Filters for Sun and Moon Images

 


The Sun with Baader Solar Film


Baader Planetarium solar film is available in a pack in sheet form with instructions for preparing a filter to mount in front of a telescope or camera to enable shots of the sun.  It is not expensive and has good optical properties for the purpose.  The Baader website is here.


I prepared a filter from the Baader film to mount in front of my Nikon E17ED teleconverter.  My initial tests were carried out using my ZS30 with an adapter as described here.  Below is the resulting image:


Sun using Baader film: ZS30+E17ED, 100 ISO, 1/800s, f/6.4, 480mm


Below is a 100% crop from the above image, showing the sunpots in more detail:


Crop from the above image



Addition of a Yellow-Green Filter


It is known in astronomy that colour filters can improve detail and contrast when using telescopes and can reduce haze.  The Wratten No 11 (Hoya X0) yellow-green (YG) filter has a transmission curve as shown by the X0 curve in the graph below.



Transmission curve for the Hoya X0 filter


As can be seen, in the visible region, the main absorption by the YG filter occurs at the blue (short wavelength) end.  Sunlight tends to be scattered more at short wavelengths, resulting in haze.  By removing the short wavelengths, the YG filter can reduce the haze and give better contrast and detail in the image.  The YG filter has a factor of 1x, that is, a reduction in light of only 1 stop.


I tested a 55mm YG filter mounted on my FZ38 with the E17ED plus the above Baader solar fliter attached for shots of the sun.  The resulting image is shown below (click on the image for the full sized view):


FZ38+E17ED with YG filter plus Baader film, 100 ISO, 1/400s, f/5.6, 486mm


The YG filter reduced the glare from the sun and did appear to improve the clarity of the sunspots.  Below is a NASA image of the sunspots for the same day that the above image was taken, that is, 19 Sep 2013.  The image above has been been rotated to match the orientation of the sun in the northern hemisphere.


NASA sunspot image for 13 Sep 2013


As can be seen, the image taken with the YG filter shows all of the labelled sunspots except for the one labelled 1847, which is quite faint.


I have made posts about these tests on the DPReview Panasonic forum at:

http://www.dpreview.com/forums/post/52098315 and http://www.dpreview.com/forums/post/52190643.




The Moon with Yellow-Green Filter


I tested the yellow-green filter used above for shots of the moon taken with my FZ38 plus shortened Nikon E15ED stacked with the Nikon E17ED.  The resulting image is shown below, after converting to B&W (click on the image for the full sized view):



FZ38+E15ED+E17ED with YG filter, 100 ISO, 1/125s, f/4.4, 486mm


The YG filter appeared to provide improved contrast and clarity compared with images I have been able to achieve without a filter.


I have made a post about this test on the DPR Panasonic forum at http://www.dpreview.com/forums/post/52204639.



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