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AstroTripper
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Reged: 01/16/13

Loc: Central Europe
Moon too bright for comfort
      #5635118 - 01/21/13 02:43 PM

Hello everyone

I'm new to astronomy and the first target for my observations was the Moon. The view was very impressive, but I quickly realized it's way too bright. It almost hurts to look at, and it's harder to see detail further from the terminator.

My scope is a SkyWatcher 150/750 mm on EQ3-2 mount. When I put in 10 mm eyepiece and 2x Barlow, the brightness is more comfortable, but pretty much everything else sucks (small exit pupil, blurry image, very sensitive to even tiny shocks).

So my question is: what can be done about it? I am aware of the existence of lunar filters, but how do I choose one appropriate for my scope? Some claim to enhance contrast, some are red, some are blue, etc., but I just want to see the Moon without my eyes hurting after a minute or two.


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rockethead26
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Reged: 10/21/09

Loc: Arizona, USA
Re: Moon too bright for comfort new [Re: AstroTripper]
      #5635160 - 01/21/13 03:01 PM

All you need is a neutral density filter or a polarizer filter. Good ones will impart no color to the view. Look on any astronomical vendor's site and search for moon filter.

Clear skies!


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Dave Chapman
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Reged: 01/27/07

Loc: Halifax, Nova Scotia, Canada
Re: Moon too bright for comfort new [Re: AstroTripper]
      #5635185 - 01/21/13 03:15 PM

Dear Astrotripper,

you have a 150 mm f/5 refractor, and you are getting a jiggly, blurry image with (effectively) a 5 mm eyepiece that gives you 150x? That combination has a 1 mm exit pupil, which does not seem too small. Before you worry about filters, you should check out your mount, which sounds not to be very steady. Check all the nuts and bolts and find the source of all this jiggling, because you should be able to observe at this magnification, and higher, clearly and with comfort. Or your optics may be suspect.

At high enough magnification, I find the unfiltered Moon not too bright, but that's me.

When the magnification is low enough to see the entire Moon, yes, you might want a filter. You just need a standard 40% transmission neutral-density filter that screws into your eyepiece, to reduce the glare. (Don't laugh, I have used a light pollution filter!) You can get fancy filters with cross-polarization that allows you to "dial up" a variable filtering effect, but they cost significantly more.

clear skies

Dave


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Moon too bright for comfort new [Re: Dave Chapman]
      #5635300 - 01/21/13 04:24 PM

A better trick than using a filter is to turn on a lot of outdoor lights... You see, the Moon is not bright at all by daytime standards and we WANT it bright in the eyepiece, because a bright image means one our eyes can resolve very well and we can see tiny details, even if the magnification is not high, which is good, since poor seeing often limits how high magnification we can use.

I often observe the Moon with my 12" dobsonian, full aperture and no filter, at magnifications of around 100x with a binoviewer. This is equal to using a binocular with about 9" aperture and 100x magnification. The image is bright and very, very sharp. If the seeing is good, I use 160x. I've yet to have a night where I can go higher with the 12". Despite the rather low magnifications, I see a LOT more detail than with my 5" f/10 refractor at the same magnifications or even higher. I've seen craterlets in Tycho with the 12" at 160x.

The trick to avoid being blinded by the Moon when you look into the eyepiece is not be dark adapted at all. If you are not dark adapted, you'll not get blinded. And if you're not dark adapted, your eyes will resolve small features on the Moon better as well. Win-win.

And with some good lights on near your telescope, you can also easily see what you're doing and don't have to fumble around looking for eyepieces, etc. Try it, it really works. I can also recommend a binoviewer, but that's a story for another day.


Clear skies!
Thomas, Denmark

Edited by Astrojensen (01/21/13 04:28 PM)


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AstroTripper
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Reged: 01/16/13

Loc: Central Europe
Re: Moon too bright for comfort new [Re: Astrojensen]
      #5635589 - 01/21/13 07:29 PM

Thanks for the tip Thomas, I haven't thought about the impact of my eyes being adapted to dark. I'll try it out next time. I'm not so sure it'll work during full moon thought. Well, I'll see for myself when the weather permits.

Dave, thank you for your insights. And yes, the mount does not seem very steady to me too. I'm blaming the flimsy aluminum legs, but maybe there's more to it (I bought a used scope). The optics seem fine to me. The blurring is only visible with Barlow lens included with the scope. And I don't expect much from it, seeing as quality Barlows can cost more than I paid for the scope. And besides, I'm not sure, but is it possible that at x150 magnification, I can be limited by atmospheric conditions, even with clear sky?


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Tim2723
The Moon Guy
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Reged: 02/19/04

Loc: Northern New Jersey
Re: Moon too bright for comfort new [Re: AstroTripper]
      #5636110 - 01/22/13 01:43 AM

Though there are lots of mixed opinions (imagine that!) a decent Moon filter is cheap and should probably be in your kit for some occasions. Another popular option is the variable polarizer. It works like a dimmer switch to give you different transmission levels, but it's more expensive.

Increasing magnification will dim the view, but you don't always want high magnification. The Moon will not harm you at any brightness, but comfort is a personal thing.


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Quinn
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Reged: 03/19/12

Loc: California, Los Angeles
Re: Moon too bright for comfort new [Re: AstroTripper]
      #5636225 - 01/22/13 04:39 AM

I agree with Astrojensen. When I am doing an observation run on the Moon I do not dark adapt my eyes. The only thing I would add is that I make sure that no stray light is travelling directly into my eye piece.

AstroTripper. I have the same rig. A 150mm /5 Newtonian mounted on a Orion AstroView GEM mount. That mount is not rated for the amount of weight you are loading on it. Simple test to just tap on the scope and see how long it takes to settle down and stop vibrating. wobble get worse as you increase EP power. With this mount the best thing you can do is try to keep the scope as light as possible. Or build a Dob Mount for it like shown at the link below.

http://www.cloudynights.com/classifieds/showproduct.php?product=54138&sor...

I did something like this and worked very well.

Quinn


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Moon too bright for comfort new [Re: AstroTripper]
      #5636227 - 01/22/13 04:46 AM

Quote:

I haven't thought about the impact of my eyes being adapted to dark. I'll try it out next time. I'm not so sure it'll work during full moon thought.




Oh, it'll work just fine, you just need more light! The full moon is one of my favorite objects, BTW. There is a lot more to see than what most people think.

Quote:

And besides, I'm not sure, but is it possible that at x150 magnification, I can be limited by atmospheric conditions, even with clear sky?




Absolutely! I am often limited to around 100x - 120x. It is easy to see if you're limited by seeing or the scope. If the image sort of boils or waves, it's the seeing. If it's the scope (or the eyepiece), then the image is always blurry, also when the seeing is good.

Most nights from midnorthern latitudes are just plain mediocre. We are always sitting between conflicting weather patterns with cold air from the north and warm ones from the south and that creates massive turbulence in the air and the temperature differences causes bad seeing. But once in a while, we can get a break and the seeing can become very good. Those are nights to savour and to remember.


Clear skies!
Thomas, Denmark


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Dave Chapman
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Reged: 01/27/07

Loc: Halifax, Nova Scotia, Canada
Re: Moon too bright for comfort new [Re: AstroTripper]
      #5636882 - 01/22/13 01:08 PM

Quote:


Dave, thank you for your insights. And yes, the mount does not seem very steady to me too. I'm blaming the flimsy aluminum legs, but maybe there's more to it (I bought a used scope). The optics seem fine to me. The blurring is only visible with Barlow lens included with the scope. And I don't expect much from it, seeing as quality Barlows can cost more than I paid for the scope. And besides, I'm not sure, but is it possible that at x150 magnification, I can be limited by atmospheric conditions, even with clear sky?




Hi Astrotripper: at a star party last night, I saw "your" telescope, and I now realize that it is a Newtonian. The unit I saw last night was brand-new, and the mount seemed sturdy enough. Examine your mount and tripod carefully for joints that need to be tightened, as your 'scope is used and things may have loosened over time.

Also, you need to check the collimation of the mirrors, especially if you have not done so since buying the used 'scope. Both jiggles and blurs will only be magnified by adding a Barlow, regardless of its quality, so you should investigate these common problems before proceeding.

Regarding magnification, I completed the RASC lunar observing program with an 200 mm (8") f/6 reflector and a 6 mm eyepiece, which gave around 200x. On occasion, atmospheric conditions interfered, but I found 200x to be a comfortable viewing magnification. Occasionally, I needed to use higher power to look for details. At powers near 300x, I was more often limited by "floaters" in my eyes than by atmospheric effects. In my opinion, you should reasonably expect to view at 150x and higher in your telescope on a routine basis, once all the mechanical and optical gremlins have been cast out!

clear skies

Dave


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Dave MitskyModerator
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Reged: 04/08/02

Loc: PA, USA, Planet Earth
Re: Moon too bright for comfort new [Re: Astrojensen]
      #5637376 - 01/22/13 05:16 PM

Quote:

A better trick than using a filter is to turn on a lot of outdoor lights... You see, the Moon is not bright at all by daytime standards and we WANT it bright in the eyepiece, because a bright image means one our eyes can resolve very well and we can see tiny details, even if the magnification is not high, which is good, since poor seeing often limits how high magnification we can use.

I often observe the Moon with my 12" dobsonian, full aperture and no filter, at magnifications of around 100x with a binoviewer. This is equal to using a binocular with about 9" aperture and 100x magnification. The image is bright and very, very sharp. If the seeing is good, I use 160x. I've yet to have a night where I can go higher with the 12". Despite the rather low magnifications, I see a LOT more detail than with my 5" f/10 refractor at the same magnifications or even higher. I've seen craterlets in Tycho with the 12" at 160x.

The trick to avoid being blinded by the Moon when you look into the eyepiece is not be dark adapted at all. If you are not dark adapted, you'll not get blinded. And if you're not dark adapted, your eyes will resolve small features on the Moon better as well. Win-win.

And with some good lights on near your telescope, you can also easily see what you're doing and don't have to fumble around looking for eyepieces, etc. Try it, it really works. I can also recommend a binoviewer, but that's a story for another day.


Clear skies!
Thomas, Denmark




Using a white light during lunar observing is an old trick that I often employ.

Dave Mitsky


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azure1961p
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Reged: 01/17/09

Loc: USA
Re: Moon too bright for comfort new [Re: Dave Mitsky]
      #5637949 - 01/22/13 10:58 PM

A variable polarizer is the most powerful light/glare supressor and can give me a 70x full moon with the comfortable light level as though it were a full page photo in a book but thru my 8". I love it. Higher mags and I use a neutral density filter with a wratten 21 orange. Beautiful warm contrasts with great luminosity but not bad at all. Romantic even and the way the mountain peaks snap sharp. Fantastic.

Pete


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Tim2723
The Moon Guy
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Reged: 02/19/04

Loc: Northern New Jersey
Re: Moon too bright for comfort new [Re: azure1961p]
      #5638177 - 01/23/13 01:45 AM

Guys, as soon as you look at the Moon through the scope you're not dark adapted. It's the same as walking into the bathroom and turning on the light. You're 'Moon blind'. The real problem is when you look away from the scope and one pupil is so constricted that you trip in the dark. Keeping the lights on and using filters helps with that.

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Eddgie
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Reged: 02/01/06

Re: Moon too bright for comfort new [Re: AstroTripper]
      #5638526 - 01/23/13 09:51 AM

As you have surmised, the brigtness is a function of exit pupil.

Any two scopes, regardless of aperture, will show the moon just as bright if the same exit pupil is used.

And like you, I find an exit pupil that is smaller than about 1mm to be simply to dim even on the moon.

As for the brightness, did you go from a relatively dark adapted eye directly to the moon at low powers?

If so, you did indeed get "Snow Blinded" because if your eye was already dark adapted and you went to the moon at low power, it overwhelmed the dark sensing rods in the eye.

The easiest thing to do is to start with higher powers when you first go to the moon, and as your dark adaption fades, brighten the view by going to lower magnifications.

This will allow your vision to transition from scotopic to photopic in steps.

You still loose your night adapted vision, but you will avoid the "Shock" to your rods.


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rflinn68
Carpal Tunnel


Reged: 03/09/12

Loc: Arkansas
Re: Moon too bright for comfort new [Re: Eddgie]
      #5648860 - 01/28/13 06:01 PM

Quote:

The easiest thing to do is to start with higher powers when you first go to the moon, and as your dark adaption fades, brighten the view by going to lower magnifications.

This will allow your vision to transition from scotopic to photopic in steps.

You still loose your night adapted vision, but you will avoid the "Shock" to your rods.




This! And I would add wait until you are done looking at other objects. Look at the Moon when you are done looking at everything else and you're ready to pack it in for the night.


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