Atik 383 bias and dark masters

[alcol620]

Hi everyone

Now I am starting out on a new career of imaging with a mono Atik 383 camera I would be grateful if contributors could post samples of what a quality master bias and master dark (depends on exposure length of course) should look like for this camera. This will enable me, once I get started to have a good idea if I have captured the correct beasts.

Many thanks for you help.

Alec

[wuthton]

There's not much to see but here you go, these are from a 314 but they will look very similar. Don't take them "on scope" put the cap on the camera and go somewhere dark and cool (i use my garage).

MasterDark_ISO0_1800s.tif

MasterOffset_ISO0_1x1.tif

[ollypenrice]

I think the darks from the 314 will actually look very different with a fraction of the noise of the Kodak sensor. I don't have any 8300 darks but the Kodaks I've used in Atiks look like snowstorms. Don't panic about this, it isn't a problem! When you take them, though, use that nice metal screw on cap Atik supply. It is there to exclude all light and it does work. The only thing which can mess with darks on a setpoint camera is light leakage.

Olly

[gnomus]

Hi everyone

Now I am starting out on a new career of imaging with a mono Atik 383 camera I would be grateful if contributors could post samples of what a quality master bias and master dark (depends on exposure length of course) should look like for this camera. This will enable me, once I get started to have a good idea if I have captured the correct beasts.

Many thanks for you help.

Alec

I have a 383.  I think wuthton may be showing off with his 314    My 383 darks look considerably noisier than that.  Both bias and dark frames will look very different, of course, depending on how much you stretch them.  

I would follow the advice from wuthton and Olly about how to capture these frames, and not worry too much about what they look like.

I found building up a dark library has been quite liberating - it was a real chore to have to redo these very night when I had the DSLR.  I am not sure how long 'library' darks and biases are good for though - does anyone know?

I got my camera in the summer when it was a little difficult to get down to -20 in the house (my wife runs the central heating way too high IMHO) - so all of my bias and darks are at -15.  Now that it is winter I wonder how much things would quieten down were I to push everything down to -20. 

Congrats on the new camera by the way.  I am really pleased with mine - which I bought after much dithering ...   http://stargazerslounge.com/topic/246649-atik-460ex-or-383l/

[alcol620]

Thanks all

I am this moment starting the building of a darks library and some bias frames. I have the camera connected to the ED80 along with the filter wheel ( just that I have spent a while sorting the spacers etc to get the 55mm and I didn't want to break it down again!). However I have a thick golf trolley rain cover over the whole shooting match so I am assuming I have darkness?

The strange thing on the bias captures, using APT, .001 exposure bin 1x1 and cooled to -25C and with a 10s delay between subs, the image on the connected laptop varied considerable from sub to sub - no idea why? The histogram was sometimes near the left-hand axis and sometimes about a third of the way across. However, when I open the individual images in Pixinsight they LOOK very similar. Where in Pixinsight can I see data that shows the brightness of individual images?

Just started to take 120s darks and my first look at them on the laptop screen is that they are consistently dark

Any views on the above?

Thanks

Alec

[gnomus]

Not sure why you need 10 seconds delay between subs with the bias frames (or the darks).  I did 100 biases - I've heard of other folks doing 200.  Are you confident you will be able to get the Atik down to -25 all year round?

Remember when you do your flats that the 383 has a shutter so you will have to ensure that each flat frame lasts a few seconds (else you will see the shutter in frame).  I had to place 2 neutral density films over my Gerd Neumann panels to get a reasonable length of exposure (7 seconds from memory).

[alcol620]

Hi gnomus

Just following the old DSLR tradition of letting the camera cool a bit!! I realise now you have pointed it out, as I am cooling anyway, no need. Thanks fo poiting it out - lots to learn. Pixinsight has a feature that will turn master bias' of say 100 subs into a superbias frame equivalent to several hundred -don't ask me how.

Just ordered a 12v controller to reduce the light level of the LCDs in my homemade light box so the histogram doesn't get too far to the right

Alec

[gnomus]

Hi gnomus

Just following the old DSLR tradition of letting the camera cool a bit!! I realise now you have pointed it out, as I am cooling anyway, no need. Thanks fo poiting it out - lots to learn. Pixinsight has a feature that will turn master bias' of say 100 subs into a superbias frame equivalent to several hundred -don't ask me how.

Just ordered a 12v controller to reduce the light level of the LCDs in my homemade light box so the histogram doesn't get too far to the right

Alec

I don't know how either, but I do use the master Super Bias that PI generates.

[alcol620]

Just produced a master super bias with a boosted stretch in Pixinsight anyone tell me if this is OK or duff? Camera is an Atik 383

[gnomus]

Looks fine to me.

[alcol620]

Thanks gnomus, new to this so reassurance is welcome.

Regards

Alec

[alcol620]

Hi folks

Me again. Have calibrated and integrated a couple of sets of dark frames taken over recent nights and each time they seem to have hot pixels that spread horizontally. They are 300s 1x1 binned subs with the master bias subtracted. I used the Atik 383 camera and the master dark has been stretched using Pixinsight.

Comments welcome

[gnomus]

I see you are at 2:1.  Also the STF does a fairly massive stretch.  That looks fine.  Here is a crop of my 20 minute master dark.

[alcol620]

Thanks gnomus, it had me worried when I saw the hot pixels spreading out horizontally. I had not seen this with my DSLR darks, although when I looked back at them there was so much noise that it was difficult to see if anything was spreading out anywhere!!

What does the 2.1 mean, hadn't taken any notice of this.

Regards

Alec

[gnomus]

Thanks gnomus, it had me worried when I saw the hot pixels spreading out horizontally. I had not seen this with my DSLR darks, although when I looked back at them there was so much noise that it was difficult to see if anything was spreading out anywhere!!

What does the 2.1 mean, hadn't taken any notice of this.

Regards

Alec

In your screenshot, you have the PixInsight window 'zoomed' in to a ratio of 2:1 (the top bar says, "Gray 2:1 integration") - the equivalent in Photoshop would be a zoom of 200% - so way beyond anything that you would normally see in the final image.

My crop is also at 2:1.

[alcol620]

Thanks gnomus, much appreciated. So when I open an image in Pixinsight and it says 1:7 this is only one seventh? I always assumed that this was full size!

[gnomus]

Correct.  I assume you know that you can zoom in and out very easily with the mouse wheel?  (Sorry if I'm teaching you to suck eggs there).

[Freddie]

Does look a bit odd though that the hot pixels appear to be moving across the stack. What does a single frame look like?

[derrickf]

The smearing of the warm pixels does look a little strange in both the above images. FWIW here is a 10 minute dark integration of 25 darks at -25C similarly stretched and displayed at 200% in PI. All the warm pixels are single pixel points rather than the smeared effect in the other 2 dark images.

[alcol620]

Oh dear, does that mean there is a problem?

[alcol620]

What camera are you using derrickf?

[Freddie]

Oh dear, does that mean there is a problem?

Depends, as said earlier, what does a single sub look like? You would expect hot pixels to be single points and remain single points in the stack.

[derrickf]

Atik 383L+

A while back while adding to my calibration library I noticed some strange drift in the average dark signal and other effects that I wasn't happy with. I changed the PSU I use for the camera (it now has its own PSU with no other devices connected) and now both bias and dark frames are consistent in level and quality

Derrick

[alcol620]

Hi Derrick

Just got myself a new Maplin dc supply unit yesterday, dives a constant 13.8v, reports suggest that keeping the voltage up from 12v keeps the noise down.

I am currently taking some more darks this evening and will post further information as soon as.

[alcol620]

Hi folks

I have had a further play around with the earlier data and have loaded the following 4 images;

Integrated 10x300s darks with no bias calibration

Integrated 10x300s darks calibrated with the super bias and repeated this with the master bias

A single 300s dark taken by the camera

Any advice as to what is going on would be welcome

Thanks