My Lens Wont Focus on my BT Red One

[harjotsingh]

We recently got a Zeiss 10-100/1.8 Mk2 T2 Vario-Sonnar T* Arriflex B mount lens for our BT Red One. We bought a B to PL adapter and it fit fine. When we went to focus the sensor we got it to focus at 50mm but only at infinity. not anywhere closer. Question is, are we doing something wrong while focusing the sensor or is the lens not going to work?
Thank you

 

[Robert Wauu]

Try adjusting back-focus.

 

[Andrew clemson]

Are you saying you can't back focus the B4 lens successfully?

Short of following the standard back focus procedures, if it is something related directly to the adapter, I would imagine Mitch Gross to be the best person to ask, as I believe he was/Is the distributer for them.

 

[Douglas Underdahl]

That's not a B4 lens. He's talking about an Arri Bayo to PL adapter.

Don't adjust the flange focal distance yet. If your camera came from Red then the flange focal distance is probably correct.

Try another PL lens and see if it focuses correctly. Compare tape and eye.

I suspect that the adapter is not seating correctly.

 

[harjotsingh]

@Robert I was talking about the back focus.

Yea andrew like Douglas said its a arri bayonet mount lens and ive tried the normal back focus procedures but it isn't achieving proper focus.

Douglas i adjusted the distance so i cant go back, and i would try another lens but i dont have another lens yet so yeah do u think its my B to PL adapter or my PL adapter on my red?

 

[Douglas Underdahl]

It's hard to tell, at this distance (on a forum) what the problem is.

The Red one has a huge range of flange focal distance adjustment, like more that .100" so if you can't get the lens to focus, then

A) your B to PL adapter isn't seating right, but like REALLY not seating right, or it's made wrong.
B) your Bayo lens mount on the 10-100 T2 is way off (nice lens, by the way)
C) A AND B above
D) there's something wrong with the Red but this is very unlikely

 

[Robert Hart]

There may be varying qualities of ARRI B to PL adaptors. What is important is the flange face of the PL portion of the adaptor is exactly at the same position on the optical axis as the flange face of the ARRI B portion of the adaptor.

You would need an engineering instrument to check this. You would get by with a vernier caliper and a straight edge.

My conclusions would be as Douglas describes above. Given you are in San Francisco, there should be lens technicians not too far away from you. I think you should use one to be assured your zoom lens works best for you by setting up your lens with the adaptor attached. He may discover and correct any flaws in the adaptor. If the adaptor is correct, then he will go after whether the lens itself is correct to its mount. If the lens has been collimated to suit an individual camera, that camera may have had a flaw, in which case the lens will be incorrectly collimated for other cameras.

If cost locks you out of using a lens technician right now, then you might check two things on your PL-ARRI B adaptor.

1. That the front face inside where the rear of the Zeiss lens makes contact, is the same distance from a common point on the front or the rear of the adaptor as the rear face of the PL-Mount flange where it makes contact with the PL mount in your camera.

2. That where there is an edge on the inside of the hole the tail of the Zeiss lens fits rearwards into, that edge is not a sharp corner but a rounded edge or chamfered edge. ---

3. At the rear of the Zeiss lens, in where the shoulder of the mount meets the flange contact face, that there is not a rounded corner (fillet).

4. If there is a sharp edge in the inside of the adaptor and this meets a fillet at the flange face on the Zeiss lens, then the adaptor may not be sliding into contact with the flange face itself but riding on the fillet and the sharp corner. This would hold the lens forward and would mean that infinity focus might not be possible.

By your description, it seems the lens may be sitting rearwards too close to the sensor. I assume you have no focus movement remaining in the lens to focus closer than infinity and this is only achievable at 50mm on the zoom movement. This suggests to me that the adaptor may be seating correctly against the flange face of the Zeiss lens.

If the adaptor has been inaccurately machined, the adaptor B flange face is slightly rearwards of the PL flange face. The Zeiss lens itself may need recollimating by a lens tech by adding shim material between the mount and the lens body. Yoou might add one or more thin paper shim washers between the front face of the adaptor and the rear face of the Ziess lens to bring it slightly forward.

This is all a very, very poor substitute for having a lens technician check it all for you properly and thoroughly.

 

[Nick Gardner]

That lens has a macro feature. Make sure that isn't engaged. if you are in macro mode and you don't mean to be, that would cause what you are seeing.

Nick

 

[Douglas Underdahl]

Ah yes! The macro mode. You press a button on the lens barrel to get into macro mode, then use the zoom ring to focus! Forgot about this cool feature. Press the button and turn the zoom ring so you are out of the green band, then try again.

 

[harjotsingh]

Thanks for the replies everyone, we have just gone on to buy a PL lens. it will be here today so ill update you on wht was at fault or ask for more help.

 

[harjotsingh]

Just tested our new PL lens and it achieves focus fine, so its not the red, probably the lens, thanks for all the help!