Skyliner 300p dob

[Astronut]

I was almost ready to order a 12" Lightbridge but after reading this thread: http://stargazerslounge.co.uk/index.php?topic=12773.0 I'm now thinking a closed tube dobsonian might be more suitable/practical and still portable enough to fit in my hatchback Citroen Saxo (with the back seat folded down). I'd like to get into imaging some time so if I get a closed tube I can get an EQ6 goto mount later and some tube rings - might work out cheaper in the long run.

Is anybody here doing successful imaging with this setup? I'm thinking of the weight of a 12" OTA on an EQ6 goto.

I've seen pictures of jarbi's 10" Skyliner on an EQ6 and it looks mightily impressive.

http://stargazerslounge.co.uk/index.php?topic=11638.0

Is there a huge weight/size difference between the 10" and 12" Skyliner OTA's?

The only differences I can see on FLO's site between the 12" EQ mounted Skyliner and the 12" dobsonian Skyliner are the tube colour (blue on EQ, white on dob.) and the dob. tube would have altitude bearing mounts attached to the tube.

http://iseestars.net/image/8175/large/image.jpg

I'm assuming the round black thing with the red inner circle (between the tube rings) is one of the dobsonian altitude bearing mounts - are these removable and would they make any significant difference to the weight of the OTA if they are?

Are there any other differences I shoud be aware of?

[Whippy]

Are you sure you'll be able to get a 12" skyliner in the back of your Saxo? I only just managed to get my old 10" skyliner into my Astra with the back seats down and it's a foot shorter than the 12" (it was boxed though).

Yes, the black/red things are the alt bearings and you can unscrew them, I did think of that but I would have taken the spider assembly/secondary off to do it, hassle. I think they're only plastic and not any real weight to them.

What I did find was that you have to be a bit careful about how you position the scope in the tube rings because at certain angles, the dob bearings get caught on the mount. That was my experience anyway, I would imagine other people would disagree...

[FLO]

The Skyliner 300P has the same f5 mirror-set as the Explorer 300P. Whilst the Skyliners are currently available, we are still waiting for the first shipment of the Explorer 300P so it is unlikely you will see a report from anyone using them for imaging - yet. If it were me, I would be tempted to buy it as a Dobsonian anyway as it would be good to have the option of both mount types.

PS: What are 'Boinc stats'?

[Astronut]

PS: What are 'Boinc stats'?

World-wide statistics for Berkeley Open Infrastructure Network Computing in a nutshell

http://boinc.berkeley.edu/

http://www.boincstats.com/

This thread gives more info:

http://stargazerslounge.co.uk/index.php?topic=776.0

Not many members in the team though - c'mon guys and gals, put those spare CPU cycles to some good use

http://www.boincstats.com/stats/user_stats.php?pr=sah&st=0&to=100∨=&ti=117875

back on topic - what's the weight difference between the 10" and 12" OTA's? Am I being too aperture greedy - is there such a thing

I haven't measured the car space yet - is the 12" tube length around the 5ft mark or slightly more? I'm roughly estimating that from the focal length.

[Whippy]

The 10" was 12.5kg boxed with the EP's and finder. So I imagine the 12" is somewhere around the 15kg mark boxed.

[Astronut]

The 10" was 12.5kg boxed with the EP's and finder. So I imagine the 12" is somewhere around the 15kg mark boxed.

I'm unable to find any specs giving the weight of the OTA.

If it is 15Kg I'm guessing it would be do-able as an astrophotography setup on an EQ6 mount then?

It's going to be quite a bit heavier than my original choice of a C9.25 (and I know that's do-able).

Can anybody give me the exact weight and length of the 12" Skyliner OTA please - I've been googling for hours and this information doesn't seem to be available anywhere.

[Whippy]

It's the same scope with a different name...

http://www.celestron.uk.com/catalogues/view_item.asp?ItemID=32728&CatalogueID=272&CategoryID=4033

[Astronut]

Are you 100% sure? The Celestron has a BK7 glass primary whereas the Skyliners use pyrex glass. Looks good in black though

I really can't understand why BK7 glass is used to make a mirror - must be more readily available than pyrex or something.

The specs only list the total weight of 36Kg (OTA + base)

The length's going to be around 5ft though - I can live with that.

I wonder if there'll be a problem mounting it on an EQ6 with tube rings later (re. the dob altitude bearings).

I can see ther might be a problem with restricted movement when rotating the tube in the rings to get the eyepiece into a more comfortable position plus another possible restriction in movement when balancing the tube length in the tube rings after fitting extra equipment at the eyepiece - I hope that won't be too much of a concern. I suppose small counterweights could be magnetically attached to the mirror end of the tube to balance heavy eyepieces + camera (assuming the tube is steel).

[Whippy]

My understanding is that Synta bought Celestron and the base is exactly the same as the Skywatcher's, and the OTA designs are the same too (does look better in Black though!), so I reckon it's the same scope.

I had to be a bit carfeful where I put my old 10" on top of the HEQ5 when I mounted it because of the dob bearings so it may be the same on the EQ6. Not sure though.

One thing though, are you planning on putting it together and leaving it permanently set up? Becasue if you're not, it's a bit of a job putting it all together and dismanteling again night after night. I'm a fairly big bloke (6' 3") and it was a bit of a struggle getting the tube on and off on my own. Then you've got the mount, counterweights etc etc, bit of a hassle.

[FLO]

The P in 300P refers to Parabolic (rather than spherical) not Pyrex. Pyrex is often chosen for its low thermal expansion but it isn't the only glass available for making mirrors. There is even an argument for using regular plate-glass.

Here's an article from Oldham Optical:

http://www.oldham-optical.co.uk/Glass.htm

[Astronut]

It won't be a permanent setup - I'd like an observatory (who wouldn't ) but my main observing site (my backyard) isn't the ideal spot for one.

I'm only 5'5" but I'm quite strong so with an EQ6 mounted newt I can see myself having to use some sort of makeshift step like an upturned milk-crate or something

I know exactly what I'm letting myself in for with assembly/disassembly of mount, tube, counterweights, etc - I used to have an EQ (on a 'portable' steel pier) mounted 8.75" newt 20 odd years ago and I remember only too well the frustrations of setting it up only to find it clouding over.

This is why I like the idea of having a dob (quick to setup) but I'd like to get into astrophotography later so an EQ mount will be necessary.

I was planning to get into astrophotography quite a bit later but I was thinking earlier today of reversing the idea (of dob first, EQ mount later) ie. getting a Skywatcher Explorer 300P with EQ6 Pro mount (which isn't available yet) and buying an additional dob mount for it (OO UK sell them) but this might involve 2 sets of tube rings - I haven't thought the idea through yet.

I'll have to do the sums if and when the price of the Skywatcher Explorer 300P is available.

outlash: when the Skyliner tube is off the dob. mount are the altitude bearing holes (ie the holes where the pins/carrying handles screw in?) open to the inside of the tube? ie. can you poke your finger through them into the inside of the tube? I'm not sure if that makes sense :?

[Astronut]

The P in 300P refers to Parabolic (rather than spherical) not Pyrex. Pyrex is often chosen for its low thermal expansion but it isn't the only glass available for making mirrors. There is even an argument for using regular plate-glass.

Here's an article from Oldham Optical:

http://www.oldham-optical.co.uk/Glass.htm

Hi Steve. I'm really dithering over this decision aren't I

I've changed my mind so many times these past few weeks that I'm beginning to think I'll never buy anything at this rate but I'll be spending soon, no worries.

I was reading that article sometime last week - interesting read.

I hadn't really thought about what the P stood for, to be honest.

While you're here, do you know the comparitive weights of the Explorer and Skyliner OTA's? I know the 12" Explorer isn't available yet (any news?) but maybe you could have a look at the 10" versions.

Also, are the tubes aluminium or steel or something else entirely?

[Whippy]

I think I know what you're asking..

You mean the actual screw holes where the handles are threaded through the dob mount and go into the OTA right? I'm not 100% sure but I'm pretty certain the holes didn't actually go through the tube itself, they just went into the bearings. When I looked down the tube to see how the bearings were fixed into place, all I saw was the bolts holding them in and nothing else.

One thing I would seriously recommend would be a right angled finderscope. As the scope is pretty low to the ground, the finder is a right pain to use, I was on my knees most of the time when looking for objects even near the zenith!

[FLO]

While you're here, do you know the comparitive weights of the Explorer and Skyliner OTA's? I know the 12" Explorer isn't available yet (any news?) but maybe you could have a look at the 10" versions.

Also, are the tubes aluminium or steel or something else entirely?

I will find the statistics in the morning and post them here

[Astronut]

I think I know what you're asking..

You mean the actual screw holes where the handles are threaded through the dob mount and go into the OTA right? I'm not 100% sure but I'm pretty certain the holes didn't actually go through the tube itself, they just went into the bearings. When I looked down the tube to see how the bearings were fixed into place, all I saw was the bolts holding them in and nothing else.

That's exactly what I wanted to know. I didn't like the idea of holes left in the tube letting in dust during storage with the tube dust cap on.

One thing I would seriously recommend would be a right angled finderscope. As the scope is pretty low to the ground, the finder is a right pain to use, I was on my knees most of the time when looking for objects even near the zenith!

Not surprising when you're 6'3". I'm almost a foot shorter so I may be ok

I will find the statistics in the morning and post them here

Thanks Steve - much appreciated.

[Astronut]

mmmmm....here I go again changing my mind

I've been having second thoughts about the prospect of mounting a 12" newtonian OTA on an EQ6 mount after reading this thread:

http://stargazerslounge.co.uk/index.php?topic=12846.0

I bow to the words of wisdom from the experienced 'in-the-field' astronomers offered in there. A big dob for visual and something smaller for imaging.

A 12" EQ mounted newt, I imagine, would be a tad awkward to handle and possibly a little on the heavy side for astrophotography when coupled with a guide scope, camera, etc, etc. even for an EQ6.

I'll have a think about my imaging options later but when the time comes an EQ6 goto will be part of the setup and I may even mount the 12" on it anyway to try it for size, as they say. The option will always be there with a closed tube newt.

I've been measuring the car space and with the back seats and passenger seat folded down there will be room for a 5ft+ tube - there wouldn't be room for a tube approaching 6ft in length though. I hope I've estimated the length of the 300P correctly.

One more little niggling doubt remains though:

I've been reading through a Skywatcher catalogue I picked up a while back and there is a highlighted paragraph in there as follows:

"The Skyliner..." (and Explorer) "...250PX model features a paraboloidal primary mirror made of low thermal expansion pyrex glass resulting in substantially shorter cooling times."

I'm guessing that's what the 'X' stands for in 250PX.

I was under the impression that all Skywatcher newtownian primary mirrors were made of pyrex

Does this mean that the 300P OTA mirror is made of plate glass or bk7 or something else?

If this is the case, then I may have to look into fitting a fan to the back of the mirror if I'm carting it from inside the house to outside.

I would have thought that a 12" mirror would benefit from pyrex more than a 10" as it's going to take longer to stabilize than a 10". I guess it wouldn't matter what type of glass was used for the smaller 8" and 6" mirrors as these would stabilize reasonably quickly.

Why have Skywatcher singled out the 10" for 'special treatment' and not the 12"? :?

Is it because they see a 10" as the limit of portability and a 12" or above is more suited to a permanent setup where thermal properties of the mirror are not really an issue?