F3 Flange Adjustment for Lens Swaps

C

C.A.Magid

Active member
The F3 manual states the flange focal length length is "necessary" to adjust:

-the first time a lens is attached
-when lenses are changed
-if the focus is not sharp at both ends of the zoom

The mechanics sound much like a back focus adjustment on a ENG setup, with one exception, it requires an allen wrench to perform.

The middle situation concerns me as we do plan to swap primes often during a shoot and would like to do so as quickly as we have become accustomed to with other gear. Think this could really slow things down and introduce an opportunity for error as lenses will be swapped while on set moving from wides to close ups and etc. May be easy to botch the adjustment in some lighting situations, without focusing aids or on the occasions a sharp external monitor is not available.

It would not be so bad if this was a thumb screw or other fastener such as those found on some lenses, other cameras or DOF adapters.

In practice have folks noticed this being critical or needed while swapping

-PL lenses of the same series...Zeiss SuperSpeeds, Compact Primes or Etc
-Moving between primes and a zoom of different makes (zeiss primes and red zoom)
-nikon mount lenses through an MTF adapter

As you can probably see from my recent posts we are seriously evaluating the camera for use on upcoming shoots and purchase.

Appreciate any first hand knowledge anyone can contribute.
 
The only reason you'd readjust is when your lenses are incorrect. And you are in for a world of hurt if you do that.... Just get your lenses collimated, your adapters adjusted to proper height and you'll never need to touch your BF adjustment- once set correctly
 
Thanks for the reply.

When it comes to PL prime glass we will be renting compact primes, super speeds, ultra primes, and S4s.

We will also be putting a Red zooms 17-50 & 50 to 150 on the camera.

Sounds like I am okay if the lens are in good shape...which they are...pristine. Never had any issues when using with Pro35 and Varicam. Would image any incorrect lenses would create focus issues there too. Although with that device you do adjust back focus to the ground glass first but the 35mm lens must project perfectly on to that.

How botched do things get if we somethings use an MTF adapter with Nikon still primes? Never on the same shoot but we will configure the camera as such back at the shop. As I switch lens mounts seems reasonable to expect to reconfigure the flange adjustment. A reasonable assumption?
 
slightly incorrect back focus with primes will not result in out of focus shots. If way off it could mean you can't achieve infinity, and it may affect whether your barrell markings are accurate. It will affect whether a parfocal zoom tracks focus correctly though. My local rental house with multiple F3's and many PL lenses say that every camera and lens combination is slightly different though and they have them labelled for the best adjustment. To me that means when you rent with your camera you may not always get it perfect though you should be very careful with zooms.
 
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Lenilenapi said:
slightly incorrect back focus with primes will not result in out of focus shots. If way off it could mean you can't achieve infinity, and it may affect whether your barrell markings are accurate. It will affect whether a parfocal zoom tracks focus correctly though. My local rental house with multiple F3's and many PL lenses say that every camera and lens combination is slightly different though and they have them labelled for the best adjustment. To me that means when you rent with your camera you may not always get it perfect though you should be very careful with zooms.
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Twilight Zone I swear....
 
Optitek - I assume you are talking about :

"every camera and lens combination is slightly different though and they have them labelled for the best adjustment."

It did sound a little weird to me as well, but I know they are smart guys - I'm just reporting what I hear from the rental house.
 
education

education

I did Lenny. Nothing to do with you I know you are a smart guy(and not patronizing you now)
Sometimes I go to these young rental facilities and don't know what to start explaining first....what a mess..
 
@optitek,

A direct question for you. I have a group of 6 fast prime Nikon lenses and 3 Nikkor F2.8 ED zoom lenses with an MTF adapter.

Which lens should I use to set the flange adjustment so it is most likely to be right for all of them?

The widest zoom (17-35mm)?

The widest prime (24mm)?

A longer fast prime (85mm F1.4)?

At this point in time if I focus with any of the zooms set at the widest it stays in focus when I zoom in, and the barrel markings are close. Or, should I take the attitude of "It ain't broke, don't fix it"?

Thanks,
Duke
 
Short answer is widest zoom wide open at very short distance- maybe 1.25ft for the 17-35. Zoom in, adjust focus, note the exact position, zoom out and try to refocus. If your position on the focus scale consistently changes (if you can refocus at the wide end) you have issues...
Now in order to get some idea where the problem lies you need to prepare.
First verify mechanically the adapter height (you can have machine shop do that easily.
Now verify you flange depth with a tool: I recommend this http://www.youtube.com/watch?v=eUVxNuR_N4s
 third thing to do is have the lens back focus verified and adjusted properly on the collimator. Remember this is your "hero lens " that will be used to determine the settings for all other lenses. And you only need to do it once unless the lens is dropped, bumped or otherwise suspect of BF problems.
If you do that I guarantee that you can swap any properly set lens on your camera and never have issues. Rental houses have this this for many years...
And if you do experience issues with other lenses it'll be just about every time lens issue- easy to fix once you know where the problem comes from.
On the second thought it may be just too complicated for most...
 
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Optitek may kill me for putting my own 2 cents in here, but in my own experience also having 3 Nikon 2.8 zooms ( 17-37, 28-70, and 80-200) the 28-70 was the easiest to use for checking backfocus mainly because the 17-35 is so wide the DOF is so deep its hard to be sure where my exact focus was. I didn't try it as close a distance though and that might make it easier.

Also I suggest before you start screwing around with back focus on your camera that you just check all the zooms and see if they seem to all be correct or if the back focus seems off are they all off in the same direction. (i.e. if you zoom in at tele and focus, do they all say need to be focused nearer at wide.) If they are off in different directions then you can be sure that either they are not all parfocal, or they have different back focus points themselves ( if that's possible at all - I imagine they either backfocus correctly at the Nikon flange distance or they won't track at all, but that's an Optitek question.) I do know that I have seen 2 28-70's one of which backfocused correctly at the same point as my other lenses and one didn't at all. I didn't try to adjust back focus for the 2nd lens and don't know if adjusting the F3 would have found a "correct spot" for that lens.

Of course if you have the tools available - follow Optitek's procedure.
 
Depth of field is deep with a wide angle, but deth of focus is not. Depth of field is in front of he lens, depth of focus is behind it. This is about adjusting depth of focus, which is far more critical on a wide angle lens.
 
Mitch Gross said:
Depth of field is deep with a wide angle, but deth of focus is not. Depth of field is in front of he lens, depth of focus is behind it. This is about adjusting depth of focus, which is far more critical on a wide angle lens.
Click to expand...

Yes I do understand that, just expressing my personal experience when trying to check back focus that the greater DOF of the 17-35 made it hard to judge with precision. Perhaps with a very large monitor it would have been better. By the same token when I tried an 11-16 it was nearly impossible to tell with precision where my backfocus was most critical because of the vast DOF.
 
Thanks for giving me a way to test it, and I will test it. I'm keeping my fingers crossed (since it seems okay so far) that I don't have to do anything about with it.

I noticed with Canon lenses that there are three definite tiers of lenses. The economy (mostly plastic) lenses, the middle (metal but not extremely fast) lenses and their top of the line L lenses.

It doesn't seem to be as clearly delineated with Nikon lenses. However, there are some Nikons lenses that are definitely better than others. They aren't clearly marked, but certain Nikon lenses seem much more professional no matter when they were made.

@mitch,
It shouldn't surprise you. I'm coming from an XH-A1 and EX1 background where I didn't have to consider which lens. I've made a major step up in cameras. Don't be condescending about honest questions please. You were here once and we all have to learn somewhere.
 
optitek said:
On the second thought it may be just too complicated for most...
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I rest my case....
Lenny, this is not art, your opinion is not that important. This is science, these are defined rules that don't just change to your liking.
They are what they are and I'm just spelling them out here-not making them up. I hope you understand that...
 
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Duke M. said:
@mitch,
It shouldn't surprise you. I'm coming from an XH-A1 and EX1 background where I didn't have to consider which lens. I've made a major step up in cameras. Don't be condescending about honest questions please. You were here once and we all have to learn somewhere.
Click to expand...

I certainly never meant to be condescending and if I came off that way I apologize. When the RED One first became popular Jacek & I spent a great deal of time explaining these processes and concepts over on REDuser. I'm talking about dozens and dozens of posts, and both of our companies released tools specifically designed to assist people in setting their flange focal depth. My observation was simply intended to be a "here we go again" as in "look at the two of us delving into this topic again." It wasn't meant to be a "what's wrong with these people" kind of statement.

If you don't know you don't know and better you should clearly ask than screw yourself later. That's what forums like this are for.


Of course, there's also Pookie's posts as well ...
 
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