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Old 09-03-2015, 03:46 PM
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pfitzgerald (Paul)
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Join Date: Jun 2013
Location: Melbourne
Posts: 625
DSLR: ISO, Exposure length & Data quantity - help sought

Hi Folks

As per the title I'm hoping that some of you have already been down this path before me and will be able to offer some guidance to make the most of my time at the upcoming SV-Astro Camp. So here goes.

At the SV-Astro Camp (20/3 - 22/3) I have two targets that I'd like to image over the Friday and Saturday night. NGC 3372 and NGC's 3293 & 3324.

My set up is a SW ED120 BD refractor with Orion guidescope package - so far I've been able to set it up in my suburban driveway and take subs up to ten minutes in length without any star trail/bloat. My camera is the Canon 60Da with an Orion x0.80 focal reducer and field flattener attached that brings the scope down to an f/6.0 and I've been running the camera using its power adaptor, rather than its battery. As all Melbournites know our LP sucks when imageing to the south from the northern suburbs - so it's a bit hard to determine the camera's sweet spot.

Mostly I shoot at ISO 800 and subs of 180 sec or 300 sec. Shooting flats, darks and bias frames isn't an issue - over the next week or so I'll build up a bank of dark frames that will hopefully cover the temperature ranges I'll encounter at SV. They'll also cover 180, 300 and 600 sec exposure wise. For combining subs, flats and darks and aligning I use Nebulosity 3.0 and then export the result, after an initial stretch, into Photoshop CS5. All of this I do on a MacBook Pro.

Ok - hopefully I've given you all enough info to help me solve the main condundrum. That is:

1. Have I chosen the best ISO setting for my chosen subjects?

2. What should be the length of my exposures? (This will be my first time imaging from a good dark sky location so I'm not sure about this wrt SNR)

3. What would be the optimum total number of light subs required for 1. and 2. for my chosen subjects to maximise bringing out the nebulosity of these DSOs in the processing process?

4. Should I also include some shorter exposures so that the brighter stars in the images aren't burnt out?

Any advice/suggestions would be much appreciated.

T.Y.A.I.A.

Paul

PS No new AP or Astro equipment has been bought leading up to this event, so weather wise it should be a good weekend.
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