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Light shrouds and professional telescopes

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#1 Lucullus

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Posted 14 June 2019 - 10:38 AM

Why do professional astronomers not use light shrouds on their truss telescopes, e.g. >=2 m in aperture, to profit from an easily achieved addition in scattered light supression? I assume the light shrouds are so wind penetrable that wind load is hardly an issue for their strong mount motors. Have there been any professional studies with the recommendation not to use them at least for the respective locations where the telescopes are placed?


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#2 happylimpet

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Posted 14 June 2019 - 11:31 AM

Why do professional astronomers not use light shrouds on their truss telescopes, e.g. >=2 m in aperture, to profit from an easily achieved addition in scattered light supression? I assume the light shrouds are so wind penetrable that wind load is hardly an issue for their strong mount motors. Have there been any professional studies with the recommendation not to use them at least for the respective locations where the telescopes are placed?

They would if there was any benefit from it, but no streetlights etc at those locations....


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#3 JamesMStephens

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Posted 14 June 2019 - 11:34 AM

Large professional telescopes are usually housed in observatories, which act as light shrouds.  You might make the case that they would still help, it would make an interesting study.


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#4 TOMDEY

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Posted 14 June 2019 - 11:51 AM

Yep. And in most installations, the dome itself provides better stray light baffling than a shroud outdoors would. If you calculate the entire photometric ├ętendue both ways, the dome wins. Roll-offs not much benefit. That's actually one more reason I have always preferred domes, even for my small telescopes. No shroud also allows the air to circulate around and through the telescope a lot more freely.

 

Ryan had baselined a full shroud for my 36-incher... but I said, "don't bother; don't need it!"  And, yep... I did indeed do the analysis. That's just one more plus favoring domes.    Tom

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#5 gavinm

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Posted 14 June 2019 - 03:08 PM

The large observatories that I've been into (and worked in) were all pretty much pitch black inside the dome (and cold). So dark that much of the acclimatisation time for the observer is memorising where everything is in the dark so you don't walk into stuff. In 99% of cases, you don't even go into the dome, but stay in the control room.



#6 llanitedave

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Posted 14 June 2019 - 03:37 PM

Yep. And in most installations, the dome itself provides better stray light baffling than a shroud outdoors would. If you calculate the entire photometric ├ętendue both ways, the dome wins. Roll-offs not much benefit. That's actually one more reason I have always preferred domes, even for my small telescopes. No shroud also allows the air to circulate around and through the telescope a lot more freely.

 

Ryan had baselined a full shroud for my 36-incher... but I said, "don't bother; don't need it!"  And, yep... I did indeed do the analysis. That's just one more plus favoring domes.    Tom

Do you have a special collection area for the lucky guano?  And I assume you keep the mirror covered when not in use!



#7 TOMDEY

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Posted 14 June 2019 - 05:18 PM

The large observatories that I've been into (and worked in) were all pretty much pitch black inside the dome (and cold). So dark that much of the acclimatisation time for the observer is memorising where everything is in the dark so you don't walk into stuff. In 99% of cases, you don't even go into the dome, but stay in the control room.

Yes, indeed! Our labs and chambers at work also like that. Dark all over except where you choose to put (very little directed) illumination. After a while, got all the knobs, controls, logistics, ergonomics, hazards memorized. With modern equipment, 1st thing is to fire up off-line, in the dark... and find all the little LEDs etc that need black tape over them! The Night Vision guys here also know what we're talking about. If you run your scope to a modest little monitor inside the dome... even that can set off flickering/strobing feedback to the camera that oscillates just like audio feedback does when the band is doing a ~sound check~ in a night club!

 

Then, inside the dome, dark-adapted... the night sky, seen up there thru the slot... looks amazingly bright! Just natural starlight is pouring down a lot of flux onto the earth!  The dome shields the scope from most of that.  Tom

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#8 TOMDEY

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Posted 14 June 2019 - 05:28 PM

Do you have a special collection area for the lucky guano?  And I assume you keep the mirror covered when not in use!

Flapper actually perches exactly there, always. And so precisely, that I just put a little waste-basket plumb below, dome always parked there, scope out of the direct line of fire. In return, he and his associates keep the mosquitos pretty well purged from our sixteen acres. They patrol every evening, starting at sunset... but flapper is the only one who tamely perches on my shoulder.   Tom

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