Kit test - (finding something to do on a cloudy night)

[Tim]

I have been gradually increasing the length of exposures I have been taking with a Baader 7nm Ha filter from FLO. The longest so far were 30 mins, but I really wanted to see if 60min was a viable proposition.

Trouble was last night, it was cloudy. It started at around 30% cloud cover, and increased to 60% and then finally wall to wall.

I am in the middle of a project on a nebula in Cassiopeia, but I didnt want to get test subs mixed up with those, so after seeing Roundycat's IC1805, and having that earmarked as my next project, I went for that. First a 30 min sub just to check things, and then 3 x 60 mins.

As it got cloudier, PHD was pinging away like mad, and losing the star for minutes at a time. I really didn't expect much from the image, as for most of the time, it was photographing clouds. But the 7nm filter did a good job of blocking the reflected light from the clouds, the only real evidence being plenty of noise.

The Starlight H9 mono camera coped very well with the 60 min subs, there was a bit of a glow along the bottom edge of the frame, maybe a bit of amp glow??? but nothing decent flats wouldnt sort out. The guiding behaved too over the course of the hour, even with gaps of several minutes without a guide star. The stars weren't completely round, but I think on a clear night they would have been.

Anyroad, here's the picture that rolled out from the four subs. Considering the continuous cloud passing over, I was very surprised with the result. Can't wait now for a proper night!!

Thanks for looking.

TJ

[SteveL]

60 minute subs! blimey... not sure i`ve seen 60 minutes clear sky in total this year...

[Tim]

I suppose they each had about 25-30mins clear sky exposure between the clouds.

There really hasnt been many opportunities for all nighters lately

[barkis]

Simply amazing is all I can think of to say Tim.

You certainly extend exposure times, and with good effect too.

That filter has some magic quality.

Ron.

[roundycat]

Tim, I don't know what scope you are using but my 1805 was 10m subs at f5. I seem to recall it was a bit misty as well so the data could have been cleaner. I did another a couple of nights later and the 60m mk ll was a lot better than the 75m mk l taken through the mist.

I just had a quick look at the mk ll and it seems a lot cleaner than your one above, don't know if this is the dreaded jpegging raising it's ugly head or not. One of the problems with long exposures is that unless you are watching every minute clouds can whip by and you never know. All that happens is you are rewarded with a noisy sub-frame.

I know this; if I had the choice between 10m and 60m subs I would choose 10 every time. Unless there is a problem recording any nebula at all at the shorter time (like with nb on some subjects) I never go above 15-20 minuttes.

I sometimes use my TMB at f8 and that makes recording faint stuff a bit chancy, all I do is take more of it. You cannot combine 3 or 4 hour-long subs in a way that will cancel out most of the noise. You especially cannot get rid of the sat trails and other stuff unless you combine a statistically meaningful number of sub frames.

You may well get some satisfaction from 'giant' exposures but your results will probably be better with shorter subs.

Dennis

[Tim]

Thanks Dennis. The sky was full of cloud, more cloud than gaps actually, which accounts for most of the noise. The first 30 mins was the least cloudy, i'll post that up when I get home as a comparison. It's probably better than the whole put together I think.

I am still in the middle of the Pacman, and noticed that on the 30 min subs for that, details come out which are simply not visible at all at 20mins, and so wondered what is the point when returns diminish.

The scope used is just a cheapy, WO72mm. I think it is around f4.8 with the flattener, not sure though.

I am hoping that the detail gained with a portion of long subs, can be added to those with shorter and mid length, and produce overall a clean image with added detail.

Again, thanks for the advice, much appreciated.

Tim

[minimalist]

Tim, that is very impressive, 60mins and no flex issues that show up. I see a bit of a greenish tinge in parts of the image, that that just me? I thought it was supposed to be grayscale, right?

Daniel

[Tim]

Should be greyscale Dan, but its 8bit jpeg from 16bit fit, who knows what happened in that process! Unless I forgot to convert maybe

There'll be no flex as I guide and shoot through the same tube.

Cheers

[minimalist]

Ahh, it may be my eyes then. Lucky you about the guiding, that's the biggest issue that's keeping me from trying longer subs.

Daniel

[James]

60 minutes I'm back up to fairly good 10 minute subs but can still see a little evidence of flexure. I tried a 20 minute the other night but the trailing was just too visible. *Sigh* I see I've still a ways to go...

Oh, nice pic by the way

James

[Tim]

This one is just the first two, 30+60min. The glow on the bottom is obvious, and the stars are a tad ovoid thanks to phd losing the star during a cloud pass and locking on to a hot pixel, so I've knocked them on the head a bit.

[Taff]

Nice Capture TJ' nice details there.Mark