ASTRO: A note for those using SBIG STL series cameras

For the last 9 months or so I've been having on and off problems with my
flats. The donuts just didn't always line up exactly. I had to use
pseudo flats in Photoshop to remove the donuts this left. Lately that
problem was worse plus there was a change in the vignetting. It was
totally dark in two corners.

Tonight it was so bad I took the camera off the scope and had a look
inside. I've done this many times before but other than a too tight
axle screw for the filter wheel I found nothing. When I opened it up I
found the IR block filter position (use for L images) was rotated far
enough it was blocking two corners of the CCD. No wonder those corners
were totally vignetted!

But why? The wheel turned freely -- too freely, I didn't feel the
resistance of the drive motor. The drive motor is mounted on one screw
that screws into a threaded hole in the front (scope side) of the
camera. A spring uses this as a pivot to push the drive against the
filter wheel's rubber ring. The problem was the screw wasn't just
loose, it wasn't in the hole at all!!! The motor was just held against
the wheel by the "spring" in the wires running to the motor. Once it
was screwed back in everything worked fine. Just a 1/10th rotation from
tight (not real tight as that locks the pivot so it won't swing) allows
the motor to rock quite a bit. Obviously this was the cause of my
misaligned flat donuts. As the screw worked its way out the
misalignment went from minor to severe as the wobble in the motor
increased with each fraction of a turn I unscrewed the screw.

I have wide temperature swings in winter, 30C swings day to night are
the norm up here. That started the screw coming loose. What kept
slowly unscrewing it I don't know. Maybe there's a vibration as the
scope slews rapidly.

If you have an STL series camera (George N does I know) and the flats
show this problem, tighten (but not too tight) that screw. I'll be
checking it each time I open the camera as preventive maintenance.

Rick

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

i've heard of that same problem Rick. I wish you would have brought it up to
the group earlier because I could have helped you on that one.

the direction the wheel turns apparently also tends to unscrew the screw
it seems that they could have rotated the wheel in the opposite direction
and you never would have seen the problem. seems that a firmware change
could do that; no?


"Rick Johnson" wrote in message
...
For the last 9 months or so I've been having on and off problems with my
flats. The donuts just didn't always line up exactly. I had to use
pseudo flats in Photoshop to remove the donuts this left. Lately that
problem was worse plus there was a change in the vignetting. It was
totally dark in two corners.

Tonight it was so bad I took the camera off the scope and had a look
inside. I've done this many times before but other than a too tight axle
screw for the filter wheel I found nothing. When I opened it up I found
the IR block filter position (use for L images) was rotated far enough it
was blocking two corners of the CCD. No wonder those corners were totally
vignetted!

But why? The wheel turned freely -- too freely, I didn't feel the
resistance of the drive motor. The drive motor is mounted on one screw
that screws into a threaded hole in the front (scope side) of the camera.
A spring uses this as a pivot to push the drive against the filter wheel's
rubber ring. The problem was the screw wasn't just loose, it wasn't in
the hole at all!!! The motor was just held against the wheel by the
"spring" in the wires running to the motor. Once it was screwed back in
everything worked fine. Just a 1/10th rotation from tight (not real tight
as that locks the pivot so it won't swing) allows the motor to rock quite
a bit. Obviously this was the cause of my misaligned flat donuts. As the
screw worked its way out the misalignment went from minor to severe as the
wobble in the motor increased with each fraction of a turn I unscrewed the
screw.

I have wide temperature swings in winter, 30C swings day to night are the
norm up here. That started the screw coming loose. What kept slowly
unscrewing it I don't know. Maybe there's a vibration as the scope slews
rapidly.

If you have an STL series camera (George N does I know) and the flats show
this problem, tighten (but not too tight) that screw. I'll be checking it
each time I open the camera as preventive maintenance.

Rick

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

I've never watched the wheel turn but judging by the time it takes to
find a filter I think it must turn both ways going the shortest route so
sometimes it tightens it and sometimes it loosens it. But since it
can't tighten it much at all as it runs into the wheel that is of little
help. But the loosening direction has lots of play against that spring
-- a good 10th of a turn. That does explain why it comes loose. Guess
they could rotate only one way as you say but then folks would complain
it takes to long to get to a filter. You can't win.

Actually last winter I did post my problem with flat not lining up. I
finally found the axle screw for the wheel was binding a bit, at least
loosening it cured the problem -- for a week or two then it was back but
very weakly. I saw the motor move as I put the wheel back after checking
the rubber ring. But it was supposed to and I didn't investigate
further. If I had I'd likely found I could rock it by moving that
screw. We'll never know for sure.

Most of the time after that it was visible only if you looked deep into
the noise and I could ignore it as the donuts were all at the edges that
were a problem. I could use the dodge and burn tool at 1% to remove
them. That only the corners were a problem at first makes sense from a
rotational point of view, that area moves further. But it got worse.
If I took the flats in the same order as I took the lights then all was
fine, reverse the order and the problem was back. Finally this last
week it has been horrid with that total vignetting at the left side
corners and donuts weren't close to matching. I couldn't get anything
new to process. Finally looked in and there it was flopping around.

I put some Locktite on the offending screw. Maybe that will hold it.
Very little though as I didn't want to get it where it didn't belong. It
could lock the motor from swiveling. Since the hole goes through the
face plate I put the Locktite into the hole from the front side and not
all the way in.

As I only do sky flats (T shirt type) and it was dark I won't know until
tomorrow if it worked for sure but the vignetting is gone.

Rick


Richard Crisp wrote:

i've heard of that same problem Rick. I wish you would have brought it up to
the group earlier because I could have helped you on that one.

the direction the wheel turns apparently also tends to unscrew the screw
it seems that they could have rotated the wheel in the opposite direction
and you never would have seen the problem. seems that a firmware change
could do that; no?


"Rick Johnson" wrote in message
...

For the last 9 months or so I've been having on and off problems with my
flats. The donuts just didn't always line up exactly. I had to use
pseudo flats in Photoshop to remove the donuts this left. Lately that
problem was worse plus there was a change in the vignetting. It was
totally dark in two corners.

Tonight it was so bad I took the camera off the scope and had a look
inside. I've done this many times before but other than a too tight axle
screw for the filter wheel I found nothing. When I opened it up I found
the IR block filter position (use for L images) was rotated far enough it
was blocking two corners of the CCD. No wonder those corners were totally
vignetted!

But why? The wheel turned freely -- too freely, I didn't feel the
resistance of the drive motor. The drive motor is mounted on one screw
that screws into a threaded hole in the front (scope side) of the camera.
A spring uses this as a pivot to push the drive against the filter wheel's
rubber ring. The problem was the screw wasn't just loose, it wasn't in
the hole at all!!! The motor was just held against the wheel by the
"spring" in the wires running to the motor. Once it was screwed back in
everything worked fine. Just a 1/10th rotation from tight (not real tight
as that locks the pivot so it won't swing) allows the motor to rock quite
a bit. Obviously this was the cause of my misaligned flat donuts. As the
screw worked its way out the misalignment went from minor to severe as the
wobble in the motor increased with each fraction of a turn I unscrewed the
screw.

I have wide temperature swings in winter, 30C swings day to night are the
norm up here. That started the screw coming loose. What kept slowly
unscrewing it I don't know. Maybe there's a vibration as the scope slews
rapidly.

If you have an STL series camera (George N does I know) and the flats show
this problem, tighten (but not too tight) that screw. I'll be checking it
each time I open the camera as preventive maintenance.

Rick

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

"Rick Johnson" wrote in message
...
For the last 9 months or so I've been having on and off problems with my
flats. The donuts just didn't always line up exactly. I had to use
pseudo flats in Photoshop to remove the donuts this left. Lately that
problem was worse plus there was a change in the vignetting. It was
totally dark in two corners.

Tonight it was so bad I took the camera off the scope and had a look
inside. I've done this many times before but other than a too tight
axle screw for the filter wheel I found nothing. When I opened it up I
found the IR block filter position (use for L images) was rotated far
enough it was blocking two corners of the CCD. No wonder those corners
were totally vignetted!

But why? The wheel turned freely -- too freely, I didn't feel the
resistance of the drive motor. The drive motor is mounted on one screw
that screws into a threaded hole in the front (scope side) of the
camera. A spring uses this as a pivot to push the drive against the
filter wheel's rubber ring. The problem was the screw wasn't just
loose, it wasn't in the hole at all!!! The motor was just held against
the wheel by the "spring" in the wires running to the motor. Once it
was screwed back in everything worked fine. Just a 1/10th rotation from
tight (not real tight as that locks the pivot so it won't swing) allows
the motor to rock quite a bit. Obviously this was the cause of my
misaligned flat donuts. As the screw worked its way out the
misalignment went from minor to severe as the wobble in the motor
increased with each fraction of a turn I unscrewed the screw.

I have wide temperature swings in winter, 30C swings day to night are
the norm up here. That started the screw coming loose. What kept
slowly unscrewing it I don't know. Maybe there's a vibration as the
scope slews rapidly.

If you have an STL series camera (George N does I know) and the flats
show this problem, tighten (but not too tight) that screw. I'll be
checking it each time I open the camera as preventive maintenance.
Unfortunately, the design of the wheel, is slightly 'lacking' here. The
screw that holds the wheel itself, if 'tightened', tends to make the wheel
too tight, and cause binding, and the motor pivot one has the same
behaviour. If left so it doesn't bind, it can slowly slacken. I used a
tiny (pinhead) drop of one of the non-permanent Loctite locking compounds,
and with the wheel removed, carefully tightened the motor screw, till it
started to bind, and then backed it off a tiny amount, till the stepper
was springing properly. Then with the stepper pulled back so it doesn't
touch the wheel, used the same sequence on this tightening it till it did
bind, and again backing off a fraction. My 'doughnuts', line up OK after
this, but there is still a tiny vignetted edge on the right (I am using
mounted filters, and the wheel stops about 0.5mm out of perfect
alignment). Hoping that a change to unmonted filters will solve this.
Though the system, will always take the shortest path between filters, if
you use the standard sequence, 'in order' round the wheel, shooting
'L,R,G,B', it starts on position 4, moves forward past the index, to
position 1, forward to position 2, forward to position 3, and then forward
again to position 4. This tends to tighten the centre bolt, but loosen the
one on the motor...

Best Wishes

Roger Hamlett wrote:

"Rick Johnson" wrote in message
...

For the last 9 months or so I've been having on and off problems with my
flats. The donuts just didn't always line up exactly. I had to use
pseudo flats in Photoshop to remove the donuts this left. Lately that
problem was worse plus there was a change in the vignetting. It was
totally dark in two corners.

Tonight it was so bad I took the camera off the scope and had a look
inside. I've done this many times before but other than a too tight
axle screw for the filter wheel I found nothing. When I opened it up I
found the IR block filter position (use for L images) was rotated far
enough it was blocking two corners of the CCD. No wonder those corners
were totally vignetted!

But why? The wheel turned freely -- too freely, I didn't feel the
resistance of the drive motor. The drive motor is mounted on one screw
that screws into a threaded hole in the front (scope side) of the
camera. A spring uses this as a pivot to push the drive against the
filter wheel's rubber ring. The problem was the screw wasn't just
loose, it wasn't in the hole at all!!! The motor was just held against
the wheel by the "spring" in the wires running to the motor. Once it
was screwed back in everything worked fine. Just a 1/10th rotation from
tight (not real tight as that locks the pivot so it won't swing) allows
the motor to rock quite a bit. Obviously this was the cause of my
misaligned flat donuts. As the screw worked its way out the
misalignment went from minor to severe as the wobble in the motor
increased with each fraction of a turn I unscrewed the screw.

I have wide temperature swings in winter, 30C swings day to night are
the norm up here. That started the screw coming loose. What kept
slowly unscrewing it I don't know. Maybe there's a vibration as the
scope slews rapidly.

If you have an STL series camera (George N does I know) and the flats
show this problem, tighten (but not too tight) that screw. I'll be
checking it each time I open the camera as preventive maintenance.

Unfortunately, the design of the wheel, is slightly 'lacking' here. The
screw that holds the wheel itself, if 'tightened', tends to make the wheel
too tight, and cause binding, and the motor pivot one has the same
behaviour. If left so it doesn't bind, it can slowly slacken. I used a
tiny (pinhead) drop of one of the non-permanent Loctite locking compounds,
and with the wheel removed, carefully tightened the motor screw, till it
started to bind, and then backed it off a tiny amount, till the stepper
was springing properly. Then with the stepper pulled back so it doesn't
touch the wheel, used the same sequence on this tightening it till it did
bind, and again backing off a fraction. My 'doughnuts', line up OK after
this, but there is still a tiny vignetted edge on the right (I am using
mounted filters, and the wheel stops about 0.5mm out of perfect
alignment). Hoping that a change to unmonted filters will solve this.
Though the system, will always take the shortest path between filters, if
you use the standard sequence, 'in order' round the wheel, shooting
'L,R,G,B', it starts on position 4, moves forward past the index, to
position 1, forward to position 2, forward to position 3, and then forward
again to position 4. This tends to tighten the centre bolt, but loosen the
one on the motor...

Best Wishes

I did use non permanent Locktite on the motor screw. I did have the
filter screw tighten and bind last winter so did the same with it back
when that happened.

I use non mounted filters. With the STL-11000 I see some vignetting but
I see the same without the filter wheel in the camera so it isn't coming
from the filters -- except when the motor screw fell out. It amounts to
no more than about 12% and easily flat fields out. I assume it is in
the design on the scope which has a 1.75" baffle tube well in front of
the camera. But to get this I had to go to a 3" focuser. Meade's 2"
system had a lot more vignetting and sagged a tad from the weight making
the stars in one corner look pretty lousy. Going to a rock solid 3"
system took the vignetting from 35% to 12%. The larger focuser allowed
me to move the camera back far enough to add an off axis guider camera
for narrow band and two eyepiece positions so I can view with the
eyepiece without removing or even moving the camera. That did cause a
slight increase in image scale from 1.02" per arc to just a tad over 1".
Cost a few seconds of arc field, about 18 in width.

If I'm taking data on the east side of the meridian I start with Red as
it is bothered the least by seeing low in the sky, move through blue and
finally L when the scope will be the highest. When on the west side I
reverse the order. That didn't help that motor screw any however!

Raining today so I can't take sky flats to verify the change. I do need
to build a good light box.

Rick

--
Correct domain name is arvig and it is net not com. Prefix is correct.
Third character is a zero rather than a capital "Oh".

"Roger Hamlett" wrote in message
...

Unfortunately, the design of the wheel, is slightly 'lacking' here. The

unfortunately in my experience the same can be said for nearly everything
produced by that particular vendor. In opinion based on my experiences
everything I have owned that they make falls short of the mark in one or
more areas.

that's why I only use their products for guiding. the many noted
deficiencies don't cause many problems with guiding.