Image interlacing with QHY6 camera attached to CCDSPEC spectrometer: EZCAP vs Nebulosity 4 software for image acquisition

Tests tonight using a compact fluorescent bulb as a light source have shown that the interlacing seen on pictures of spectra taken with the QHY6 camera attached to my CCDSPEC spectrometer occur only with Nebulosity 4 software when image is over-exposed and not with QHYCCD Astronomy Camera’s own proprietary camera acquisition software EZCAP, even when over-exposed.

I described this issue in two previous posts:

Issue with interlacing on FITS images taken in Nebulosity 4 with QHY6 camera on CCDSPEC spectrometer

Effect of altering exposure on QHY6 camera attached to CCDSPEC spectrometer on spectra of daylight and compact flourescent bulb 1/8/2018

I added a post on the hardware support on for QHYCCD Astronomy Camera’s own website¬† asking for help on explaining this phenomenon. They have asked me to try out image acquisition using their own proprietary software for the QHY6 – EZCAP. I downloaded the latest version ( and installed this on my Dell Inspiron 15 5000 series laptop (Windows 10 64 bit edition), and compared images of spectra taken through the CCDSPEC (no telescope) with QHY6 at different exposure settings using EZCAP or Nebulosity 4 to see whether interlacing occurred.

Note that FIT files taken with both image acquisition software packages could be opened and analysed in PCSpectra software (proprietary software supplied with the CCDSPEC spectrometer).

EZCAP acquired spectra in order of exposure from short to long exposure times:

The fourth exposure is a very lengthy 3 seconds in length. The photos of the spectra clearly show that there is NO interlacing occurring with images taken with EZCAP, even when highly over-exposed. The spectra show the plateauing out at the top of the graph when peaks go above 16000 intensity counts (y-axis) with loss of data as result and confirm Dr Elliott’s statement that, when taking photos of spectra, need to ensure that intensity remains < 16000.





Nebulosity 4 acquired spectra in order of exposure from short to long exposure times:

These images show that interlacing does occur with Nebulosity 4 at longer exposure times – the last image (number 7) is 3 seconds in length.




To confirm the finding that the interlacing is only seen with Nebulosity 4 and not with EZCAP, I took another final long exposure EZCAP image (3 seconds):

The image shows white-out in large areas and significant plateauing on the spectrum BUT no interlacing. The horizontal lines seen on this image are dust in the 50 micron wide slit – that is evident as there is unequal spacing between them.


Need to re-calibrate CCDSPEC/QHY6 for use with EZCAP:

Also notice in the spectra above, that the wavelengths recorded on the x-axis differed for similar peaks on the compact fluorescent bulb spectrum between images recorded with EZCAP software vs Nebulosity 4 software. The calibration file used was the same – it had been created after calibration using a compact fluorescent bulb with the same hardware and using Nebulosity 4.
I therefore needed to recalibrate the CCDSPEC/QHY6 for when I use EZCAP – I have discussed this re-calibration in a post 4/8/2018.

Re-calibrating CCDSPEC/QHY6 combination for photos taken with EZCAP Image Acquisition software 4/8/2018

The reason for needing to recalibrate when different image acquisition software is used is discussed in Dr Elliott’s post 5/8/2018:

Why different image acquisition software programmes result in need to recalibrate CCDSPEC/QHY6


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