Annoying artifact right in the middle of my images

[meryck]

I've been imaging for a few months now with my ZWO ASI034 MC camera, and I've been very happy with the results.

When I've seen dust-related artifacts in SharpCap, I've simple cleaned the window and sensor with compressed air - and it worked great.

Now I have a stubborn one I can't solve - a dull blob right in the middle of the image, which limits what I can do with the camera.

I think I've established that it's due to the glass window on the imager. The blob can be clearly seen in SharpCap if the window is on the camera (which is pointed at a dim light source), but it disappears when removing the window and pointing just the raw sensor.

However, inspecting the window reveals absolutely nothing - it's got not a single speck of dust or blemish I can see. Previously, I've always been able to see the culprit. But this time, NOTHING. I'm sure there must be something there, so why can't I see it?

It's started to result in wasted evenings with clear skies, which is a tragedy of the worst kind. Any suggestions on how I can identify and fix this problem?

[ronin]

Any suggestions on how I can identify and fix this problem?

Bit obvious - attach an image of the culprit/problem. :grin:

Suspect you have done the classic thing, write post, read post, hit Post.

Picture/image got left somewhere on the PC.

[Alien 13]

I have had "invisible" smears on a DSLR sensor before and found that shining a UV light (a blue led will do) will often make it show up.

Alan

[meryck]

Hmm.. I thought that at first but then why would the blemish disappear when removing the window? I'll post photos as soon as I'm back at my PC.

[happy-kat]

Aren't those compressed air thingies actually not great, I use a rubber hand buffer blower, it is just air no compressed other stuff in it. Compressed air cans were anything but just air in the item I was reading about them.

http://stargazerslounge.com/topic/238868-air-in-a-can-to-get-crud-off-of-primary/?fromsearch=1

[Leveye]

Sensor swab time. They work great on the window as well as directly on the sensor. That or a 60/40 mix of distilled water and isopropyl alcohol and really good cotton swaps or an untreated tech-wipe. 

[meryck]

@Leveye: Thanks for the suggestionI think that's my only plan. I've found the guide in the ZWO manuals - and the blemish I see looks exactly like their example of dust on the sensor window.

The manual suggests using alcohol and lens paper / cotton buds for the window, with extra care if cleaning the sensor itself. I think the sensor is OK, so I'll have a go at the window with alcohol. Fingers crossed it solves the problem...

[JamesF]

To be honest I'm not surprised that you can't see anything on the sensor window.  Sometimes I've not even been able to find them with a magnifying glass.  A speck no more than a few hundredths of a millimetre across can appear huge on the camera sensor.

James

[ollypenrice]

To be honest I'm not surprised that you can't see anything on the sensor window.  Sometimes I've not even been able to find them with a magnifying glass.  A speck no more than a few hundredths of a millimetre across can appear huge on the camera sensor.

James

That's been my experience as well. Don't expect to be able to see them every time.

Olly

[meryck]

I bought some alcohol swabbing wipes designed for camera senors, and cleaned the window. Then I air-blew the sensor with a hand pump. Now there's only one blemish left and it's in the top left corner away from the action... so happy days! Now will try to capture Saturn at opposition tonight and put it all to the test! Thanks for all your advice.

[Tommohawk]

.. lots of annoying smudges here too... commonly called clouds.

[meryck]

.. lots of annoying smudges here too... commonly called clouds.

That's a shame. I have clear skies forecast for tonight. Hope it comes true...