Cine Lens Focus Question

[Scott Lamoreaux]

Bought the 24 XEEN cine lens and have a question regarding focus. Being this is my first true cine prime lens (I know its not one of the better names but I read some good things about them for the price) I find that unless I stop the lens down completely, I'm having trouble focusing on distances further than 50'. Is this normal?

When I use a standard still Canon L glass lens, I can be at 2.8 but still focus at any distance via the focus ring. I'm racking focus to infinity on my XEEN 24 and objects at further than 50' still won't be in focus and I can't rotate the focus ring anymore. my only option is to stop down more which still doesn't look as sharp as it should.

Any help would be great.

Took a quick and dirty video of the issue: https://vimeo.com/175738487

Thank you,

Scott

 

[jordan levy]

that is definitely not right, either then lens is no collimated properly or your back focus is off on the camera.
id say its probably the lens, but someone with experience with xeen might be able to chime in better.
but no, its not right.

 

[Scott Lamoreaux]

that is definitely not right, either then lens is no collimated properly or your back focus is off on the camera.
id say its probably the lens, but someone with experience with xeen might be able to chime in better.
but no, its not right.

I tried using a Canon 24-70 to test and even at f/4 it still can get tack sharp on the building.

What would the back focus on the camera being off indicate?

 

[Phil Holland]

What would the back focus on the camera being off indicate?

You have discovered it essentially.

If your back focus is off there's a very good chance your focus scales on your lens is off, you won't be able to achieve infinity focus, or you won't be able to achieve the closest focus distance depending on which way the sensor needs to go.

Ideally you check your back focus before every shoot. On some shoots, you check it more often. Heat, vibration, and other things are your enemy in regards to this.

 

[Phil Holland]

Also, side note. Don't ever make 3 threads for the same topic ever again please

 

[Scott Lamoreaux]

Also, side note. Don't ever make 3 threads for the same topic ever again please

Sorry Phil - My bad - I wasn't sure which section it went under and intended to delete the thread however Im still not sure how to do that for the future? When I click Edit I don't see an option to delete...Wont happen again.

Is there a tutorial for adjusting the back focus screw? I can't seem to locate it in the DSMC2 Scarlet-W manual other than the location of the screw itself.

 

[Scott Lamoreaux]

Nevermind figured it out - Although I had a super hard time finding an allen key to fit that tiny screw. I followed the steps in another thread using the a focus chart. One of my Canon L lenses was a bit off but I set it to the XEEN lens and most of my other Canon lenses seem to be almost exactly the same too.

Thanks again - What causes this to come out of whack?

 

[Phil Holland]

Nevermind figured it out - Although I had a super hard time finding an allen key to fit that tiny screw. I followed the steps in another thread using the a focus chart. One of my Canon L lenses was a bit off but I set it to the XEEN lens and most of my other Canon lenses seem to be almost exactly the same too.

Thanks again - What causes this to come out of whack?

Tool advice, spend $28 and buy this Sidewinder:

http://www.red.com/store/products/sidewinder

I have this on me at all times. Not to kiss too much butt, but it is the most useful tool you'll ever have in terms of camera rigging.

Back Focus can come out of whack via time, temperature, vibration, gremlins, you name it. Manufacturing tolerances and dust even come into play when it comes to lens mounts too.

You can adjust it via chart method (works good for zoom lenses for the most part), "by eye infinity" (I don't really recommend this), or using something like the RED Focus.

 

[Scott Lamoreaux]

Thanks Phil -