Back to forums

Weird star shape

Samyang 135mm T2.2 VDSLR MK2 Canon EOS 6D Help Needed Coma
6 replies•229 views
Haakon Rasmussen avatar
Haakon Rasmussen avatar
I just bought this lens a week ago, and i am testing it out. It is good, but it has weird star shape on larger stars in every corner.  Does anyone no what it is? Can anything be done with the lens, or does the search for a good lens continue?  This is a crop from upper left corner. It is stopped down to f2.8 with a step-down rings. It looks the same with f2. I used a EOS 6D camera.

CS Haakon
andrea tasselli avatar
andrea tasselli avatar
It's called either inverted lighthouse effect or cat's eye. Your marginal rays are seriously clipped from the outer 1/3 of the sensor on. It would also help if you were to spell it out what lens is that. I hope you're not using auto-sharpening on the jpeg (because it just looks like that)…
Haakon Rasmussen avatar
Haakon Rasmussen avatar
Thank you, Andrea. It is the Samyang 135mm VDSLR T2.2 MK2 lens. Could be that the Software used auto-sharpening. Can the Lighthouse Effect be fixed? Or is better on this lens to use a crop-sensor?
andrea tasselli avatar
andrea tasselli avatar
In could be fixed (there is another thread here about that) but it is expensive in terms of man-hours and not 100% effective so doing for many instances isn't really worth your time. And yes, using a crop sensor would reduce the issue, hopefully. Why using a video lens when the standard Samyang lens is a very good bet?
Die Launische Diva avatar
Die Launische Diva avatar
Have a look at this post in another thread here. If I were you, I wouldn't worry, or maybe stop the lens at f/2.8 with its iris as I am not confident that an aperture mask will work well when taking flats. Personally I find no reason to buy a lens just to stop it down. The stars are perfect for its price and focal ratio. Many Astrobinners are happy with this lens.

I am also using the Samyang 135mm f/2 and I don't bother with the star shapes. It is what it is, it is dictated by pure geometry which also impacts several other more expensive optics.
Haakon Rasmussen avatar
Haakon Rasmussen avatar
Hallo Andrea,

I got it cheap (250€), and was planning using it wide  open,  or with step-down rings. 
And thanks again for your help.
Haakon Rasmussen avatar
Haakon Rasmussen avatar
Die Launische Diva:
Have a look at this post in another thread here. If I were you, I wouldn't worry, or maybe stop the lens at f/2.8 with its iris as I am not confident that an aperture mask will work well when taking flats. Personally I find no reason to buy a lens just to stop it down. The stars are perfect for its price and focal ratio. Many Astrobinners are happy with this lens.

I am also using the Samyang 135mm f/2 and I don't bother with the star shapes. It is what it is, it is dictated by pure geometry which also impacts several other more expensive optics.

Yes,  Launsiche Diva, you are right. I will use the lens wide open, and ignore the "Lighthouses". Perhaps i can manually correct them.  So thank you.  I will also use the lens with my IMX571 camera.