Canon 50D dark circles in photos

[Manav]

Hi,

I just got a Canon 50D and last night I tried a bit of astrophotography. It was too cold so I finally packed up. Afterwards, when I attempted to take terrestrial photographs I noted that they had a dark circle. I tried taking a couple of shots and the circle usually remains in the same place in one or photos is slightly to the bottom.

I'm not sure why this is any ideas, I might technical support on Monday.

See the following example

The black line points to the circle (http://s564.photobucket.com/albums/ss84/andronicus_/?action=view&current=IMG_0099.jpg)

[p3nn]

I guess it could be a number of things. How are you trying to take the photo's. Is it cam only or through a telescope. Prime focus or afocal? Are you using a barlow. Does it go away if the barlow is removed (assuming the barlow is in use),.......

Could be dust on the lens/ccd chip? I get similar when imaging the moon with a barlow in place and I understand using a flat white to subtract from the pic is supposed to help re that

The more info you can give re your setup the better for those who may be able to help

[Manav]

Hi,

The photo I attached (See above) was using a EFS 18-55 Canon lens in normal mode (CAM only).

All photos I take now have a small circle which wasn't there before last night's attempt at astrophotography.

Regards

[citivolus]

It is dust somewhere in your imaging train, most likely on the IR filter glass in front of your sensor. You can likely remove it using a puff of air from a lens cleaning bulb.

Regards,
Eric

[Manav]

I didn't think dust would create circles such as this the camera is new and I only took the lens of for the second time last night. I'll try your idea and see if it works. Thanks

[Manav]

Celebrated to early! Long exposure shots (30sec) give me the following two circles. I have no idea what this is and its really getting on my nerves :mad2:

Pic1 (http://i564.photobucket.com/albums/ss84/andronicus_/IMG_0108.jpg)

Pic2 (http://i564.photobucket.com/albums/ss84/andronicus_/IMG_0109.jpg)

[DavidU]

Your 50D has an ultrasonic dust removal system to remove sticky or wet particles (the dust removal system vibrates the low-pass filter to shake off dust particles; wet or sticky particles.
Have you blown off the CMOS front filter?

[citivolus]

You'll find that the size of the dust spot will vary as you alter the focal ratio. Setting your camera to f/22, defocusing, and pointing your camera at an evenly illuminated roof will show you the location of all the dust on the filter, if you really want to see how dirty it is.

[matt]

You need to first of all work out where the dust or other material is in your imaging train.

Remove the lens and look through the viewfinder of your camera at the sky. This will quickly tell you whether the blemish is on your lens or somewhere within the camera.

Then you need to use a puffer/blower to see if the blem is on the camera's mirror or on the sensor, which you can get to by using the menu to select Manual Clean of sensor.

Also, try blowing some air up into the area directly above the mirror where the focusing screen is housed.

If that doesn't fix it, you might need to look at cleaning all three surfaces (sensor-mirror-focusing screen) to look at removing some kind of residue from their surface.

Hope you get it sorted:)

[mithrandir]

You don't need long exposures to find dust bunnies. Shooting a patch of blue sky works just as well.

Yours look like dust on the glass cover for the CCD. It doesn't take a very big fleck to make a noticable spot since it covers a few pixels. If it is on a lens or filter, the fleck is probably bigger and changing the aperture or focal length changes the size.

I got rid of the ones on my Sony CCD with a blower after running it through the cleaning cycle to lock the mirror up. Just make sure you don't touch anything with the nozzle, and after each squeeze pull the nozzle out of the camera before you release the pressure so it doesn't draw any dislodged dust back into the bulb. (Professional grade blowers have a non-return valve to stop that happening.)

Try to work in a clean room. Holding the camera mount down so the dust falls out and more doesn't fall in helps too.

By the way, your profile implies you aren't far from here. :)

Andrew

[Manav]

Thanks for the response everyone my Saturday has been quite stressful ever since I first noted this. I hope it is dust and nothing else will try taking some dusting advice and see if it cleans this issue. (No pun intended)

Andrew: I'm considering joining ASNSW hopefully, we can catch up sometime in the future.

Matt: Thanks I'm might grab that dust puffer/blower from the camera shop. Will read the manual in the meantime. :sadeyes:

[acropolite]

I don't want to scare you, but it could also be oil, Canon's have a habit of splashing lubricant around inside the camera, so much so that Canon was offering free cleaning for some of it's high end professional models (1D).

[Geoff45]

It's definitely dust and shouldn't be a problem. I took my camera to Canon at North Ryde and they cleaned it for free. For astrophotos flats will get rid of the dust effects.

[Manav]

I think its fixed thanks guys!