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parfocal incompatible with autofocus?

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Bob Cole
parfocal incompatible with autofocus?
on Apr 5, 2017 at 10:18:57 am

I've been holding off buying a 4k camera, even though there are several great models, because of the cost of a good zoom lens. I thought I'd found the ideal solution: Sony's18-110mm e-mount for the FS7M2. But on the B&H site, I read this: "According to Sony, the lens acts like a parfocal lens with the electronic autofocus function engaged. Actual parfocal lenses cannot be auto focus lenses and auto focus lenses cannot be actual parfocal."

Is this true? For the classic interview shot (and many others), I'd like to be able to zoom in, MANUALLY focus, and zoom out with confidence that I still have focus.

What are you folks using for this situation? I really like shooting with wide apertures, but I also like the shot to be in focus.

Bob C


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Gary Huff
Re: parfocal incompatible with autofocus?
on Apr 5, 2017 at 4:17:09 pm

[Bob Cole] " I read this: "According to Sony, the lens acts like a parfocal lens with the electronic autofocus function engaged. Actual parfocal lenses cannot be auto focus lenses and auto focus lenses cannot be actual parfocal." Is this true? "

No, it's not true. The Canon 18-80 f/4 is parafocal and autofocuses just fine. I would also ask where you saw this exactly because I cannot find it on the page for the lens you mentioned, either in the overview, Reviews, or Q&A.


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Bob Cole
Re: parfocal incompatible with autofocus?
on Apr 5, 2017 at 6:30:58 pm
Last Edited By Bob Cole on Apr 5, 2017 at 6:35:34 pm

Please note that I was referring to the Sony 18-110mm lens, not the Canon.

I got this information by posting a question on B&H's site for the Sony FS7M2. A staff member replied, and I got an email summarizing his answer, which is what I quoted. Oddly, when I looked on the B&H site, I didn't see his reply, only my posts.

edit: I just looked for the Canon lens, and can't find a reference to it. I'd be glad to know about any parfocal zooms in this range, autofocus or not.

I appreciate the response!

Thanks!

Bob C


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Bob Cole
Re: parfocal incompatible with autofocus?
on Apr 5, 2017 at 6:41:58 pm

Gary, I'm glad to hear that the second-hand info from Sony is wrong. I found the lens, finally (Canon CN-E 18-80mm T4.4) and the description does indeed say it is parfocal.

Do you own or use one? Is it parfocal when you are in manual focusing mode?

Thanks!

Bob C


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Gary Huff
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 2:33:59 pm

[Bob Cole] "Do you own or use one? Is it parfocal when you are in manual focusing mode?"

I do own one and it is parafocal and works great, even when you have AF turned on. The Sony you mentioned is *not* parafocal, not mechanically. It is a cheat where Sony uses the AF feature on the camera you have it mounted on to "fake" being parafocal. I can do this with non-parafocal EF lenses on my C300 Mark II as well. The Canon 18-80 is parafocal mechanically and works with Canon's DPAF focusing system.


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Bob Cole
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 3:02:54 pm

Great! This is very interesting. It is fantastic that it works in manual focus mode, and that's all I really care about. Thank you very much!

I'm very curious about how it works with AF or DPAF turned on.

The simplest example: interview, shallow DOF. Rack in, focus on the nearer eyeball, zoom out and reframe. Now, a lot of other things appear in the picture: some lab equipment in the foreground, and artwork on the wall behind the subject.

How does the AF work here?
1. How do you tell the lens/camera to focus on that eyeball, rather than the shirt, or the beaker in the foreground? Or does the AF allow you to set a focus point?
2. If you are able to lock in the original focus point... What if the subject is a bouncer, who leans in and leans back all during the interview?
3. If AF continues to operate... When you zoom out and compose the shot, so that the eyeball is now in a different position in the frame, how does the AF know not to focus on the eyeball's old position within the frame, which might be the painting on the wall?

Thanks for the info!

Bob C


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Gary Huff
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 3:14:12 pm

[Bob Cole] "How does the AF work here?"

I usually have the AF set to "Face Detect" for interview situations. The C300 Mark II's sensor size is the equivalent to 35mm motion film, so we're not talking about insane shallow DOF like on the 5D or Sony A7 series. I have shot hours upon hours of footage this way and the focus is nailed 99% of the time. I have it set to a toggle so I tend not to leave it on unless the subject is moving around significantly.

For this spot, I had a single operator who was running the camera, but she was primarily moving it on the Dana Dolly for the parallax effect. I had the C300 Mark II set to Face Detect for the entirety of the shot, just in case there was any issue with the focus (this is not the 18-80 which wasn't available at the time).

uTalk

For this spot, it was just me running the camera, so I had Face Detect turned on so that the camera would track and focus as I zoomed out. This is the 70-200 f/4.

Mercados de O’liva

Unfortunately I don't have any 18-80 examples yet as I have only had it since very late December, and most of what I have shot with it hasn't been released yet. However, the functionality is the same as with the above examples.

Now, all the DPAF gives you is a targeting reticule that you can move around and Face Detect. It doesn't "lock-on" objects or anything.


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Todd Terry
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 3:22:25 pm

I'm going to butt in here and ask a stupid question, just because I want to educate myself...

But... I thought virtually all real cine lenses (and I'm assuming video zooms) were parfocal.

Are they not?

I know some SLR zoom lenses are not (and are only varifocal), but I thought that all legit lenses for motion work are.

I'll freely admit I shoot very few zooms (I'm a primes guy), but I have been shooting for 3+ decades now and don't recall ever having to use a zoom that wasn't parfocal.

Or have I just been totally missing something for a quarter century???

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Gary Huff
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 4:09:25 pm

[Todd Terry] "I thought virtually all real cine lenses (and I'm assuming video zooms) were parfocal."

I guess that means how you define what a "real" cine lens is.

[Todd Terry] "I know some SLR zoom lenses are not (and are only varifocal), but I thought that all legit lenses for motion work are."

What separates a "legit" lens for motion work from a "non-legit" lens? If I shoot motion work with a lens that would not fall under definition of "non-legit", does that mean the definition still works?


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Todd Terry
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 4:19:03 pm

I mean a "proper" cine lens... lenses that were designed for motion picture work... as opposed to SLR still zooms that have been repurposed for motion work. Of course this wasn't a consideration before the DSLR explosion.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Gary Huff
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 4:27:44 pm

[Todd Terry] "Of course this wasn't a consideration before the DSLR explosion."

Very true, I don't think the Sony 18-110 is trying to be cine-style, but definitely video-centric with its servo zoom. Cine-style zooms are expensive, heavy, and manual, which aren't a good option when you don't work with budgets that routinely allow you a 1st AC (I'd rather spend that on a gaffer if it's either/or).

I will say that in my time on film and commercial sets, I routinely see cine-style zooms as opposed to primes. Now, I would say the Canon 18-80 is a cine-style zoom that happens to have electronics in it, which is the best of both worlds. It's compact, it has a servo, and it's parafocal. Canon also markets it as a Cinema lens. Though, truth be told, I'd have the 17-120 if I could afford it, and use that 90% of the time.


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Todd Terry
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 4:45:51 pm

[Gary Huff] "if I could afford it, and use that 90% of the time."

Yup... and thus the problem with cine zooms.

Even though I rarely if ever change a focal length during a shot, sometimes it does get tiresome changing primes and I wouldn't mind having a zoom mounted instead. The only zoom I ever use is my vintage Russian Foton 37-140mm, which is beautiful glass and gives pretty much exactly that vintage Cooke Speed Panchro look that most DPs still go crazy for... but it is slooow as molasses.

In a perfect world there'd be a very wide range cine zoom that is also very fast and lightweight... and affordable. Say, something in the old Angénieux range of 12-120, that was f/2.0 or faster, wasn't a foot long and six pounds, didn't flare, and didn't cost as much as my first house. Unfortunately you are more likely to find a leprechaun.

Canon does make two great (and fast) cine zooms that I'd love to have... but for range I'd need both of them and last time I looked they were pushing 50 grand each (and are still quite large and heavy). I haven't even come close to being able to justify that as a purchase, and no rental houses in our area stock them.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Gary Huff
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 8:07:44 pm

[Todd Terry] "In a perfect world there'd be a very wide range cine zoom that is also very fast and lightweight... and affordable. "

Unfortunately, that defies the laws of physics. Fast, lightweight, and with a useable range. Once you start making it heavier, that means more materials. Once you start making it more useable wide open, that's more craft in the creation of the glass. More materials needed and precision in the glass means its more expensive.

I'll take what Canon is doing with the f/4 Cine zooms as a fine trade-off with the modern sensors that have greatly increased sensitivity.


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Todd Terry
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 8:17:16 pm

[Gary Huff] "Unfortunately, that defies the laws of physics."

Obviously... hence my leprechaun analogy. Or Unicorn.

The Canon f/4 is probably a decent trade-off... but a lot slower than I'd like.

The Canon 14-60mm is reasonably fast at f/2.6... but that's not great range on the long end, and it's $43,000.

For something in the f/4 range I'll stick with my Russian Foton.

It's definitely a challenging world sometimes, optically. And otherwise.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Bob Cole
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 7:02:41 pm

Great work! and very interesting examples of AF. And very impressive, that relatively inexpensive Canon "still" lenses with AF can be so useful with video.

I have to find a C300M2 somewhere to try it out, but meanwhile:

With Face Detect, can you select a particular face and have the camera track it, changing focus as that one face moves closer to the camera? If the person walks behind an object for a second, will Face Detect hold its fire and keep the focus at the setting where the face disappeared from view?

Bob C


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Gary Huff
Re: parfocal incompatible with autofocus?
on Apr 6, 2017 at 8:10:38 pm
Last Edited By Gary Huff on Apr 6, 2017 at 8:10:56 pm

[Bob Cole] "With Face Detect, can you select a particular face and have the camera track it, changing focus as that one face moves closer to the camera? If the person walks behind an object for a second, will Face Detect hold its fire and keep the focus at the setting where the face disappeared from view?"

You can pick the face you want to use. It will highlight all faces it detects and you use the joystick to swap around which face is targeted. Unfortunately, if it loses the face, the DPAF resorts to the adjustable targeting reticule, and it currently does not target where the face was last detected. So if you had targeted in the lower third of the frame, and the person whose face you are detecting turns their head to talk to someone behind them, it will immediately switch to the DPAF target and focus on whatever is there. I have asked Canon to fix this so that the DPAF target is adjusted to be where the last area of face detection was, but this has yet to be implemented.

You can tell the C300 Mark II to only use Face Detect, and so it does nothing when it loses the target, but then you'll have to disable AF and go manual if you need to focus on anything else. And to switch it back to normal DPAF operation, you have to go through the menus, so it's not ideal.


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