You can download the latest Bahtinov Grabber without autofocus (32 and 64 bit in one zip) here Bahtinov Grabber without autofocus (7885).

This same release is available in 32 bit as well: download Bahtinov Grabber 32 bit (8357) 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

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

download: RegistaC# (2783)
.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!

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 (3045)

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 (3189) 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:

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:

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

- 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 by Mike Salway improved

Jupiter animation Mert

Jupiter animation Mert improved

Download “Maskulator” here: Maskulator (8443)
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

I could not resist to take the next step:

The Bahtinov grabber (14206) gives your absolute focussing error (in pixels), so even with a simple non-absolute motorized focusser it should be possible to develop a fully automatic focus control.

There is now only one Bahtinov grabber version, one that includes autofocus control. It is not necessary to use autofocus of course, of you just want to determine the focus error live.

Ingredients:

- Celestron 8 inch telescope

- JMI motofocus (simpleDC motor that is able to rotate the focuser knob, prevents telescope shake while focusing)

- Shoestring PC focus control unit (USB box that gives PC control over the JMI motofocus)  ASCOM driver here

- ASCOM, open software platform for controlling “any” focusser

When you have selected the capture area (live view of my Philips ToUcam in VirtualDub in my case), the software starts detecting the focus error. I used an artificial star (Maglite LED torch, with a tiny pinhole on some household aluminium foil at about 15 m distance, just within focal range of the telescope.) and a water-jet cut aluminium Bahtinov mask.

As soon as you hit any of the buttons in the “focusser” box, an ASCOM dialog asks you to connect to which focusser. Then you can manipulate focus, left or right, or… autofocus!

Autofocus works in 5 steps:

- 1: check unitial focus error: must be smaller than 100 pixels to continue to step 2 otherwise stop autofocus

- 2: backlash removal: motor starts slowly until the bahtinov pattern changes sinificantly

- 3: determine sensitivity: move until bahtinov pattern changes 5 pixels and determine how much the motor has to move per pixel change

- 4: fine focussing

- 5: When both the focus error and the 15s averge focus error is smaller than 0.5 pixels: “AF Ready”.

download application

You can also point your webcam with its original lens to an image of Bahtinov spikes to test:

or test it on a set of three dark artificial lines, by checking the “dark lines ona lighter background” checkbox:

Or even point it at a movie in your browser (from YouTube for example) to see it track focus live: