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Dust and / or dirty marks - Where in the imaging train?

swag72

By swag72
in Imaging - Discussion

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swag72

swag72

Posted
Posted

As you can see with a quick screen grab, I have some dirt / dust that I want to get rid of. Problem is, I can't find it!!!

I have cleaned the front of the lens and inside as well - Still there.

I have cleaned both sides of my reducer / flattener.

I have cleaned my filters and the camera front - Still there.

What I am struggling with is that I can not get them to move. I rotate the camera, no change - So that suggests to me they are not on the camera. I have rotated the filter wheel and the reducer, and they don't move. Even turning the optic - And they don't move!!

So where the hell are they? No scratches or marks that I can see on the front optic. After cleaning, they are unmoved.

So what are they and where are they?!!!

Cleaning undertaken with Baader wonderfluid and the accompanying cloth.

post-18339-133877719581_thumb.jpg

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Jessun

Jessun

Posted
Posted
If you rotate the camera and they don't move, they are on the camera/ccd!

Agree. But these are big so perhaps more likely to be stains than dust. Which means that more than just the odd blow of air is required.

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derrickf

derrickf

Posted
Posted
As you can see with a quick screen grab, I have some dirt / dust that I want to get rid of. Problem is, I can't find it!!!

So what are they and where are they?!!!

Cleaning undertaken with Baader wonderfluid and the accompanying cloth.

You can use the following formula to estimate where they are:

Distance (in mm from surface of the CCD) = (p X F X d) / 1000

where:

p= pixel size in microns)

F= focal ratio of the imaging system

d= dust shadow diameter in pixels

Once you know this distance it should be fairly easy to identify which element in the imaging train needs to be cleaned.

HTH

Derrick

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FraserClarke

FraserClarke

Posted
Posted

So what are they and where are they?!!!

Dust grains, because they are so uniform in size. Derrick's equation will tell you where they are, but, given what you've said, my guess would be that they are on the inside of the CCD cover glass. In which case, you're best to leave them be. They should come out of the images with flat fields.

Fraser

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r3i

r3i

Posted
Posted
You can use the following formula to estimate where they are:

Distance (in mm from surface of the CCD) = (p X F X d) / 1000

where:

p= pixel size in microns)

F= focal ratio of the imaging system

d= dust shadow diameter in pixels

Once you know this distance it should be fairly easy to identify which element in the imaging train needs to be cleaned.

HTH

Derrick

Or go here and let the computer do the work: Dust Donut Calculator

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  • 2 years later...
Dangerous-Dave

Dangerous-Dave

Posted
Posted

You can use the following formula to estimate where they are:

Distance (in mm from surface of the CCD) = (p X F X d) / 1000

where:

p= pixel size in microns)

F= focal ratio of the imaging system

d= dust shadow diameter in pixels

Once you know this distance it should be fairly easy to identify which element in the imaging train needs to be cleaned.

HTH

Derrick

Thanks for this, saved me from posting my CCD back to Starlight Xpress for a clean and reseal.

Distance = 7.4 x 4 x 36 = 1065mm = on the primary!

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ChrisLX200

ChrisLX200

Posted
Posted

They are tiny and close to the sensor (but not on it) so conclusion would be the CCD window. Anyway, they've gone now but they might appear huge but in fact they are so tiny only a strong light will show them up. Further, static attraction seems to make them fly right back on after you wipe them off!  BTDT. Next time I;m thinking I might try to neutralise the static before cleaning mine.

ChrisH

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  • 5 months later...
Kenza

Kenza

Posted
Posted

Cheers all. Gave the CCD another clean and they seem to have gone. Hurrah!!!

Hi Sara! I have the exact same problem with my CCD. How did you get rid of the dust? Did you clean the sensor or just the window?

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