Share:

We have updated the forum software 🙂 ! We are now working on upgrading the whole site and the Forum to a dark theme...  so please refresh your internet browser twice to properly update the forum appearance AND functionality... Check your internet browser for the refresh function, on windows, this usually is the F5 button, but it depends on your internet browser.

calibrate star colors  

  RSS

(@hans_van_overzee)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 26
July 14, 2018 00:50  

For my pictures I use a modified canon 600D. I have noticed by using the calibrate star colors the red colors of nebulae disappear.

So I use only use remove light polution. Is this right or am I missing something?

This topic was modified 8 months ago 2 times by Hans van Overzee

ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2071
July 19, 2018 21:59  

Hi Hans @hans_van_overzee,

I think it's safe to say, that the red color is not gone. Probably the initial star color calibration settings need to be adjusted a little bit. Have you played with the settings?

Have you checked enabling the saturation in the preview filter?

If you share your data, I will have a look at it 😉

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


ReplyQuote
(@hans_van_overzee)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 26
July 22, 2018 15:09  

Ha Mabula,

Thanks for your offer, it is most appreciated.

I will send you the stacked, light pollution and star color Tiff files by wetransfer.

The picture is made with 14 lights of 4 minutes,  6 darks, 20 flats and 50 BIAS frames.

Thanks a lot!

Hans

This post was modified 8 months ago by Hans van Overzee

ReplyQuote
(@hans_van_overzee)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 26
July 24, 2018 22:04  

I just noticed something I use een light polution filter on my camera.

I did not use this in the program.

Does this make a big difference for the quality of the end result?

Hans

This post was modified 8 months ago by Hans van Overzee

ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2071
July 26, 2018 16:21  

Hi Hans @hans_van_overzee,

Thank you for providing your data.

A light pollution filter should increase contrast in your data, especially when used in heavily polluted areas of the sky. It accomplishes this by blocking part of the regular visual wavelengths as you know. This means that not all color of all stars and nebulosity are recorded by your camera since it is blocked by the filter.

This then usually means somewhat different settings in the Star Color Calibration tool. The settings to be used in this tool are dependant on both the used camera and the used filters. If you use another filter, the settings will be different.

This is your data that you corrected for gradients, looks great by the way 😉

BeforeStarColorCalibration Hans ngc7000

The data is very red though, this is partly due to the filter. The star colors, especially blue ones, are not correct, they are blue/green, which is called cyan. So a small correction is needed I think.

This is what I get with the star color calibration, the initial red color dissapears, because due to the filter, red is much stronger as expected with regard to the blue and green wavelengths. We need to correct for this in the settings of the tool:

model Black Body and extinction

star rejection kappa 2.00

blue-red: 0.10 (making it redder !)

B-G vs G-R

slope 0.80

constant -0.15 (reduces green cast)

B-R vs G-R

slope 1,60

constant -0.15

StarColorCalibration Hans ngc7000

Select star areas not too much affected by the Red Nebulosity of the clear Hydrogen alpha emissions clouds 😉

Let zoom in on a blue and yellow star, left is before calibration, right is after:

NotCalibrated
StarColorCalibrated

What do you think of this calibrated result?

HansVanOverzee NGC7000 StarColorCalibrated

I used these preview filter values on the calibrated data, to give you an idea of what I did with the preview filter:

PreviewFilterSettings

Kind regards,

Mabula

This post was modified 8 months ago 2 times by Mabula Haverkamp - Admin

Main developer of Astro Pixel Processor and owner of Aries Productions


ReplyQuote
(@hans_van_overzee)
Main Sequence Star Customer
Joined: 2 years ago
Posts: 26
July 27, 2018 15:05  

Ha Mabula,

Thanks a lot for your very long answer.

This will bring me a lot further.

Kind regards,

Hans


ReplyQuote
Share: