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Can you observe through glass?


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20 minutes ago, neil phillips said:

Somebody needs to make optical quality windows. Sounds cheap doesn't it. Wonder how far you could go with that idea. Makes me think of Baaders optical window film

They already have, they are mounted cleverly on a hinge allowing you to swing them out, removing them from the optical train :) 

Ok I'll get my coat !

Jim 

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I would say to this that if for health reasons/disabilty/location etc if you can only view through windows then this is better than not viewing any of the nights sky wonders. Views of the moon, and major planets should be doable, along with some DSO’s. If you can view from outside this is much more preferable as you will get much better views in any equipment used. If I remember from when I was in my early teens (many moons ago now!) I used to observe the moon and major planets after sunset from my back bedroom window in my parents house quite successfully for the scope I first had way back then. 

Edited by Knighty2112
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7 minutes ago, Merlin said:

Years ago a well known British amateur astronomer, possibly G.D.Hole, had a window pane optically worked for £10,000.

That’s quite something! If I had a spare £10,000 back in the day then I may have considered that as an option too from my old bedroom window! ;) 

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3 hours ago, Stu1smartcookie said:

Care to elaborate Louis , for the record .  :) 

Click the link and read the Wikipedia article? :icon_scratch:

Basically, some of the largest and nearest stars have been professionally resolved.  You didn't put any qualification on "best and largest telescope".

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7 hours ago, Louis D said:

Click the link and read the Wikipedia article? :icon_scratch:

Basically, some of the largest and nearest stars have been professionally resolved.  You didn't put any qualification on "best and largest telescope".

I believe you really did know what I meant but if that’s the way we are going on here then , hmmm .. 

 

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On 01/04/2023 at 15:50, Louis D said:

Sure you can observe through glass.  Can you observe well through ordinary window glass, no.  Generally, you can still pick out the high contrast details like the positions of Jupiter's moons and the features along the moon's terminator.

If you go to the trouble of replacing your glass with optical glass polished flat to within 1/10th wave or better and coat it with anti-reflective multicoatings, you'd stand a much better chance of being able to do critical observing of low contrast objects.

Consider this.  I don't know of a single observatory, professional or otherwise, that observes through glass of any type.  The scope is always open to the elements.

What if the astronomer wears glasses 😀

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15 hours ago, Merlin said:

Years ago a well known British amateur astronomer, possibly G.D.Hole, had a window pane optically worked for £10,000.

The problem as I see it for professional usage, how do you keep an optically flat window perpendicular to the telescope's optical axis at all pointing angles and positions?  It might be possible with a slit aperture in a domed observatory with some sort of expanding bellows to maintain the seal around it to avoid thermal air currents.  Another issue would be thermal strain on the glass if there is a temperature differential between the inside of the observatory and the outside world.  Also, reflected light could become an issue causing glare on the optical window.  Perhaps with enough engineering forethought and post-implementation rework, it might be doable.

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I have at times reclined on my sofa and used binoculars to look at the night sky through my closed very large Velux. Yes it is actually a Velux.

At one point I was convinced that I was observing a dark nebula only to find out in daylight the nesting wagtails had left a ‘message’ on the optical window.

I have since designated it Jenkins Wagtail Dark Nebula. Good luck capturing that and processing it.

Marvin

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A Sky & Telescope article some years ago showed an amateur’s domed observatory with high-grade cling film stretched across the slit. There was a small heater under it.

The observer said he was getting diffraction limited images.

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Depends on what you expect and want.

Take the RSPB Garden Birdwatch, spend an hour observing, identifing and counting little feathered fiends. At a guess 98% of the people observe through a sheet of rather mucky glass. So observing is possible.

But for rather exact astro observing the result at your eye will not be great. So Yes, just don't expect high quality. Additionally your angle of view will be constrained. Straight out might be half, or a quarter, reasonable. At say 30 degrees off the normal then blurry. And the zenith is usually impossible. Something called a roof or ceiling.

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  • 5 weeks later...
On 07/04/2023 at 06:12, StevieDvd said:

What if the astronomer wears glasses 😀

Valid question.  I do, and I sometimes pick up reflections off of my eyeglasses on bright objects.  I'll shift my head angle slightly to move the reflection to be less annoying.

Also, off-axis light rays in wide angle views will suffer from chromatic aberrations, so I have to roll my entire head to look at the edge so the edge rays are entering my eyeglasses perpendicular to them.  This causes me to lose the opposite side of the view.

Contacts cure most of these ills, but I can't stand wearing them.

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A thing you can try Louis is to do what I did. Get a cheap pair of specs and take the lenses out. 

Next, cut the lenses down to fit into eyepiece cups. I hold them in with a bit of blue tack.

Before reducing the size of the lenses, put a small disc of easy to remove sticky paper on each side of each lens to protect the surfaces while you saw and file the rest of the lenses away.

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@Merlin How do you sort out the precise positioning of the eyeglass lens wrt the position the eye will be above the eyecup.  My spectacle lenses are varifical with astigmatism correction and a bit of prism, not only are they way too expensive to destroy a set according to your instructions, but I am convinced it would be impossible to know which bit the lens needed to be positioned where.  

IME I've never had any problems viewing whilst wearing glasses, but I do find that I get on perfectly OK if I just take my specs off.  I think its because you only have to focus one viewing eye *unless you have bino viewers.

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Hello, funny way of phrasing the question: of course you look through glass with your scope, but through a "glass window"  no way, reflections, dirt, malformation of the window pain--just not worth it. At least the window should be open, but then a lot of air turbulence!

There is nothing  that can replace fresh air! ;- )

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2 hours ago, LukeSkywatcher said:

I've never had an issue with viewing through a window. The only thing to be mindful of is that the heating in that room is switched off.

You probably don't want to view through vintage glass, though.  My daughter's house has many original 120 year old window panes.  Even to the naked eye, they make the outside world look a bit like funhouse mirrors.  Glass flows due to gravity and ends up with waviness over the decades.

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4 hours ago, Merlin said:

A thing you can try Louis is to do what I did. Get a cheap pair of specs and take the lenses out. 

Next, cut the lenses down to fit into eyepiece cups. I hold them in with a bit of blue tack.

Before reducing the size of the lenses, put a small disc of easy to remove sticky paper on each side of each lens to protect the surfaces while you saw and file the rest of the lenses away.

I would probably just buy a Tele Vue Dioptrx first, even if it doesn't fit every eyepiece I own.

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4 hours ago, JOC said:

IME I've never had any problems viewing whilst wearing glasses, but I do find that I get on perfectly OK if I just take my specs off.

Lucky you.  My 2+ diopters of astigmatism renders bright stars as spikes and dim stars simply wink out of existence without my eyeglasses.  It's not until I get down to about 1mm exit pupils that the astigmatism effects fade, but never quite disappear.

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The reason for why I use reduced specs lenses is because I have double-vision. Without the lenses inserted in the eyepiece cups, I wouldn’t be able to use the binoviewer and also some of the binoculars, where  eye relief is short.

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16 hours ago, Merlin said:

The reason for why I use reduced specs lenses is because I have double-vision. Without the lenses inserted in the eyepiece cups, I wouldn’t be able to use the binoviewer and also some of the binoculars, where  eye relief is short.

I could see that being an issue.

Over a couple of decades ago, I recall reading about some who had fresh prescription blanks cut and mounted into filter housings by his optician to attach to the bottom of eyepieces.  The poster claimed they worked well to correct astigmatism in his eye, but optical designers claimed that it wouldn't work if they were used before the eyepiece rather than after.

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