Which 10 inch DOB would you choose?

[Steve1976]

Ok so I am dead set on getting a 10 inch DOB and just have some questions -

Is the Meade Lightbridge significantly better than Skywatcher models?

I noticed a 10 inch SW Pyrex - is this still parabolic or is it inferior in some way?

Would a 10 inch Dob be good for AP of DSO's? I know there are better scopes suited for this purpose but if it is still possible then I would probably spend a little extra for auto-tracking (observing is still more important to me than imaging).

Oh, one final question - which accessories would be deemed essential other than good EP's?

[dweller25]

1. I think it's swings and roundabouts between the Meade and Skywatcher 10" dobs.

2. Yes the Skywatcher is parabolic.

3. A dob is not good for AP.

4. A rear mounted cooling fan.

HTH

[Ben Ritchie]

If money/delivery time etc. aren't an issue i'd probably go for a Orion Optics 250L deluxe with 1/8th or 1/10th wave optics (you asked which 10" dob i'd choose ), if either of the above is i'd probably choose the SkyWatcher 250px - the Meade is broadly similar, so an element of personal preference there. I don't personally believe one is much better/worse than the other, they're both Chinese imports built to similar standards.

Would a 10 inch Dob be good for AP of DSO's? I know there are better scopes suited for this purpose but if it is still possible then I would probably spend a little extra for auto-tracking (observing is still more important to me than imaging).

Not really, you really need an equatorial mount - the auto-tracking Dobs are Alt-Az, so even if the tracking is good enough for long exposures (it probably isn't) you'll still get field rotation. They're fine for webcam imaging of the moon/planets though.

Oh, one final question - which accessories would be deemed essential other than good EP's?

I'd say a decent RDF (Telrad or Rigel Quikfinder) and it's well worth replacing the standard finder with a right-angle model, to save on neckache. Depending on your choice of eyepiece you might want a coma corrector - good for long focal length ultrawides, although don't buy until you decide that coma bothers you.

[Steve1976]

Thanks mate, how much would one of the cooling fans set me back?

[johninderby]

The Skywatcher is every bit as good as the Meade quality wise and it has the advantage of a better and easier to use truss system and a Pyrex low expansion parabolic mirror as well instead of the Meade's plain plate glass mirror. The only thing that I think is better on the Meade is the focuser. However you can get a better quality crayford than the Meade's for £89.99 that is just a straight forward bolt on replacement.

For DSO's you should really be thinking of an EQ mounted scope. Although you can get tracking or GOTO for the Skywatcher dob it will never be really suitable for AP other than a bit of lunar/ planetary due to the limitations of it's Alt-Az dob mount.

Other than EPs as you have mentioned another finder such as a Telrad or Quikfinder and a Right Angle 9x50 finder will be really usefull. And as mentioned with the Skywatcher a better focuser.

Considering the Pyrex mirror and better truss system I would recommend the Skywatcher. Of course at 10" a truss isn't really necessary and the solid tube Skywatcher would be cheaper and a bit lighter as well.

John

[dweller25]

Thanks mate, how much would one of the cooling fans set me back?

I used a computer case fan - £5

[Steve1976]

Thanks, you guys are a huge help as always!

[johninderby]

80mm Fan £1.45 delivered.

http://cgi.ebay.co.uk/80mm-Internal-Desktop-PC-CPU-Fan-Computer-Case-Cooling-/280522463636?pt=Computing_ComputerComponents_Fans_Heatsinks_SR&hash=item4150711994

John

[LukeSkywatcher]

Q: Is the reason people use built-in fans on their Dobs simply to reduce the cooling down time before observing or do the fans run for the duration of the observing session to keep the scope optics at an ambient temp?

[johninderby]

Q: Is the reason people use built-in fans on their Dobs simply to reduce the cooling down time before observing or do the fans run for the duration of the observing session to keep the scope optics at an ambient temp?

It all depends on your local conditions and the mirror itself (plain plate glass, Pyrex or other low expansion glass). While cool-down is the main purpose some people do find that they can help while observing.

With my 14" OO dob I never need the fan while observing.

John

[LukeSkywatcher]

Thanks John. I've always just accepted the fact that many Dob owners have fans on their scopes but never thought to question why.

I somehow thought that it was to keep the electronics cool...............but most Dobs dont have electronics of any kind on them.

Silly i never thought about THAT until NOW.

But i'm now glad i asked.

[bombassa]

Where will the GSO-style dobs fit in? Money-wise they seem to be at SW level.

[johninderby]

The Meade Lightbridge dobs are made by GSO and so they have the same mirrors. GSO dobs aren't readily available from UK dealers but are stocked by the German dealers. Telescope House does sell the 12" GSO dob under their own Revelation brand name though.

John

[John]

I've owned a Meade Lightbridge 12" and Skywatcher 8" and 10" solid tube dobs. Optically there was not much to choose between them but the Meade needed quite a few mods to get it to the point where it was a useful instrument whereas the Skywatcher's seemed to work pretty well "out of the box".

[yeti monster]

It would appear that, rather than a rear mounted fan, a fan which pushes air across the front surface of the mirror offers better results, as it washes away the turbulent air currents associated with large pieces of glass in optical equipment.

http://stargazerslounge.com/equipment-discussion/114379-cooling-newtonian-mirror.html

[dweller25]

The fan needs to do three things :-

1. Cool the primary

2. Remove the boundary layer from the front of the primary.

3. Remove tube currents.

I find a rear mounted fan with a baffle does all three jobs simultaneously.

It's quite interesting to turn the fan off when the mirror appears fully cooled - the views go softer after about 15 seconds - that's the boundary layer reforming, so the mirror is still not cool enough even though if you do an out of focus star test it appears to be.

The boundary layer is a very subtle temperature difference but it's effects are significant.

[Moonshane]

I actually have both and run then simultaneously on my 12" dob. I have just ordered a 40mm fan for my 6" which will be behind the mirror, pushing air up the tube. mainly for cooldown when I have the fans on full blast, both caps on and air being blown out of the focuser but I then turn down the voltage on my transformer to reduce the blowage to a whisper for observing. I feel this prevents vibration, still does the jobs it's supposed to do and also prevents the mirror cooing too much and dew forming.

the single small fan on the 6" will probably work just from the rear and should be enough to do everything I think. I'll report back when it's fitted - probably via this thread http://stargazerslounge.com/equipment-reviews/112331-orion-optics-uk-6-f11-dobsonian-review.html

in answer to the post's question, if you want to do AP in the future of DSOs I am not sure a flextube or a truss design would be good for this due to collimation changes on an EQ mount. I personally don't like the idea of a tracking dob as for me their's more involvement with the observing if you nudge and drift etc but that's just me. plus your Skymax would probably be better for planets and lunar photography anyway?

on the above basis and assuming you eventually want to go for AP on an EQ6 or similar (which will cost more than your scope) then I think the 10" solid tube SW non tracking dob would be best.

if you want better quality optics for things other than DSOs (eg doubles and planets) then you'd be better spending a little more on an Orion Optics dob and maybe a top optics 10" f6 would fit the bill well? not cheap though.

you might be better forgetting AP for now for DSOs and buying the biggest dob you can handle for DSOs visually. you can then buy a small wide field ED refractor in the future with a good quality GOTO mount if you wanted to get into AP later. I am no imager though so bear this in mind but many people have at least two scopes and for different types of targets. those into AP probably have even more, plus a computer, guide scope, CCD, webcam, DSLR and a partridge in a pear tree.