Aperture Like Decibels?

Hi,

Is there any way to quantitatively relate aperture to human eye response? In the audio world, the deciBel is used. At a given sound level, a doubling in power will result in 3 dB increase. To double the actual sound pressure level, a 10 fold increase in power is necessary.

Is there an analogous situation in telescopes in terms of the apparent brightness to the eye? Or is the relationship purely linear with aperture?

Cheers,
Matt

Matt,
Its nice to see an audiophile in the astonomoy world. I bet if you sealed up the OTA. installed an Epicenter, and wraped it with dynamat you could get at least 3db......).

Now to be serious.....I think your compairing apples to oranges with DB/brightness to the eye. I'm not saying I'm r1ght about this but here is my best guess. SPL is mesured as a given pressure in a cabin, so not only do you hear it but you feel it aswell. When you hear a frequency of 100hz or lower, it is vibrating your tympanic membrane. Which in tern vibrates the auditory ossicles of the inner ear which vibrate the cochlea of the inner ear. These vibrations are then picked up by the vestibular nerves and sent to the brain. So when you increse the SPL by 3 DB it in a sense doubles your "power" because of the increse in vibration or SPL. Your eye has no vibrating organs to pick up waves except for the iris which opens and closes when exposed to diffrent levels of light. With that said, at night your eye will be dialated to allow as much light as possible though the lens. Your eye is sealed and filled with a viscus liquid that refracts the light onto the retna. When the light increses your iris contracts to relieve the stress on the retna from to much light. When looking at a faint DSO the more aprature you have, the more light will pass to your retna. If you double your aprature, does it increse your sence of sight 10 fold? I don't think so. If you looked at a terestral object though your scope with a doubled aprture, you would see a huge diffrence, possibly even go blind. Its just too bad we didn't retain the evolutionary trate of the eskomos. They are said to have a reflective coating on the macula lutea of the inner eye which allows them to pick up more light!! Guess thats because the nights are longer during the winter the further north you travel.

E mail me if you have any more questions.
[email protected]

Thats my best guess,

Jay
)

PS and people told me that I would never realate my learnings in college with real life issues.....boy were they wrong (hee hee)

No, the relationship between increase in the amount of light and the perceived brightness by the eye is approximately logaritmic. This means that doubling the amount of light results in ~30% increase in perceived brightness. This helps the eye to function more efficiently in handling enormous differences in absolute brightness that it encounters on everyday's basis.

The response could easily be expressed in decibels, which are also a logarithmic form. For any given increase in the amount of light, expressed in decibels, the perceived brightness by the eye would be 1+(dB/10) times higher.