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 Stunningly beautiful, glaringly bright - the Moon

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GSX1402



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Join date : 2011-09-14

PostSubject: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:40 am

I spent some time looking at the moon with my 10" Newt and a 28mm eyepiece. It was a breathtaking view. The moon is captivating and beautiful. I never realized it was possible to see so much detail on the moons surface, especially near the transition from dark to light (terminator?).

I could study the moon for hours. But on the other hand, I couldn't. The moon is extremely bright! Do you remember the old camera flash bulbs that were in commmon use before electronic strobe flash supplanted them? Those bulbs were really bright, much brighter than strobes, and they'd leave a residual indistinct but vaguely bulb-shaped floating blue image wandering around in your field of vision for a minute after the bulb went off.

Looking at the moon was like that. After looking for a half minute or so, I'd step away from the telescope and the vision through my viewing eye was reduced and obstructed in just the same manner as the flash bulb effect. I put on my darkest sunshades, and it helped a little, but I still couldn't look at the moon for more than 30 seconds or so at a time. I finally quit viewing long before I had my fill of the moon because I was afraid I might damage my eyes. It was pretty uncomfortable to view after a while.

I found this Orion moon filter that looks like a dark neutral density filter. http://www.telescope.com/2-Orion-13-Transmission-Moon-Filter/p/5594.uts?keyword=moon%20filter

Is this a worthwhile filter for viewing the moon? Is it useful only for the moon? Orion says it helps you to see more lunar detail. Are there other makes with greater or lesser light transmission or higher quality glass that do a better job? Are there any disadvantages to using a lens like this? Do you use one to view the moon?
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jack45



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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:42 am

Hi, My experience with observing the moon was similar to what you are describing (not too bright with apertures 8" and under at resonable magnification ie 5x per inch of aperture and greater (the greater the magnification the more the moons image is spread out,so less light coming from unit of area). For scopes of about 10" and upward the amount of light coming to your eye increases with the square of the diameter of your mirror.At present my main scope is a 14" dob which gathers 2x that of your 10".For me I use 10x-20x per inch of aperture for comfortable viewing (I dont find a moon filter of much use(seems to destroy contrast)).BUT the best solution for comfy moon viewing is to invest in a binoviewer.Binoviewers split the light cone to halve the light intensity arriving at the eye (now each eye as you now have both eyes involved).My moon walks are now very comfortable,with both eyes engaged to provide stereo views ie no longer is the moon too bright,and now I see a globe with distinct curvature (as oppossed to a flat disc lacking character).Many think of the moon as a nuisance object,as it dominates in brightness over other objects they find more interesting.However I like you find it a fascinating object to gaze in awe at.Enjoy.
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astrolover

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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:42 am

Indeed, the moon is a wonderful object, particularly in the region of the terminator. It seems bright... but look at it during the day... how bright is it really...

A few thoughts here...

- The brightness of the moon or of any extended object depends on the exit pupil or put another way, the magnification per inch of aperture.

- The surface brightness of the moon (or any extended object), that is the light per unit area of the image on the retina, can never be brighter than it is naked eye, a telescope does not make the moon brighter, it just makes it larger. A telescope can make an extended object dimmer though.

- Compared to most other astronomical objects, the moon is bright. How bright it is... Look at it during the day, it's not that bright, it doesn't suddenly get brighter at night.

- The moon is appears bright in your telescope because your eye is dark adapted. It is bright enough and large enough that you lose your dark adaptation, a good thing... the rods in your eye are responsible for your night vision, they are not sensitive to color and the resolution is comparatively poor, they are designed to allow you to see in the dark.

Your cones, sometimes called your color vision, are less sensitive to light but offer better resolution as well as color... As Terran noted, the views of the moon were spectacular. Better resolution + color is what you want. Dark adaptation is good for fainter objects but not for bright objects. Many planetary observers recommend actually keeping lights on nearby when viewing the planets to avoid having the eye become dark adapted. Keeping a light on, also helps alleviate the sense that you cannot see in that one eye.

So, go with the flow... let your eye tell you what is right. I never use filters for viewing the moon... using my color vision, the views are comfortable at any exit pupil/magnification.

- Increasing the magnification dims the view. If you are viewing the moon at 100x in an 200mm telescope, that's 2mm exit pupil, the beam of light leaving the eyepiece is 2mm in diameter. When you increase the magnification by a factor of 2 to reasonable 200x, the diameter of exit pupil decreases by a factor of two, it is now 1mm... the light is now spread out over 4 times the area so the moon is 1/4 as bright and in fact may seem somewhat dim...

- Again... It is counter intuitive but the maximum possible surface brightness of the moon, the light per unit area of on the retina, does not increase with the aperture of the telescope, whether I am viewing the moon in a 60mm telescope or a 600mm+ telescope, the maximum surface brightness can never exceed that of viewing the moon naked eye...

Just some stuff to think about.
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quadredun



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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:44 am

I think filters have a place they are a personal choice my eyes are very sensitive to bright and i find the moon when past 1/2" full a little uncomfortable under 100x in my 4.5" for long sessions.I use a ND%50,moon(green),and variable polarizer.I do like the variable polarizer you can adjust the level to your comfort.The moon in one of my favorite objects 6 years of observing and she still captivates me every time.I like to shoot the moon as well have a look at the link in my sigline i do some cool things with the settings on the camera to produce some unique moon shots.

Russell
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Smidge



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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:47 am

My eyes tell me it's painfully bright with a large aperture scope Very Happy . Like Russell, I use a variable polarizer to dial in just the right amount of light for comfortable viewing.
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Paulio



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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:51 am

The moon can be just as bright in my 60mm as it can be in my 25in... Your eye, it is simply adapting to the image brightness by switching to your day vision.. the one that offers better resolution and offers color perception.
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scopeman

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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:51 am

The Moon, in ANY telescope, will never appear brighter than looking down at the sidewalk at noon on a sunny day. The resultant "Moon-blindness" is no different from walkng in to a darkened movie theater on a summer afternoon. In other words, you're not going to harm yourself Moongazing. Many of us, myself included, don't find Moon filters necessary; indeed I prefer an unfiltered view. But, there's no harm in using a decent ND filter if it makes your observing more comfortable.

Enjoy
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AstroJunkie
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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:53 am

I found viewing fine last night without any moon filters, i just let my eye get used to going from darkness to light. Once adjusted it's fine.

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Proton



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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:53 am

I prefer to view the moon for extended periods using an ND13 filter. I find it is easier on the eyes when you want to switch targets to non lunar. Even when looking high power.
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Darkmatter



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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 12:54 am

I've tried neutral density and variable polarizing filters on the Moon. The Moon has very dark, inky black shadows, and extremely bright, white areas. Filters tend to make the blacks grayish, and tint the lovely whites.

Also, with time and experience, you'll get used to the brightness level your telescope delivers. You don't really need a filter.

Guests at our star party sometimes complain that Jupiter is too bright.

If you've been observing for some time, here is an interesting experiment. Look at Jupiter with your "observing eye." If you've been spending time observing, it will probably look quite comfortable and show a wealth of detail. Now look with your non-observing eye. I think you'll find it looks overly bright and exhibits some glare, and detail is harder to make out than with your "observing eye."
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cyberstace

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PostSubject: Re: Stunningly beautiful, glaringly bright - the Moon    Wed Sep 14, 2011 1:04 am

I find i do not need a filter too.
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