View Full Version here: : NGC5128 with bonus dust donuts!
16-06-2012, 09:11 PM
New scope, and some new equipment.
Sadly this is not the first light for the scope, but so far its the only thing presentable.
Getting rather annoyed with the dust donuts though - many of my images are destroyed by them. No matter how much i clean the FF and camera sensor, there is always at least one dust donut!
Starting to get a bit disappointed in the lack of sensitivity on the camera as well. Even bright objects require high ISO and long exposure times. M8 requires 10min subs at minimum to get detail out of it. Just a few more paychecks and it will be time to ditch the DSLR for a CCD.
Anyway, pretty happy with the new scope, but star colors are lacking. Trying to figure out why, i think my white balance is off on the camera. Bright stars also seem to grow a tail on this scope. Not sure what that is, possibly a FF problem. New FF in the mail so will see how that goes.
Anyway, here it is. As per usual, comments, suggestions or critiques are very much so appreciated.
25x300sec subs at ISO 1600.
No bias, 10 darks and 20 flats (flats weren't very helpful, guess im doing something wrong). Processed with PI.
16-06-2012, 09:33 PM
It's a great image regardless of your dust bunnies.
What is your routine for taking flats?
How long is your exposure time? What does your histogram read? Where is the bump? It should be about a third of the way across.
Which camera do you have?
16-06-2012, 10:14 PM
It's a Canon 1100d.
The flats are done at ISO100, 0 second exposure. This puts a hump at slightly before 1/3 of the histogram.
1 second exposure puts it past 2/3.
Flats are taken with a lightbox (home made) with an EL sheet as the light source.
At the beginning of each session, i focus the scope on a star to get the scope into focus. Make sure its all aligned etc.
Then take flats - 10 flats, then rotate the box 90 degrees then another 10 flats. So 20 in total.
Then do whatever imaging i am doing.
Ive tried DSS and PixInsight for stacking, both give the same result. I attached an unedited image with just a stretch applied to it. Some of the result is from light pollution, but the circular shape leads me to believe that the flats aren't working (well).
I tried with 0 second flats, 1 second flats and even 300 second flats (300second flats at ISO 1600 - no idea why i made these!) All of them seemed to not do a whole lot.
Streaking noise is another problem, haven't found a solution for that yet, but PI's noise reduction works pretty well.
16-06-2012, 10:31 PM
The 1100D, like the 550D, doesn't like imaging when the temperature is above 10C. Once the temp drops, those streaks of thermal noise will start to fade. Once it gets down to 0C your photos should become silky smooth.
With the 550D I remove most of the streaks in CS3 using the Carboni Action "vertical banding noise reduction". I have to rotate the image to make sure the streaks are running the right way.
try just taking one set, don't rotate the light box.
You should be able to see the dust bunnies on the individual flat shots.
For example, my flats are generally taken at the same ISO I shot my lights with. The exposure time I use is around 1/250th - 1/350th of a sec.
16-06-2012, 10:41 PM
Stretched a few of the flats and had a look.
They all look like waves for some reason, and the 1 second flat... I don't even want know what happened there.
I think next time i will try taking the flat at 1/250th or 1/350th at ISO 1600.
16-06-2012, 11:06 PM
You're coming to Astrofest aren't you? You should join us in the rotunda. It's where all the cool kids go to process and share hints and tips. :)
16-06-2012, 11:30 PM
You really have to mod your camera as the IR cut is way to strong, if you check my 1100d modding thread you will see the massive change this makes. http://www.iceinspace.com.au/forum/showthread.php?t=88886 post 23
At ISO 1600 your really pushing the 1100D in normal temps, try a DIY cooler box. Atm my wife is running hers at iso 800 and just using more subs. If your just using the camera for AP work and run it via usb, you could loose the LCD which would also aid cooling.
As for dust just use an air duster made for electronics and camera before each session, a quick squirt will do the trick. Lol lived at Accia ridge for a bit and I sure know about the dust when it blew in from the in-lands. Your image looks sweet to me wish we had some clear skys tonight in melbourne town :(
Edit: dam just scrolled down that thing is filthy, have you tried a sensor swab that maybe oil or something?
17-06-2012, 12:26 AM
Sorry, i should have mentioned - this is modified. I followed Gary's instructions (same as that thread basically) and removed the IR (blue) filter. The star color problems are new, and i did set a customer white balance profile on the camera, so my thoughts are that that is somehow causing issues. My stars seem to be bluer than normal. Ive reset the camera the auto white balance which was working fine before.
I tried ISO 800, it just wasn't sensitive enough i found.
An example, here is a test run i did at ISO 800.
NGC3247, 10min subs x 15. As you can see, the nebulosity is only just coming in. This probably needed 20min subs.
That being said, there was less noise.
Yep - the long dust/hair is stuck fast between the sensor and the plastic casing, even a swab cant remove it. The other stuff comes off. Sadly i did use my dust remover (aka blower) on the camera, then attached the FF straight away, but somehow the dust remains. Will have to try with some cleaning fluid.
17-06-2012, 12:28 AM
Yes i will be there. Ill make sure i get myself to the rotunda.
Will probably have a CCD by then, so hopefully noise will be less/not a problem.
20-06-2012, 08:08 PM
Bumping this as its a perfect place to ask;
I checked out the two flats i took (0sec and 1sec).
After doing some reading i found that the area to aim for in terms of ADU is 30,000 for a DSLR.
My 0 second shots are ~8000 ADU and the 1 second are ~54000.
I didn't need to stretch my 0 second shots to see dust marks, so it looks like it has helped but i guess with the ADU being so low, it didn't get all of it. The shot does have a wave affect on it though, which might be the reason why it doesn't really do anything to my images? (see 1st image). Is this wavy affect normal?
The 1 second shots are just a sheet of grey un-streteched.
I stretched my 1 second shots and got a color pattern. No idea what it means, but im guessing it cant be good (see 2nd image).
How strange. The 2nd image as FITS format comes out looking like a pattern my mother would use in sewing. In jpg form its a sheet of grey.
Next time ill try for ~30,000 ADU and see how that goes.
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