16x Manual lens breathes-Waah!

[Mark Sasahara]

Karl puts a focus gear right over the rubber focus ring. Like the DVX, it's not quite the infinite spinning of the focus ring but it's close. I forget, the 20x is about 100° rotation of the focus ring, from closest focus to ∞. Don't quote me.

I'm still waiting to actually get my CineTech and I'm chomping at the bit to shoot more. 'Course I'd be REALLY psyched to shoot some 35mm FILM.

If you go to the Cine Tech website there's a pic of it right on the home page.
http://www.cinetechonline.com/index.html

[Jeff Miller]

I was testing some stuff today and put the 16x manual on today to try this breathing thing.

I did notice, if you use the backfocus ring to focus, it does not breathe. There was stuff in my living room that was some eight feet away from each other and it worked. This wasn't a real super-duper test, and the backfocus isn't a very suttle control, but if you are trying to do something goofy it has a cool effect (it was like Duke reaching for the mace can during _Fear and Loathing in Las Vegas_...)

(sorry if this is common knowledge, but noone else mentioned it :)

[Mark Sasahara]

Uhhhh, nope. Been a while since I've seen the movie. I think I was tripping when I saw it :~)

That won't work because you'll be spending all your time trying to get the back focus corrected. Nice try. Once you set the back focus, it's best not to muck with it. I want to be able to use my follow focus rig so that I, or my 1st AC can pull focus, reliably, repeatedly, take after take. If I have to rack focus, I'll take the minute to switch over to the 20x auto lens as we prep for that shot. I have a gear ring for the 20x from Cine Tech, so I can use my ff rig. I've already had to do the switch a few times.

[Mark Sasahara]

We were somewhere around Barstow on the edge of the desert when the drugs began to take hold. I remember saying something like “I feel a bit lightheaded; maybe you should drive...” And suddenly there was a terrible roar all around us and the sky was full of what looked like huge bats, all swooping and screeching and diving around the car, which was going about a hundred miles an hour with the top down to Las Vegas. And a voice was screaming: “Holy Jesus! What are these goddamn animals?”...

...Wait! We can't stop here! This is bat country!

[Jeff Miller]

Then maybe you are more familiar with the scene from _Earnest Goes to Jail_ when the gents are talking across the room and the toaster pastry pops up in front of the camera (which Bobby then shoots with a .45). That was a nice pull :) "Burn 'em!!!"

I agree messing with backfocus is bad hat. But if your are recording stuff like gingerbread target practice and drugged-out attourneys then you're already breaking the rules, why not get the shot. I can definately see myself putting some tape marks on that ring and telling the audience "lets look HERE now..." :D

All this talk kind of makes me wonder how the 20x can do this with no problem. There's video glass that won't breath but I think it's more commonly heard in the same sentence as "DigiBeta" or "broadcast". The 20X glassware is nice but not five digit price tag nice. My uneducated guess is it's adjusting the zoom when you spin the focus ring. That doesn't sound too hard when both controls are already servo'd; you just need to write a table containing the known degree of breath error at varying zoom settings, then touch the zoom slightly whenever some operator spins the focus ring.

[Bill Pryor]

All zoom lenses breathe some, and most primes do too, except for the really, really expensive ones

[Daniel Kohl]

I wish I were more familiar with the manual lenses you guys are talking about. But even though I am not, I just wanted to mention the "trick" which is similar to moving the back-focus, but without the same potential calibration consequences. And that is - to use the Macro to do focus racks.

Do the 14x and 16x manual lenses have a macro adjustment?

[Daniel Kohl]

I also seem to remember that the degree of breathing in lenses has something to do with wether focus adjustment occurs outside or inside the lens. That is to say that lenses where the whole focus barrel turns when focusing; breath more than ones where the elements inside the barrel move without the entire barrel rotating. There are some lenses that actually get longer when you change the focus. Do these breath more than the others or less?

[Jeff Miller]

Daniel K -
Yes the 16x does have Macro, not sure about the 14x. Your trick is cool but macro is kind of a small-ish range at the end of the ring. I admit I didn't try the macro lock for what I did, I just turned the whole ring.

Out of curiosity, is it a big deal to loose your back focus calibration? When I was done playing I just centered the front focus, pointed across the room, brought the back somewhere close then fined with the front. I'm asking cuz I really don't know, it seems like if you weren't supposed to change your backfocus they wouldn't put a ring there (but then good luck getting bayonet adaptors to work lol :)

[Daniel Kohl]

What happens when your back focus is out of wack is that the focus will change when you zoom. That means zooming in for focus is no longer accurate. It's a pain to get this re-adjusted because you can only do this by trial and error. And you need something which shows exact focus in the wide angle end of the lens. That is difficult to exactly determine because everything looks sharp at the wide angle end. There is a special pattern that you is good for checking this, called a (seemansstern in Germany)... man I've been away from home too long ... I don't know what it's called in English (sea mans star?).

I don't know if there are other things that can be adversely effected by incorrect back focus, like lens markings not being accurate, but there may be.

Back focus is there, because, in this imperfect world, sometimes the distance from the lens to chip can vary from one camera to another, or can change over time. Especially if you use the camera a lot and hard.

I hope that this makes sense.

[Bill Anderson]

Mark, and all. Are you saying that with the XL2 follow focus rig, on a NON manual canon lens, it will hit the marks and pull acurate focus despite these crazy spinning barrels?

[Jeff Miller]

Daniel, yes that does help, thanks. So when you get proper back focus set up, can you mark it somehow, and it will remain accurate? (except for chip drift, camera/lens wear and etc). That way after a goofy focus trick you could easily restore the correct setting.
We use a wide angle adaptor on a movie's JVC that requires back focus adjustment every time you install it, I don't know how the director keeps it straight.

[Bill Anderson]

If you dick with the back focus you'd better have a decent sized monitor at hand because markings are a ballpark indicator - there is a fairly critical point of focus, particularly if you're going to the big screen or are zooming in on a subject and then pulling back out and expecting to hold critical focus. On set is not where I'd choose to start mucking with back focus, there are alternatives.

[Daniel Kohl]

I would tend to agree with Bill. The adjustment can be very tiny, sometimes. And it is possible that things like; if you move the back-focus ring counter-clockwise it will change the back-focus differently than if you turn it clock-wise. Making marks useless. The ring is not made to be used in the way you are suggesting. I think the idea of doing a rack-focus this way is brilliant as a last ditch solution. But I wouldn't recommend it as a standard MOA. Unless you have another "standard" lens which you can use for all the other shots. One "tricky" lens and one "Safe" lens.

[Mark Sasahara]

<<<-- Originally posted by Bill Anderson : Mark, and all. Are you saying that with the XL2 follow focus rig, on a NON manual canon lens, it will hit the marks and pull acurate focus despite these crazy spinning barrels? -->>>

Bill, yes the 20x auto lens will be able to hit focus marks because as part of the Cine Tech follow focus kit I got, there is a geared ring to go around the lens' focus ring. That interfaces with the gear on the follow focus drive. That's how a ff works, once the gears are enmeshed, you can repeatedly hit your focus marks and do pulls. The Cine Tech Titanium SL has a moving stop on the outer part of the focus wheel that will hit the witness mark arm, thereby stopping the focus. www.cinetechonline.com

I am trying to figure out how to prevent the zoom and focus rings from spinning forever, but that is most likely some type of physical modification on the ring to make them stop. I will post about that later.