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phoenix
May 12, 2009, 16:00:57
Hi folks

I have an opportunity to purchase a UV-pass filter from a friend at a good price but I am not sure if it's worth trying to using it with my DBK21.

I notice in an earlier thread (http://www.theimagingsourceforums.com/showthread.php?t=319793) the following comment suggests that the DBK has a 'protective glass' that blocks UV light so this part of the spectrum can not be used.

'CCDs are sensitive down to about 250 nm, but since the CCD's protection glass blocks UV light, we cannot use this part of the spectrum.'

Firstly, I was under the impression the DBK's CCD was exposed to the 'elements' and there was no filter/glass covering the sensor - Does the DBK21 have a protective glass or not? If so, does it allow/not allow UV light?

Secondly, according to sony's ICX098BQ specs for the DBK colour CCD (pdf file on the "specification" pages of cameras: http://www.astronomycameras.com/en/p...r/dbk21af04as/) it seems that the sensor is not sensitive to UV light as shown on the 'spectral sensitivity characteristics' graph showing the blue spectrum only sensitive to 0.2 at 400nm compared with the DMKs ICX098BL spectral sensitivity at about 0.5 at 400nm. Or is this plot showing only the blue spectrum and the graph simply does not included the UV sensitivity?

Appreciate your advice.

Thanks in advance.

Regards
Steve

Stefan Geissler
May 12, 2009, 16:27:13
Hi Steve,

The diagram in the sensor specification shows only the for human eyes visible wave length from 400 to 700 nm. I think, the sensors are a little bit sensible below 400 and above 700nm. But I can not say anything about the sensitivity in wave length under 400nm, only I guess it will be less the shorter the wave length is.

However, there is no filter in the protective glass of the CCD as far as I know.

phoenix
May 12, 2009, 16:43:47
Hi Stefan

Many thanks for the quick reply and information provided.

Can I just confirm that there is in fact protective glass covering the DBK CCD? Just that as far as you know there is no filter on or in the protective glass? Thanks.

Just that I have always been using a 1.25" UV-IR-cut filter with the DBK but if I was going to look at undertaking a little IR as well as UV imaging with the DBK (despite the DMK being more appropriate), I was also going to purchase a 'clear' 1.25" filter simply for protection of the sensor. But knowing that it is already protected by glass then this is one less filter layer to use. Although small dust bunnies may still work there way under the protective glass so a 'clear' filter may still be necessary.

appreciate your thoughts.

Thanks again for the UV info - appreciated.

Regards
Steve

Stefan Geissler
May 12, 2009, 16:53:40
Hello Steve,

It is, as I told you: There is a protective glass. You should be able to see it directly on the sendor. And I do not know, whether there is a filter in. But since the CCD is IR (bigger than 700nm) sensitive, why it should not be a little bit UV sensitive?

There can not be any dust under the glass. We speak about the rectangle directly on the CCD chip itself.

Cleaning The CCD Chip Of DMK/DFK/DBK Cameras

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.

phoenix
May 13, 2009, 02:46:19
Hi Stefan

Many thanks for your detailed reply - very helpful and much appreciated.

Kind Regards
Steve