OT - Photoshop question

On Mon, 25 Sep 2006 17:33:41 GMT, Jonathan Silverlight
wrote:

In message , Pete Lawrence
writes
On 19 Sep 2006 13:59:10 -0700, wrote:

Such as writing that CMOS as seen in DSLR have QE up to 50% when in all
likelyhood we are talking 8-10% here. Or such as recommending 800 or
1600 ISO for deep-sky work. Or as saying that you need the mirror
lock-up if you want to shoot the planets/moon/sun. From what I've read
it seems to be heavily centered on Canons and the Da in particular.

To be fair to Jerry, the reference to QE was based on the empirical
findings of Roger Clark and others which show a paeak QE in the green
part of the spectrum at around 50%.

800-1600 ISO is used because most DLSR imagers don't autoguide. Again,
to be fair to Jerry, he does explain that lower ISO values will give
better results if you can use them.

The Canons are the best DLSRs for atrophotography for numerous
reasons. The 20Da is the best non-modified model in the range for the
purpose so it's not surprising that these would be heavily mentioned.

Um, shouldn't that be _modified_?
According to http://www.bobatkins.com/photography/digital/eos20da.html
it's apparently done specifically for astrophotography, with the
blocking filter modified and mirror lock-up added.
And according to
http://telescopes.com/products/canon-canon-eos-20da-digital-slr-38611.html
it costs $2495 - read pounds, at least - has a live preview and _has
been discontinued_ :-(

No. By modified I'm referring to the term used to describe cameras
which are bought for the purpose of having their IR filters removed.
Hutech and others actually sell Canons that have been modded in this
way. A commercially available camera is un-modified while a
comercially avilable camera that has been modified is modded.

It's true that Canon have discontinued the 20Da. There were only a
small number made across the world unfortunately - hence the high
(very high for the extra features provided IMO) price.

--
Pete
http://www.digitalsky.org.uk

Pete Lawrence wrote:
On 19 Sep 2006 13:59:10 -0700, wrote:


Pete Lawrence wrote:
On 19 Sep 2006 05:47:17 -0700, wrote:


Pete Lawrence wrote:
On 18 Sep 2006 12:46:58 -0700, wrote:

And since I'm off topic already, 'Photoshop for Astrophotographers' and 'A
Guide to Astrophotography with DSLR Cameras', both by Jerry Lodriguss.
Any thoughts on these?

The first one is a valuable resource. I can't say much about the second
one as I haven't got it. From the excerpts I've read I can do without.

The second one is actually very good indeed, packed with lots of
information, examples, tutorials and links to other sites.
--

A lot of the stuff on the second one (basically most of the processing
tips) are very similar in the first one so there is some overlap. There
are quite few points which I found where either wrong or misleading.

Such as?

Such as writing that CMOS as seen in DSLR have QE up to 50% when in all
likelyhood we are talking 8-10% here. Or such as recommending 800 or
1600 ISO for deep-sky work. Or as saying that you need the mirror
lock-up if you want to shoot the planets/moon/sun. From what I've read
it seems to be heavily centered on Canons and the Da in particular.

To be fair to Jerry, the reference to QE was based on the empirical
findings of Roger Clark and others which show a paeak QE in the green
part of the spectrum at around 50%.

800-1600 ISO is used because most DLSR imagers don't autoguide. Again,
to be fair to Jerry, he does explain that lower ISO values will give
better results if you can use them.

I stand by to what I wrote befo reading the excerpts from the book
you got the idea that the author didn't know much about it first hand
(so here relied on others' opinions on the subject) and his only direct
experience was with the Canons. Not covering in full depht and by first
hand experience the Nikons is a bit of blunder if you want to market it
to the general audience, IMO.

Besides, most of the chaps I know that use DSLRs do autoguide (in order
to have 5min plus exposures) so your comment cames a bit as a surprise.



The Canons are the best DLSRs for atrophotography for numerous
reasons.

They might be the easier to use but not the most effective out of the
box, with the exception of the Da, of course. Yet the Da is a bit of
white fly, most of the poeple using DSLRs don't have it.

Andrea T.

On 26 Sep 2006 07:46:52 -0700, wrote:


Such as writing that CMOS as seen in DSLR have QE up to 50% when in all
likelyhood we are talking 8-10% here. Or such as recommending 800 or
1600 ISO for deep-sky work. Or as saying that you need the mirror
lock-up if you want to shoot the planets/moon/sun. From what I've read
it seems to be heavily centered on Canons and the Da in particular.

To be fair to Jerry, the reference to QE was based on the empirical
findings of Roger Clark and others which show a paeak QE in the green
part of the spectrum at around 50%.

800-1600 ISO is used because most DLSR imagers don't autoguide. Again,
to be fair to Jerry, he does explain that lower ISO values will give
better results if you can use them.

I stand by to what I wrote befo reading the excerpts from the book
you got the idea that the author didn't know much about it first hand
(so here relied on others' opinions on the subject) and his only direct
experience was with the Canons. Not covering in full depht and by first
hand experience the Nikons is a bit of blunder if you want to market it
to the general audience, IMO.

Besides, most of the chaps I know that use DSLRs do autoguide (in order
to have 5min plus exposures) so your comment cames a bit as a surprise.

Jerry is part of the huge Yahoo digital_astro DSLR userbase from which
a lot of the information that populates the book is gleaned.

http://tech.groups.yahoo.com/group/digital_astro/

I haven't frequented the site for a while now but it was certainly he
case that a large majority of the images that were taken on there were
unguided stacked short exposures.

The Canons are the best DLSRs for atrophotography for numerous
reasons.

They might be the easier to use but not the most effective out of the
box, with the exception of the Da, of course. Yet the Da is a bit of
white fly, most of the poeple using DSLRs don't have it.

So which in your opinion is the most effective out of the box?

--
Pete
http://www.digitalsky.org.uk

Pete Lawrence wrote:
On 26 Sep 2006 07:46:52 -0700, wrote:


....

The Canons are the best DLSRs for atrophotography for numerous
reasons.

They might be the easier to use but not the most effective out of the
box, with the exception of the Da, of course. Yet the Da is a bit of
white fly, most of the poeple using DSLRs don't have it.

So which in your opinion is the most effective out of the box?


Of those of which I have direct knowledge the D50, factoring in the
cost obviously. I understand is a pain in the back to use in the so
called 'mode 3' but that can be automated, if you're willing to do a
bit of DIY.

Andrea T.

wrote:

Of those of which I have direct knowledge the D50, factoring in the
cost obviously. I understand is a pain in the back to use in the so
called 'mode 3' but that can be automated, if you're willing to do a
bit of DIY.

I own a D70 and am willing.
Can you tell us more about this?
Pointers?

Iordani wrote:
wrote:

Of those of which I have direct knowledge the D50, factoring in the
cost obviously. I understand is a pain in the back to use in the so
called 'mode 3' but that can be automated, if you're willing to do a
bit of DIY.

I own a D70 and am willing.
Can you tell us more about this?
Pointers?

Go he

http://www.sfu.ca/~dmunro/DSLRnotes.html

and he

http://www.hapg.org/astrocables.htm

Andrea T.

On 27 Sep 2006 04:37:36 -0700, wrote:


Iordani wrote:
wrote:

Of those of which I have direct knowledge the D50, factoring in the
cost obviously. I understand is a pain in the back to use in the so
called 'mode 3' but that can be automated, if you're willing to do a
bit of DIY.

I own a D70 and am willing.
Can you tell us more about this?
Pointers?

Go he

http://www.sfu.ca/~dmunro/DSLRnotes.html

and he

http://www.hapg.org/astrocables.htm


Interesting articles. I have a variety of darks from both the Nikon
D50 and the Canon 350D and the amp glow from the Nikon is much more
noticable than that shown by the Canon.

The Nikon is a nice camera - a good quality build. I found the build
of the Canon a little too retro for my tastes. The results they
generated were pretty similar but the Canon IMO definitely had the
edge going just that bit deeper for the same conditions, using the
higher end ISO settings, which is where most DSLR users use them to be
honest.

Ergonomically, the Nikon wasn't that impressive in the dark. No
illuminator to allow you to check on the body panels what values you
were using and fiddly double hand setting requirements.
--
Pete
http://www.digitalsky.org.uk

Pete Lawrence wrote:
On 27 Sep 2006 04:37:36 -0700, wrote:
...

Interesting articles. I have a variety of darks from both the Nikon
D50 and the Canon 350D and the amp glow from the Nikon is much more
noticable than that shown by the Canon.

Well, there seems to be conflicting reports on this issue. My D50 has
basically nearly no amp glow, one dim spot on the upper left edge (low
x high y) about 100 pixels in diameter and with central intensity
(10x10 square) about 23 ADU, this at about 20 degC after 180s exposure.
In fact it is hardly noticeable in long exposures unless you check the
darks.


The Nikon is a nice camera - a good quality build. I found the build
of the Canon a little too retro for my tastes. The results they
generated were pretty similar but the Canon IMO definitely had the
edge going just that bit deeper for the same conditions, using the
higher end ISO settings, which is where most DSLR users use them to be
honest.

Setting higher ISO obviously has no effect whatsoever on the number of
collected photons and henceforth on the signal itself so I wonder this
might be related to other issues other than sensitivity.


Ergonomically, the Nikon wasn't that impressive in the dark. No
illuminator to allow you to check on the body panels what values you
were using and fiddly double hand setting requirements.

Well, I don't fiddle with it very much. Set pretty much the ISO and off
I go with the remote, as with lenses I usually have a preset marker to
infinity. The only real hassle is that I have to do the human
intervalometer, if you see what I mean...

Andrea T.