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Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
Mike,
Hmmm, I wouldn't know. Our eyes are more sensitive in the green range though the curve looks very red.
Loke
>
> From: "Mike Cook, AF9Y" <mwcook@concentric.net>
> Date: 2002/08/04 Sun PM 04:36:17 EDT
> To: astro-photo@seds.org
> Subject: Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
>
> I'm almost sure that it is a linear scale. At least the plot for M57 taken by
> the same group is linear since it matches some of my direct measurements.
> As a side note, look at the spectrum for a firefly:
>
> http://www1.harenet.ne.jp/~aikow/firefly.gif
>
> Given all the energy 600nm, why do fireflies appear yellow green rather
> than red?
>
> Mike
>
>
> From: lkt <tan@cox.net>
> To: astro-photo@seds.org
> Subject: Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
> Date sent: Sun, 4 Aug 2002 16:36:04 -0400
> Send reply to: astro-photo@seds.org
>
> > Mike,
> >
> > Thats a good point. Do you know if "intensity" is on a log or a linear scale. There is no
> > data most of the way down to 400nm. If we assume a log scale and just extend the line
> > down to "0" at 400nm (big guestimate), the central wavelengths of the star is in the
> > "3.5" range and the 400nm region in the "0" range. Assuming a log base 10 scale, then
> > 10^3.5=3162. In otherwords, the 400nm intensity is fainter by 3162 times the central
> > wavelength intensities. If the star was near saturation with 2^16 adus then the 400nm
> > region would be in the 20 adu region. This would certainly be in the noise. If the star
> > has bloomed and is quite a bit above saturation, the 400nm region could be noticeably
> > higher then 20 adu. If we assume that the curve flattens off at "2" for 400nm (just like
> > it did for the high end wavelengths), we would certainly detect this as this is only 31X
> > fainter than the central region. Nevertheless, to do this right, one will have to
> > integrate the curve.
> >
> > If intensity was on a linear scale, and the intensity flattened off somewhere appreciably
> > above 0, we would definately detect it.
> >
> > Bottom line is, we need the data from 450nm down to 400nm as it could make a huge
> > difference whether we can detect it or not.
> >
> > Loke
> >
> >
> >
> >
> > >
> > > From: "Mike Cook, AF9Y" <mwcook@concentric.net>
> > > Date: 2002/08/04 Sun AM 11:26:20 EDT
> > > To: astro-photo@seds.org
> > > Subject: Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
> > >
> > > But just how much energy does a typical B class star emit above 450nm?
> > > For example, the bright blue star (SAO33458) in the lower left corner of
> > > Rob's image is a B class star. Take a look at a typical B class spectrum:
> > >
> > > http://www1.harenet.ne.jp/~aikow/HD203025.gif
> > >
> > > The energy starts to fall off dramatically below 475nm. On top of that,
> > > you have the increased atmospheric absorption.
> > >
> > > Still, there may be enough defocus and enough light collected to cause
> > > the halos. Even Rob's blue filter focus could have been off for one
> > > of the multiple images. I guess we won't know for sure until someone
> > > does the before/after cutoff filter test.
> > >
> > > Mike Cook
> > > AF9Y
> > >
> > >
> > >
> > >
> > > From: lkt <tan@cox.net>
> > > To: astro-photo@seds.org
> > > Subject: Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
> > > Date sent: Sun, 4 Aug 2002 3:34:39 -0400
> > > Send reply to: astro-photo@seds.org
> > >
> > > > Mike,
> > > >
> > > > The QE of the KAF3200E is 30% at 400nm and the KAF3200ME is 60% at 400nm. The QEs are
> > > > about twice as high at the central blue peak (450nm). The Custom Scientific blue
> > > > filter passes 90% at the central peak and 50% at 400nm (approx). At 390nm it still
> > > > passses 30-40%. So for either chip, if I did my math correctly, the effective
> > > > sensitivity at 400nm is 1/4 that at central blue (450nm). It's still very high. I
> > > > believe that it's high enough to show a halo around bright blue stars if the light is
> > > > not focused. Note that a lot of the bright blue stars might take up half to all the
> > > > dynamic range of the CCD, i.e. 2^16 when near saturation. The fractional portion of
> > > > the 2^16 which is out of focus could very well be noticeable. This is especially so
> > > > is you apply DDP to non-linearly skew the light curve. Notice that when you apply a
> > > > larger DDP amount, the blue halos are more noticeable.
> > > >
> > > > Loke
> > > >
> > > >
> > > >
> > > > >
> > > > > From: "Mike Cook, AF9Y" <mwcook@concentric.net>
> > > > > Date: 2002/08/04 Sun AM 01:24:16 EDT
> > > > > To: astro-photo@seds.org
> > > > > Subject: Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
> > > > >
> > > > > Loke,
> > > > >
> > > > > Maybe. But, the CCD response on the blue end is not that much better
> > > > > than commercial film. And Nikon's performance for a single mid band
> > > > > focus is so good that it is hard for me to believe that a blue center focus
> > > > > would not be sufficient. An easy test would be to check a blue filter
> > > > > focused image with and without the IDAS filter which cuts off everything
> > > > > below 410nm. If there is a significant difference in FWHM between
> > > > > the two images, then we would have the answer.
> > > > >
> > > > > Mike
> > > > >
> > > > >
> > > > >
> > > > > From: lkt <tan@cox.net>
> > > > > To: astro-photo@seds.org
> > > > > Subject: Re: Re: [APML] IC1396 CCD with Schmidt-like FOV
> > > > > Date sent: Sun, 4 Aug 2002 0:59:25 -0400
> > > > > Send reply to: astro-photo@seds.org
> > > > >
> > > > > > Mike,
> > > > > >
> > > > > > Like I said in another response, chromatic abberation is continously changing
> > > > > > from in focus to more and more out of focus. Splitting focus to RGB just ensures
> > > > > > that you are in focus within the central wavelengths of the 3 filters. Most APOs
> > > > > > are well corrected for visual wavelengths but the CCD is has a much wider
> > > > > > spectral sensitivity. Remember the IR focus problems of the past. Well, to a
> > > > > > lesser degree, this is happening at the low end of the blue spectrum as well. I
> > > > > > believe the camera lens makers mostly optimize their color correction for color
> > > > > > film. Both Tech Pan and CCDs have extended blue and IR response. For the blue
> > > > > > filter especially, you might be way out of focus for the lower wavelengths even
> > > > > > if you focused for the center region of the blue filter. I believe the blue end
> > > > > > of the spectrum goes out of focus exponentially. Some of the ATM guys here can
> > > > > > coonfirm or correct me on this.
> > > > > >
> > > > > > Loke
> > > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > From: "Mike Cook, AF9Y" <mwcook@concentric.net>
> > > > > > > Date: 2002/08/03 Sat PM 07:38:35 EDT
> > > > > > > To: astro-photo@seds.org
> > > > > > > Subject: Re: [APML] IC1396 CCD with Schmidt-like FOV
> > > > > > >
> > > > > > > Loke,
> > > > > > >
> > > > > > > Thanks for the insightful comparison. I would like to further understand
> > > > > > > your comments about the chromatic aberration of Nikon ED lens. I have the
> > > > > > > Nikon 180 F/2.8 ED lens and have not seen this problem. Michael Covington
> > > > > > > has also commented about the excellent chromatic aberration performance of
> > > > > > > the Nikon ED lens here:
> > > > > > >
> > > > > > > http://www.mir.com.my/rb/photography/hardwares/speciallenses/180nikkor.htm
> > > > > > >
> > > > > > > Besides, why should chromatic aberration of a lens be much a problem
> > > > > > > anyway? If you refocus for each of the RGB filters and register the images with
> > > > > > > a program like RegiStar, it would appear to be a non issue. What am I missing?
> > > > > > >
> > > > > > > Mike Cook
> > > > > > > AF9Y
> > > > > > >
> > > > > > >
> > > > > > > >From: lkt <tan@cox.net>
> > > > > > >
> > > > > > > >............ The Nikon ED lens has noticeable blue haloing on the bright blue
> > > > > > > > stars. Imagine how much nicer your image could have been w/o chromatic
> > > > > > > > abberation. The blue custom scientific filter allows light into the CCD
> > > > > > > > detector almost all the way down to 400nm. .................
> > > > > > >
> > > > > > > Mike Cook, AF9Y
> > > > > > > http://www.af9y.com
> > > > > > > mwcook@cris.com
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
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> > > > >
> > > > >
> > > > >
> > > > > Mike Cook, AF9Y
> > > > > http://www.af9y.com
> > > > > mwcook@cris.com
> > > > >
> > > > >
> > > > >
> > > > >
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> > >
> > >
> > >
> > > Mike Cook, AF9Y
> > > http://www.af9y.com
> > > mwcook@cris.com
> > >
> > >
> > >
> > >
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>
>
> Mike Cook, AF9Y
> http://www.af9y.com
> mwcook@cris.com
>
>
>
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