LRGBHa

[Demonperformer]

I have a set of colour filters (Opticstar 1.25" LRGbB Imaging Filters.) on the way, and (if/when I get a reply to my email to FLO re SGL discount) a 35nm Ha filter (I'm opting for the 35nm version, due to the limitation on exposure length of my equipment).

Assuming same length subs with each of the filters, what sort of ratio do people use for each filter? (Same number of subs for each? More or less subs for one of the colours?)

Now I guess that at least in part the answer is going to be 'it depends on what you are imaging'. Well, in detail I don't know yet. But with my passion for open clusters, I am probably going to be inclined initially towards objects classified in NGC as "Cluster with nebulosity" (if that helps:)).

The camera I will be using is a SXV-H9 mono.

It is really just a rough guide I am after (not an in-depth technical explanation that I won't understand:iamwithstupid:) to put me in the ballpark.

Thanks.

[MODS: I think I might have put this in the wrong section. Please move if you deem it appropriate. Thanks]

[SteveL]

Just a quick point about the 35nm Ha filter... the wider bandpass of this filter wont let any more Ha in than a 13nm or 6nm, but what it will do is allow more noise and light pollution in either side of the Ha emission wavelength. If you can, go for the narrower bandpass filter option.

[roundycat]

exposure differences between filters depend on the spectral sensitivity of your camera and the transmission of the filters. The condition of the sky will add its own curiosity value. Ergo, you have to work it out yourself. Start with identical exposures and see what the unprocessed colour balance is like.

What you are imaging is irrelevant.

I tend to vary the exposure to fit the filters in my ST10 but you can get much the same effect by shooting more subs for the denser filter.

Dennis

[Demonperformer]

Dennis, fair enough. Splitting the subs equally between all the filters was my default position, so I have lost nothing by asking.

Steve, I hear what you are saying. My concern with the narrower band filter was that there may be so little on the subs (because of my limited exposure length) that DSS will not be able to do its job of registering and stacking it with the other colours. Am I understanding you correctly that if I was not getting enough Ha recorded on the 7nm filter, what I would be getting on the 35nm filter would not really be Ha at all?

[SteveL]

The other way round.... a 35nm bandpass Ha filter will give you Ha data plus extra stuff either side of that specific wavelength (noise mostly), whereas a 7nm filter will still give you the same amount of Ha data but less noise either side of that wavelength. A wider bandpass doesnt give you extra Ha data, but a narrower bandpass filter will give you much better contrast between Ha data and non-Ha data.

[johnrt]

When you say you're limited exposure length, what sort of time are we talking here? 5mins +/-?

Dennis, fair enough. Splitting the subs equally between all the filters was my default position, so I have lost nothing by asking.

Steve, I hear what you are saying. My concern with the narrower band filter was that there may be so little on the subs (because of my limited exposure length) that DSS will not be able to do its job of registering and stacking it with the other colours. Am I understanding you correctly that if I was not getting enough Ha recorded on the 7nm filter, what I would be getting on the 35nm filter would not really be Ha at all?

[Demonperformer]

Thanks for the clarification, Steve

John, Being on an altaz mount, if I start going much over 30s, I am liable to start getting tracking. So definitely -

[shaunster]

You may find you dont get much through the filter in 30seconds

[Demonperformer]

That was the original thought that prompted my 'opting' for the 35nm filter, which I now realize is not an answer. It may be that any worthwhile Ha imaging will have to wait until I can get an EQ setup. But then I will still have the limit on exposure length imposed by LP.

[johnrt]

I would go with what's been said already and don't think it's worth attempting any narrowband imaging if you're limited to 30 secs, put the money towards an EQ mount and stick to the broadband filters for the time being.

Narrowband filters deal with light pollution quite well, so I wouldn't worry too much about your exposure length when you get an EQ mount and narrowband filters.

That was the original thought that prompted my 'opting' for the 35nm filter, which I now realize is not an answer. It may be that any worthwhile Ha imaging will have to wait until I can get an EQ setup. But then I will still have the limit on exposure length imposed by LP.

[Demonperformer]

Narrowband filters deal with light pollution quite well

Now that is something I hadn't considered. Maybe there is hope for me afterall:)