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Advice on complete dome setup with all equipment.


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 ... For the galaxies, other than M31, M101 and M33, you need a focal length beyond the range of mortal refractors. Many people have at least two focal lengths available, but once you get to much over a metre of FL you need to start thinking about the more up market mounts if you want the system to perform to its limits comfortably. ...

I'm sure this is a silly question but is there much point in going beyond 1m of focal length? For most people seeing will probably be limited to 1" or more which at 1m focal length is about 5 microns. So would longer focal lengths reveal anything or just give a better view of how bad the atmosphere is? Or are the longer focal lengths simply a fact that ultra fast scopes require some complex optics to overcome aberrations practical considerations lead to longer focal lengths.

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Well, I'm going to disagree with your Prof. The Celestron C14 has a focal length of an utterly monstrous 3.91 metres. This means that, even in the widest of widefield eyepieces, your field of view is

Old wisdom always says don't build an observatory as part of another inhabited building.  The main reasons being heat - currents of warm air ruining the seeing above the building, and vibration - any

You wouldn't use 5 micron pixels in a long FL system. You'd be better with the 9 micron of the 11000 chip, for instance. Or you'd bin a small pixel camera 2x2, but for the reasons you suggest. I think

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I'm sure this is a silly question but is there much point in going beyond 1m of focal length? For most people seeing will probably be limited to 1" or more which at 1m focal length is about 5 microns. So would longer focal lengths reveal anything or just give a better view of how bad the atmosphere is? Or are the longer focal lengths simply a fact that ultra fast scopes require some complex optics to overcome aberrations practical considerations lead to longer focal lengths.

You wouldn't use 5 micron pixels in a long FL system. You'd be better with the 9 micron of the 11000 chip, for instance. Or you'd bin a small pixel camera 2x2, but for the reasons you suggest. I think it certainly is worth going to long FL, yes, for small targets. I can get far more resolution out of Yves' 2.4 metre FL than I can from the metre of my TEC140. You also get the scale. This is at 2.4 metres, as an example;

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-Sc3kgzc/0/X3/M51%20DEC%20VERSION%20clip-X3.jpg

Olly

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Well, I'm going to disagree with your Prof. The Celestron C14 has a focal length of an utterly monstrous 3.91 metres. This means that, even in the widest of widefield eyepieces, your field of view is going to be very limited. I have a far smaller SCT here with a FL of 2.5 metres. Quite honestly I find this a boring telescope to use because of the cramped field.  It's fine on some things but I also have a 20 inch F4 which collects four times as much light and still has a wider field of view! So my question is, In a large dome where you have room for a 14 inch or larger Newtonian telescope what is the advantage of  such a long focal length? The only answer I can come up with is that it will give great planetary views and planetary images with a fast frame camera. For the rest it will be a pain.

Deep sky imaging; the C14 is F11. Uesless! No other word for it. Exposure times for this scope would be 4.84 times longer than with a Takahashi FSQ refractor. A 10 hour image in the F5 scope would take 48.4 hours in the C14. (Note that they would not be used on the same targets or take the same pictures, so I'm not falling into 'the F ratio myth' but pointing out the comparitive signal strength on the chip. It's signal to noise which matters, whatever your target.) Celestron now do a focal reducer which brings the scope down to F7.7, which is still slow and the corrected field will no longer cover a full frame chip. This kind of focal length is great for small planetaries and distant galaxies. The nebulae are out. They won't fit on the chip. Is this what you want? I image at FLs of 530, 980 and 2380mm. I like having them all available. Being limited to just the big one would be frustrating. For one thing, it not only needs clear nights, it needs nights of stable seeing. Shorter FLs are more productive. If you go for this kind of FL, though, buy a serious mount. Paramount, Mesu, 10 Micron, Astro Physics. Take lots of advice from practising imagers on what will work at this kind of FL. Don't, whatever you do, believe the adverts. Not many mounts can work at these focal lengths. Trust me, I do this for a living.

I once helped commission a telescope housed in a large Ash Dome. It was stunning. The guy who built it for the owners said that it went together like a dream and just one  small item was missing. This was duly sent immediately. I was really impressed by this dome.

Telescopes; the devil is in the detail! The SCT is a specialized instrument and absolutely not a 'do all.' The little it does, it does well. 

Olly

Olly,

Thank you again for the tremendous information.  I think I realized what the discrepancy is.  I don't believe my professor is thanking about photography.  I think he's assuming just basic observational stuff.  Which, seeing as there's a big difference, I wonder what the best thing is for me.  Now I'm thinking maybe just a good all around standard scope like the one he suggested for viewing things.  I'll be able to take photos of some things with it.  I absolutely won't be able to take photos of everything, at least not without great difficulty and software.  The questions I come up with is will I want to take photos of deep sky stuff?  I love general photography because you can make it your own.  But as far as this stuff, why all the effort when you can download a much better image of the same thing from the same angle that's taken from far better conditions we have, space?  I know almost everyone here would disagree with that statement and I'd love to understand why.  Given this mindset would I be best to get a very very good mount, then get a SCT for now.  Then if I want to get more into photography I can throw other scopes on the mount.  Might that be the best way to go about it?

My professor sent me this link to other home built observatories.  I'm sure you're all familiar with it but if not here it is.  http://obs.nineplanets.org/obs/obslist.html

I also, finally, got on the roof yesterday and took a photo of myself next to the structure to get an idea of size.  I didn't go inside but I measured the inside diameter from the floor below and it seems to be about 15 feet (4.6 meters for those who use the proper scale).  The view of the image is facing the south which is nearly unobstructed above the horizon.

Thank you all so much for the information.  I'm slowly starting to get a very basic idea of what's going on.  And the more a learn the more I realize there's a lot I do not yet understand. :)

Best,

Gene

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The next thing to do is actually go inside that room and see how the roof beams/trusses have been installed. I would expect that they go across, in parallel, from wall to wall rather than from the wall to the center as that's the easiest way and won't need a vertical center support. If I'm right you will have to work out a way of maintaining at least a rim around the circumference to mount the dome onto and allow some kind of rain drainage. The other alternative is to mount a custom made (expensive!) dome onto that upper existing rim assuming that it's solid enough to take the weight and particularly the shear forces from the wind. These can be a lot higher than many people think and could easily blow away even a heavy item of that size if it's not nailed down securely.

May the Force be with you.

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Good question about the motivation to take pictures but I think I can answer it in two ways.  FIrstly, think of playing a musical instrument. It would be crazy to argue that people shouldn't bother because the professionals can do it better. Listening to a record (or a concert) is simply not the same activity as playing an instrument. Both are valid but different. And in the end wouldn't the approach you suggest (looking at Hubble images in this case) end up making us spectators in all aspects of our own lives? Why cook when you can buy prepared food? Why travel when you can watch a travelogue? Why do a sport? Where would this end? No, doing and watching are not the same thing.

Secondly, I can take pictures that Hubble can't take. This is focal length again! I'm playing a supporting role at the moment in trying to build up the highest resolution image of a part of the sky that has ever been taken (we think.) This is why I'm so keen on shorter focal lengths. A 14 inch cannot compete with the professionals but, ironically, a four inch can. It can take pictures the professionals don't, wouldn't and can't take with their big scopes.

The tower looks even better from up there! Brilliant! It reminds me of the Scottish castle in Ian Banks' The Crow Road with its rooftop observatory.

Olly

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But as far as this stuff, why all the effort when you can download a much better image of the same thing from the same angle that's taken from far better conditions we have, space?

Couldn't agree more! Hence why I bought a big light bucket for the best visual experience possible! Ditch the idea of an sct on a silly expensive and complicated mount, and get a BIG goto dobsonian with some quality 82deg eye pieces.

Then sit back and enjoy brilliant visual observing with simplicity and ease.

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Gene,

I am in awe of your house!

 But as far as this stuff, why all the effort when you can download a much better image of the same thing from the same angle that's taken from far better conditions we have, space?  I know almost everyone here would disagree with that statement and I'd love to understand why.

Why play an instrument, when there are gifted people in the world making CDs?

Why ride a motorcycle when people like Marc Marquez can beat the best in the world at 20 years old?

Why paint a picture when people like Van Gogh, Picasso, Monet all did better?

Why go for a swim when there are people like Michael Phelps.

Why walk up a hill when people like Reinhold Messner can climb Everest without supplementary oxygen?

As Olly has said, the pleasure is in the doing, not in the end result. I take rubbish images of the night sky. I know that my images will never hold a candle to the likes of Olly's, Damian Peach and others. I live in the northwest of England, at sea level, bang on a coast that seems to live under perpetual cloud. It's probably one of the worst places to attempt astrophotography that you could find. Yet the amazement that I felt when I saw a distant galaxy in one of my pretty poor images will stay with me for years.

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But as far as this stuff, why all the effort when you can download a much better image of the same thing from the same angle that's taken from far better conditions we have, space?

Couldn't agree more! Hence why I bought a big light bucket for the best visual experience possible! Ditch the idea of an sct on a silly expensive and complicated mount, and get a BIG goto dobsonian with some quality 82deg eye pieces.

Then sit back and enjoy brilliant visual observing with simplicity and ease.

Don't agree at all regarding imaging but totally agree regarding visual observing.

Olly

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