Quote:
Originally Posted by Krumlov
One of the earlier posts linked to a PDF which seemed to indicate that using various coloured filters would enhance particular colours (eg. "#12 Yellow Enhances red and orange features on Jupiter and Saturn") . Is this only going to work on larger scope as you have indicated or is the PDF saying that it enhances the detail but you still don't see the colour?
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I may need to clear up a point, and explain another.
My original quote of needing a "20" scope to see colour" refers to seeing colour in only the brightest of nebulae, such as M42. And then this IS limited because we are using our very human eyes in a very low light level situation. This is very important to keep in mind. A nebula filter, of any description, will not help with colour rendition in this situation if you can't see colour in the object without it.
The planets themselves are bright enough that colour can be seen in them in even small scopes. HOWEVER, using filters will alter the way we perceive the colours that are transmitted. Filters work by absorbing certain colours and transmit others. The resulting image will be predominately of the colour the filter is, and the "enhanced" details are usually darker in appearance. That is the way that these features are enhanced.
I'll give you an everyday example: CRICKET. You may have noticed that in the One Day game in the evening, some fielders will be using yellow coloured sunnies. Yellow in this situation helps our eyes by increasing contrast, making the white ball more easily visible.
Now, if you want a more balanced colour image of the planets, you will need to reduce the entire spectrum as evenly as possible, not selectively. This is only achieveable with the "greying" element of polarizing filters, or neutral density filters.
Another example, I've two scopes I love using are my 17.5" f/4.5 (a fast light bucket), and an 8" f/10 SCT (a typically slow cat.). I much prefer the image of the planets produced by the 8" over the 17.5" if no filters are used. In the bigger scope, the image is so bright that any detail is washed out. Sure I can make out many more moons around Saturn, but I can't make out any real banding on the disk. The 8" is a much better planetary scope as the image isn't washed out. The only way I can see the same details in the 17.5" is by using polarizing or neutral density filters.
A FINAL WORD OF CAUTION: Don't get sucked into buying heaps of colour filters. You really, really won't be using them very much. I've got three, one red, one yellow and a blue 80A. It is the latter one I most use, and only to help me make out the Great Red Spot on Jupiter. That happens two or three times a year. See what I mean?