What filters for Galaxies tonight?

[PatG]

Going to try a bit of EAA this evening. Hopefully to observe some galaxies. 

Its clear skies here in Somerset, although a bit windy!

Going to be using a LX90 200mm SCT on a HEQ5 with a Lodestar x2 mono camera and some focal reduction.

Contemplating whether to use either an Astronomik UHC or a Ha filter, or a basic IR/UV cut out.

Which would you use??

 

 

 

 

[catburglar]

I suspect the best advice might be to point as far away from the moon as possible.

Because you’ve got some refractive elements with your set up (corrector plate and reducer) I think you’ll need the IR cut to get sharp focus ( a reflector can focus IR and visual wavelengths at the same point so can sometimes get away without one).

I’d definitely leave the H-alpha out of the equation… Since galaxies emit across the range of visible wavelengths filters tend to be less effective- or at least that’s the conventional wisdom, but I’d be interested to see if the UHC does help at all.
 

[bosun21]

In my experience galaxies are best viewing without any filters whatsoever. Apart from maybe a light pollution filter. But that’s just my opinion.

Edited March 20, 2022 by bosun21
Spelling error

[catburglar]

2 hours ago, Stephen Waldee said:

I do not personally think that a modern SCT of good quality produces chromatic aberration in the corrector that would show up on an image, objectionably, so that one would need an IR/UV cut filter to remove it.  I personally can't think of one single published amateur galaxy image that has thorough documentation of gear used, employing an SCT, that mentioned having also employed an IR/UV cut filter

The OP stated that they were expecting to use some sort of focal reduction and therefore this will most likely exacerbate the poor focus of IR wavelengths to which the lodestar is quite sensitive. Whilst we don’t see UV/IR cut filters listed in the equipment for images captured with SCT’s they do in fact include a UV/IR cut filter in the majority of cases -it’s called the Luminance filter in an L-RGB sequence. I don’t have the specifications for all manufacturers but many have cutoffs at around 400nm & 700nm- in the UV and IR ranges.

[Cosmic Geoff]

Many astro cameras eg. the ASI224MC require an IR-cut filter to achieve the correct colour balance with an OSC colour image.  I do not see that any other lind of filter will be any use for EAA of galaxies.