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Re: [APML] New Horsehead - an interesting comparison?
Philip,
Welcome to the world of round images. (G) Question, have you cropped the
horse from the film image at full resolution to compare it to the CCD image?
I wonder how the two would compare. I'm really not trying to be biased
against CCD images, but the image scale and star sizes of the film image are
much more pleasing to me.
Very nice images, even if it is "yet another".
Jim
----- Original Message -----
From: "Philip Perkins" <philip@astrocruise.com>
To: <astro-photo@seds.org>
Sent: Saturday, January 19, 2002 12:31 PM
Subject: [APML] New Horsehead - an interesting comparison?
> I've been slow processing the images from southern France in December -
too
> much time away on business trips unfortunately. But anyway here is the
> latest of my images from southern France... it is of the Horsehead (yet
> another!) taken with the RCOS 12.5" working at f/6.75 with the AP focal
> reducer. Guiding was with the ST-4 using a custom OAG designed by Chuck
> Vaughn. The camera was the Pentax 67 using hypered Kodak GPY
> (PPF). During the trip I ran out of both freshly hypered film and N2 gas,
> so the last two exposures of the four stack were taken using film that was
> hypered in June 2001 with no gas purge. One of the problems with this
> image is that I did not properly assess the effective f/ratio (T-stop)
> hence all of the negatives were somewhat underexposed (these were my first
> film images with the RC):
>
> http://www.astrocruise.com/horserc.htm
>
> I found it interesting to compare this image with a CCD image of the
> Horsehead which I took during the same trip (some of you who subscribe to
> the SBIG list may have seen this before). The interesting thing is that
> the CCD image was taken using the exact same telescope and optical
> configuration just two nights later (conditions were very similar):
>
> http://www.astrocruise.com/horse.htm
>
> It seems to me that the two images could hardly be more different
> considering that they were of essentially the same object taken with
> exactly the same optics. The huge additional field covered by the film
> image stands out strongly of course, as does the response to the very
> bright star Alnitak. I don't know that a CCD camera would ever be able to
> record Alnitak in such an 'analogue' way. The CCD image has its own
> strengths and would probably be considered as the more technically
accurate
> rendition. To me this is an interesting illustration of the vastly
> different results that can be obtained from film and CCD. They both have
> their strengths but they serve a different purpose.
>
> The important thing not to forget is the vastly different image scale of
> the two original images. It is easy to lose sight of this when viewing
> images on a monitor. Whereas the CCD image is displayed at its full
> original resolution, the film image has been downscaled massively to fit
> the monitor resolution. The original film image will make a high quality
> 20"x20" Lightjet print with no upscaling at all, whereas the CCD image
will
> make a 6"x4" print with no upscaling. Of course, the CCD image will
> tolerate upscaling rather better, but even so the CCD image will never
come
> close to the print size obtainable with the film image. The issue of
> detector size in relation to the making of large prints has no
> reasonable answer with current CCD technology. The number of CCD mosaics
> required to emulate the film image would be impractical. Moreover the
film
> image, with its rather saturated colours, will make a very fine Lightjet
> print. With modest upscaling it will easily make a quality 30"x30" print.
>
> Very different, I think you'll agree... comments welcome!
>
> --Philip
> Philip Perkins - philip@astrocruise.com
> Wiltshire UK & Luberon France
> Astrocruise - http://www.astrocruise.com
>
>
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