Re: [APML] IC1396 CCD with Schmidt-like FOV

["Chris & Jennifer Cook" <ccjd@ix.netcom.com>]

Loke -
You feel the blue halos are caused by the ED lens.  I thought of that but
did not think that's what it would be.....  Rob's image has some severe
halos...is the Nikon ED really that bad.......?

Chris


==================
Chris Cook
Astronomical Photography
www.abmedia.com/astro


-----Original Message-----
From: lkt <tan@cox.net>
To: astro-photo@seds.org <astro-photo@seds.org>
Date: Saturday, August 03, 2002 6:50 PM
Subject: Re: [APML] IC1396 CCD with Schmidt-like FOV


>Rob,
>
>I guess I should chime in here since the Schmidt was mentioned. I looked
>at your CCD version and my Schmidt one at:
>
>http://www.starryscapes.com/nebula/cepheus_ic1396.html
>
>My thoughts on this are that the CCD is a better resolution detector
>than Tech Pan. So for the same focal length scope, the CCD will be
>better resolved, assuming equal optical quality. The CCD detector will
>also have lower noise. The vdB142 section of your image is better
>resolved than my Schmidt one by this argument since they both use a
>300mm lens. My 8" f/1.5 Schmidt is also a 300mm lens. One other
>difference here is, I believe the Schmidt is a much better optical
>system than a Nikon ED lens. Since it's a mirrored system, the amount of
>color is very minimal. You only get some color due to the corrector
>plate. 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.
>
>Of course, the big advantage of the Schmidt with TP is the field. The
>Schmidt can illuminate a large image circle (relative to its aperture).
>The image on my website has been cropped. Here is a smaller version
>showing the whole field.
>
>http://www.starryscapes.com/tmp/ic1396_small.jpg
>
>You will need a Nikon lens with a rather short FL to match this field.
>35mm film is 24mmx36mm and the KAF3200 is 10mmx15mm. Using the longer
>dimension, 36/15=2.4. So to match the field of the Schmidt with TP, you
>will need a 125mm lens. I would like to do some widefield work with a
>CCD camera but I cannot find a very well corrected 125mm lens. I mean
>one which is as well corrected as a mirrored system. Furthermore, I
>believe (w/o proof) that the resolution of the ST10 with a 125mm lens
>cannot rival TP with a 300mm Schmidt. But when you get to this FL, I
>believe the CCD approach will lose in resolution to the Schmidt with TP.
>If you can find a 125 colorless lens, you might do better. Of course,
>one can do what you have done, that is to use a longer FL lens for
>higher resolution at certain areas but this technique can apply with the
>Schmidt as well. That is provided you can find a bigger Schmidt, one can
>use the  bigger Schmidt to "fill in the details".
>
>Alternately as technology improves, you can get a much larger CCD array
>than the KAF3200. I know these chips are available but not currently
>affordable within reason. If you can get one the size of a 35mm film,
>you can use the 300mm lens, provide the same field with better
>resolution.
>
>Another issue with widefield images is the almost certainty that there
>will be a very bright star in the field. Note, Antares in the Rho
>Ophiuchus region. Here the linearity of the CCD is it's bane. Saturated
>or bloomed stars are not very pretty and can be a severe limitation to
>your exposure lengths thereby limiting the nebulosity you can attain by
>longer exposures. You can do an h-alpha channel to help but I would
>guess color accuracy might suffer a bit here. To me color accuracy is
>very nebulous in our field of pretty pictures anyway.
>
>I am not claiming that either technique is better, just that there are
>quite a bit of tradeoffs to be made. These are just my thoughts. Feel
>free to disagree.
>
>Loke
>
>
>
>
>
>
>
>Robert Gendler wrote:
>>
>> 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/
>>
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