Problem - Black dots in captures - ASI120MC

[Perene]

Why are all my captures like this?

http://i.imgur.com/6t5OC2q.jpg

[Perene]

I tried to clean the 90" diagonal, the ASI itself... but still those black dots are all over the captures. When I cleaned the ASI it seems the problem became even worse.

When I cleaned the diagonal mirror a little some dark spots were not there anymore. But I bet this is a defect in the ASI camera itself.

I tried to clean the ASI using a specific tissue and Isopropyl alcohol as recommended by the store tutorial.

Is there a way to capture anything with a crystal image? No dark spots?

I am returning the camera to the store if this issue can't be fixed.

[steppenwolf]

The spots are very dark, indicating that the contaminant is either on the sensor or the glass protective cover if there is one - certainly very close to the sensor. To help discover where it is, use an extension tube instead of the diagonal to take the latter out of the equation. If the spots are still there, don't use a brush, use a high power blower like this one which is available in most countries to blow the contaminant off with the camera held upside down (sensor downwards). Take another test shot to see if the spot has gone or moved. If it has moved, repeat the process.

[knobby]

Try taking a shot then another one with the cam rotated slightly then another one with the filter turned slightly... It will help to locate the spots

[Perene]

The spots are very dark, indicating that the contaminant is either on the sensor or the glass protective cover if there is one - certainly very close to the sensor. To help discover where it is, use an extension tube instead of the diagonal to take the latter out of the equation. If the spots are still there, don't use a brush, use a high power blower like this one which is available in most countries to blow the contaminant off with the camera held upside down (sensor downwards). Take another test shot to see if the spot has gone or moved. If it has moved, repeat the process.

I only tried to clean the glass protective cover where the "filter" is attached below the glass. I didn't touch in the exposed part where the chips are.

However when I tried to clean the glass protective cover it seems the problem got worse. I used more than once the tissue with the Isopropyl alcohol but no way the dark spots were all removed, in fact new ones are now appearing. In my 1st test two could be seen, now I believe there are 4 or 6. What do you mean by " use an extension tube instead of the diagonal to take the latter out of the equation"? What is an extension tube?

I suppose if the diagonal itself or the primary mirror from the telescope have both some kind of stain or something like that it explains why the camera is showing all captures like this?

I tried blowing air to this camera but it seems it is not dust the problem, because if it was dust then by now it would have been removed. Right? Or perhaps my blower is not good enough for this kind of job?

When you say "sensor", you mean the chip itself? This is the camera: http://i.imgur.com/GBpSMTa.jpg

When you unscrew the red top you can see all the circuits but obviously I didn't even work on this area.

[steppenwolf]

What do you mean by " use an extension tube instead of the diagonal to take the latter out of the equation"? What is an extension tube?

I am hoping to narrow down the search for the problem by simplifying the light path. Currently, you have a diagonal in place between the telescope and the eyepiece - this diagonal, of course, has an optical surface which *may* have dust on it. By removing the diagonal completely, if the spots remain, we will know that they are not being caused by debris on the diagonal's mirror surface. I am assuming that the only way to achieve focus is by having the diagonal in position - so, I am suggesting that you use an extension tube to make up the missing length when the diagonal is removed. An extension tube is a simple tube with a nosepiece the same diameter as the front of the diagonal and an eyepiece holder at the back - see photograph below which shows both a 2 inch and a 1.25 inch extension tube for just this sort of purpose:-

[Perene]

I was wondering if there are particles of dust attached to the camera sensor, instead of the glass I mentioned before. If so, how can you remove them? Perhaps using a cotton swab from the cleaning kit (not using any liquid)?

How can a particle of dust gets so attached to the sensor? If this is normal I really can't see how can this camera can ever provide me with a clear picture.

[knobby]

If you do as I suggested a few lists back it will prove where the dust is...

[Perene]

The spots... And I can't follow your suggestion because the filter is locked into the camera.

The store suggested I should also use isopropyl alcohol with a tissue to try removing gently the dust from the sensor which seems to be immune to the air I pumped into it. It is really attached to the sensor, it seems.

I removed the diagonal and connected the camera to the telescope (no need to use an extension tube) and the results were the same.

They also suggested I could use a lenspen for the sensor.

Now this is what I don't understand. How can a piece of tissue soaked in a liquid can be applied in this area and at the same time the camera can't get damaged? Is this a bad advice?

[knobby]

You can turn the whole of the top of the camera... It unscrews, just do it about a quarter of a turn to see if the dots move

[astrojohnarthur]

The way I was told to clean sensors and glass surfaces was to

1. Use hand blower to get rid of large scale contaminants. Not a spray can blower which puts propellant on the surface.

2. Use the brush end of a lens pen to swipe off smaller contaminants.

3. Use the pen end, this is either made of chamois leather or carbon particles and absorbs greasy smears.

Don't use isopropyl alcohol as it entrains water onto the surface and leaves smears.

Pure alcohol (from chemist) or eclipse lens cleaning fluid (methanol-poisonous) doesn't smear.

Microfibre cloth should only be used to remove water from a surface not to wipe.

Pec pads (see amazon) are the best things to wipe with as they are lint free and can be used with alcohol/eclipse fluids.

It can still be very frustrating and sometimes I think you just cause more static and attract dust no matter what you do.

Good luck, John.

[perfrej]

As seems to be the consensus, dust that looks like that is actually ON the sensor. As soon as they move out from it they turn into doughnuts. You need to swab it off and blow the housing out completely. Compressed air is actually OK if it comes from the expensive cans you buy in a real camera store. The cheaper ones can contain anything, including butane - yes, BUTANE. Go figure...

/per