New CMOS ASI183MM camera

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Re: New CMOS ASI183MM camera

Postby Terry Bohlsen » Sun May 13, 2018 6:12 am

Hi Christian
I have purchased one of these cameras mostly to use on my LISA rather than on a LHIRES.
I was very interested in your comment about minimal rippling.
Unfortunately I have found that there is still rippling at least with the LISA.
Below are 2 flat frames taken with the internal lamp of the LISA. The first was taken some time ago with a ATIK314+ and a regular slit.
The second is with the ASI183MMpro. They are not exactly comparable as the second one was taken through a different slit- a photometric slit with the wide end. The narrow part should be the same though.
The rippling is similar in both cameras. Maybe slightly more pronounced with the ASI183.
This is annoying but it is easy to remove on the LISA with the flat frame.
flatATIK314.jpg
ATIK314+ flat frame LISA
flatATIK314.jpg (55.86 KiB) Viewed 390 times

ATIK314+
flat.jpg
ASI183MMpro flat frame LISA
flat.jpg (36.82 KiB) Viewed 390 times

ASI183MM pro

Terry
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Australia
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Re: New CMOS ASI183MM camera

Postby Robin Leadbeater » Sun May 13, 2018 11:30 am

Hi Terry,

These low resolution ripples are from a different source, most likely interference fringes between much thinner layers in the sensor itself. (Most sensors show these to a varying extent. The sensor used in the ATK314 is one of the best in this respect, it is very severe in the Kodak KAF chips). The ripples in high resolution spectra are interference fringes from the cover glass which apparently depends on whether the sensor cover glass is AR coated. (for example the ATK314 is very good, the ATK414 is terrible)

Cheers
Robin
Last edited by Robin Leadbeater on Sun May 13, 2018 11:37 am, edited 1 time in total.
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
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Re: New CMOS ASI183MM camera

Postby Robin Leadbeater » Sun May 13, 2018 11:36 am

Terry,

I have a comparison set of flats showing the relative severity of low resolution fringes. If you send me your asi183mm flat as a fits I could compare it with other sensors.

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
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Re: New CMOS ASI183MM camera

Postby Christian Buil » Mon May 14, 2018 9:33 am

Hi Terry,

I confirm the Robin discussion. Low resolution ripple are induced by detector layers.

The ASI183MM detector ripple is well visible on my graph "ASI183MM vs ATIK460EX absolute quantum efficiency" on the web page:

http://www.astrosurf.com/buil/asi183mm/

This quantum efficiency spectral modulation is very classic with silicon-based detectors. We must not worry about it.

If the flat-field is correctly obtained and applied, there is no problem, this type of instrumental modulation disappears perfectly after post-processing.

Christian B
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Re: New CMOS ASI183MM camera

Postby Robin Leadbeater » Mon May 14, 2018 12:52 pm

Hi Terry, Christian

Here is Terry's flat added to the bottom of my collection of low resolution ripples. (the ASI183MM is not calibrated in wavelength) The ASI183MM is definitely poor in this respect. A problem for slitless spectroscopy (eg with the Star Analyser). A good flat would be definitely needed for slit/fibre spectrographs. (I can still see some residual ripples ~2%pp with my ALPY600 and ATK428 camera even after flat correction using the internal flat lamp.)

Cheers
Robin
Attachments
lowres_ripples_by_sensor_update.png
lowres_ripples_by_sensor_update.png (41.69 KiB) Viewed 320 times
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
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Re: New CMOS ASI183MM camera

Postby etienne bertrand » Tue May 15, 2018 2:51 pm

With this ripples, you think that this CMOS ASI183MMPro is possible to use with LhiresIII ?

The problem for the Atik414EX is with LhiresIII in high resolution near Ha it's not possible to use it, because ripples + important frenges.. it is the same way ofr this ASI183 ?
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Re: New CMOS ASI183MM camera

Postby Robin Leadbeater » Tue May 15, 2018 4:53 pm

Hi Etienne,

etienne bertrand wrote:With this ripples, you think that this CMOS ASI183MMPro is possible to use with LhiresIII ?


You will see these ripples at wide wavelength spacing in low resolution spectra with the LHIRES but a good flat should remove them. The very narrow ripples in high resolution spectra (with the 2400 grating at H alpha) come from the the cover glass, not from the sensor material. Christian's measurements confirm that this camera does not show this problem (probably because the cover glass is AR coated)

Cheers
Robin
LHIRES III #29 ATIK314 ALPY 600/200 ATIK428 Star Analyser 100/200 C11 EQ6
http://www.threehillsobservatory.co.uk
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Re: New CMOS ASI183MM camera

Postby etienne bertrand » Wed May 16, 2018 8:54 am

Thanks to Benjamin and Robin, I'm always in reflexion for buy it...
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Re: New CMOS ASI183MM camera

Postby etienne bertrand » Fri May 25, 2018 11:31 pm

Christian, comment fixes tu cette caméra sur le Lhires ? car sur leur site ZWO affiche un back focus de 6.5mm (j'ai qu'une bague pour Atik que j'ai poncé pour un back focus de 12/13mm
Peut on espérer une nouvelle série de cette caméra sans l’énorme électroluminescence ?
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