Dual Imaging setup - L + OSC or L + RGB?

[ian_bird]

Hi

I have a WO FLT98 plus AO, OAG, Filter Wheel with 2" LRGB and SX H18. Sat on top via a Baader Stronghold is a WO 72 Megrez. All sat on a CGEM DX.

I am thinking of going Dual Imaging with this lot.

So what I am thinking is that I should capture Luminance via the 72 Megrez as it is not an APO. Then capture either OSC or RGB with the FLT98. Good idea or wrong way around?

Anyone tried this? Which would you go for - OCS or RGB?

My other question is how to sync the exposures. I am using Maxim DL to control the AO/OAG and SX H18. When it downloads guiding stops (Why - what's with that? Could they not multithread?). So I need to make sure the Megrez is not still exposing when the FLT98 is downloading. I will use a second session of Maxim DL (Or Artemis Capture) to run the Megrez.

Another thought is to run three sessions of Maxim - one to guide continuously - and one each for the two cameras. Then I would not need to worry about the lack of guiding during download - but I would not be able to dither.

If I go L + RGB I will need another CCD for the Megrez. Perhaps an Atik 314L. Or if I go L + OSC then I will have to put the H18 on the Megrez and get a OSC for the FLT98.

Any thoughts or tips (Even if it's "Don't try this!") most welcome.

Cheers

Ian

[ian_bird]

Ooops!

The Megrez *IS* an APO! How did I miss that!

So I could go FLT98 Lum plus 72 Megrez OSC or RGB.

That would give me the H18 on the FLT98 - which would be best for Lum.

So now it's down to the OSC/RGB question and the guiding/sync questions.

Sorry about that.

Cheers

Ian

[steppenwolf]

I have a very similar dual imaging set-up. I capture OSC with my FLT98 and SVXF-M25C as this is a true APO and I capture Ha and/or Luminance using my Megrez 72 and an SXVF-H9 with Atik EFW2 filter wheel. The sensor in the H9 is much smaller than the M25C so my image resolution is set by the H9 but many a fine image has been captured with an H9 so I'm not too worried about this although ideally, I'd like a mono APS 'C' sized sensor instead - maybe if I win the lottery?

I recently produced a two-part 'How to Article' for S @ N magazine showing how I arranged it all but here's a quick shot of my system on an EQ6 mount:-

[steppenwolf]

My other question is how to sync the exposures. I am using Maxim DL to control the AO/OAG and SX H18.

I have an old version of MaxIm DL and I certainly can't (successfully) run two or more sessions of it so I guide with the Megrez and capture the mono data all with MaxIm DL but capture the OSC data using Starlight Xpress' own software.

[ian_bird]

Steve

Thanks for that. Glad to know it can be done!

Could I ask what you mean by "FLT98 ... as this is a true APO". Does that mean the Megrez is not an APO?

I was going to run the other copies of Maxim in Virtual Machines. I am an IT Consultant - so pretty easy for me to do. Just wish I was an AP Consultant!

So you seem to be in favour of L + OSC rather than L + RGB. Is that based on the equipment you have - or is the equipment you have based on L + OSC being better than L + RGB?

So many questions!

Cheers

Ian

PS - And I though the LRGB versus OSC debate was complicated!

[Gina]

Well I'm buying a second mono 314L+ for my dual imaging rig as I believe this to be the most versatile. Not yet sure about the second scope but for a start I'll use the ED80 and ST80. Hoping to be able to afford an Esprit 80 later on so then it would be Esprit 80 and Evostar 80 ED.

[steppenwolf]

Could I ask what you mean by "FLT98 ... as this is a true APO". Does that mean the Megrez is not an APO?

The Megrez uses ED glass but it is still a doublet - it gives reasonably good colour correction (not as good as, say, the ever popular SW ED80) but an apochromatic telescope corrects all three colours (red, green and blue) whereas no matter how good a doublet is, it can only correct for two colours. I think of the Megrez 72 and SW ED80 as being 'semi-APO' if you like! Both are certainly better at correcting chromatic aberration than a standard fast Crown and Flint achromat.

I was going to run the other copies of Maxim in Virtual Machines. I am an IT Consultant - so pretty easy for me to do. Just wish I was an AP Consultant!

Hmmm, you and I need to talk! In a previous life I was up to speed with PC operating systems but that was a while ago now and I have no idea how to set up a virtual machine although I understand the concept I'd love to do it though......

So you seem to be in favour of L + OSC rather than L + RGB. Is that based on the equipment you have - or is the equipment you have based on L + OSC being better than L + RGB?

Simply based on the equipment available. However, to try and get the two fields of view as close to one another as possible, conveniently, I use the OSC with the longer focal length FLT98 without a focal reducer but with a field flattener (Hotech) and the smaller sensor mono CCD with the shorter focal length Megrez with a focal reducer. This doesn't correct the disparity between the pixel counts of the two systems but it allows me to make the best use of that hard won data! These are the two FOV's that I achieve, the smaller being the Megrez/H9 combo:-

[ian_bird]

Thanks for the feedback. Very interesting.

So how do you deal with dithering? Or do you not bother?

And the sync exposure bit? How do you handle that? If I don't have to dither it's not a problem - just guide in a separate session - so the two imaging rigs can do their own thing. But if I need to dither then I have to sync the downloads! That sounds like a major PITA!

A trip to the South Coast might be in order! IT Consultant meets Dual Rig AP Consultant!

Thanks again for the feedback. Nice to know it is do-able before I start!

Cheers

Ian

[steppenwolf]

It's certainly doable, Ian and worthwhile too. I don't worry about synchronising the two cameras, I just let them get on with it! Currently I don't dither but both my CCD cameras have Sony chips so they are pretty quiet.

[ian_bird]

It's certainly doable, Ian and worthwhile too. I don't worry about synchronising the two cameras, I just let them get on with it! Currently I don't dither but both my CCD cameras have Sony chips so they are pretty quiet.

Ah! Now that makes a bunch of sense! Thank you! I was getting too hung up on the "You must dither" mantra!

Thanks! You have given me the courage to give it a go!

Cheers! Big time!

Ian

Gina - let me know how you get on. I vote that we start a Dual Imaging Rig forum in here!

[Gina]

I will certainly be posting my results and findings I have done dual rig imaging before but it was with DSLRs (1100D) cooled to near ambient and using Astronomik Ha and OIII clip filters and 200mm f4 lenses - can't say it was a great success. I have agreed to buy a 2nd mono 314L+ which I hope to get near the end of this month

I have never tried dithering. I try not to dither too much Sorry CRT

[Mark72]

I'm trying to use both scopes the same time but I use two computers.

Luminance with 2m RC and colour from Televue 101. I use dither but I giude with OAG at 2m, so it does not effect Televue at all.

The main trouble is auto-focusing; I'm trying to sync them so that they are focusing when the mount slews to a focusing star.

Mark

[ollypenrice]

Hi Ian, I'd think about narrowband in the Megrez and LRGB in the 98. The 98 is a true apo, as discussed, and luminance is just RGB but all at the same time, so that needs full apo-dom just as RGB does. However, NB uses near-monochromatic light so needs no colour correction. A semi apo is more than good enough. I've used a WO ZZS 66 to catch Ha and O111 and found it ridiculously competent. In broadband it struggles.

At these focal lengths emission nebulae will be your main targets, probably, and HaLRGB or HaRGB will serve you superbly well. Ha and O111 are slow so a full run in the 98 on (L)RGB will be well seved by an equivalent narrowband run. Not only that, but from your site NB will give top quality data. That's the way I'd do it. On emission nebulae you often need relatively little LRGB data, just enough to find star colour and a little three dimensionality in the nebulosity. Applying Ha as surrogate H beta in the blue channel is also a good idea, especially if you tweak the contrast curve into the Ha when adding it to blue so that it doesn't just replicate the Ha in red.

I could never image without NB input on emmision nebulae and many galaxies.

Olly

[ollypenrice]

PS I should have added that Registar is the tool of choice for all forms of aligning and resizing.

Olly

[Gina]

PS I should have added that Registar is the tool of choice for all forms of aligning and resizing.

Olly

Yes, I find that even if I'm taking very rapid RGB subs for stars I still need RegiStar to align the colours (even with guiding).

[steppenwolf]

I use MaxIm DL for aligning my disparate images as I have found that a two star manual alignment works very well (with the smaller images selected as the reference frame but I have heard very good things about Registar.

[ian_bird]

Thanks for that Olly. Most useful!

Cheers

Ian