Back focus of RED ONE in 2k.

Donghyug kim · January 28, 2009

I wonder about backfocus problem on RED.

If we use that in 2k setting, is there a backfocus problem ? or not?

Edited January 28, 2009 by deanr

Brian Drysdale · January 28, 2009

I wonder about backfocus problem on RED.
If we use that in 2k setting, is there a backfocus problem ? or not?

First point that you need to use your real name rather than a handle in this forum, it's one of the rules.

The RED backfocus will need to be correctly set up when using 2k as well 3k or 4k. It's the same any camera, otherwise your shots very likely will be soft, especially using shorter focal lengths and wide apertures.

David Mullen ASC · January 28, 2009

There isn't a "problem" per se, but it's something you need to check during prep and check occasionally over the course of a shoot. It's easy to check and easy to adjust if necessary. 2K, 4K, etc. doesn't matter. If it's off, it will affect your focusing using measurements, and it will make it hard to get sharp shots at wide angles.

Go to My Controls and change your Display Name to a real first and last name with a space between them. Thanks.

John Sprung · January 28, 2009

Back focus was a major pain back in the tube camera days. It shouldn't be anywhere near as bad with big single chip cameras. Clairmont a few years back found that they could beef up the mounts on three chip cameras and substantially reduce the problem, even for 2/3". Even on film cameras, the flange focal distance needs to be correct. It's the rental house that handles it for film.

-- J.S.

Chris Keth · February 1, 2009

If you're shooting in the 2k setting, you might notice off backfocus where you might not shooting 4k. Since the RED just crops the sensor, you would be using wider lenses which require more precisely set backfocus.

Keith Walters · February 2, 2009

Back focus was a major pain back in the tube camera days. It shouldn't be anywhere near as bad with big single chip cameras. Clairmont a few years back found that they could beef up the mounts on three chip cameras and substantially reduce the problem, even for 2/3". Even on film cameras, the flange focal distance needs to be correct. It's the rental house that handles it for film.

-- J.S.

I think it was mostly a major pain for film guys trying to use a video camera for the first time.

With most lenses it was a very simple adjustment that could be knocked over in a few seconds, once you knew what it was for and how to adjust it.

2/3" Tube based cameras had quite low native resolution, and so were heavily dependent on detail correction, which made sharp focus really easy to spot.

Liittle black and white CRT viewfinders were more than adequate for focussing your average Saticon-based TV camera, but it was and is a completely different story with HD cameras. Unfortunately this has meant and still will mean many shed tears in the rushes screening room!

John Sprung · February 2, 2009

I think it was mostly a major pain for film guys trying to use a video camera for the first time.

Yes, because on film cameras, techs at the rental house did it, and it held for the duration of your project, and probably many many more. On video cameras, you had to mess with it all the time.

-- J.S.

Keith Walters · February 3, 2009

Yes, because on film cameras, techs at the rental house did it, and it held for the duration of your project, and probably many many more. On video cameras, you had to mess with it all the time.
-- J.S.

In general film cameras don't get particularly warm in operation and so the lens mounts can be relied on to be thermally stable. Video cameras are completely different in that they normally have to be running all the time to enable you to set up shots, particularly so with tube cameras where you also had to allow the camera tubes time to warm up and the grey scale and registration to stabilize.

"Having to mess with it all the time" is a bit strong. If you're charging people money to run their camera, you're expected to know about problems like this, and if you know exactly what to do, there is no "messing about" involved. Hardly any different to checking the gate or keeping an eye on the battery monitor.

People who have been caught out are naturally inclined to try to paint the need for back focus adjustment as a major issue, but if you've sort of "grown up" with video cameras, back focus is just one simple task among a dozen or so other simple chores that you have to be familiar with if you're going to get regular work. (Of course back focus assumes particular importance in that it's one thing that you definitely can't fix in post).

Tim Carroll · February 5, 2009

I've watched a tech at a rental house adjust the "back focus" of a RED camera with a PL mount. He was having a difficult time of it. Had to set the camera up on a collimator and use a calibrated lens. And the way the back focus was adjusted on the mount (this was a somewhat early RED production camera, though it did have the "updated" PL mount, not the very original one that had the issues), but it was kind of a turn-buckle type of adjustment, and took the tech quite some time.

How does one adjust this in the field? You can't use a FFD gage on it, can you? It would seem that the FFD gage probe would damage the CMOS sensor.

Best,

-Tim

David Mullen ASC · February 5, 2009

I've watched a tech at a rental house adjust the "back focus" of a RED camera with a PL mount. He was having a difficult time of it. Had to set the camera up on a collimator and use a calibrated lens. And the way the back focus was adjusted on the mount (this was a somewhat early RED production camera, though it did have the "updated" PL mount, not the very original one that had the issues), but it was kind of a turn-buckle type of adjustment, and took the tech quite some time.

How does one adjust this in the field? You can't use a FFD gage on it, can you? It would seem that the FFD gage probe would damage the CMOS sensor.

Best,

-Tim

You adjust it in the field just like with any video camera, generally using a Seimens star chart if you have one. The procedures though are slightly different if you have a zoom versus a prime on the camera.

Tim Carroll · February 5, 2009

You adjust it in the field just like with any video camera, generally using a Seimens star chart if you have one. The procedures though are slightly different if you have a zoom versus a prime on the camera.

So you are just using the image in the viewfinder or on a monitor to see if it is sharp?

Best,

-Tim

David Mullen ASC · February 5, 2009

So you are just using the image in the viewfinder or on a monitor to see if it is sharp?

Best,

-Tim

You use the Peaking Function in the viewfinder to help when using a Siemens Star Chart -- it becomes very obvious then when it is sharp.

Stephen Williams · February 5, 2009

You use the Peaking Function in the viewfinder to help when using a Siemens Star Chart -- it becomes very obvious then when it is sharp.

Hi David,

Ideally you should record a file & look at the pixels 1:1.

Best,

Stephen

John Sprung · February 5, 2009

You adjust it in the field just like with any video camera, ....

How often do you have to adjust it? I'd expect a reasonably well built big chip camera to be more stable and less critical than a 2/3". How does it compare with Genesis for needing frequent adjustment?

-- J.S.

David Mullen ASC · February 6, 2009

I didn't need to adjust it on the RED regularly -- it was pretty stable.

You can't adjust it on the Genesis yourself, it's a regular PV mount so Panavision techs have to do any flange-depth adjustments. But I never had a problem with it.

John Sprung · February 6, 2009

Thanks, that's exactly my point. You've got enough to do on the set without adding another adjustment you have to make and worry about.

-- J.S.

Rob van Gelder · March 3, 2009

We have now one Red camera shooting a feature in the jungle of Thailand, the average temperature is now between 37-42 degrees Celcius.

The focus puller has said that the wide-angle lenses like a 12 and a 14mm Ultraprime do not always seem sharp when exactly focused on say a 3 ft target.

Probably the backfocus must be off a bit, but the longer lenses do not show this problem so much.

I advice the assistant to check the back-focus frequently with the peaking function/focus assist and adjust the MARK on the lens if needed.

The reason is that the temperature can change every setting and it is better to keep the adjustment so most of the lenses work within small tolerances. The few wide angle lenses need extra attention but to keep adjusting the camera mount is asking for more problems in the long run.

With wide angle lenses, calculate and rely on the depht of field.