Filter Wheels

ACE offers a broad range of filter wheels up to 102mm capacity . These products are completely different from the flimsy boxes offered by others. ACE filter wheel boxes are machined from a single block of 6061-T6 aluminum, have integral light-lock seals and are designed to take heavy detectors without flexing. They can be found in research laboratories and observatories all around the world, on telescopes up to 8-m aperture.

Key Benefits

  • Single or double-stack wheels
  • Housed in a box or available for bench-mounting with or without the box
  • Low profile and low mass due to CNC machining
  • Absolute encoder system with precision bearing spring detent lock
  • Most ACE models are available with 10 µm repeatability for perfect flat fielding
  • Oversized axles with precision radial bearings (40 mm bore or larger typical)
  • Available for control through Maxim-DL image processing and data acquisition software
  • Available with motors specified by customer for integration into other equipment
  • ACE SmartFilter™ controller uses RS232 communications for custom integration
  • Custom interface plates to telescope and camera, or use standard T-thread mount
  • Very high speed filter change available upon request (0.3 to 1 second)

Single Filter Wheel

An ACE filter wheel with one wheel, for St. Paul School.

A single wheel in a dust and light-tight box machined from a solid block of 6061 aluminum.

The model shown here has a custom-designed interface for a small telescope and CCD camera.

It is also available with a standard T-thread mount.

Total weight is only 1200 grams (excluding filters).

Low profile (20 mm for model shown)

Available with custom engraving for easy identification and theft deterrent.

Dual Filter Wheel

A dual filter wheel box.

Two stacked wheel with 14 filter capacity, 2-inch square. Full computer control.

Filters accessible through a change door.

Repeatability typical < 10 µm for perfect flat fielding.

Low profile (50 mm for double stack wheel)

Designed for mounting heavy detectors without flexing

Optical Bench Models

A filter wheel box for mounting on an optical bench.

Two stacked wheels designed for use on an optical bench.

Filters jackets accessible through a change door.

Photograph shows filter box custom designed for a major defense contractor.

Filters are housed in removable jackets and are inclined at 1.5° to prevent spurious reflections.

Rear side of box has polished surface to reflect heat from black-body source.

Complete custom design - we can do the same for your project and welcome your phone call.

Custom design and manufacture

The unique filter wheel design of Gettysburg College Observatory.

The box shown here was designed for Gettysburg College Observatory. It comprises two wheels and allow a diagonal mirror (mounted in the upper wheel) to direct light to an eyepiece port for public viewing. In order to maintain the back focal distance of the telescope a chimney arrangement was designed. ACE provides its customers with 3-D solid models before custom machining commences.

We can provide control of the wheels through SmartFilter™ or through a multi-axis control card or by using intelligent servo motors such as Silvermax. We work with your requirements to produce the finest astronomical instrumentation. ACE filter wheels can be found at telescopes around the world and have been incorporated into instruments for 8-meter class observatories.

Custom designs include "box-less" models for use inside Schmidt cameras, ultra-thin models for use at prime focus or other limited space applications, and numerous other design concepts. Please call to see what we can do for your application.

ACE SmartFilter™

Filter wheel box with SmartFilter controller attached.

The ACE SmartFilter™ is an embedded controller that permits RS-232 command and control of ACE filter boxes.

  • Talks with Maxim-DL image processing and data acquisition software application.
  • Used for custom integrating into control system with RS-232 or G.P.I.B. interface.
  • Real-time LCD readout of filter positions and system status.
  • Controls single or dual stacked wheels.

The most common commands are:

Syntax Command Notes
CS Check System Move to filter 0 then cycle through all filters and back to 0. Repeat for second wheel if present.
HM Home Move wheel to a detent position if it is out of detent
n UW Using Wheel For dual wheel systems select the current filter wheel (1 ≤ n ≤ 2)
n MV Move Move to filter n where (0 ≤ n ≤ 9)
n EX Exercise system Used for Certificate of Inspection. Visit 50 random positions and report back status. Timeout if any errors. Repeat n times.
? Short Status Prints out a short status report (see below)
+ Long status Prints out a long status report (see below)
RS Reset Resets the CPU (equivalent of cold restart)
HELP Help Prints out a complete list of available commands with instructions
> Prompt Returned when a command has completed

The output from the ? and + commands permits real-time robotic instrument control

W1 = 3
W2 = 0
UW = 1


  • W1 = Filter position for Wheel 1
  • W2 = Filter position for Wheel 2 (only reported for dual wheel systems)
  • UW = Using Wheel (only one wheel is active at a time - reported only for dual systems)

The + command is used to get a full status report:

W1 = 3
W2 = 0
UW = 1
NF = 8
NW = 2
EO = 2
FL = 0

Version: 28-Sep-02 Copyright(c) A.C.E.
Type HELP for a list of all valid commands


The first three lines are identical to the short status report (? command).


  • NF = Number of Filters (4 <= NF <= 10)
  • NW = Number of wheels (1 <= NF <= 2)
  • EO = engraving offset - factory set - do not adjust
  • FL = FAULT (TRUE when last move failed, else FALSE)

For single wheels the W2 and UW lines are omitted.