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 !

Sep 29, 2008

Barnard's Star

(voir ici pour une traduction automatique de cette page en français)

This is the star with the highest proper motion of the Heavens: more than 10" every year. See the Wikipedia page on this star here.

I took this picture yesterday, with my Canon 350D DSLR piggy-backed on the C8, with the 85mm f/1.8 lens. Single 30 seconds exposure, no processing except contrast enhancement, and double size for clarity. It is possible to see stars of magnitude 14 on this picture...

The bright star on the left is 66 Oph, magnitude 4.8. It is highly overexposed, and appears less bright than it should be. This is due to the limited dynamic range of the Canon EOS 350D captor . Its design range is 12 bits (4096 values) per pixel. 1 bit is lost in the electrical noise (seen as the sigma value of a dark frame), and 2 more in the suburban sky background. So only 9 bits remain, giving a dynamic range of 512 values, which corresponds to log2.5(512) = 7 magnitude range. As stars of magnitude 14 can be detected, everything above magnitude 7 is overexposed, and appears dimmer than it should be... This is not a problem, since only 66 Oph is brighter than mag 7 here (next bright star is 7.6).

Sep 24, 2008

Field of view and true magnification of Canon binos

Here are my measurements.

Canon 18x50 IS:
  • The apparent field of the bino is 62 degres (from Polaris to over Alpha And).
  • The real field is 3.85 degres, measured to be midrange from Delta Cas to Gamma Cas (3.60 degres) and Delta Cas to SAO 11444 (4.13 deg).
  • Thus the real magnification is 62/3.85 = 16x, not 18x !

Canon 10x30 IS:
  • The apparent field is 48 degres (from Polaris to M31).
  • The real field is 6 degres (from Beta And to 2/3 between Mu And to Nu And).
  • Thus the real magnification of the 10x30 IS binos is 48/6 = 8x, not 10x !
I wonder if this is standard practice among bino manufacturers ?

Sep 23, 2008

Observation of Variable and double stars

Yesterday I was able to observe some interesting stars using the Canon 18x50 IS binos. These observations were made on Sep 22 at 20h30 UT.

Delta Cephee

This is a variable star and a double star. Blue compagnon (Mag=6) was clearly resolved, at 41". As variable is orange, contrast is beautiful. Variable star magnitude was equivalent to white Epsilon: 4.2.

According to CalSky, the minima of this star was on Sep 17 at 22.9h UT. As the period is 5.36634 days, the next minima was on Sep 23 at 7h40 UT. My observation was then 0.47 days before minima, very close to minimum brightness.

23rd, 20UT, 0.5 days after minima, 4.2.
Sep 24th, 20UT, 1.5 days after minima, about 3.7.

Beta Lyra

Its luminosity was equivalent to Gamma Lyra (=3.2).
Mimima: Sep 13th at 18.3h UT. Observation at Minima + 9.09 days, or next Mimina - 3.82 days : near maximum.

Sep 24th, 20UT, 12 days after minima, about 3.6.

Zeta Lyra

This is a double star (47"), clearly visible.


Sep 23rd: Easily resolved (35").

Sep 21, 2008

Some old pictures

Spring 1977, Grenoble.
60x700 refractor.

Spring 1986, col de l'Arzelier.
Ready to watch Halley's comet !

Mauna Kea, Hawaii, December 1996.

Mt Palomar, Mai 1997.

A more modest observatory near Grenoble.

Old Astro pictures

Here is M57 in Lyra, taken on June 4 1996 from Austin, Texas. 6 minutes single exposure, on Kodak 1000 ISO film. Olympus OM-1 camera, Lumicon Easy Guider.

Here is also M57, taken 11 years later with a smaller telescope, with a single 30 "exposure...on a digital camera (Canon EOS 350D).

This is M13 in Hercules, also 6 minutes single exposure, from Austin.

Comet Hyakutake, near Austin, Texas, April 1996.


Dim comet.

Edge-on galaxy.

Sep 16, 2008

How does the Canon 18x50 IS binoculars compare to the 10x30 IS ?

(Voir ici pour une traduction automatique de cet article en Français)

After searching for years (literally), I was finally able to pick up a good deal on Canon 18x50 IS binoculars out of EBay (thanks to the cheap $!). I have been using the smaller 10x30 IS for 7 years, and always found them very good. But I wanted (of course) bigger magnification, and more brightness.
Here are my impressions after a few weeks'use.

The optical quality is near-perfect, no problem even on the edge of the image. The stabilization is very good, better than on the 10x30: it starts faster, in less than a second images are rock solid. The button is of the "press to start, press to stop" type : no need to keep it pressed as with the 10x30, this is very convenient.
The eye cups are not as good though. They are too big, and don't fit my eyes, I had to remove them. The 18x50 IS are much heavier than the 10x30, but they are perfectly manageable.

The magnification gain is amazing. I am now able to see much details in passing airliners, that I was not able to see with the 10x30.

The brightness is on par: I can see stars of magnitude 10.5, while with the 10x30 I was limited to 9.5. This indicates they are 2.5 brighter, which is consistent with theory (50*50/30*30 = 2.8).

Watching the moon is amazing: it appears as a big 3D ball. Much details can be seen, such as Mons Pico (even with no shadow), a mountain range only about 20 km wide.

The image hand-help is the same as on a tripod, this is simply amazing.

From time to time, the image appears a little bit blurred or fuzzy. This is probably due to high-speed vibration in the image, caused by the shifting lens correcting shaking. As magnification is high, it is visible from time to time.

On a tripod, with stabilization on, the image appears to slowly drift in one random direction, for about two seconds, than reverses direction, and the cycle starts again in another random direction. I would be interested to know if other owners experience the same thing ?

Overall, these binos are amazing.

Sep 15, 2008

VirtualBox and VMware server ESX

When using the VMware Infrastructure Client GUI to connect to the VMware ESX Hypervisor, I encountered a nasty problem. It was not possible to upload a Virtual Machine image, or even an iso image to boot on. Every attempt to add a file to a datastore ended with an "IO error"popup, and the file was not copied.

The GUI was running inside a Windows XP virtual machine, running inside VirtualBox.

When running the GUI from a native Windows machine, it worked.

There seems to be an issue in the way the VMware Infrastructure Client GUI interfaces the VirtualBox disk driver.

Versions used:
VMware Infrastructure Client 2.5.0.
VMware ESX Server 3i 3.5.0.
VirtualBox 1.6.4.

Sep 9, 2008

Astrophotography without equatorial mount

Yes, it is possible !

This picture of M31 goes to magnitude 15. Click on it to see it fullsize.

It was taken with a Canon EOS 350D mounted on a fixed tripod. The lens was the Canon 85mm f/1.8.

77 exposures of 4 seconds each were taken. Then Iris software was used to align and stack all 77 images. The resulting exposure is 5 minutes.
Aligning the images takes a lot of time, because each one has to also be rotated to account for field rotation (this is done automatically by Iris). Each image takes about 37 seconds of processing on a Xeon @2.8Ghz.

From the same image, this extract shows the "R And" variable starfield. It is taken from the lower right corner of the above image. "R And" is the yellowish star on the left of the star marked "97". It is surrounded by companion stars whose magnitude is shown (without the decimal point). The magnitude estimate is 8.8.

This star goes from magnitude 6 (bright) to 15 (dim) in about 250 days, then goes back up to 6 in about 150 days. Magnitude 15 is about 2.5^(15-6)=4000 times less brillant than magnitude 6 !

See this previous post when star was at minimum.

Here are the latest observations of this star.

Il est tout a fait possible de faire de l'astrophoto sans monture équatoriale !

L'image de M31 monte à magnitude 15. Cliquez-la pour la voir en pleine résolution. Elle a été prise avec un boitier Canon EOS 350D fixé sur un trépied fixe. L'objectif est un Canon 85mm f/1.8. 77 poses de 4 secondes chacunes ont été prises. Ensuite le logiciel Iris a été utilisé pour aligner et compositer les 77 images. L'exposition résultante est de 5 minutes.
Aligner les images prends beaucoup de temps sur le pc, car chaque image doit etre tournée pour prendre en compte la rotation de champ (cei est fait automatiquement par Iris). Le temps de traitement de chaque image est d'environ 37 secondes sur un Xeon @2.8Ghz.

Un extrait de cette image montre le champ de l'étoile variable "R And". L'extrait se trouve en bas a droite de l'image principale, et "R And" est l'étoile jaune à gauche de l'étoile indiquée comme "97". Elle est entourée d'autres étoiles dont la magnitude est indiquée (sans le point décimal). L'estimation de la magnitude de "R And"est de 8.8.

Cette étoile descends en luminosité de la magintude 6 à 15 en 250 jours, puis remonte à 6 en 150 jours. La magnitude 15 est environ 2.5^(15-6)=4000 fois moins brillant que la magnitude 6 !

Le précedent message contient une photo de l'etoile au minimum.

Voir les dernieres observations de cette étoile.

Sep 3, 2008

Aerial Photos of new road in Montbonnot

Here are some aerial photos of the industrial park of Montbonnot, that show the soon-to-be-opened new RD11M road. These pictures show both ends of the new road.

These pictures were taken with a small radio-controlled airplane.
More details and pictures can be found here.

Voici des photos aériennes de la zone industrielle de Montbonnot, montrant la nouvelle route RD11M (pas encore inaugurée). ces images montrent les deux extrémités de la nouvelle route.

Ces images ont été prises avec un petit avion radio-commandé.
Plus de détails et d'images ici.