A remote controlled flip Bahtinov mask and lamp for focusing and flats
I got a little tired of getting my butt off my couch many times during an imaging session to place my Bahtinov mask on my FSQ106 to check focusing. This irritation finally motivated (forced) me to do something about it: I wanted a remote controlled flip mask so that I could just stay in the house for the entire imaging session.
After a quick check on the web, I found that the only commercial source for flip masks and lamps are made by Alnitak. Unfortunately, the price for a pair of flip mask and lamp are very expensive: they will set me back by about $1000! My thoughts then went onto designing my own. A quick sketch of my ideas showed that I can make a pair for about half the price! In fact, it turned out to cost about $700 that included fixing mistakes. If the work was error free, it would have cost around $400. You can see the cost break down in the bill of materials.
Note: The reason why I wanted a mask and lamp pair is because of balance. IMO, it is rather odd to have only one device mounted on one side the scope that causes an immediate imbalance.
Here is a movie demonstration of how my flip mask and lamp works
I made the following design decisions so that both the cost of materials and the software investments were low.
The structural material that I chose for building the flip mask and lamp is mostly 3 mm thick black acrylic. I have used this type of material in the past for my other projects and although can be quite brittle if not handled properly, 3 mm thick acrylic is strong, light and cheap enough for this type of structure. The structure is made by cementing the parts laser cut parts together. The laser cut design can be found in the Ponoko directory.
Since the design required a flip mask and lamp pair, it was natural for me to select the master and slave paradigm. I chose the master controller to control the Bahtinov mask and the slave to control the lamp. The principal parts used in the design are as follows:
- A servo controller made by Pololu called the Maestro.
- A servo that rotates greater than 270 degrees: the Feetech FR5311M.
- A sprocket and chain system for connecting the servo to the mask and lamp.
- Interlock switches to indicate where the mask or lamp is
- A mechanical lever switch
- A Hall switch
- A lamp made from an electroluminescent panel with dimmer and power inverter.
- I wasn't too happy with the spectrum of the EL panel and had to add Roscolux colour filter sheets to the lamp so that the RGB components were balanced. See the assembly manual for the colour sheets that I used.
An assembly manual is available that highlights the important steps in the manufacture of the controllers. However, the more obvious steps have been excluded.
There are electronics to be built as well. The Eagle files for building the master and slave controllers are in the eagle directory.
I used the 6 channel Maestro servo controller to save effort on both the electronic and software design. If you plan to run this system on a Mac OSX Sierra, the firmware on the controller must be at least version 1.03. See this [link](See https://www.pololu.com/docs/0J40/4.f).
I have written a simple Python script to control the system. The required Python version is 3.
This Maestro python library is used by the flipit.py programme to talk to the Pololu Maestro.
For convenience, the maestro.py library is distributed with flipit.py.
Just copy the entire flipit directory to a user directory.
python flipit.py
By default the serial port flipit.py defaults to is
- COM3 on Win10.
- /dev/cu.usbmodem00183281 on Mac OS X Sierra.
Other serial ports can be specified as an argument.
python flipit.py [SERIAL_PORT]
Help is always available
python flipit.py -h
All the software, documentation, hardware that I have written is copyright 2017 C.Y. Tan.
All software is released under GPLv3
All documentation is released under Creative Commons Attribution-ShareAlike 3.0 Unported License or GNU Free Documentation License, Version 1.3
All hardware is released under CERN Hardware Open License v1.2