F3 sensitivity against EX1

[Michael Power]

Hi Alistair

Returning to question of cheapish zooms, I've been experimenting with a few APS-C or DX of varying length and stop and not having much joy. What about a Nikon 35-200mm 3.5-4.5? If I had enough light to work at f4.5 which is the minimum iris for the 200mm end of the lens and I started at 35mm then zoomed in to 200mm, will I still loose 1 stop of light during the zoom? I've never worked with variable iris zooms before so am in the dark here (pun and all).

My need for an extreme zoom range is to emulate my EX1 which I've been using to shoot the occasional lecture. It's a great camera and much as I would like to keep it as a back up/B camera, economics dictate I sell it. And the money I earn from shooting these simple talks is not enough to warrant lashing out on an Optimo or Red zoom. At the same time, the F3 is ideal for a bunch of other projects.

[Thierry Humeau]

Michael,

Unfortunetely, until Sony comes out with its own motorized zooms, there is nothing in the SLR lenses world that will give you the range and ease of use of the EX1 built-in optic. Aside from the limited zoom factor and high F-Stop of those APS-C lenses, I really have a hard time finding lenses with proper focus rings and mechanisms. In the age of AF, sadly, the manual focusing capability of newer lenses has became more a survival tool than a critical one. On a side note, I discovered a very interesting piece of glass made by Sigma a few years back but now discontinued, the 50-150mm F2.8 zoom. A very good choice for sitdown interviews when in need of 2 different frame values. It also has a very nice and smooth manual focusing ring.

Take care,

Thierry.

[Leonard Levy]

Nikon 18-200 is what I use for this purpose. Image quality is still quite good but you are slowed down because its varifocal and the iris changes from 3.5 - 5.6 . Despite limitations it allows me to shoot a very wide range of B roll when I need it.

[Alister Chapman]

It is correct that if you have a zoom where the iris ramps, if you stop down to the smallest aperture the lens will then remain at that aperture as you zoom.

I wrote up a report on using the F3 run and gun here: PMW-F3, Run “n” Gun, is it worth the effort? | XDCAM-USER.COM

[Michael Power]

Hi Alistair

I had read your report, thanks for that. To clarify, the amount of light hitting the sensor will decrease going from the widest to the longest zoom length, even set at f5.6 on a f3.5-5.6 lens?

Digressing, I'm very interested in your adapter for mounting 2/3" ENG lenses, although one of the not insignificant factors for going to an F3 from my EX1 plus Letus was to avoid the extra weight of the adapter and second lens. When do you anticipate selling some?

[Alister Chapman]

If you set the iris to f5.6 it will remain at f5.6. If you set it to f3.5 it will ramp down to f5.6.

I have some production prices for the adapter now and I'm trying to decide whether to go ahead. I need to make 200 units to make it viable, which requires quite considerable up front investment.

[Michael Power]

When you comment that the iris at f5.6 will remain at f5.6 through the zoom range, are you referring to the light that makes it through the lens to the sensor or the physical setting of the ring? On one of the lenses I've tested with that goes from 28mm to 300mm, f3.8-5.6, even at 5.6 the light drops considerably (but the rings stay put) as you zoom in.

[Brian Drysdale]

The iris stays at the f stop, but when you increase the focal length on the zoom lens, the diameter of the front element is no longer large enough to give you that stop. It's a compromise that lens designers use to keep lenses compact.

Non ramping zooms are larger than those that ramp, for example this was noticeable when Fujinon brought out non ramping high end versions of their video lenses for shooting drama - the size difference was considerable