Vari ND filter issue

[Filthy]

First off, forgive what feels like total beginner ignorance. HDSLR world is very new to me and I'm pretty confused. Having issues using a Genus Vari ND filter on the end of 300mm Canon F4 lens. I have it mounted on my GH2 via adapter. The lens works great indoors without the filter on. However, as soon as I step outside and slap the filter on, I can't get critical focus. There is always some level of blur and a weird glow around any of the highlights. Why is this only an issue with this lens? No problems what-so-ever with an EOS 50mm 1.4 or Tokina 11 - 16mm (with or without filter). Was really hoping to use that tele lense with an doubler, but then the problem is even worse! Plus the IQ gets pretty soft anyway. Is there some fundamental rule regarding long lenses and the GH2 that I'm not aware of? Could it be the Kippon adapter?
Please advise.

 

[GrahamH]

My Lightcraft Workshop VariND works fine on wide and normal lenses but becomes fairly unusable at any focal length above 100mm ... there are a few threads here by other folk reporting similar results.

 

[MR Fanny]

for me with a fader ND image degrades also as you go up in the focal length. even with the 14-140 kit lens when you get up to 140 it aint pretty. some say the sing ray is a lot better in this regard.

 

[JonathanS]

The Light Craft Workshop FAQ page mentions that the FaderND exhibits a softening of the image at longer focal lengths: http://www.lightcraftworkshop.co.uk/faqs.html

This is one of the areas they claim to have improved for the FaderND Mk II.

 

[GrahamH]

I have the Mark II ... (can't comment on whether its better than the Mark I used to be)

 

[iflight]

I'm using the 14-140 with a DIY Vari ND comprised of a really nice Marumi Super DHG CPL + a Hoya LP and everything looks sharp up at 140mm.