The diameter is φ80mm/3.15".

Our Vespid Retro lenses are sold in sets. If you only want a couple of the lenses, we recommend that you contact below rental house for rental: 
LVR in New York: https://lvrusa.com/?product=dzofilm-vespid-retro-full-frame-7-lens-set-ef-pl
PRG in LA: https://www.prg.com/en/markets/tv-and-film

The lens controls the generation and effect of flare and halation by adjusting the angle and intensity of the light, which can be adapted to more shooting themes.

Yes, Vespid retro can be used with KOOP rear filter.

For the mount changing, please check out below Tutorial:
https://www.dzofilm.com/support/lens-tutorial/738.html
Please noted that the suggested torque is 0.4Nm.

For the parfocal adjustment, please check out the Tutorials on our site: https://www.dzofilm.com/support/lens-tutorial/753.html

The main differences are as follows:
(1) The coating colors are different, Vespid Retro is silver and Vespid Prime is black.
(2) The picture of Vespid Retro is colder, and the style has a sense of retro.
(3) The glare of Vespid Retro is golden yellow, which is obviously stronger than Vespid Prime.
(4) Vespid Retro lenses are sold in sets only.