Wratten Filters 101

[Mak the Night]

I’ll admit to not exactly being filter *bloke and the only filters I’ve really had any success with are the Baader Neodymium and UHC-S filters. I suspect that for coloured filters to be used with any real success an aperture of 150mm or above is preferred on most reflecting telescopes due to the light loss imposed by the filter itself. 

*British colloquial term roughly translating as ‘guy’.

Wratten filters are named after the British inventor Frederick Wratten who founded the first photographic company around 1877. Later, along with C. E. Kenneth Mees, dyed gelatin coloured filters were developed by the company and became known as Wratten filters. Their company was acquired by Eastman Kodak in 1912. Hence why filters are often referred to as Kodak Wratten filters.

Below ~ the six (2x 25 Red & 80A Blue) Celestron Wratten Filters mentioned

Below are some filter applications and the corresponding effects of six Wratten filters that are often included in sets (especially Celestron). I’ve gleaned this mostly from the Internet and the Celestron Filter Guide. It was more of an academic exercise than anything else for me to try to understand colour wavelengths and the various effects on the astronomical observation of planets with certain filters. I hope it can be of benefit to anyone else.

12 Deep Yellow (74% light transmission): Minus blue filter. Improves contrast. 

Jupiter: Darkens atmospheric currents, enhances orange & red features.

Mars: Reduces blue & green light, darkens maria & oases, lightens desert regions.

Saturn: Darkens atmospheric currents, enhances red features of the belts.

Venus: Reveals low contrast surface features.

21 Orange (46% light transmission): Contrast filter for blue and blue-green absorption. Longpass filter blocking visible wavelengths below 530 nm. 

Jupiter: Improves belt detail, enhances polar regions.

Mars: Similar to Wratten 12, also sharpens yellow dust cloud boundaries.

Saturn: Improves band structure, highlights blue polar regions.

Venus: Good for daylight observation to reduce sky brightness.

25 Red (Tricolour A, 14% light transmission): Used for colour separation and infrared photography. Longpass filter blocking below 580 nm.  

Jupiter: Useful on blue clouds.

Mars: Useful in observation of polar caps, sharpens boundaries of dust clouds.

Saturn: Useful on blue clouds.

Venus: Useful in daylight observing, can also make deformations in the terminator visible.

56 Light Green (53% light transmission).

Jupiter: Increases visibility of the Great Red Spot.

Mars: Increases contrast of polar caps.

Venus: Useful for studying cloud formations.

58 Green (Tricolour B, 24% light transmission): Colour separation.

Jupiter: Increases GRS visibility, useful for low contrast blue & red atmospheric hues.

Mars: Increases contrast of polar caps & low clouds.

Saturn: Enhances white atmospheric features.

Venus: Useful for cloud studies.

80A Blue (30% light transmission): Colour Conversion. Raises the colour temperature.

Jupiter: Enhances boundaries between the reddish belts, useful for GRS.

Mars: Very useful during the *Violet Clearing, helps studying surface features and polar caps.

Saturn: Enhances low contrast features.

Venus: Increases contrast in dark shadings in upper atmospheric clouds.

*Violet Clearing ~ an infrequent or rare clearing where surface features can allegedly be observed with a blue or violet filter which some have speculated to be an optical illusion.

[John]

It's interesting stuff.

I've had a couple of sets of decent quality coloured filters over the years which covered most of the Wratten #'s described above. Personally I didn't find they really added anything to the planetary viewing experience for me so I don't have any now. After glowing reports raising expectations I found the actual viewing experience rather a let down.

I expect there are some who really swear by them though. Personal experiences and preferences on filters seem to vary pretty widely

[Mak the Night]

It's interesting stuff.

I've had a couple of sets of decent quality coloured filters over the years which covered most of the Wratten #'s described above. Personally I didn't find they really added anything to the planetary viewing experience for me so I don't have any now. After glowing reports raising expectations I found the actual viewing experience rather a let down.

I expect there are some who really swear by them though. Personal experiences and preferences on filters seem to vary pretty widely

Yeah, it's interesting to read about Wratten filters and their origins and uses (astronomical or otherwise). But like you, I haven't had any real success with coloured filters. I always assumed I needed more aperture or something. I'd like to observe Mars as it gets closer next year with the Baader Neodymium possibly stacked with the Wratten #12 or #21. I was particularly interested in the fact that yellow and orange filters are often used in the movie industry to improve contrast. I was also told that the Baader Contrast Booster filter works a lot like a less intense Wratten yellow filter.

Oddly, the only filters I had any success with were the yellow and orange ones for daylight (early dawn) sessions observing the Moon. The Celestron filters in the picture above are from the AstroMaster and Eyeopener kits. They are not badly made, but I wouldn't consider them high quality. 

[Mak the Night]

And this is interesting: http://karmalimbo.com/aro/pics/filters/transmision%20of%20wratten%20filters.pdf 

[John]

I can't seem to make that link work

[Mak the Night]

http://karmalimbo.com/aro/pics/filters/transmision%20of%20wratten%20filters.pdf

How's this?

[John]

http://karmalimbo.com/aro/pics/filters/transmision%20of%20wratten%20filters.pdf

How's this?

Thats great - I can read that now

Can't really understand it all though .....

[Mak the Night]

Thats great - I can read that now

Can't really understand it all though .....

Yeah, a lot of it, OK, most of it, loses me as well. lol

[LukeSkywatcher]

Got my 1st set of coloured filters in an EP kit. Tried them and found no use..........so basically gave them away. Few yrs later, bigger scope and i thought i'd like them. Bought another set and have never used them.

I think they are just a money maker for retailers.

[Mak the Night]

Got my 1st set of coloured filters in an EP kit. Tried them and found no use..........so basically gave them away. Few yrs later, bigger scope and i thought i'd like them. Bought another set and have never used them.

I think they are just a money maker for retailers.

Mine (pictured) were supplied with the Celestron AstroMaster and Eyeopener Kits. I actually find the individual filter boxes more useful now for my Baader UHC-S and Neodynium filters. I plan to get some Lumicon filters as well. The Celestron filter boxes fit nicely into one of my eyepiece cases.

[Mike73]

Coloured filters can work very well but I can understand why a lot of people find they don't do anything for their views of the planets.

I use them a lot for observing Jupiter, the main thing to remember is that the colour filter will enhance a certain feature of the planet but also reject and reduce contrast in other features at the same time. So I use a #82a for white ovals in the NTB and to enhance TZ's, a #27 for festoons and a #8a as a good general filter to boost contrast in dark ovals and oval BA in the STB.

When the seeing conditions are very good I prefer no filters at all.....but how often does that happen??!!

[Mak the Night]

Coloured filters can work very well but I can understand why a lot of people find they don't do anything for their views of the planets.

I use them a lot for observing Jupiter, the main thing to remember is that the colour filter will enhance a certain feature of the planet but also reject and reduce contrast in other features at the same time. So I use a #82a for white ovals in the NTB and to enhance TZ's, a #27 for festoons and a #8a as a good general filter to boost contrast in dark ovals and oval BA in the STB.

When the seeing conditions are very good I prefer no filters at all.....but how often does that happen??!!

What size aperture are you observing Jupiter with a filter?

[Mike73]

What size aperture are you observing Jupiter with a filter?

Thats a good question.

I think that in order to see the smaller features on planets you do need decent resolution so for me anything over 8" and filters will work.

I'm using a 12" dob at the moment, I did have a 4" frac a couple years ago which worked really well in poor seeing conditions but I found the maximum (x170) magnification pretty restricting when it came to seeing detail and filters didn't help at all.

[Mak the Night]

Thats a good question.

I think that in order to see the smaller features on planets you do need decent resolution so for me anything over 8" and filters will work.

I'm using a 12" dob at the moment, I did have a 4" frac a couple years ago which worked really well in poor seeing conditions but I found the maximum (x170) magnification pretty restricting when it came to seeing detail and filters didn't help at all.

OK thanks. I'm planning on getting a 9.25" SCT soon so I may try some of my Wratten filters with it. I will probably have more success with the Baader Neodymium though. If I can catch Jupiter early in the morning with my 4" Mak I'll try the Baader, weather permitting of course lol.

[Mike73]

OK thanks. I'm planning on getting a 9.25" SCT soon so I may try some of my Wratten filters with it. I will probably have more success with the Baader Neodymium though. If I can catch Jupiter early in the morning with my 4" Mak I'll try the Baader, weather permitting of course lol.

Yeah I'm certainly not saying that you need a big scope to get great views but the above was just what I found and personally preferred.

I liked the Neodymium for full disk views, it gave a nice natural colour to planets as well.

[John]

The good thing about coloured filters is that they are pretty low cost items (compared to many astro goodies !) so at least you can try them without risking much.

[Mak the Night]

Yeah I'm certainly not saying that you need a big scope to get great views but the above was just what I found and personally preferred.

I liked the Neodymium for full disk views, it gave a nice natural colour to planets as well.

I don't know, I've suspected for a while that certain coloured filters would work far better with apertures of at least 150mm and above. The Neodymium is surprisingly useful for a lot of things and works well on a 102mm Mak.

[Mak the Night]

The good thing about coloured filters is that they are pretty low cost items (compared to many astro goodies !) so at least you can try them without risking much.

They can be low cost, but I've seen a set of four 1.25" Orion filters for over £80. 

[RT65CB-SWL]

I don't know, I've suspected for a while that certain coloured filters would work far better with apertures of at least 150mm and above. The Neodymium is surprisingly useful for a lot of things and works well on a 102mm Mak.

The Neodymium filter works well on my 'scopes too! - see my signature below.

[philj]

Sorry but Im a big fan of filters on planetary with my refractors, achro and apo alike. Mars responds well to filters due to the brightness and low contrast detail, different filters pick out different features. Saturn responds well also. Been using them for about 15 years now. On lunar I find the blue my favourite over nd filters. I must get me a violet (venus) filter one day

[John]

Sorry but Im a big fan of filters on planetary with my refractors, achro and apo alike. Mars responds well to filters due to the brightness and low contrast detail, different filters pick out different features. Saturn responds well also. Been using them for about 15 years now. On lunar I find the blue my favourite over nd filters. I must get me a violet (venus) filter one day

Thats interesting Phil. Do you favour a particular brand / quality level or are they all "much of a muchness" ?

[Charic]

I've used Cokin and Wratten  filters in the past to enhance my photographic requirements, and they worked very well indeed.

As for astronomy related visual astronomy, I'm not sure they would make much of a difference to my eyes now, or before, so I don't own any coloured filters at present for the telescope,  and more so for me, I don't see any Planets from my location, being surrounded by obstacles, and street lights, so no real requirement  for them, for now, although  If I moved house, that could change!

I have seen Jupiter  under perfect conditions, the image is still etched in memory? I saw colour, full banding, clear transit shadow, and all this from being patient, having the right conditions for seeing, the scope at the right temperature, fully collimated  and the right eyepiece for the situation, which was probably the 12mm at the time, possibly the 8mm, without checking my previous threads!

[RT65CB-SWL]

Sorry but Im a big fan of filters on planetary with my refractors, achro and apo alike. Mars responds well to filters due to the brightness and low contrast detail, different filters pick out different features. Saturn responds well also. Been using them for about 15 years now. On lunar I find the blue my favourite over nd filters. I must get me a violet (venus) filter one day

AstroBoot have got the GSO branded one (No: #47) for £2.75 + p&p

£2.00 cheaper then when I purchased mine from them earlier this year.

BTW - I don't normally use filters, (except Lunar/Moon & Neodymium).

[Mike73]

The good thing about coloured filters is that they are pretty low cost items (compared to many astro goodies !) so at least you can try them without risking much.

I experimented with many of the cheaper filters available then bought decent polished Lumicon and Baader filters in the colours I preferred. I don't know how much difference there is in polished vs cheaper filters but I like to keep anything thats in the optical train as good as I can and even the decent filters aren't bank breakers TBH.

[Mak the Night]

Sorry but Im a big fan of filters on planetary with my refractors, achro and apo alike. Mars responds well to filters due to the brightness and low contrast detail, different filters pick out different features. Saturn responds well also. Been using them for about 15 years now. On lunar I find the blue my favourite over nd filters. I must get me a violet (venus) filter one day

How do your observations tally with the effects filters have in planetary observing as stated in my original post? Would you agree with them overall or do you find certain colours work better for certain planetary characteristics and phenomena? I did find yellow and orange filters useful for daylight lunar observing as they tended to turn the blue sky black and provided more contrast.