Re: Two of a Kind in Leo

Bob Enouen

Very helpful!  I get what you are saying about the seeing. I was surprised that Maui had worse seeing at times (based on the twinkling of the stars) than my backyard in Ohio.  I can only assume this was due to the greater variability in the air currents coming off the ocean vs Ohio farmland. It also had less light pollution and was Class 4 Bortle on the light meter at the closed airport by Kahana. 

Thanks again!

Robert J. Enouen
Cell 513-504-4410

On Mar 13, 2022, at 4:31 PM, chris1011@... wrote:

The 12" aperture needs very good seeing to get the best resolution (by the way Bortle numbers have nothing to do with seeing, it's strictly light pollution). I have a 175 F8 refractor set up next to the 305mm. It has a .8x reducer, so it's running around F6.4 with a ZWO 6400 camera. On all nights the star resolution in the refractor image was the same as the Honders, between 1.7 to 2 arc sec FWHM. Occasionally the winds came over Kohala mountain and the seeing deteriorated. The stars mushroomed to 5 arc sec FWHM in both instruments. The refractor did not have any clear advantage. 

The 305 faster F# does not result in higher light gathering. Light gain is always proportional to clear aperture. The 175mm has a clear aperture of 175mm. The 305 has a central obstruction which reduces the clear aperture by 25%, so it acts more like a 260mm clear aperture lens. It is about 40% faster even with the central obstruction. 


-----Original Message-----
From: Bob Enouen <renouen@...>
Sent: Sun, Mar 13, 2022 6:22 am
Subject: Re: [ap-gto] Two of a Kind in Leo


Beautiful - Thanks for sharing!  The image quality is amazing.

In your experience, would your highest quality refractor ultimately provide a sharper image than an amazing reflector like this Honders?  I realize there is a huge difference in light gathering between an f3.8 and f8 (1 minute = 4 minutes) or in this case 3’ 20” vs. 13’ 20” for an equivalent f8, but is there another trade off for equal focal lengths?

I have my optimal setup with my Class 5 Bortle observatory based AP1600 non AE (wait listed for AE) combined with APPC Pro, and I’m just planning for the next OTA.

BTW - we were also in Maui a couple of weeks ago and here’s a pic of Dudette that I took while snorkeling off Slaughterhouse beach.

All the best!

Robert J. Enouen
Cell 513-504-4410

On Mar 13, 2022, at 5:56 AM, Roland Christen via <chris1011@...> wrote:
This is a preliminary shot, color will be added later when I get a chance.

Skies remained dark and clear here in Hawaii and even with the Moon at first quarter the sky was dark enough to capture some very faint galaxies in and around this grand pair in Leo. The 305 Honders gathers light very quickly so the exposures had to be limited to 600 sec to prevent burning out the cores of the two bright galaxies. 

The secondary mirror on this scope has some schmutz on the periphery which causes the spikiness in the brighter stars. Will clean it some day when I get around to it. I'm not one to obsess about how all the stars look, I'm more interested in how faint it can record stuff in the night sky. Imaging with this scope is a piece of cake. Focus is set and forget with no re-focusing needed after cooldown. It takes about 1.5 hours for the optics to settle down after sunset, and then the images are sharp the rest of the night. 

The 1600 AE mount is run unguided using a 98 point model in APCC-APPM. I usually let it run all night after I go to bed around midnight. We get an occasional small cloud on some nights, which doesn't cause any issue when I go unguided. 

I have imaged with guiding active in MaximDL-6 and one night I set the mount up to shoot a series of 25 narrowband exposures and went to bed. After 10 exposures a cloud must have passed overhead and Maxim lost the guide star. Unfortunately MaximDL is not set up to deal with high resolution encoder mounts (which can go unguided), so it went searching for the guide star. It did eventually find one, but it was about 1/4 degree away from the image I was shooting. If the program had simply turned corrections off when the guide star dimmed out, the mount would have kept the image right where it was supposed to be. Instead I lost the last 15 of the 25 exposures that I had set up for.


Roland Christen

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