OSC Only ....... Option 1, Option 2 or Option 3?

[ChrisLX200]

ChrisLX200 .... ok I'm listening. What's your routine for using the camera? Do you have two USB cables running to the PC - one for the camera and another for the filter. Are they both controlled from the same application? Do you have to refocus when you change filters? If you do, do you use a remote focuser, requiring yet another cable presumably, or do you refocus at the telescope? Do you use each RGB filter in turn, and then luminance, or cycle round these in some way?

I have a separate USB hub on the scope, some cameras (like Starlight Express) have a hub actually fitted to the camera and you plug the filterwheel into that - so just one cable between scope and laptop/PC. Because you usually have a guider requiring its own USB connection, and also the mount often has a USB connectionas well, then simply having a separate hub at the telescope is the best option.

I'm really critical about achieving perfect focus so yes, I refocus between filters. However, there will be a fixed offset (relationship) between the focus points for the different filters. They may be quoted as being 'parfocal' with each other so that you focus with one and all the rest are supposedly at the same focus position. Not in my experience! The difference is perhaps only slight but IMHO worth adjusting for. If you are less critical then you can ignore it or use fixed offsets to adjust focus, just use the plain glass filter (the 'L' of an LRGB filter set) and then add or subtract a small amount for each of the others. Of course, that has to be done using an electric focuser because the adjustments are small. If using a manual focusing system (say, a BMask) the differences between the filters might hardly be noticeable anyway.

You have many options for the way you collect data using a mono camera and filters. Some collect all of one channel before moving onto the next filter, some prefer to cycle round the filters. So for LRGB it would be LRGBLRGBLRGB etc., or LLLRRRGGGBBB. For me, considering I refocus between filters, I go for the latter - complete one channel before moving onto the next. All of this is automated by your image capture program by creating some sort of 'sequence' which controls the filterwheel and camera. I use SGPro (Sequence Generator Pro) which not only does that but also automates the focusing and the scope positioning. Once you have used SGPro there really isn't any looking back, and the imaging session becomes boring as it ticks along so you look for other stuff to do :-) 

ChrisH

[Ouroboros]

Chris - thanks. Some good ideas there. I'd not thought of using a USB hub at the scope. It might even help me using a DSLR and a guide camera. I'd have to think of ways to power it outside. I use Backyard EOS with my Canon 450D so I'm familiar with sequencing. I would have thought it was pretty essential for LRGB.

Yeah, you're almost persuading me that setting up with a mono CCD and filter kit, even from scratch as I do, may not be that much more difficult or complex than what I do already .... and that can easily take an hour or so as I get everything in place ready before I start polar aligning, 3 star alignment, finding and framing the target etc etc.

[smudgeball]

Yeah, you're almost persuading me

...we're all waiting for the button press

[Ouroboros]

The Buy button you mean? Chuckle. I'm planning to talk to suppliers at the IAS.

[ollypenrice]

Whether you need to refocus between filters or not depends on your pixel scale and your optics. I don't feel that I do and so I don't. My pictures are out there and if you feel they're soft on focus then you do. (Maybe don't tell me though!!!       ) I have good optics, yes, and huge pixels, so my systems are not very exacting. Bear in mind, though, that with OSC you cannot refocus between filters. You have a One Shot Compromise. (Do I win a £5 Brain of Britain postal order for this inspired play on acronyms?) At least with mono it remains an option.

If in doubt, shoot RGB without refocusing and then shoot L at its own critical focus. But - ah, curses, L IS RG and B! Oh no! 

Olly

[ChrisLX200]

One thing you can do with a mono camera is choose _when_ to shoot each channel, so you can choose to shoot the Blue as your target is at its highest (blue tends to get lost at lower elevations). The extra flexibility of going mono is yours to explore and to take advantage of!

ChrisH

[bbblue]

Button pressed!

I might add ..... some considerable time spent researching, taking note of all of your comments and discussion has helped.

Many thanks.

[Coco]

Trying to take OSC images when there is a Moon about is a nightmare for gradients. If your skies are not regularly great having a Moon about can spoil what little chance you have.. at least with Mono you can be getting on with some Ha..

[smudgeball]

Button pressed!

And what did you decide on ?

[bbblue]

In an ideal world I would have both a OSC and a Mono but have opted for a mono:

Atik 460 + wheel + LRGB filters.

Thanks again for your comments etc

[Davey-T]

Don't think you've ever mentioned what you're going to stick it on mount wise.

Dave

[bbblue]

Hi Dave

I am lucky enough to have a permanent setup which includes an Eq6. I am also fortunate to have really dark skies ....... no street lighting at all in my village.

[Davey-T]

Should be well set up then, no excuses, be expecting some first class images 

Dave

[smudgeball]

Atik 460?

Good choice!

Sony chips are far superior to those really old kodak ones.

..........I'll get my coat!

Neil

[pyrasanth]

I will throw my 10 pence into this discussion. I don't like my Atik 490 OSC camera. I'm pretty sure it would be great in the Arizona desert on a fast telescope but from my light polluted garden- forget it. I have not been able to take 1 sub that I've been happy with. The gradients are simply horrible & the colour shift takes much work to balance. I would sooner use filters any day of the week. I'm thinking of selling the 490 as it gets very use & buying a replacement 490 mono which I know would get used.

[ChrisLX200]

I will throw my 10 pence into this discussion. I don't like my Atik 490 OSC camera. I'm pretty sure it would be great in the Arizona desert on a fast telescope but from my light polluted garden- forget it. I have not been able to take 1 sub that I've been happy with. The gradients are simply horrible & the colour shift takes much work to balance. I would sooner use filters any day of the week. I'm thinking of selling the 490 as it gets very use & buying a replacement 490 mono which I know would get used.

Somebody should make that comment a sticky... :-)

ChrisH