Binned and Drizzled NGC2070 Field

[avandonk]

This is only nine exposures of 32 minutes each binned X2.

A great deal of care was taken with darks and bias to make sure they did not introduce noise.

This is the drizzled image.

https://www.flickr.com/photos/343863...in/dateposted/


By the way when binning X2 you only get one quarter of the read noise.

It helps to have at least one hundred bias frames and about seventy dark frames. It also helps to download at the slowest speed for your camera.

Bert

[SimmoW (SIMON)]

Ah lovely! Any details on your latest equipment, esp camera? I love the faint waves extracted

[xelasnave]

Most impressive Bert and thank you for your expert tips.
Alex

[cometcatcher (Kevin)]

Fantastic detail Bert! Quite an awesome image.

[multiweb (Marc)]

Beautiful details and depth.

[Stonius (Markus)]

Originally Posted by avandonk

A great deal of care was taken with darks and bias to make sure they did not introduce noise.
[...]
It helps to have at least one hundred bias frames and about seventy dark frames. It also helps to download at the slowest speed for your camera.
Bert

Hey Bert,

would you care to elaborate on 'a great deal of care'? Does it just mean taking lots of them as outlined later on? Or are there some pixinsight tricks you're holding out on us?

Also I think I read you don't get much benefit above 30 callibration frames - you're more than doubling that to get presumably half the read noise again. I take it you're seeing a noticable difference?

And one more - how does downloading at the slowest speed make a difference? With checksums I find that digital data either makes it or is totally corrupted, there is no incremental loss as with analog transmission. Which leaves the idea that the chip is read more slowly when transmission speeds are slower. Is this the case? Or is it just read then buffered and transmitted at whatever speed is set (in which case I'm not sure what difference it would make?)

Thanks for posting. Amazing results. You obviously know what you're doing. I'm just trying to get a grasp on the reasoning behind these subtleties you hint at.

Best

Markus

[gregbradley]

A terrific image Bert. You got a ton of detail there and those waves near the bottom right are new to me.

Greg.

[Ross G]

Another great photo Bert.


Amazing detail....I love the swirls!


Ross.

[avandonk]

Greg I made a mistake! I had inadvertently ticked the optimise box for dark correction in PixInsight. This is a big no no when there is signal everywhere because you get under-correction for the dark. The PI algorithm fails under these circumstances.

Below you can see the first image is of 90 darks stretched to show all its glorious variation.

It is obvious where the waves are coming from! The rings are a bit like tree rings and they are due to variations in impurities of the original single crystal of Silicon the chip is made from. All chips are made from slices of a cylindrical single crystal of Silicon grown by slowly withdrawing a single 'seed' crystal slowly out of a melt of pure silicon. This is then usually zone purified to get even higher purities.

This is same NGC20270 data done with no optimisation of the darks. 10MB

https://www.flickr.com/photos/343863...in/dateposted/


My excuse I was tired and just wanted a quick result. My failure was to take more care and think it through. At 69 I suppose I am starting to lose it a bit.

Stonius I think that the noise is a tad higher at faster transmission rates due to the electronics converting and reading the data in the camera. I am sure that there is a Fourier type element involved.


The advantage of many darks especially at very long exposures is due to the amount of cosmic rays corrupting the data.

I also do a CCD flush before each exposure and for the bias and dark frames. You would be amazed what gets left behind in the wells from bright stars in exposures and cosmic rays in bias and darks.

I once thought I had found two comets in one field! It was just the leftover signal from two of the bright stars in Orion from a previous run made diffuse by dithering.

This does not matter normally but when one is pushing the system to get very dim stuff all the tiny artefacts start to look like some sort of signal.

We used to have a saying in CSIRO. "One man's noise is another mans signal." It is often difficult to separate signal from noise when one is groping in the dark.

Bert

[avandonk]

Here is a newer image with more data 15 subs of 32 min each. Total of eight hours exposure.


https://www.flickr.com/photos/343863...n/photostream/


Bert

[clive milne]

Outstanding Bert!

[Atmos (Colin)]

Great image Bert, very deep for sure!

[avandonk]

What is important is that in hindsight binning X2 always gets you more signal by a factor of four for the same exposure. With a modern CCD camera your read noise also is reduced by a factor of four.

My optic is an F3 200mm clear aperture of 600mm FL. In reality because of the central obstruction of 106mm it has the approximate light gathering power of a refractor that has an aperture of 176mm and FL of 600mm.

One could argue till the cows come home about losses at each surface of refractors versus mirrors and compound systems like mine.

The take home message is all you folks out there with slower systems binning X2 and drizzling with PixInsight works.

My next test will be RGB data if the clouds ever go away. Bert

[avandonk]

I dug up a full resolution image as the core of the Tarantula was saturated in the binned data.

I used HDRComposition in PI to combine the full res data and binned data into a 32 bit linear image. I then applied HDRMultiscaleTransform to a stretched 32 bit image to bring the very bright bits out so they will display at 8 bits.

This image has a dynamic range of 21 bits.

Full res image here

https://www.flickr.com/photos/343863...in/dateposted/



Bert