2x stretch factor with Kowa Prominar Anamorphic 16-H?

[bootsie]

I did a bunch of photos with the Kowa Prominar Anamorphic 16-H on my 5D MKII and they look absolutely wonderful.

But I noticed after a factor x 2 stretching in Photoshop (11232x3744) that circular objects are not perfectly round, but somewhat distorted. The stretch is less than 2 times, rather 1.84.

So what is the exact stretch factor for that lens? How do I calculate it?

 

Thanks for your interest and regards.

[Julian]

By photographing a perfect circle and stretching the image till it's perfectly round.

Try a test as close as possible and as far away as possible. There could be differences...

[JohnBarlow]

All scopes of a telescopic design are guaranteed to perform at the stated magnification at the infinity focus setting only.

 

For example a 2x scope will range from 2x at infinity focus to 1.5x at 0.5m

[bootsie]

All scopes of a telescopic design are guaranteed to perform at the stated magnification at the infinity focus setting only.

 

For example a 2x scope will range from 2x at infinity focus to 1.5x at 0.5m

Thank you. This clears things up! 

[Caleb Genheimer]

I have this same lens, and JohnBarlow is correct. Depending on the taking lens and distance to the subject, the Kowa can vary from 2X to 1.5X squeeze. That's why when I film people I always crop to 2.40. That way, I can vary the stretch down from 2X if need be.

[bootsie]

Thanks for this useful information! I'm gonna adjust my workflow accordingly.