Yep, this is due to the physical optics of the lens. The f/stop is the ratio of the focal length of the lens divided by the diameter of the aperture. As you zoom in the focal length increases, but the diameter of the lens does not increase to match it.

Thanks for the quick replies. So it looks like I'm stuck with a $2500 camera that doesn't really have manual controls. We often shoot in situations where the light levels change while we're shooting and where we have to zoom quickly to frame from shot to shot. Apparently this camera, and I suspect our NX5U as well, won't allow this to happen.

Except in studio situations I can't imagine how these cameras could be useful. Not, it would appear, in run-and-gun of theatrical shooting. Am I missing something?

Maybe B&H will buy them back. (Sigh!)

Merry Christmas,

Jack

@Jack

As mentioned by others, the f stop is a limitation of the zoom lens. However, when set to manual, you should be able to have limited within a certain range. Did you set the camera from auto to manual or only use the buttons to control one of the functions?

Old Smoke: The camera is in full manual. In that mode you're essentially limited in what the iris control will allow.

Perhaps I'm missing something, but with the PD-150 and PD-170, for example, you can set the iris at f-2.8 and zoom for the next hour as you frame shot after shot in a live dramatic piece, music video, etc. If necessary the iris setting can be changed in mid-shot. When we're shooting on construction sites we frequently have to adjust the iris as we follow an engineer from one part of the site to another.

In other words, there's no connection between iris and zoom. Set the iris and it stays there, regardless of what else is changed -- zoom, gain, shutter speed.

This does not appear to be the case with the X70, seriously limiting its usefulness I'm afraid.

Jack

I have the AX100 which has the same lens and the lowest I can lock the iris is f4.0 over the whole zoom range.

> "In other words, there's no connection between iris and zoom. Set the iris and it stays there, regardless of what else is changed -- zoom, gain, shutter speed."

You're missing the point. These cameras only allowed you to adjust the f-stop as low as the zoom would allow even when zoomed out. To you, it seemed as if they were independent but they were not. Newer cameras allow you to set the f-stop lower when zoomed out. You are interpreting this as a limitation when zoomed in but it is not. To put it another way, if your camera only went down to f3.7 would would be perfectly happy because you could zoom in and out all day long and it would never change. Think about it!

Based on Kelly's explanation that "the f/stop is the ratio of the focal length of the lens divided by the diameter of the aperture.", I would guess that the aperture was larger on SD cameras than HD cameras which allows them to stop down lower when fully zoomed.

Welcome to the world of HD and tiny sensors. ;-)

~jr

PXW-X70 has a 1" sensor. 20megapixels. The intelligent auto features on these newer cameras is much more advanced than the 150's. They adapt to different lighting situations better than most operators can do manually. People are correct about the standard practice of zooming in, setting f stop and keeping it there even when you wide out. Applies to DSLRs too.
You're getting 10bit 4:2:2 color in camera with both HDMI and SDI out. 12x optical zoom with very high quality 24x digital zoom. That's why it costs what it costs... Otherwise, you would have been just as well off getting an Sony a6000 on sale for less than 600.00 with lens and getting great video out of that with better low light performance.

If you're editing in Vegas, why not use the fade to black clip option?

On a few occasions i've been asked by the court to capture a few things, audio, video, and stills. Editing things out after the fact was unacceptable. If something wasn't to be in the recording, it must not be recorded to begin with. Of course, this can end up with some jarring transitions.

Going back to the OP's other question - Jack, does the camera not have a thumbscrew at front left hand corner, to close down aperture?

I'm looking at the x70 as a possible camera next year, so appreciate your experiences.

Yes it does, same as the AX100 but you can't set it lower then f4 when fully zoomed in. only on full wide does it allow f2.8. The published spec on Sony's website actually states f2.8-4.5.

It's not a question of "allow", it's a physical limitation of the design. Higher end zoom lenses may maintain a constant f stop over the range of focal length.

Bob.

It's a variable aperture lens. This has been the norm in still cameras for decades, but in that world having the shutter change to compensate is not a big deal.

The reason people do variable aperture lenses is really about marketing and keeping the camera size down. Marketing to list the camera has having 2.8 capability, albeit limited. If your lens did 2.8 at full tele, the lens and therefore camera would be some amount bigger and heavier. With variable, they "cheat" and let the aperture go faster on the wide end without the lens getting any bigger. Specsmanship.

If constant aperture is your requirement then it sounds like 3.7 is your limit on that cam.

Where in the Federal Rules does it state that you have to fade to black when going off record? I've seen thousands of deposition videos and years ago you would see some fade to black, but now I'd say it's about 1%. As long as there's a verbal announcement it's not jarring, nobody cares about some cinematic effect at a deposition.
Anyway, why can't you simply roll the iris selector wheel to closed if you need fade to black?

Or flip a lens cover closed? By so doing is the cameraman making it clear that this is the official end of taping? Or is it just cosmetics, given that no editing is allowed?

ScorpioST: This has nothing to do with Federal Rules. At least two of our client companies require "fade to black" in their contracts. Don't ask me why; it's what they want.

The X70 will not allow a fade to black using the iris scroll wheel. If it did that would be easy.

Our solution, after trying to "fade" using the lens cap, which proved very unsatisfactory, has been to use a small piece of black foam-core and slide it down over the lens.

The X70 is a great camera and the workarounds have resolved the problems.

Jack

Didn't realize you can't close the iris on X70.....that seems absolutely bizzarre.

I guess the client is always right, even when it makes no sense. I would probably just do it in post. I can't imagine anyone would have an issue, not like it's a substantive change or edit.

You can assign the 'Gain' to the little thumb wheel adjustment and manually lower the exposure to a point that the video becomes black.

VidMus: Good idea! Will try it immediately. Thanks for the suggestion.

Jack