Re: [dq-rules] Digest Number 213

[Arturo Algueiro Melo <aleam00@yahoo.com>]

Hi, Martin...

> Where did the 'factor of 6' for cats come from? 

Searching through Google.com , with the keywords:
cat "night vision" -goggles -device -telescope -cameras,
I found on the site: http://www.szgdocent.org/cats/a-cat1.htm , The following:

Night vision: A cat's eye is adapted primarily to hunting in low light. It comprises mostly of rod
cells which provide greater detail in low light but don't provide colour vision. In contrast, we
have more cone cells. Cats have cone cells too, but fewer and sensitive mainly to green and blue.
A cat also has another night adaptation, the tapetum lucidum. This reflective mirror-like layer at
the back of the eye bounces light back to the eye sensors for a second round of processing. It
also gives the cat its typical "glow-in-the-dark" eyes. A cat?s night vision is 6 times better
than ours because it has vertical pupils, while we have round pupils. In the dark, vertical pupils
can open to allow 3 times more light into the eye, and in the daytime, it closes to slits which
better controls light entering the sensitive eye. 

> Are cats eyes generally able to see 6 times 
> farther away than humans? Or is it that with 
> altitude (sitting in a tree, etc) they have a 
> less obstructed view. Perhaps just adding an 
> extra value of, say, 6 to 20 hexes (depending on 
> the size of the cat or other conditions) to their 
> vision range would be more appropriate.
 
Cat vision isn't more accurate than human's at daylight; it just gets more light at night. Also,
they are almost unsensitive to red.


> I have not studied night vision or IR goggle for 
> a while, but it seems to me that the range of 
> this type of apparatus is dependant more on the 
> conditions (relative difference in size and 
> temperature difference between heat source and 
> background for IR and actual ambient light 
> available (for scatter) and reflectivity of the 
> target for night vision). Thus for IR a hot tank 
> stands out from farther away because it is much 
> hotter than its surroundings and is large.

Agreed.

Best regards...    Arturo

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