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Ben Chase
14-Apr-2008, 19:38
Looks like Darwin wrote up a pretty good article on testing some of the myths associated with ND Grad filters.

http://singhray.blogspot.com/

I learned a couple things myself. Makes me feel better about moving to the 4x6 size grads :)

Eric James
15-Apr-2008, 10:06
Though informative and somewhat enlightening - the problem I have with his comparisons is that he assumes that the transition zones (within a filter type) are precise and uniform. Maybe their manufacturing process allows for such precision, but from what I've seen, I doubt it. Have you seen the "How it's Made" episode on Lee lighting gels and camera filters - the segment showing the woman hand dipping the GND filter material suggests that Lee's approach is anything but precise.

The argument for hand holding larger GND filters is sound. I've tried hand holding P-sized filters without too much success; 4X6s would easier for sure - more room for operator error.

Ben Chase
15-Apr-2008, 11:51
Though informative and somewhat enlightening - the problem I have with his comparisons is that he assumes that the transition zones (within a filter type) are precise and uniform. Maybe their manufacturing process allows for such precision, but from what I've seen, I doubt it. Have you seen the "How it's Made" episode on Lee lighting gels and camera filters - the segment showing the woman hand dipping the GND filter material suggests that Lee's approach is anything but precise.

The argument for hand holding larger GND filters is sound. I've tried hand holding P-sized filters without too much success; 4X6s would easier for sure - more room for operator error.

Yep - Those are good points.

There is always variation in every manufacturing process. I think a good gauge for the manufacturer are how tight the tolerances are, and how often the output is within the process (within tolerances). I didn't see that episode, but I've got my DVR set to record every one of that series, so hopefully it will pop on again soon!

The hand-dipping doesn't bother me too much as long as it is within good tolerances and the QA is sufficient. Although it's easy to make the argument that automating a process through machinery and tooling is much more precise, I think the relevant question is, how much variation is there in that hand-dipping process, and is that level of variation relevant to the overwhelming majority of images made using those filters? If not - then I can't say that I agree that hand-dipping is a bad thing.

I am not familiar with how Singh-Ray does their ND grads - so I don't know if the process is similar or not.

Helen Bach
15-Apr-2008, 16:17
It struck me as odd that the effect of aperture was tested with a 17 mm f/4 lens. That's an entrance pupil of only 4.25 mm diameter at the maximum. From the experience I've had with them on 35 mm movie cameras, I'd expect there to be a more noticeable difference in effect if you start with a larger entrance pupil - or more specifically a larger angle subtended by the entrance pupil at the filter plane.

Best,
Helen

timparkin
16-Apr-2008, 04:58
It struck me as odd that the effect of aperture was tested with a 17 mm f/4 lens. That's an entrance pupil of only 4.25 mm diameter at the maximum. From the experience I've had with them on 35 mm movie cameras, I'd expect there to be a more noticeable difference in effect if you start with a larger entrance pupil - or more specifically a larger angle subtended by the entrance pupil at the filter plane.

Best,
Helen

Also, the 17-40 has a nodal point so close to the front of the lens it's almost not beleiveable but an aperture that is towards the rear of the lens.. A non-retrofocus design (or at least one not as extreme as the 17-40) would be a better choice for this test which would also probably have nodal point and aperture coincident.

Tim