RE: [APML] Transit exposure help

["Jeff Ball" <jeffball@astro-photography.com>]

Ernie,
Thanks so much for the work.  This data may be very pertinent to me as
one option for me is to Barlow the Canon 10D on the Traveler for f12ish.
I am really hoping for some ocean haze to cool the exposure on the
horizon.  After that, it is filtered only.  Thanks again for the work.  

Best regards,
Jeff Ball
www.astro-photography.com
 

-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]
On Behalf Of emastroianni
Sent: Saturday, June 05, 2004 1:46 PM
To: astro-photo@seds.org
Subject: [APML] Transit exposure help

Hello, all,

I took the opportunity to test my transit photography setup a few days
ago, when we had very clear morning. 
I used a Meade ETX90, a Nikon D100 digital camera and an Identi-View
full-aperture solar filter. 
Essentially, the ETX90 is a 1250mm f/13.8 mirror lens when used at prime
focus with a digital SLR.
What works for me may not work for you. 

The sky was extremely transparent and dry on the morning of June 3. I
cannot imagine conditions that would produce a brighter sunrise.  The
sun was immediately too bright to shoot or look at without filtration. 

5:21 am, 1/30 sec., ISO 1600 – Sun had just cleared the horizon. 
5:26 am, 1/60 sec. ISO 1600
5:31 am  1/80 sec. ISO 1600
5:35 am  1/100 sec. ISO 1600 – Sun had brightened nearly two stops in 14
minutes. 

Control exposure: 
10:34 am, 1/320 sec. ISO 400 – Sun well up in a dry, transparent sky. 

All these exposures produced images of equivalent density, if that term
can be applied to digital. I was surprised at the results. 
While everyone’s systems are different, if you know what exposure works
for you when the sun is high in a clear sky, you can extrapolate:

1/320 sec @ ISO 400 is about 5 ˝ stops brighter than a sunrise exposures
of 1/30 @ ISO 1600.

Throw in some humidity or high cirrus clouds and all this data is
worthless. 

Ernie Mastroianni
Whitefish Bay, Wis.
http://home.wi.rr.com/astrophotography


 

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