Done something a bit daft - bought an OOUK VX16 Dob

[Commanderfish]

Had a decent session last night in the back garden, although trees are now covering the Southern Treasures

Paracorr Type 1 really cleaned up the stars to points, I love it!  Much more refractor-like.  I don't think I will be viewing without it.  Interestingly, it enables me to bring the Explore Scientific 82 30mm, Ethos 21, 13 and 10 to focus without an extension tube on the original focuser (35mm travel, IIRC). I was also able to bring the Ethos 8 and 6 to focus in 1.25" mode by adding a 2" to 1.25" adapter (actually I was using a Parallizer but basically the same difference).  Once I get my feathertouch with the 63.5mm travel drawtube, I'll be able to focus the 8 and 6 without adding an adapter/parallizer.  I'll have to experiment with the settings on the Paracorr though.

Light pollution was noticeable (partly as Ive just got back from Cornwall), humidity was high so transparency was not great.  

M13 had lots of starts and contrast was better than the C9.25 with nicer, wider fields to frame the object, but the transparency and LP were a little hampering.  Still the best light polluted view I've had. 

M81 and M82 visible, M82 was wuite bright, but LP stopped me drawing much detail out of them in that bit of the sky (I have the most LP to the North of me).

Andromeda and it's two companion galaxies were visible in one field (ES82 degree 30mm).  Despite the LP I saw more detail than I ever have before in my back yard.  This will be amazing from a dark site.

Caught glimpses of the Sagitarius Star Cloud between trees and houses, looked good but obviously the field is too narrow to really appreciate it.

Lots of detail on the Wild Duck Cluster (which was getting a bit low), LP was spoliing the view a bit though (I've been spoilt by Cornish dark sky).  

Veil and Witches Broom were visible with Castell Oiii but there was a little cloud in that area.  

Cruising through the Milky Way in Cygnus and Aquila was pretty cool.

The downside is the narrow field, particularly now I'm using a paracorr.  I'm down to about 1.34 degrees True Field.  Not sure that there's anything that can be done about this though.

Thinking about mounting an ST80 or even ED80 as finderscope.  The Antares Versascope 10x60 is great but I miss having a wide field scope coaxially mounted.  What's the largest scope people have fitted as a finder?  an ST80 probably?  Has anyone fitted an ST 102 perhaps? I know lots of weight at the top causes issues in most dobs, but with the VX series you can slide the tube in the rings to find the balance point.  Not sure you can do that in most dobs?

[Paul73]

Glad that you got to give the beast a good run out. Re the LP, give it a go on some more PN's and high globs. Then you will really see the difference!

Re: Fov. Two scopes is the only answer. I have an ED 80 that sits quietly on its Sky Tee waiting for the relaxed wide field cruise. Mounting it on the dob tube sounds like recipe for a bad back! You can get bigger specialist finder scopes or even spotting scopes which might work better.

Paul 

[Commanderfish]

Ok an Aluminium ED80 with Ethos eyepiece and 2" diagonal around 5kg might be pushing it.  Not so much worried about my back, but to balance the scope I might have to slide it so far through the tube rings that it might catch on the dob base. 

But a Startravel 80mm only weighs 1.3KG, plus a bit more for an ES  carbon fibre 2" diagonal (which I have to spare at the mo) and another 1Kg for a big eyepiece - total 2.5Kg.  That is not so drastic on a 29Kg OTA on a 15 Kg base is it?  Besides, just when I think I have mine balanced, the mirror end starts tipping down, that 16" mirror cell must weigh more than all the other components of the scope; the body is relatively thin aluminium.

Has anyone mounted a Vixen clamp onto a dob near the finder position?  I fear this would require some drilling...  Once a clamp is in place I could play around with different fracs as finders - first try my ED80 and if it's too heavy, get a startravel 80 or 102.

[Commanderfish]

I've realised that I can get a wider field in this scope by using a Panoptic 41mm (68 degree).  With a Paracorr, I'd get 1.51 degrees instead of 1.34 degrees with the ES30mm 82 degree.  Here's the thing:  the exit pupil would be a whopping 10mm as the scope is an F4.  What is it like viewing such a large exit pupil?  The ES30mm 82 gives a 7.5mm exit pupil and it does sometimes seem that it's a nicer view looking through the Ethos  21mm with its 5mm exit pupil - though that could just be increased mag.

[Commanderfish]

Had a decent session last night with the VX16, using the Antares Versascope 10x60 and Baader SSV RDF as finders.  I also had my ES ED80 Triplet and Starwave 152 out on the Ercole Giro.

Finding objects: The Antares is the best finder I've used short of the ED80.  Definitely helps locate brighter DSOs.  An 80mm frac would of course be even better.  In my moderate light pollution, the Antares  can pick up brighter DSOs like M13 Glob , M31 Andromeda, M2 Glob, but not fainter objects like galaxies M81 and M82.  For fainter objects I did use the ED80 and Starwave 152 to locate them, then looked at the position of the ED80's red dot and replicated it with the VX16's red dot.  I am still keen to see whether there's a way of fixing a short tube 80mm achro to the VX16, most likely at the existing finder location which is further down the tube than the focuser.

There was some high light cloud coming and going but transparency was good and the skies got nice and dark after about 11pm. Seeing was decent. 

The VX16 really showed it's chops tonight. Most of the time I was surfing with the ES30mm 82 degree producing x61 and 1.34 degrees TFOV.  With the Paracorr type 1 and reasonably good conditions, the views were pin sharp and refractor like on star fields and open clusters. Close to Apo standards on star fields in fact, though when pointing at a very bright star there was flare coming out of the star which looked like it precisely replicated the spider vanes of the secondary.  Anyone know if this is normal and whether it can be reduced/eliminated?  

The Double cluster shone with more stars than I've ever seen from my garden. Nice to have 1.34 degrees instead of the 1.05 degrees I used to get from my previous large aperture scope, the C9.25.  Not as good a field as 2 or 3 degrees in a frac, but still a signficant improvement on the C9.25 which the VX replaced in my line up.

I located at least two new objects to me, one is the glob M71 in Sagita (IIRC) which I have only seen very dimly before as a very faint smudge.  It was definitely there, more clearly in the VX16 with some stars resolved.  Still seems a very diffuse glob but it was there.  I also located M2; I don't recall seeing this before, it was visible in the 152 Achro so this is new to me because I wasn't concentrating on this bit of the sky this time last year.  In the VX16 M2 resolved nicely into a pretty glob.  It was in fact somewhat prettier than M13, which was getting lower and plagued by cloud when I tried it.

Above M71 was the Dumbbell nebula, which was very clear in the VX with or without Castell Oiii. The clouds came in shortlly after I started viewing it though, so I didn't get a chance to use more than x61.

The VX16 was also very nice surfing through Cassiopeia and Cygnus.  Easy to pick out random tiny star clusters and study them.

Overall I'd say that the quality of the optics in this scope are really excellent; better than any other newt/dob I've looked through before - but that's not many as I've always been a refractor nut!  Will be interesting to see what more experienced eyes like Stu make of it at our next local meeting.

The OOUK friction brake proved useful, particularly when changing eyepieces.  Reminds me very much of tightening the clutches on the Ercole Giro.

[Stu]

Diffraction spikes off the secondary spider are totally normal. I struggle with them myself, having similar tastes to you in terms of apo fracs, but once beyond the bright objects they are a non issue, and the resolution you get from the aperture shows its colours. The only way to get rid of them is to use a curved vane secondary support or some kind; there are many designs with varying benefits. In reality they do not get rid of the diffraction, but rather they smear it around equally so it is less noticeable. There are arguments for and against either option.

Regarding a 'mega finder', I believe @Scoot has tried mounting a Tak FS60 on his 16" Sumerian. There are various devices you can use such as the Baader Witty and the Baader Stronghold which allow you to mount scopes and maintain alignment adjustment

http://www.teleskop-express.de/shop/product_info.php/info/p4135_Baader-Stronghold-tangential-assembly---up-to-7-kg-load--black-.html

[Commanderfish]

I may have found another solution to the finder issue.  This little package ought to do the trick  - the rings fit a synta shoe.  

http://www.ontariotelescope.com/80MM-Right-Angle-Correct-Image-finder-Scope-125X-_p_319.html

The other solution of course is to buy their Synta fit rings and bracket, and slot in an 80mm of your choice, like an orion 80mm.

 

[Stu]

Antares do one I think....

http://www.rothervalleyoptics.co.uk/antares-12-x-80-right-angled-erect-image-finderscopes.html

[Commanderfish]

Cheers Stu,

I was tempted by that 12 x 80 RACI, as I have an Antares 10 x 60 RACI and it's good.  However it's out of stock at RVO

I was thinking about ordering one from Ontatrio Telescopes who have supplied me before,  but in the end I've taken a punt on an ST80.  Steve at ENS has 3 of them going for £75 each, in good nick. I've ordered some rings with screws that don't stick out very far and fits onto a Synta finder shoe.  Still works out a little cheaper than the Antares 12 x 80 though the ST80 comes without diagonal and eyepiece.

The Antares 12x 80 weighs 0.9 Kg plus 0.3 Kg of rings and accessories, the ST80 weighs 1.3Kg plus rings, so I'm hopeful that the rings I've ordered are up to the job.  I've also done the sums and I'm not adding much weight to my dob finder set up as I will be removing a heavy multi-finder adapter.  As the OTA can be slid around in the dob rings I think it should be fine anyway.

I'll probably use the RACI prism from my 10 x 60 and a Maxvision 24mm 68 degree for a 4.1 degree TFOV at x16.7 mag.  The RACI prism only has 22mm of clear diameter though so might vignette - I'll see how it goes.

I'm thinking that the ST80 should work a little better than the Antares 12 x 80 as a wide field scope because it's going to give more magnification to increase contrast, the focuser will be more solid and I suspect the optics might be a little better - for low power wide field anyway.

Basically what I'm trying to do is get as close to my ED80 + Ethos finder/widefield scope from my Frac/Giro set up at less than 2Kg instead of 5Kg.  Let's see how it works out...

[Paz]

On 08/09/2016 at 15:07, Commanderfish said:

I've realised that I can get a wider field in this scope by using a Panoptic 41mm (68 degree).  With a Paracorr, I'd get 1.51 degrees instead of 1.34 degrees with the ES30mm 82 degree.  Here's the thing:  the exit pupil would be a whopping 10mm as the scope is an F4.  What is it like viewing such a large exit pupil?  The ES30mm 82 gives a 7.5mm exit pupil and it does sometimes seem that it's a nicer view looking through the Ethos  21mm with its 5mm exit pupil - though that could just be increased mag.

The 10mm exit pupil just means that the whole field of view wont fit through your pupil. Instead if seeing the whole field to the field stop you would only see a bit of it, limited by your pupil size, which will probably be between 5mm and 7mm.

You would therefore see a different bit of the image as you move your eye around.

[Moonshane]

Not quite as I understand it. You don't lose field (you can still see the field stop) but it's the same as if you put an aperture mask over the end of the scope and you therefore 'lose' aperture.

[Paz]

2 hours ago, Moonshane said:

Not quite as I understand it. You don't lose field (you can still see the field stop) but it's the same as if you put an aperture mask over the end of the scope and you therefore 'lose' aperture.

Thanks for your polite note of correction - I realise you are right.

One never stops learning!

[cs1cjc]

2 hours ago, Moonshane said:

Not quite as I understand it. You don't lose field (you can still see the field stop) but it's the same as if you put an aperture mask over the end of the scope and you therefore 'lose' aperture.

And of course the secondary shadow is enlarged, which I have found less of a problem in practice, than some others apparently do.

[Commanderfish]

Yes this could be an issue, I can see the secondary shadow at 30mm when viewing the moon, which in practise is not an issue.

 

 

[cs1cjc]

On 12/09/2016 at 20:02, Commanderfish said:

Yes this could be an issue, I can see the secondary shadow at 30mm when viewing the moon, which in practise is not an issue.

 

 

You are more likely to see the shadow when viewing bright objects and the pupil is contracted.

[Commanderfish]

Update:

 

I've flcoked the top 80% of the tube plus the secondary.  I've done the back of the secondary to insulate it a bit in order to postpone dew formation.  I've done the sides as some say it helps with glare catching the edges.  

I've fitted an ST80 with a 2" GSO focuser and a 20mm 100 degree Explre Scientific eyepiece.  This mounts to a finder shoe via a set of Antares 80mm rings.  Believe it or not the finder shoe does hold the lot in place!

I've had no problem balancing the dob, I didn't even move the tube in the rings - I had 2Kg of finders and adapters there before.  The only thing is, when the OTA is pointed near the zenith, the weight of the finders pulls the scope further toward the zenith even with the friction brake on.  It can be held steady though.

Still waiting for my Feathertouch and adapters.  I also need to assemble a dew shield, but I need more flocking material to line the dewshield.  I'll probably flock the bottom of the tube just above the primary too

[scarp15]

Great, looks good and yes they do balance well when heavy eyepieces or such as with your finder scope are installed, pointing near to Zenith requires a fair bit of dob hugging anyhow. With my VX14, I also flocked the tube in stages - kept only buying a couple of rolls at a time from FLO. Initially the secondary area and as you mention, also consider that this helps to an extent absorb dew. I did managed to do mine without removing the spider, after the secondary, it is worth next time flocking around the Primary, as this to might help by a small margin to help gain a little contrast and preventing light scatter. When I had the mirror out for cleaning, I did flock the entire tube, which is perhaps not that necessary but still good to complete, though with my VX8L I have only flocked around the secondary and primary area and will likely leave it at that.  With both scopes, I have at least so far, never felt the need for making a dew shield.