Oct. 2010
This month I finally broke down and
purchased a wide field of view camera, an Orion StarShoot Pro V2 color
camera, for imaging those large objects. My Meade DSI color
camera still works fine but I got tired of building mosaics of big
objects like the Pleiades, Andromeda, Rosette nebula, and the like.
The smaller pixels and large format makes a big difference in the
quality of the images.
I did however run into one problem, that being vignetting. The
DSI, having such a small FOV didn't suffer from that problem.
I ended up with a hot spot in the center of the image and the
outer edges were darker. To eliminate the vignetting I had to
apply flats during the processing of the raw images. I had been
shooting my flats during the day after taking the images by placing two
layers of T-shirt material over the end of the OTA and shooting flats.
I had applied these flats to my images but got all kinds of odd
results form reverse vignetting , light edges and dark central region to
a gradient problem across the image. I beat my head against this
for a number of weeks and finally decides that there has to
be something wrong with the flats. Perhaps stray light leaking in or
something.
Jan 2011
The problem I had with my previous flats prompted me
to build a light box to use in shooting them. I had read
about them but didn't think I needed one.
I made my box out of 1/4" foam core board readily available at Staples
and othe4r office supply houses. The box is a 12" cube with one
end having a 10" hole cut in it which fits the dew shield of my
SN8 . The segments are held together with the ubiquitous Duct tape
. I used blue painters tape to fasten the outside back cover which
should allow me to easily remove it should I need to replace
a bulb.
I put one 12v 25mA mini lamp ( purchased at Radio Shack) in each
corner of the back that fits over the dew shield. I placed another
panel with a 10" hole over the back about 3/4" from the one
holding the bulbs. This provides a bit more stability to the box when
slid over the dew shield.
I power the lamps with a 9V source to keep the brightness down.
I have only made one set of flats with it so far but have
noticed that there is a marked improvement in the quality of the
final image. I still need to experiment with the flats to
insure I get the best ones.
(stay tuned for updates )
