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Exposure time im space

 
 
John Bean
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      07-03-2007
On Mon, 02 Jul 2007 19:35:29 -0600, "Roger N. Clark (change
username to rnclark)" <(E-Mail Removed)> wrote:

>John Bean wrote:
>> On Sun, 01 Jul 2007 21:09:03 -0600, "Roger N. Clark (change
>> username to rnclark)" <(E-Mail Removed)> wrote:
>>
>>> John Bean wrote:
>>>> On Sun, 01 Jul 2007 14:04:51 -0600, "Roger N. Clark (change
>>>> username to rnclark)" <(E-Mail Removed)> wrote:
>>>>> and if
>>>>> it has an atmosphere, the absorption of sunlight through
>>>>> the atmosphere.
>>>> So you think the planetary atmosphere wouldn't affect a 18%
>>>> grey card?
>>> That's why I said "absorption of sunlight through
>>>>> the atmosphere."

>>
>> You didn't, Roger. You said:
>>
>> "Assuming you wanted to expose an 18% gray card, then
>> the exposure would be the square of the relative distance
>> of the planet from the sun compared to the earth."
>>
>> No mention of effect of atmosphere in the calculated
>> exposure, which is why I asked.

>
>You didn't read the next paragraph in the same post,
>where I said:
>
>"If you want to expose for the average scene brightness
>on that planet (or moon), then you also need to take into
>account the reflectivity of the planetary surface, and if
>it has an atmosphere, the absorption of sunlight through
>the atmosphere."
>
>Please read the complete post before jumping to conclusions.


Of course I read the whole post, you're certainly jumping to
conclusions. My (incorrect) understanding of it was:

"Assuming you wanted to expose an 18% gray card..." followed
by your calculation, then an implied:

"[alternatively] If you want to expose for the average scene
brightness..."

That's what prompted my question, and my acknowledgement
after you clarified it. No need to be so pompous about it.

--
John Bean
 
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Nick Fotis
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      07-10-2007
Let's suppose someone sends on a space probe (or with an astronaut) a camera
with a sensor like the Canon 5D, and a sensor without an IR-blocking filter
(only optical glass).

My 'what if' question is: Could someone do interesting (optically and
scientifically) photography in the outer planets with these two commercial,
off the shelf (sorta) sensors?

Let's leave environmental problems that could preclude operation of the
cameras (like temperatures, cosmic radiation, dust on the sensor or
humidity) off the discussion (after all, we could "just" make a super-duper
housing like these for underwater photography (I know, I am simplifying
things 'a bit' ).

Cheers from a HOT Athens,
N.F.
 
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Mike Russell
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      07-10-2007
"Nick Fotis" <(E-Mail Removed)> wrote in message
news:f6vs1p$2sct$(E-Mail Removed)...
> Let's suppose someone sends on a space probe (or with an astronaut) a
> camera
> with a sensor like the Canon 5D, and a sensor without an IR-blocking
> filter
> (only optical glass).
>
> My 'what if' question is: Could someone do interesting (optically and
> scientifically) photography in the outer planets with these two
> commercial,
> off the shelf (sorta) sensors?
>
> Let's leave environmental problems that could preclude operation of the
> cameras (like temperatures, cosmic radiation, dust on the sensor or
> humidity) off the discussion


My take - and it will be interesting to see what Roger has to say - is that
with an attitude control system to aim and otherwise control the camera,
power, and a transmission system to return the image, yes, some very
interesting images indeed could be produced by these cameras. The quality
would probably be superior to what we're getting back now, considering that
the outer planet probes were launched a decade or more ago.

> (after all, we could "just" make a super-duper
> housing like these for underwater photography (I know, I am simplifying
> things 'a bit' ).


Or, you seem to be saying, a camera to be handled by an astronaut.
Absolutely - this would work, modulo a few details as you say.
--
Mike Russell - www.curvemeister.com


 
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Roger N. Clark (change username to rnclark)
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      07-11-2007
Mike Russell wrote:
> "Nick Fotis" <(E-Mail Removed)> wrote in message
> news:f6vs1p$2sct$(E-Mail Removed)...
>> Let's suppose someone sends on a space probe (or with an astronaut) a
>> camera
>> with a sensor like the Canon 5D, and a sensor without an IR-blocking
>> filter
>> (only optical glass).
>>
>> My 'what if' question is: Could someone do interesting (optically and
>> scientifically) photography in the outer planets with these two
>> commercial,
>> off the shelf (sorta) sensors?
>>
>> Let's leave environmental problems that could preclude operation of the
>> cameras (like temperatures, cosmic radiation, dust on the sensor or
>> humidity) off the discussion

>
> My take - and it will be interesting to see what Roger has to say - is that
> with an attitude control system to aim and otherwise control the camera,
> power, and a transmission system to return the image, yes, some very
> interesting images indeed could be produced by these cameras. The quality
> would probably be superior to what we're getting back now, considering that
> the outer planet probes were launched a decade or more ago.


Yes, I agree. There are in fact spacecraft scenarios where
a Bayer array camera would be great in my opinion.
Convincing others is a challenge, however. Often on a fast
fly-by, a high resolution color picture could give an
amazing amount of detail. What we have now are typically
lower megapixels CCD with a filter wheel, so to get color,
you must take 3 separate pictures, then later combine them
later reprojecting to compensate for spacecraft motion.
(Example: Cassini with a 1-megapixel CCD; of course it was
designed in the early 1990's.)

The challenge is convincing other scientists that such a camera
would be worth the expensive spacecraft resources over
a multiple filter solution. Filters allow one to cover
a larger wavelength range with more channels (e.g. 8 to 12
wavelengths from 3000 to 10,000 angstroms instead of
just red, green and blue). My personal preference
would be a high megapixel context RGB (Bayer) camera
plus a lower spatial resolution imaging spectrometer.
Such systems have been proposed.

>> (after all, we could "just" make a super-duper
>> housing like these for underwater photography (I know, I am simplifying
>> things 'a bit' ).

>
> Or, you seem to be saying, a camera to be handled by an astronaut.
> Absolutely - this would work, modulo a few details as you say.


I agree.

Roger
 
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Nick Fotis
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      07-11-2007
Roger N. Clark (change username to rnclark) wrote:

> Yes, I agree. There are in fact spacecraft scenarios where
> a Bayer array camera would be great in my opinion.


Suppose that today someone can make a radiation-hardened version of the
Canon 1D MkIII sensor (or the 5D, if you want more megapixels).
What lense(s) would you add to it?
I suppose the 28-300L IS in a motorized version is out of the question?

> Convincing others is a challenge, however. Often on a fast
> fly-by, a high resolution color picture could give an
> amazing amount of detail. What we have now are typically
> lower megapixels CCD with a filter wheel, so to get color,
> you must take 3 separate pictures, then later combine them
> later reprojecting to compensate for spacecraft motion.


I suppose that indeed, cases like a fast flyby would be perfect for a
one-shot camera sensor.

The description you gave, reminds to me large format scanning backs.
If you have all the time in the world (not always possible, e.g. you want to
record volcano activity during a fast flyby), this slow, measured approach
may work (and then, how do you send back all this mass of data? 20+ MB
compressed RAW files don't sound a great idea to me).

> The challenge is convincing other scientists that such a camera
> would be worth the expensive spacecraft resources over
> a multiple filter solution. Filters allow one to cover
> a larger wavelength range with more channels (e.g. 8 to 12
> wavelengths from 3000 to 10,000 angstroms instead of
> just red, green and blue). My personal preference
> would be a high megapixel context RGB (Bayer) camera
> plus a lower spatial resolution imaging spectrometer.


Would the cost of such a COTS sensor offset the somewhat limited wavelength
range it would record? O we just could use the 'astronomy' edition of the
Canon 20DA, without the IR-blocking filter, in a secondary body.
What about the possibility keeping the lens fixed and exchanging sensors
during flyby?
This would be too heretical for your scientist coworkers I guess

>>> (after all, we could "just" make a super-duper
>>> housing like these for underwater photography (I know, I am simplifying
>>> things 'a bit' ).

>>
>> Or, you seem to be saying, a camera to be handled by an astronaut.
>> Absolutely - this would work, modulo a few details as you say.


Yes, this would be the second scenario - like the Apollo astronauts who used
modified Hasselblad cameras on the moon (if I am not mistaken, already
dSLRs are used across the space shuttle and ISS).

Cheers,
N.F.
 
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Roger N. Clark (change username to rnclark)
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      07-13-2007
Nick Fotis wrote:
> Roger N. Clark (change username to rnclark) wrote:
>
>> Yes, I agree. There are in fact spacecraft scenarios where
>> a Bayer array camera would be great in my opinion.

>
> Suppose that today someone can make a radiation-hardened version of the
> Canon 1D MkIII sensor (or the 5D, if you want more megapixels).
> What lense(s) would you add to it?
> I suppose the 28-300L IS in a motorized version is out of the question?


Moving parts on a spacecraft mission are generally high risk.
So fixed lenses would usually the better way to go.

Regarding "radiation-hardened:" that means specific
requirements, and consumer cameras may have components that
already are "hard" and just need testing and certification.
More and more standard electronics are getting tested and
qualified for use in spacecraft. There are also different
classes: lower ratings can be used in some scientific
instruments, but spacecraft health and navigation must
use the highest rated components. Things like the
"error 99" remove the batteries are a red flag to not
be used on a spacecraft (no one there to take out the
batteries) .

>
>> Convincing others is a challenge, however. Often on a fast
>> fly-by, a high resolution color picture could give an
>> amazing amount of detail. What we have now are typically
>> lower megapixels CCD with a filter wheel, so to get color,
>> you must take 3 separate pictures, then later combine them
>> later reprojecting to compensate for spacecraft motion.

>
> I suppose that indeed, cases like a fast flyby would be perfect for a
> one-shot camera sensor.
>
> The description you gave, reminds to me large format scanning backs.
> If you have all the time in the world (not always possible, e.g. you want to
> record volcano activity during a fast flyby), this slow, measured approach
> may work (and then, how do you send back all this mass of data? 20+ MB
> compressed RAW files don't sound a great idea to me).


Take a look at the MRO HIRISE camera: 20,000 pixels across, by
some length (40,000 if I remember correctly). They can only
send down an image occasionally. Data return to Earth is one of the
major limitations to deep space probes.

>> The challenge is convincing other scientists that such a camera
>> would be worth the expensive spacecraft resources over
>> a multiple filter solution. Filters allow one to cover
>> a larger wavelength range with more channels (e.g. 8 to 12
>> wavelengths from 3000 to 10,000 angstroms instead of
>> just red, green and blue). My personal preference
>> would be a high megapixel context RGB (Bayer) camera
>> plus a lower spatial resolution imaging spectrometer.

>
> Would the cost of such a COTS sensor offset the somewhat limited wavelength
> range it would record? O we just could use the 'astronomy' edition of the
> Canon 20DA, without the IR-blocking filter, in a secondary body.
> What about the possibility keeping the lens fixed and exchanging sensors
> during flyby?
> This would be too heretical for your scientist coworkers I guess


Again moving sensors around means moving parts. Moving parts add
weight, need power and software. It is usually cheaper to add
a second camera. For example, the Cassini spacecraft orbiting
Saturn has two CCD cameras: 1 megapixel sensors with a narrow
angle camera lens (i.e telephoto) and wide angle, both fixed
lenses.

Roger
 
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Larry Bud
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      07-13-2007
On Jul 1, 9:05 am, Don Stauffer in Minnesota <(E-Mail Removed)>
wrote:
> On Jul 1, 6:20 am, Alfred Molon <(E-Mail Removed)> wrote:
>
> > Just curious - assuming you were on a planet, Mars, Saturn, Venus,
> > Neptune etc., what exposure time would be necessary to take a photo at
> > ISO 100 and F4 or F8 ?
> > --

>
> > Alfred Molon
> > ------------------------------
> > Olympus 50X0, 7070, 8080, E3X0, E4X0 and E5X0 forum athttp://tech.groups.yahoo.com/group/MyOlympus/http://myolympus.org/photosharing site

>
> The light falls off as the square of the distance. Find a chart of
> planetary distances in AUs (one AU is radius of earth orbit). Or,
> convert from miles (1 AU = 93,000,000 miles). Now, square the number
> of AUs, this is the factor the earth exposure time must be multiplied
> by.
>
> As an example, I believe mars is about 2 AU. Thus one must make an
> exposure four times what it would be on earth.


That's assuming the same % of light penetrates the atmosphere of each
planet. Mars has a very thin atmosphere, so I would expect a larger %
of the light that arrives at Mars reaches the surface.

Not to mention the cold. What kind of havoc would that have on a
digital camera?


 
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John Bean
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      07-13-2007
On Fri, 13 Jul 2007 05:04:48 -0700, Larry Bud
<(E-Mail Removed)> wrote:
>Not to mention the cold. What kind of havoc would that have on a
>digital camera?


It would improve its noise performance

--
John Bean
 
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