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mbrickley

Linearity of Atik 460Ex for scientific use

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HI

I am interested in using the Atik for variable star phootmetry amongst other things and I couldnt find good validate ddata for its linearity so I've spent a happy day makinga  constant light source imaging box as per Berry and Burnells Image processing book and producing some reliable data for the linearity of the 460Ex (and hence one would expect the underlying sony chip) over its full ADU intensity range.

The results are frankly stunning regards the ability of this camera to perfiorm as a linear measurement tool: The linearity is within 0.01% of the linear regression up to over 99.5% of its range and the overall r squared approaches 1. This means that under fairly rigorous testing the camera is completely reliable as a photometric tool over its entire ADU range and I think puts to bed the idea that you can only use this ABG camera up to some arbitary ADU (50% of range is often quoted).  This result suggest the camera does as well as a NABG camera to all intents and purposes as regards linearity at least and thus makes an excellent tool to partner with a small telescope (ie matching the small pixels) as a scientific tool for photometry and by extension more esoteric pursuits such as galaxy morphology analysis and the like.

I'm really suprised by this data but I think Atik should feel very pleased with themselves.

Incientially I have no contact with Atik other than as a now very satisfied customer.

graph attached. post-11825-0-54480600-1396730786_thumb.j

 Cheers Mark

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I've now had a chance to calculate some other parameters for my 460ex based on the data I collceted as above:

readout noise = 3.84 electrons

conversion factor (gain) = 0.26 electrons / ADU. This implies a  ccd photosite contains at full readout 65535 = 17039 electrons which is just under 3k less than the full well capacity as quoted by Sony of 20k . This 10% or so overhead may account for the linearity up to the full adu count, see above. I suspect the manufacturer has set the maximum adu to keep the readout within the linear range of the chiop. 

Since the maximum possible accuracy for magnitude determination vareid with the inverse square root of this (see http://www.britastro.org/vss/ccd_photometry.htm) this implies a maximum magnitude accuracy of 0.007 magnitudes but of course in real terms sky noise and maybe read noise will be the poroblem.

dark current = 0.001524 electrons per pixel  s-1. This is negligible at all sensible exposures

all in all the camera should perform well for photometry

Its interesting to note that at all reasonbale exposures the error induced by both read noise and dark current is about 1 adu and therefore can be ignored.

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