Rare pattern stars on samyang 135

Looks to me like the stars are all streaking in the same direction which leads me to think this is an issue with tracking/guiding rather than backfocus, which should look opposite on the different edges of the frame. 

The image doesn't look similar to this, although the issue could perhaps be a bit more prominent in the lower right corner perhaps:


How are you tracking/guiding the lens?

Observatório Astrográfico do Boqueirão:
Hello JRO_RM,

Yup.. Your problem is related with tilt or backfocus, or both. I had the same problem on mine, until I spend some nights fixing it with very narrow M48 0.25mm rings and a camera tilt plate.
At F/2 is like the RASA's and Hyperstar.. very difficult to adjust the stars.

Regards,

What distance did you use to accourate backfocus.Now i have exactly 44,5 mm

=16pxWhat distance did you use to accourate backfocus.Now i hace exactly 44,5 mm

Mine is at 44,75mm when I’m using the SHO 2mm thickness filters.. but if use the Optolongs I have to reduce it one of the 0.25mm rings.. but this is in mine.. you have to do some tests on yours and figure it out the correct backfocus I’m yours since he can change from camera to camera.

If you want to keep things at F/2 you need some M48 or M42 shimmer rings and find yourself a Tilt plate. I suggest a Gerd Neumann or a Baader tilter rather the ZWO, Thisbe because the adjusters are on the side instead on the front of the plate. This will save you time and gives you a better corrected field of view without put the camera out everytime to adjust it.

The rings help you fine tunning the backfocus. Alternatively you can put an Askar Backfocus adjuster along with one of the tilt plates that I mentioned, but make sure you don’t put more than the backfocus required for the lens counting with the one from the camera. The Askar is very usefull because saves you also time and is super precise. The lens bayonet need also to be changed for a M48 plate like the one sold in FLO..

Regards, Cesar

Looks good there. Same camera/setup? It just leads me even more towards guiding/tracking being the issue at hand.

The pattern you are seeing aren't uncommon, I've seen them with one of my copies as well. Getting an aperture mask should sort it out but personally I haven't bothered.

This is from a far corner in one of my own images where you can see it too but it doesn't get that bothersome IMO:

Hi again. I´m take some pics tonight and i have the same problem. My stars aren´t rounder and i don´t know why. I tried with 43-44-45 mm and the same result. I can´t get perfect stars in the middle of fov. I don´t know what can try now. i tried with and without guiding, only 5 seg exposure. Any idea?

Tony Gondola:
Does the elongation line up with your RA or DEC axis?
What do 1 second exposures look like?

It depends. I think is  I have tightened the adapter too much and it may cause artifacts. 1 second exposure its the same issue, indeed whe i try to focus with asiair, the stars has elongation on live view

Tony Gondola:
So we can definitely say that it's an optical issue at it's base, possibly made worse with tracking issues. What I would do to caricaturize the issue further would be to rack a bright star out of focus, place it in the center of the fame and shoot a series of really short exposures you can then stack. This should give you a very clear view of what's happening.

ok, i just did some testing and found the problem. It was a filter uv/ir that I had in front of the lens and that must have been incorrectly placed and caused the distortions. Now I have taken several exposures and they look point stars