Leroy's Filter Evaluation

... not satisfied with seeing ...

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For many years, I had known about color filters, but ignored them. Too many other things to do with my money, I had told myself after my first case of aperture fever. But when I got my 12-inch (and even my 10-inch) SCT, I was actually a little disappointed with views of the planets because there was so much light, it actually distracted from the view. This of course can be mitigated with increased magnification, but with more aperture, you will sooner hit what I call the seeing ceiling.

Photography has utilized filters for years, so it is natural that they found their way into observing. The photo at right utilized a Red filter for improved contrast on the Moon, just 16.5 hours before Full. The 48mm photographic filter has long been the 2" eyepiece standard in Astronomy. There has been some shift from this lately, perhaps due to the 48mm filter having fewer and fewer applications in photography. If you want to acquire a set of your own, you should read what I went through to get mine.

I had always been intrigued by the lists of what could be seen with which filters. You'll see these lists in many places: perhaps most prominently in the Orion catalog, or in Dickinson & Dyer's The Backyard Astronomer's Guide, and especially as an info sheet from the telescope manufacturers (Meade and Celestron) who sell them.

These recommendations had always intrigued me. Since one of the attributes of a filter is amount of light transmitted through it, expressed as a percentage (which I believe is bound to the definition of the Kodak Wratten #), I had realized early on that some of these filters had a minimum required aperture for use. Orion hints at this aspect. Knowledgeable dealers will tell you about this.

I am telling you this so you can factor into the evaluations I have written here, how it may differ if your telescope is of larger or smaller aperture compared to mine.

Full aperture Solar Filter	Notes
Thousand Oaks	type2+7 for Meade SCT-10 (Optical Density 5.0; 0.001% transmission)
Celestron	#94139 Baader Astro Solar for C5
Kendrick	Sun Finder for Telrad
Nebular Filters	Mfg. #	Notes
Meade	#911B	Broadband, rear cell thread
Meade	#911N	Narrowband, rear cell thread
Meade	#911X	O-III, rear cell thread
Orion	#5656	Ultra-Block Narrowband LPR, rear cell thread
Lumicon	LLDS48	Deep Sky, 48mm
Lumicon	LLHBE48	H-Beta, 48mm
Lumicon	LLOXY48	O-III, 48mm
Lumicon	LLUHC48	Ultra High Contrast, 48mm
Sirius Optics	MV1-1	Minus Violet, 1.25"
Sirius Optics	PC1-1	Planetary Contrast, 1.25"
Skylight Filter	Wratten #	Notes
Meade	#1A	rear cell thread
2" Color Filters	Mfg. #	Wratten #	T% (FF)	Color
Celestron	94120-01	#1A	86%	Skylight
B+W	022 48E	#8	83% (2x)	Light Yellow
B+W	060 48E	#11	62% (~2x)	Yellow-Green
Vernonscope	12	#12	74%	Yellow
Vernonscope	15	#15	67%	Deep Yellow
Celestron	94120-03	#21	46%	Orange
B+W	041 48E	#22	~25% (4x)	Red-Orange
Celestron	94120-04	#23A	25%	Light Red
B+W	090 48E	#25	14% (5x)	Red
Vernonscope	30M	#30	58%	Magenta
Celestron	94120-05	#38A	17%	Deep Blue
Celestron	94120-06	#47	3%	Violet
Hoya	X1	#56	53%	Light Green
Vernonscope	58	#58	24%	Green
Hoya	80A	#80A	30%	Medium Blue
Hoya	85A	#81A	—	Light Orange
B+W	KB 1.5 48E	#82A	73% (~1.1x)	Pale Blue
Hoya	85B	#85B	63%	Medium Orange
Hoya	ND2	#96ND	50%	Neutral Density
B+W	101 48E	#96ND	50% (2x)	Neutral Density 0.3
B+W	102 48E	#96ND	25% (4x)	Neutral Density 0.6
B+W	103 48E	#96ND	13% (8x)	Neutral Density 0.9
1.25" Color Filters	Mfg. #	Wratten #	T%	Color
Meade	07528-1	#8	83%	Light Yellow
Meade	07529-1	#11	78%	Yellow-Green
Meade	07530-1	#12	74%	Yellow
Meade	07528-2	#21	46%	Orange
Meade	07530-2	#23A	25%	Light Red
Meade	07529-2	#25A	14%	Red
Meade	07528-3	#38A	17%	Dark Blue
Meade	07529-3	#47	3%	Violet
Meade	07528-4	#56	53%	Light Green
Meade	07530-3	#58	24%	Green
Meade	07530-4	#80A	30%	Blue
Meade	07529-4	#82A	73%	Light Blue
Meade	07531	#96ND	13%	Neutral Density 0.9

Accessories: I have tried my best, whenever possible, to make sure that all of my adapters, and relevant accessories, are threaded to accept filters whenever possible. This gives the greatest flexibility for using filters. Colors and attributes: I have used manufacturer names for colors, so there is some variation for the same Wratten #s. The same goes for transmission characteristics. FF: Filter factor, used by camera filter manufacturers; like T%, but more useful for computing f-stops to adjust light metering T%: Tranmission percentage Note: items (if any) in Gray are on order, or will soon be.

Evaluation

Read how I acquired a set of 2" Filters. In the evaluations of colored filters below, I make reference to the recommendations used in the Orion catalog. I feel their material is representative of the other sources mentioned above, and picked their information for no other reason.

I have spent quite a bit of time, out of nearly a half-dozen observing sessions, trying out different filters. Some of my earliest efforts in this area were not methodical enough, for me to feel comfortable reporting on. However, the highlights of these sketchier experiments are worthing mentioning, so they have been included here. The goal will be to have an evaluation on a given object when at its optimum, i.e. opposition, greatest elongation, etc. All references are to use with my 30 cm. (12") f/10 Schmidt-Cassegrain Telescope, except where noted.

I have given ratings for how well the filter matched the entries in the Orion catalog for what was actually observed. These are: POOR, FAIR, OK, GOOD, VERYGOOD, EXCELLENT. NOTCHECKED was used if the characteristic it purportedly enhanced was not observed, i.e. for dust storms on Mars, but no dust storms in progress.

Colored Filters

Quick Summary

Orion catalog:

#8 - Light Yellow - lunar/planet contrast
#11 - Yellow-Green - Jupiter
#12 - Yellow - lunar/planet contrast, Uranus/Neptune
#15 - Deep Yellow - Mars, Saturn, lunar contrast, b/w photo UV blocker
#21 - Orange - Mercury, Mars, Jupiter
#23A - Light Red - lunar/planet detail, daylight Mercury/Venus
#25 - Red - Mercury, Mars, Saturn, Lunar/Omega/Rosette b/w photos
#38A - Deep Blue - Mars dust storms, Saturn, Jupiter
#47 - Violet - Venus
#56 - Light Green - Lunar detail, Martian caps/clouds
#58 - Green - Venus w/80A, Mars, Jupiter, Saturn, streetlight neb
#80A - Medium Blue - Mars, Jupiter, Saturn, Lunar glare - Must buy!
#82A - Pale Blue - stack for film color balance

Sun

Day-time:

EXCELLENT—Works great in a C5 w/Celestron Baader Astro Solar full aperture filter.
Some people prefer the unfiltered color of the Baader/Mylar filters. I like to use the #21 for my day-to-day solar routine. I couldn't detect any difference in contrast or detail, just that each took getting used to.
By merely holding the Meade 1.25" #21 up to the eye side of the eyepiece, I compared my Celestron 48mm (2") #21 and couldn't see much difference in the color on the Sun. Looking through both side by side at semi-green grass, or the white tube of my telescope, the Celestron looked a little darker.
I have also compared the color of #21 with a Baader filter to a 10" Thousand Oaks (full aperture) filter hand-held naked-eye to the Sun. The coloring is very close.
Still need to try the two options actually through a telescope.

Orion catalog:

#21 - corrects for color of Mylar filters

Mercury

Day-time:

not evaluated

In Sunset:

not evaluated

Twilight:

not evaluated

Night-time:

not evaluated

Orion catalog:

#15 - daytime observation
#21 - daylight contrast
#23A - daylight/twilight
#25 - contrast against blue sky
#47 - surface detail
#80A - orange twilight viewing

Venus

Day-time:

ø #15 low-contrast cloud detail EXCELLENT

ø #15 daytime observation EXCELLENT

ø #21 daylight contrast VERYGOOD

ø #23A daylight/twilight EXCELLENT

ø #30 — GOOD

ø #47 contrast, reducing glare and twinkling EXCELLENT

ø #47 surface detail EXCELLENT?

ø #58 cloud patterns EXCELLENT?

ø — other filters on list not evaluated NOTCHECKED

Notes:
On November 14, 2000 UT, during the favorable elongation and four and one-half months before inferior conjunction, I setup for a daytime observation session and tested only a few 48mm filters at 122x: I noticed how far elongated from the Sun Venus was on Monday [11/13/2000], so I went to my backyard, marked a spot in the snow so I would know where to find it again soon (hopefully). Soon was Tuesday [11/14/2000], so I got my telescope out at about 3:30 PM after confirming Venus in binoculars.
I got an hour-and-a-half of observing in with six different color filters. The filters helped the brightness problem immensely. Also, I was able to see a dark region on the bright side along the equator just inward from the terminator of our gibbous sister-planet. This region was seen in three of the filters, and was impossible without filtering, due to the combination of thermals initially in the telescope and later passing high-level, thin clouds. After the clouds had passed, it sharpened up nicely.
I found that the most of the filters I tried did a nice job of softening Venus down from its normally boiling self. The #23A and #15 were both excellent for daylight views and better than the often recommended #21 for this purpose.
On this particular occasion, I tried six filters (#15, #21, #23A, #30, #47, and #58) out. I was able to see a dark region in the cloud cover with three of them in my 12". I didn't take notes, but I am certain of the #15, #23A, and the third was either the #47 or #58.

#30 I bought this filter on the advice of Gary Hand, based upon reports he had received from his customers. It only helped in general with the dimming down of the planet, but did nothing to enhance the contrast of the surface features I saw above.

In Sunset:

not evaluated

Twilight:

not evaluated

Night-time:

not evaluated

Orion catalog:

#8 - low-contrast cloud detail
#11 - cloud detail
#12 - low-contrast cloud detail
#15 - low-contrast cloud detail
#15 - daytime observation
#21 - daylight contrast
#23A - daylight/twilight
#25 - contrast and cloud definition
#47 - contrast, reducing glare and twinkling
#47 - surface detail
#56 - cloud detail
#58 - cloud patterns
#80A - orange twilight viewing

Moon

Day-time:

not evaluated

Night-time:

ø #30 — VERYGOOD

ø #80A surface detail (significantly) EXCELLENT

ø — other filters on list not evaluated NOTCHECKED

Notes:
This may be a tough subject to cover, because I can imagine that the lighting angle of sunshine on the Moon's surface can place a big factor in the evaluation of filters. I will attempt to note the approximate phase with individual filter entries below.

#30 approaching third-quarter Moon, night time or early morning twilight (I was not taking detailed notes at the time). I did note that this filter was my new, second favorite for the Moon, after the #80A.

#80A excellent, from Full Moon, to partial phases, I have tried this one out on three different occasions and phases.

Orion catalog:

#8 - surface detail
#11 - surface detail
#12 - surface detail
#15 - surface contrast
#21 - terrain
#23A - surface detail
#38A - surface detail (slightly)
#47 - dark features
#56 - surface detail
#58 - surface detail
#80A - surface detail (significantly)
#82A - surface detail

Mars

Day-time:

not evaluated

Twilight:

not evaluated

Night-time:

ø #8 maria OK

ø #11 contrast of maria and polar caps GOOD

ø #12 maria OK

ø #15 polar caps and orange desert regions GOOD

ø #21 surface features in small scopes VERYGOOD

ø #22 — VERYGOOD**

ø #23A reddish areas, plains, and maria EXCELLENT

ø #25 surface detail in larger scopes —

ø #38A dust storms NOTCHECKED

ø #47 faint clouds during "blue clearings" NOTCHECKED

ø #56 polar caps and low clouds GOOD

ø #58 melt lines around polar cap GOOD

ø #80A polar caps and high clouds VERYGOOD

Notes:
On May 13, 2001 UT, about five weeks before the very favorable opposition of June 2001, I had the fifth observing session of this aparition since Christmas 2000, using a 17mm Nagler type 4 (180x) w/48mm filters: The OTA was definitely chilled down this time, and the seeing was definitely a challenge, but I think for Mars this time around, the difference was seen in the improved size of the disk. In white light, I began to notice moments of stability that would wink in. It is kind of interesting how the brain can store these things like I imagine a CCD camera does combined with the user doing stacked frames. There was a subtle hint of the South Polar Cap.
Distinctly separated from the cap was a very definite lateral maria just above. It spans 70-80% of the disk at that latitude. The SPC is something like a tenth the disk's vertical diameter. I also saw several circular spotted maria near the meridian in the north as well. It took a little while to build up this degree of acuity of surface details, but I was just so intrigued by what I was seeing, I couldn't help myself.
I observed Mars steadily from 6:30 to 8:30 UT (12:30-2:30 MDT). I used filters during the last hour and-a-half of the observations. With a shorter period at the end dedicated to just white light again.
Another fellow (Craig) I was swapping and comparing views with was using a Tele-Vue 102 Refractor.

#22 was purchased on the recommendation of a telescope shop owner I buy from. I wasn't thorough, and another observer thought it was nearly as good as the #23A. For me, it seemed to wash out the disk to a flat orange, but I suspect I had a moment of very bad seeing given what Craig had said. He was the last to leave before me, and I didn't want to keep him too long. He was clearly interested in my filter trials, but also worried about falling asleep on the drive home. I will recheck this filter the next time I have a chance.

#25 was rather dim even for 12" light grasp. However, it did bring out one of the northern circular maria as a very dark region. I'm not sure I'd recommend the #25 for a 10", and definitely not an 8".

#38A was not checked as the degree of surface detail did not seem to indicate any dust storms were likely. I probably should have tried this one and #47 anyway, but it was late.

#58 I had noted in the field as "OK", but I upgraded to "GOOD" in this writing. I was biased because I saw no melt lines. That could be due to none being present, or requiring higher power and/or better seeing to see them. Upon reflection, this filter did do a good job of separating out the SPC from the surrounding region, and reinforced my mind's white light notion of a separation between the SPC and the long horizontal maria region I mentioned above.

#80A definitely enhanced the caps (#15 confirmed a smaller, North Polar Cap) and did as advertised. There was a "hazy" light colored (#80A is a "blue" filter) mass over much of the northern hemisphere. Given these results, I probably should have tried the #47, but I didn't take the time as it was getting late and I was getting tired.

Jupiter

Day-time:

not evaluated

Twilight:

ø #30 — EXCELLENT

ø — other filters on list not evaluated NOTCHECKED

Notes:
On October 19, 2000 UT, several months prior to opposition I setup for an early-morning (10:30 UT) observation session at w/#30 48mm at 145x: I came back out to my telescope at 14:00 UT to find twilight and thin, high-level cirrus impinging upon Jupiter.

#30 I bought this filter on the advice of Gary Hand, based upon reports he had received from his customers. I saw more detail in mild daylight and cirrus than I did with a nearly third-quarter moonlit, clear, night sky.

Night-time:

ø #25 bluish clouds POOR

ø #58 contrast of GRS and subtle red and blue hues OK

ø — other filters on list not evaluated NOTCHECKED

Notes:
On October 19, 2000 UT, several months prior to opposition I setup for an early-morning (10:30 UT) observation session at w/48mm filters 145x to 200x: With a nearly third-quarter Moon in the morning sky, I experimented with a few filters on Jupiter, mostly a preliminary check for how much light loss the filters yielded.

#25 yielded too much light loss for my 12" SCT.

#58 was pushing the limits of my 12" SCT's light grasp.

Orion catalog:

#8 - orange and red belt features
#11 - orange and red features
#12 - orange and red belt features
#15 - orange and red features
#21 - bands and festoons
#23A - blue clouds and polar region
#25 - bluish clouds
#38A - boundaries of reddish belts and bright zones
#56 - low-contrast blue and red hues
#58 - contrast of Red Spot
#58 - contrast of subtle red and blue hues
#80A - orange and purple belts, white ovals
#82A - orange and purple cloud belts

Saturn

Day-time:

not evaluated

Twilight:

not evaluated

Night-time:

not evaluated

Orion catalog:

#8 - orange and red belt features
#11 - orange and red features
#12 - orange and red belt features
#15 - orange and red features
#21 - bands and festoons
#23A - blue clouds and polar region
#25 - bluish clouds
#25 - ring contrast
#38A - subtle details in cloud belts
#47 - ring structure
#56 - surface contrast
#80A - subtle shadings
#82A - orange and purple cloud belts

Uranus

Night-time:

not evaluated

Orion catalog:

#12 - detail in larger scopes

Neptune

Night-time:

not evaluated

Orion catalog:

#12 detail in larger scopes

Comets

Twilight:

not evaluated

Night-time:

not evaluated

Orion catalog:

#8 - dust tail, and coma
#12 - definition of coma and dust tails
#38A - bright comet gas tails
#58 - brighter comets
#80A - contrast of some comet tails
#82A - comet tails

Photography

Found:

not evaluated, However this filter certainly improves contrast (see B&W photo at top of page)

Orion catalog:

#25 - LPR in black & white film

Chromatic Aberration

Found:

not evaluated

Orion catalog:

#82A - suppression

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Last Update: 12 November 2002.

Leroy's Filter Evaluation

... not satisfied with seeing ...

my

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ø	#15	low-contrast cloud detail	EXCELLENT
ø	#15	daytime observation	EXCELLENT
ø	#21	daylight contrast	VERYGOOD
ø	#23A	daylight/twilight	EXCELLENT
ø	#30	—	GOOD
ø	#47	contrast, reducing glare and twinkling	EXCELLENT
ø	#47	surface detail	EXCELLENT?
ø	#58	cloud patterns	EXCELLENT?
ø	—	other filters on list not evaluated	NOTCHECKED
Notes: On November 14, 2000 UT, during the favorable elongation and four and one-half months before inferior conjunction, I setup for a daytime observation session and tested only a few 48mm filters at 122x: I noticed how far elongated from the Sun Venus was on Monday [11/13/2000], so I went to my backyard, marked a spot in the snow so I would know where to find it again soon (hopefully). Soon was Tuesday [11/14/2000], so I got my telescope out at about 3:30 PM after confirming Venus in binoculars. I got an hour-and-a-half of observing in with six different color filters. The filters helped the brightness problem immensely. Also, I was able to see a dark region on the bright side along the equator just inward from the terminator of our gibbous sister-planet. This region was seen in three of the filters, and was impossible without filtering, due to the combination of thermals initially in the telescope and later passing high-level, thin clouds. After the clouds had passed, it sharpened up nicely. I found that the most of the filters I tried did a nice job of softening Venus down from its normally boiling self. The #23A and #15 were both excellent for daylight views and better than the often recommended #21 for this purpose. On this particular occasion, I tried six filters (#15, #21, #23A, #30, #47, and #58) out. I was able to see a dark region in the cloud cover with three of them in my 12". I didn't take notes, but I am certain of the #15, #23A, and the third was either the #47 or #58.
#30 I bought this filter on the advice of Gary Hand, based upon reports he had received from his customers. It only helped in general with the dimming down of the planet, but did nothing to enhance the contrast of the surface features I saw above.

ø	#30	—	VERYGOOD
ø	#80A	surface detail (significantly)	EXCELLENT
ø	—	other filters on list not evaluated	NOTCHECKED
Notes: This may be a tough subject to cover, because I can imagine that the lighting angle of sunshine on the Moon's surface can place a big factor in the evaluation of filters. I will attempt to note the approximate phase with individual filter entries below.
#30 approaching third-quarter Moon, night time or early morning twilight (I was not taking detailed notes at the time). I did note that this filter was my new, second favorite for the Moon, after the #80A.
#80A excellent, from Full Moon, to partial phases, I have tried this one out on three different occasions and phases.

ø	#8	maria	OK
ø	#11	contrast of maria and polar caps	GOOD
ø	#12	maria	OK
ø	#15	polar caps and orange desert regions	GOOD
ø	#21	surface features in small scopes	VERYGOOD
ø	#22	—	VERYGOOD**
ø	#23A	reddish areas, plains, and maria	EXCELLENT
ø	#25	surface detail in larger scopes	—
ø	#38A	dust storms	NOTCHECKED
ø	#47	faint clouds during "blue clearings"	NOTCHECKED
ø	#56	polar caps and low clouds	GOOD
ø	#58	melt lines around polar cap	GOOD
ø	#80A	polar caps and high clouds	VERYGOOD
Notes: On May 13, 2001 UT, about five weeks before the very favorable opposition of June 2001, I had the fifth observing session of this aparition since Christmas 2000, using a 17mm Nagler type 4 (180x) w/48mm filters: The OTA was definitely chilled down this time, and the seeing was definitely a challenge, but I think for Mars this time around, the difference was seen in the improved size of the disk. In white light, I began to notice moments of stability that would wink in. It is kind of interesting how the brain can store these things like I imagine a CCD camera does combined with the user doing stacked frames. There was a subtle hint of the South Polar Cap. Distinctly separated from the cap was a very definite lateral maria just above. It spans 70-80% of the disk at that latitude. The SPC is something like a tenth the disk's vertical diameter. I also saw several circular spotted maria near the meridian in the north as well. It took a little while to build up this degree of acuity of surface details, but I was just so intrigued by what I was seeing, I couldn't help myself. I observed Mars steadily from 6:30 to 8:30 UT (12:30-2:30 MDT). I used filters during the last hour and-a-half of the observations. With a shorter period at the end dedicated to just white light again. Another fellow (Craig) I was swapping and comparing views with was using a Tele-Vue 102 Refractor.
#22 was purchased on the recommendation of a telescope shop owner I buy from. I wasn't thorough, and another observer thought it was nearly as good as the #23A. For me, it seemed to wash out the disk to a flat orange, but I suspect I had a moment of very bad seeing given what Craig had said. He was the last to leave before me, and I didn't want to keep him too long. He was clearly interested in my filter trials, but also worried about falling asleep on the drive home. I will recheck this filter the next time I have a chance.
#25 was rather dim even for 12" light grasp. However, it did bring out one of the northern circular maria as a very dark region. I'm not sure I'd recommend the #25 for a 10", and definitely not an 8".
#38A was not checked as the degree of surface detail did not seem to indicate any dust storms were likely. I probably should have tried this one and #47 anyway, but it was late.
#58 I had noted in the field as "OK", but I upgraded to "GOOD" in this writing. I was biased because I saw no melt lines. That could be due to none being present, or requiring higher power and/or better seeing to see them. Upon reflection, this filter did do a good job of separating out the SPC from the surrounding region, and reinforced my mind's white light notion of a separation between the SPC and the long horizontal maria region I mentioned above.
#80A definitely enhanced the caps (#15 confirmed a smaller, North Polar Cap) and did as advertised. There was a "hazy" light colored (#80A is a "blue" filter) mass over much of the northern hemisphere. Given these results, I probably should have tried the #47, but I didn't take the time as it was getting late and I was getting tired.

ø	#25	bluish clouds	POOR
ø	#58	contrast of GRS and subtle red and blue hues	OK
ø	—	other filters on list not evaluated	NOTCHECKED
Notes: On October 19, 2000 UT, several months prior to opposition I setup for an early-morning (10:30 UT) observation session at w/48mm filters 145x to 200x: With a nearly third-quarter Moon in the morning sky, I experimented with a few filters on Jupiter, mostly a preliminary check for how much light loss the filters yielded.
#25 yielded too much light loss for my 12" SCT.
#58 was pushing the limits of my 12" SCT's light grasp.