Where to start with LRGB filters?

[badgerchap]

I'm getting ready to make the jump to a dedicated CCD after enjoying myself with a DSLR. After having read post after post about mono vs. OSC I'm definitely going to go for the former. I'm ridiculously attracted by the prospect of being able to capture data when theres a bit more moonlight around.

I'm probably going to go for an Atik, either the 314L+ or 420.

However, I'm not sure which filters are best to start off with.

Obviously I want to save money - I'm a student so I really shouldn't be buying any of this! Therefore, price is of course a concern. However, I don't want to waste the money I do spend on something I'm going to want to replace in 6 months.

I seem to see a lot of people going for the Baader set. Are they a good place to begin? I really want to minimise any halos and artifacts, and I want to start picking out some smaller targets, i.e. planetary nebulae and some smaller galaxies. I've enjoyed the big targets with my DSLR, but it really is time to get some Ha too, although that may have to wait cash-wise.

Any muchly appreciated,

Badgerchap

[JamesF]

I think when people talk about imaging with filters when the Moon is out they're talking about narrowband with Ha, O3 and S2 filters rather than LRGB.

That said, for LRGB I think this is the Baader set you should consider:

http://www.firstlightoptics.com/rgb-filters-filter-sets/baader-lrgbc-ccd-filter-set.html

The 314L+ comes up second hand now and then both in the mono and OSC versions. You could save yourself a lot of cash getting a used mono model.

Don't forget that you'll also need a filter wheel. Electric ones are nice, but cost more and the software that comes with the Atik cameras will only control their own filter wheels. Capture software that will control other ASCOM filter wheels is not usually available for free. In the scheme of things, a manual filter wheel isn't a huge cost to swallow if you decide you want to upgrade later.

James

[earth titan]

I took the plunge this spring and don't regret it at all. I bought the package deal that came from FLO and the basic baader filters in there are fine. As James points out, the Atik wheel only works with their own Artemis software but the software is so good, you won't need to worry.

When you do get it, welcome to the learning curve

Processing of LRGB is a steep but fun curve. In addition to the kit, you may need some additional processing software. I found DSS limited as it struggled to properly align frames of different colours. I went the whole hog and bought Pixinsight which although expensive, works brilliantly even after meridian flips.

[ollypenrice]

I think you'll see a 314L on Astobuysell at the moment.

The Baader LRGB set (not the very cheap absorption ones) is, in my view, the place to begin. Personally I prefer them to the costly Astrodon colour set but that's probably a minority opinion. You might pick some up second hand from someone moving to 2 inch. In moonlight LRGB has no advantage over OSC but, as James says, Ha is fairly moon-proof, though not entirely. The Baader 7Nm is a good place to start. These are truly parfocal, too. I found them so even at F3.9.

Olly

[badgerchap]

I think when people talk about imaging with filters when the Moon is out they're talking about narrowband with Ha, O3 and S2 filters rather than LRGB.

Indeed - sorry, getting ahead of myself

Thanks for the input all. I think I'll head towards the Baader set mentioned.

Is a filter wheel ABSOLUTELY necessary? I had planned on getting one anyway, but just for the sake of argument, is it not feasible to manually change the filter after each colour run and then realign with a mask on APT?

[RikM]

I use the Baader LRGB set plus the 7nm Ha in a 5-place manual filter wheel and love them.

It is theoretically possible to use one filter at a time, screwed onto the nosepiece of the camera but in practise you really don't want to do this. All the faffing with taking flats during clear sky time, then stripping out the camera, changing the filter, realigning, reaquiring your target, refocusing, getting the guiding going again...compared to thumbing a wheel to the next position and pressing start.

[badgerchap]

Now you put it like that, it does sound like a bit of a faff!

I think a manual filter wheel will do, though I may try building an electric one at some point!

[JamesF]

I think a manual filter wheel will do, though I may try building an electric one at some point!

For me so far the real benefit of a motorised filter wheel has been the ability to put in parfocal filters and take RGB or LRGB images in turn without having to actually be present at the scope. Taking the images in turn means you stand a reasonable chance of coming out of an interrupted session with at least some data that's useful.

On the other hand, if I'd not picked up the filter wheel second hand I'd have gone for a manual one and lived with the need to sit at the scope or to take a number of images with each filter at a time. It's not exactly a big deal and it saves buying an expensive motorised filter wheel (Atik's own) to work with Atik's capture software, or buying a different capture application.

So I think you're making the right decision to stick with a manual one for the moment.

James

[r3i]

It's definitely worth keeping an eye on the secondhand market. I've also recently been putting together a mono setup to go alongside my existing OSC. I've managed to pick up everything secondhand so far including an SXV-H9 (the Starlight Xpress equivalent of the Atik 314) plus LRGB & NB filters. I've gone for 2 five slot manual wheels, one for the LRGB filters and one for the NB filters. It would have been nice to get a motorised wheel but I wanted to keep a lid on the cost and using a manual wheel I think won't be no great hassle.

The only possible weak point in my setup is the RGB filters that I got with one of the wheels which are the low cost Wratten type ones - they'll do me for now while I'm taking my first steps in the mono world but I'm sure I'll want to get the better Baader ones later on.

[RikM]

It's definitely worth keeping an eye on the secondhand market. I've also recently been putting together a mono setup to go alongside my existing OSC. I've managed to pick up everything secondhand so far including an SXV-H9 (the Starlight Xpress equivalent of the Atik 314) plus LRGB & NB filters. I've gone for 2 five slot manual wheels, one for the LRGB filters and one for the NB filters. It would have been nice to get a motorised wheel but I wanted to keep a lid on the cost and using a manual wheel I think won't be no great hassle.

The only possible weak point in my setup is the RGB filters that I got with one of the wheels which are the low cost Wratten type ones - they'll do me for now while I'm taking my first steps in the mono world but I'm sure I'll want to get the better Baader ones later on.

That's where I'm headed as well. I have a second-hand SXV-H9 and am planning to get a second manual wheel for a set of NB filters.

[ollypenrice]

Manual wheels are fine and are by far the most reliable!! There are two disadvantages.

-They are not lightproof so you can only do flats in the dark, which really means panel or lightbox flats.

-They will not keep your filters perfectly clean so you will need flats for each channel. Many people are convinced that this is always necessary but I find a single flat works perfectly for all channels. I use lum. Several other imagers I know do likewise nowadays.

Olly

[badgerchap]

May I get some clarification on something here then please? When taking LRGB shots with an electronic wheel, do people tend to take one of each colour before starting a sequence again, or do they tend to take a stack of L, a stack of R, one of G and one of B? I had assumed the latter up until now. If there is a distinct advantage to the former though, I am tempted to fork out for an electronic wheel, especially with what Olly said about flats - they're still a bit of a weak point of mine so the easier they are the better.

[JamesF]

As I said, I tend to cycle through the filters because if I plan to take 90 subs and only get 45 then at least I have something to work with for a complete image. That would be a real faff to do with a manual wheel. There's no reason however that you couldn't use a manual wheel and take, say, ten subs from one filter, then the next, and keep going until you get as many as you want. That would keep the filter-switching under control whilst hopefully still leaving you with enough data to create an image if your imaging session was curtailed.

James

[badgerchap]

Ah right, I see what you mean now - kind of anti-cloud insurance!

[JamesF]

Exactly so

James

[MartinB]

I have the Baader CCD LRGB set along with a set of their 7nm narrow band filters. I also use a Hutech IDAS light pollution filter when doing LRGB. These filters reflect away the light wavelengths not required. They are more expensive to produce than simple absorption filters and great claims are made for high transmission rates and the precision of their band pass. There is intense competition between filter manufacturers and you sometimes have to be careful to read through the hype. I also have a set of Baader absorption filters which I use for my very infrequent planetary imaging. These filters actually work very well for deep sky LRGB imaging and are a fraction of the cost of the CCD filter sets. OK, the band pass may not be as tightly controlled and transmission may be minimally less but, give that you are on a tight budget they are well worth a look. In the future, when you have graduated and are earning pots of money you could upgrade and still have the absorption filters for other uses (solar system imaging, observing).

You also need to think about infra red blocking. The Baader set I have come with both plain and IR blocking clear filters. If you are using a reflecting scope then you don't need IR blocking for your luminence imaging (better sensitivity without) but you still need it for your colour subs.

Narrow band filters are expensive. If you are going to splash out stick with Ha at first. Ha subs can be combined with LRGB very effectively when imaging emission nebulae.

Doing LRGB without a filter wheel is a nightmare, manual filter wheels are manageable. Electronic filter wheels seem a huge extravagance until you have used one! I much prefer to rotate through the filters as I go along for the reasons stated.

[ollypenrice]

Good point from Martin on UV.

The hard nosed answer to how to plan a sequence is easy. Shoot red and green at the lowest elevations and luminance and blue at the highest. In reality this tends to matter most when imaging low targets which never rise much.

The humane answer is to protect yourelf against despair by going LRGB, LRGB with an electronic wheel!

Olly

[badgerchap]

In the future, when you have graduated and are earning pots of money....

Ha! That'd be nice - wish I shared the enthusiasm! "Mature" student studying Astrophysics - think those pots might be quite small

Aside from that, thanks for the input. May give a quick look to the Baader absorption filters. Honestly, I'm quite happy getting less-than perfect results while I'm a CCD newbie - As long as I can improve upon my DSLR work I'll be content to wait a few more years for better - and also narrowband - filters. I will be honest though, I'm not expecting to be much cop at this overnight. Definitely gearing up for that steep learning curve!

[badgerchap]

Good point from Martin on UV.

The hard nosed answer to how to plan a sequence is easy. Shoot red and green at the lowest elevations and luminance and blue at the highest. In reality this tends to matter most when imaging low targets which never rise much.

The humane answer is to protect yourelf against despair by going LRGB, LRGB with an electronic wheel!

Olly

Awwww you're just throwing more questions at me now! Is this because red and green penetrate the "thicker" atmosphere better, but the blue is less penetrative?

[ollypenrice]

Awwww you're just throwing more questions at me now! Is this because red and green penetrate the "thicker" atmosphere better, but the blue is less penetrative?

Exactly. Your house wall can't stop radio wavelengths but it doesn't have much trouble with red light! Red is less affected by atmospheric density and green is a funny thing in AP since it really just determines colour balance. Lum holds the detail and blue is a beggar for bloating in dense atmoshere (or any atmosphere!!) So go for L and B in your best (highest) sky and scoop up the junk where you can!!

But, honestly, just get an image. LRGB, LRGB, has a lot going for it.

Olly

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/22435624_WLMPTM#!i=2277139556&k=FGgG233

[MartinB]

But if you've got light pollution then low down red gets properly messed up

[ollypenrice]

But if you've got light pollution then low down red gets properly messed up

Aha, I didn't know that. I'll step back from this one!

Olly

[kirkster501]

I have recently jumped into CCD imaging as well with 460EX, Baader LRGB filters and EFW2 wheel. LRGB is more than enough to be getting on with IMO whilst you build up your workflow and processing skills - like I am doing now! Worry about NB laterz!

Setting up the CCD is easier than a DSLR I am finding since the CCD is so sensitive you don't need to use an EP to get aligned; point it anywhere and then focus. there will always be stars in the FoV. AstroTortilla really comes into its own with a CCD!!!!!

[davew]

On the other hand, if I knew then what I know now, I would have left the LRGB for another year or two and just bought an Ha filter. With a guided 6" F4 Newt 10 to 15 minute subs are easily within reach.

Just a camera, one filter and the correct size tube to fit it all together. How much cheaper and easier would you want ?

Next birthday an OIII filter and then you can colour in all the images you've made ( If you feel you have to ).

You can always steal the colour from the DSLR.

It's all a matter of personal preference.

Dave.

[badgerchap]

Aha, I didn't know that. I'll step back from this one!

Olly

Is this post just a sly way of letting us all know how little light pollution you have down there in France?