Oct 22, 2008


34 exposures of 100s each, with Canon EOS 350D and Canon 85mm f/1.8.

The goal was also to image "R And", my favorite variable star.

Oct 14, 2008

Color balance with EOS 350D

I photographed a white piece of paper in full sunshine, at noon, in raw mode.
I cropped the center of the image, and developped it in 48 bits. Here are the stats reported by Iris on the center part:

Red: Moyenne : 667.6 Médiane : 671 Sigma : 14.6 Maximun : 742.0 Minimum : 413.0
Green: Moyenne : 1294.5 Médiane : 1310 Sigma : 35.4 Maximun : 1481.0 Minimum : 508.0
Blue: Moyenne : 1106.0 Médiane : 1114 Sigma : 26.0 Maximun : 1245.0 Minimum : 540.0

Taking the median, the RGB adjustments should be:

R: 1.95 (1310 /671)
G: 1
B: 1.18 (1310/1114)

or (reversed, to avoid overflowing on integers):

R: 1
G: 0.51 (671/1310)
B: 0.60 (671/1114)

Oct 13, 2008

To pretrait or not to pretrait, that is the question...

When doing astronomical images, it is sometimes better NOT to do pre-processing. When the number of dark frames is small for example, as it adds more noise to images than it can remove.

Here are some discussions about this.

Here are 2 images, obtained from the same raw pictures: 30 30-seconds images of m31, taken with Canon 85mm f/1.8.

This one has no pre-processing: hot pixels are visible as small red, green and blue strings (click on it to see it larger).

This one had full pre-processing: dark, flats and offset. When viewed full-size, it doesn't have more signal (it probably actually has less), and overall is doesn't look as good. I only had 1 dark frame to use, as well as only 1 offset and 1 flat field.

For comparision, this one has no pre-processing, but only 10 images stacked together (3 times less). The signal/noise ration is clearly less than the first one with 30 images.

Oct 10, 2008

XInclude, jaxp and xerces

XInclude defines a powerful way to control inclusions of xml fragments in another xml file:
xpointer="xpointer(string-range(chapter/p[1],'Sentence 2')/range-to(string-range(/chapter/p[2]/i,'3.',1,2)))">

This looks good, however in reality none of the current parser implementations support that ! For example, Xerces (implemented in jaxp 1.3 & 1.4) only supports xpointer="element(...)". This makes it almost useless, unless a whole tree has to be included. It is not possible to easily merge two xml files this way.

Frédéric Laurent already noticed this 3 years ago... It's time for a Java expert to implement it in Xerces !

Oct 8, 2008

In the backyard...

Sunday afternoon at home... Roe Deer ("Chevreuil").

Always a magical moment...

Oct 7, 2008

Aerials Photo over Meylan, France

Here are some recent Aerial Photos taken in the Meylan area:

More pictures can be seen on my RC Blog.

Oct 5, 2008

Reticule eyepiece and resolution

Here are the corresponding arc measures when the 12.5 mm Baader reticule eyepiece is used with the Celestron 8 (no focal reducer). For example, the small circle represents 15 arc seconds of diameter.
15 seconds is also the size of one pixel on the EOS 350D with the 85mm lens.

Oct 4, 2008

Virtualization is not.

Creating a "virtual machine" with VirtualBox or VMware is misleading, no "virtual machine" is created, only a virtual view of the real underlying hardware, which must be physically present. Usually, "virtual" refers to something that doesn't exist at all, which is not the case here.

In comparison, platforms emulators are real virtual machines. For example, MAME can emulate hardware that doesn't physically exist anymore. In that sense, it can really create a "Virtual Machine".

Oct 1, 2008

Satellite galaxies of M31

It is little known that M31, the Great Andromeda Galaxy has not 2 but 4 satellites:

M110 (NGC 205), the ellongated one north of M31 (mag 8.9)
M32 (NGC 221), the round galaxy south of M31 (mag 9.0)

NGC 185 (mag 10.1)
NGC 147 (mag 10.5)

I was able to capture all 4 of them in this simple picture, a composite of 12 individual images taken with the camera piggybacked to my C8, with no guiding. No preprocessing was done, and the frame when a plane crossed the field was also included... Image still goes to magnitude 16.5 !

Right above the white border, on the top part, the variable star VX And is easily located, due to its vivid red color.

Compact camera and Infinity focus

I usually set my Pentax A20 to infinity focus when doing Aerial Photography. However, I just discovered that it just isn't right:

Here is an extract from a distant scene taken with Autofocus: it is sharp.

Same scene taken with focus set to Infinity: completely blurred !

Hyperfocal mode gives bad results as well !