Step down rings on a Samyang 135mm?

[900SL]

Hi

 

I have a 77 - 52mm step down ring which fits to the front thread of my SY 135 f2

This reduces the effective aperture to f 2.8 (ish) but I have been wondering whether this will cause more problems than it solves

Am I correct in assuming that the focal plane will remain very shallow (because the camera is wide open at f2) and that the sharpness will not be as good as if it were stopped down normally using the diaphragm to f2.8?  OK, I get rid of diffraction spikes but if this results in a bloaty image I might reconsider..

[Adreneline]

8 minutes ago, 900SL said:

I have a 77 - 52mm step down ring which fits to the front thread of my SY 135 f2

I use a 77 - 49 sdr and I have seen only benefits from using it with my SY135. I have not noticed any deterioration in images and star shapes are better across the frame, especially in peripheral areas. Personally I don't want diffraction spikes on my stars so would rather use a sdr than stop down the lens to f2.4 as many users choose to do.

 

 

[powerlord]

It will only be bloaty if you are out of focus. But yes, personally I always stop my SY down a stop or so. I actually mount a 2" L-extreme on the front of the lense which works well.

stu