I have been battling with this artifact that I'm getting on some images..On Saturday night the viewing was reasonable good so I ventured out in an attempt to capture the Helix...These single images are both 10min exposure at 800 asa, yet one has a distinct line in the bottom of the image...this is consistant .... it's always the same in the frame that is affected by the artifact.... There is what appears to be amp glow in the top left... but this artifact has me stumped... The camera is an unmodded 450D..I have it in prime focus on my Skywatcher reflector.
Hoping someone may have had a similar problem that they may have a solution for...
Paul, my initial reaction to this is something is in the way of the ccd chip in your optical train somewhere. But... I could be wrong. Looks like this due to the "shadow" effect (green tinge). My next thought is there is a distance object (like corner of a roof) which you think you have cleared but havn't?
Thanks for the quick reply coolhandjo...these frames are consecutive...that's what has me beat...complete darkness .... I was thinking at one stage backlighting through the viewfinder...but I have ruled that out...No obstructions around.... nothing in the path....
Are you running the cables near pwm cables for the dew heater?
2nd
Are you shooting direct from live view? as I have had artifacts when I shoot long exposure direct from live view, I turn off live view before starting an exposure and I no longer have artifacts. This will ony work on the diagonal red artifact on the left hand side of frame. The other artifact at the bottom has me stumped.
Brett
Last edited by bert; 17-08-2009 at 01:22 PM.
Reason: clarification
Thanks, Bert , Humayun..Greg..... not running any dew heaters (would be handy though ) I make sure the leads are well separated...I only use live view for initial focus....then remote shutter release with the mirror locked up....I was even thinking that the flashing light on the camera was getting in somehow...but it's only sometimes that the artifact appears...so ruled it out...
Thanks Barry, ok on your suggestions...those two single images are consecutive...I didn't touch anything on the 'scope...just using the "T" adapter connected to the MPCC...into the focuser...it's so frustrating...In the examples shown ,I was using ICNR...but I have had the same results without ICNR...
I have to say that it looks like something in front of the imaging chip, but far enough away that you will still get some light through (Hence the stars in the black bit).
I suspect the mirror lockup is not working correctly, but really it's just a guess.
You are obviously imaging through a scope. Try doing a guided image just through the camera and its lens, fitted to the mount. If you are still getting the problem, I would be returning the camera to Canon for a looksee. You did state that is an unmodded camera, so surely this would be covered by warranty assuming it is still within the warranty period.
It's nothing to do with cable electrical interference etc.
It's your mirror or shutter curtain getting stuck part of the way for part of the exposure, this must be intermittent so you don't see it happen all the time.
What you can do is try and replicate the problem by taking the cover off the camera and pressing the button and have a look and see if the mirror or shutter curtain fully retracts each time.
You may have to try it a few times and see how you go.
Thanks, Andrew.....just checked it out and everything seems in order...mirror movement looks ok....doesn't hang down or get in the way....shutter function looks ok too....Exfso...not a bad idea...see if I can replicate the problem with similar settings with a standard Canon lens....
hmmm... that's a weird one. Maybe a read-out problem. Seems to be a brighter column on the left bottom edge just ahead of the black part from left to right. That's consistant with the read-out pattern of the camera. I have had that on individual stars having a black streak next to them.
Because this "feature" is at the lower part of the image, it means the obstruction is at the upper part of the light path.
Definitely auto-focussing mirror (it is behind the main mirror).
Probably the (plastic) pin that keeps it closed is broken. This was notorious problem with 300D and 350D cameras, according to various reports on the web.
Good excuse to modify the camera.. because it has to be dismantled in order to insert the new (metallic) pin.
Thanks for all your input.... I thought I would see what Canon had to say re the problem....I sent them the images and details...their technical services team at Canon suggest that I take the camera to their Service centre for repair. After viewing the images, they think there is something intermittently obscuring the sensor... I will do a few more tests tonight just with the standard lens and see if I can reproduce the fault....And guess what!!! I'm about a month and a half out of warranty!!.....maybe if I plea my case that this is the first time I have used the camera with time exposures..... (which is true)...they may be a little sympathetic...... fingers crossed !!
Help!!!....
) I make sure the leads are well separated...I only use live view for initial focus....then remote shutter release with the mirror locked up....I was even thinking that the flashing light on the camera was getting in somehow...but it's only sometimes that the artifact appears...so ruled it out...
.....maybe if I plea my case that this is the first time I have used the camera with time exposures..... (which is true)...they may be a little sympathetic...
... fingers crossed !!
