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revans
Carpal Tunnel
Reged: 09/26/05
Posts: 1536
Loc: Fitchburg, MA
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Hi all,
Has anyone looked at the moon through an apodizing (i.e. Lyot) mask? Some say that it is only useful for planets... but others say it also reduces effects of air turbulence and increases contrast on the moon....
Just curious...
Rick Evans
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Rick Evans
http://www.freewebs.com/revans_01420/
"The universe is there for us to see, but it cannot be understood without learning its language -- mathematics." Galileo Galilei
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Tim2723
The Moon Guy
Reged: 02/19/04
Posts: 5153
Loc: Northern New Jersey
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Hi Rick,
You'll have to forgive my failing memory. I did make an apodizing mask several years ago; there were a number discusions about them. I recall making it from window screen. Is that the type you mean?
If I recall correctly, I used it first on Jupiter and Saturn. I recall seeing the image of Saturn in the center of the field ringed with fainter ghost images of the planet. I didn't notice any marked improvement. I believe the theory is that the center image would be improved and that one ignores the ghost images. On the Moon I found it hopelessly useless. Since the Moon fills all of the field the ghost images aren't off to the sides as they are for the planets which occupy only the centermost spot of the field, but instead overlap one another. All the images are jumbled together.
But again, my memory is imperfect. They are easy and cheap enough to make though, and quite a bit of fun to toy with.
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The crwth will set you free!
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Bill Weir
Pooh-Bah
Reged: 06/01/04
Posts: 1362
Loc: Metchosin (Victoria), Canada
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I am a strong proponent of using them for planetary and double star observing. I haven't found them to be of any benifit for Lunar observing.
Bill
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6'' Orion SkyQuest
12.5'' f/5 Custom Truss Dob
William Optics 80mm ZenithStar ED II
f/5 25" newtonian on a giant GEM, any time I want
Observing sessions grand total for 2009, 102.
So far in 2010, 16.
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revans
Carpal Tunnel
Reged: 09/26/05
Posts: 1536
Loc: Fitchburg, MA
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Tim,
I made one using an aluminum window screen. I suppose that the "spectral" or rainbow images of a planet and lunar features are caused by the grid like pattern of the screen.
However, commercial continuous gradient apodizing masks are available and do not use a grid material. So... I wonder if they would have the drawback of these rainbow/spectral ghost images? I don't know why they would... and so I am exploring trying to get one of these apodizing filters...
Rick
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Rick Evans
http://www.freewebs.com/revans_01420/
"The universe is there for us to see, but it cannot be understood without learning its language -- mathematics." Galileo Galilei
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Tim2723
The Moon Guy
Reged: 02/19/04
Posts: 5153
Loc: Northern New Jersey
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That sounds interesting, Rick. Do you have a link to these commercial filters? Back in the day it was just window screen (that much I do remember).
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The crwth will set you free!
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revans
Carpal Tunnel
Reged: 09/26/05
Posts: 1536
Loc: Fitchburg, MA
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Tim,
The commercial ones are not cheap and would be used like eyepiece or webcam adapter filters rather than over the objective lens.
Edmunds optics has one (the reversed bull's eye filter) here:
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=3121
there is another company, the Reynard company also has them but they are even much more expensive:
http://www.reynardcorp.com/filters-bullseye-apodizing-filters-c-1_28-l-en.html
I have also thought of buying a 5 inch bk glass circular blank 1/8 inch thick (this is optical glass) and gluing concentric rings from a neutral density gelatin sheet over it. That would be for use over the objective of my 5 inch refractor. The cost here would be under $200 which is still expensive.
Rick Evans
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Rick Evans
http://www.freewebs.com/revans_01420/
"The universe is there for us to see, but it cannot be understood without learning its language -- mathematics." Galileo Galilei
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revans
Carpal Tunnel
Reged: 09/26/05
Posts: 1536
Loc: Fitchburg, MA
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It is also likely that only an apodizing mask placed over an objective lens will work.... such a mask may well be useless if its location is instead attached to a webcam or an eyepiece in the telescope optical train instead of being over the objective lens...
Rick
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Rick Evans
http://www.freewebs.com/revans_01420/
"The universe is there for us to see, but it cannot be understood without learning its language -- mathematics." Galileo Galilei
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