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Zed
Guest
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 Posted: Thu May 10, 2007 1:11 am Post subject: CA gets worse with time? |
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The chromatic aberration was never that good with my 1st digicam: an Olympus
C4040 from the start but I'm sure it got worse after a while. My current
PowewrShot A710IS was virtually free from it when bought but is showing
increasing levels of it.
It's either my fertile imagination or physical wear in the cams?! |
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Marvin
Guest
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| Posted: Thu May 10, 2007 4:25 pm Post subject: Re: CA gets worse with time? |
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Mike Jacoubowsky wrote:
| Quote: | The chromatic aberration was never that good with my 1st digicam: an
Olympus C4040 from the start but I'm sure it got worse after a while. My
current PowewrShot A710IS was virtually free from it when bought but is
showing increasing levels of it.
It's either my fertile imagination or physical wear in the cams?!
I have no idea if this could be a cause, but over time you can get a fair
amount of condensation and even mold on the inside surfaces of the lenses.
Could that possibly distort light in such a way as to increase CA? What
*would* the effect of mold be on an image (besides presumably making it a
bit softer)?
--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com
Mold would scatter light, and affect the resolution. It |
should not introduce CA. Ca is caused by the differences in
the refractive index vs wavelength of each lens element.
This is controlled by the choice of materials of the
individual elements. It does not change with time. |
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Chris Malcolm
Guest
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| Posted: Fri May 11, 2007 12:35 pm Post subject: Re: CA gets worse with time? |
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Marvin <physchem@cloud9.net> wrote:
| Quote: | Mike Jacoubowsky wrote:
The chromatic aberration was never that good with my 1st digicam: an
Olympus C4040 from the start but I'm sure it got worse after a while. My
current PowewrShot A710IS was virtually free from it when bought but is
showing increasing levels of it.
It's either my fertile imagination or physical wear in the cams?!
I have no idea if this could be a cause, but over time you can get a fair
amount of condensation and even mold on the inside surfaces of the lenses.
Could that possibly distort light in such a way as to increase CA? What
*would* the effect of mold be on an image (besides presumably making it a
bit softer)?
Mold would scatter light, and affect the resolution. It
should not introduce CA. Ca is caused by the differences in
the refractive index vs wavelength of each lens element.
This is controlled by the choice of materials of the
individual elements. It does not change with time.
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THe only thing I can think of that would increase chromatic aberration
would be misalignment of the lens or a lens element due to a serious
knock. If that happened you'd very likely to get asymmetric CA, i.e.,
different at left nd right or top and bottom. With a properly aligned
lens it ought to be good in the middle and degrade symmetrically
towards the edges.
But note that most cameras are built to take pretty serious knocks,
e.g. the not uncommon nasty noise on a windy mountain summit of a
dropped DSLR hitting rock :-)
--
Chris Malcolm cam@infirmatics.ed.ac.uk DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[http://www.dai.ed.ac.uk/homes/cam/] |
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