Planetary filter

[matt]

While I appreciate there is a wide variety of coloured filters which are very handy for looking at individual and specific planets, can anyone recommend a filter which helps reduce the brightness/glare of an object like Jupiter while significantly increasing contrast and thus detail???

I'm just looking for a filter which helps bring those details out without introducing any of its own colour ... sort of a neutral type filter???

Thanks

[Robert_T]

Originally Posted by matt

While I appreciate there is a wide variety of coloured filters which are very handy for looking at individual and specific planets, can anyone recommend a filter which helps reduce the brightness/glare of an object like Jupiter while significantly increasing contrast and thus detail???

I'm just looking for a filter which helps bring those details out without introducing any of its own colour ... sort of a neutral type filter???

Thanks

Hi Matt, I have a range of colour filters, but for that purpose I use a light blue filter. It reduces the glare without much apparent change in colour.

cheers,

[matt]

Thanks Rob.

Yeah... I've got coloured filters as well but was hoping there might be something "uncoloured" which does the job???

[Robert_T]

Matt, I suspect that anything that cuts down glare will intro some colour - eg just look at the range of sunglasses. The pale blue is a bit like a good pair of shades that cut glare with very little false colour... I often forget I have it there.

cheers,

[iceman (Mike)]

Have you tried an ND filter?

[Robert_T]

Originally Posted by iceman

Have you tried an ND filter?

Ah, good point Mike, do Neutral Density filters have any shading?

[iceman (Mike)]

Not colour, just darker.. The sort of look like a grey when you look at the filter, like a pair of tinted (without colour) sunglasses.

[janoskiss (Steve H)]

Yes, ND and/or crossed polarisers for variable brightness is what you need.

[ving (David)]

if you are looking to cut dow glare why not just stop down the aperture?
create an aperture mask and it will do the same job for you...

[janoskiss (Steve H)]

No it will not. If you reduce the aperture, you also reduce the angular resolution of the scope in proportion. A filter dims the view but preserves resolution.

[ving (David)]

oic!

well it works for me

[matt]

Yeah, a ND filter sounds about right. So does the crosses polarisers. I like the idea of rotating one of those to vary the amount of light through depending on the subject's brightness.

I may also get myself a light blue filter just to compare, and to have handy in my filter kit. It may offer other qualities not found in the ND and polarising filters???

Definitely don't want to lose resolution due to stopping down the aperture

Thanks for all your help. Now, what's the sobbing sound? Oh yeah, that's the sound being made by my credit card

[Robert_T]

Matt if you do get a colouredfilter as well as the ND make sure it's a pale or light blue - I have this, a blue and a dark blue filter but the latter two introduce significant colouration.

cheers,

[Starkler (Geoff)]

I find that throwing away light merely reduces the eyes ability to see fine details.

I have a vari polariser and used it twice only before deciding that such filters dont help me at all.

[matt]

yeah Rob, a light blue filter, like i said I might buy in my last thread

[Robert_T]

Originally Posted by matt

yeah Rob, a light blue filter, like i said I might buy in my last thread

don't worry Matt, It's just my old eyes... I can barely see the belts of jupiter without a webcam let alone read other people's posts properly

[matt]

you're right, mate. just having a lend.

Shame about your old eyes. At least you've got adequate optical compensation (overkill) what with the c9.25 and the Mewlon!

[ausastronomer (John Bambury)]

Originally Posted by Starkler

I find that throwing away light merely reduces the eyes ability to see fine details.

I have a vari polariser and used it twice only before deciding that such filters dont help me at all.

The 1st person that has posted the "totally" correct answer IMO. Whatever filter you use will reduce the amount of visible detail. A 9" scope is not large and it doesn't need a glare reducing filter IMO.

If you're going to observe a planet with a Neutral Density filter you may as well save yourself the expense of the filter and just wear your sunglasses at the eyepiece.

One possible option that "has" been mentioned that works reasonably well is the light blue filter that Robert mentioned. The correct "wratten number" for this filter is an 80A light blue. This filter will reduce the glare a little without reducing too much detail. It will enhance some surface features and reduce others. It will however render unnatural colours to all the features.

Another filter that works "reasonably well" is the Sirius Optics "planetary contrast" filter. This filter cuts the glare a little and gives a similar view to the 80A light blue, but doesn't "dampen" the image quite as much as the 80A. Its not a bad option but the filter is a "surface coated" filter and quite delicate. I think Baader also have a planetary filter that probably works ok but I havent tried it.

I actually own lots of filters suitable for planetary observing including 12, 2" Hoya colour filters, a 2" Variable polariser, a Sirius Optics planetary contrast filter and at the end of the day I never use any of them on Jupiter or the moon in my 10" scope, nor in larger scopes for that matter.

CS-John B

[janoskiss (Steve H)]

I certainly don't need filters in my 8" on any of the planets. But when viewing (or showing others) the full Moon at moderate magnifications, the ND filter comes in handy.

When looking at Mars during last year's oppositions through Darren's 12" at Snake Valley, the ND and/or a polariser filter seemed to help.

[dhumpie]

I find I prefer the views sans filters (even in the 10") although I sometimes use the scratched 80A blue filter that 1 ponder's kindly "donated" to me

Darren