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Category: Solar Imaging
Imaging In Hydrogen Alpha with Color CCD Cameras
Posted on Apr 21, 2011, 2:31 pm Author: Jen Winter
 

Daystar recommends MONOCHROME CCD imaging whenever possible for best results.

The recent availability of CCD cameras and DSLR cameras has offered a simple opportunity for solar observers to image the Sun in Hydrogen Alpha with a Digital SLR camera.  Please be advised, however, that due to the nature of monochromatic light and its effects on a CCD camera, certain effects usually occur. 

The DSLR imager must be aware that most camera manufacturers (Canon and Nikon) use an IR blocking filter which greatly reduces the transmission of Hydrogen Alpha light. DSLR cameras without this IR blocking filter will have better sensitivity imaging in Hydrogen Alpha. 


 

The imager should also appreciate that the COLOR CCD chip is constructed in a way that only 1:4 sensors detect red light.  The other 3 sensors only detect blue and green because the pixels are actually permanently covered with a colored dye for each corresponding color.   So a color CCD chip (in a DSLR or a CCD camera) will only offer 1/4 the sensitivity and 1/2 the resolution of a monochrome chip.  Simple math shows that a chip in monochrome will offer 4x the effective resolution of the same chip in color.

Additionally, the software of the color CCD camera will most certainly to the honor of averaging data from all 4 pixels.  This means your good 1:4 pixels will be averaged with the 3:4 bad pixels which collected no red light.  This farther reduces the effective resolution and image quality of your photo. 


Another effect present in CCD imaging of monochrome light is the interference pattern - or Newton's Rings.   The effect is similar to interference testing of an optical surface between two flat surfaces.  The sensor and cover slip cause a small interferometer inside the camera and cause a Newton's Ring moire' pattern.  The CCD chip must be tilted to a minor degree to prevent this pattern.  Recent advances in aftermarket adapters offer a simplified solution for the issue.   This effect is a concern for both color and monochrome sensors. 

An optional accessory is available from DayStar (MG-0408) which can be used between the DSLR and SolaREDi to adjust the light angle and extinct the interference pattern.


 


Tagged Keywords: DSLR, imaging, CCD, Chip, Color, Solar, DayStar, Filter, camera, newtons, rings

Next »  MonoChrome cameras

Comments
IR filtration of Hydrogen Alpha
 
IR blocking filters in DSLR cameras is a common problem very well known in the astrophotography community. Camera manufacturers assume that the average consumer doesn't need to capture above 600nm in color. Because chips tend to be very sensitive in Red, the manufacturers prefer to just "filter early" for better exposure control aimed at the average consumer. This, unfortunately, blocks the 656nm wavelength needed for Hydrogen Alpha. This problem plagues night time Astrophotographers imaging nebulae as well as solar observers. No, this is technically considered "NIR" or Near Infrared, but the name of the IR vs NIR is irrelevant if the light is being blocked to the camera chip. Astrophotographers with Canon cameras have relief by being able to have the IR filter removed by a professional. This solves the sensitivity problem, but not the 1:4 pixel resolution or averaging problems inherent to the color DSLR CCD chip. Hutech has performed these chip modifications in the past. We now see that they offer a line of new cameras with the modification already installed at: http://www.sciencecenter.net/hutech/canon/index-mod1.htm
 
Posted by Jen Winter on Nov 14, 2011, 4:01 pm


IR Filter
 
Hi i was reading Jen Winters article on monochrome cameras which i found very interesting but i think she may be mistaken about the presence of a IR filter affecting the Ha signal, i believe that it makes no difference on signal as a Ha filter is a precision line filter with the IR band lying far beyond. Phil
 
Posted by Philip Reed on Nov 5, 2011, 3:43 pm



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