SW Esprit 100 - pincushion/barrel distortion measurement/graph Sky-Watcher Esprit 100ED · Christian Koll · ... · 4 · 500 · 0

Austronomer76 4.82

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!
rhedden 9.48
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...
Edited ...
Austronomer76 4.82
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!

PS: Thanks for liking my photos!
Falling_Skies 0.00
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.

AliAlhawas 1.20
·  1 like

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.

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