View Full Version : CCD chip glass cover

April 20, 2009, 03:37:54
I have a DMK 41AU02.AS - This unit is not suppose to have any filters in front of the CCD chip. However, I have noticed it does have a cover.

Is this cover suppose to be there or should the chip be bare?

Under normal circumstances I would not worry about it. However, I am using my DMK for narrowband solar Ha (Hydrogen alpha) imaging and I have noticed that I am getting rather bad 'Newton's Rings'. This phenomenon is due to the use of filters in from t of the CCD chip causing resonance waves to feedback.

If this filter/cover should not be there, how difficult is it to remove? I understand that making such a modification could void the warranty.


Stefan Geissler
April 20, 2009, 11:58:30

The glass in front of the CCD ist supposed to be there in order to prevend it from being damanged. If you remove this glass, then you may damage the CCD.

Cleaning The CCD Chip:

We are often asked how to best clean the surface of the CCD chip. Below is a list of the preferred methods.

1) Compressed Air From Air-Blower

Compressed air is usually sufficient to remove most foreign bodies from the surface of the CCD chip. We recommend using an air-blower, such as from Edmund Optics, and not compressed air from an aerosol. Compressed air from an aerosol may contain other chemicals (propellant, water, oil etc.) which could damage the surface of the CCD.

For details, see www.edmundoptics.com.

2) Hama Lenspen MiniPro II

A company called Hama manufactures a product, which is ideally suited to the task: Lenspen MiniPro II. It is available online and from most well-stocked photography stores. One side of the pen has a brush on it, while the other, a small cleaning surface. The later is suited to efficiently removing dirt and fingerprints.

For details, see www.amazon.co.uk.

3) Microfiber Cleaning Cloth

Although a microfiber cleaning cloth is a very viable option, it can be tricky to get the cloth onto the surface of the CCD chip through the camera’s mount opening. A cotton swab (UK: Q-Tip) can help here.

4) Pure Alcohol (at least 90%)

This can be purchased from most chemists. Never use Isopropanol, as it draws moisture from the air, which results in streaks on the surface of the CCD.

5) Alcohol Substitute

Instead of pure alcohol, Methanol or a liquid called Eclipse can be used (Eclipse is essentially Methanol). However, we do not recommend this approach, as Methanol is highly poisonous.

6) Combination Of All Above

Of course, all approaches can be mixed!

Do not worry about touching the glass in front of the CCD chip. It is pretty robust. Only by rubbing glass, sand or diamond on the surface can it be scratched.

If you have any questions about cleaning your astronomy camera’s CCD chip, please do not hesitate to contact us.

April 20, 2009, 18:55:49
Thanks for the cleaning information. However, the issue is not with a dirty cover as it is with a resonance feedback I am getting while imaging at a narrowband (Ha) wavelength. Please see the attached picture for a better illustration as to my issue.

This originates at the camera as the 'Newton's Rings' do not turn with the image. This image was taken out-of-focus so you can better see the rings. However, they do show up in regular solar images as well.


Stefan Geissler
April 21, 2009, 09:56:20
I must confess that I never saw this effect before. Please note that we are only the camera fab but not optical experts. I would *guess* that this effect is due to interferences caused by the CCD protections glass.

April 21, 2009, 16:58:43
No worries. Thanks for the input Stefan. I'll report back if I find a suitable solution.


April 22, 2009, 20:24:50
Ironically, as it turns out I don't have to worry about any of that after all.

Last night while putting my DMK41 away, I dropped it. I had just removed the nose-piece so I could put the small cap on. As Murphy's Law would have it the camera hit one of the tripod leg knobs just right so that the cover glass cracked.


I took the camera apart to get the broken glass out in hope of salvaging the situation. The chip looked good. But after putting everything back together, and plugging the unit in. I saw several scratches and pits in the silicon sensor. Needless to say I am very saddened. I have only had the camera for about a month now. It was great while it lasted.

Stefan Geissler
April 23, 2009, 08:52:43

what a disaster!

However, the CCD can be exchanged. You may go in contact with our US office.

Repairing the camera is much cheaper than buying a new one.

December 4, 2010, 07:41:59
Did you ever find a solution to removing this cover glass ? We are having the same issue in a laser-profiler application. Many thanks!

Stefan Geissler
December 6, 2010, 09:38:57

It is not recommended to remove the glass.

December 20, 2011, 10:23:42
Did you ever find a solution to removing this cover glass ? We are having the same issue in a laser-profiler application. Many thanks!

Did you try removing the glass cover? Or did you find another solution? I want to measure the profile of a laser beam emitted from an OM3 multimode fiber in the near-field. I want to measure the profile at distances of 0...20 microns (µm) from the fiber tip in steps of 1 µm. Any ideas?

December 22, 2011, 05:16:16
I am well aware of TIS concerns about removing the glass over the chip, and I am not advising anyone to do it, but I will say that there have been very recent comments at the Cloudy Nights Forum in the Solar System Imaging Forum, that this is not at all difficult to do. I know of more than a few people who have done this successfully.

Stefan Geissler
December 22, 2011, 07:58:26
Hello Flyer,

You may post a link to the Cloudy Nights Forum, so other users can read this too.

December 23, 2011, 04:59:12

It appears that I was incorrect in my previous post. Sorry! I confused removing of the IR filter with removal of the chip cover. Perhaps you had best delete my earlier post. Here is a sources for removal of the IR filter:


Stefan Geissler
December 23, 2011, 08:21:16

it is no problem confusing the filter with the glass, I guess many peoples do so.

December 25, 2011, 00:13:12
There has been much discussion about this at Cloudy Nights recently. Today someone posted this link. It shows in great detail how one might convert a DFK camera to a DBK by removing the IR filter: