Extension tubes on anamorphic lenses?

[Haris Mlivic]

Is it possible to have extension tubes on anamorphic lenses, for the purpose of focusing closer?

 

How does it effect the optics (beside the usual loosing infinity focus and such), and is there a difference between having it on a lens with rear-anamorphic element or one with front-anamorphic element?

 

Also, is it better to use diopters in this case? or are the pros/cons the same as on spherical lenses?

 

Thanks!

[Dom Jaeger]

Extension tubes won't work on any anamorphic lens that I'm aware of because they tend to have dual optical arrangements, spherical and cylindrical, which have separate settings. Some will have a rear spherical lens set to infinity or nearby, while a front anamorphic section does the focussing. Others will have both a spherical and an anamorphic group change position during focus, while still others may have set anamorphic and spherical groups with a spherical focussing front group.

 

In every case, simply extending the back focus (which is what extension tubes do) does not bring the object plane of focus closer, it just blurs the image. Well, sometimes it can bring the close focus minimum a little closer, but there is only a very limited range of back focus adjustment before the image quality suffers.

 

Rear anamorphic lenses won't work with extension tubes either, since they are essentially an adapter taking the image from the back of a spherical lens and anamorphising it. Once again there are two settings - both the distance from spherical lens to anamorphic adapter, and from adapter to film plane, are crucial to the image quality. You can't just extend one distance in order to focus closer.

[Haris Mlivic]

Awesome, thanks for clearing that up Dom. Appreciate it!

[cole t parzenn]

What about diopters?

[Tommaso Alvisi]

Diopters work fine, you just have to use 4.5" or 138mm ones...