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RED 17-50mm on film camera -- not focusing!


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#1 Steve Zimmerman

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Posted 11 January 2012 - 10:41 PM

My greatest apologies for double posting, but I figure this is the better forum for this.


I just got a new Red Pro Zoom PL mount 17-50mm shipped to me. The PL mount slides in all the way, the tabs touch the steel of the camera mount, but it cannot be locked on, the tabs seem slightly too thick. We measured and they are just slightly thicker than a PL lens we have that fits. The mirror clears the lens back just fine.

More importantly-- the focus is WAY off. When zoomed in to 50mm, and I focus on a point 8 ft away, the witness marks show between 20 and 50 ft! Zoomed out it loses focus. Obviously the back focus is off. I heard these lenses were used on Arricams, and PL mount is PL mount, right?

I am using a PL mount Konvas 1M. I have used Arri Super speed lenses on this just fine. The camera has been collimated very recently. I've seen videos of this lens on lots of different digital cameras all focusing well, so why would it focus badly on mine, if all PL specs are the same? The first version of this lens which became the Digioptical 18-50mm on BH Photo says it works with Digital or film cameras, one would think this one would as well.

Do I need to modify the lens? Kubrick got that NASA lens to work right? I don't have that much money... Its sad a beautiful affordable lens does not work. I was guaranteed that RED would have this perfectly collimated when I asked before I bought it.

We are poor filmmakers, I sold my old fuzzy lenses and pooled all our money into this one lens! We are very upset. :(

If anyone has ideas how we can get this fixed, let us know.

Thanks Steve
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#2 Stephen Williams

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Posted 11 January 2012 - 11:24 PM

You need to put the lens on a collimator or on another camera & see what happens.

My greatest apologies for double posting, but I figure this is the better forum for this.


I just got a new Red Pro Zoom PL mount 17-50mm shipped to me. The PL mount slides in all the way, the tabs touch the steel of the camera mount, but it cannot be locked on, the tabs seem slightly too thick. We measured and they are just slightly thicker than a PL lens we have that fits. The mirror clears the lens back just fine.

More importantly-- the focus is WAY off. When zoomed in to 50mm, and I focus on a point 8 ft away, the witness marks show between 20 and 50 ft! Zoomed out it loses focus. Obviously the back focus is off. I heard these lenses were used on Arricams, and PL mount is PL mount, right?

I am using a PL mount Konvas 1M. I have used Arri Super speed lenses on this just fine. The camera has been collimated very recently. I've seen videos of this lens on lots of different digital cameras all focusing well, so why would it focus badly on mine, if all PL specs are the same? The first version of this lens which became the Digioptical 18-50mm on BH Photo says it works with Digital or film cameras, one would think this one would as well.

Do I need to modify the lens? Kubrick got that NASA lens to work right? I don't have that much money... Its sad a beautiful affordable lens does not work. I was guaranteed that RED would have this perfectly collimated when I asked before I bought it.

We are poor filmmakers, I sold my old fuzzy lenses and pooled all our money into this one lens! We are very upset. :(

If anyone has ideas how we can get this fixed, let us know.

Thanks Steve


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#3 Dom Jaeger

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Posted 12 January 2012 - 12:56 AM

It can happen that a PL mount is manufactured out of tolerance, the flange wings are too thick and it won't lock onto a camera. The wing thickness should be between 1.90 and 2.00 mm thick.

But if the lens isn't seating properly it will throw the focus out. It will be worse at the wide end, where back focus is more critical. The discrepancy you described would occur if the lens was sitting more than half a mm forward of the flange.

So I'd say the combination of mount not locking and focus not reaching infinity suggests something is fouling before the lens is properly seated. Maybe internally like a baffle or the groundglass holder. Maybe externally like the lens barrel hitting the sloping front of the camera. Maybe the locating pin is too tight. Check everything carefully and see if you can't work it out.

The other possibility is that the circular edge of the lens cavity in the camera mount is not bevelled enough, and/or the mating part of the lens mount - the corner where the flange wings meet the rear lip - is rounded or not properly undercut.
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#4 Steve Switaj

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Posted 12 January 2012 - 01:29 PM

I've seen this exact problem before, and, as Dom points out, it is was caused by the mount on the lens being machined with a very slight radius at the point where the "ears" meet the "barrel" of the mount (for very legitimate reasons involving stress concentrations and machine tool bits).

Most camera mounts have a slight chamfer on the edge between the throat and the flange, and this provides some space for the typical small radius on the mating part.

On this particular combination of lens and mount the radius was bigger than the chamfer and things didn't play well. The lens ended up seating on the interference fit, and thus a fraction of a millimeter too far forward, but still felt OK and seemed to lock in solidly.

Took a bit of head scratching, because everything individually tested OK, and there were no obvious problems mounting the lens.
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#5 Gustavo Penna

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Posted 09 February 2012 - 12:33 AM

Ive never heard of some one with the budget to shoot 35mm on an Arricam that would not have enough budget to shoot with real professional 35mm lenses.

Ive had people asking me to rent my Arri 435 extreme with out my lens, but I won't do it.
The main reason why your lens wont work on a "professional" film camera, is simply because the lens are made by red. red never made a lens before, that's a fact, so they have hired a machine shop to put plastic sigma lens on aluminum barrels with some nonsense numbers written on them.
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#6 Mark Dunn

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Posted 09 February 2012 - 05:44 AM

Can you not just send it back? If you specified exactly what you wanted it for, then it's not fit for purpose.
Failing that, we have distance selling laws here which give you a short time to return an item for any reason or none. Have you?
That's assuming of course that you have already asked for and been refused a refund.
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#7 Steve Zimmerman

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Posted 09 February 2012 - 12:55 PM

We returned the lens to RED and got a refund. Just looking at that cheap plastic tube coming out from the lens when zooming... :huh: We got a deal on some Zeiss Compact primes (Mk1), and guess what? They fit fine on my PL mt. Konvas, and they focus. Red is rather loose on their specs, I guess. PL mount should mean that they fit PL mount. They should start calling them "RED PL mt". RED Customer Support was also annoying. You have to nag them on the phone to get timely responses.

Edited by Steve Zimmerman, 09 February 2012 - 01:00 PM.

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