Use of a Full Frame camera (Sony A7S*) for solar H-alpha ?
* partially also valid for the monochrome STL11000M

Fluorite Perl-Vixen 102/900 refractor, Coronado SM90+BF30
+ 1.6x Antares 2" barlow (in order to fill the sensor at best otherwise what would be the reason for using a full frame !?)

 

Single frame from the pool of 70 color mode ARW RAWs in the continuous 30s capture, Batch converted in PNGs with ufraw-batch using this method and in my case better than a command line, this elaborated shortcut I can modify at will when changing of directories : "C:\Program Files (x86)\UFRaw\bin\ufraw-batch.exe" "U:\SonyHAlpha\B&W\*.ARW" --out-type=png --compression=99 It gives a funny green background image ... (click images to enlarge full size)	Filename - _DSC7196.JPG ImageDescription - Make - SONY Model - ILCE-7S Orientation - Top left XResolution - 350 YResolution - 350 ResolutionUnit - Inch Software - ILCE-7S v1.10 DateTime - 2015:05:10 13:03:14 WhitePoint - 0.31 PrimaryChromaticities - 0.64 YCbCrCoefficients - 0.30 YCbCrPositioning - Co-Sited ExifOffset - 484 ExposureTime - 1/100 seconds FNumber - 0.00 ExposureProgram - Manual control ISOSpeedRatings - 1250 ExifVersion - 0230 DateTimeOriginal - 2015:05:10 13:03:14 DateTimeDigitized - 2015:05:10 13:03:14 ComponentsConfiguration - YCbCr CompressedBitsPerPixel - 1 (bits/pixel) BrightnessValue - -3.24 ExposureBiasValue - 0.00 MaxApertureValue - F 1.00 MeteringMode - Multi-segment LightSource - Auto Flash - Flash not fired, compulsory flash mode FocalLength - 0.00 mm UserComment - FlashPixVersion - 0100 ColorSpace - Uncalibrated/Unknown (-1) ExifImageWidth - 4240 ExifImageHeight - 2832 InteroperabilityOffset - 38300 FileSource - DSC - Digital still camera SceneType - A directly photographed image CustomRendered - Normal process ExposureMode - Manual White Balance - Manual DigitalZoomRatio - 1.00 x FocalLengthIn35mmFilm - 0 mm SceneCaptureType - Standard Contrast - Normal Saturation - Normal Sharpness - Normal Maker Note (Vendor): - Color Mode - B&W Lens Type - -1 Thumbnail: - Compression - 6 (JPG) ImageDescription - Make - SONY Model - ILCE-7S Orientation - Top left XResolution - 72 YResolution - 72 ResolutionUnit - Inch Software - ILCE-7S v1.10 DateTime - 2015:05:10 13:03:14 JpegIFOffset - 38588 JpegIFByteCount - 2459 YCbCrPositioning - Co-Sited
Single JPG from the continuous pool of 70 shooted in monochrome mode RAWs (continuous 30s capture) Note : only the JPG are monochrome ... the RAWs remain the same, in color !

 

Final result (20150510 ~ 8 AM UT) with 103 .ARW RAWs acquired in 1 min
(monochrome mode = do nothing on RAWs)

 

 

... transformed in PNGs
then registered with AS!2 "planet gradient mode", best 80% kept, 50/50 conv.

Finalisation : Wx (Wavelet adjustments, synthetic flat) , Irfanview (AAC auto adjust colors)
(click for full size)

 

My personal conclusion on this almost 2 year study :

The result is interesting but only after a lot of PC time consuming processing work !
The Sony A7S is 12Mpix but when framing the Sun, about 4Mpix is not used (lateral empty borders) this reduces the useful area to 8 Mpix.
With only 1/4 of the 8 Mpixels being "red pixels", the equivalent true H-alpha resolution is only about 2 Mpix.
Moreover the IRCut filter of the "unmodified" camera reduces a lot the sensitivity (~75% !) in H-alpha which results in poor contrast.

Capturing the whole Sun at about 1500 mm F on a full frame sensor is only a dream !
As with the full frame STL11000M (I tried in the same setup and I have sold now),
there is a strong inhomogeneity of H-alpha over the whole solar disk, due to the large angle of the monochromatic light beam.

Lowering gamma on one original frame shows well the H-alpha inhomogeneity...

I remember that the inhomogeneity problem was already very slightly visible with a modified for H-alpha Canon APS-C camera.
With a Full Frame camera (monochrome or color), it is just worse ...
It could be still interesting to (re)test recent modified APS-C cameras with standard or even "Bayer matrix pealed" sensor.

To be compared with this earlier picture (I guess I would do better now) done in a 1 min drifting mode
with the (3 x cheaper BTW) 2 MPixels ASI 174MM which is, after a good year of different trials, my choice.