AF100 Back focus. Adjustable?

[Razz16mm]

For Jan or those who have had hands on exposure to AF100.

Is there any form of user back focus adjustment, either via sensor block or lens mount?

[Jan_Crittenden]

For Jan or those who have had hands on exposure to AF100.

Is there any form of user back focus adjustment, either via sensor block or lens mount?

It is more of a film camera mount, so that Back Focus is resolved in mounting the lens. PL lenses resolve minor differences with shims, supplied with every lens, but once properly shimmed for a particular camera, that is all that is needed. Think about your 35mm still camera, did you every have to adjust back focus on that?

Best,

Jan

[Razz16mm]

It is more of a film camera mount, so that Back Focus is resolved in mounting the lens. PL lenses resolve minor differences with shims, supplied with every lens, but once properly shimmed for a particular camera, that is all that is needed. Think about your 35mm still camera, did you every have to adjust back focus on that?

Best,

Jan

Thanks Jan.

[Ryan Patrick O'Hara]

It is more of a film camera mount, so that Back Focus is resolved in mounting the lens. PL lenses resolve minor differences with shims, supplied with every lens, but once properly shimmed for a particular camera, that is all that is needed. Think about your 35mm still camera, did you every have to adjust back focus on that?

Best,

Jan

Regarding the flange distance on the mounts, I think it's a little inaccurate to compare stills photography to cinematography. Of course photographers do not need to adjust their flange depth by tiny increments! Photographers don't have 1st ACs relying on very accurate and small measurements on the lens barrel!

I'm glad there will be an ability to shim the mount. It's necessary. :) Very necessary.

Edit: if using cinema glass... using photography glass not so much... as there wont be precise focus marks on the barrel anyhow.

[LightMast]

Correct me if I am wrong....but......When using an adapter, the distance marks on the lens become inaccurate anyway, so the A/C would have to pre-calibrate and note new marks for the lenses. Tell me if I am off base here, but I thought the adapters shift everything a small amount, even the Inf. mark.

[Yak]

Correct me if I am wrong....but......When using an adapter, the distance marks on the lens become inaccurate anyway, so the A/C would have to pre-calibrate and note new marks for the lenses. Tell me if I am off base here, but I thought the adapters shift everything a small amount, even the Inf. mark.
I would be surprised if the markings differed, all of the adaptor that I have seen do not add any glass to the optical path so the back focal point of the lens should not change. Each lens is designed to focus on a set film-plane/sensor.

[vagarob]

Correct me if I am wrong....but......When using an adapter, the distance marks on the lens become inaccurate anyway, so the A/C would have to pre-calibrate and note new marks for the lenses. Tell me if I am off base here, but I thought the adapters shift everything a small amount, even the Inf. mark.

the Hot Rod PL Adapter for m4/3 doesn't require any back focusing adjustment either "we install a PL compatible lens mount and shim it so that the flange focal depth is accurate. If you are using calibrated lenses- your focus marks will all line up."

http://www.hotrodcameras.com/products/

[LightMast]

Great information guys, thanks. I'll be sure to make sure any adapter I pick up has the correct flange depth. I'll also note in this thread any I find that do not.

[Ryan Patrick O'Hara]

Correct me if I am wrong....but......When using an adapter, the distance marks on the lens become inaccurate anyway, so the A/C would have to pre-calibrate and note new marks for the lenses. Tell me if I am off base here, but I thought the adapters shift everything a small amount, even the Inf. mark.

No. Usually the adapter *tries* to compensate and get the mount the correct flange distance away... as all lenses for X mount have X distance on the backfocus to hit the sensor. It is important the flange is accurate to the lens specifications, which should be the same for lenses of that mount type. Despite adapters attempting to be accurate, small amounts of difference can cause inaccuracies. This is where adjustable flange distances, shimmed mounts, or imaging block adjustments can help.

[Ryan Patrick O'Hara]

ps: Correct me if I'm wrong but back focus is the distance where the lens projects, and flange distance is the distance between the flange and sensor... meaning the correct term for this thread would be adjustable flange distance... because changing the back-focus of a lens would require the lens optics to adjust/change, not the mount.

Cameras can adjust flange distances by either moving the mount further or closer, or moving the sensor block closer or further. Back-focus would be adjusting the individual lens and it's operation. Thus the AF-100 can't really change back focus. Only the flange distance to sensor.

[Barry_Green]

Never used any stills or cinema camera that had any type of backfocus adjustment. For that matter, I don't think I've ever seen a video camera that has a backfocus adjustment either. In video, the backfocus adjustment is on the lens.

Only time I've seen adjustable backfocus is on the Red One.

[Ryan Patrick O'Hara]

Never used any stills or cinema camera that had any type of backfocus adjustment. For that matter, I don't think I've ever seen a video camera that has a backfocus adjustment either. In video, the backfocus adjustment is on the lens.

Only time I've seen adjustable backfocus is on the Red One.

That's because I'm 99% sure back-focus is only adjustable on the lens. :)

Flange focus and back focus are often interchangeably used and confused terms. Back focus is the point where the lens focuses the light to a point... if the lens is focused at 5 feet, the lens will focus the light 5 feet away from the sensor to the sensor plane. If the lens focuses that light to a point of focus either in front or behind the sensor (which is set at the correct flange depth for that mount), the backfocus is off. That is an issue of an individual lens.

Flange focus is the distance from the flange of a lens to the sensor. This distance, when set correctly, is the distance needed for the back-focus to come to a point upon the sensor at the correct place. If the back-focus is correct but the flange distance is not set to where it should be for that mount, all lenses of that mount will not have accurate focus marks and may be unable to reach or may over shoot infinite focus. If the flange distance is off a pL mount, an entire lens set with correct back-focus will not work properly.

[Barry_Green]

Yeah yeah yeah, you know what I meant. :)

[jpmulligan]

Never used any stills or cinema camera that had any type of backfocus adjustment.
Is this not the same function that newer Canon still cameras provide in there MicroFocus Adjustment feature, allowing fine tuning of the focus for any particular lens? Or am I not understanding the issue?

[look696]

back focus adjustment means to adjust the lens on the mount to maintain focus from wide angle to tele ..... i hope this is correct, cause english is not my mother tonue ....

[Doctor Wu]

Back focus adjustment and flange focal distance are two sides of the same coin.

Back focus adjustment on the lens allows you to throw the plane of focus, calibrated to infinity subsequently collimated to other marks, back further or forwards much like a back focus adjustment on the camera (such as on the RED).

You can have back focus adjustments on both primes and zooms, for example Zeiss DigiPrimes have back focus adjustments on a collar. It's just that zooms are far more unpredictable in their focus when their back focus is off due to their complex optical formulas, which is why it's often much harder to backfocus a zoom so that the whole wide to tele range maintains focus at all distances, than a prime.

I intend to purchase an AF100, but both the Scarlets and Epics will have back focus adjustments on their bodies, which to me follows their cred that they are making cameras for "professionals". It's just that as everyone knows, the release date for RED cameras are always uncertain.

[LightMast]

I intend to purchase an AF100, but both the Scarlets and Epics will have back focus adjustments on their bodies, which to me follows their cred that they are making cameras for "professionals". It's just that as everyone knows, the release date for RED cameras are always uncertain.

Does that mean the AF100 isn't for professionals? I'm a professional. I'm buying one. I guess I'll be an amateur whenever I use it.

There are sure a lot of flame baiters around here pumping up Red lately. Especially with recent join dates.

[Ryan Patrick O'Hara]

Back focus adjustment and flange focal distance are two sides of the same coin.

Back focus adjustment on the lens allows you to throw the plane of focus, calibrated to infinity subsequently collimated to other marks, back further or forwards much like a back focus adjustment on the camera (such as on the RED).

You can have back focus adjustments on both primes and zooms, for example Zeiss DigiPrimes have back focus adjustments on a collar. It's just that zooms are far more unpredictable in their focus when their back focus is off due to their complex optical formulas, which is why it's often much harder to backfocus a zoom so that the whole wide to tele range maintains focus at all distances, than a prime.

I intend to purchase an AF100, but both the Scarlets and Epics will have back focus adjustments on their bodies, which to me follows their cred that they are making cameras for "professionals". It's just that as everyone knows, the release date for RED cameras are always uncertain.\

Red does not have back-focus adjustment. Only flange. Learn the difference. Cameras only have flange adjustments.... lenses have backfocus.

Red Camera's (redone, epic, scarlet) only have adjustment for flange distance, not backfocus. Back-focus is on the lens.