Help! Dust on the sensor!

[toml42]

This is only the third time my new ccd camera has been out of the box, but i'm worried that there is some internal dust already.

I just took this image, and after spotting the smudge i removed the camera and dusted the front glass plate, then rotated the camera and put it back in and it was still there.

I know it'll probably flat field out, but is it normal to come up against a problem like this in a ccd so quickly? It's a little disappointing. Is there anything i can do? Should i attempt to return the camera?

help!

[RobH]

Welcome to the 'dust on the sensor' club......dust particles wait in ambush for CCD cameras, especially new ones .

Maybe cameras on space probes built in super sterile environments don't have them, but I doubt it, they are amazingly cunning when it comes to finding an opportunity to deposit themselves onto a CCD.

They always find a way to get themselves into the worst possible part of the image too....usually in the middle of a lovely bit of nebulosity!!

All of my cameras have dust on them....it's a pain but not unduly worrying, and they will be removed by the good use of flats.

What is potentially much more damaging is scratching the optical window while cleaning it.

If it gets really bad, give it a clean, but, just like scope mirrors and lenses, only ever clean them if really neccesary.

Cheers

Rob

[toml42]

cheers, glad it's not just me.

It was only a cautionary dab with a lens cloth, won't happen again, i promise!

I just took a rudimentary flat by pointing at a wall and it seems to have got rid of most of it, i'll try for a better quality flat in the day

[riklaunim]

Cotton bud + Baader optical wonder. That will remove small dust particles that show up on image but can't be blown away etc. Clean the optical window and if that doesn't help - you will have to open it and clean the sensor...

[toml42]

Now that i've got it inside under the light i can see the offending dust particle and it's definitely inside, just above the sensor.

I don't think i'd be comfortable opening it up, surely that can only do more harm than good?

[blackparticle]

You can get CCD cleaning swabs online. Be careful though, some are wet (with a type of isopropyl alcohol) and some are dry.

If you use a wet one, then you might find it leaves a smear afterwards and you'll have to then follow this up with a dry one to remove the smear.

The wet-ones are useful if its not just dust on the sensor and something a bit more stubborn.

The swabs are only supposed to be used for cleaning the sensor once and shouldn't be kept for future use though they make quite good tools for just brushing off tiny dust specs from lenses and filters as well after you've cleaned the sensor.

Its also worth getting one of those specialist rubber air-pump blowers as well as blowing into them with your mouth can often do more harm than good. They are fairly cheap, usually under a fiver.

[FraserClarke]

Now that i've got it inside under the light i can see the offending dust particle and it's definitely inside, just above the sensor.

You can work out exactly where it is by measuring the diameter of the ring (in millimeters) and multiplying it by the f/ratio of the scope. That gives you the distance of the dust from the sensor (focal plane). I suspect you'll find it is on the window (maybe back side).

[RobH]

I seriously wouldn't worry about it.

A dust bunny like that is easily removed with flats, and you should be taking flats anyway.

You can't clean/dismantle your camera every time a bit of dust appears!

Rob.

[Photosbykev]

I must admit I hate dust bunnies and will clean my camera sensors whenever one appears. Taking flats does help to hide the effect of a dust bunny but they can't replace the data being blocked by the dust.

I routinely clean my DSLR sensors and I've already cleaned the sensor on my new DMK41 which is only a week old.

[toml42]

Using flats, i can't get my image looking significantly better than the second image i posted. Is this normal, or do i just suck at flats?

Is it possible that the dust has 'settled' or moved slightly since the initial image was taken?

[x6gas]

You can work out exactly where it is by measuring the diameter of the ring (in millimeters) and multiplying it by the f/ratio of the scope. That gives you the distance of the dust from the sensor (focal plane). I suspect you'll find it is on the window (maybe back side).

I've been thinking about this (obviously for some time!) but I don't really understand it! How do you measure the diameter of the dust donut on a digital image? Isn't the view entirely arbitrary?

[Gina]

I've been thinking about this (obviously for some time!) but I don't really understand it! How do you measure the diameter of the dust donut on a digital image? Isn't the view entirely arbitrary?

I don't really know but I would think it's the size of the doughnut compared with the image size. Then, knowing the real physical image/sensor size, you can work out the actual doughnut size.

[x6gas]

That might make sense, but my faith has taken a knock!

[Gina]

I can understand that!

[FraserClarke]

I've been thinking about this (obviously for some time!) but I don't really understand it! How do you measure the diameter of the dust donut on a digital image? Isn't the view entirely arbitrary?

I don't really know but I would think it's the size of the doughnut compared with the image size. Then, knowing the real physical image/sensor size, you can work out the actual doughnut size.

Yeah, you know how big each pixel is (usually stated in microns), so you measure how big the doughnut is in pixels, and convert to microns/millimeters...

[icrusoe]

Don't mean to thread jack, but could someone explain what "taking flats" is and how it gets rid of dust bunnies?

I assume when someone mentioned taking a flat of a wall, the purpose is to ensure all pixels are at the same gain? So taking the flat, would raise the gain of the pixels under the dust bunny? My terminology is probably off here as well.

[x6gas]

No not really...

Flats give you an image of the optical defects in the imaging train; things like dust bunnies and vignetting. You can then use flats in image processing software to reduce or completely remove the effect of the defect. You need to take flats at exactly the same setup as your lights though (same filter, focus, etc.)

[icrusoe]

Ahh ok. So are the flats layered to reduce the defect?

[x6gas]

The flats are divided in to the lights, I believe, but the software generally does all this for you.

Jim Solomon's website http://www.saratogaskies.com/articles/cookbook/index.html explains all and there are other threads on SGL that discuss the process in detail too.

[icrusoe]

Wow, that website is a great read. Thanks for the link!

[tingting44]

wow that picture is AWSOME!!! that really sucks u got dust on it all ready after its 3rd use¬! have u sorted it out yet

[goose35]

You can work out exactly where it is by measuring the diameter of the ring (in millimeters) and multiplying it by the f/ratio of the scope. That gives you the distance of the dust from the sensor (focal plane). I suspect you'll find it is on the window (maybe back side).

Old post i know but hooray for search

I used this to find the dust was on my filter at the end of a coma corrector exactly 80mm from sensor plane (16mm donut ring on images x f5 focal ratio)

[Dave In Vermont]

Cleaning a CCD is frightening to many. Here's a youtube on it:

And these are useful toys from Lenspen:

https://www.uniquephoto.com/cleaning-products/lenspen-sensorklear-ii-with-articulated-tip-sk-1a-/?utm_source=google&utm_medium=paid_search&utm_campaign=paid_search_google_pla&scid=scplp2484813&gclid=CPTQhtnvmsgCFcQUHwodxysLfQ

You can find these all over the web.

Dave