Calib. of Flange Focal Distance on Aftermarket PL Mount

[Jorge Díaz-Amador]

I'm going to be shooting my first RED project before the end of the month. I will be working with an early camera (around #250) that will have the Birger PL mount.

I wanted to know what is the preferred procedure to set up the Flange Focal Distance on this camera? I have ALL the tools, but I have never set up a digital camera. Can the distance be measured physically (to the surface of the protective glass, with a teflon tip on the gage and very low pressure), or does it have to be checked optically (test lens, collimator, and a high-res monitor).

I'm thinking the second method will be more accurate, but if the first is safe, this would allow a tech to quickly rough-in the mount and get within about 50 microns of the best setting. Then the rest is tweaked with the monitor.

Anyone have experince doing this?

 

[Steve Gal]

I just set up a camera and I put it up on my richter collimator. Pretty accurate. You need to get a lens that you know is set correctly. You will also need to stop down a little on the lens to reduce flair. Also make sure the image you are looking at through the collimator is bouncing off of the actual sensor and not the OLPF. And you cannot use a gauge to check depth because of the OLPF being in the way.

 

[Jorge Díaz-Amador]

Hey Steve,

Are you saying that you are looking at the image bounced back from the sensor surface to the Richter's eyepiece?

 

[Steve Gal]

Yes, I am

 

[Jorge Díaz-Amador]

...Sorry, as opposed to looking at the image on a monitor? Basically, it sounds like the same procedure as checking the ground glass depth.

I've always found that stopping down does help with the image quality on the collimator, but it increases the tolerance of the depth of focus, and the most sensitive setup is with a lens with really shallow depth. Is the flare excessive?

 

[Steve Gal]

...Sorry, as opposed to looking at the image on a monitor? Basically, it sounds like the same procedure as checking the ground glass depth.

I've always found that stopping down does help with the image quality on the collimator, but it increases the tolerance of the depth of focus, and the most sensitive setup is with a lens with really shallow depth. Is the flare excessive?

First off, I don't like to use a monitor for checking focus. I only use the optical viewfinder. I also set to green with a green filter installed in my collimator since that represents the middle tolerance. You could check with Red and Blue also but Green should be the best. Yes you are right that stopping down increases the tolerance but it also cuts down on flair which can interfere with what you see. Use a wide angle lens for best results. I used a cooke 18mm S4. You need to use your experience and study the image that the collimator gives you.

 

[chuck colburn]

Always autocollimate your lenses wide open. For two reasons. 1 it's the most sensitive and accuret way to do it, and 2 some lenses have focus shift when stopped down.

 

[BASSAM MSSALATIE]

Lens collimation

Lens collimation

i always wonder about FFD that any backfocus should be adjusted for camera and lens here is example for lens with PL mount

is this ? must be adjusted the BLUE LINE which presents the distance between back glass element and the top most end of PL mount ?

or the RED line whic presents the distance between the begining and the end of PL mount ?:blush: :whistling:

 

[Steve Gal]

No the measurement is from the red line at the beginning of the arrow and gets measured to the mysterium sensor.

 

[BASSAM MSSALATIE]

thanks Steve :
i know about This . but i am asking about this PL mount calibration
how do you define where it will be located exactly on that lens
i mean PL mount lens CALIBRATION ? :clown2:

 

[Michael Hastings]

thanks Steve :
i know about This . but i am asking about this PL mount calibration
how do you define where it will be located exactly on that lens
i mean PL mount lens CALIBRATION ? :clown2:

I think that part is irrelevant - the metal part that extends inward could be any depth as long as it didn't hit anything in the camera. As far as the lens calibration it is just a matter of whether is focus at the 52mm distance from the flange when the object is at the marking on the focus scale.

 

[Steve Gal]

thanks Steve :
i know about This . but i am asking about this PL mount calibration
how do you define where it will be located exactly on that lens
i mean PL mount lens CALIBRATION ? :clown2:

I don't know any other way to answer your question. You can't measure where the PL mount will sit since on on any given lens it will be different. On a collimator you then you fine tune with shims. I think you mean collimation not calibration.

 

[BASSAM MSSALATIE]

I think you mean collimation not calibration.

YES thats is why i used this :clown2: cause i look like that
THANKS FOR YOUR HELP

 

[Jorge Díaz-Amador]

What kind of lens is that? If you had the manufacturer's specs for back focus, you could measure from the vertex of the rear element and figure out where the PL mount should go.

You have to have a pretty good idea of where that needs to be before machining a lens for a new mount. Measure twice, cut once.

 

[BASSAM MSSALATIE]

What kind of lens is that? If you had the manufacturer's specs for back focus, you could measure from the vertex of the rear element and figure out where the PL mount should go.

You have to have a pretty good idea of where that needs to be before machining a lens for a new mount. Measure twice, cut once.

THANKS JORGE you have been very helpfull

 

[Matthew Duclos]

Well explained Jorge. Everything you said is accurate.