Hi, Tom,
I started out with a Canon EOS 20DA on an 8" scope, although sometimes I used it on a 3" or 6" refractor.
You will unquestionably get something pleasing using the gear you have, and the exposures you suggest. It will effortlessly pick up the stars, and their colours. It will easily pick up the cyan coloured OIII nebulosity and the blue hydrogen beta, and (more so on other objects) it will easily pick up any reflection nebulosity. But it may struggle a bit with the cherry red H-alpha because the infrared cut-off filter will tend to exclude reject perhaps 50-70% of it, making it fainter and grittier.
As you probably already know, your gear will work fine with the brighter galaxies, with just about any globular or open clusters, and with the very brightest dozen or so emission nebulas. NGC 6188 is in the intermediate category - within reach.
Using narrowband filters, you would still have that limitation, but the stars, air glow, light pollution, and any reflection nebulosity will be greatly attenuated, making the nebulosity (that you would have picked up even without the filters) much more obvious.
Going to a cooled CCD is a
huge step forward. For the same exposure, the background grit snow and fog is enormously reduced. Hydrogen alpha nebulosity will be detected at - bit of a guess here - two or three times the efficiency. And, if you are at a dark site, and guiding and tracking will allow it, you can take hugely longer exposures.
Bit of personal prejudice: Natural colour is great, spectacular, beautiful, for open clusters, globulars, and most importantly galaxies. But for me (others will disagree vigorously) nebulas in natural colour tend to look like a piece of raw cryo-vac meat: a nasty purple. (We've seen some skilled examples recently where people have avoided that butcher-shop look.) On the other hand, nebulas really call out for narrowband imaging. And it can be done when there's a bit of moon about, and from the outer suburbs.
The attached thumbnails show my early attempts at 6188 using a DSLR and natural colour, and then using a ccd and narrowband filters, both from suburbia, but using an 11" scope. Details lost to history. (our current best attempt, a few years old, is
here).
Summary: You'll certainly get pleasing results on the Ara nebula using the gear you have and the exposures you suggest, but should a CCD camera and narrowband filters fall into your hands ...
Very best,
Mike
