Planetary "shoot-out"

[Peter Drew]

Second "attempt" at comparing telescopes on Mars.  "Attempt" as quickly variable seeing and poor transparency didn't do them any favours.  This time, the regular 16" SCT and SW 150ED were joined by a Vixen 4" Flourite, 8" F8 Newtonian with 1/20 wave (claimed) OOUK optics and a 20" F3.5 Dobsonian.  As near as possible, a magnification of around 250x was used on each by way of a Baader 8-24 and TV Nagler 3-6 zoom.  The immediate impression was that the 16" SCT was giving the best overall view although the 150ED was slightly crisper, the dimmer image not swamping the detail as much and a somewhat steadier focus.  The 8" F8 didn't really get a fair trial as it was awkwardly positioned and too heavy to easily move to a better place, all of these telescopes are currently under the same dome and it needs several rotation adjustments to give the telescopes a clear view.  The Vixen gave the typical well defined refractor view but at 250x it was too dim to fully appreciate, in better conditions it would have been impressive for its aperture. The 20" was a bit overkill for the conditions but worth a look as it was set up during the day whilst I fitted some encoders for "push-to" operation.   Interestingly, what looked like decent collimation with a Cheshire appeared nowhere near according to a defocused Mars so I tweaked it a bit whilst looking at the image, F3.5 is not very forgiving!.  Not the night for a large telescope though. Although the seeing didn't improve later, the telescopes settled and started to perform better, ultimately the 150ED seemed to give the best consistent image due to its better focus stability.  The colours were more noticeable in the refractors, including the atmospheric dispersion.  Overall an enjoyable 10pm-12.15am session, probably the last for a while according to the forecast.    🙂           

[Nik271]

I think for UK skies anything over 6 inches is too much for visual planetary observation as the seeing is generally worse than the theoretical scope resolution. For imaging or deep sky it's a different story of course. That 20inch Dob must be quite something!

[Peter Drew]

On 18/09/2020 at 16:36, Nik271 said:

I think for UK skies anything over 6 inches is too much for visual planetary observation as the seeing is generally worse than the theoretical scope resolution. For imaging or deep sky it's a different story of course. That 20inch Dob must be quite something!

It is, but it would easily fit inside our 30" Dob.    🙂

[Nik271]

5 hours ago, Peter Drew said:

It is, but it would easily fit inside our 30" Dob.    🙂

Hehe, Peter, I was imagining this Dob in a back garden... until I looked up your location web site and checked the equipment photos. Wonderful collection! And excellent outreach work you are doing over there!

Nikolay

 

[Paul73]

Sounds like an interesting couple of hours. Shame that the 20pv Dob wasn’t better placed. Wonder if it could have lived with the fracs??

Paul

[Peter Drew]

1 hour ago, Paul73 said:

Sounds like an interesting couple of hours. Shame that the 20pv Dob wasn’t better placed. Wonder if it could have lived with the fracs??

Paul

I have it a little better prepared now ready for the next available session.       🙂

Edited September 21, 2020 by Peter Drew