First go at it (Lagoon/Triffid and Eta Carina)

[Benjamin (Ben)]

Had my first chance to try some astrophotography and came up with the following images. The first was a pretty wild attempt at the Lagoon and Triffid with a few stacked short exposures (small number of darks too all at ISO3200) with a poorly aligned mount and hit and miss focus. All pretty terrible! The second image of Eta Carina I spent much more time drift aligning, managed to use my homemade Bahtinov mask to focus in liveview on my Canon 600D and pushed exposures to 2 minutes. I've put up an unprocessed single frame (2 minutes at ISO800) and an image processed through Nebulosity comprising 3 frames at ISO1600 and 2 frames at ISO800 (both 2 minutes) with a small number of darks subtracted (would have had more darks to subtract but my camera battery died!). Haven't subtracted any bias or light frames. I'm very interested in using these images to document my visual observations so not trying to win any awards but would really appreciate advice on simple things I can do to refine the technique. Want to limit the number of exposures/darks and be able to move on to the next target reasonably quickly. I'm using an ED80 (with a .80 focal reducer) on an EQ3-2 driven mount.

[Benjamin (Ben)]

This was the first attempt at it all... Not so great although I'm keen to get the same composition again one day.

[Atmos (Colin)]

You've done a good job with Eta Carina, you could probably hit the saturation a bit harder but I personally like vibrant and bold

The second, as you have said, is suffering from a less than perfect polar alignment but the composition is perfect! Definitely say have another go at it!

Something else you may want to consider for the future is doing flat frames, you'd be surprised just how much of a difference that they can make.

Good job though

[Benjamin (Ben)]

Thanks Colin. My concern with flats, darks and bias frames are the extra time they take to produce. If I'm documenting my visual observations I need to move quite quickly, although through the ed80, with the .80 FR, I'll likely get a few objects in one shot. If I took 10 2 minute subs (so that with the eq3-2 I'd probably have 6 or 7 useful shots) what would be a useful number of darks and flats I'd need for that process to be effective? Also how do you take your flats? Many thanks for he advice :-)

[Atmos (Colin)]

The good thing abou darks and bias is that they do not have to be taken at the same time as your lights.
Taking flats with a DSLR can be done in a few seconds as well. I have a light box I place over the front of the telescope/lens, put the camera on automatic and take a dozen shots in a couple of seconds.

[Benjamin (Ben)]

Great. I assume that darks should match the subs in terms of number , temperature, length and ISO (so could be done whenever at the right temperature). If understand what you're saying is that flats should be taken in the same conditions, with the same ISO and a similar number, but duration is irrelevant? I was thinking of using a white iPad screen perhaps for flats? Bias I have no idea about bit assume this is also about the state of the camera in the conditions the subs were taken in?

[Atmos (Colin)]

Having a similar number of darks is a good idea and yes, should be take under the same conditions. The good thing about them is that they can be used later on as well, for other shots.
Bias is very easy, just keep the same ISO and go with the quickest shutter speed, 1/8000 for my Nikon D700.
Flats are whatever exposure gives about a 50% histogram, I find that putting it on Aperture Priority makes this easy, just set my aperture as the same as lights (if using lens) or just on Programable (P)(Automatic) for a telescope.

[Benjamin (Ben)]

Many thanks Colin. This should all be in a beginners forum but appreciate the advice and it makes it all very clear what is required. I imagine taking flats close to the time you take the image is better given the possible variability of dust elements etc. in the image train. When do you take them? If the plan is to tack the photography onto visual observations I'm guessing I could do this while packing down at the end or while setting up at the beginning to avoid ruining dark adaption?