Skip to main content

Calibration of the human eye

1 post / 0 new
PIERRE REISS's picture
Calibration of the human eye

Is it possible to detect disparities of the human eye, depending on the observers? If true, what would be an unpersonal device, in order to analyse the spectral answer of the human eye?

(This set of ideas results from reflections between two AAVSO observers, DMIB and PREB, after a common observation night)

1 _ What happens?
During a short amount of time (15mn), the visual measures on the same star show, in the AAVSO database, a spread of 0.4 to 0.8 magnitude. Much more as what one expects from the 2 objective factors:
_ ability of an observer to estimate a 0.1 magnitude spread.
_ reference stars on AAVSO maps are given with an accuracy of 0.1 magnitude.
When an observer locates a variable star 'in the middle' of 2 references 7.24 and 7.44, he will read '72' and '74' on the AAVSO map, and then he will publish '7.3'; when the same observer locates the same star 'in the middle' of 2 other references 7.26 and 7.46, he will read '73' and '75' on the AAVSO map, and then he will publish '7.4'. Giving a 0.1 magnitude spread.
_ Measures worsening cases are sufficiently rarely noticed, and then neglected (light pollution, moon, light clouds, plane tracks, low in the sky, near observing limit, observer's tiredness).

2 _ Measure of the spectral signature of the eye's sensitivity.
Design a device, which, for a given wavelength, simulates a stars field on a black background, with an extra light source, shaped as a little ring and which provides a sequence of increasing magnitudes, by 0.1 magnitude steps. Using this device, the observer notices at which step of the sequence, he detects the ring (its place is unknown and random).
A similar sequence is provided for a scale of several wavelengthes.
One gets a curve, giving sensitivity threshold depending on the wavelength: the observer's signature.

3 _ Results and questions.
Giving a large sample of variable stars visual observers, which is the most likely spectral signature? Is there an important spread for some wavelengthes (red for instance)?
The sensitivity threshold is not the same, with the use of different instruments (naked eye, binoculars, Schmidt-Cassegrain telescop with or without star diagonal). Is there a change in the spectral signature, depending on those optical add-ons?

4 _ Other influences.
The Purkinje effect (red stars) needs to use the device only with out-of-axis vision.
Some magnitude measures are done, looking the sensitivity threshold by gradual unfocusing of the instrument. Is there the spectral signature affected by such a practice?

5 _ Design of the physical device.
(It cannot be a software on a laptop, due to the poor scale of magnitudes available on a screen, and its non-logarithmic nature).
Are you candidate? Any suggestion?

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484