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GoldFocus - Feature Comparison

Focus Technique Features
Focus Technique Aperture
Mask		 Computer
Assisted		 Task-
Optimized
GoldFocus Yes Yes Yes
'By Eye' No No No
Hartmann (Scheiner) Mask Yes No No
Diffraction Spike Mask Yes No No
Modified Hartmann Mask Yes No No
Bahtinov Mask (visually) Yes No No
Bahtinov (3rd party software) Yes yes No
Minimum FWHM No Yes No
Minimum HFD No Yes No
Minimum Sigma No Yes No

An overview of all focus techniques may be found at Focus Techniques.

Aperture Mask

Many focus techniques use an aperture mask to produce a distinctive diffraction pattern in the image of a bright star.  The effectiveness of these aperture masks varies, including some popular masks which are actually detrimental to good focus.  When used with the accompanying GoldFocus Analysis Software, the GoldFocus Mask is much more effective than any other mask.

Computer Assisted

A computer assist means computer software is used to measure focus quality, usually real-time.  The primary benefit of a computer assist is that a computer can analyze an image and calculate an objective focus measure.  In contrast, focus techniques which rely upon visual assessment of focus, with or without a mask, must rely upon subjective judgment.  The GoldFocus objective computer assist is much more accurate than visual subjective judgment and other computer assisted measures.

Task-Optimized

Task-optimized refers to techniques which are both:

  • designed to accomplish a specific task, and
  • optimized to be as efficient as possible at that task

Only GoldFocus is comprehensively task-optimized for the specific task of accurate focus.

Optimized Task-Specific Features
Focus Technique Objective Focus-
Only		 Resolving
Power		 Wave-
Lengths		 Speed
GoldFocus Yes Yes Yes Yes Yes
'By Eye' No No No No No
Hartmann (Scheiner) Mask No No No No No
Diffraction Spike Mask No Maybe No No No
Modified Hartmann Mask No Maybe No No No
Bahtinov Mask (visually) No Maybe No No No
Bahtinov (3rd party software) Maybe Maybe No No No
Minimum FWHM Maybe No No No No
Minimum HFD Maybe No No No No
Minimum Sigma Maybe No No No No

Objective

GoldFocus is designed to optimally and objectively measure focus, greatly improving the quality of focus.

The Bahtinov Mask with 3rd party software is objective, however the Bahtinov mask has design deficiencies which severely limit its objective accuracy.

The Minimum FWHM, HFD, and Sigma techniques are objective, however they use significantly sub-optimal measures of the quality of focus.

All other techniques rely upon subjective judgment for focus.

Focus-Only

The GoldFocus High-Precision and Plus Collimation Masks are designed to objectively measure focus and to be independent of diffraction limits and astronomical seeing.

The Diffraction Spike, Modified Hartmann, and Bahtinov Mask visual techniques are largely unaffected by diffraction limits.  However, their accuracy is diminished by poor astronomical seeing and their subjective nature.  The inherent blurring of astronomical seeing makes it more difficult to visually distinguish the precise diffraction spike locations. See Focus Techniques for discussion of how these aperture masks are used visually.

All other objective measures - Minimum FWHM, HFD, and Sigma - are general-purpose measures which also include the effects of diffraction limits and astronomical seeing and do not measure focus-only.

Resolving Power

GoldFocus is designed to very reliably achieve the near-best resolving power.  All other techniques are adversely affected by various factors which diminish focus accuracy and therefore reduce resolution during your imaging session.

Wavelengths

GoldFocus is designed to be equally effective across the visible light spectrum and narrowband wavelengths within visible light.

Different wavelengths of light affect all other focusing techniques because it affects both the diffraction pattern of aperture masks and the diffraction limit the overall star image.  For example, 760nm red light has a diffraction limit twice as great as 380nm blue light.

No other focus technique addresses the effects of various light wavelengths in focusing.

Speed

GoldFocus is designed for speed in achieving accurate focus by requiring fewer images to achieve excellent accuracy.

Visual techniques usually require some trial-and-error in order to make comparative subjective judgments.  Minimum FWHM, HFD, and Sigma usually require additional images to estimate and minimize errors or to support additional proprietary algorithms in their specific software.

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