Archive for the ‘astronomy’ Category

Bahtinov grabber without autofocus

Saturday, September 29th, 2012

Since most people likely do not use the autofocus function, Bahtinov Grabber without autofocus is a further simplification: it does not depend on the Ascom driver (.NET still required though).

You can download the latest Bahtinov Grabber without autofocus (32 and 64 bit in one zip) here Bahtinov Grabber without autofocus (3837).

Bahtinov Grabber goes 64 bit (and 32 bit update)

Thursday, June 23rd, 2011

This is the introduction of a 64 bit release of the grabber. Download Bahtinov Grabber 64 bit (6618) here.
It was tested in combination with ASCOM 5.5b. Make sure you have that installed.

This same release is available in 32 bit as well: download Bahtinov Grabber 32 bit (5370) here.

Main changes:
- generic, more accurate calculation of focus error. Also works for masks other than the standard 20 degrees
- choice which R,G,B channel(s) should be part of the line detection
- audible feedback

Polar alignment check using a single plate solve

Sunday, October 31st, 2010

This is how:

- set up your mount
- point telescope or camera towards Polaris
- take long (30s?) exposure of which the first 10s are static and the last 20s rotating the RA axis for 180 degrees

This results in an image that both show a star pattern and a set of circles.
By “plate solving” (finding the celestial coordinates) of the star pattern and drawing a RA, DEC grid you can see how much your polar alignment is off. Perfect polar alignment will result in concentric star trails and RA DEC grid.

Plate solving can be done with


Tuesday, September 22nd, 2009

Yet another non-rigid registration and stacking tool.
This time using the “demons” technique for non-rigid registration (matching) of AVI frames.

I hope the enforced workflow makes the use of the software clear by itself:

download: RegistaC# (1566)
.NET 2.0 required if not already installed

The application was entirely written in C# (VS2005 express), making use of the FFTW library for FFT (wavelet filtering and global shift detection) and the AVI library from Codeproject.

The idea is

1. open avi and select a nice frame
2. align all other frames to that frame
3. measure quality of all aligned frames in preferred region of interest
3. average best X% frames
4. correct all sharp frames for seeing using “demons”
5. stack again for final result
6. apply wavelet sharpening

after that you can re-iterate alignment, seeing correction, frame selection etc. quite ad-lib.

Here is an explanation of the demons technique: demons powerpoint

feedback more than welcome!


3D images from 2D

Monday, September 14th, 2009

You can turn a simple 2D image of a planet or the moon into a “3D” image using this 3Dfication.

Make sure you make square crop that fits the planet or moon with only a small margin, of the image you want to use for 3Dfication. Using animation, you can make movies like this and this. AVI’s need the DivX codec.

download: 3Dfication (1793)


Periodic error and Polar alignment error model

Tuesday, September 8th, 2009

Using linear algebra, a model for calculating the trails that stars produce when making astrophotos from an equatorial mount was created.

An ideal mount that is perfectly parallel to earth rotation axis results in photo’s with pinpoint stars.
In the real world, the stars will always produce trails. Main causes are

- imperfect polar alignment
- periodic error of the (worm) drive
- RA drive rate that is different for siderial rate

Download Star Trails (1772) here.

All of these parameters can be played with in this model.

What I learned from the simulations:

For DEC=0 and a small polar alignment errors, the stars will describe a vertical line over 24h:

24h DEC 0

For DEC>0 and a small polar alignment errors, the stars will describe an ellipse, over 24h. The ellipse will be wider for larger DEC:

24h DEC 30

The periodic error will always add a wiggle in RA to the curve:

24h DEC 30 plus PE

Automatic planetary animation beautyfication in Matlab

Wednesday, August 26th, 2009

Using a “simple” Matlab script it is possible to fully automatically enhance planetary animations:

- shift between frames is corrected using “center of mass”
- color balance/brightness of all frames balanced is matched against the best frame

An example based on work by Mike Salway.

Jupiter Animation Mike Salway

Jupiter Animation Mike Salway

Jupiter Animation by Mike Salway improved

Jupiter Animation by Mike Salway improved

Jupiter animation Mert

Jupiter animation Mert

Jupiter animation Mert improved

Jupiter animation Mert improved

Neptune and Jupiter

Sunday, August 23rd, 2009

Two 30s exposures, ISO200, F/8, f=200mm are enough to reveal their apparent motion across the stars.

Neptune and Jupiter photographed 4 days apart on August 19 and 23 2009.

Neptune and Jupiter photographed 4 days apart on August 19 and 23 2009.

“Dark” skies of Holland

Saturday, August 1st, 2009

Some parts of The Netherlands are somewhat less light polluted, like “de Veluwe“, a forest-rich ridge of hills.

These images were made with the Nikon D90 and a 80-200 F/2.8 zoom lens, with typical exposure times of about 10 minutes, mounted on the Kenko Skymemo. A single exposure of 5 minutes, ISO200, F/2.8 still resulted in a reasonably exposed image (not over-exposed by light polution).

Simulate you own mask diffraction pattern

Tuesday, July 14th, 2009

You can load any type of mask and simulate the diffraction pattern for any wavelength.

Download “Maskulator” here: Maskulator (3766)
Version 5.0, July 18 2009

Updates will follow. Planned features are:

- full color spectrum in one image DONE in V2.0
- save as AVI DONE in V3.0 sample AVI here, divx codec used
dowload DivX codec here
- save as bitmap DONE in V3.0
- V4.0 bug fixes in number of frames
- V5.0: write AVI compressed in codec of choice