An evening of bias and dark frame images

[steppenwolf]

The continuing poor conditions in the South of England were an excellent opportunity to update my Bias and Dark frames in readiness for the next clear spell - this is the closest I have got to imaging for 9 days. Having then spent some time checking for gamma ray hits, I finally found a favourite that I would like to share with you - I hope you appreciate it's beauty as much as I do.

A single 600 second exposure with my SXVF-M25C attached to my 80mm ED Refractor with lens cap attached in a dark dome with the PC screen turned off. The image was BIAS subtracted in MaximDL and finally processed in Photoshop where I reduced it for website use:-

[Pauln]

It's very.......er...restful.

[Jaffa007]

I was just about to make a comment about white speck's......... then realised it dust on my screen

D'oh #-D

Good work

James

[SteveL]

OK, I think you have lost the plot

[themos]

I spotted 7 hot pixels

[steppenwolf]

OK, I think you have lost the plot

Hi Steve, well, we've met so you already know!

I spotted 7 hot pixels

That's about what I made it too not bad in a sensor with 6,112,512 pixels to choose from!

I got so stir crazy last night that I considered joining the dots to make my own constellation

[MikeP]

That is fantastic I can see the dust lanes quite clearly ...... well, about as well as I normally can.

Mike

PS Candidate for POTW?

[beamish]

:D Hang on, is this the old "black cat in a coal cellar" joke ??

[Paxo]

OK Steve, I've stared at it for half an hour now, I still can't see anything.

I've heard of withdrawal symptoms, if I were you I'd have a sit down!

Steve

[Cloudwatcher]

That is fantastic I can see the dust lanes quite clearly ...... well, about as well as I normally can.

Mike

PS Candidate for POTW?

So can I! So can I.......... dozens of them! :shock:

I'll have to have a closer look in Hi-Res.

CW

[barkis]

I thought it was the summer triangle. I could only see three.

I thought, that'l never get the POTW.

Is this indicative of imaging withdrawal symptoms then.?

Ron.

[steppenwolf]

It's amazing how a post essentially meant to be an amusing (OK, I have a strange sense of humour!) and different slant on the frustration over the awful skies can produce such enquiring input! Here is a cropped but not reduced version of the hit:-

Tonight, I shall mainly be taking 600 second binned 2 x 2 darks so that I am geared up to take Ha images in the 'Summer'. Just let me know if you'd like me to post a sample 8)

Is this indicative of imaging withdrawal symptoms then.?

Sadly so .................

[robindurant]

AT LAST! Astronomy we can all practice, regardless of the weather, thanks Steve

Robin

[steppenwolf]

AT LAST! Astronomy we can all practice, regardless of the weather, thanks Steve

It's even better than that, Robin, I set the session running and went to bed as I didn't have to rotate the dome once!

[aries]

I was just about to make a comment about white speck's......... then realised it dust on my screen

D'oh #-D

Good work

James

No it's not............

I can see at least 4............

[Sam]

Nah - I can't see the inside of lens cap - can't be a very good camera!

:D

and seriously - what's a bias?

Sam

[aries]

A "Bias", is what your kids say in the toy shop, eg, Bias this please Dad, or,

Bias some of these please Mum...........

:D :D

I'll get me Coat...................

[steppenwolf]

and seriously - what's a bias?

I prefer Aries' answer but to be serious for a minute, a BIAS frame is an image taken in the dark for an extremely short exposure time specifically designed to capture NO light at all - honest! It is used to compensate for pixel-specific 'offsets' in the CCD sensor and the attendant electronics used in the readout process. This is necessary as the manufacturing process cannot ensure that each pixel will behave exactly like it's neighbours.

[CELESCOPE]

I award this POW

Is it called the blank Nebula , STeve ,or Greys Nebula ehehhehehehhehhe ,

only joking now , hope that dont restrict me from any Drizzle cake

[Trevor]

Steve

Look I think you need to ask Jane to make you some nice cake……..now about those hot pixies where exactly are they? don’t say at the bottom of the garden.

[Tim]

Which rather twisted tale brings us to the serious question of whether it is worth having a 'library' of darks, bias and flats for use with a specific camera, rather than taking them each night. (always seems to be a waste of precious clear nights to spend half the flickin night takin pics of nuthin......or is it just me?)

To make it accurate enough, would you have to do the same for each degree of temperature change?

Also, one for each length of exposure you plan to use, ie, one for 300 secs, one for 600 secs etc.

Or are the CCD's so prone to gradual disintegration that what is good at 600 secs and 18 degrees one month will be useless in 12 months time?

Is there a definitive, accurate answer to all of this? You know, the kind that doesn't begin with "I think", or "Fred says...", or "Probably..."

The only thing I have noticed, is that on my PL-130 webcam, which can do anything up to 10 secs exposures, every extra half second of exposure brings extra hot pixels to light. But then I only use that for guiding, and its easy to pick them from stars, as they are the ones that dont go out of focus

On the dslrs, the stray pixels I have noticed, usually blues or greens, hardly seem to show at all.

What we need, HINT HINT HINT is an easy to read, easy to follow, easy to apply guide to taking all necessary shots to provide DeepSkyStacker with all the information it nags for, and to provide the best possible starting point for a great image.

So maybe some other dedicated astrophotographer, who is frustrated by the weather, and who has respected experience (not to mention a whole catalogue of published pics and POTW, APOD etc etc) could maybe one day write such for us lesser plebs.

Just think, instant limited immortality.

So, who's gonna share the lurve?

Cheers

TJ

[Tim]

I award this POW

Is it called the blank Nebula , STeve ,or Greys Nebula ehehhehehehhehhe ,

only joking now , hope that dont restrict me from any Drizzle cake

Hmm, is that 2x Drizzle or 3x?

[steppenwolf]

So maybe some other dedicated astrophotographer, who is frustrated by the weather, and who has respected experience (not to mention a whole catalogue of published pics and POTW, APOD etc etc)

I qualify for some of those attributes so here's my take on the question of Darks.

Neither of my Starlight Xpress CCD cameras has 'set point cooling' but that hasn't stopped me from using a 'library' of darks to calibrate my images with. However, my library comprises of 20 each of 200, 300, 400 and 600 second dark frames. Having taken each dark image, I BIAS subtract them and then stack each exposure set using 'average' attributes to produce 'masters' for each of the four exposure values. I find that this is more than adequate for the purpose and in tests that I have carried out, my non-temperature controlled dark frames have always improved my images although it does have to be said that both my CCD cameras are very low noise anyway.

The software I use for acquiring and calibrating my images is MaximDL and this (in common with other programs) can autoscale my darks to interpolate suitable values for exposure values that I have not got actual matching dark frames for.

You may be amused to note that I have a library of BIAS frames too and I stack these using 'average' to produce master BIAS frames and it is the masters that I use to bias subtract my darks!

In summary, I believe that a library of dark frames will work very well with a Peltier cooled CCD and I would not wish to take my dark frames at the same time as the image frames as life is just too short when imaging under UK skies!

[RobH]

I also am building up a library of dark frames, and have a set of bias frames ready for use.

I got an old fridge from freecycle and have been putting the camera in there, together with a thermometer with a remote sensor and am using that to set my dark frame temperatures. I regulate it by using the fridge thermostat and opening the door a crack if needed.

With the Atik 16HR, you can get away without darks for exposures less than 6 or 7 minutes but I like to do things the proper way, and the fridge makes it dead easy, p,us you can keep your beer cool too

Steve....your image is obviously something of the Zen variety

Cheers

Rob

[barkis]

I know hypering film, and making a cold box to increase the film sensitivity was a pain, but we seem to have just taken a sideways step with CCD having to go through all this darks, Bias, and flats, and goodness knows what else. I knew it wasn't going to be easy, but it seems a lot more preparation is required to get the results one seeks. I hope the use of these extra frames, is an automatic process in the system, and placing them in the correct order in the queue is all that is required.

Ron.