wide angle

Lenny you need to make sure that the lenses by themselves are set correctly. Otherwise you'll never know what's wrong and will keep chasing the lenses.
At least get your widest lens set correctly and use it and the camera to set the others. Don't start your adjustment with the longest lens- it's least sensitive to back focus.
And to minimize the Dof always check up close and wide open.
I've got to make a video- there is so much misinformation floating on the forums. Lenny FYI it has nothing to do with you -you are doing the best you can - but unfortunately it's not the right way to do it.
I've done this for 25 years now and have worked on more lenses than most here have seen in their lives so I should know.
Lenny please don't take it personal I'm trying to help....
 
Nothing personal, but I stand by my thinking on this.
If I get a chance to go somewhere where I can check the lens independently i will do it but its not available. I do know where there is a collimator which would be great.
I only started with the long lens because I knew it. I found the 28-70 and the 17-50 to be very sensitive. I know the long lens is not. And the widest lenses just have too much DOF to notice minor.
My thinking on this was that if the lenses are parfocal then they should be set to track only at the correct Nikon flange focal depth.
Chances are they will either be Parfocal at that distance they will never do it . The fact all four lenses tracked focus at the same at that setting creates a damn sure liklihood that it is correct for Nikon.

I checked at numerous distances always with the iris open and double checked lens barrel footage markings as well and again on all my primes.. Can't understand what you think I'm doing wrong.

Tomorrow I expect to be testing some more with a larger 24"monitor
Bottom line tho is it works
 
Checked all my zooms again today on a 24" monitor. Same results. Next toime I plan to bring my PL adapter and try it with the rental houses PL lenses to see if my F3 back focusa holds for both. However the shop ( Chater camera ) has 5 F3's and says back focus is different on every one and on every PL adapter so they have them all labeled for each camera.
 
You can just mechanically measure the PL adapter. It should be 33mm flange to flange. I think our save and grace is that at 1080 resolution you are not pushing the lens hard enough to see small variances in back focus. It will definitely affect the Dof front/back balance...
 
The shop I was at has a tool to measure the PL adapter so that's what i will do. Unfortunately they have nothing similar for the Nikon mt and told me people just don't expect the still lenses to be parfocal so they don't bother with it.
 
Nikon flange is as well defined as PL so there is no reason why it couldn't be measured. If you need the same quality form Nikon glass you should adjust it with the same precision. Otherwise you are not going to get the same performance- simple as that....
 
I'm afraid we will have to agree to disagree as the shibboleth goes. The tools you suggest are not available to me or many people and the method I describe is logical though I admit only precise to the extent I can see on a 24" monitor but that's pretty damn close, as close as anyone's eyes will be for focusing in the field anyway and close enough for 2.8 Were I shooting a feature I might double check the lenses if possible
 
I guess using Dial Indicators, Micrometers, Calipers and a little basic math is a lost art.
No wonder so many adapters are machined so poorly.
At least one person in this thread seems to know what he is talking about.

Good Luck!

Dave
 
David, Its just not nice to tell people they don't know they're talking about. With all due respect for professional measuring tools the proof is in the pudding and this is a practical question for me and many others. BTW - I asked a number of excellent techs about this discussion and they all agreed with me.
So let me try to be clear:

First - just measuring with dials and micrometers only tells you whether the mechanical distances of the flange and lens are correct, it is an important piece, but if there are optical inaccuracies they trump the mechanical.

Second we are dealing here with the practical tolerances for focus on a video camera. A 28mm PL master prime perfectly collimated at 2.8 on an F3 will be only be as accurately focused as the operator or assistant can see on the monitor on set. Rarely is that any bigger than 24" and rarely would the operator have anything as precise to judge with as a Century precision chart.
If I have found that I can on a 28-70 at 2.8 - zoom-in, focus and then pull back to 28mm (at variances distances from the chart), and still remain focused to my eyes with a chart and a 24" monitor, then I'll bet my paycheck I'm standing in as good stead as my neighbor with the the 28mm prime. Or as we like to say in my musical world "its close enough for jazz."

Moreover if the same seems to be true for a 17-35 , and an 80-200 and apparently an 11 - 16 (though that's harder to judge because its so damn wide) then I'd say the chances we have the correct flange focal distance for Nikon are pretty likely.

Will I test these with a Nikon repairman if I get a chance and test them with a collimater - yes as soon as I get the opportunity. In the meantime - I'm working , I'm in focus and letting others know that some of the Nikon zooms seem to be parfocal. Though I would not assume yours are without rigorous testing, you do not need a lab to get close enough for 1080.

Lenny
 
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Lenny,
What technical basis do you have to claim that proper tools are irrelevant?
Does the fact that cameras got cheaper and are accessible to a lot more people somehow changes the laws of physics?
Are the cameras and lenses designed to bypass them? How?
Yes you may get lucky and get it working, good for you. But it's a different story to claim it to be the right way to do it- because it's not.
This is how owners operators get in trouble with production and their reputation hurts, the opinion about their gear hurts, etc.
And this industry is all about connections (which isn't these days...)
You may not care about it but others do. So make it clear-that's all. I guarantee that any half decent production will find the petty cash in their budget to get the gear serviced and calibrated. It's pennies compared to the liability. Just the matter of planning....
It should be a crucial part of pre production- it has been for every professional in our industry for many years and this is one thing you don't want to change....
 
Optitek,
I never said that proper tools are irrelevant only that there is more than one way to skin a cat and you can learn plenty with just a chart. Moreover everything I've said follows the laws of physics as far as I've ever understood them. This discussion started with me mentioning that some of the Nikon zooms are parfocal and warning that some are not. i explained how I determined that and nothing you've said has critiqued my method. I was trying to be helpful.
I agree that I could and intend to obtain more precision with optical tools but until I get a chance everyone I've spoken to including the techs at a very good local rental house agree with me completely. Frankly its common sense and it deserves some respect as well.

I can assure you that the vast majority of people putting still lenses on their Canon's, AF100's and F3's don't even know what parfocal and back focus means and have never even looked at a chart - so anything to help them is a step in the right direction. No doubt you're right though that many of them would better of going to someone like you.

I think that's the end of this discussion for me.
 
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I know that you are trying, and I respect that. A lot....
But all that you've mentioned makes little sense. Why would you need a collimator to set the RR rig? Why not just use a depth gage?
A little knowledge can be dangerous...
Lenny, again, nobody likes to be called incompetent publicly- I know...
Don't take it personally- I'm sure you are a talented professional (ok now I'm patronizing- I hate that myself)
This is a strictly technical issue that needs to be addressed.
I almost prefer talking to guys with no clue about back focus, collimation, etc. because I can start them off the right foot without having to fight " the beast of habit" first...
Good Luck to you and your endeavors....
 
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