Re: [ATM] More on aperature stops

["Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>]

Mel,

In general, I've noticed this on several occasions. Also the difference is
very clear: a crisp moon vs. mars as seen through a haze.

> You're confusing a number of factors
>
> 1. Time of observations: maybe the scope had reached some degree of
> equilibrium by the lunar observation
The scope is kept in the garage, which is almost equal to exterior temp.
Mirror is only 6"/19mm, which shouldn't take all that long to cool. Also,
there was not a directed smear, just a halo of maybe 10% mars diameter.

>
> 2. Magnification: maybe the lunar observation was too low of power to show
> the effect

They were the same, up to 200x.

>
> 3. Eyepiece: same, different?

The same.

>
> 4. Position in FOV: if moon positioned to cover the thermal smear effect,
> then it won't be seen

As I said in the original post, it did not look like the heat smear, but
more like a circle-symmetric halo. Something that I would expect to be
caused by scatter more than heat effects.

>
> 5. Angle in FOV: if moon rotated to cover the thermal smear effect, then
it
> won't be seen

See 4

>
> 6. Total brightness: lunar limb across its length has more total
brightness,
> and might obscure the thermal smear effect (better to use Venus to
compare)

See 4

>
> 7. Different positioning angle in the sky: if thermal effect caused
locally,
> aiming in other direction may entirely avoid it

Mars and teh Moon were about the same elevation.

>
> 8.9.10...et al  Try to control the factors, otherwise you'll never figure
it
> out, or worse, attribute it to the wrong reason(s)

Yes, guess so. It's something to get to in any case.
My original question was whether the decreased eye pupil size could cause
the difference. I guess it should'nt, since the aperture stop needs to be in
front of the mirror to be effective (unless the problem is in my eye, of
course. not likely though: as far as I can remember both eyes gave similar
results).

Thanks anyway,
/AtM

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