Images appear black and white instead of color

[Moonstruck]

Dave, thanks, I will re-post the banding issue as a new topic.

[turfpit]

John

From the data you posted in viewtopic.php?t=5332 you are correct that the flat frames are over exposed. The bias and dark frames look OK.


The guidelines for capture are:

• Lights: decide on exposure, gain and brightness settings

• Darks: use same settings for exposure, gain and brightness as lights

• Bias: use same gain and brightness as above but reduce exposure to minimum.

• Flats: use same gain and brightness as above but reduce exposure until the histogram is around 50% saturated. Expect exposures of the order of 80 - 125 ms. The value will depend on the brightness of the illumination and how thick the cloth is.

Some modern low noise CMOS camera don't need bias frames. Some cameras need bias frames with 1 - 2 s exposures. Easy way is to capture bias frames and process with and without and see if you can tell the difference. The time penalty for capture is only a few seconds.

Your flat frame in FITS Liberator:

over-exposed-flat.JPG (96.47 KiB) Viewed 710 times

Aim for a mean value of around 30,000 ADU. The histogram will help with this by adjusting the exposure to achieve around 50% saturation. The images below are for an Altair 183C CMOS camera. Note that in the FITS Liberator image the histogram does not touch the left or right hand sides and the Mean ADU is around 30,000 for the 125ms exposure. When adjusting the histogram concentrate on the luminance (white) part. A 40 - 50% value here will be ok. The green caste is caused by the Bayer matrix having 2 green pixels to 1 red and 1 blue. This gets dealt with in processing.

colour-camera-flat-frame-in-FITS-Liberator.JPG (145.83 KiB) Viewed 710 times

colour-flat.JPG (59.66 KiB) Viewed 710 times

This should be enough background to get you to progress.

I emphasise that all figures given are guidelines only. It is impossible to be precise given the number of combinations of equipment out there.

See viewtopic.php?t=596 for my documented struggle with M42.

Dave

[turfpit]

John

Having thought about your green image and studied the individual examples of frames I think your green M51 above has been debayered correctly. The green is brought about by the bad flats being used. With my 183C, I have always had flats with a green hue but this does not appear after the frames have been calibrated and stacked.

I think your best way forward now is to reset the camera defaults (hold down Control key while connecting the camera in Sharpcap) and acquire some more data.

You could try to capture some more flats with the scope/camera inside and see if those produce a better stacked image. That way you are not wasting good sky time with experimentation.

Dave

[Moonstruck]

Thanks very much Dave for all the info. This was my very first time I took calibration frames so hopefully next time they will be better! Good to know my green screen issue may have been caused by my bad flats too.

[turfpit]

John

Almost certainly good flats will allow the green caste to be handled by calibration. Download https://esahubble.org/projects/fits_lib ... nload_v30/ which will help you check your settings (see images in post above).

Good luck.

Dave