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I plan to buy an Atik 460EX camera. I seem to recall a conversation a couple of years ago about some issues folks were having with interference patterns on the images. This camera seems to be ideal for use with the LHires III. Can anyone tell me if these fringes negatively affect spectrum quality? My understanding is they show up in the flat field, so would flatfielding the spectral image remove any fringe artifact?

Keith Graham

Hi Keith,

As far as I am aware there have been no reports of fringes from the cover glass in high resolution spectra with the LHIRES and cameras like the ATK460 using the Sony ICX694 CCD. I have the similar ATK428 camera with the smaller version of the same CCD (ICX674) and that is completely free of high resolution fringes (If present they are a big problem as they are very difficult to remove even with a flat (Because the LHIRES has significant flexure, you have to take the flat with the spectrograph pointed at the target and even then the fringes in the flat often do not exactly match those in the star spectrum because of subtle differences in the light path)

At low resolution, all CCD have some ripples in the spectral response, typically a few hundred angstroms apart, which appear independent of the spectrograph design. They are a few percent peak to peak in the ICX694/ICX674, higher than in the previous generation Sony CCD like the ICX285 (which incidentally was also free of high resolution fringes) but can be larger in some CCD (eg in some Kodak KAF CCD) These are less of a problem though as they generally respond well to removal by a flat.

Robin

Thanks, Robin. This is a big help. I am recently having issues with my ST8XME in that the noise patterns in images are not consistent, so the darks are not consistent in their removal. I am wondering if such things happen to sensors as the camera ages.This is why I am considering a newer camera and the 460 when binned appears to have the same pixel size and fov as the ST8 with much less noise.

From my own experience and that of others (Valérie Desnoux, and more...) I have not fringes by using a Lhires III 2400 l/mm linked to a Atik460EX for the Hapha region (I observe fringes only in the IR, near 8500 A).

See also first results of the psi Per operation (Lhires spectra): http://www.spectro-aras.com/forum/viewt ... f=8&t=1916 and ARAS archive.

Christian

Thanks for the information, Christian. Glad to hear the fringes are not an issue.

Keith

It is the Atik 414 which gives the interference patterns.

Stu Todd wrote:It is the Atik 414 which gives the interference patterns.

Not exclusively. Cover glass fringes at high resolution are seen with many sensors and will occur in any manufacturers' cameras using these sensors.
For example the CMOS sensor in the ZWO ASI178MM http://www.spectro-aras.com/forum/viewt ... f=8&t=1727

Robin

Keith,

I can confirm my Atik 460 does not suffer from fringes and works well, but the 414 does due to the cover glass.

I use a Lhires and 2400 grating.

Regards,

Jack

Essex UK