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,
+ 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,
Filename - _DSC7196.JPG
Maker Note (Vendor): -
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.