Viewing by eye versus astrophotography

I wouldn't disparage visual deep-sky observing because it is as valid a
pursuit in the hobby as any other, I'm only saying that for me it has
always been true that each gray blob looks very much like the previous
gray blob and the next gray blob, even with a largish Dob (18" being
the largest I have observed with for any length of time).

One "gray blob" looking like another is a good point, and I think it raises
the issue of being a good visual observer. Again, please do not assume that
I am saying that you are not - I have never observed with you! However, I do
find that most of the folks I observe with do not observe well. They do not
research what they can see (thanks to the imagers!) and they do not spend
sufficient time at the eyepiece to see as much as there is to be seen.
Visual observing is a skill, and I think that a lot of folks never even
realize that let alone acquire some level of proficiency. Of course,
everyone takes their observing as they like it, and that is great. However,
I do believe that a little bit of knowledge and skill would help a lot of
folks get more out of visual observing.

Dennis

Davoud:
I wouldn't disparage visual deep-sky observing because it is as valid a
pursuit in the hobby as any other, I'm only saying that for me it has
always been true that each gray blob looks very much like the previous
gray blob and the next gray blob, even with a largish Dob (18" being
the largest I have observed with for any length of time).

Dennis Woos:
One "gray blob" looking like another is a good point, and I think it raises
the issue of being a good visual observer. Again, please do not assume that
I am saying that you are not - I have never observed with you! However, I do
find that most of the folks I observe with do not observe well. They do not
research what they can see (thanks to the imagers!) and they do not spend
sufficient time at the eyepiece to see as much as there is to be seen.
Visual observing is a skill, and I think that a lot of folks never even
realize that let alone acquire some level of proficiency. Of course,
everyone takes their observing as they like it, and that is great. However,
I do believe that a little bit of knowledge and skill would help a lot of
folks get more out of visual observing.

As one who was strictly a visual observer for many years (except for
photographing bright Solar-System objects, comets, and eclipses) I
agree entirely.

Davoud

--
Don't re-elect the failures of the past eight years.

usenet *at* davidillig dawt com

Dennis Woos:
...In fact, here is an image of Jupiter - homemade
5" reflector with homemade mirror made by my younger son when he was 12
years old:

http://www.woosfamily.net/~dennis/Ju...1_ps_50pct.jpg

Well, you can tell your son that that's a good image by any measure.

Davoud

--
Don't re-elect the failures of the past eight years.

usenet *at* davidillig dawt com

On Oct 6, 6:51*am, Chris L Peterson wrote:
Just keep in mind that any definition you use is your own. The idea of
magnification simply isn't used by imagers because it isn't useful...

It sometimes takes visual observers a while to get away from the concept
of magnification when they image, but they always get there g. All
that really matters is image scale (resolution) and field of view...


Chris,

Very good inputs to this thread, as usual. I adhered to your point of
view regarding image scale until I was pressed by my wife about what
magnification the image was on the display. I told her that it
depends on how close you are to the monitor, which was not a
satisfying answer! Then I reconsidered that people typically sit
about 1 1/2 feet from their monitors, and that it is helpful to
compare the size of the image to a visual telescopic view. I came up
with this estimate for my system:

http://tinyurl.com/3f7q9t

I appreciate all aspects of imaging, but I come down with Paul
Schlyter's view about take pleasure of a visual view. No matter how
"superior" images are, for me, they are like listening to the stereo
versus seeing the music live. Images on a monitor never put a shiver
down my spine; they never transport me to the object. But that's just
my view on the subject. Astronomy is a great hobby thanks to the many
ways it can be enjoyed.

Tom

On Tue, 7 Oct 2008 22:51:37 +1100, "Peter Webb"
wrote:

I note some excellent photos were taken on a 85 mm aperture refractor.
Somebody in a telescope shop recommended a refractor - I never really
considered them - is there something special about refractors and
astrophotography ?

No, they are simply one type of telescope design, and every design has
its advantages and disadvantages. The advantage of a refractor is that
it tends to be the most structurally solid type, exhibiting little
flexure and seldom requiring collimation. Refractors usually have more
optical surfaces, so they often have higher order corrections allowing
smaller spot sizes farther from the optical axis- useful if you have a
large sensor. On the other hand, they often show chromatic aberration,
which is a problem for single-shot color or unfiltered imaging. Also,
they never provide a lot of aperture, and what aperture they do provide
is expensive in comparison with reflective designs. Aperture is what
determines total exposure time, so if you have a small scope, you'll
need longer imaging sessions. Of course, the smaller aperture also means
a smaller, lighter scope, which can be used with a smaller, less
expensive mount.

Like most issues of astronomical equipment, it's all about tradeoffs.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Davoud:
...a telescope with an eyepiece simply cannot show what is
shown on this page of mine
http://www.primordial-light.com/deepsky.html.

Peter Webb:
Brilliant photos.

Thanks for that kind remark. I've seen better and I'm trying to do
better. I'm not one to blame others for my own shortcomings, but poor
skies in the mid-Atlantic region of the U.S. are killing me.

I note some excellent photos were taken on a 85 mm aperture refractor.
Somebody in a telescope shop recommended a refractor - I never really
considered them - is there something special about refractors and
astrophotography ?

Some of my photos were made with a 76mm refractor.

You are no doubt familiar with the Mac-PC flame wars that erupt from
time to time on the Web--Mac users are Commies, PC users are Nazis, or
vice-versa, and so on.

Those wars are minor scuffles compared to the Reflector-Refractor wars
that have devastated entire worlds. I don't participate in those wars
because I don't have sufficient knowledge of the advantages of the two
systems to argue the matter, even if I were inclined to do so.

Instead, my deep-sky imaging 'scopes are a a 180mm modified Newtonian
reflector _and_ a 106mm refractor. I choose which 'scope to use based
almost entirely upon whim. It is true, however, that the layout of my
tiny observatory makes it more convenient for me to use my astronomical
CCD camera on the refractor and my modified DSLR on the reflector. I'm
not locked into that configuration, however. I decide which camera to
use on which 'scope based on my non-scientific, or at best,
quasi-scientific, assessment as to which camera is more suitable for a
certain target. I often decide based on the results I have seen from
others' work. I am not a researcher; my objective is to produce pretty
pictures.

It's worth noting that, all other things being equal, refractors are a
bit easier to use than most reflectors. A fast astrograph such as my
180mm f/2.8 Newtonian is difficult to focus. I have fixed that problem
with a RoboFocus and a speed reducer. I stole that idea from this web
page http://tinyurl.com/epsilonrobofocus.

Probably the most obvious tell-tale as to whether a photo was made with
a Newtonian or a refractor is the diffraction spikes that are visible
on bright stars on Newtonian images (and on images from
Ritchey-Chretien designs such as the Hubble). Some people love the
spikes and others hate 'em. SAA participant Anthony Ayiomamitis
simulates the metal vanes of the secondary-mirror support that cause
these diffraction spikes by fixing threads to the front of his
refractors, and he does it to beautiful effect, IMO. See, for example,
his photo of M45 at http://www.perseus.gr/Astro-DSO-M45.htm. Those
stars "should not" have diffraction spikes because Mr. Ayiomamitis used
a refractor. As I noted, some would reject them because they are
artificial. I like 'em; beauty remains in the eye of the beholder. I
haven't seen many complaints about the (genuine) diffraction spikes on
the Hubble images, either.

In other words, I don't know if there is anything special about
refractors and astrophotography.

Davoud

--
Don't re-elect the failures of the past eight years.

usenet *at* davidillig dawt com

On Tue, 07 Oct 2008 15:25:34 GMT, Davoud wrote:

Those wars are minor scuffles compared to the Reflector-Refractor wars
that have devastated entire worlds...

Happily, like the fabled Goto-Star Hop wars, these seem to have
disappeared into the past. I think most people have caught on to the
idea that there are some questions that can't be answered with simple
good/bad responses.
_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

In article ,
Tom Polakis wrote:
............
I appreciate all aspects of imaging, but I come down with Paul
Schlyter's view about take pleasure of a visual view. No matter how
"superior" images are, for me, they are like listening to the stereo
versus seeing the music live. Images on a monitor never put a shiver
down my spine; they never transport me to the object. But that's just
my view on the subject. Astronomy is a great hobby thanks to the many
ways it can be enjoyed.

Your comparison with sound recording was good! And the comparison can
be brought further: just like astronomical imaging can show us things
we wouldn't be able to see otherwise (such as UV, IR, X-ray, radio images,
or just images of very faint objects), sound recording too can make us
hear things we wouldn't hear otherwise (e.g. the sonar echoes of bats,
or sounds too weak to be audible to us). However, the pleasure of
actually seeing or hearing something we *can* see and hear is much
bigger than viewing an image or listening to a recording, no matter how
good the image/recording is.

One related side note: young people today are more and more unwilling
to pay for CD records, they prefer to download their music for free from
the Net. But this may not be just simple greed, for young people of today
spend more money on attending live gigs than earlier generations. Perhaps
preference of live over recorded is an important factor here?

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stjarnhimlen dot se
WWW: http://stjarnhimlen.se/

In article , Davoud wrote:

A fast astrograph such as my 180mm f/2.8 Newtonian

A Newtonian isn't an astrograph... http://en.wikipedia.org/wiki/Astrograph


Probably the most obvious tell-tale as to whether a photo was made with
a Newtonian or a refractor is the diffraction spikes that are visible
on bright stars on Newtonian images (and on images from
Ritchey-Chretien designs such as the Hubble). Some people love the
spikes and others hate 'em. SAA participant Anthony Ayiomamitis
simulates the metal vanes of the secondary-mirror support that cause
these diffraction spikes by fixing threads to the front of his
refractors, and he does it to beautiful effect, IMO. See, for example,
his photo of M45 at http://www.perseus.gr/Astro-DSO-M45.htm. Those
stars "should not" have diffraction spikes because Mr. Ayiomamitis used
a refractor. As I noted, some would reject them because they are
artificial. I like 'em; beauty remains in the eye of the beholder. I
haven't seen many complaints about the (genuine) diffraction spikes on
the Hubble images, either.

The creation of those diffcation spikes is interesting, and clearly
shows that being realistic isn't the same as being beautiful.

In modern sound recording/editing software there's a comparable
phenomenon: one common digital filter emulates the distorsion of those
old vacuum tubes !!!! Why would anyone want to deliberately add
distorsion to their own recordings? Well, they like the sound.....




--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stjarnhimlen dot se
WWW: http://stjarnhimlen.se/

In modern sound recording/editing software there's a comparable
phenomenon: one common digital filter emulates the distorsion of those
old vacuum tubes !!!! Why would anyone want to deliberately add
distorsion to their own recordings? Well, they like the sound.....

My younger son has built and uses two vacuum tube guitar amplifiers, and has
no interest in messing around with modern solid-state equipment emulating
vacuum tube sound/distortion. He has taught me that the "instrument" is not
only the electric guitar, but also includes the amplifier and the speakers.
This is not obvious (at least to me), as amplifiers and speakers are
purchased separately and are connected to the guitar with cables, etc.
However, in a more limited way all musical instruments are made up of
sub-instruments that can be mixed and matched (piano actions, flute head
joints, bassoon bocals, violin bows, etc.) In fact, one can argue that the
musical instrument includes the venue and the listener's ears and aural
processing. Compare this to the idea of a telescope including the sky
conditions and the observers's eyesight and visual processing. A good
musician plays the whole instrument, not just the part under their fingers.

Dennis