Blackmagic Forum

I've never operated anything but a camcorder with an existing ''zoom" button that allowed me to zoom in or out while the autofocus was doing its thing.

With the Blackmagic (or any camera that doesn't have autofocus) you have to zoom by simultaneously operating the zoom and the focus ring on your lens.

In some cases, I assume this must be quite tricky. (unless you're using infinity focus?)

Is there a product out there that makes this zooming thing a little bit easier? Like some kind of follow-focus that works with the zoom and the focus ring...?

I want to be able to achieve nice, long zooms that would otherwise require me to set a bunch of markers on my follow focus... not very practical.

Thanks!

Most DSLR zoom lenses are not parfocal, meaning they typically don't hold focus when you change focal lengths.

Related info here:
http://herefortheweather.wordpress.com/ ... al-lenses/

Peter J. DeCrescenzo wrote:Most DSLR zoom lenses are not parfocal, meaning they typically don't hold focus when you change focal lengths.

Related info here:
http://herefortheweather.wordpress.com/ ... al-lenses/

Peter, thanks for the reply

However, I'm not sure what you mean by this...

Are you implying zooming in and out won't be an issue, because lenses will adapt to the focus?? I'll be using MFT lenses on the pocket...

Thanks.

Keeping your subject in focus will be an issue when zooming in & out using most DSLR-type lenses, because most of these lenses will go out of focus as you zoom in/out.

They go out of focus (they don't "hold" focus) when zoomed because most of these lenses are not parfocal. A lens designed to be parfocal holds focus while zoomed.

Also, the BMPCC pocket camera does not feature continuous auto-focus. As a result, it doesn't compensate for most (digital AF) non-parfocal lens' inability to hold focus while being zoomed.

There are more details in the blog post I referred you to above.

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IF you need to zoom in/out during a shot, you benefit from parfocal lenses; they also help in getting perfect focus before the shot (zoom in very close, set the focus, then zoom out to frame the image to your liking). So parfocal lenses are good to have anyway.

Yet i must say that i seldom see need to zoom during a shot!

Mac Jaeger wrote:IF you need to zoom in/out during a shot, you benefit from parfocal lenses; they also help in getting perfect focus before the shot (zoom in very close, set the focus, then zoom out to frame the image to your liking). So parfocal lenses are good to have anyway.

Yet i must say that i seldom see need to zoom during a shot!

In narrative filmmaking, zooms can be quite effective! Watch anything by Leone or Kubrick for examples!

I saw zoom used quite a lot on Django Unchained. A baddie comes into shot, zoom in fast to their face.

Nice gif example here:
http://gifrific.com/calvin-candie-zoom-in-and-nod-django-unchained/


Jules

SO no RIG that will make zooming and focusing at the same time easier?

Max Normandin wrote:SO no RIG that will make zooming and focusing at the same time easier?

The solution isn't a "rig". The solution is using a parfocal lens.

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Peter J. DeCrescenzo wrote:

Max Normandin wrote:SO no RIG that will make zooming and focusing at the same time easier?

The solution isn't a "rig". The solution is using a parfocal lens.

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What parfocal MFT zoom lens will work on the bmpcc, if any?

Max Normandin wrote:What parfocal MFT zoom lens will work on the bmpcc, if any?

I don't think there is a native MFT zoom lens that is parfocal, but I could be wrong.

I believe Panasonic, Olympus & Tamrom are the only makers of native MFT zoom lenses. You could ask them if any of their lenses are parfocal or not.

As noted above in my blog post about parfocal lenses, there are non-MFT lenses (most which are fully manual) that can be adapted to MFT for use on a BMPCC pocket cam.

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Kessler Cine Drive

Not cheap but usefull for a single camera operatorer.

You could use a Super 16 C mount zoom with an adapter, as these are film lenses, they shoul hold focus through zoom, I know the Ziess does. Denny

You could also try a piston zoom. This means that the zoom and the focus are on the same control, so it's really easy to operate both simultaneously with a single hand.

http://www.thelensdoctor.co.uk/page11.html

This guy sells a few decent ones. I bought a Tokina 80-200MM lens from him, and it works beautifully.

You'll find that some lenses that are not parfocal will not keep focus when zooming in, but WILL keep focus when zooming out.

In the ancient past, we always set the focus on a parfocal lens by zooming all the way in. They would then hold focus as you zoomed out. If you ever tried to set focus while wide, the larger DOF would give you good focus but when you zoomed in, it would usually be off as the DOF narrowed.

The secret to a parfocal (and we never even heard of that word back in the day) lens was to zoom in all the way, focus and then pull back to the shot you wanted. As long as you didn't touch the focus, it would be sharp if you zoomed in.

mhood wrote:... The secret to a parfocal (and we never even heard of that word back in the day) lens was to zoom in all the way, focus and then pull back to the shot you wanted. As long as you didn't touch the focus, it would be sharp if you zoomed in.

Yep, that's how a proper parfocal lens works. They are a dream to work with!

That's why I was excited to learn that the Sigma 17-50mm f2.8 IS APS-C lens appears to be parfocal, as shown in the 2nd-half of this video:


Unfortunately it's a relatively short zoom, but for cameras that have compatible lens mounts, it appears to be a very good value.

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Peter J. DeCrescenzo wrote:That's why I was excited to learn that the Sigma 17-50mm f2.8 IS APS-C lens appears to be parfocal, as shown in the 2nd-half of this video:

If only that lens was one of the "new" Sigma lenses, after they decided it's worth putting some effort into the design and materials of a lens.

Max Normandin wrote:In narrative filmmaking, zooms can be quite effective! Watch anything by Leone or Kubrick for examples!

Sure, I don't say no one needs it. Just I don't, usually. But then againg this may be because i rarely do narrative work - it's a very different way to approach filming than what i come from (mostly ENG and Docu).