ASTROMECHANICS ASCOM Guide

astromechanics.org
ASCOM Canon Lens Controller
Simple solution for external focus & iris drive
Device assembly and software using manual
This manual is related to ASCOM platform based usage
APR/2019
ASTROMECHANICS

STEP 1: Device assembly
Assembly process is easy, use the diagram below. Choose the right parts depending on your lens and
camera:
17 mm adapter is ideal for monochrome camera (ASI1600MM for example) with filter wheel. 17 mm
(ASCOM Canon Lens Controller) + 20 mm (ZWO EFW) + 6.5 mm (ZWO cooled camera) = 43.5 mm;
26.5 mm adapter is suitable for color camera (ASI294MC for example). 26.5 mm (ASCOM Canon
Lens Controller) + 11mm (T2 ring) + 6.5 mm (ZWO cooled camera) = 44 mm.
Assembly diagram
Now 26.5 mm adapter is a combination of 17 mm base adapter and 9.5 mm spacer. This design will be
much more versatile. 17 mm base adapter has no filter mount (designed for use with the filter wheel). 9.5
mm spacer has M28.5x0.6 thread for mounting 1.25" filters.
Use cases of ASCOM Lens Controller

Drawing of 17 mm base adapter
Drawing of the standard spacer (9.5 mm)

Minimal adapter thickness (17 mm) is limited by spring electrical contacts and standard lens mount
mechanism;
By default, the spacer thickness is 9.5 mm. In this case, the total thickness of the assembly with the
adapter is about 26.5 mm. This solution is suitable for cameras with back focus of about 17.5 mm
(most of the QHY/ZWO/SBIG, etc). As you know, the back focus of Canon lenses is 44 mm;
Moreover at your request, we can adapt the thickness of the spacer to match your particular setup.
For example, QHY8L/10/12 cameras have a back focus of about 20 mm. Therefore the spacer
thickness must be 44 –20 –17 = 7 mm. We can make this spacer especially for you.
ASCOM Canon Lens Controller
Mount ASCOM Lens Controller on your camera. Achieve a secure fit, the connection should be
tough and have no backlash.
Attach your lens. Rotate the lens clockwise until it locks. To remove the lens, press and hold the lens
lock mechanism button and rotate the lens counterclockwise. Attach and remove your lens only
when the USB cable is disconnected!
Connect ASCOM Lens Controller to your computer using USB-Mini cable. Your cable has a dual
USB-A connector for high current consumption lenses. In most cases, it is enough to connect only
one connector (main, data transfer), even for large white Canon telephoto lenses. But if you need
more power use a second (power) connector. You can even connect it to an external power supply
and get more power than from standard USB ports.
Configuration
USB 2.0
USB 3.0
USB 2.0 / USB 3.0 +
External power supply
Main connector
2.5W
4.5W
2.5W / 4.5W
Power connector
2.5W
4.5W
unlimited *
* depends on the selected power supply

Note: When testing the ASCOM Lens Controller, first connect it directly to your computer. Then you
can test it with various USB hubs. Keep in mind that connecting both connectors to unpowered
(passive) USB hub doesn’t make sense because it is powered from a single computer port. Moreover,
several connected devices can share the power supplied. In this case, the correct functioning of the
device is not guaranteed. Use powered (active) USB hubs for proper operation.
USB cable with dual connector
Powering the device from external power supply

STEP 2: Software installation
The software doesn’t require high performance from the user computer. Basic software components:
Microsoft Windows XP/Vista/7/8/10;
ASCOM Platform V6.x. or higher.
Install the software from downloaded package. Before installing the ASCOM driver you must install a special
driver for communicating with ASCOM Lens Controller (FT232RL chip). The device uses a standard and
popular FT232RL chip for USB connection instead of a cheap CH340G in old version. FT232RL is the most
reliable and frequently used chip for creating virtual COM ports based on USB connection.
Usually these drivers are installed automatically (you may need to connect to the Internet), but if it doesn't
happen, then you can install them manually. You can download the latest version of the driver on the
official website: https://www.ftdichip.com/Drivers/VCP.htm. There you can download drivers for other
operating systems (Linux, Max OS X).
You can also find the driver in the appropriate folder of the distribution package. Open Drivers folder and
click on CDM21228_Setup.exe. Follow the install wizard instructions. This process can take few minutes and
will be completed automatically.
Then double click on CanonEF Lens Driver Setup.exe.
Installation process is very simple, just follow instructions on the screen.
Install Wizard window
Note: If you need lens control software for Linux and Mac OS X, please visit this page: https://rti-
zone.org/macosx_x2focuser_plugins.php. Rodolphe Pineau has created great X2 plugins for various
systems. You can control the device even with a Raspberry Pi!

STEP 3: Driver usage
After installation is completed open your focusing software (Maxim DL, FocusMax, etc.) and choose the
driver using standard ASCOM controls and dialog windows. Maxim DL based example is shown below.
Observatory control window
ASCOM Focuser Chooser window

Choose ASCOM CanonEF Lens Driver and click Properties.
Driver setup dialog window
You need to configure several parameters in this window:
COM Port Number - virtual port created by operating system for the connected device (COM8 for
example). You can find port number in the Windows Device Manager.
List of available COM ports
Lens Model –select your lens from a drop down list. Canon lenses by default, but you can add and
describe own lens compatible with Canon EOS protocol.
List of available lenses

This can be done by editing lens.txt. Click on the highlighted link.
Fast link to lens.txt
Append new entry to the end of this file: specify lens name and enumerate all aperture values of
your lens according the simple pattern. Be careful, syntax is important!
Lens description in lens.txt
Note: For zoom lenses with a different range of aperture values at different focus values
(Canon EF-S 18-55 f/3.5-5.6) set the range for the planned for use focal length. For example:
at 18 mm f/3.5: | 3.5 4.0 4.5 5.0 5.6 6.3 7.1 8 9 10 11 13 14 16 18 20 22 25 29 32
at 55 mm f/5.6: | 5.6 6.3 7.1 8 9 10 11 13 14 16 18 20 22 25 29 32
This doesn’t apply to zoom lenses with constant aperture value (Canon EF 70-200 f/4 for example).

Select the aperture value you want to use.
List of available aperture values
Click Connect button to start the driver.
Starting the driver

Now you can use the driver for manual and auto focus procedures. Test the driver in manual mode, check
focus movements and aperture control.
Focus tab
Note: All focus positions are relative. The driver will return 5000 after power up (USB connection) regardless
of the real focus position. Absolute positioning doesn't make much sense, because there is no normal
position feedback (encoder, etc). The user can focus manually, and the controller (and even the Canon
camera) will not know anything about it.
If you want to change the aperture value, call the driver setup dialog box (click on Setup menu item),
change aperture value settings and click OK. You don’t need to reconnect the driver. Changes will take
effect immediately.
Popup menu