From: "James Lerch" 
To: "ATM List" 
Reply-To: "James Lerch" 


----- Original Message -----
From: "John Sherman" 

> Hi James,

Hi John,

> >"OH MY GOD" terrible...
> >Silver Coat Total = 171
> >
> >Aluminum Coat Total = 174
>
> >
> >So, Now what to do with this Data?
>
> These two totals are very close to each other. Have you tried visual
> observing with the old silver and the new aluminum? And is the visual
> difference as close as the numbers suggest? On objects such as the Blue
> Snowball, does the old silver provide a greener view?

Did you catch the new data I created for the images, if not see further down.

We did some observing the night we coated the mirror with Al, and the
results showed no apparent increase in brightness on objects like the
planets / M42.  However, the increase in Contrast was (simply put)
Incredible!!!!

> It would be interesting to put one of each in your binos. But then you'd
run
> into the problem of one eye being different than the other.

Reminds me of an interesting event last night.  After viewing the Moon in a
mono-scope, I viewed thru my bino and panicked for a moment.  One eye was
WAY brighter than the other, then it dawned on my dominant eye lost its
night vision on the mono-scope, and viewing thru the bino was plain
disturbing at first :)

> >Can I convert this into a % reflectivity knowing that the
> >uncoated mirror surface should have a reflectivity of 4%??
>
>
> Doesn't the aluminum coating have about 86%, giving you
> something else to go by?

Well, here's the rub, I don't use pure Al for my coatings, I use an Al
alloy of Al, Fe, & Si (Aka Reynolds Wrap Heavy Duty Aluminum Foil)  I
use this primarily as its easy to get and its much more durable the pure
unprotected Al (IMHO)

Assuming the alloy still has something like 86% reflectivity, and using the
new results below (Average RGB of each image)

Dark Frame = 1.8
Uncoated = 4.6
OLD Silver = 44.1
Aluminum = 54.7

This gives us the following results:

Uncoated = 4.6%
Old Silver = 68.8%
Aluminum = 86%

These results still pass the 'common sense' test, so who knows... ;)

James

--- BBBS/NT v4.00 MP