Re: [APML] Recovering poorly focused images

[Chris Schur <comets133@yahoo.com>]

Emmmanuele,  fixing bad focus on film images is not as
simple as on CCD images such as using deconvolution or
sharpening.  The problem is the film imags have for
one, a high level of saturation in the core of the
stars and data is usually lost here.  The PSF is
complex for star images with film as well, not usually
following a precise gaussian distribution.  There are
only two solutions to this problem.  One, is desparate
but has saved my rear on numerous occasions.  Using
photoshops erode filter, you can SOMETIMES recover
large bloated stars by shrinking them and not terribly
rendering artifacts in the subject.  Apply the erosion
filter and fade (under edit) some percentage starting
at say 50%.  Other wise option 2 - grit your teeth and
chalk that one up to learning and retake the shot.

I hope this helps.  Chris
--- Emmanuele Sordini <vega@bloomingstars.com> wrote:
> Hi list,
> I just got a roll of Supra 400 developed from my
> last astrophoto trip to 
> shoot Comet Q4. Some photos are slightly out of
> focus: I used a 300-mm f/2.8 
> Tamron lens, and while fumbling in the dark I must
> have accidentally hit the 
> focusing wheel, thereby throwing it past infinity.
> It's a pity, because (as per Murphy's laws) this
> happened to my longest 
> (i.e. potentially best) exposures. 
> 
> So I ask you all (and particularly to the image
> processing gurus out there): 
> is there any thingamabob to somehow "undo" the bad
> focusing and rescue those 
> shots? I know this is a case where a program doing
> some "deblurring" or 
> "deconvolution" would come in very handy, and a
> proper PSF (Point Spread 
> Function) could be easily determined (since the
> cause of the blurring known 
> a priori): however, I'm a bit confused as to what
> the best choice would be. 
> 
> Any thoughts/references/links? 
> 
> Thanks in advance,
> Emmmanuele Sordini 
> 
> 
> _______________________________________________
> Astro-Photo mailing list
> Astro-Photo@seds.org
> http://seds.org/mailman/listinfo/astro-photo



	
		
__________________________________
Do you Yahoo!?
SBC Yahoo! - Internet access at a great low price.
http://promo.yahoo.com/sbc/
_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo