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Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
Loke,
I see what you are saying. If the chromatic aberration was that bad though
wouldn't all the stars would be fuzzy? The stars are actually pretty tight
with the exception of the bright blue stars.
Rob Gendler
Email: robgendler@att.net
Web site: http://www.robgendlerastropics.com/
----- Original Message -----
From: "lkt" <tan@cox.net>
To: <astro-photo@seds.org>
Sent: Sunday, August 04, 2002 12:51 AM
Subject: Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
> Rob,
>
> The chromatic abberation you see in lenses cannot be gotten rid of by
focusing. Lets use the typical blue filter for example. Say it passes
400nm - 500nm. You focus as best as you can for 450nm. But 400nm is still
out of focus. The focus is shifting continously from 500nm down to 400nm. It
is not possible to bring all the wavelengths of light to the same focus
because they are all different. This is a bit of an exageration, as every
lens is a bit different.
>
> Now if you have a hundred 1nm wide filters with center wavelengths from
400nm to 500nm, and you take 100 exposures from 400nm to 500nm and refocus
for each of them. Then register/scale and reconstruct your blue channel,
then you will have pretty good focus.
>
> I believe most ED lenses for cameras are corrected for color film and
probably not well corrected down to 400nm. I have no proof for this
statement. Zeiss makes two superachromat lenses at 250mm and 350mm for
Hasselblad. See:
>
> http://www.zeiss.de/C12567A8003B58B9?Open
>
> They claim color correction from 400nm - 1000nm within the Raleigh limit
of focusing uncertainty. There must be a reason why they separated out these
two lenses as ebing better corrected than the rest.
>
> Loke
>
>
>
>
>
> >
> > From: "Robert Gendler" <robgendler@worldnet.att.net>
> > Date: 2002/08/03 Sat PM 09:07:51 EDT
> > To: <astro-photo@seds.org>
> > Subject: Re: [APML] IC1396 CCD with Schmidt-like FOV
> >
> > Chris,
> > Thanks. As I mentioned in my response to Loke I doubt its
> > chromatic aberration. I focused carefully for each filter. If you
> > check out Lokes image or any film image for that matter it is
> > common to see halos around bright stars. In the CCD world DDP
> > seems to accentuate this. BTW the lens is far from an APO. The focus
> > was significantly different through each filter. When using my FSQ106
> > I never need to focus separately for each filter.
> > Rob Gendler
> > Email: robgendler@att.net
> > Web site: http://www.robgendlerastropics.com/
> > ----- Original Message -----
> > From: "Chris & Jennifer Cook" <ccjd@ix.netcom.com>
> > To: <astro-photo@seds.org>
> > Sent: Saturday, August 03, 2002 6:26 PM
> > Subject: Re: [APML] IC1396 CCD with Schmidt-like FOV
> >
> >
> > > Hi Rob -
> > >
> > > Beautiful images as always!
> > > I got a question though. What is causing the bluish halos around the
> > > brighter stars?
> > >
> > > Chris
> > >
> > >
> > > ==================
> > > Chris Cook
> > > Astronomical Photography
> > > www.abmedia.com/astro
> > >
> > >
> > > -----Original Message-----
> > > From: Robert Gendler <robgendler@worldnet.att.net>
> > > To: astro-photo@seds.org <astro-photo@seds.org>
> > > Date: Saturday, August 03, 2002 10:24 AM
> > > Subject: [APML] IC1396 CCD with Schmidt-like FOV
> > >
> > >
> > > >Hi all,
> > > >Using Nikon 180mm and 300mm lenses and the ST10
> > > >I've created a widefield color image of the IC1396 complex.
> > > >The inner detail of the nebula was imaged with the 300mm lens
> > > >(using HA and red as luminance) and the outer portion was taken
> > > >with the 180mm giving the generous FOV (straight RGB). I believe
> > > >the FOV and detail compare favorably with schmidt camera and
> > > >medium format film images of this object which demonstrates
> > > >that large field color imaging can be done successfully with CCD
> > > >and camera lenses. The widefield image is at
> > > >http://www.robgendlerastropics.com/1396Large.html
> > > >A cropped higher res version is at
> > > >http://www.robgendlerastropics.com/1396Small.html
> > > >The lenses were mounted on the ST10 using Steve Mandels adaptor
> > > >and were secured on the mount using two losmandy adjustable tube
rings.
> > > >The 150mm ring fit perfectly around the ST10 while the 125mm ring
> > > >supported the lenses. I have two pictures of the setup at
> > > >http://www.robgendlerastropics.com/camera300.jpg
> > > >http://www.robgendlerastropics.com/camera180.jpg
> > > >Enjoy!
> > > >Rob Gendler
> > > >Email: robgendler@att.net
> > > >Web site: http://www.robgendlerastropics.com/
> > > >
> > > >
> > > >-- APML Archives at <http://astro.umsystem.edu/apml/> ---
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> > > >
> > >
> > >
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> >
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>
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