Art Gecko

How far does that push the histogram spikes to the right? I do agree with keep the ISO as low as possible to help the SNR, but as I'm not getting the length of exposures you guys are getting, I have to push the ISO up to get a clear gap between the left hand edge and the start of the spike... If you're both using around 800 I might have to bump it up as high as 6400 to gather that light!

Nice shot Bob, out of interest what ISO are you imaging at? I might join the fun on this target tonight if it stays clear as I've never even tried finding it before!

I'm afraid I use Lynkeos for stacking as I'm on Mac... I did get DSS running through wineskin, but my poor Mac is so old it'd take a month for DSS to stack 250 subs!

M100 and co. 250x15s subs, darks and flats applied. Shame I didn't pick out the 2 subs with the satellite streaks in them, D'oh! Definitely liking the shorter exposures as 62.5 minutes is the longest total I've had so far with my DSLR.

wimvb's argument stands as far as i can see... when you look at a graph of SNR over time, longer exposures win! On the graph above (which I can't take credit for creating, sorry if this is a no no and please delete if I'm in the wrong for posting it) you can see how longer exposures have a better SNR over time... the problem with my set up is I'm not autoguiding... even as I sit here writing this, my camera is outside taking shots and I have no idea if they're good or not... my target area is about the thickness of the curve line on the graph, which means I'm open to drastic amounts of noise whether my shutter is open for 10 or 30 or 60 seconds... the only real variables are polar alignment, wind (and other vibrations), and the quality of the camera sensor... And how picky I am over my subs when I stack them... which is where I feel I've made the most improvement recently. I'm now quite picky, I'll sacrifice a sub that isn't quite sharp enough to my eye so that it doesn't detract from the final picture, whereas I used to just let the computer asses the quality and stack them blindly... but the computer doesn't necessarily see things the way I do.... everything is a juggle for me in this game, it's fun to experiment to see what the best you can get with what you've got is... and that's what this thread is for, is it not? I'm so glad you pointed me here @bobro thank you

Well Bob, the best summery I can come up with is that the 50s subs had a better general luminance, but because there were only 22 subs and no darks, there was simply not enough data to remove the noise... Whereas the 10s subs had 136 frames to remove the noise... but lacked in luminance... Not sure if raising the ISO would actually help with this or whether it would bring the noise level up to a point beyond it being worth it? In any case I like the way the combined exposures compliment each other in the final image.... Unfortunately I still wasn't happy with the final image so I did another one! (cropped version to show the extra detail in the core) Probably going to be out imaging again tonight (got to make the most of the weather!) so I might try 15-20 sec subs and see if I can get the best of both worlds.

.... and let's face it... I was always going to do a composite of both!

The results of my experiment are in! So, as I said before, this is 2 shots... one taken with 50sec subs and one with 10sec subs, no darks, 30 flats. I gathered a total of 50 mins worth of exposures for each set. ISO1600. Each image was processed very simply using nothing more than curves and levels (black point eye-dropper in levels to set the background luminance)... so no complicated processing techniques used at all! 1st: The set of 50sec subs came out at a total of 18.33 mins (36.6% of the total subs) 2nd: The set of 10sec subs came out at 22.66 mins (45.3% of total subs) So, not much difference between the total time to be fair... But very different outcomes. I'm still not sure which one tips the scales?

Beautiful image Nige! Good to see you got the NR sorted out!

That's pretty much how I understand the theory as well Bob, you're right I will have to make sure it's as controlled as possible all the way through... I can use the same set of flats, but darks would have to be taken separately for each session... so do I get the same number of darks? or go for the same total time value? or sack off the darks and just do flats?.... also, as you say, the processing will have to be duplicated.. I think there's a way of saving the processing information and applying it to another image in photoshop.... I don't know how to do it yet... but I'll look into it.... otherwise I'll go for a simple stretch that I can duplicate myself and compare the difference. Art

I might do a little experiment tonight, since I do my imaging unguided I tend to throw away a lot of my shots as they're not up to scratch... So I'm thinking I might pick a nice easy but interesting target like M51, spend an hour imaging at 45-50sec subs, then spend an hour imaging at 10-15sec subs and stack them as two separate images to see which one has the longer total integration time... Will have to make it fair though, so if I say session1: 50s subs, 10s delay... 1 hour in time, means 50 mins worth of subs. session2: 10s subs, 5s delay... 1 hour in time will give me 40 mins worth of subs, so if I spend 1 hour 15 mins I should get the same total of 50mins to compare against..... I'm simply interested to see which set will yield the longest total exposure after stacking, but also what effect the shorter/longer subs have in the final outcome in terms of signal/noise. This is purely for my own interest really, but I'll post the results if anyone is interested.

Nice capture Bob!

Thanks Bob, I know what you mean about the blue.. I didn't boost the saturation at all, I heard somewhere that having focus slightly off infinity boosts the colour somehow? Might be what happened here as I really struggled to keep the saturation down with this one... But I do like the variety in the star colours! I edit in Photoshop, I've no idea what the differences are between that and GIMP, but I'm always adjusting the levels of individual channels to keep the RGB histogram balanced, then color balance controls to adjust the hue of each colour in the highs and lows to stop any one colour from taking over... I know this shot doesn't give a particularly good example, but my M51 shot (a page or two ago) was processed more or less the same way and shows a better balance... the way I see it, if the colour is there, go with it... if it isn't, don't try and push it too far!

My offering from last night.... M101. 52x50s subs plus 15 darks and 35 flats. Ever so slightly off with the focus on this one, hence the double diffraction spikes if you look very closely... My bad really as I should have kept checking it, but I'm blaming the hazy cloud while I was setting up Still, didn't turn out too bad. Art

That is a Top Tip!! Thanks Bob, I'll give it a try.. is there any particular reason you used ptfe? Art

Nice job! I do like the sombrero! It's not a target I've managed to get myself, hope to one day but it'll have to be away from home as neighbours houses block my view

I'm afraid I've only got the basic EQ3-2 mount with motors and polar scope, but I've been looking into modding the controls so I can think about guiding... big plunge though for me with limited funds to make it all happen.. lots to buy! I do agree though, the top tip is good polar alignment and balance... I've had problems with my collimation lately, something else that's important... the problem is my focuser drifts either side of centre, whether I'm reeling in or out, and it effects the coma quite badly if I don't get it spot on... I guess that's one of the many troubles with budget AP... a better focuser will cost me the same as a better OTA

My computer can't handle RAW simply cos it's a 10yr old mac-mini and that in itself is a problem for astrophotography... most computer programs written for AP are windows only... DSS is windows only... unless you patch it through wineskin, which I tried, but because the mac is so old with only 2Gb memory it literally takes days to process even jpegs... I tried it with RAW data once... about 50 subs with darks and flats, left it running while I went to work for the day.. when I got home it had an ETA of 132 hours 45minutes... so I switched it off and carried on using Lynkeos, which is mac friendly and only takes me an hour or so, but not RAW compatible... that's my reason anyway, hope that helps Art

Thanks Nige, it's a lot smoother than before, so much nicer to process! One day I'd like to start guiding myself, but not much point while I'm still shooting jpeg.. got to prioritise what I spend out on first! Is yours a Goto? Or modded RA and Dec motors? Your sombrero is looking real nice with the added data.. one of my fave galaxies!..and 120s on the Pinwheel!! Nice!! I never go above 60s! Looks like you might have clipped the background a little in processing though? I can see mottling around the galaxy edge, I've got this myself in the past when trying to push the gradient removal too hard... not that I'm any kind of authority on AP! It's all personal taste in the end, but thought I'd mention it as it improved my shots (I'd like to think at least) when someone pointed the same thing out to me .. still a fine job mate, well done!

This was a test run to see if my computer could handle a small jump from Normal to Fine quality jpeg (a new PC is needed before I can start shooting in RAW)... seemed to work, just took a little longer! 44x30s with darks and flats. M106 and friends.

Nice shot Nige, the Sombrero is not an easy target from the UK, you must have a good view to the south! I also agree with Peter, it's very worthy of the SGL challenge!

Managed to get out and do some imaging a few nights ago in between the cloud blankets, it was a 99.8% full moon so I picked a target a good distance away: M51 I have been experimenting recently with shooting in RAW, but I'm afraid my computer is very old and simply can't cope with it, so alas this was shot in Normal quality jpeg. So this is 63x30 sec subs at ISO 3200 (total 31.5 mins) plus 25 darks and 35 flats... Typically had to throw away over half my subs, but that's normal for me operating without autoguiding... and all part of the fun! Hope the colour balance looks ok... I always find there's a difference when viewed in browser and with varying devices... my favourite is the wider field shot but I've included a cropped version for those that like a close up. Comments and critique welcomed. Enjoy, Art.

Ok, so I didn't make it out tonight to get that better shot.... My T-ring had arrived when I got home from work, so I tried the DSLR on the scope... As I figured, it didn't reach focus and my scope is now in bits as I figure out a way of rebuilding it with the focal length extended enough for the camera... But I did manage to get a shot through the telescope with my iPhone and this one isn't processed on the pc.... so here's my entry to STUpod.... an iPhone image through a telescope...

Very True!... In that case I might have another go tonight... It was pretty hazy last night where I am, Metcheck astronomy weather forecast said it was 30% high cloud coverage... tonight it's say 4% so hopefully better seeing conditions

Haha it's a good shot..... But I'm not sure it's THAT good!