Image of the day

Captured by
Michael Scherman

The Moon and Some Sagittarius goodies

My Account

New to Astromart?

Register an account...

Need Help?

Best Camera for H-Alpha Solar Photography?

Started by spaceflight, 07/05/2004 12:04AM
Posted 07/05/2004 12:04AM Opening Post
I have an Solar Spectrum H-alpha sub .3 Angstrom filter on addition to visual observations, would also like to image as well..does anybody have any recommendations for a camera which would be most suitable for this type of work...I am interested in true color images (or at least replicating the colors as they appear though the Eyepiece or at prime focus)..

Thanks for you help!!




Preserving Space History for the Future
Posted 07/05/2004 03:21PM | Edited 07/05/2004 10:34PM #1
"True color" for solar H-a is sometimes mis-understood.

H-a is a monochromatic signal at 656nm which is in the visible Red part of the spectrum.
The RAW images should be nothing but varying intensities of RED. Any hints of orange,
yellow, pink etc. indicates some other color has contaminated the RED signal (this can
be the result of signal leakage between adjacent pixels, and/or over-exposure).

Many consumer grade digicams use micro-lens filters, allocating a percentage of pixels
for Red, Green, or Blue. A typical arrangement (Bayer Masking) allocates 25% of
those to the Red channel... ergo: 3/4's of the H-a signal falls upon "dead" pixels.
This does not mean that those cameras cannot be used to capture good H-a images,
but that a dedicated monochromatic camera can do a much better job (where 100% of
the pixels can gather signal).

Whatever camera you ultimately decide upon, you should be aware of another nuance
of solar H-a: it is a narrow-band signal (extreme narrow-band!). With a bandwidth
of less than an Angstrom, this can create optical havoc unseen in "normal" wide-band
images. Most notably is a phenomenon called "Newton's Rings":

This is an interference pattern that may be present on any imaging device using a
windowed array (glass covered CCD) or other parallel optical surfaces. Two cameras
can come off the same assembly line one after the other... one with the problem and one
without it (no mfg's currently check for narrow-band performance, not even SBIG)
The only way to be certain the camera will not have this shortcoming is by trying
it before buying it.

(Phew) If you're still with me, consumer grade digicams can produce good solar
H-a images. My own penchant had been towards DSLRs, specifically Canon EOS (I have used
A Nikon CP995, Canon D60 and 10D, and now an SBIG STL11k)... but do try before you buy!


PS: Here's what a RAW image looks like, vs the extracted RED channel processed in grayscale
and then recombined and colorized (these are all from the same initial image). Note that the
RAW appears dark, as it is an RGB image which as mentioned previously, uses only 25% of the




Aw heck, one more image while we're at it... and yes, I'm a sucker for false color!

(Info for this image can be found at )

--- ---