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SW Esprit 100 - pincushion/barrel distortion measurement/graph

Sky-Watcher Esprit 100ED Astrometry
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Christian Koll avatar
Christian Koll avatar
Hello,

I am wondering if anybody has ever checked on any pincushion/barrel distortion of the Esprit 100.

This question arose during astrometry/plate solving with "Astrometrica" asteroid identification software, where the result was, that my (RAW) image from the Esprit 100 was heavily distorted.
I also experienced problems when stitching a mosaic along the small side of the frame to get a 16:9 mosaic (usually, you stitch your mosaics along the long side of your frame).

So before I set up a square grid against a bright background in my back yard to take some pictures and check for any pincushion/barrel distortion, I am wondering if anybody has done this yet. Could not find anything seaching on the net.

With distortion pictures described above I could work out lens correction parameters in Photoshop before attempting to stitch my images to a mosaik.

Thanks & CS!
Chris
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rhedden avatar
rhedden avatar
I have not previously heard of this kind of distortion with the Esprit 100ED.  I have a couple of questions before the thread goes any further.

1)  Could you please confirm that you are using the stock Sky-Watcher 1.0x field flattener with your Esprit 100ED, not a third-party reducer?

2) Could you also show your corner stars (e.g., with aberration inspector) so we can validate that your back-focus distance is correct?


Edited to add: It appears that you are using a full-frame camera with your 100 ED.   We are therefore talking about having a properly corrected imaging circle for a full frame sensor, correct?  Nice images in your gallery…
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Christian Koll avatar
Christian Koll avatar
Sorry I did not specify that:

Yes, I am using a full frame camera (QHY600L) on my Esprit 100 and yes, I use the original Skywatcher flattener.
My Esprit was quality picked and optically optimised by "Teleskop Austria" - but it's all stock parts carefully adjusted for the best performance over the full frame.

I have dialed-in my backfocus and tilt adjustment carefully, which was quite an ardous process with such a small pixel full frame camera.
But I am happy with my result.

Please note that I don't have any difficulties in stitching a mosaic along the long side of the frame, this all works fine.
I also don't have any other issues like abberations, or similar.

I was just puzzled that somebody using Astrometrica on my frames (that software does a plate solve) statet that my pictures were quite distorted.
But I have not experienced any issues with plate solve in NINA (using ASTAP) or in Pixinsight image solver (although the latter sometimes fails, despite having checked "distortion correction").

While I recently experienced some problems with stitching a 2-panel mosaic on the short side of the frames (which is something you usually don't do that often) I thought, maybe I can compensate for any distortions before trying to stitch the mosaic.

If nobody has ever done that with the Esprit and the original flattener, I will make some test shots of a square grid and see, if there are any pincushion/barrel distortions. I will post those photos in this thread.

Best regards!
Chris

PS: Thanks for liking my photos!
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Niko Geisriegler avatar
Niko Geisriegler avatar
Hello Christian!

Unfortunately, I can confirm that the flattener from Lacerta/Skywatcher does not manage the full format. Also many discussions with Tommy Nawratil have not led to a satisfactory result.
With the 6d anyway a horror, with the Ra, already a little better but still not the yellow of the egg. The only thing that helps is the 2.5 inch version that TS offers. I have only made one pano of the Boogie Man and M78 and that with Apsc. 
The Esprit is great, as long as you don't mind the corners.

CS,
Niko
Concise
Ali Alhawas avatar
Ali Alhawas avatar
Hi,

Got the SW100 ED before 6 years, No issue like this.
Last year I faced stars elongated in some corners, I unscrewed the focuser, flush it forward a little to perfectly contact the body then tighten the screws again,
Problem solved..

It is better to upload untouched image here to clarify the issue.

CS!