RE: [APML]: Solar Images Show Ghosts? Help!

[Benjamin Gomes-Casseres <ben@alliancerevolution.com>]

Scott,

I did the same test run a month ago with a 4" Takahashi, Thousand Oaks, no 
field flattener or reducer, and got exactly the same result. My 
interpretation is that the second image is produced by reflections between 
the primary and the Thousand Oaks filter (I.e. bounce from first surface of 
primary to Oaks-which is a mirror!-and then sent back down the tube as a 
second image.) One way to test this for sure would be to tilt the Oaks very 
slightly between one (over) exposure to the next and see if the reflection 
in fact shifts. I have not done this, and my scope is down in Curacao as we 
speak. So, if you have time, I'd love to hear your results from such a test 
to fully nail this analysis.

The corroborating evidence I do have is a full series of shots of the 
quarter moon which were, again, grossly overexposed at the end of the 
series. No reflections! So, I conclude it's the presence of the solar 
filter.

At any rate, you will be shooting partial shots at around 1/125 or 1/250 or 
1/500, right? Should be no problem there. And your total shots will be 
without filter, so again, no problem, even for "long" exposures. But with 
anything longer than 1/4 or 1/8 sec or so, you will have trailing, I guess.

The only thing I would wonder about is if you really need the field 
flattener. I'm not familiar with how bad the curvature would be without 
that on the solar image, but remember that only the edge of the sun will 
show whether you're in focus or not...the corona will probably not suffer 
much. And, any time you introduce extra optical elements in the system, you 
loose transmission and possibly create minor internal reflections on bright 
parts. In your case it increases your FL a bit, but not much. I will shoot 
at the unadorned prime focus, as I did in Baja in 1991. I did not have any 
reflection problems at that event, not even during 3sec shots of totality.

Let me know results of the "tilt test", if you do it. Good luck!

Ben

www.alliancerevolution.com/astro




-----Original Message-----
From:   Scott L. Taylor [SMTP:spicy@best.com]
Sent:   Friday, January 23, 1998 2:14 AM
To:     astro-photo@nightsky.com
Subject:        [APML]: Solar Images Show Ghosts? Help!


Hi Everyone,

I've been practicing my sequence and routine for the Feb. 26th Solar
Eclipse and just got back a roll of Kodachrome 64 slides tonight and have a
problem with "ghosting" in the longer exposures.