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Old 28-07-2021, 07:38 AM
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pmrid (Peter)
Ageing badly.

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Join Date: May 2008
Location: Cloudy, light-polluted Bribie Is.
Posts: 3,665
Imaging with Barlows

You can’t escape Dawes! I guess that’s my main take-away from last night’s session. I wanted to grab some Saturn and Jupiter last night. They were in prime position, the sky was clear and quite cool. All the auguries were good.

Having consulted the specs for my choice of cameras and barlows, I decided to use a EOS 500D with a range of Barlows. And the scope for the night was my BD80.

I have a choice of 4 Barlows. 2 are by Svbony ( a x2 and a x3) but both of those had to be put aside because their barrel is sufficiently smaller that it was pushed out of alignment as soon as the screw of the compression ring is tightened. The tilt is obvious. The barrels are 0.25mm smaller in diameter than those of the GSO (x5) and the Bintel (x2) that were my remaining choices.

For precise focus I used a Bahtinov mask on Archenar to get it just right.

Then the choice of capture software. I began with SmartCap using a routine I found on Cloudy Nights that allowed my EOS to play nicely with SharpCap. My plan was to do Live Stacking. No deal. LiveStack relies on having multiple stars for its alignment routine to work and of course that just isn’t possible with planetary imaging. So I just set up for doing a series of 5000 frame AVI’s but that was a dud with both planets. Despite the care taken with focus, there was just not enough surface detail to work with. Dawes strikes!

The x2 Barlow was no better and image scale that much smaller to boot.

So I turned away from planets and had a run at the 4-day off-full moon. And I just used the x2 Barlow here but although focus was bang-on and the EOS 500D is a 15MP camera, the final images just lacked any crispness at all. They were soft and fuzzy. Not what you want for a moon shot.

So my little play with Barlows was a dud.

Once again, it became clear that if I want clarity and image scale, I’m going to have to move to more aperture and higher focal ratios.

Astronomy is a great source of humility isn’t it?
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