I think I've found my niche. The laziness of unguided astrophotography out the window is my thing.
First pic is open cluster NGC 5460 in Centaurus. It's interesting as it has a little galaxy on the left called PGC 50448 and another fainter one embedded PGC50388 (thanks Ron). Of course the galaxies are distant background objects, not in the cluster itself.
Bintel 8" F4 Newtonian, 55 x 30 seconds, HEQ5 Pro unguided, Pentax K-5.
Bigger at Astrobin. http://astrob.in/172126/B/
Second pic - Centaurus A. Bintel 8" F4 Newtonian, Baader MPCC MKIII, 196 x 30 seconds, HEQ5 Pro unguided, Pentax K-5.
Bigger at Astrobin. http://astrob.in/172311/0/
Centaurus A was discovered in 1826 by Scottish astronomer James Dunlop in Parramatta New South Wales. Distance is 10 - 16 million light years. It's the 5th brightest galaxy in the sky and a massive radio source. The center of the galaxy contains a supermassive black hole with a mass equivalent to 55 million solar masses. Stole that from Wiki. It's quite a fascinating object.
Third pic - This is NGC 6231 in Scorpius, taken over 3 nights between clouds. Wiki says this is also known as the northern Jewel Box. The cluster is estimated to be about 3 - 5 million years old. Very young compared to our own 5 billion year old star.
Capture details: 137 x 30 seconds in the cloud gaps, 8" F4 Newtonian, Baader MPCC MKIII, Pentax K-5.
Bigger at Astrobin. http://astrob.in/172705/0/
Fourth pic - Good old M7 with dark dust lanes. The usual gear. 36 x 30 seconds.
Bigger at Astrobin ---> http://astrob.in/172388/0/
Thanks Ray. Well why not. As long as we're having fun! I think we make up for a lot of the short falls of being unguided with lots of subs. Big fat, fast, low F ratio light buckets help also.
Why the 30 second subs? Multiple reasons, first of all up here in hell, I mean the tropics, it gets hot and stays hot all night. According to the experiments I've done the single largest contributor to thermal noise when it's hot is time. 1 minute subs have twice the thermal noise at 30C of 30 second subs so why bother? Winter may change this for a short while during June/July.
The second reason is cloud. We get layers of cumulus at night that sweep over. Shorter subs means I can shoot in the cloud gaps. All of the above pics were taken in cloud gaps. Guiding would not have been possible due to constant loss of guide star.
Third reason, tracking error. While I can get 1 minute subs without guiding, the percentage loss of subs is greater. My two cats have been known to ruin a few subs too lol.
Fourth reason, the K-5 has an inbuilt interval timer. It only works up to 30 seconds. Yeah I know external ones can be bought. It's on the list.
Fifth reason, at F4 here in light pollution land, 30 seconds hits the noise floor anyway.
Sixth reason, it's just so easy! And I'm lazy lol. I have tracking gear and may drag it out during winter, if we ever get any.
Yeah, great excuses Kevin. You can help yourself with a $20 intervalometer from ebay, as long as you remove the batteries when not in use. A small current flows even when turned off.
raymo
I often do 30 sec subs too - for some of the same reasons, especially the one about being lazy. One less thing to set up. Hey - but at least I still take my scope outside .
I just noticed the similarity between your 6231 and my 4755, both
have a smallish bright cluster in the centre of a packed star field.
You have a carbon star, and I had the prominent red star in 4755,
but unfortunately it is obscured by a diffraction spike.
raymo
Thanks Dunk. I can set mine for as many subs as I want. I usually do 30 at a time. Another drawback of doing intervalometer shooting is lack of dithering. When I did it manually I would dither every 3 subs or so to reduce repetitive noise. I dither 3 times per session my preset way but it's not enough.
And yes lots of subs = lots of storage space and time in DSS. But it's the only way with cloud. I shot 5 targets last night. Long subs would not have been possible. Too cloudy. It will take a couple of sessions to finish them but I'm amazed I can shoot anything in this weather. It rains every night yet I can still shoot between showers. I don't think any of the other locals are game to take the scope out!
Why the 30 second subs? Multiple reasons, first of all up here in hell, I mean the tropics, it gets hot and stays hot all night. According to the experiments I've done the single largest contributor to thermal noise when it's hot is time. 1 minute subs have twice the thermal noise at 30C of 30 second subs so why bother?
Twice the exposure time gives you double the thermal current but less than twice the noise. It's actually SQRT(2) or approximately 1.4 times. The big advantage of longer subs is that you start to overcome the read noise which is often considerable.
Rick, what does read noise look like? Isn't it subtracted by darks?
Hi Kevin,
Read noise is random, like shot noise. It adds an amount of uncertainty to every pixel value. In luminance this will appear as a speckle or roughness in areas that should be smooth.
Read noise is incurred each time you read an image from the sensor. If you had a sensor with no read noise then stacking 600 x 1 second images would give the same result as stacking 10 x 60 second images. There is no way to remove read noise. The best you can do is make your subs long enough that the effect it has is negligible.
Darks are used to subtract dark current. Dark current has random noise associated with it as well.
Thanks for that Rick. I suspect with my DSLR that by 30 seconds it's already overwhelmed by noise from everything else. At least in summer. Different story in winter.
.
your and raymo's recent posts are making me appreciate open clusters a bit more 
