M51, ten minute exposure

Hi,
I was out last night as we had a clear sky, I tried imaging saturn but the seeing was just terrible, I couldnt figure it out until I went outside the dome and realised that a strong wind was blowing.
So I tried imaging some deepsky stuff instead, the wind did occasionally catch the dew shield as you can see form the below image (stars not perfect).
This is a single 10 minute exposure with the 300D on the whirlpool galaxy, the orig image is very slightly bigger but was cropped out., I had to use a IDAS light pollution filter to help with light pollution, the rising 3/4 full moon didnt help either, the sky was start to get a slightly blue hue to it.

www.irishastronomy.org/user_resources/fi...600-008_a%20_m51.jpg
You may need to turn your monitor brightness and contrast up full to see this.

Some dark imperfections are also visible, I put this down to dirt either on the filter or camera chip, either way there was no way I was cleaning it at 2 in the morning, and the battery was dead before I got a chance to try and take some flat images.
I actually took a dark frame for this but found that the red thermal noise induced in the dark frame was no where near as much compared to the galaxy image, no settings were changed and the dark was taken immediately after the main image, hence the wierd background colours to the right of the image.
In my tired state at 2.15am in the morning when I took the image, I forgot to set the camera to raw mode and imaged in the low res position instead :oops: so maybe the camera processed the image differently before it sent it to the pc, its one to follow up on.
I did some minimal processing in photoshop, levels/curves....

I autoguided with the lidl skylux piggybacked on the 12", I used a 3x barlow and the toucam with guidedog to do the job, with a small bit of work i got guidedog working but found it was overcompensating, so I reduced the compensation amount and seemed to work best at a value of 10, but it still wasnt perfect.

The canon battery is really starting to let me down with these long exposures, I took over 5 exposures which amount to over 40 minutes and the battery was almost flat, Just as I'm getting into it, the bloody thing dies, I'm going to have to get one of the ac/dc converters for this and retire the battery from this use. I'd built it myself but I dont have a spare dead battery to fit into the compartment.

So its clear whats needed here, 40+ of these exposures stacked should give a very good image, that amounts to over 6.5 hours of exposures, and then there are the flats, darks and all that. If I removed the IDAS filter it would help but then skyglow comes into it, maybe I'm using the wrong filter, any thoughts??
Using filters with this kind of imaging is really showing the insensitivity of the 300D, a proper ccd camera would be the job here.

Dave, that's a good effort under windy skies.

The canon battery is really starting to let me down with these long exposures, I took over 5 exposures which amount to over 40 minutes and the battery was almost flat, Just as I'm getting into it, the bloody thing dies

I find this also with the canon battery, 45 mins is about max time in the cold, I think this holds 1100mAh, I have also 2 other non-canon batteries which fit the 300D, and have 1500mAh - 7.4Volts of power, but beware, always keep an eye on the buggers!

Keith..

Good job under such poor conditions, Dave.

On my second monitor I can see the dust motes you refer to. I dont think they are on the chip. I have the same problem and cleaning the chip didnt change the position of the dust motes, so its in the optical train somewhere (at least on my setup).

There is a little trick which you can use to get the values right in guidedog. Set the value way too high and what you see is that when it makes a compensation in one direction, it immediately makes another in the opposite direction (cause its over corrected) not just keep reducing the valueuntil it doesnt do this anymore. Alternatively try guidemaster which auto calibrates and sets these values for you.

As for the darks, one is no good, you need the average of at least 6 - 10 to be useful.

I'm looking forward to seeing what you can get when you're in a position to take dozens of these images, with flats bias and darks frames etc.

Keep it up.

Dave

That's pretty good tracking for a 10 minute exposure.

I think your imaging train needs a thorough cleaning to get rid of the dust motes - flats may help but there's a lot of debris there. Judging by their size, I'd say they're close to the chip. Perhaps the Barlow too (or was that just on the Skylux?).

I found that taking images during the day (cloudy or not) really highlighted them. I took each part out, startting at the PowerMate, cleaned it and then reshot an image. If the motes were still there, I took the next closest item to the CCD (the IR filter)... and so on. The CCD was the last item I had a go at.

Dunno how viable this is for you, but the DSI rarely comes off the scope now - that way there's no chance of any crud getting in there.

Those red spots are pretty ubiquitous. What are they from? Are they hot pixels?

There also seems to be a fair degree of vignetting.

Bummer about the battery...

As regards the filter, I'm not sure what your light pollution is like but Celbridge couldn't be too much better. Personally, I use no filters at all - of course my images aren't top drawer - and I really see no reason to.

Perhaps its the combination of the filter and the 300D. Have you checked out the QE of the Canon chip versus the blocking wavelengths of the IDAS filter? It may be a bum steer but that's all I can think of.

It might be worth taking a shot with then without the filter, perhaps over ever increasing exposure lengths, and see what the difference is.

At the risk of starting a DSLR vs purpose designed CCD war go get an SBIG or Finger Lakes imager - it'll give your nerves a better time, if not your wallet...

BTW - I had a lash in Maxim and after a bit of processing (in mono) you've captured a fair bit of detail there and its nicely framed.

€0.02

Dave

Thanks lads for the feedback,
I'll be taking the filter off later tonight and giving it a clean, it looked a bit dusty today, but I didnt think it would lead to such a dramatic effect.
Funny thing about the red pixels and vignetting, neither are visible in the original image, its only when I really pushed the levels do they appear.
I know whats worsening the vignetting, my optical path at the moment is

Scope + GEG + microficuser + flipmirror + filter + camera.
I left in the flipmirror as it helps centering, but it has increased the amount of vignetting in the system, so it'll be coming off. I'll also experiment without the filter.
Supposidly, this is the best filter for the 300D, then again thats on red nebula, I have not checked to see how it halps with galaxies, although it supposed to reduce sodium and other emissions right across the spectrum.

The worst thing about the weather here is that you cannot go out again tonight and have a retry, and build on it. Having big time gaps between clear nights doesnt help at all and you're almost starting from scratch again when it eventually clears.

Dave - what's a GEG?

What software do use for capture? If you use Maxim DSLR, the focus mode can be used to take short sequential exposures (it doesn't save the files). By examining each image, you can use your hand paddle to center accordingly. You can switch the image into corsshair mode for better alignment.

The motes may be elsewhere in yopur system too. Given that you have a dome, how about lashing the light on and taking images tofigure out the worst contaminated piece?

I know what you mean about the gap between clear nights - very frustrating. If we had say 3 or 4 consecutive nights, our systems would be honed to perfection. I believe there'e a week of clear nights predicted. Oh yeh, we're in Turkey :roll:

Dave