RE: [APML] 4x5 astrocamera (again?)

[Wei-Hao Wang <wang@IfA.Hawaii.Edu>]

Hi Dave,

The spot size on the spec is only for reference, I think. 
In reality, diffraction, seeing, film grain, and halation
will always add a finite size to the stellar image.
The last two are usually the most important ones for focal
length <1000mm.

Wei-Hao


On Fri, 7 May 2004, D. Kodama wrote:

> Loke,
> 
> Correction -- I was looking at the wrong graph.  My scope's spec states
> that the spot size gets as small as 14 microns.  So it would seem that if
> this is true, with the right film I could be undersampling at 2500 DPI.
> 
> Dave
> 
> 
> 
> > Loke,
> >
> > That should be so, but I wonder sometimes.  I would think that I should be
> > able to distinctly see the film grains in scans if I were oversampling the
> > film but I can't see it on the finer grain films like E100.
> >
> > The spot size spec for my 4" scope (the only one I have info on) is 30
> > microns so 25 micron sampling is not enough for that.  The question is the
> > particular film itself.  I haven't pursued it further, but I have wondered
> > if the combination of the film grains randomly "sampling" the image plus
> > the scanner's uniform pixel sampling shouldn't be taken into account when
> > trying to determine the critical scanner sampling frequency.
> >
> > At any rate, I prefer to be conservative about the scanning.  If you have
> > some information on definitive studies on films and scanning, I'd be
> > interested in hearing about them.
> >
> > Dave
> >
> > P.S.  Eventually I hope to try tricolor tech pan also.  For that I would
> > think I definitely need the full scanner resolution.
> >
> >
> >
> >
> >> Dave,
> >>
> >>  When you scan at 2500 dpi, this is equivalent to 10um per pixel. Does
> >> your
> >> color film have this resolution? Probably not. I would guess that even
> >> 25um
> >> per pixel is more resolution than the film plus optics gives. So all the
> >> extra data gives you no additional information. You might as well scan
> >> at
> >> a
> >> lower resolution.
> >>
> >> Loke
> >>
> >>
> >>
> >>
> >>> -----Original Message-----
> >>> From: astro-photo-bounces@seds.org
> >>> [mailto:astro-photo-bounces@seds.org]On Behalf Of D. Kodama
> >>> Sent: Friday, May 07, 2004 9:55 PM
> >>> To: astro-photo@seds.org
> >>> Subject: Re: [APML] 4x5 astrocamera (again?)
> >>>
> >>>
> >>>
> >>> Wei-Hao,
> >>>
> >>> Thanks for the info on 4x5 film choices.  I recently picked up my own
> >>> combo 4x5" and 6x9cm setup (Mitsuboshi) so the info is appreciated.
> >>>
> >>> Regarding E100SW, awhile back I tried it in 4x5 format but found that
> >>> it
> >>> had a tendency to go to yellow-green on long exposures.  I thought the
> >>> "W"
> >>> (warm) version of E100 would have better red response for nebulosity,
> >>> but
> >>> the green seems to overwhelm things.  I'd be interested in hearing if
> >>> anyone has had a similar result.  I just shot a couple of test frames
> >>> before becoming too busy to proceed further.
> >>>
> >>> By the way, one of the "downsides" of 4x5" is the size of the digital
> >>> files.  My scanner can only do 2500 DPI, but at that resolution a
> >>> 48-bit
> >>> TIFF file is 750,000,000 bytes!
> >>>
> >>> Dave Kodama
> >>>
> >>>
> >>> > Date: Thu, 6 May 2004 15:27:29 -1000 (HST)
> >>> > From: Wei-Hao Wang <wang@IfA.Hawaii.Edu>
> >>> > Subject: Re: [APML] 4x5 astrocamera (again?)
> >>> > To: astro-photo@seds.org
> >>> > Message-ID: <200405070133.i471Xml07592@galileo.ifa.hawaii.edu>
> >>> > Content-Type: TEXT/plain; charset=us-ascii
> >>> >
> >>> > Hi Bobby,
> >>> >
> >>> > Yes, E100S is discontinued.  Now only 4x5 format (perhaps some
> >>> > 120 format E100SW) is available.
> >>> >
> >>> > Wei-Hao
> >
> >
> >
> 
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