Size is the Limit

[DAVE AMENDALL]

Hi all, what would be the largest Dob that could be used comfortably in a 2.2 metre dome Observatory bearing in mind that the observer is slim build. Is this a question for the Dobsey or Obsey men or both ?..............Dave

[Dave In Vermont]

What is the fastest focal-ratio you'd be willing to settle for? This would help determine the maximum aperture you could go for.

Might be a question for math-freak!

Have fun -

Dave

[DAVE AMENDALL]

I would think  F5 Dave

[Dave In Vermont]

The dome is 2.2 meters? Okay. So now figure the length of the OTA - factoring in the OTA needing to be somewhat raised off the ground/floor. And the distance to bump into the dome itself. Then plug-in the different possible apertures of the mirrors and multiply by '5.'

See how big and aperture you can go to before you run out of room and go <Bump!>...

This isn't meant to be an exact formulae. I'm not a 'math-freak,' but I think you can see how to approach this problem.

PEMDAS Away!

Dave

[Cosmic Geoff]

I'd be curious to see the final answer. I don't think my f5 8" Newt would fit comfortably in a 2.2m dia (1.1 m radius) dome if Dob mounted.

Dob outfits are portable, so an observatory would not appear to be a high priority for one.

With a dome that small maybe you should think "SCT".  Potentially the observatory will cost much more than the telescope anyway.

[John]

Pulsar Observatories reckon that their 2.2 metre dome can accomodate a 14" SCT or a 12" EQ mounted newtonian. I suspect the limt for a dob might be 12" - 14" depending on the focal ratio.

[Louis D]

Have you ever seen photos of larger dobs in "observatories"?  They're generally roll-off roof sheds with low walls to accomodate the very large swing and low viewing positions of a typical dob.  A 2.2 meter dome is about 7 feet in diameter.  6" to 10" dobs generally have about a 6 foot turn diameter.  It could be less if the tube is mounted more centrally rather than at one end similar to Teeter dobs.  It would be a tight fit to say the least.  That, and you'd have to raise the base to get views above the walls.

Generally, smaller domed observatories house EQ mounted shorter tubed refractors, SCTs, Maks, or Newts on a pier.  The key is that the tubes are generally mounted near their midpoint to minimize their swing footprint.  The pier gets them up high enough to see over the wall.