Dobsonians - pros and cons?

[LeeB]

I am that strange animal that likes to sit on the fence of the telescope world and have versions of  eq goto, eq manual, newts fracs and dob. The dob I made myself after rescuing a mirror from the skip. All of the above have there times and places, the dob is a great tool when all you want to do is observe, simply plonk it and look. Finding stuff is easy and the nudge becomes second nature, as for high mag use I have never struggled up to 300x as the base is super smooth with no backlash. Of the bigger scopes I own the dob gets most use because of the fast setup. I find that these days all nighters rarely happen and its then and at star parties that the goto is the tool. (I still take the dob along though) as a teaching tool the dob also wins you can leave it in the hands of a new astronomer young and old and they discover the heavens for themselves. I my opinion all should have a dob even imagers for that occasion when you just need a quick look, its also nice to move around the garden to see past any badly placed trees.

[AndyWB]

One question though..

Which is better, the Sky-watcher Skyline 250mm or the Revelation (GSO)?

I noticed the Revelation has a better base, dual focuser and a cooling fan.

Yeah, this question has come up a few times recently. It seems that in the past the GSO mirrors on their scopes weren't coated, and so didn't last very long, compared to the Skywatcher ones. Nobody is sure if that is still the case though.

My thought is that if mirrors are comparable quality and longevity, well, the Revelation is very tempting. I think everyone is just waiting for someone else to bite the bullet, though.

[Moonshane]

it all really depends on what you are comparing them to. e.g. a 12" dob is quite large and cumbersome for some people but certainly less than a 16" dob or a 6" f8 frac, tripod and counterweights.

broadly my pros and cons below assume comparison with a 10" f5 dob and a 120mm f8 achro refractor on a giro type mount and counterweight as I believe they have similar bulk and set up requirements strength wise.

the dob will :

benefit from a telrad and right angle finder

show the image upside down to the map so orientation is simply a matter of turning the map upside down

be set up in about 5 minutes easily by one person

need moving in two lumps

need cooldown time of maybe 30 minutes if stored indoors

need collimating (just a minor tweak) on most occasions

provide more detailed views of solar system objects

provide more detail and 'depth' to all deep space objects

be easy to track objects at high power manually if well adjusted

be easy to modify and improve (e.g. flocking etc)

maintain the eyepiece in a similar position (height varies only)

sometimes have the eyepiece in a low position - observing chair recommended

have diffraction spikes

may show some coma with good quality / astigmatism with inferior eyepieces

have stars that are not as sharp as a refractor (other than directly on axis)

be unsuitable (largely) for imaging

the mount is extremely stable with almost no settling time

the refractor will:

benefit from a telrad and right angle finder

show the image reversed left to right to the map so orientation is a little trickier than with the dob

be set up in about 5 minutes easily by one person

need moving in two lumps, maybe three

need cooldown time of maybe 30 minutes if stored indoors - yes, large fracs need to cool down too

need no or very little collimation

provide less detailed views of solar system objects

provide less detail and 'depth' to all deep space objects

be easy to track objects at high power manually if well adjusted

be less easy to modify and improve (e.g. flocking etc)

maintain the eyepiece in a similar position (height varies only)

sometimes have the eyepiece in a low position - observing chair recommended

have no diffraction spikes

won't show coma

have sharper pin point stars all over the field (eyepiece depending) 

be unsuitable (largely) for imaging unless on an EQ mount

the mount will have some settling time but only a second or so

Broadly it comes down to aperture. aperture gives more depth to the view and reveals some objects from non-dark sites that are not visible with less aperture. whilst a 10" dob is easily handled by mos people a 10" refractor would be managed by almost no people on a regular mount/dismount scenario. if you want larger apertures, a dob is cheaper, more convenient, more stable and of higher quality for the same price point.

[Stargazer_00]

The best point about a dob is that you can an amazing amount of aperture for your money!

I guess a con could be that some dobs require you to be seated at lower elevations due to the pivot point.  A height adjustable chair is a basic requirement for a dob owner in my opinion.

[Naemeth]

The best point about a dob is that you can an amazing amount of aperture for your money!

I guess a con could be that some dobs require you to be seated at lower elevations due to the pivot point.  A height adjustable chair is a basic requirement for a dob owner in my opinion.

Refractors are the same, just the other way around. They require seated observation at higher elevations.

[emadmoussa]

Refractors are the same, just the other way around. They require seated observation at higher elevations.

Was about to say...

[emadmoussa]

it all really depends on what you are comparing them to. e.g. a 12" dob is quite large and cumbersome for some people but certainly less than a 16" dob or a 6" f8 frac, tripod and counterweights.

broadly my pros and cons below assume comparison with a 10" f5 dob and a 120mm f8 achro refractor on a giro type mount and counterweight as I believe they have similar bulk and set up requirements strength wise.

the dob will :

benefit from a telrad and right angle finder

show the image upside down to the map so orientation is simply a matter of turning the map upside down

be set up in about 5 minutes easily by one person

need moving in two lumps

need cooldown time of maybe 30 minutes if stored indoors

need collimating (just a minor tweak) on most occasions

provide more detailed views of solar system objects

provide more detail and 'depth' to all deep space objects

be easy to track objects at high power manually if well adjusted

be easy to modify and improve (e.g. flocking etc)

maintain the eyepiece in a similar position (height varies only)

sometimes have the eyepiece in a low position - observing chair recommended

have diffraction spikes

may show some coma with good quality / astigmatism with inferior eyepieces

have stars that are not as sharp as a refractor (other than directly on axis)

be unsuitable (largely) for imaging

the mount is extremely stable with almost no settling time

the refractor will:

benefit from a telrad and right angle finder

show the image reversed left to right to the map so orientation is a little trickier than with the dob

be set up in about 5 minutes easily by one person

need moving in two lumps, maybe three

need cooldown time of maybe 30 minutes if stored indoors - yes, large fracs need to cool down too

need no or very little collimation

provide less detailed views of solar system objects

provide less detail and 'depth' to all deep space objects

be easy to track objects at high power manually if well adjusted

be less easy to modify and improve (e.g. flocking etc)

maintain the eyepiece in a similar position (height varies only)

sometimes have the eyepiece in a low position - observing chair recommended

have no diffraction spikes

won't show coma

have sharper pin point stars all over the field (eyepiece depending) 

be unsuitable (largely) for imaging unless on an EQ mount

the mount will have some settling time but only a second or so

Broadly it comes down to aperture. aperture gives more depth to the view and reveals some objects from non-dark sites that are not visible with less aperture. whilst a 10" dob is easily handled by mos people a 10" refractor would be managed by almost no people on a regular mount/dismount scenario. if you want larger apertures, a dob is cheaper, more convenient, more stable and of higher quality for the same price point.

Nice comparison, would be great if you could do a similar one regarding SCTs as well?

[swamp thing]

The thing I like best about using a Dob is the freedom it gives you as an observer. The freedom to move the scope in any direction at any speed.

[Stargazer_00]

Even ludicrous speed?

[Bart]

Pro, and I'm no con.

Joking. Never owned a frac, but a Dob is a lot easier to use than a reflector on an EQ mount. Love Dobs, dead easy to use and great aperture. I have a GSO/revelation 10" and the alt/az is a dream to use

Barry

[emadmoussa]

Pro, and I'm no con. Joking. Never owned a frac, but a Dob is a lot easier to use than a reflector on an EQ mount. Love Dobs, dead easy to use and great aperture. I have a GSO/revelation 10" and the alt/az is a dream to use Barry

I heard the Revelation ones are smoother to move around. Did you get it from Teleskop Service in Germany?

[Stargazer_00]

I don't want to get too far into this but I heard a number of times that the GSO mirrors are less likely to be consistantly of similar quality unit to unit when compared to the Synta branded scopes.

There is no conculsive evidence of this but it isn't disputed to my knowledge.

I questioned Telescope House on this fact when at the IAS earlier this year and the guy's reply was "if you enjoy the views what does it matter what quality the mirrors are, you are paying £1500 for a 16" dob here so it'll be good no matter what at that price you can't go wrong".  Obviously I was dicussing the 16".  I would argue that the mirror quality is important.

[Tinker1947]

There's a nice 300mm Dob in the Buy and sell section.....posted today.....

[John]

I don't want to get too far into this but I heard a number of times that the GSO mirrors are less likely to be consistantly of similar quality unit to unit when compared to the Synta branded scopes.

There is no conculsive evidence of this but it isn't disputed to my knowledge.

I questioned Telescope House on this fact when at the IAS earlier this year and the guy's reply was "if you enjoy the views what does it matter what quality the mirrors are, you are paying £1500 for a 16" dob here so it'll be good no matter what at that price you can't go wrong".  Obviously I was dicussing the 16".  I would argue that the mirror quality is important.

Thats my take too. I've owned a couple of GSO mirrored scopes in the past and I've owned a couple of Skywatchers and I'd pick the latter brand if buying again. In the USA quite a lot of folks get their GSO mirrors re-figured whereas you rarely seem to hear of Skywatcher / Synta owners doing the same.

If you can pick up an Orion Optics dob used then even better as the optics are great and they are lighter than the chinese dobs. My 12" OO F/5.3 dob is as light as the Skywatcher 10" F/4.7 dob but my old 12" Lightbridge was considerably heavier.

[emadmoussa]

There's a nice 300mm Dob in the Buy and sell section.....posted today.....

Too huge..

[Bart]

I heard the Revelation ones are smoother to move around. Did you get it from Teleskop Service in Germany?

Yes, very good service. Offered to deliver it to Ireland FOC. Couldn't argue with that! Owned it a couple of years and love it. My 16" gives better views on most objects but the GSO is significantly easier to use. It's just the right size to move around, smooth as anything while nudging, love it. Views pretty darned good too!!

Barry