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## Re: Cleaning my CCD camera

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• ... I don t see how (I ll talk to the creator of that calculator). Assuming the dust mote s actual diameter is insignificant then the distance should equal the
Message 1 of 20 , Apr 1, 2013
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--- Mark Striebeck <mark.striebeck@...> wrote:
> Putting in my values: 4.54 microns, 6.3 focal length,
> 200 pixels leads to 2.8 mm distance to ccd chip.

I don't see how (I'll talk to the creator of that calculator).

Assuming the dust mote's actual diameter is insignificant then the distance should equal the shadow diameter times the f-ratio, right? (simple geometry)

diam = 4.54u*200 = 0.9mm
distance = 0.9*6.3 = 5.7mm

BTW, here is another calculator:
http://www.wilmslowastro.com/software/formulae.htm#Dust

But 6mm is pretty close-in and may be inside the camera but is too far to be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG is not reduced?

Try to find a build diagram of the camera to see what might be at that distance. Is there an internal filter wheel? Otherwise just assume that most of the dust is on the window and clean it.

Stan
• Hi Stan, Thanks for the reply. Yes, thinking of it, it s hard to see how a small dust particle almost in front of the CCD camera could blow up so much. With
Message 2 of 20 , Apr 1, 2013
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Hi Stan,

Thanks for the reply. Yes, thinking of it, it's hard to see how a small
dust particle almost in front of the CCD camera could blow up so much. With
this other calculator I get a distance of 5.72mm - still small. But
couldn't this be on the optical window of the camera which is in front of
the chip?

I measured the diameter on a 1x1 binned raw image (i.e. no processing or
such) - I uploaded it here:
https://dl.dropbox.com/u/71789253/00012610.A.FlatField.fit.

My camera is a Starlight Xpress H694, the closest surface outside of the
camera is the filter in the filter wheel which is ~30mm from the chip.

MarkS

On Mon, Apr 1, 2013 at 8:45 AM, Stan <stan_ccd@...> wrote:

> **
>
>
> --- Mark Striebeck <mark.striebeck@...> wrote:
> > Putting in my values: 4.54 microns, 6.3 focal length,
> > 200 pixels leads to 2.8 mm distance to ccd chip.
>
> I don't see how (I'll talk to the creator of that calculator).
>
> Assuming the dust mote's actual diameter is insignificant then the
> distance should equal the shadow diameter times the f-ratio, right? (simple
> geometry)
>
> diam = 4.54u*200 = 0.9mm
> distance = 0.9*6.3 = 5.7mm
>
> BTW, here is another calculator:
> http://www.wilmslowastro.com/software/formulae.htm#Dust
>
> But 6mm is pretty close-in and may be inside the camera but is too far to
> be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG is
> not reduced?
>
> Try to find a build diagram of the camera to see what might be at that
> distance. Is there an internal filter wheel? Otherwise just assume that
> most of the dust is on the window and clean it.
>
> Stan
>
>
>

[Non-text portions of this message have been removed]
• Hi Stan & Mark, That’s about the distance between the CCD and the front window. I think that you will find that they are nearly all on the outer surface of
Message 3 of 20 , Apr 1, 2013
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Hi Stan & Mark,

That’s about the distance between the CCD and the front window. I think that you will find that they are nearly all on the outer surface of the camera window.

Regards,
Terry (SX Ltd)

From: Stan
Sent: Monday, April 01, 2013 4:45 PM
To: ccd-newastro@yahoogroups.com
Subject: [ccd-newastro] Re: Cleaning my CCD camera

--- Mark Striebeck <mark.striebeck@...> wrote:
> Putting in my values: 4.54 microns, 6.3 focal length,
> 200 pixels leads to 2.8 mm distance to ccd chip.

I don't see how (I'll talk to the creator of that calculator).

Assuming the dust mote's actual diameter is insignificant then the distance should equal the shadow diameter times the f-ratio, right? (simple geometry)

diam = 4.54u*200 = 0.9mm
distance = 0.9*6.3 = 5.7mm

BTW, here is another calculator:
http://www.wilmslowastro.com/software/formulae.htm#Dust

But 6mm is pretty close-in and may be inside the camera but is too far to be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG is not reduced?

Try to find a build diagram of the camera to see what might be at that distance. Is there an internal filter wheel? Otherwise just assume that most of the dust is on the window and clean it.

Stan

[Non-text portions of this message have been removed]
• Thanks Terry - that s what I figured. What is your (starlight xpress) recommended way to clean that window? I found contradicting recommendations: some say to
Message 4 of 20 , Apr 1, 2013
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Thanks Terry - that's what I figured.

What is your (starlight xpress) recommended way to clean that window? I
found contradicting recommendations: some say to clean with a (super) soft
brush (I have one that I use for cleaning my DSLR sensor that I keep sealed
at all times), others say that you should do it with (low) pressure air.

MarkS

On Mon, Apr 1, 2013 at 10:14 AM, Terry Platt <tplatt@...-uk.net>wrote:

> **
>
>
> Hi Stan & Mark,
>
> That�s about the distance between the CCD and the front window. I think
> that you will find that they are nearly all on the outer surface of the
> camera window.
>
> Regards,
> Terry (SX Ltd)
>
> From: Stan
> Sent: Monday, April 01, 2013 4:45 PM
> To: ccd-newastro@yahoogroups.com
> Subject: [ccd-newastro] Re: Cleaning my CCD camera
>
>
> --- Mark Striebeck <mark.striebeck@...> wrote:
> > Putting in my values: 4.54 microns, 6.3 focal length,
> > 200 pixels leads to 2.8 mm distance to ccd chip.
>
> I don't see how (I'll talk to the creator of that calculator).
>
> Assuming the dust mote's actual diameter is insignificant then the
> distance should equal the shadow diameter times the f-ratio, right? (simple
> geometry)
>
> diam = 4.54u*200 = 0.9mm
> distance = 0.9*6.3 = 5.7mm
>
> BTW, here is another calculator:
> http://www.wilmslowastro.com/software/formulae.htm#Dust
>
> But 6mm is pretty close-in and may be inside the camera but is too far to
> be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG is
> not reduced?
>
> Try to find a build diagram of the camera to see what might be at that
> distance. Is there an internal filter wheel? Otherwise just assume that
> most of the dust is on the window and clean it.
>
> Stan
>
> [Non-text portions of this message have been removed]
>
>
>

[Non-text portions of this message have been removed]
• The best way to clean any optical surface is wet. For the front window of just about any CCD camera (unless it leaks liquids badly), any pro-quality lens
Message 5 of 20 , Apr 1, 2013
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The best way to clean any optical surface is wet.

For the front window of just about any CCD camera (unless it leaks liquids badly), any pro-quality lens cleaning kit should do the job adequately.

By 'pro' in this context I mean a professional photographer; a professional astronomer would be more likely to use dangerous chemicals, such as acetone, to clean a flat surface. That's how we do it at the Tzec Maun Observatory. We also use industrial (not medical) grade gloves - they come quite a bit thicker than most medical gloves, which makes them safer for handling objects with metal edges, and are just as clean out of the box. Avoid gloves with various kinds of 'improvements' such as talc.

For optical surfaces, the key problems are various forms of adhesion - chemical bonding, electrostatic forces being the two most common you run into.

Chemical bonding occurs when dust or other particles get on the surface, and then the surface gets wet. It takes force to remove such dirt; a liquid facilitates removal both by helping to break the chemical bonds, and to lubricate the surface against scratches once stuff does get loose. Liquid also reduces/sliminates static charge.

it can be surprisingly hard to remove dust particles when static charge is present. I recall cleaning a sensor's cover plate once. It took me about 15 minutes; I was finally successful when I imagined my little brush to be a broom, and I carefully swept up the dust into a tiny tiny little pile, and then mechanically forced it against a second brush which acted as my 'dust pan'. <g> Otherwise, there are situations where you can brush and brush and brush and nothing ever seems to leave the surface. I've even watched through a magnifying glass as the material I brushed off the top of a cover slip jumped back onto the surface (from the brush, and from the side of the casing) as I lifted the brush.

Thus: wet cleaning is always the best approach. Still, you need to obtain the right materials (able to break those bonds, won't damage seals, etc.) and develop good techniques (gloves, disposal, etc.)

Ron Wodaski

On Apr 1, 2013, at 10:26 AM, Mark Striebeck <mark.striebeck@...> wrote:

> Thanks Terry - that's what I figured.
>
> What is your (starlight xpress) recommended way to clean that window? I
> found contradicting recommendations: some say to clean with a (super) soft
> brush (I have one that I use for cleaning my DSLR sensor that I keep sealed
> at all times), others say that you should do it with (low) pressure air.
>
> MarkS
>
>
> On Mon, Apr 1, 2013 at 10:14 AM, Terry Platt <tplatt@...-uk.net>wrote:
>
>> **
>>
>>
>> Hi Stan & Mark,
>>
>> That’s about the distance between the CCD and the front window. I think
>> that you will find that they are nearly all on the outer surface of the
>> camera window.
>>
>> Regards,
>> Terry (SX Ltd)
>>
>> From: Stan
>> Sent: Monday, April 01, 2013 4:45 PM
>> To: ccd-newastro@yahoogroups.com
>> Subject: [ccd-newastro] Re: Cleaning my CCD camera
>>
>>
>> --- Mark Striebeck <mark.striebeck@...> wrote:
>>> Putting in my values: 4.54 microns, 6.3 focal length,
>>> 200 pixels leads to 2.8 mm distance to ccd chip.
>>
>> I don't see how (I'll talk to the creator of that calculator).
>>
>> Assuming the dust mote's actual diameter is insignificant then the
>> distance should equal the shadow diameter times the f-ratio, right? (simple
>> geometry)
>>
>> diam = 4.54u*200 = 0.9mm
>> distance = 0.9*6.3 = 5.7mm
>>
>> BTW, here is another calculator:
>> http://www.wilmslowastro.com/software/formulae.htm#Dust
>>
>> But 6mm is pretty close-in and may be inside the camera but is too far to
>> be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG is
>> not reduced?
>>
>> Try to find a build diagram of the camera to see what might be at that
>> distance. Is there an internal filter wheel? Otherwise just assume that
>> most of the dust is on the window and clean it.
>>
>> Stan
>>
>> [Non-text portions of this message have been removed]
>>
>>
>>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
>
>
>
• Hmmm, I found so many sources who warn from exactly this and recommend only dusting (e.g. http://www.arksky.org/asoclean.htm . And only revert to (liquid)
Message 6 of 20 , Apr 1, 2013
• 0 Attachment
Hmmm, I found so many sources who warn from exactly this and recommend only
dusting (e.g. http://www.arksky.org/asoclean.htm . And only revert to
(liquid) cleaning if absolutely necessary.

On Mon, Apr 1, 2013 at 10:43 AM, Ron Wodaski <yahoo@...> wrote:

> The best way to clean any optical surface is wet.
>
> For the front window of just about any CCD camera (unless it leaks liquids
> badly), any pro-quality lens cleaning kit should do the job adequately.
>
> By 'pro' in this context I mean a professional photographer; a
> professional astronomer would be more likely to use dangerous chemicals,
> such as acetone, to clean a flat surface. That's how we do it at the Tzec
> Maun Observatory. We also use industrial (not medical) grade gloves - they
> come quite a bit thicker than most medical gloves, which makes them safer
> for handling objects with metal edges, and are just as clean out of the
> box. Avoid gloves with various kinds of 'improvements' such as talc.
>
> For optical surfaces, the key problems are various forms of adhesion -
> chemical bonding, electrostatic forces being the two most common you run
> into.
>
> Chemical bonding occurs when dust or other particles get on the surface,
> and then the surface gets wet. It takes force to remove such dirt; a liquid
> facilitates removal both by helping to break the chemical bonds, and to
> lubricate the surface against scratches once stuff does get loose. Liquid
> also reduces/sliminates static charge.
>
> it can be surprisingly hard to remove dust particles when static charge is
> present. I recall cleaning a sensor's cover plate once. It took me about 15
> minutes; I was finally successful when I imagined my little brush to be a
> broom, and I carefully swept up the dust into a tiny tiny little pile, and
> then mechanically forced it against a second brush which acted as my 'dust
> pan'. <g> Otherwise, there are situations where you can brush and brush and
> brush and nothing ever seems to leave the surface. I've even watched
> through a magnifying glass as the material I brushed off the top of a cover
> slip jumped back onto the surface (from the brush, and from the side of the
> casing) as I lifted the brush.
>
> Thus: wet cleaning is always the best approach. Still, you need to obtain
> the right materials (able to break those bonds, won't damage seals, etc.)
> and develop good techniques (gloves, disposal, etc.)
>
> Ron Wodaski
>
>
>
> On Apr 1, 2013, at 10:26 AM, Mark Striebeck <mark.striebeck@...>
> wrote:
>
> > Thanks Terry - that's what I figured.
> >
> > What is your (starlight xpress) recommended way to clean that window? I
> > found contradicting recommendations: some say to clean with a (super)
> soft
> > brush (I have one that I use for cleaning my DSLR sensor that I keep
> sealed
> > at all times), others say that you should do it with (low) pressure air.
> >
> > MarkS
> >
> >
> > On Mon, Apr 1, 2013 at 10:14 AM, Terry Platt <
> tplatt@...-uk.net>wrote:
> >
> >> **
> >>
> >>
> >> Hi Stan & Mark,
> >>
> >> That�s about the distance between the CCD and the front window. I think
> >> that you will find that they are nearly all on the outer surface of the
> >> camera window.
> >>
> >> Regards,
> >> Terry (SX Ltd)
> >>
> >> From: Stan
> >> Sent: Monday, April 01, 2013 4:45 PM
> >> To: ccd-newastro@yahoogroups.com
> >> Subject: [ccd-newastro] Re: Cleaning my CCD camera
> >>
> >>
> >> --- Mark Striebeck <mark.striebeck@...> wrote:
> >>> Putting in my values: 4.54 microns, 6.3 focal length,
> >>> 200 pixels leads to 2.8 mm distance to ccd chip.
> >>
> >> I don't see how (I'll talk to the creator of that calculator).
> >>
> >> Assuming the dust mote's actual diameter is insignificant then the
> >> distance should equal the shadow diameter times the f-ratio, right?
> (simple
> >> geometry)
> >>
> >> diam = 4.54u*200 = 0.9mm
> >> distance = 0.9*6.3 = 5.7mm
> >>
> >> BTW, here is another calculator:
> >> http://www.wilmslowastro.com/software/formulae.htm#Dust
> >>
> >> But 6mm is pretty close-in and may be inside the camera but is too far
> to
> >> be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG
> is
> >> not reduced?
> >>
> >> Try to find a build diagram of the camera to see what might be at that
> >> distance. Is there an internal filter wheel? Otherwise just assume that
> >> most of the dust is on the window and clean it.
> >>
> >> Stan
> >>
> >> [Non-text portions of this message have been removed]
> >>
> >>
> >>
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
> > ------------------------------------
> >
> >
> >
> >
>
>
>
> ------------------------------------
>
>
>
>
>

[Non-text portions of this message have been removed]
• I didn t find anything on that link that is opposed to what I was saying. Their remonstrance about dusting is really only saying: if there is stuff that is not
Message 7 of 20 , Apr 1, 2013
• 0 Attachment
I didn't find anything on that link that is opposed to what I was saying. Their remonstrance about dusting is really only saying: if there is stuff that is not chemically bonded, yeah, go ahead and remove that first.

I certainly wasn't suggesting you should clean when it's not necessary. <g>

Ron Wodaski

On Apr 1, 2013, at 10:58 AM, Mark Striebeck <mark.striebeck@...> wrote:

> Hmmm, I found so many sources who warn from exactly this and recommend only
> dusting (e.g. http://www.arksky.org/asoclean.htm . And only revert to
> (liquid) cleaning if absolutely necessary.
>
>
> On Mon, Apr 1, 2013 at 10:43 AM, Ron Wodaski <yahoo@...> wrote:
>
>> The best way to clean any optical surface is wet.
>>
>> For the front window of just about any CCD camera (unless it leaks liquids
>> badly), any pro-quality lens cleaning kit should do the job adequately.
>>
>> By 'pro' in this context I mean a professional photographer; a
>> professional astronomer would be more likely to use dangerous chemicals,
>> such as acetone, to clean a flat surface. That's how we do it at the Tzec
>> Maun Observatory. We also use industrial (not medical) grade gloves - they
>> come quite a bit thicker than most medical gloves, which makes them safer
>> for handling objects with metal edges, and are just as clean out of the
>> box. Avoid gloves with various kinds of 'improvements' such as talc.
>>
>> For optical surfaces, the key problems are various forms of adhesion -
>> chemical bonding, electrostatic forces being the two most common you run
>> into.
>>
>> Chemical bonding occurs when dust or other particles get on the surface,
>> and then the surface gets wet. It takes force to remove such dirt; a liquid
>> facilitates removal both by helping to break the chemical bonds, and to
>> lubricate the surface against scratches once stuff does get loose. Liquid
>> also reduces/sliminates static charge.
>>
>> it can be surprisingly hard to remove dust particles when static charge is
>> present. I recall cleaning a sensor's cover plate once. It took me about 15
>> minutes; I was finally successful when I imagined my little brush to be a
>> broom, and I carefully swept up the dust into a tiny tiny little pile, and
>> then mechanically forced it against a second brush which acted as my 'dust
>> pan'. <g> Otherwise, there are situations where you can brush and brush and
>> brush and nothing ever seems to leave the surface. I've even watched
>> through a magnifying glass as the material I brushed off the top of a cover
>> slip jumped back onto the surface (from the brush, and from the side of the
>> casing) as I lifted the brush.
>>
>> Thus: wet cleaning is always the best approach. Still, you need to obtain
>> the right materials (able to break those bonds, won't damage seals, etc.)
>> and develop good techniques (gloves, disposal, etc.)
>>
>> Ron Wodaski
>>
>>
>>
>> On Apr 1, 2013, at 10:26 AM, Mark Striebeck <mark.striebeck@...>
>> wrote:
>>
>>> Thanks Terry - that's what I figured.
>>>
>>> What is your (starlight xpress) recommended way to clean that window? I
>>> found contradicting recommendations: some say to clean with a (super)
>> soft
>>> brush (I have one that I use for cleaning my DSLR sensor that I keep
>> sealed
>>> at all times), others say that you should do it with (low) pressure air.
>>>
>>> MarkS
>>>
>>>
>>> On Mon, Apr 1, 2013 at 10:14 AM, Terry Platt <
>> tplatt@...-uk.net>wrote:
>>>
>>>> **
>>>>
>>>>
>>>> Hi Stan & Mark,
>>>>
>>>> That’s about the distance between the CCD and the front window. I think
>>>> that you will find that they are nearly all on the outer surface of the
>>>> camera window.
>>>>
>>>> Regards,
>>>> Terry (SX Ltd)
>>>>
>>>> From: Stan
>>>> Sent: Monday, April 01, 2013 4:45 PM
>>>> To: ccd-newastro@yahoogroups.com
>>>> Subject: [ccd-newastro] Re: Cleaning my CCD camera
>>>>
>>>>
>>>> --- Mark Striebeck <mark.striebeck@...> wrote:
>>>>> Putting in my values: 4.54 microns, 6.3 focal length,
>>>>> 200 pixels leads to 2.8 mm distance to ccd chip.
>>>>
>>>> I don't see how (I'll talk to the creator of that calculator).
>>>>
>>>> Assuming the dust mote's actual diameter is insignificant then the
>>>> distance should equal the shadow diameter times the f-ratio, right?
>> (simple
>>>> geometry)
>>>>
>>>> diam = 4.54u*200 = 0.9mm
>>>> distance = 0.9*6.3 = 5.7mm
>>>>
>>>> BTW, here is another calculator:
>>>> http://www.wilmslowastro.com/software/formulae.htm#Dust
>>>>
>>>> But 6mm is pretty close-in and may be inside the camera but is too far
>> to
>>>> be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG
>> is
>>>> not reduced?
>>>>
>>>> Try to find a build diagram of the camera to see what might be at that
>>>> distance. Is there an internal filter wheel? Otherwise just assume that
>>>> most of the dust is on the window and clean it.
>>>>
>>>> Stan
>>>>
>>>> [Non-text portions of this message have been removed]
>>>>
>>>>
>>>>
>>>
>>>
>>> [Non-text portions of this message have been removed]
>>>
>>>
>>>
>>> ------------------------------------
>>>
>>>
>>>
>>>
>>
>>
>>
>> ------------------------------------
>>
>>
>>
>>
>>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
>
>
>
• Many many years ago, when I was doing my own B/W photo printing, I had a special dust brush for cleaning off negatives. Static would normally cause the dust
Message 8 of 20 , Apr 2, 2013
• 0 Attachment
Many many years ago, when I was doing my own B/W photo printing, I had a special dust brush for cleaning off negatives. Static would normally cause the dust particles to return to the negative so the brush had a radioactive emitter strip that eliminated static charges as you wiped off the dust. The strip had a life of only a few years and was an alpha particle emitter. It worked very well.

Phil

--- In ccd-newastro@yahoogroups.com, Ron Wodaski <yahoo@...> wrote:
>
> The best way to clean any optical surface is wet.
>
> For the front window of just about any CCD camera (unless it leaks liquids badly), any pro-quality lens cleaning kit should do the job adequately.
>
> By 'pro' in this context I mean a professional photographer; a professional astronomer would be more likely to use dangerous chemicals, such as acetone, to clean a flat surface. That's how we do it at the Tzec Maun Observatory. We also use industrial (not medical) grade gloves - they come quite a bit thicker than most medical gloves, which makes them safer for handling objects with metal edges, and are just as clean out of the box. Avoid gloves with various kinds of 'improvements' such as talc.
>
> For optical surfaces, the key problems are various forms of adhesion - chemical bonding, electrostatic forces being the two most common you run into.
>
> Chemical bonding occurs when dust or other particles get on the surface, and then the surface gets wet. It takes force to remove such dirt; a liquid facilitates removal both by helping to break the chemical bonds, and to lubricate the surface against scratches once stuff does get loose. Liquid also reduces/sliminates static charge.
>
> it can be surprisingly hard to remove dust particles when static charge is present. I recall cleaning a sensor's cover plate once. It took me about 15 minutes; I was finally successful when I imagined my little brush to be a broom, and I carefully swept up the dust into a tiny tiny little pile, and then mechanically forced it against a second brush which acted as my 'dust pan'. <g> Otherwise, there are situations where you can brush and brush and brush and nothing ever seems to leave the surface. I've even watched through a magnifying glass as the material I brushed off the top of a cover slip jumped back onto the surface (from the brush, and from the side of the casing) as I lifted the brush.
>
> Thus: wet cleaning is always the best approach. Still, you need to obtain the right materials (able to break those bonds, won't damage seals, etc.) and develop good techniques (gloves, disposal, etc.)
>
> Ron Wodaski
>
>
>
> On Apr 1, 2013, at 10:26 AM, Mark Striebeck <mark.striebeck@...> wrote:
>
> > Thanks Terry - that's what I figured.
> >
> > What is your (starlight xpress) recommended way to clean that window? I
> > found contradicting recommendations: some say to clean with a (super) soft
> > brush (I have one that I use for cleaning my DSLR sensor that I keep sealed
> > at all times), others say that you should do it with (low) pressure air.
> >
> > MarkS
> >
> >
> > On Mon, Apr 1, 2013 at 10:14 AM, Terry Platt <tplatt@...>wrote:
> >
> >> **
> >>
> >>
> >> Hi Stan & Mark,
> >>
> >> That's about the distance between the CCD and the front window. I think
> >> that you will find that they are nearly all on the outer surface of the
> >> camera window.
> >>
> >> Regards,
> >> Terry (SX Ltd)
> >>
> >> From: Stan
> >> Sent: Monday, April 01, 2013 4:45 PM
> >> To: ccd-newastro@yahoogroups.com
> >> Subject: [ccd-newastro] Re: Cleaning my CCD camera
> >>
> >>
> >> --- Mark Striebeck <mark.striebeck@> wrote:
> >>> Putting in my values: 4.54 microns, 6.3 focal length,
> >>> 200 pixels leads to 2.8 mm distance to ccd chip.
> >>
> >> I don't see how (I'll talk to the creator of that calculator).
> >>
> >> Assuming the dust mote's actual diameter is insignificant then the
> >> distance should equal the shadow diameter times the f-ratio, right? (simple
> >> geometry)
> >>
> >> diam = 4.54u*200 = 0.9mm
> >> distance = 0.9*6.3 = 5.7mm
> >>
> >> BTW, here is another calculator:
> >> http://www.wilmslowastro.com/software/formulae.htm#Dust
> >>
> >> But 6mm is pretty close-in and may be inside the camera but is too far to
> >> be on the coverslip. Are you sure that flat is binned 1x1 and that JPEG is
> >> not reduced?
> >>
> >> Try to find a build diagram of the camera to see what might be at that
> >> distance. Is there an internal filter wheel? Otherwise just assume that
> >> most of the dust is on the window and clean it.
> >>
> >> Stan
> >>
> >> [Non-text portions of this message have been removed]
> >>
> >>
> >>
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
> > ------------------------------------
> >
> >
> >
> >
>
• So, all I did was to clean the camera window with some air (not compressed, but with a little bellows that I normally use for my DSLR) and then with a DSLR
Message 9 of 20 , Apr 6, 2013
• 0 Attachment
So, all I did was to clean the camera window with some air (not compressed,
but with a little bellows that I normally use for my DSLR) and then with a
DSLR cleaning brush (which I always keep sealed). And now my flats look
like this:
http://3.bp.blogspot.com/-2LOuEM_EUYo/UWD5yTIFzkI/AAAAAAAAinM/huB9RuJGF1Y/s320/00013383.jpg

I wish all problems would be so easy to fix ...

Thanks for all the advice.

MarkS

On Tue, Apr 2, 2013 at 6:48 AM, phils67 <plsherman@...> wrote:

> **
>
>
> Many many years ago, when I was doing my own B/W photo printing, I had a
> special dust brush for cleaning off negatives. Static would normally cause
> the dust particles to return to the negative so the brush had a radioactive
> emitter strip that eliminated static charges as you wiped off the dust. The
> strip had a life of only a few years and was an alpha particle emitter. It
> worked very well.
>
> Phil
>
>
> --- In ccd-newastro@yahoogroups.com, Ron Wodaski <yahoo@...> wrote:
> >
> > The best way to clean any optical surface is wet.
> >
> > For the front window of just about any CCD camera (unless it leaks
> liquids badly), any pro-quality lens cleaning kit should do the job
> adequately.
> >
> > By 'pro' in this context I mean a professional photographer; a
> professional astronomer would be more likely to use dangerous chemicals,
> such as acetone, to clean a flat surface. That's how we do it at the Tzec
> Maun Observatory. We also use industrial (not medical) grade gloves - they
> come quite a bit thicker than most medical gloves, which makes them safer
> for handling objects with metal edges, and are just as clean out of the
> box. Avoid gloves with various kinds of 'improvements' such as talc.
> >
> > For optical surfaces, the key problems are various forms of adhesion -
> chemical bonding, electrostatic forces being the two most common you run
> into.
> >
> > Chemical bonding occurs when dust or other particles get on the surface,
> and then the surface gets wet. It takes force to remove such dirt; a liquid
> facilitates removal both by helping to break the chemical bonds, and to
> lubricate the surface against scratches once stuff does get loose. Liquid
> also reduces/sliminates static charge.
> >
> > it can be surprisingly hard to remove dust particles when static charge
> is present. I recall cleaning a sensor's cover plate once. It took me about
> 15 minutes; I was finally successful when I imagined my little brush to be
> a broom, and I carefully swept up the dust into a tiny tiny little pile,
> and then mechanically forced it against a second brush which acted as my
> 'dust pan'. <g> Otherwise, there are situations where you can brush and
> brush and brush and nothing ever seems to leave the surface. I've even
> watched through a magnifying glass as the material I brushed off the top of
> a cover slip jumped back onto the surface (from the brush, and from the
> side of the casing) as I lifted the brush.
> >
> > Thus: wet cleaning is always the best approach. Still, you need to
> obtain the right materials (able to break those bonds, won't damage seals,
> etc.) and develop good techniques (gloves, disposal, etc.)
> >
> > Ron Wodaski
> >
> >
> >
> > On Apr 1, 2013, at 10:26 AM, Mark Striebeck <mark.striebeck@...> wrote:
> >
> > > Thanks Terry - that's what I figured.
> > >
> > > What is your (starlight xpress) recommended way to clean that window? I
> > > found contradicting recommendations: some say to clean with a (super)
> soft
> > > brush (I have one that I use for cleaning my DSLR sensor that I keep
> sealed
> > > at all times), others say that you should do it with (low) pressure
> air.
> > >
> > > MarkS
> > >
> > >
> > > On Mon, Apr 1, 2013 at 10:14 AM, Terry Platt <tplatt@...>wrote:
>
> > >
> > >> **
> > >>
> > >>
> > >> Hi Stan & Mark,
> > >>
> > >> That's about the distance between the CCD and the front window. I
> think
> > >> that you will find that they are nearly all on the outer surface of
> the
> > >> camera window.
> > >>
> > >> Regards,
> > >> Terry (SX Ltd)
> > >>
> > >> From: Stan
> > >> Sent: Monday, April 01, 2013 4:45 PM
> > >> To: ccd-newastro@yahoogroups.com
> > >> Subject: [ccd-newastro] Re: Cleaning my CCD camera
> > >>
> > >>
> > >> --- Mark Striebeck <mark.striebeck@> wrote:
> > >>> Putting in my values: 4.54 microns, 6.3 focal length,
> > >>> 200 pixels leads to 2.8 mm distance to ccd chip.
> > >>
> > >> I don't see how (I'll talk to the creator of that calculator).
> > >>
> > >> Assuming the dust mote's actual diameter is insignificant then the
> > >> distance should equal the shadow diameter times the f-ratio, right?
> (simple
> > >> geometry)
> > >>
> > >> diam = 4.54u*200 = 0.9mm
> > >> distance = 0.9*6.3 = 5.7mm
> > >>
> > >> BTW, here is another calculator:
> > >> http://www.wilmslowastro.com/software/formulae.htm#Dust
> > >>
> > >> But 6mm is pretty close-in and may be inside the camera but is too
> far to
> > >> be on the coverslip. Are you sure that flat is binned 1x1 and that
> JPEG is
> > >> not reduced?
> > >>
> > >> Try to find a build diagram of the camera to see what might be at that
> > >> distance. Is there an internal filter wheel? Otherwise just assume
> that
> > >> most of the dust is on the window and clean it.
> > >>
> > >> Stan
> > >>
> > >> [Non-text portions of this message have been removed]
> > >>
> > >>
> > >>
> > >
> > >
> > > [Non-text portions of this message have been removed]
> > >
> > >
> > >
> > > ------------------------------------
> > >
> > >
> > >
> > >
> >
>
>
>

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