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RED 18-50 focus through zoom

jimhare

jimhare

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Hi All,

My 18-50 doesn't hold focus through the zoom. Is this to be expected or can it be calibrated/adjusted?

I got together with Dave Farland yesterday to compare and his held quite well. We tried both lenses on both bodies and the results were pretty consistent, seems to be my lens.

Any thoughts? Anywhere in Sydney I can have the lens adjusted?

Thanks!

Jim Hare
 
I have looked at a few of these lenses on my collimator and some are better than others. Back focus can be adjusted by shims (which you would need to get from RED) but I don't know how to adjust the front focus on this lens. I am sure it can be done though.
 
Thanks Steve. I thought shims were eliminated with the new PL mount, or is this something different?
 
jimhare said:
Thanks Steve. I thought shims were eliminated with the new PL mount, or is this something different?
Click to expand...

I am talking about the lens back focus, not the camera. The lens uses shims in the rear under the PL mount and they are very similar to the Cooke S4 shims but my S4 shims were very slightly different size and didn't fit. That is why you will need to order them from RED.
 
Some of them float their focus around a bit and some don't If yours does it can sometimes be minimized, sometimes not. You can send it to RED but it may be considered "within spec."
 
Mitch Gross said:
Some of them float their focus around a bit and some don't If yours does it can sometimes be minimized, sometimes not. You can send it to RED but it may be considered "within spec."
Click to expand...


If it's being sold as a "Cine Lens" it should hold focus over the zoom range.

I got some playtime with the Red 50-150 and it had the same problem.

The Good:

-It keeps constant volume which is good and won't suck dust into your camera every time you zoom.

-Nice optics, free from observable CA on a monitor. Seemed to have good resolution and contrast.

-Better focus / zoom feel than Red's 18-50, less "gritty" suggests better internal mechanics, and forecasts longer service life.

The Bad:

-Did not hold focus over zoom range. It was not on my camera so I can't rule out that it was set wrong on the camera, but the host camera was from a reliable rental house that I think knows how to set FFD.

-Breathes quite badly. Worse at the wide end than the long end.

-Focus went way beyond infinity, a little bit would be useful for calibration, but this was a bit much.

I'd be interested in doing further tests if anyone local to LA wants to put theirs up against the Cooke 10-1 mk2 or whatever other similar range lenses we can dig up on the day... Just send me an email.

Matt Uhry
www.mattuhry.com
 
My 18-50 holds focus through the zoom but when it hits 18mm, it goes out of focus. If you back off a little from 18mm, it snaps back in focus. Overall, I am happy with this lens and so has everyone who has rented it from me. I have seen others that were not acceptable to me.
 
I just picked up an 18-50 the other day, a used one. It holds focus on the longer half of the zoom range, but drifts a bit on the wide end. Overall, it's not as "gritty" as many of the 18-50s I've used.

Optically, it's pretty good, mechanically it's just so-so. Anyway, not really covering new ground here. I had to suck it up and pick one up as I needed a compact zoom for a bunch of handheld and steadicam work I'm doing over the next few weeks. Overall it's a great lens for what I ended up paying for it, so no complaints and will be better than renting glass the whole time I'm using it over the next few months.

...It will hold me over until I can get my hands on an Arri LWZ-1. I'm still looking for a deal on a used one, if anyone has any leads. ;-)
 
Steve and Jeff, that sounds like the experience I'm having. I got the 18-50 used as well for around US$4300 so I'm not complaining.

Ultimately I'm not too concerned about it, just wanted to know if this was considered within normal acceptable limits or if you intend to adjust the lens to correct it.

Thanks for your comments, much appreciated.

Jim
 
Not even the venerable Ang 25-250 HR holds critical focus all the way through its zoom, unless you're using a narrow stop to get deeper focus.

-Thor
 
Thor Wixom said:
Not even the venerable Ang 25-250 HR holds critical focus all the way through its zoom, unless you're using a narrow stop to get deeper focus.

-Thor
Click to expand...

On the contrary - my Cine zooms, cooke 25-250 and cooke 18-100 hold focus perfectly over the zoom range on my Red. It's not the exception. If your HR is not working it's out of tune or your FFD is off.

Matt Uhry
www.mattuhry.com
 
More likely there is looseness in the cams and the lens needs an overhaul. A well-tuned 25-250 HR will hold focus throughout its zoom range.
 
Thor Wixom said:
Not even the venerable Ang 25-250 HR holds critical focus all the way through its zoom, unless you're using a narrow stop to get deeper focus.
-Thor
Click to expand...

HAHAHAH. I BEG to differ my friend.
You show me an HR that doesn't hold focus through the zoom and I'll show you a technician that can properly adjust a zoom lens.
You wanna focus on a fly on a wall from 25 all the way to 250, done!
 
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