Question for Dome owners (and anyone else who can pitch in)

[x6gas]

Hi all,

I've always wanted an obsy and always wanted a dome and as my 50th lap of the sun nears, I've decided to start making the dream a reality.

I'd really like a dome (not the place for a convo on dome versus ROR) but I have a question - what kind of headroom is 'safe' for the width of the dome shutter versus the scope(s)?

I am looking at a ScopeDome but the shutter aperture of the 2m dome is 'only' 590mm.  The largest scope I have is 280mm aperture so plenty of headroom there but I want to mount my two FSQ85 scopes side-by-side on an ADM mounting bar and that means that the scopes are 400mm (not 500mm as I originally posted) dew shield to dew shield.  The dome will be fully automated but 190mm wriggle room seems pretty skinny and I don't want any possibility of the dome getting in the way of the light path or vignetting etc.

The 3m dome has a 1m shutter aperture - and I love the look of it - but the 2m comes fully assembled and automated which I confess is quite attractive.

Any thoughts from dome owners or anyone else with an opinion would be very warmly welcomed... unless that opinion is to go for a roll-off-roof!

Thanks, Ian

Edited September 23, 2019 by x6gas
Corrected width of side-by-side scope set up

[Laurin Dave]

I can't see that it will work on that length of side by side bar, I'd investigate constructing a shorter one and having the Taks as close as possible . Also as the scopes are offset from the centre of the dome the effective width of the shutter aperture (ie as seen by the scopes) will be less than 590 mm. 

[pmlogg]

The current version Pulsar 2.7m appears to have a 700mm shutter.  The original version was wider at  780mm.  I've not tried side-by-side; I have one piggy-backed on the other, but the total height of the pair is less than  your biggest scope.  Of course when your scope pair is on one side or other of the mount the two scopes would no longer be side by side, but at the extreme would be above each other, reducing the effective width.

[x6gas]

51 minutes ago, Laurin Dave said:

I can't see that it will work on that length of side by side bar, I'd investigate constructing a shorter one and having the Taks as close as possible . Also as the scopes are offset from the centre of the dome the effective width of the shutter aperture (ie as seen by the scopes) will be less than 590 mm. 

Of course!  That makes perfect sense... but makes it much harder to judge what would work.

My measurement / memory / typing were wrong and the actual width of the dual scopes is 400mm not 500mm as I originally posted so there is a bit more relief (the other measurement included bits of the bar which obviously doesn't matter).  Can really use a shorter bar as I need to accommodate the motorised focuser and allow for full rotation of the filter wheel...

[x6gas]

10 minutes ago, pmlogg said:

Of course when your scope pair is on one side or other of the mount the two scopes would no longer be side by side, but at the extreme would be above each other, reducing the effective width.

That's true.  I need to figure out the interplay of the horizontal orientation of the scopes as you point out and the off-centre impact that @Laurin Dave mentioned...  I guess I could just chuck it on the mount and take some measurements rather than trying to calculate it...

Thanks for the reply!