Focus pulling wide dolly shots when subject is far away

[Nicolas U Hepburn]

Hi everyone,

I'm not sure if it's an issue of using a photographic lens instead of a cine one. When I shoot a scene with my Sigma 18-35 at 35mm 2.8 and my subject is around 3 meters (around 9 feet) away from the camera while doing a push-in with a slider (2.6 feet distance between points A and B of the slider), I always find the subject to be too soft for my liking and the two focus points are so close that it is impossible to follow. If the subject is closer to the camera I don't have any issue at all and the subject is perfectly sharp. Now, I know that the further away the subject is the less movement is required to adjust focus. Should I just deep focus in these circumstances?

[Raymond Zrike]

It does sound like a limitation of the photo lens you are using. Cine lenses have much longer focus throws. 

[Mark Dunn]

When it comes to the mechanics of focussing, the requirements of stills and MP photography are not only different, but opposed. A short focus rack is a positive advantage in stills as the autofocus can be quicker, but as you've found it works against you when pulling focus, which is of course unique to cine. If you need to use this lens, and keep shallow focus, the only solution is to practise.

7 hours ago, Raymond Zrike said:

Cine lenses have much longer focus throws. 

The extreme example is the f0.7 Zeiss lens Kubrick rebuilt for the candlelit scenes in "Barry Lyndon" , which had a focussing helix that rotated through two full turns- 720deg.

[Nicolas POISSON]

According to this Depth-of-field (DoF) calculator...

https://www.dofmaster.com/dofjs.html

...If you are using a full-frame camera, the total DoF in your case should be 1.29m, ranging from 2m50 to 3m80. It should be enough to keep a sharp image on the whole 86cm distance of your slider. However, you have to set the focus when your slider is more or less at the middle of its travel, to use both sides of the DoF. All these calculations are theoretical and rely on the "circle of confusion". They use a default value, which might not be adequate, but its impossible for the common user to decide what better value to use.

Most still lenses with auto-focus have other drawbacks:

- manual focusing is indeed "fly by wire" type: the focus ring does not move anything, it just tells the camera body what was the rotation, and the body tells a motor inside the lens to move accordingly. This is not very precise

- moreover, the relationship between rotation and focus change is usually not linear and depends on the speed of rotation. For a same angle, the fastest you turn the ring, the greater the focus change. This is of great help for stills, as it makes an intuitive "coarse / fine" focus search. But you cannot have a very repeatable action when pulling focus in video. Some camera bodies allow to change the relationship to "linear", but the very common Panasonic GH5 and Sony A7III don't.

Edited November 9, 2023 by Nicolas POISSON

[Nicolas U Hepburn]

9 hours ago, Raymond Zrike said:

It does sound like a limitation of the photo lens you are using. Cine lenses have much longer focus throws. 

I guess I have to just rent a cine lens for those shots. Thank you!
 

1 hour ago, Mark Dunn said:

When it comes to the mechanics of focussing, the requirements of stills and MP photography are not only different, but opposed. A short focus rack is a positive advantage in stills as the autofocus can be quicker, but as you've found it works against you when pulling focus, which is of course unique to cine. If you need to use this lens, and keep shallow focus, the only solution is to practise.

The extreme example is the f0.7 Zeiss lens Kubrick rebuilt for the candlelit scenes in "Barry Lyndon" , which had a focussing helix that rotated through two full turns- 720deg.

Focus peaking tells me the image is in focus at that distance (9 feet) when the lens is at or close to infinity so I can't really follow the slider movement when the points on the wheel are less than a few millimeters apart and the camera movements is considerably longer than that. I might be able to use the A and B point feature on the nucleus wheel which would make the throw longer between those points. On medium-wide shots when the focus mark isn't close to infinity like in this scenario, I can keep it well in focus the entire way because there is more depth between the subject and the background and the two focus point are further apart and most importantly not that close to infinity which on this lens doesn't seem to be very accurate. I guess, as you said,  that I need to adapt to how a regular photography lens works instead of making it adapt to my needs. Thank you!

 

 

1 hour ago, Nicolas POISSON said:

According to this Depth-of-field (DoF) calculator...

https://www.dofmaster.com/dofjs.html

...If you are using a full-frame camera, the total DoF in your case should be 1.29m, ranging from 2m50 to 3m80. It should be enough to keep a sharp image on the whole 86cm distance of your slider. However, you have to set the focus when your slider is more or less at the middle of its travel, to use both sides of the DoF. All these calculations are theoretical and rely on the "circle of confusion". They use a default value, which might not be adequate, but its impossible for the common user to decide what better value to use.

Most still lenses with auto-focus have other drawbacks:

- manual focusing is indeed "fly by wire" type: the focus ring does not move anything, it just tells the camera body what was the rotation, and the body tells a motor inside the lens to move accordingly. This is not very precise

- moreover, the relationship between rotation and focus change is usually not linear and depends on the speed of rotation. For a same angle, the fastest you turn the ring, the greater the focus change. This is of great help for stills, as it makes an intuitive "coarse / fine" focus search. But you cannot have a very repeatable action when pulling focus in video. Some camera bodies allow to change the relationship to "linear", but the very common Panasonic GH5 and Sony A7III don't.

I'm using a Pocket 6k so it would be a 35 sensor. I should try the method of focusing in the middle of the slider's travel thank you for suggesting it. Thank you!

[Nicolas POISSON]

I do not know the BMPCC 6K, but on many cameras the intensity of the focus peaking can be adjusted. When set to "strong" or "high" or anything like this, the peaking is easy to spot, but also very permissive. It displays as "in focus" objects that aren't.

[Nicolas U Hepburn]

On 11/9/2023 at 2:06 PM, Nicolas POISSON said:

e BMPCC 6K, but on many cameras the intensity of the focus pe

I checked and you're right. I used to have it on low but for some reason it was set to high. Reason being I started focus peaking on the shinobi but for that shoot I just used the p6k monitor and didn't check the focus peaking settings. Thanks!

[Jeff Bernstein]

On 11/9/2023 at 9:43 AM, Mark Dunn said:

The extreme example is the f0.7 Zeiss lens Kubrick rebuilt for the candlelit scenes in "Barry Lyndon" , which had a focussing helix that rotated through two full turns- 720deg.

All of the candlelit scenes were done entirely without artificial light, by candlelight and reflectors alone, necessitating the development of custom lenses. Alcott told American Cinematographer, “Kubrick located three 50mm f0.7 Zeiss still lenses, which were left over from a batch made for NASA. We had a nonreflex Mitchell BNC which was sent over to Ed DiGuillo to be reconstructed to accept this ultrafast lens.” DiGuillo wondered why Kubrick wanted special lenses developed, when there were already lenses that would suffice for candlelit scenes, provided that artificial light was used. He said he wanted to preserve the natural patina and feeling of these old castles at night as they actually were. DiGuillo continued, “The addition of any fill light would have added an artificiality to the scene that he did not want. To achieve the amount of light he actually needed in the candlelight scenes, and in order to make the whole movie balance out properly, Kubrick went ahead and push-developed the entire film one stop—outdoor and indoor scenes alike.”

 

One problem with these custom-fitted lenses was that they had virtually no depth of field at such low light levels. Alcott had to gauge the lenses’ focal settings by doing hand tests from two hundred feet down to four feet. He and Douglas Milsome came up with an elaborate system using closed-circuit video with a grid placed over the TV screen to mark the range within which actors could move and still remain in focus.

 

Rodney Hill, “Barry Lyndon”, in The Stanley Kubrick Archives, ed. Alison Castle (London : Taschen, 2008), 422–4.

 

 

 

 

Edited November 11, 2023 by Jeff Bernstein