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mindburner

last nights attempt at M51 with 1100D

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Hi folks,

Out tonight having another go at M51, with 800 ISO this time and no filter. I have set my scope up without PHD running again and using 120 sec exposures. So far the individual pictures look much better and I can see more detail on the screen in APT than I could two nights ago.

It's a bit misty here, so hope I can get an hour or two in before it's useless.

Clear skies everyone.

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As I understand it, darks should be done at the same time as subs in the same scope orientation - its temperature which is the key point here. Flats can be done any time after but scope must, must be left in the scopes imaging orientation. As many subs as possible,'ideal' minimum is 30 above which its the law of diminishing returns - as many as possible.

After imaging, stop tracking/guiding, cap on, shoot as many darks as possible - 15 to the sub quantity if you can. Then take bias if required - they are quick at 1/4000 so say 15-20 again. Flats again quick at 1/200 approx and 15 ish is ample. These are just guidelines. Its what time you have at the end and what the weather is about to do. I stay with it from start to finish but I am retired so time is not a consideration. One thing is that you can save darks for future use in temperature files - eg 5C 3C 0C -3C -5C -10C etc. Some I believe dump them after a year and start over! Don't know why unless its degradation.

I am like you - no space for an obs. The mount stays out and all other comes inside in a dry cupboard. Yeah, its a pain to lug it all out but I can do this in 15 minutes or so. Check polar align at dusk, fire up the s/w and your ready to slew to a single align and then target.

I'll bring the mount back into the garage if I know there is going to be a prolonged cloudy spell or if its going to get in the way.

Edited by obscura

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Hi,

Thanks for the advice on darks, flats and bias. My imaging session ended soon after posting last night when the mist completely obscured my view. So I did my darks and bias and packed up before everything got too wet.

I have a summerhouse next to where I observe, so my scopes go into a blanket box (very dry and safe) and I lift the mount + pier off the concrete block and put it on to a trolley, it gets wheeled in to the corner of the summerhouse. Like you say it's a bit of a pain, but I prefer to have it all put away everytime. It's also in Mrs DrR's way as well if I leave it out.

I tried processing the 20 lights from last night but most haven't shown enough detail due to the mist and what's left didn't stack to give a better result than two nights ago. A bit disappointing, but that's the way it goes.

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I think that the summerhouse isn't really making efficient and effective use of the ground. Perhaps it falls down one night and an obsy appears in its place? I am always in the way no matter where but anything for peace.

I had a try a couple of nights ago and abandoned after an hour or so due to haze. Tonight looks good - and its blowing a gale. Maybe tomorrow.

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Hi,

Like Gina's obsy I worked for around 8 months building the summerhouse and decking, so don't think I could really pull it down. It's actually quite handy, I have power in there, my server and a nice leather sofa, plus it's warm and dry and secure.

It's great here, no mist, the wind is dropping and it's crystal clear. I have to get up early tomorrow and I can't make tomorrow night, but the forecast for Sun nite looks good, so I am pinning my hopes on then.

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Hi DR Robin. I have noticed that the subs I am taking tonight are much more noisy than tha the subs from last week. I think the hot weather is to blame. Last night it was so warm after 12 that the first sub I took was like 'join the dots' there were so many noisy pixels. I am currently trying to image m106 and in my logcabin in the back garden.

Like yourself I have to tow the NEQ6 out to the observing site on my homemade trolley, carry out the scope and I also have a tea trolley type effort that I use to hold the laptop and spare batteries etc.

I have got it down to a fine drill, but it's a bit of a pain sometimes.

Did you manage to get any more subs of m51. Your image was very sharp and I think if the the subs were increased, a lot of the noise may be cleared up.

I am working on a DIY cooler at the moment, with some limited success. Like Gina, I am having issues getting the actual peltier sorted out.

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Hi,

Thursday night turned out to be a complete loss. Before the mist rolled in completely I only managed to get a few subs and the contrast on them was poor. I think I have to put the filter back in.

Also I need to get PHD working. I have made a bracket to allow metro put my finder guider scope on to my C11, so it should be good to go.

I have been away sailing this weekend, but it looks good for tonight so will get set up and give it a go.

I have never played with a Peltier cooler, but if you get stuck on the electronics, remember I am an electronics engineer, so if you need any help with anything let me know.

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hi

PHD is a super program. Just don't get the latest beta version as I found it just kept saying 'star saturated' even when it was ok. THe older non betawas fine though. Caused me a few nights hassle that one.

I may take up your kind offer of help with electronics. I am building an old school bench PSU using 4x power transistors. I got it running fine with low current/ low voltage draws but it died on me upon pulling 4A. The circuit is supposed to be good for 10A. The transformer I have is a good quality 9.7A toroid. I am in the process of replacing a dead power transistor and driver transistor, hopefully it will fire back to life then. Although the current adjustment didn't seem to work 1st time around.

Anyway just if you had a minute to look it over

best regards

Hi,

Thursday night turned out to be a complete loss. Before the mist rolled in completely I only managed to get a few subs and the contrast on them was poor. I think I have to put the filter back in.

Also I need to get PHD working. I have made a bracket to allow metro put my finder guider scope on to my C11, so it should be good to go.

I have been away sailing this weekend, but it looks good for tonight so will get set up and give it a go.

I have never played with a Peltier cooler, but if you get stuck on the electronics, remember I am an electronics engineer, so if you need any help with anything let me know.

Edited by mindburner

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Hi,

I was out last night until 01:30 getting some good subs of M51. I had a go with PHD, but it kept loosing lock on the star so decided to take some subs without it, about 25 to be exact.

I then decided to give PHD another go, didn't change anything and it just worked fine, so rattled off another 35 subs. DSS is just trying to make some sense of it all now whist I get on with some work.

Yes send a copy of your circuit, either post it here or send a private message, which ever you prefer. Or send it direct to my email which is anything at drrobin.co.uk.

I once designed an old school linear power supply, a class D (PWM) power supply and have designed a couple of switchers as well. Actually, if you want the best smoothing, make a battery charger (linear of course) and float charge a battery, that gives you a very smooth output and gives you a battery backup if someone pulls the plug. Batteries are also good at delivering high pulse currents, typical of what your motors might draw. Anyway I am rambling now.

Robin

Edited by DrRobin

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great being out isn't? I was very tempted but after 2 nights back to back until 3AM, I decided to catch up on the ZZZ's

I got an ok image of the eagle nebula over the 2 nights with lots of nebula coming through, although a bit too much red data

Your m51 should come along nicely now with more data. DSS does a good job of producing a nice clean output. Although it can loose some of the finer detail. I found that the final image can look very grey and washed out, but once saved and brought into say Photoshop, the image was ok.

The main issue I had, apart from it packing up after a while was the current control had no effect, despite the fact that I had checked and confirmed the circuit was wired correctly. I then though maybe there is a fault in the schematic. Very interesting about the batter charger. There may be ways to improve this circuit with smoothing.

here's a link to the circuit

This is maybe off topic but hopefully others may find it interesting.

Edited by mindburner

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Hi,

Thanks for the link, I had a look at the circuit and the most likely cause of the problem is that one 2N3055 has been taking all of the load, with the other three mostly not doing anything.

I am guessing that the 2N3055 that has gone has a short circuit between base and emitter and that would have caused the BD139 to blow as well.

The problem with parallel up four 2N3055s is that it is very difficult to get them to all take the same drive current, ideally they should be matched transistors, from the same batch and the emitter resistors should also be matched.

I checked the specs on the 2N3055, it is good for 15A and 115W power dissipation so if you only need 9A, it might be okay with just one. If you let me know the toroid voltage and the ouput voltage range (9-12V or only 12V?), I could work out a few figures for you and check maximum power dissipation.

You will also need a fairly good heatsink for the power transistors and I suspect a heatsink for the resistors, plus probably a fan. Power resistors are available in aluminium bodies, suitable for mounting on a heatsink.

If you are just after a 12V output at say 10A, there are probably more modern designs that would be more suitable/stable/less likely to blow up. You can keep your transformer and just change the control electronics.

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Hi,

Thanks for the link, I had a look at the circuit and the most likely cause of the problem is that one 2N3055 has been taking all of the load, with the other three mostly not doing anything.

I am guessing that the 2N3055 that has gone has a short circuit between base and emitter and that would have caused the BD139 to blow as well.

The problem with parallel up four 2N3055s is that it is very difficult to get them to all take the same drive current, ideally they should be matched transistors, from the same batch and the emitter resistors should also be matched.

I checked the specs on the 2N3055, it is good for 15A and 115W power dissipation so if you only need 9A, it might be okay with just one. If you let me know the toroid voltage and the ouput voltage range (9-12V or only 12V?), I could work out a few figures for you and check maximum power dissipation.

You will also need a fairly good heatsink for the power transistors and I suspect a heatsink for the resistors, plus probably a fan. Power resistors are available in aluminium bodies, suitable for mounting on a heatsink.

If you are just after a 12V output at say 10A, there are probably more modern designs that would be more suitable/stable/less likely to blow up. You can keep your transformer and just change the control electronics.

That's fantastic. Ye only one of the power transistors was dead, the other 3 were ok, so it took the bullet. Your description makes perfect sense to me.

The heat sink I am using is a solid block of aluminum with the transistors bolted to it. I may mount a small fan to it to help with any heat issues.

The resistors sort of float in mid air as I have them soldered directly to the transistors and the other ends commoned.

Here is the spec of the tranny from RS

Yes I may be better with a more modern design than this. I chose it because I was at least a bit familar with the concept of it and it seems easy to build. WOuld you have any better links to more robust designs that I could attempt with my basic circuit skils

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Hi,

I would have a look at an LM338T (or similar). It is capable of 5A (7A peak), but depends on your voltage differential. It's fully contained and is thermally and over current protected.

If you need a total load of more than 5A, just add a couple of devices in parallel, but don't common the outputs, just have separate feeds of 12V, 5A each. Best of all they are cheap (sub £2).

Seperate feeds would be good as far as noise and stability is concerned, run your mount off one feed, the Peltier cooler off another and your imaging cameras/guiders off a third.

You can keep your toroid, rectifier and smoothing circuits and there isn't much to connect after that. No power resistors to warm up and less thermal issues, just mount the regulators on a good heatsink and away you go.

BTW, a metal block isn't always a good heatsink. It can soak up a lot of heat, but if it can't dissipate it to the air, it just gets warmer and warmer, until you go over maximum temperature. A heatsink with fins is the best, these are probably easily available as add ons for fast processors and will have a fan.

My first stack of M51 (25 out of 60 subs) was a little lacking in detail, DSS chose a lot of frames from earlier in the evening where there was a lot of light in the sky. I am currently re-stacking, forcing it to use the later frames.

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Hi,

Okay, second stack of 23 frames and then processed is attached below. I think it is better than may last attempt. I have refined the images in DSS and it is currently stacking 15 frames, which may or may not provide a better image.

The bottom is cut off as M51 drifted before I got PHD working correctly. The next stack doesn't use these frames.

Stack of 23 on the left, 15 best frames on the right, vote for your favourite!

post-23264-133877780716_thumb.jpg

post-23264-133877780726_thumb.jpg

Edited by DrRobin

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2N3055s are not very efficient, have low gain and belong in the Ark. I used them for my heavy duty battery charger purely because I already had them.

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Hi,

One last stack of M51 from last night. This time 20 frames, picked the best first (jpg viewer) then stacked in DSS. I think it is the best of the lot.

post-23264-133877780789_thumb.jpg

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Excellent! Weather conditions must have been far from perfect.

How many calibration frames did you manage to get at the end.

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Hi,

5 darks and 5 bias, no flats as I am not set up yet to do them. I probably should have taken more darks but after fiddling for ages with PHD, I was running out of time.

Only my second try with the 600D and M51, so pretty pleased.

It's going to have to be a weekend job from now on, it just gets too late as I reckon it's not dark enough before 11:30.

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That really is good then if only 5 darks/bias. How can my 120 frac compete with your 8" and 11" scopes? Back to the drawing board.

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Hi,

Do you take Flats and if so how do you do them? I have been looking at an EL Panel.

I have a further 3 darks and 5 bias from two nights, the set up was the same and temperature was within 1 or 2 degrees. I am guessing I could also use these?

In total I took nearly 60 lights but discraded around 35 due to PHD not running (small star trails) or background too light. Not sure what the recommended lights to darks to bias to flats is?

About 1 to 4?

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You can use darks from previous sessions if all is the same but specifically temperature. Needs to be the same as the subs.

Darks - I did try to equal sub count but DSS reckon 10 -20 each of darks, bias, flats and I follow that as high as I can.

Flat panel you can make yourself very cheaply.

2 x 48 12V white led pack from ebay - a few pounds (car sort)

White opal perspex also from ebay. Need enough to cover two apertures.

So three layers

Bottom - 2 x 48 white leds

Middle - First opal perspex layer

Top - Second opal perspex layer. (the scope aperture sits on this one)

Make a cardboard mockup to get the gaps right so that you end up with a nice even flat glow on the upper perspex.

I built mine from thin mdf but many here in SGL build them from that white foam board.

I use this white foam board to line the inside of my box and one thickness is enough to support the perspex. Make sense?

There are a few threads in SGL that may explain much better than I but its a start point.

Edited by obscura

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