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Date: 20 Jul 2007 15:09:40
From: brucegooglegroups
Subject: planetary filters
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I have a 4.5 Dob and recently purchased a set of 4 basic planetary
filters.
http://www.telescope.com/shopping/product/detailmain.jsp?itemID=83&itemType=PRODUCT&RS=1&keyword=filters
I tried them out viewing Jupiter and they made no difference in the
view- I couldn't see any detail. The viewing conditions weren't
optimal, but I wanted to see if they made any difference.
Are the filters only useful at certain times- e.g. when the Great Red
Spot transits? S&T listed the transit times for the Great Red Spot
this week, and I will try the filters out then, weather permitting.
Bruce
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Date: 20 Jul 2007 16:46:49
From: canopus56
Subject: Re: planetary filters
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On Jul 20, 5:15 pm, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On Fri, 20 Jul 2007 16:07:42 -0700, canopus56 <canopu...@yahoo.com>
> wrote:
>
> >Because planetary filters rely on a color contrast effect to work,
> >they require that enough light enter your eye to trigger color
> >vision.
>
> That's not true. The color is still there, even if it's below your
> photopic threshold. As any old-school photographer knows, color filters
> have dramatic effects on B&W images, and they affect the apparent
> contrast of some objects even when they are quite dim and your eye can't
> see any color.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatoryhttp://www.cloudbait.com
Thanks Chris, Then the "large apeture" disclaimers seen in many
product inserts for planetary filters relate to what? - Canopus56
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Date: 21 Jul 2007 04:43:19
From: Chris L Peterson
Subject: Re: planetary filters
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On Fri, 20 Jul 2007 16:46:49 -0700, canopus56 <canopus56@yahoo.com >
wrote:
>Thanks Chris, Then the "large apeture" disclaimers seen in many
>product inserts for planetary filters relate to what? - Canopus56
I'd guess it's mostly the usual value of aperture: you can operate at
higher magnification, and therefore spread the image across more retina.
That is the single most useful thing you can do to improve contrast.
In general, aperture doesn't impact image brightness when a scope is
used visually. Big scope or small, the amount of color you'll see should
be the same.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Jul 2007 16:07:42
From: canopus56
Subject: Re: planetary filters
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On Jul 20, 4:09 pm, brucegooglegroups <brucegooglegro...@hotmail.com >
wrote:
> I have a 4.5 Dob and recently purchased a set of 4 basic planetary
> filters.. . . . I tried them out viewing Jupiter and they made no
> difference in the view- I couldn't see any detail. . . .
> Are the filters only useful at certain times- e.g. when the Great Red
> Spot transits? S&T listed the transit times for the Great Red Spot
> this week, and I will try the filters out then, weather permitting.
Color planetary filters work by a color contrast effect. "What you
see is that a filter lightens tones of objects colored similarly to
the filter and darkens tones of objects colored dissimilarly." Kodak.
1998. Using Filters (Kodak Workshop Series) (The Kodak Workshop
Series) (Paperback). Each filter's effect can be seen by looking at a
garden with different colored flowers during daylight. That type of
daylight practice can attune you to the type of image changes to
expect when you use the filters on planets.
Because planetary filters rely on a color contrast effect to work,
they require that enough light enter your eye to trigger color
vision. For many planetary filters, this means that they will only
trigger a color contrast effect when they are used with large
apetures, e.g. - 8 to 12 inches. You may find that there is "large
apeture" fine print in your product insert's descriptions for various
colors. For example, dark red transmits so little light, it can only
be used with 10 or 12 inches of apeture.
This is why many 4 to 10 inch scope owners turn around and immediately
buy supplemental filters that are light colored and that transmit a
larger amount of light, e.g. Rod's suggestion. (80A is a good filter
for use on Jupiter. It brings out the polar cap belts.)
In summary, the filters may work - but just not on your 4.5 inch
apeture. At your next star party, try a filter on a planet on your
smaller apeture scope and then try it on a colleagues larger scope.
Finally, it is possible for them to bring out small detail but that
detail will be too small to be resolved by your 4.5 inch scope.
Again, compare the image in your scope with a larger scope.
Some rule of thumbs are pick filters that are the same average color
of the planet that you are observing. A red filter on Mars, a blue
filter on Venus or an orange filter on an orange Jupiter. To bring
out detail that is expected to be blue or green, pull a filter that is
the target color's opposite on the color wheel, e.g. - red to see
green or blue detail on a "red" planet like Mars or Jupiter and a blue
filter to see red detail on a "blue" planet like Venus.
Here is a table that I prepared that summarizes filter effects by
planet.
http://members.csolutions.net/fisherka/astronote/plan/pcfilt/PlanetaryColorFiltersTable.html
Clear Skies - Canopus56
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Date: 20 Jul 2007 23:15:23
From: Chris L Peterson
Subject: Re: planetary filters
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On Fri, 20 Jul 2007 16:07:42 -0700, canopus56 <canopus56@yahoo.com >
wrote:
>Because planetary filters rely on a color contrast effect to work,
>they require that enough light enter your eye to trigger color
>vision.
That's not true. The color is still there, even if it's below your
photopic threshold. As any old-school photographer knows, color filters
have dramatic effects on B&W images, and they affect the apparent
contrast of some objects even when they are quite dim and your eye can't
see any color.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Jul 2007 15:41:51
From: RMOLLISE
Subject: Re: planetary filters
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On Jul 20, 5:09 pm, brucegooglegroups <brucegooglegro...@hotmail.com >
wrote:
> I have a 4.5 Dob and recently purchased a set of 4 basic planetary
> filters.http://www.telescope.com/shopping/product/detailmain.jsp?itemID=83&it...
>
> I tried them out viewing Jupiter and they made no difference in the
> view- I couldn't see any detail. The viewing conditions weren't
> optimal, but I wanted to see if they made any difference.
>
> Are the filters only useful at certain times- e.g. when the Great Red
> Spot transits? S&T listed the transit times for the Great Red Spot
> this week, and I will try the filters out then, weather permitting.
>
> Bruce
If the seeing ain't there, forget seeing detail, filter or no filter.
That said, a blue 80A filter can help with Jupiter. The improvement is
subtle, mind you, but it's there. Also, until you gain some experience
with the planet you probably won't see much. Finally, make sure your
scope is well collimated.
Unk Rod
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