Lunar imaging with filters
Posted: Wed Apr 29, 2020 12:44 pm
In the February 2020 issue of Astronomy Now Magazine there was an article entitled Making Light Work. This article contained a section on Wratten Filters and how the various filters could benefit lunar/planetary imaging. Further information to complement this post can be found at https://britastro.org/taxonomy/term/147.
I have some of these filters and loaded up a budget 5 slot manual filter wheel as follows: 1) yellow #12, 2) orange #21, 3) red #25, 4) blue #80A, 5) no filter. This configuration was used on 27th April 2020 against an 18% waxing moon with intermittent cloud. Here is a comparison between no filter (worst image) and a red filter (best image).
Note how the red filter brings out detail on the crater floors and crater walls. The filter has the added benefit of steadying atmospheric turbulence. A filter such as the one used can be found at https://www.365astronomy.com/Castell-25 ... -1.25.html.
Equipment: Celestron C8, JMI Motorised Focuser, f6.3 reducer, manual filter wheel, Altair 183M camera.
Capture: SharpCap 3.2, SER Player (to check test video captures).
Processing: Autostakkert!3, Registax 6.1, GIMP 2.10
Capture Settings: Capture Area = 1920x1200 (reduced area = increased fps), gain = 400, SER 2000 frames,
Exposures: no filter 5.4ms, yellow 4.8ms, orange 6.1ms, red 10ms, blue 8.8ms. These give 60% histogram saturation.
In order to aid comparison, all processing was carried out using identical settings.
AS!3
surface, improve tracking, AP size = 48, stack best 25% (of 2000), output to TIFF.
Registax
wavelet scheme = linear, wavelet filter = default, layer 1 = 10, layer 2 = 30, layer 3 =10.
GIMP
Filters > Enhance > Sharpen (Unsharp Mask), radius = 2, amount = 0.750.
Colors > Shadows-Highlights, shadows = 50, highlights = 50.
Colors > Brightness-Contrast, contrast = 0.010.
Color > Levels, gamma= 1.25
The crop, for comparison, shows craters Endymion, Atlas & Hercules.
All give an improvement over no filter (above) with red giving the best definition. Further testing will be needed as yellow is supposed to enhance lunar mare and blue enhance lava flows and rays. These tests can be carried out as more lunar features become available over the coming days.
The filters will also enhance planetary features and tables describing such can be found on the internet.
Dave
I have some of these filters and loaded up a budget 5 slot manual filter wheel as follows: 1) yellow #12, 2) orange #21, 3) red #25, 4) blue #80A, 5) no filter. This configuration was used on 27th April 2020 against an 18% waxing moon with intermittent cloud. Here is a comparison between no filter (worst image) and a red filter (best image).
Note how the red filter brings out detail on the crater floors and crater walls. The filter has the added benefit of steadying atmospheric turbulence. A filter such as the one used can be found at https://www.365astronomy.com/Castell-25 ... -1.25.html.
Equipment: Celestron C8, JMI Motorised Focuser, f6.3 reducer, manual filter wheel, Altair 183M camera.
Capture: SharpCap 3.2, SER Player (to check test video captures).
Processing: Autostakkert!3, Registax 6.1, GIMP 2.10
Capture Settings: Capture Area = 1920x1200 (reduced area = increased fps), gain = 400, SER 2000 frames,
Exposures: no filter 5.4ms, yellow 4.8ms, orange 6.1ms, red 10ms, blue 8.8ms. These give 60% histogram saturation.
In order to aid comparison, all processing was carried out using identical settings.
AS!3
surface, improve tracking, AP size = 48, stack best 25% (of 2000), output to TIFF.
Registax
wavelet scheme = linear, wavelet filter = default, layer 1 = 10, layer 2 = 30, layer 3 =10.
GIMP
Filters > Enhance > Sharpen (Unsharp Mask), radius = 2, amount = 0.750.
Colors > Shadows-Highlights, shadows = 50, highlights = 50.
Colors > Brightness-Contrast, contrast = 0.010.
Color > Levels, gamma= 1.25
The crop, for comparison, shows craters Endymion, Atlas & Hercules.
All give an improvement over no filter (above) with red giving the best definition. Further testing will be needed as yellow is supposed to enhance lunar mare and blue enhance lava flows and rays. These tests can be carried out as more lunar features become available over the coming days.
The filters will also enhance planetary features and tables describing such can be found on the internet.
Dave