Dome vs Roll off ?

[JamesF]

I have been wondering about having drop-down sides on a roll-off roof design.

My original design was for a flat pent roof, but whilst that can give plenty of headroom it makes getting the scope close to the horizon awkward (if not impossible) unless some of the wall rolls away with the roof. When you have the opportunity to be able to see down to five degrees above horizontal you want to use it A gabled roof might allow the sides to be lower but has the disadvantage of reducing headroom for the same height of building and being heavier and more difficult to construct.

A pent roof with fold-down sides seems like a reasonable compromise and has the advantage of being able to leave sides up for shelter if required.

James

[ollypenrice]

I have been wondering about having drop-down sides on a roll-off roof design.

My original design was for a flat pent roof, but whilst that can give plenty of headroom it makes getting the scope close to the horizon awkward (if not impossible) unless some of the wall rolls away with the roof. When you have the opportunity to be able to see down to five degrees above horizontal you want to use it A gabled roof might allow the sides to be lower but has the disadvantage of reducing headroom for the same height of building and being heavier and more difficult to construct.

A pent roof with fold-down sides seems like a reasonable compromise and has the advantage of being able to leave sides up for shelter if required.

James

Quite right; and why not have some sides roll with the roof? I've done that on both my dwarf wall roll offs. Then you have a flap which seals up the end between the rails. I didn't want my dwarf walls higher than 1.2 metres because we have good horizons. Also, don't forget that when you image past the meridian on a GEM the scope gets lower and lower so, finishing off in the west, your walls really do need to be quite low or they'll be there in the picture! You can have different wall heights on different sides to fit your site and interests.

How would drop down sides work? Would the rails drop down with the sides? If they didn't, wouldn't they still be there and getting in the way? I think I'd worry about not having the rails on predominantly fixed walls - or I may be entirely missing your point which isn't unlikely....

I was worried about getting the roof-and-upper-sides stiff enough in wood alone so the first one, which is quite wide, I welded up in steel. However, I had a go at an all-wooden structure for the second one which is only 2M wide. I'm useless at woodwork and don't do proper joints but with a bit of triangulation it worked out fine and is very stiff. I put some rail on top of the low door so I have to remeber to close the door when rolling!

My ill fated remark about headroom earlier on was based on the idea that an imager might well want the dwarf walls at a low height and, in a 2M dome, that would offer limited headroom half way from walls to centre. Of course, in a dome you can raise the dwarf walls and the pier to match without getting into wind issues but your dome ends up less small and more tall.

Olly

The all wooden version under construction. (When closed there is no standing room but you can get in to open it or use the PC etc)

The larger, steel framed roof and sides..

[JamesF]

That second one is a bit of a monster

James

[nytecam]

The option of Dome v RoR, for me in UK, is a no brainer as I'd go for the former everytime. I've built 6 domes v nil RoR. However it appears most go for a RoR for perhaps ease of construction and less intrusive build on the garden scene. Personally I don't see the point of a RoR - I can stand on the patio anytime with the sky above and dew wetting everything below [and ending the session] as well as the curse of local light pollution.

Domes give complete protection of observer and instrument but do have a minor disadvantage in that the objects observed need to be seen/imaged in some order otherwise the dome will be in a flat spin zapping all over the sky.

[ollypenrice]

That second one is a bit of a monster

James

Heh heh, it is and it won't win a beauty contest but the scope inside is a bit of a monster as well (blame Yves!) and the warm room has a bed in it.It looks more normal when closed up by day!

Nytecam, I don't have UK dew to contend with but, come now, there is no comparison between an open patio and a roll off. Your instrument stays put, your computer stays put, you can have a warm room if you want to, you have wind protection up to a point.. When the wind is bad enough to get the scope I find, down here anyway, that is also bad enough to have got the seeing and you're pretty well scuppered. I don't have any local light pollution at all but I take your point about sites where you do need to exclude it. Clearly a dome wins there.

A thought on domes; they don't have to be domes, do they? A square shape can rotate on a round ring. If you wanted more headroom and less burglar advertizing why not make a rotating top observatory that looked square when closed? Just a thought. Easier to make, too, perhaps? Or what about a square 'total rotator' without dwarf walls? Again, easy to make and just like a normal shed.

Olly

[The Sailor]

The one thing I like about the dome is that it keeps direct light out from the streetlight a few metres away and my mount is not sticking up outside as with the RoRo.

[Gina]

Very interesting idea Olly A turret sort of Might be a bit of a problem "squaring the circle" to make the top rotate. Hmmm... I can see lots of problems... interesting all the same Buy yourself an ex-army tank, replace the gun with a scope (or two). Cover with camouflage paint - job done Great security too

[pete_l]

I don't have any local light pollution at all but I take your point about sites where you do need to exclude it. Clearly a dome wins there.

The problem of "direct" light pollution (i.e. light getting to the observer and ruining his/her night adaptation) doesn't really arise for imagers.

Though for visual observers, either in an obsy or not, the easy solution for "in the eye" LP is the sort of cloth cover that 19th century photographers used.

[JamesF]

I had thought about a sort of turret, so the construction would still look like a shed with a proper roof. I came to the conclusion that it would just be too awkward.

James

[JamesF]

The problem of "direct" light pollution (i.e. light getting to the observer and ruining his/her night adaptation) doesn't really arise for imagers.

Though for visual observers, either in an obsy or not, the easy solution for "in the eye" LP is the sort of cloth cover that 19th century photographers used.

People tend to get a bit stroppy when you start sticking those all over their lights though.

JAmes

[The Sailor]

What I have done to eliminate direct LP is to let the bottom flap of the slit down only so that it covers the roof of the houses and street light.

Jim

[ollypenrice]

The one thing I like about the dome is that it keeps direct light out from the streetlight a few metres away and my mount is not sticking up outside as with the RoRo.

Pefectly good point in favour of domes.

When it comes to squaring the circle with a fully rotating turret the only circle you need to construct is the one for the bearings. If you make a structural floor with a circular hole in it you can build a square shed on that. They used to make square rotating sun sheds with a wall missing, this being the side you turned towards the sun. My neighbours had one in my childhood and they were just called summer houses, logically enough..

Olly

[mister brot]

just spent close to an hour reading this dome or roll off topic..for those of you who don't know I have recently got re-infected with the love for astronomy virus and can't figure out why it took more than 20 years for this to happen....anyway not to get to far off topic, the more I learn here on this forum the more I get excited of all the possibilities - for ex. with computers (viewing/tracking) and all the other stuff like using webcams atapters and,and,and,ex,ex,ex, it is making my head sometime spin....thought before.....

1. get telescope

2.take telescope outside.

3. look at stars

4.take scope back inside

.....had not realized how big amature astronomy was ......upps off topic again

anyway..about topic was looking on the web at different pics and stories on building these observatories and ran across a site where this guy writes about and has pictures from beginning to end of his build,,and I might say how very impressive this is and to say I think there isn't an astronomer out there who wouldn't like to have something like this in his garden...this is for me my dream someday to have....In advance would like to thank those who will help me with future questions I might have (and believe me I got a ton of them so be prepaired )

here is a link to this roll off I was talking about....and if this person is here on this forum then sir my hat is off to you well done!!

http://www.google.de/imgres?q=roll+off+roof+observatory&um=1&hl=de&sa=N&biw=1241&bih=619&tbm=isch&tbnid=rTvBwHeuJRI_RM:&imgrefurl=http://www.rocketroberts.com/astro/observatory.htm&docid=KiBqWPda05RltM&imgurl=http://www.rocketroberts.com/astro/images/observatory45.jpg&w=600&h=415&ei=FbRRUOSNI6n04QTyvIGIDA&zoom=1&iact=hc&vpx=834&vpy=257&dur=7595&hovh=188&hovw=270&tx=160&ty=153&sig=117564635486385380935&page=1&tbnh=130&tbnw=170&start=0&ndsp=18&ved=1t:429,r:16,s:0,i:123

[ollypenrice]

It's a good job on a grand scale, all right, but the need for these piers drilled through from Australia has been discussed before! We image with a telescope the same size and it stands on a normal garage base-type concrete pad with no issues whatever. I'm all for the easy life and that's one area in which I'd save effort!

Olly

[The Sailor]

I would have liked to have seen a panorama of his horizon, I am thinking it is a bit limited with what trees we can see. He has put a lot of effort in that build, it good, but for me not much sence, unless he is a lumberjack

Jim

[Gina]

Hmm... Rather overengineered IMO. No warm room so those roll-off beams and posts look untidy. With all those trees around he doesn't need low walls so a simple roll off roof was quite adequate.

Such an enormously big and deep hole for the pier and then he makes the pier in several pieces - strange that. That size hole and tons of concrete would suit a metre sized mirror rather than a 14".

In that location I think a tall round building with a dome on top would probably have actually been less trouble

[mister brot]

these things my be true the fact that he put so much hard work into it imo shows how much he is dedicatid to astronomy....may be overkill but if you got the money and you are in no hurry...then why not.....again I am no expert to judge, I'll leave that all to you all anyway it sure inpressed me

[The Sailor]

In that location I think a tall round building with a dome on top would probably have actually been less trouble

Exactly what I was thinking by the end of the page, would give him just that little bit extra height, pier straight down to the ground and warm room below. Now I know that the trees will probably grow higher and I did think of this but who knows. Anyway, a solid building with a lot of skill gone into it .

Jim

[ollypenrice]

Yes, and in the end you also want to enjoy the build in your own way. If that guy said 'Would you like me to come and build you one at your house?' the answer wouldn't take long to announce!

Olly

[The Sailor]

Don't quite get that but never mind.

Jim

[malc-c]

here is a link to this roll off I was talking about....and if this person is here on this forum then sir my hat is off to you well done!!

http://www.google.de...,r:16,s:0,i:123

And people thought I was going over the top with my foundations.... !

To be honest that's not a complicated build, although he has over engineered it to be. There used to be a pinned thread on this sub forum, with a selection of build threads... including mine, Gina's and several others. Most of which are larger and have warm rooms, and are larger than his 8 x 12 (not boasting but mine's 2.4m x 4.8mm as is Gina's I beleive) - that thread is well worth a look

[Gina]

Mine's in the Design stage list thread Not only is the design finished, it's built (except for ongoing minor titivating)! And yes it is about that size and includes a warm room. It is more complicated than his. My views are much better than his so I "need" to cover lower angles and therefore have part of two walls rolling off with the roof and another folding down.

[The Sailor]

After looking at all the designs on here I have decided that if I can rebuild it will be a round flatroof affair, the slit as normal , two story rather than outwards, a warm room beneath. A couple of reasons, one it will lift me above direct LP and the other is a smaller footprint on the garden. The wall and roof of the upper floor moving rather than just the roof, with the controls set off from the wall but lower than th slit. Maybe one day it will come about untill then I will put up with what I have

Jim

[Gina]

That sounds a very interesting design Jim

[ollypenrice]

Don't quite get that but never mind.

Jim

I'd say yes. It's over engineered but that isn't a fault unless you want to economise on cash and time. I get the feeling that this guy likes to work that way and if he likes it he should do it. That's all I meant.

Olly