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Cosmic Geoff

Mars & Saturn, 21 Aug, 8" & 5" scopes

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For once I set up my two catadroptic imaging scopes together to see how they compared, and how well the smaller one cut through the crud.

C8 SCT on SE mount, ASI 120MC, ADC, processed in Registax6, 3000 frame video.

Celestron 127mm Mak on Nexstar SLT mount, wood tripod, ASI120MC , ADC, processed in Registax6, 3000 frame video.

The 127mm images are slightly smaller, placed second.   The bigger scope seems to do better.  I thought that Saturn did not change much and was just a seeing test target, but the shadow of the planet on the rings is now distinctly asymmetrical.   The dark smudges in the C8 Mars images correlate well with real features.  Mars altitude about 11 deg. The dust storm seems to be over.

The seeing was better than it's been for a while. 

MarsC-25-22_42_03.jpg

MarsC30-4ep22_40_50.jpg

MarsK25-23_24_41.jpg

MarsM25-23_23_25.jpg

SaturnC30-4ep22_35_28.jpg

MarsC30-4ep22_32_03.jpg

SaturnM22_13_50.jpg

SaturnM22_14_50.jpg

Edited by Cosmic Geoff
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Good comparison but yeah, the 8SE wins.... although that's what you'd expect from a bigger scope.

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Really good comparison, both scopes do a great job for their size, but yeah the C8 certainly fulfils the goals of apparent size, brightness, and resolution. 

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I did something similar when I upgraded my 6SE to an 8SE and was really impressed with how much better the images were.

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  • Similar Content

    • By Cosmic Geoff
      Here is an image of Jupiter, taken around 6am on 15 Feb with my C8, ASI120MC, +ADC, processed in Registax6 from around 30% of 3000 frames.
      I am fairly pleased with it considering that the altitude of the planet was only about 12 deg. and the seeing looked bad when I tried to focus on a star.  And it shows the Great Red Spot.
       

    • By Cosmic Geoff
      I had another go at imaging the shrinking Mars, this time without and with a x2 Barlow lens.  The results are better with the Barlow, which is what one is led to expect.   For whatever reason (probably bad seeing and/or low planets) when I tried a Barlow previously it just made the blur bigger.  Equipment: C8 SE, ASI120MC, x2 Skywatcher kit Barlow element screwed directly into 1.25" barrel of the ZWO camera.   This does seem to give x2 in practice.  I did not use an ADC on the grounds that I shouldn't need one with Mars at an altitude of over 40 degrees.
      3000 image video captured with Sharpcap. Processed in Registax6.  I found that the Sharpcap exposure histogram did not appear to work on such a small image, so had to estimate the exposure.   Yes, optical ADC correction would be better, but the dispersion seemed very small.  Blowing up the image x2 in Registax showed a small colour fringe, which I took out with a single point of correction.
      The images show some surface detail though the contrast is low (if you are using a flatscreen try viewing from below: 🙄)  Mare Sirenum, with Mare Acidalium just discernible foreshortened at upper right. 


    • By Cosmic Geoff
      Here is an image of Mars I made on 9 Jan this year, with a C8 SE, and ASI120MC camera.  The images are rather small (around 7" dia).  Mars is now much higher in the sky than at opposition, so it seemed worth taking a few farewell images as it diminishes in size. Captured with Sharpcap.
      I did not use the ADC - the images are corrected for AD in the processing in Registax.  This is from a run of 3000 images.  I have included a x3 Photoshop zoom of the same image to indicate the size of Mars at opposition on the same scale.  I was quite pleased to record some surface detail, corresponding with the position of Syrtis Major.  If I'd had more time, I could have tried some images using a Barlow lens. I have just discovered that I can unscrew the lens section from a Skywatcher x2 Barlow and screw it onto the 1.25" nosepiece of the ASI120MC, which will give a more modest zoom (I think).


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