Date: Tue, 09 Aug 2005 09:49:03 -0000
   From: "Stefan Seip" <stefan.seip@t-online.de>
Subject: Re: .. CANON EOS-20DA ... My first impressions

Thanks Philippe for showing us your impressive results. Here are my
first impressions of the 20Da:

------------------

It just arrived, the NEW Canon EOS 20Da, optimized for
astrophotography.

I think it is a limited version of the EOS 20D, but spezialized for
astrophotographers. Of course you can use the 20Da without any
limitations for daytime photography also. The 20Da is more sensitive
in the red at 656.3nm, the light of many glowing nebulas, because of
a modification of the IR cut filter in front of the CMOS chip. And
the 20Da allows live focussing on the TFT screen at the camera
backside! In the 'B' (bulb) position you can choose 'FC' for 'Focus
Control'. After pushing (and holding down) the shutter release the
mirror flip up and the center of the image is shown live on the TFT
screen. That is perfect to find the best focus!

Click

to see the 20Da emblem. Externally only the emblem is the difference
between the 20Da and the 20D.

And click
here for an image showing the 'Focus Control' setting in the display
of the 20Da.

First I wanted to determine how much more sensitive the 20Da is
compared to a 20D. I measured that at daylight through an Astronomik
H-alpha filter with a bandwidth of 15nm. I figured out, that the
increase of sensitivity at 656nm is

0.55

That means round about a half exposure step. With other words: A red
nebula imaged with the 20D in 90 seconds, the 20Da needs only 60
seconds for the same result. Not much better, but better than
nothing...

Click

for an image showing a part of the test images, both captured with
absolutely the same parameters and an exposure time of 0.5 seconds.

It would be interesting to compare the 20Da against a modified 20D
without any IR blocking filter at all.

BTW: A power supply unit to run the 20Da with the 110/220V of your
house is included and must not sold seperately.

Here are two snapshots of the 20Da in use:

Click

to see the Canon EOS 20Da, connected with a T-adapter to the
flatfield lens of an AP refractor, the battery grip BG-E2 is optional

And

for another one showing the Canon EOS 20Da, connected to an Astro- Physics 155mm (6") refractor.

-kidding on-
The display of the 20Da shows the Orion Nebula M42, captured with the
20Da at daylight!  :grin:
-/kidding off-

Update 1:
---------

Regarding the noise, the 20Da and the 20D are at the same level. I
photographed a poster with both cameras in a relatively dark room. I
used ISO 800 settings and 8 seconds exposure time. I tried one image
with and one image without automatic noise reduction (which means an
automatic substraction of a darkframe).

Click

to see the results.

The white balance was manually set to 'Daylight'. You can see the
slightly higher sensitivity in red of the 20Da. That causes a slight
red tint as well as the brighter impression. For daylight images, you
can easily fix that red tint with any image processing software. But
regarding the noise, I can´t see any difference. Surprisingly the
automatic noise reduction makes a very small difference only, if any.


Update 2:
---------

Last night I had some clear hours so I started to compare the two
cameras at the sky.

Click

for an image fraction in original size, captured with the Canon EF-S
lens 2.8/60mm Macro. The exposure time was 5 minutes at f/2.8 and ISO
100 settings. No darkframe was applied. I hope you can see the shape
of the Northamerica nebula in both images.

I procressed both images in the same way, so they are comparable.

I don´t wanted to make a 'pretty picture' but I wanted to see if and
how much the better red sensitivity of the 20Da is an advantage in
real life.

You can see the result: It IS an advantage!

Update 3:
---------

Some words about the live focus at the TFT screen of the camera. It
works phantastic! That feature was added to the 20Da to support the
astrophotographers, but I find it useful for non-astrophotographers
too.

Click

for a view of the camera backside, showing the star Vega through a
85mm lens. You can see, that the star is not sharp.

And click
to see the same scene after Vega was focussed properly.

The camera magnify the center of the image as much as possible. That
means one image pixel is matching to one pixel of the TFT screen. To
find the best focus is 'a walk in the park'.

I made a focustest with the Canon EF-S 2.8/60mm Macro lens: I
centered Vega in the field, so even the autofocus of the camera had a
chance.

Click

for the result of my focus test.

The autofocus did a very bad job (left image). Even after several
trials it doesn´t find any focus better than that one! The image in
the middle is much sharper. I focussed that manually while looking
through the view finder of the camera without any aid (magnifying
glass or something like that). I tried my very best (of course: with
the help of a magnifying glass it would be able to find a better
focus, however). The right image was focussed with the live method on
the TFT screen of the camera, that the 20Da provides exclusively. It
was very easy to find the best focus that way, and there was never
any doubt that this IS the best focus point indeed.

The three images are showing an image fraction in original size
(100%), the bright star is Vega and above Vega you can find the
double double Epsilon Lyrae (here only double of course). All three
images were made with the Canon EOS 20Da, 60 seconds exposure time,
f/2.8 and ISO 100 settings.

------------------

Thanks for reading. Thats all for now from the 'Canon test lab'  ;).

Best wishes
Stefan

http://www.astromeeting.de

PS: Sorry for my rusty English.