Re: [APML] Hybrid approach: First light results Pentax 6x7 Lens use onCCD camera with filter wheel/focuser

[George Anderson <georgea@cam.org>]

Very nice and interesting results.
I am envious of what you are able to capture in 10 minutes with HA
filtering.
How long before you put an 80mm or wider lens on the camera?
I was under the impression that the veil was best with an OIII filter as
opposed to HA. You should (if I am correct) get a stunning shot of the
veil with the OIII.

George Anderson
Montreal Canada

Clear skies and good health

> Richard Crisp wrote:
> 
> I have been experimenting with a homemade adaptor to permit Medium
> Format
> (6x7) Pentax camera lenses to be used with my Astronomical CCD
> cameras. The
> adaptor also features support for a color filter wheel and digital
> focuser.
> 
> One of the interesting properties of the medium format lenses is their
> long
> back focus. That permits me to easily add a color filter wheel and an
> inline
> digital focuser. If I were to use a lens for a 35mm camera I would
> have
> significantly less back focus and would probably be unable to use the
> focuser.
> 
> The other interesting thing about the medium format sized lenses is
> that I
> am using only a small part of the "sweet spot" in the center of the
> FOV. I
> am thinking that may permit me to still take good images without
> having the
> world's most expensive optics etc.....
> 
> I completed the initial configuration of the adaptor late Sunday
> evening,
> Aug 1. Of course as luck would have it I was clouded out at home. The
> next
> two nights also featured significant cloud cover. Last night, however,
> I had
> a break in the clouds long enough to permit me to take a few test
> exposures with the
> 150mm Takumar f/2.8 lens I initially used.
> 
> Initial results show elongated stars in the lower right corner of each
> image. Furthermore there is some defocusing in that part of the image.
> This
> all points to a tilt of the lens axis relative to the optical axis. My
> next
> move will be to add a tilt adjustment (push pull screws) to
> hopefully permit that to be "tuned out".
> 
> In interest of documenting what I have done, I have prepared a web
> page that
> shows pictures of the adaptor in action, as well as test images. Some
> are
> terrestrial (the first ones) and the ones from last night. For indoor
> shooting under normal room lighting, I was using an [OIII] filter with
> 30
> second exposures. The indoor images are not dark subtracted or flat
> fielded.
> The astro images were dark subtracted but not flat fielded.
> 
> Comments welcome.
> 
> http://www.narrowbandimaging.com/pentax_6x7_lens_adaptor_page.htm
> 
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