Exposure time:
Imaging solar vs. nighttime astrophotography is very different. Dark sky
imaging requ ires lo ng exp osure time s to capture e nough light. Solar
imaging offers a mple light , so expo sures should be very short. Plus,
fluctuations in seeing dictate that short <1/10 second frame rates will be
better, as seeing cells move quickly to distort the image and can come
and go during a long exposure.
Short exposure webcam imagers are better than l ong exposure
CCD cameras when imaging the sun.
Because the sun ha s a range of
brightnesses, automatic
exposure doesn’t work well. A software interface that allows the
user to control the exposure settings manually is very important.
Exposures for promi nences taken th rough a DayStar with a we bcam
style camera might be ab out 1/15 – 1/ 100
th
of a se cond. Exposures for
surface detai l woul d be even shorte r exposure with about 1/ 300 to
1/500
th
of a second.
Bit depth:
Solar activity encompasses a wide dynamic brightness range from bright
solar flares to faint eruptive or floating prominences quite a distance from
the solar limb. In order to capture all these features, we recommend the
use of 12 bit or 16 bit cameras. Normal 8 bit came ras can be u sed, but
will typically only be able to image ei ther the surface or prominences,
necessitating multiple bracke ted expo sures and su bsequent
recombination in a computer. 12 bit or 16 bit cameras enable capturing
these features in the same exposure, simplifying the image processing.
Focal reducers:
Because of the long effective focal length at the output of the Quark, the
image scale will be quite l arge and small (1/2” o r below) image sensors
will only ca pture a fractio n of the whole solar disk in one fram e. Larg e
pixel sizes (9 microns and above) will enable a larger field of view.
Alternatively, a focal re
ducer can be em ployed
between th e Quark an d th e came ra. Simple 1.2 5”
screw in focal redu cers can be atta ched to the
camera nosepiece to allow a wider field of view wit h
small (1/2”, 1/3”, ¼” ) sensor cameras. Mo re
distance b etween the focal re ducer and came ra
surface will result in more focal r eduction and l arger fiel d of view.
