2020-02-02 Palindrome Day

Today is a palindrome day, i.e. the date written in the format YYYYmmdd can be read in reverse order to give the same result.

An article in a swiss newspaper reported, that this is the first palindrome day for 900 years, a little thinking about the problem easily will give you dates like 2001-10-02, 2010-01-02 or 2011-11-02 that are also palindrome days, but only for the format yyyyMMdd, different dates are palindrome dates for ddMMyyyy. I was curious to see how many palindrome days in either format exist from a given date (I used the year 1 AD (there is no year 0!!!), so I created this little script that prints out all the palindrome days since 01.01.01, days that are palindromes in both formats are highlighted:

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Full spectrum modification of a Nikon D7000 – Part I

After I bought the D750 I rarely used the D7000 any more. As it has been heavily used it would probably not get a lot if I sold it, so It mostly stayed in the closet.

Then I learned that the Nikon D7000 sensor is still used in current astronomical CMOS cameras (e.g. ASI071MC Pro or QHY168C) apart from the cooled sensor the main advantage of the astronomical cameras is the better response to H-alpha emission because of different IR-cutoff wavelength.

H-alpha emission is the red light created when young, hot stars excite hydrogen gas in the interstellar medium. Regions of onging star birth are usually distinctly red. Sadly regular DSLR cameras pick up that red light only very faintly.

After a discussion with a colleague of the Vorarlberger Amateur Astronomen I plucked up the courage to take the camera apart and get rid of the IR blocking filter. Read More

Lenses and constellations

Modern lenses provide pinpoint stars in nighsky photos, But this reduces all stars to small points, constellations are almost unrecognizable.

This is an image which is a part of a timelapse sequence taken with a Sony #RX100 IV camera. Mars, Saturn and the Milky Way are clearly visible.

Sony RX100, f/1.8, 15s, ISO 3200

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Meade LXD-650 Declination Runaway repair

The last time I wanted to do some deep-sky astrophotography, I ran into an issue with our astronomy club’s LXD-650 mount – immediately after switching it on the declination motor started to run at high speed.

After some research on the internet I was able to resolve the issue, by tweaking the setting on the potentiometer responsible for the declination encoder LED light.

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Lenses for Astrophotography

Astrophotography Lens Test

A test of wide-angle lenses for astrophotography on FX format. The shots were taken from suburban conditions, the camera was mounted on a static tripod without guiding. The left image is always the full frame, the middle one is the center, and the right one is the upper left corner of the image. Read More

Solar Pinhole Observations

Most people don’ t realize that the bright spots below a tree in the grass are actually images of the sun formed by small holes created through overlapping leaves in the tree’s branches. Because the sun is a sphere, the images are also circular (depending of the angle of the surface).

A similar situation occurs when the sun shines through the small holes in blinds  – round images of the sun are projected against the foor or wall. The images become interesting when the sun’s disk is obscured by something, e.g. the moon during a solar eclipse or trees when the sun is rising or setting on a wooded horizon. Read More

How to create time lapse video using a webcam

Simple Time-Lapse

Time-lapse animations have always fascinated me. With a time-lapse you can make things visible to the human eye that are normally happening too slow. The movement of stars in the sky or the process of putting up a house are very interesting to look at when the clock has been accelerated.

Apart form creating time-lapse animations using my own pictures I also found it worthwhile to create them from web-cam images. A webcam near the place I live provides images of quite high resolution. With the little script below, I was able to create this video: Fog over Dornbirn

I found that for videos that include clouds it is ok to take a frame every 5 seconds or so. As I don’t have the time and patience to save the webcam images manually, I created this bash script which was improved by Jürgen Hofer subsequently:

# !/bin/bash
# copyright Philipp Salzgeber - www.salzgeber.at
# adapted by j! for cleaner results
# first cmd line parameter is the delay in seconds (optional, default is 60)
# script stops if there is the file 'killme' in directory (for remote stop via dropbox)


let "pause= $divider * 90 / 100"
while [ ! -f ./killme ]; do 
 #wait for zero crossing
 secs=$(date -u +%s)
 let "mod= $secs % $divider"
 while [ $mod -ne 0 ]; do
 secs=$(date -u +%s)
 let "mod= $secs % $divider"
 # create a filename with date and time portion
 filename=$(date -u +"%Y%m%d_%H_%M_%S").jpg
 # use wget to download the current image from the webcam
 wget -nv $url -O $filename
 # wait
 sleep $pause;
echo exit condition found

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Creating Double Page JPEG images from PDF

While in the process of making a photobook in Lightroom I wanted to review the book before actually ordering it. For this I wanted to have the pages in JPEG format instead of one big PDF.

It turns out that with ghostscript one can easily extract the images.

I am using cygwin on a Windows 7 64 Bit operating system to work with ImageMagick, Ghostview and the like.

But before I was able to use ghostscript I had to fix this error I was getting about the font Arial.ttf not being found, after some research I found that creating the missing directories and adding a link to the font in the Windows directory fixes that issue:

mkdir /usr/share/fonts/
mkdir /usr/share/fonts/TTF
ln -s /cygdrive/c/Windows/Fonts/arial.ttf /usr/share/fonts/TTF/

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