The use of consumer digital cameras by amateurs for the purposes of amateur astrophotography has seen a tremendous explosion the past few years fueled by stunning astrophotographs, particularly of the solar system. Similarly, the recent popularity of h-alpha imaging of our closest star has also been experiencing dramatic interest from the same amateur community (a sample h-alpha setup and configuration is available here, here and here). However, the use of the same digicams used to produce dramatic images of the moon and the planets is in direct contrast to the results obtained when imaging our sun.

As indicated by Figure 1, imaged by the author during the Mercury transit in early May, the sun is characterized with some gorgeous prominences around the solar disk but, regrettably, there is little to no detail for the solar disk which was also equally active and interesting at the same time (the lack of disk detail was so bad that the transitting Mercury was barely visible)!

Analysis of the constituent RGB channels for this image (Figures 2(a)-(c)) reveals some very surprising and disappointing results. Aside from the active limb details readily visible in the RGB composite, we have a serious amount of disk detail suddenly available in the Green channel which is not visible in either the RGB composite or the R and B channels individually!

These results are diametrically opposed to what one would expect since the h-alpha system isolates a specific wavelength (652 nm) of hydrogen and, as a result, we would expect to find the R channel to be 100% signal with the G and B channels being totally black which is something easily verified at the eyepiece. Although these results due to signal leakage represent a step backward, we can use the information at hand to rectify the deficiencies which characterize most consumer digital cameras already in use to produce dramatic h-alpha images with both prominence and disk details (this problem of signal leakage has also surfaced with the use of webcams for the imaging of Mars during the recent opposition and where the best results have been produced with I/R blocking filters in place).

Although the RGB composite was properly exposed using a Nikon Coolpix 995 (ISO 100, 1/125th sec), the Green channel representing our only source for disk detail is dramatically underexposed. However, if we were to purposely saturate the camera’s chip by using an exposure about 3 times that for the proper RGB composite (Figure 3), we will end up with sufficient leakage in the Green channel which will provide an excellent and properly exposed solar disk with details. Coupled with the original RGB composite where limb details have already been captured (Figure 1), we are now in a position to produce a complete h-alpha image of the sun and in spite of the limitations and challenges imposed by the overwhelming majority of consumer digital cameras.

The weeks that followed the Mercury transit were used to extensively study the behavior of my Nikon Coolpix 995 and which I confirmed with other fellow amateurs locally and internationally to be true for most other digital cameras as well. The five-step procedure I have developed is as follows:

	Step 1:		Take three to four exposures at each exposure setting starting from 1/2 sec and going all the way to 1/1000 sec. We would like more than one sample at each exposure in the event seeing changed slightly while the exposure was been taken.
	Step 2:		Take the best sample image at 1/2, 1/30, 1/125 and 1/1000 (since you took 3-4 of each) and split the RGB components. If you are lucky (!), you will see signal ONLY in the R channel. This is true, for example, for the Canon 10D and its precursor (D60).
	Step 3:		If you indeed have signal ONLY in R, step through the various exposures taken from 1/2 to 1/1000, convert to grayscale and then look for the image with the best detail. This should provide you with the exposure setting that you should be using for all h-alpha imaging.
	Step 4:		If Step 3 led you to exposures where there is also signal in the G and/or B channels, you have the same problem that most of us do. To this end, you will have to save all three channels (R, G and B) for each of the exposures from 1/2 to 1/1000 sec in grayscale and then step through all of these to find which channel and at what exposure you are getting the best signal. For my Nikon Coolpix 995, the Green channel at 1/15th sec using ISO 100 represents my best combination as I invariably have my optimal signal.
	Step 5:		Also take 3-4 images at each exposure setting after setting your digital camera in B&W mode to see if there is anything there being produced of potential interest. My initial results look promising and may represent a means in avoiding the signal leakage.

Step 4 is a logistical nightmare but is perhaps the only means to producing something when the equipment is not doing what it is supposed or we wish it to do. The above steps will allow you to extract the disk details (filaments, plages, sunspots, granulation) which add a further dimension to h-alpha imaging and it is something that should not be overlooked or ignored. Once you have established the critical combination of channel and optimal exposure for the disk details, take one-third of the optimal exposure for the prominence images off the solar limb. Using the WAND command in Photoshop, we then combine the image with the solar disk details with the image of the prominence details to form a master h-alpha image with both disk and limb details (Figure 4).

I have not investigated the use of the Luminance IR-blocking filter from my CCD camera/filter wheel combination. I have a suspicion that this route may be a more direct and orthodox means to proper h-alpha imaging with my Coolpix and something that should invariably be equally accurate for all digicams.

The above five steps should be considered by users of any digital camera irrespective of brand or model name, for the issue of I/R leakage is widespread. The only possible variable from one digicam model to another should be the optimal combination of RGB channel and exposure setting as per Step #4 above.

Solar imaging in h-alpha is a tremendous exercise yielding stunning results of our closest star. Not only does the sun not sleep (:-)) BUT it allows the dedicated amateur astrophotographer to observe and image both during the day and night. Yes, this translates to even more sleep deprivation but it is worth it. Trust me!!!