Using filters with a PST

[moriniboy]

I have noticed that when thin cloud passes in front of the sun the disc granulations appear to be more pronounced.

My stock of filters currently stretches to a just an LP and a polarising, has anyone tried any coloured ones to see if they will make the granulation more visible?

[Merlin66]

As the final image is a very narrowband Ha image, only a red filter can work.

An ND filter (moon filter type) may help.

[Peter Drew]

I've tried many filters to try and produce this cloud effect without much success so far. The only guaranteed way forward is to double stack which is very expensive compared to clouds!. Perhaps a lit cigar fitted to the dewcap might help.

[moriniboy]

Borrowed some filters and the best seems to be the polarising filter #3, may just be that it reduces the glare but there is a definite subtle improvement in my 32mm Kellner.

For reference here is a list of the filters tried:

Polarizing #3

Blue 82a

Light pollution

Red 23a

Skyglow moon

Orange 21

Green 56

Yellow 12

ND96(0.9)

[Ibbo!]

I use a vari-polarizing sometimes it works sometimes it does not

I think it is very seeing dependant

Steve

[JamesF]

The one way I have considered using a filter with the standard PST is to put a 35nm Ha filter on a step-down ring on the front of the OTA. Not particularly to improve the image, but just to reduce the amount of energy entering the tube and in particular the amount that the mini-ERF has to reject.

James

[cathalferris]

Something I've seen is that local seeing through a cloud can be much improved than the free sky around it. Others have noticed this, especially when planet observing. It's not an effect that can be duplicated with a filter locally at the scope. The fact that the final image is Ha, means that all that a filter will do is change the overall brightness at the eyepiece. Single polarising filters may have an effect purely due to the possibility of the emission of polarised light from the Sun, but crossing polarised filters won't have a useful effect.

I'd love to know what the mechanism is that causes that calming effect when the local seeing is pretty poor. I've never seen the calming effect to work when seeing is good though - the cloud boundary can make seeing worse