2000mm focal length dob: Worth it?

[Wiu-Wiu]

I might upgrade my viewing power from 12" to 16" in the future. 

Having coma on my mind, I am thinking about which mirror to choose, more specifically, the F-ratio. 

My 12" is rather short, and maybe even a bit too short, as I usually end up bended halfway forward, looking at objects low in the south. My back can tell you what a strain it is. 

I could go for a short dob, but would that introduce more coma - but regarding the fact I usually don't look high in the sky, is focal length (read: scope length) really an issue? 

 

The telescopes I was looking at were around 2000mm in focal length. That would at some point make me need something to stand on - I am 1m85. 

Bear in mind I like sketching, so getting to sit down is a real treat. 

 

Longer dob owners, please weigh in here? 

[Paul73]

My f4 16” Dob needs an expensive coma Corrector to keep things under control. But, the eyepiece is generally at a very convenient height for a standard observing chair. These scopes are big enough already without making them even more cumbersome!!

I couldn’t use it without the corrector (Parracor in my case). 

Paul

[vlaiv]

I'm 1m83 but when thinking about 16" dobs - my primary concern is eyepiece height and observing comfort.

Eye level is lower than persons height, and sometimes I like to share a view with friends - some of them have smaller height, so my guess is that max EP height should not go over 1.5m for comfortable viewing of most grownups.

16" can be be F/4.5 - 1800mm FL and F/4 - so 1600mm. You need to account for dob base, distance of secondary to focal point (it will be something like 400mm), but I reckon that F/4.5 is proper FL for 16" scope. I don't like the idea of step ladder in the dark for observing near zenith.

With F/4.5 you need coma corrector and possibly the best way to go about it is to look for integrated CC - one that is pre adjusted to focal position, so you don't have to fiddle around with spacing for different eyepieces.

[Wiu-Wiu]

I already have the Explore Scientific HR Comacorrector for my 12" so I pretty much have that under control; only 2 of my EP need a different setting and I usually only use those for wider views as they are the largest EP in my case. The only difference with the paracorr is it doesn't have the presets but I need to fiddle it until at correct distance.

My observing chair is adjustable but I'd have to see to which height I can comfortably (and safely) sit. 

 

Paul, how is observing with your f/4? Do you need anything to stand on or raise your feet off the ground? As most people, I'm not getting younger and the scope will need to work for ages  

[alan potts]

Mine is 18 inch F 4.3 and has a F/L of 1980mm, I have to stand on a 12cm brick when directly overhead, not that often I have to say. So give you some idea, I'm 1cm taller.

Alan

[Wiu-Wiu]

Do you have to stand up a lot or can you usually sit down? I'm trying to figure out if I would have to sketch standing up...