Stepping down a 200mm f2.8 prime lens?

[Astroblagger]

How do I stop down a canon 200mm f2.8 prime lens? As the stars in getting are quite bloated at f2.8?

[RAC]

You can put it on a Canon camera, set the aperture to what you want then hit the DOF preview button and then take the lens off the camera with the button held on. If you want to stop it down without causing diffraction spikes then get a lens cap and lathe a hole in it the right size.

My 200mm f2.8L is really good with only blue having a little problem around the corners. I made an external aperture mask using a lens cap. I would only run it stopped down to f3.5 when using a blue filter.

[steppenwolf]

If you like diffraction spikes - and they can be most attractive - then stopping down as suggested above is fine. However, if you don't want the spikes, I'd suggest buying a 72mm to 52mm filter adaptor for the front of the lens to act as an aperture mask as this will stop it down to around f4 but won't produce any diffraction spikes.

[ollypenrice]

Or...

Olly

[Coco]

I have a 72-52 stepping ring and micro focuser ring set if your interested?  You can have the stepping ring if you want the focuser set?