Posts Made By: Todd Leen

Folks,

I just found these forums. Nice stuff up here.

Here's a mosaic of Cygnus / Cepheus from shots
taken summer and fall 2002.

35mm Pentax 55mm 1:1.8 @ f/3.3
Various exposures in range 10-17min composed.
E-Chrome 200, standard processing
Piggyback on AP-400

Folks,

Here's a second. Casseopeia and
the Perseus Double Cluster.

35mm E-Chrome 200, standard processing
Pentax 55mm 1:1.8 @ f/3.3.
Exposure time NA.
Piggyback on AP400
Nov, 2002

Cheers
Todd

Folks,

I'm wondering if anyone has tried Ilford's
DELTA 3200 black and white film for astrophotography.
It has good red sensitivity past H-alpha (653nm), but poor
reciprocity. (Perhaps it needs hypering.)

Another Ilford emulsion that might be interesting
is SFX200. I has very high red sensitivity - out
to over 700nm. The tech sheet from Ilford doesn't
mention reciprocity characteristics for this film.

Has anyone tried either of these emulsions, either
hypered or unhypered, for astrophotography?

Thanks
Todd

Folks,

I've finally rented a scanner for my slides,
and so can post a couple of items.

Although I like the contrast in the version
of the North America nebula slide, it loses
some of the wispy edge details of softer versions.
Any suggestions on processing are welcome.

Tak Sky-90 at f/4.5, 40 minutes, Elite-Chrome 200,
normal processing.

Cheers
Todd

Folks,

And here's my first prime focus picture
of M31. I intend to go back for a deeper
exposure to compose with this one. Comments
welcome.

Tak Sky-90 @f/4.5, 30 minutes, Elite-Chrome
200, normal processing.

Cheers
Todd

Folks,

Another recent image.
Three, 40 minute exposures on E-200 stacked
in Registar. Tak Sky-90 @ f/4.5 riding on
an AP-400, guided with STV/E-Finder.

Imaged at Gary and Carolyn Strong's Juniper
Sky in the Oregon desert.

Cheers
Todd

Folks,

I'm writing to solicit some help from seasoned
film imagers. I'm getting decent results, but
not as wonderful as some I've seen. So I hope
to pick up some pointers here.

You can also regard this as a processing challenge!

I've been using Elite Chrome 200 with standard
developing on a Tak Sky-90 with f/4.5 flattener/
reducer. The camera is a Pentax KX from the mid-
seventies. Scope is mounted on an AP400 GTO, with
auto-guiding via STV/e-Finder.

Focus is set using a spare Pentax body equipped with
a Ronchi screen at the film plane. I obtain best
focus with the Ronchi screen, and then slew the scope
back and forth (at 1X sidereal rate) using the Ronchi
grating as a knife-edge. I focus manually
(no MotoFocus). Then I swap out the focusing body
for the real camera.

For scanning, I use a (rented) Nikon 4000 or 8000,
scan at 4000dpi, 14 bit, 4x overscan, and
usually reduce to 2700dpi (via bi-cubic interpolation
in PhotoShop 7) for manipulation.

The attached example is an UNPROCESSED image of
Gamma Cygni. (I posted a processed version on
August 21, 2003.) This is actually a stack of
three exposures 2 x 1 hour + 1 x 40min, registered,
histogram matched ("calibrated"), and averaged
in RegiStar.

I believe this is a good starting point, but have
some questions

(i) I *believe* the focus is good. The next post
has a portion of the image at full scale (i.e.
2700 dpi). How does one critically assess focus?

(ii) The brighter stars have a definite RED halo.
Presumably this is from scattering in the red layer.
Is there another currently available astro film that
doesn't show this so prominently?

Is there a recipe for removing this in PhotoShop 7?

(iii) When I stretch the histogram to enhance the
nebulosity, the stars bloat, and sometimes merge.
I've used the star reduction trick in Jerry Lodriguss'
book, but I rather dislike routines that make me change
the image to 8 bit before the very end ...

More to the point, I'd prefer to select the
complement of the stars BEFORE stretching
the histogram. Any suggestions?

I've also tried the Screen-Mask-Invert routine,
from Jerry's book, but always get low-contrast results.
Enhancing the contrast then bloats out the stars,
so this isn't working for me.

(iv) I understand that negative film has greater
dynamic range than slide film. Any particular
suggestions for currently available negative film?
What improvements might I see relative to Elite Chrome
200? What's the down side?

Thanks in advance. I'm hoping the more seasoned
imagers can help me make progress. At the moment,
mine aren't getting any better.

Thanks in advance.

Todd

Folks,

Here's a piece of the Gamma Cygni image
at full scale -- if you can help me evaluate
focus, please do.

Thanks
Todd

Folks,

I've recently started using a Mamiya 645
w/ 80mm f/2.8 for piggyback photos. I
was surprised to find a fair amount of
coma with the lens working at f/4.0

Does anyone have experience with this?
Has anyone used the (faster) 80mm f/1.9 lens?

I'd prefer not to stop down higher than f/4.5
as that's where my prime focus refractor works.

Any experienced opinions on these lenses would
be welcome.

Thanks
Todd

Folks,

My prime focus shots from the October
new moon (using my usual rig, site, and
exposure times) are way past the sky-fog
limit. Was this enhanced sky glow
from the recent solar activity, or
enhanced film sensitivity because
the temperature dipped down to 25F
during the imaging session.

I've been doing prime focus astrophotography
for less than a year and so have no
experience with film in the cold, or
with significant sky glow. I've
settled on Elite Chrome 200 for most
of my shots, and routinely run 45-60 min
exposures through my f/4.5 refractor at
a site in the Oregon desert.

During the October new moon, I returned to
this desert site and ran some exposure of
targets fairly high in the sky (M31, M44,
IC1396), using my usual equipment, film,
and exposure times. The film came back
with far brighter sky background - perhaps
even unusable - than usual. I'm talking
about the sort of difference one would see
from 1-2 stop overexposure of slide film
in a daylight picture.

Two things were different from my usual
conditions: 1) There was intense recent
solar flare activity. 2) For the first
time, the temperature dipped below 32F
while using this film.

What's the experience with E-200 in the
cold? Does the sensitivity increase by
one to two f-stops going from 40F to 25F?

If weather permit I'll do the experiment
now that the cold weather is here and the solar
activity has subsided. But I'd like to
know other's experience with E-200 in the
cold, or with deep sky pictures during the
recent solar activity.

Oh - there was no aurora visible from
the site during the evening I was
imaging. My log notes say that the
sky was not "terribly dark" that night,
but my visual calibration of sky glow is
not accurate - I'm not in the habit of
recording the highest magnitude stars
visible. Does this practice, in fact,
give one a sufficient gauge to adjust
exposures by?

Thanks in advance.
Todd