graphworlok
30-04-2011, 12:44 AM
So, about 15 months or so ago i was given a "toy" plastic 50mm scope as a present... a few days later i was trying to image through it with a webcam.
Just over a year ago i managed a bargain on ebay - 8" newt, EQ3 with motor, and a pile of assorted bits - mainly, a clock motor. After assorted images of planets, etc and the moon, we bought an EOS40D, which is way too heavy to be used with my scope/mount combo, seems to work quite nicely on the EQ mount itself..
I have mainly been imaging sections of the milky way (30 second exposures while pointed towards it, tweak position until the cloudy stripe is "centered")
Now i am after longer exposures and getting more picky about what i try to image, as well as running into other assorted issues (dew, too much balance, bright moons, etc)
My question - Drift aligning with a wide-field type DSLR lense (18-55mm "kit" lense@55mm"
My current technique i have been trying over the past few weeks has been this:
Align tripod with compass, level, etc.
Point camera "straight ahead" (so should be pointing directly at true southern pole,)
(shamelessly modified from many other websites)
Using laptop+gphoto2 to control camera, take a 480 second exposure@ISO100. No tracking. Tweak the east/west and lat. knobs as needed until non-rotating stars are centered. Repeat images until stars appear centered.
Then take repeat with same eposure/ISO settings, but with motor engaged, and controller/timer in hand
Track for 30 seconds(or so)
2x forwards for 220 seconds
Reverse for 220 seconds
If my alignment is off, i will see the stars appear as V's - the 30 seconds of tracking creates a bright spot for the "start" point, so i can tell which way they are moving
Stars above/below the south pole will either drift up or down compared to the bright "start" point
Stars to the east/west will drift left or right
I then log the image name, examine which direction and how much the drift is to the "up" and "right" (whether stars are drifting up/down and left/right)
Tweak the latitude or east/west alignment knobs. Log which way and how much (turns of lat CW or CCW, same for east/west adjustment)
Image again
Compare changes in star drift
Repeat
Eventually i get to the point where the stars are solid lines (as far as i can tell) in both axis rather than V's, and as i progress, the turns-of-the-knobs go from being 2 turns to 1, 1/2 or 1/4 turns until i find myself zooming on on a 10MP image@200x to try and see which way the lines end up
So, i have to ask
Am i completely insane? Does this make sense to anybody else? I have gotten to the point where i can then track for a full 7 minute exposure and the stars still appear as points, but once i point my camrea "up" at the milky way, i still get oval stars. I am sure part of it is slop in my cheap mount , as some is the increased distance of the stars from the pole exaggerating any error, however further alignment becomes problematic due to the camera being at a very odd angle, making it hard to determine how to correct
Any suggestions?
Just over a year ago i managed a bargain on ebay - 8" newt, EQ3 with motor, and a pile of assorted bits - mainly, a clock motor. After assorted images of planets, etc and the moon, we bought an EOS40D, which is way too heavy to be used with my scope/mount combo, seems to work quite nicely on the EQ mount itself..
I have mainly been imaging sections of the milky way (30 second exposures while pointed towards it, tweak position until the cloudy stripe is "centered")
Now i am after longer exposures and getting more picky about what i try to image, as well as running into other assorted issues (dew, too much balance, bright moons, etc)
My question - Drift aligning with a wide-field type DSLR lense (18-55mm "kit" lense@55mm"
My current technique i have been trying over the past few weeks has been this:
Align tripod with compass, level, etc.
Point camera "straight ahead" (so should be pointing directly at true southern pole,)
(shamelessly modified from many other websites)
Using laptop+gphoto2 to control camera, take a 480 second exposure@ISO100. No tracking. Tweak the east/west and lat. knobs as needed until non-rotating stars are centered. Repeat images until stars appear centered.
Then take repeat with same eposure/ISO settings, but with motor engaged, and controller/timer in hand
Track for 30 seconds(or so)
2x forwards for 220 seconds
Reverse for 220 seconds
If my alignment is off, i will see the stars appear as V's - the 30 seconds of tracking creates a bright spot for the "start" point, so i can tell which way they are moving
Stars above/below the south pole will either drift up or down compared to the bright "start" point
Stars to the east/west will drift left or right
I then log the image name, examine which direction and how much the drift is to the "up" and "right" (whether stars are drifting up/down and left/right)
Tweak the latitude or east/west alignment knobs. Log which way and how much (turns of lat CW or CCW, same for east/west adjustment)
Image again
Compare changes in star drift
Repeat
Eventually i get to the point where the stars are solid lines (as far as i can tell) in both axis rather than V's, and as i progress, the turns-of-the-knobs go from being 2 turns to 1, 1/2 or 1/4 turns until i find myself zooming on on a 10MP image@200x to try and see which way the lines end up
So, i have to ask
Am i completely insane? Does this make sense to anybody else? I have gotten to the point where i can then track for a full 7 minute exposure and the stars still appear as points, but once i point my camrea "up" at the milky way, i still get oval stars. I am sure part of it is slop in my cheap mount , as some is the increased distance of the stars from the pole exaggerating any error, however further alignment becomes problematic due to the camera being at a very odd angle, making it hard to determine how to correct
Any suggestions?