Advice on Dobs

[wulfrunian]

Hi,

I've been thinking about changing my scope, and browsing round the net found this forum, you seem like a helpful lot so thought I'd join up and ask for some advice

At the moment I've got a Meade GOTO scope, an 8 inch SCT. Unfortunately, I'm just finding that with the limited time I've got, and as an observatory's not practical for me, I'm just not using it. I think I need one which I can get outside and start observing in a few minutes, which is why I'm thinking about swapping to a Dob instead.

So my questions are - first, your thoughts, does this sound like the way to go for me? Do you have any recommendations when looking for Dobs? - makes, size of mirror - what's the largest mirror size that gives a scope that's still easy to move around?

Also, my brother is into photography and wants to try a bit of astrophotography. Obviously we'd be limited without a driven scope, but is there anything you can achieve - shots of the moon, planets?

Many thanks!

[dobserver]

Hi and welcome to the forum.

I've had the Meade Lightbridge 12" for a month or two and I love it to bits! It is nearly as big as me (which isn't actually that hard!) and not the most convenient implement, but its size does not cause insurmountable problems - I actually managed to bring it in on my own the other night!

I love its simplicity and no-nonsense quality. And the way you decide what to look for and just go and find it - sooooo satisfying

If you need portability without compromising on aperture then the 10" might be a cool move. You can still see a lot with the 10" yet it is easier to handle. I have willing help on hand whenever I need it, otherwise I would have chosen the 10" I think.

I was spoiled at the Salisbury Star Party by camping next to two avid 16" Lightbridge owners

They turned me on to astronomy and the wonders of being a Dob owner - and made me desire the biggest one I could get my hands on

The other benefit of the Dob is the way it makes you learn the sky. I am loving the gradual process of becoming a Human Goto.

Steph

[kniclander]

agree with all Steph says - I have a 10inch skywatcher solid tube - on the limits of one person portability as a complete unit but OTA can be taken off the mount and put back in a few seconds. I love it. I had a 6" dob and the 10" makes a big difference.

[John]

I have a 12" Lightbridge dobsonian as well. A 12 is about the largest that one person can manage on their own I would say.

Incidently I used to have an 8" SCT as well and made the swap to a dobsonian for more or less the same reasons you state - I went to an 8" dob and was pleased to find that, as well as the ease of use that the others have mentioned, the views were just as good, if not a little better than the SCT provided.

John

[wulfrunian]

Thanks for the replies, that's very encouraging, I think this will be the route I take. 10 inch sounds like the best compromise between aperture and practicality.

Looking around at what's available, I noticed the Skywatcher flextube dobs as well as the solid tube ones. I assume the flextube will weigh less and will be easier to store - are there any disadvantages to them?

[themos]

You can't put the tube on an equatorial mount (as easily), as a future option.

[johninderby]

The Skywatcher dobs are very good with excellent optics, and the 10" has the advantage of a Pyrex mirror that cools down a lot quicker than the plate glass mirror of the Lightbridge. The 10" Flextube actually weighs a couple of kg more than the solid tube. The truss system of the Flextube adds more weight than the equivelent length of solid tube.

I have the 10" Flextube Auto and swapped the OTA for the solid tube as it keeps colimation better and there is no need to buy a light shroud. The Flextube is shorter when collapsed so if storage space is really tight it can be an advantage.

John

[wulfrunian]

Yes I see, that makes sense, thanks. How heavy is your 10 inch then John, and how long is the OTA? The other thing is that I suppose the auto might be an option if we want to do bits of astrophotography - is the driver an integral part of it, or can it be attached and detached as you need it?

[johninderby]

The 10" OTA is about 44.5" long and weighs about 14kg and the base weighs about 17kg. I've added a new focuser and added some counterweights so mine weighs slightly more. I added carrying handles to the OTA which makes it very easy to carry, in fact the OTA can be carried one handed using the main handle. The OTA drops onto the base and just one knob secures it in place.

The Auto drive system is built into the base and must be used to observe with, as while the OTA can be pushed to a new approximate position without affecting tracking the movement is too stiff to observe manually. But using the hand control movement is so smooth you wouldn't want to do it any other way. With it being an Alt-Az system astrophotography is really limited to short exposure Lunar / planetary.

I'm using a SynScan hand control for full GOTO and a GPS unit as well. The GOTO is not yet factory approved, but so far has been working perfectly and is simply a matter of plugging in the new handcontrol that has been updated with the latest Alt-Ax firmware with no mods needed.

John

[Phil Fargaze]

Wassat Johninderby! You`ve managed to pimp your Flextube Auto to Goto?

[johninderby]

There has been a lot of discussion about GOTO with the SkyWatcher Auto dob on several forums. Officially SkyWatcher has delayed the GOTO upgrade stating that the firmware needs more work before the GOTO upgrade is officially released. The upgrade simply consists of unplugging the standard tracking hand control and plugging in a standard SynScan handcontrol upgraded to v3.07 firmware as fitted to the Skymax AZ-GOTO mount.

As it's unofficial at the moment it's a do it at your own risk type of thing. Although as it doesn't involve altering anything on the scope you could plug the standard handcontrol back in if the scope needed repair under warrantee I suppose.

Here's part of an earlier posting I made on the subject.

-----------------------------------------------------

10" SkyWatcher GOTO GPS dob

I've been testing out the 10" SkyWatcher Auto with a SynScan hand control and so far so good. Updated the HC firmware to V3.07, plugged it in and it worked perfectly first time. I also plugged in a SkyWatcher GPS mouse, and again no problems and it works perfectly as well. I will have to wait for some better weather to test it out properly yet but I think GOTO accuracy is about the same as the Celestron SLT.

Here are a few things I have noticed about factors that will affect the performance.

1. Balancing the OTA properly is absolutely essential to minimise any play in the ALT drive.
   
2. Replacing the standard focuser with a decent dual speed crayford will greatly reduce any movement of the OTA while focusing as the fine focusing knob takes such a light touch to move.
   
3. Or fit an electric focuser, which should work particularly well if trying some imaging.
   
4. From reading various reports it appears that there is some variation in the amount of play in the AZ and ALT movement present in various scopes. I suspect that there is some variation in how the clutches are set when the scopes are shipped.
   

Overall while I'm very pleased with the results so far you have to keep in mind that it's still a relatively low budget scope with compromises. Great for visual (very nice optics) but for imaging the compromises in the design will start to show. Should be capable of some nice lunar/planetary imaging though just so long as you are prepared to live with the limitations of imaging with a low budget GOTO system.

John

[Phil Fargaze]

Thanks, very interesting johninderby.

Back on topic.... I had an 8" Orion USA dob which served me well and was very portable, I`m now with my 10" dob and it is still easily portable and the extra light grasp makes it worth while lugging the extra weight about.

Don`t forget wulfrunian that if you want to take a scope outside and observe straight away you will have the problem of thermal currents in the OTA.

[Mikea]

I too have been thinking about going for a dob, but I'm confused about johninderby's set-up You seem to have the Auto dob mount, but with a completely different OTA - where did that come from and what happened to the flextube? or did you not have a flextube? The fact that you can "unofficially" make it GOTO is appealing to me. I did think the flextube was a good idea, but then you have to keep recollimating it and putting the shroud on - which is a bit of a pain.

Or maybe I should go for an EQ mount?

Actually, I think I like your dob setup - I want one!

[wulfrunian]

Thanks Phil - are you saying that you can't observe straightaway with a Dob till it's cooled down, or that the image won't be as clear until it has? Does this problem get worse the bigger the OTA is? We do have a garage / utility room on the side of the house which is unheated, which is where I'll be keeping the scope, so that might help matters.

Does the Skywatcher come with a cover / cap for when it's stored?

Also, does anyone know any dealers in the West Midlands area where they have these kind of scopes in stock, so I could see them in the flesh before making a final decision?

Sorry lots of questions but I want to get this one right

[Mikea]

Questions are good - keep asking wulfrunian! If you are planning to keep your scope in an unheated utility room, then that is the best place. The bigger the mirror, the longer it takes to cool down to ambient air temperature. I'd be a little wary of putting a scope in a shed or garage because of the hordes of spiders we seem to get down here (Devon).

[reelfoot]

i purchased a orion XT8i in june this year and really like it. i now have my eye on a skywather, larger of course, since my 10 yr old grandaughter is my stargazing partner now , so we need 2 now lol and my dog rowdy allways goes with us but he aint getting a scope just yet any scope you choose you will have a great time, that's what is is all about for us good luck on your next purchase DOB's are great scopes

[johninderby]

I too have been thinking about going for a dob, but I'm confused about johninderby's set-up You seem to have the Auto dob mount, but with a completely different OTA - where did that come from and what happened to the flextube? or did you not have a flextube? The fact that you can "unofficially" make it GOTO is appealing to me. I did think the flextube was a good idea, but then you have to keep recollimating it and putting the shroud on - which is a bit of a pain.

Or maybe I should go for an EQ mount?

Actually, I think I like your dob setup - I want one!

It was a Flextube Auto but I preferred the solid tube so I swapped the Flextube OTA for a solid tube OTA. The only change needed is to swap the tube mounting parts from the sides of the OTAs. The holes drilled in the tubes are identical so no mods needed, just a straight forward bolt on job.

John

[Mikea]

Ah ok - thanks for explaining! It's a pity they don't sell the solid tube OTA with the auto dob mount.

[Sunwind]

so if I understand correctly, skywatch are going to be releasing an auto mounted solid tube dob, they just need to get the firmware sorted or something? or am I totally on the wrong track here.

[johninderby]

As far as I know SkyWatcher isn't intending to release a solid tube Auto dob, although they could easily do it as there aren't any new parts involved or any modis needed.

SkyWatcher was supposed to release the upgrade option a little while ago to make the Auto into full GOTO but they pulled the upgrade at the last moment. Apparently it was delayed in order to make some changes to the handcontrol firmware but the latest version of the firmware seems to work fine.

There are all sorts of rumors on various forums about the "real" reason for the delay but google the subject and make up your own mind.

John

[ollypenrice]

I don't think anyone has answered your question about Dob photography. It is possible but only in a very limited way to the brightest solar system objects.

Even if you had it tracking, I doubt it would track accurately enough for any real improvement over untracked and for longer exposures you get field rotation in an Alt-Az mount anyway. (Unless you are on the North Pole...)

Olly

[wulfrunian]

Thanks, that's what I thought - but it would be possible to do lunar photography then. I need to get over to the imaging forum to see what equipment we'd need :-) When you say the brightest solar system objects, does that mean we'd be able to get the brighter planets, say up to Saturn?

[Phil Fargaze]

When the moon occulted saturn a little while back, I managed to get a decent picture of them both through the dob, using the afocal method, and that was with a normal digital camera and not a DSLR. I was quite pleased with the result. Mind you it could have just been blind luck...I can try to post the picture later when my daughter has finished using my laptop!

[wulfrunian]

How do you do that then Phil? Do you just need an adapter to attach the camera to the eyepiece?

edit - PS - does it make a difference whether it's DSLR or not?

[Odd Dob]

You can't put the tube on an equatorial mount (as easily), as a future option.

Has someone managed to get a flextube on a equatorial mount?