th wave PV. Nichol Optical price a finished 1/8 wave PV 16" F/4.5 and flat at £1,750.

[Scooot]

Unless these guys have suddenly revolutionised the mirror making process it can't be PV.

It is more likely that the publicity is written by a marketing agency with even less knowledge of optics than me! If someone knowledgeable wrote this.....

Reputable retailers need to be so careful about copying and pasting marketing guff into their websites. It has made me think twice about availing myself of a new Delos in this weekend's sale. I might give them a ring, and dependent on their response, make a purchase. Or not (the Delos, not the scope).

Paul

It could be very misleading marketing guff, if they'd put 1/8 wave or 1/10 it might not have seemed so far fetched and could easily catch out the less knowledgable. I don't suppose it's covered by trading standards but it should be, but maybe impossible to enforce.

[vlebo]

It could be very misleading marketing guff, if they'd put 1/8 wave or 1/10 it might not have seemed so far fetched and could easily catch out the less knowledgable. I don't suppose it's covered by trading standards but it should be, but maybe impossible to enforce.

That's why , at least with the Flextube 350p , you know what you are getting.

[Ptarmigan]

I asked them

Yet they still have not modified or thought fit to clarify their web page ? !

Im glad you added "some extent" to your caveat

I was very tempted at their last sale to go for one of these but I did not know a lot about PVs and RMSs then and all the discussion at that time ( thanks SGL ) , similar to this, put me off and they lost a sale.

Full-on Caveat Emptor was ok back in the '60s (with car-salesmen, Rackmann etc. ) but these days we _like _trust_ as well as legislation and if a company is happy to blindly copy marketeers literature then , ,

well I'll go elsewhere and pay more if needs be (I could have bought two, one for each eye that was not a prob! )

[Ptarmigan]

I should perhaps add that if they had discussed (or made sensible) on their website what SGL had discussed for me, I might well have considered the price worth the punt,

but the doubt had been sown by then

and now my thoughts have turned to other possibilities.