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The fickle nature of imaging


Anweniel
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After a bit of a PB with Sunday nights M109, a bit of a low tonight. Started with some awkward trailing issues leading me to drop exposure times to ~30s after boasting of 2 and 3 minute exposures just a couple of days ago this was bit of a let down tbh. After a stray leg knocked the mount a put things even further out I decided fate was telling me something so knocked it on the head early this evening.;)

Target tonight was M81 + M82 and in retrospect I think I used up all my luck locating them as I was expecting to do a lot of hopping to find these, aiming generally in what I thought was the right direction, a single exposure revealed fairly clearly in the liveview Bode's! Can never be this easy again I am sure!

Anyway I will drop the resulting stack of a dozen 30s exposures to show how some nights a plan doesnt come together, no George Peppard moments tonight!

Was hoping to sort out my Flats issue but since the data was pretty worthless I have forgone the calibration pictures tonight ;)

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Hi, I see you're learning that none of this is easy. I'd suggest the biggest single thing to get sorted is some sort of autoguiding. Without that you'll always be limited to the 30secs or so and as a result you'll wont get the data you need. You got the focus and framing well sorted. Flats etc wont really add an awful lot until the guiding is sorted.

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I have to agree... you'll be limited in exposure length for this pair with an AltAz mount. Looking at the image, it looks like you've got some rotation effects anyway... it may be that 30s is a bit too long... how does each sub look ? It's also come out a bit green... not sure why. A good effort with the kit you have though. Galaxies can be pretty tough targets when you have an autoguided EQ mount...

Edited by jgs001
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oh the individual subs are terrible. It all seems really to depend on the night as the PA is pretty rustic, I tweaked the levels a little just to bring out the detail I didnt make much effort though considering what I was working with, hence the greenish hue. Some reason a little weight to the green seems to make some detail jump out a bit more for me. Im sure another night I can get the longer subs going on these it seems a bit hit and miss to me but the funs in the trying ;)

CGEM is on the list no question of a doubt but making do with what I have at the moment is probably putting me in good stead for when that time eventually comes. Its very easy for me now to just keep rolling out the excuses, alt/azi mount, terrible LP, unmodded cam, inexperience etc etc but its no good if you dont try to improve which is what I am aiming for just seems tonight has been a 2 steps back rather than one forward but its all part of the process I guess ;)

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Do you rebalance every night, and are these with the Megrez ?? If so, it's simpler... but either way, you want the tail to be slightly heavier, it ensures the gears engage constantly. I was able to get 60 seconds consistently with my NexStar until I properly balanced it, when I was lucky to get 10 seconds.

Persistence will get you good results... but be prepared to work hard at it... you might want to consider (once you've got that trailing under control) aiming for 120-150 x 30s subs... that will net you a surprisingly large amount of information, even with an unmodded camera.

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Thanks for the advice John, actually I do rebalance each night as I take teh whole scope off including dovetail and rings. This is so I can take the flats with the imaging train unaltered. I always tried to balance it dead centre but had fears some gear slipping was happening, just assumed it was just a bit much weight for the mount.

I never thought to shift weight slightly to tail so thanks for that advice I shall do this from now on.

Aye I think I have been working a bit harder lately trying to iron out the issues work out what has been right what has been wrong and what to do to improve. I think I discovered that levelling on the alt/az is essential to get pretty spot on as it seems to track MUCH better level than if its slightly out and I have attached a bubble to make sure I get this as good as pos, the eq mounts are, as I understand, much more forgiving of level tripods.

30s seems a pretty consistent sub length to get good results from as you say I also think that due to the lack of stability in those telescopic legs its taking a lot longer than you would think for the whole system to settle and I tend to leave it a good hour before trying to push on the exposure lengths (also gives lovely time for the optics to cool down ;) )

Must admit I havent given enough data to any of my images yet and a long night winning hard got data is on the cards.

Again thanks for all the help it is appreciated

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Very true.... levelling is critical on the little AltAz mounts. Also, drop the legs to their lowest position... it's not really too important for viewing with anyway... you want the system as stable as possible, short legs on the tripod is more stable.

You don't want to put it too much tail weight, just a smidge, enough to ensure the gears are constantly engaged, that the mount is always lifting against something. eq mounts are indeed more forgiving of being level, but it doesn't hurt, and is good practice anyway. You should be able to push the sub length if you're working low in the east or west... low can be a bit of a challenge of course, thanks to the thicker atmosphere you're imaging through... swings and roundabouts really... I did manage 2 minute subs with my NexStar, but as I also lost 50% due to drive train errors, it really wasn't worth it... an interesting experiment though. As for flats... why dismount it all ? Just point the scope horizontally whilst still mounted.

Once I'd got my NexStar working nicely again (after trying to improve the balance... ) I didn't dismount the scope, until I got my EQ mount, there wasn't really a need, I found it all light enough, it was easy to cart around fully setup.

I've never, with my fracs, worried too much about cooldown time... generally it's been pretty good within the time it takes to setup., and I don't think I ever waited for more than 20 to 30 seconds for the wobbles to stop... might be worth looking at tweaking the leg bolts if it's that loose.

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Being boxed in, in my little back garden means I cant get away with dropping the legs too much but they are as low as possible.

Im surprised mainly with the 3 minute sub because it was so good and contradictorily it was high in the sky, approaching zenith when I made it.. thats why I was a bit baffled by it ( but very happy ofc!)

i have to dismount as I prefer to take the flats inside and to get the setup inside I have to go through 2 doors very close to each other at 90degrees and its very awkward, I would love to leave it setup but traversing those doors is a nightmare without removing the OTA from the mount plus with a 4 year old runing round the house I prefer the equipment packed away when not in use. Taking flats outside may be problematic too as the sodium street light I have a the back of the garden reflects an orange glow off everything, even the walls :)

I probably do go overboard with the cooldown nowadays but its less hassle I guess than refocussing after an insufficient period, everything is tight ( as far as I have checked - I think its everything !) but it does seem to produce better subs over time or perhaps its just my imagination only nore experience and playing will tell.

At least from your advice I think I have everything covered so hopefully it will all get over. Lets see eh :)

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People don't often realize how much work you have to put into getting good results and all the different aspects that make for a good session. Its been a while now since I got into all this and I have lost count of the many cold cold nights spent outside till 2am trying to get it right. You reach a point when guiding becomes essential for those harder targets but you can go a long way doing unguided subs before that happens.

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