Dob.. thinking and making..

[NickK]

Well I have sort of .. permission to make a visual dob so in the spirit of compromise...

* it's a truss type so it doesn't take masses of room..

* I make the woodwork first... then at some point get the mirrors (probably orion optics)

Now I've see through a 16" dob.. and the thought that seeing some colour form m51 for example is what I'd really target.. I have a refractor already that really does a good job but when it's APing the dob will be for having a look around

Really thinking 16 or 18".. 

[Beulah]

Go as large as you can afford but think about the Focal Ratio, try and obtain a fast mirror, if the objective is for a more mobile scope.

Ideally, you would be able to see through the eyepiece without a stepladder. Trust me, it can be an absolute pain when you have driven out to a dark site and forgot the steps or stilts...

[ronin]

Go for as large as you will actually use and be able to handle.

A 16" scope you do not use is pointless and a lot get 16" scopes and then seem to give up.

Large does not mean something that you can just haul around as the first injury means it sits unused.

One cold night, one strained muscle. :eek:

[ronin]

Is your AP rig in an observatory and so sat waiting for you to apply life to it in the form of electricity or is the idea to take out an EQ6 and scope (Guide system ?) set up the mount, attach scopes, acquire target, check it is running and getting images. Then set about hauling out and constructing a 16 or 18 truss dobsonian ?

If the latter then how long does it take to set up the EQ6 and get to the imaging stage where the setup starts collecting it's first exposure?

Also I guess any set up of the truss will have to be done in the dark as you will not be wanting to shining a light around when imaging, and setting up the truss first reduces the imaging time.

[NickK]

Is your AP rig in an observatory and so sat waiting for you to apply life to it in the form of electricity or is the idea to take out an EQ6 and scope (Guide system ?) set up the mount, attach scopes, acquire target, check it is running and getting images. Then set about hauling out and constructing a 16 or 18 truss dobsonian ?

If the latter then how long does it take to set up the EQ6 and get to the imaging stage where the setup starts collecting it's first exposure?

Also I guess any set up of the truss will have to be done in the dark as you will not be wanting to shining a light around when imaging, and setting up the truss first reduces the imaging time.

It takes about 15 minutes at the moment to set the AP rig setup, then it's locate the target and start. Although not fully complete it will be faster in future for various reasons.

I'm lucky that I have a conservatory to act as a warm room and a garage attached to the garden. So things can be cooling down pre-assembled with a dust cover.

[swamp thing]

Hi Nick

You won't see colour in M51 no matter how much aperture you have. Galaxies only show colour in overexposed images.

Next. Best to disregard any advice that informs you that big scopes may cause strained muscles. This is utter nonsense as no one will be lifting any of the heavy components of a properly constructed large truss scope. 

The only pieces one will be required to lift is the UTA and this is light. it only consists of a couple of plywood rings and some other bits. Think large drum. never seen a one man band collapse with muscle strain

I would opt for 18" myself. Its the kinda last size before they start getting bulky. Over 18" and things like doorways start to become obstacles.

[NickK]

Hi Nick

You won't see colour in M51 no matter how much aperture you have. Galaxies only show colour in overexposed images.

Next. Best to disregard any advice that informs you that big scopes may cause strained muscles. This is utter nonsense as no one will be lifting any of the heavy components of a properly constructed large truss scope. 

The only pieces one will be required to lift is the UTA and this is light. it only consists of a couple of plywood rings and some other bits. Think large drum. never seen a one man band collapse with muscle strain

I would opt for 18" myself. Its the kinda last size before they start getting bulky. Over 18" and things like doorways start to become obstacles.

I'm lucky because the garage has a door straight onto the garden so as long as it fits through that with minimum of fuss then it will fit in the car too. I can make a ramp if it needs moving and it becomes too heavy (I'm early 40s..).

At the moment it's in the planning stage and probably will be like this for a while - it may end up being a summer build project but we'll have to see. Gives me a lot of time to think and to look at things such as ideas to get the truss as rigid as possible but also light and not obnoxious to put together in the dark.

I did get a faint blue in Luke's dob but my thinking here is to go for a fast mirror. My only concern is coma - being spoilt by the Pentax where you get pinpoint stars and very flat field. So that is something else I'm interested in minimising but that's something I can add to along the way.

I may be tempted to build a little 4f finder scope with a CCD that has a Odriod target screen. That way it would act as a backup to visual finder.

[swamp thing]

For Coma correction I used this on my large dob. IMO this is the future in coma correction.

[mapstar]

Next. Best to disregard any advice that informs you that big scopes may cause strained muscles. This is utter nonsense as no one will be lifting any of the heavy components of a properly constructed large truss scope.

The only pieces one will be required to lift is the UTA and this is light. it only consists of a couple of plywood rings and some other bits. Think large drum. never seen a one man band collapse with muscle strain

I would opt for 18" myself. Its the kinda last size before they start getting bulky. Over 18" and things like doorways start to become obstacles.

Hi Nick

What Steve says is true, assuming you either wheel it out of the garage (what you are doing) or have a transit van to wheel it out of when you get to a dark site.

If not then 18" is about as big as can be lifted if its a traditional obsession style dob. Anything bigger and its a struggle on your own unless you go light weight construction. We don't all have easy access to dark skies.

Damian