From: Milton Aupperle <milton@outcastsoft.com>

Date: February 9, 2009 1:46:04 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Venus from Toronto

Hi Jim;

Great minds think alike. I shot venus last night (February 8) with the C8 at prime and then with 2.5x televue (F25) using the Grasshopper in 16 bit mode with a Schuller UV Cut filter from Calgary. This was just as the sun went down and the Jet stream was way north and far south of me for a change (split into two strands).

http://groups.yahoo.com/group/Astro_IIDC/files/Planetary/Venus_20090208_180653L_MJA.jpg

That was 130 out of 1479 frames. I was shooting at 66 ms exposures with mid level gains.

You can see what looks like a darkening area in the souther half, which seems to split the bright limb in two halves. I shot 7 movies (6.3 gigabytes), two at prime initially and then five at 2.5x and refocussed between shots.  I also move venus around on the cropped CCD too, so that it can't be some small speck of dust making fake patterns too. You can see this broad darkening in 6 of the 7 movies, except the first movie where I overexposed the limb for prime focus.

Prime focus I was shooting with zero gains at 33 ms exposures because the Grasshopper's EXHAD mono CCD is so much more sensitive than the TIS 640x470 mono camera is. With a 2x barlow I needed about 266 ms exposures and high gains with the TIS, where as the EXHAD Grasshopper and 2.5x televue, 66 ms and medium gains were fine.

It's clear right now (weather forecast says it's supposed to be snowing), so maybe I'll luck out and shoot venus again tonight. The NAM 300 mb forecast:

http://weather.unisys.com/nam/12h/nam_300_12h.html

looks pretty good right now for Alberta.

The rest of the week is supposed to be cold and snowy, but the forecasts have been wildly wrong for the past few weeks, who who knows.

TTYL..

Milton Aupperle

On 9-Feb-09, at 1:16 PM, jimchung2338 wrote:

Seeing was predicted to be good to very good on Friday night, Feb 06,

and I captured Venus just as the Sun was setting through an old Baader

UV filter and a glass filter that transmits UV but blocks UV.  This is

because the previous generation of Baader Venus/UV filters suffered

from IR leakage and Milton brought my attention to this fact last year.

No discernable cloud patterns this time.

Imaged with PGR Flea CCD at 66mS and f20 with C8.

http://tech.groups.yahoo.com/group/Astro_IIDC/files/Planetary/Venus020609.jpg