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Beginner problem w/ focus and backfocus

Petri Teittinen

Petri Teittinen

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Hi everyone!

I finally received the missing piece of the puzzle (i.e. RED Drive) some days ago and have been trying to wrap my head around the R1 in all its glory.

I have two problems wrt to focusing; hope someone can help.

1) Backfocus. I attached a Nikon 50mm prime and set up a focusing pattern 1,5 meters away from the sensor plane. I then turned the lens focusing ring until it read 1,5 meters. Then I loosened the two backfocus screws and started turning the backfocus 'ring', first clockwise, while standing behind the camera. The image got softer/fuzzier, so I started turning it counter-clockwise.

After several full rotations I could see the image finally getting sharper on the 7" LCD. As I didn't have a proper backfocus pattern (yet), I had printed one on a piece of paper with a 600dpi laser printer as a temporary measure. After several more rotations, I could suddenly see the fibers of the paper on the LCD (using R1's magnification feature) and the focus pattern looked razor sharp. At the same time I noticed the backfocus ring would not turn counter-clockwise any more, i.e. it had reached the end of its run. Is that normal?

2) Focus. What could be the explanation for this: the stationary item I'm shooting looks sharp and in focus on the 7" LCD (verified using the magnification feature) but once I open the file in Redcine-X, the image/item looks soft and out-of-focus?

I'm sure I'm doing something wrong, but I need someone to tell me what it is I'm messing up here.

cheers,
.: petri
 
Hi Petri,

I am certainly no expert and I may be doing more harm than good with my response here... But I am almost certain that you don't need to do anything even close to a full rotation of the collar when backfocusing.

I was lucky enough to have Steve Gibby help me with the setting the backfocus on my camera when I changed the mount from PL to Nikon. It seem a fairly minimal move... perhaps an inch or two at the most... clockwise I believe, however, I could be wrong on that part. Also, I believe that you need a sharp zoom lens to set the backfocus properly. Steve used the Nikon 17-35. Once he found a sharp focus at 17mm, he then made sure he had the same sharp focus at 35mm without having to move the collar. Also he used a focus chart... obviously.

It might be best to take the camera to a local rental house to have them help you out... or find an experienced Red user in your area. I can tell you, having seen him do it, I surly would have screwed it up had I tried it myself without the benefit of detailed and exact instructions.
 
Julio Quintana said:
In my experience, you can't loosen the two screws on the back focus ring too much or else you with throw the focus off again whenever you try to tighten them. Maybe that's happening to you?
Click to expand...
Hmm... I don't think so. I checked the LCD once I had tightened the screws and I could still see the fibers of the paper, and the focus pattern looked very sharp.
 
Omar Saad said:
But I am almost certain that you don't need to do anything even close to a full rotation of the collar when backfocusing.
Click to expand...
OK... I had to turn mine for more than 10 rotations; all the way counter-clockwise as far as it would go, like I mentioned. That's pretty weird, when compared to your experience.

Also, I believe that you need a sharp zoom lens to set the backfocus properly.
Click to expand...
I read RED's quick start guide before I started setting the backfocus. It says "Attach a medium length prime lens to the camera, (50 to 75mm) and set the lens focus to match the appropriate distance the camera is away from the chart". An 'old-school' friend of mine also talked about using a zoom lens and setting the backfocus so the focus wouldn't drift when going from zoom to wide etc. but I haven't gotten round to trying that out yet. I'm waiting for a proper focus chart to arrive from Abelcine.

It might be best to take the camera to a local rental house to have them help you out... or find an experienced Red user in your area.
Click to expand...
If everything else fails, sure :)
 
This may be obvious, but what are you viewing the file in REDCine-X at? Full resolution or at one of the fractional settings, such as 1/8 or 1/4? If you're doing that the image will look pretty fuzzy.

Just a thought.
 
Jan Balster said:
This may be obvious, but what are you viewing the file in REDCine-X at full resolution or at one of the fractional settings, such as 1/8 or 1/4? If you're doing that the image will look pretty fuzzy.
Click to expand...
That's a good point; forgot to mention it in my post. I'm using '1/2' on a 30" LCD at 2560x1600 resolution, with the video window taking up most of the screen real estate. Selecting "Full" with "Fit W" results in an error message "Your video card does not support the current resolution".

Another thing I forgot to mention: I shot the footage at 4.5K.
 
Petri -

If you are using the RED Nikon mount, then you should have to turn the adjustable collar no more than about 1/8th of a turn from where it was with the original PL mount. My guess is that you

A) are using a seriously incorrect 50mm lens or

B) you set your lens to 1.5 FEET instead of 1.5 meters?

C) have attached the nikon mount with the spacer plate still installed?

Please see this video

http://www.youtube.com/watch?v=IhmolBMtDzg
 
Douglas Underdahl said:
My guess is that you
A) are using a seriously incorrect 50mm lens or
B) you set your lens to 1.5 FEET instead of 1.5 meters?
C) have attached the nikon mount with the spacer plate still installed?
Click to expand...
Hi Doug, and thanks for posting!

I'm using Jacek's Nikon Prolock mount, and it's correctly installed (finally, ahem). (A) is possible, certainly; it is one heck of a cheap-o lens. I guess I should re-do backfocus with a better lens. (B) is also within the realm of possibility; I'll take another look at the lens markings to make sure.

But 1/8th of a turn? It took me several rotations to start seeing any improvement in the image focus. Well, once the chart arrives, I'll re-do the whole thing from scratch.
 
My experience echos Doug's comments. Changing from Nikon to PL only took a slight amount of adjustment.
 
Set it with a Wider Lens, 24mm or 25mm, after checking close distances, Make sure Infinity hits the mark. Or go outside and find a bright shiny object very far in the distance and find the focus,
 
Or better yet, purchase the Optimator from Jacek. What you are describing does not seem like a normal situation at all, and you need to take that 50mm lens out of the equation. Always try to work with a test lens that you know is good for this kind of calibration.
 
If you're going to set backfocus with a lens, go with the WIDEST lens you can find and set focus to infinity. Focus on something off in the distance that has noticeable detail. Brick wall, trees, whatever. With a 50mm lens and a chart only a few feet/meters away, you'll never hit it, especially if the lens marks or collimation are not accurate to begin with.

Or find someone with a proper tool to set your backfocus. Optical collimator, NULL lens, Optimator, etc..
 
Thank you everyone for all your valuable advice, it's much appreciated.
 
Jochen Schmidt-Hambrock said:
I would bet that setting a cheap Nikon lens to 1,5 meter is very "open to interpretation" ;-).
Click to expand...
Apparently so! :)

I went from Nikon to PL and back lots of times and never had to turn the mount more than an 1/8 rotation.
Click to expand...
Well, I never went from PL mount to Nikon mount... and by that I mean I never used the PL mount, never had a lens attached to it and never set its backfocus. Maybe the PL mount was nowhere near correct backfocus when RED shipped the camera; I have no idea.
 
picture

picture

Petri,
Send me a picture of how you installed the mount- maybe I can tell from it...
The best way to set your back focus is with a short zoom pointed at a chart at close distance(the closer the better). The distance doesn't matter for the zoom- all you need to do is get the focus sharp at the long end with the focusing ring on the lens , zoom out wide and refocus with the focusing ring on the camera-don't touch the lens's focus ring now. Now zoom back in(long end) and repeat....
do it as many times as necessary until both your zoom ends are as sharp as they can be... Remember- long end: lens focus-wide end: camera focus.(only)
Here are some videos:
Nikon Prolock install and 11-16 tokina focus:
http://www.youtube.com/watch?v=ssSQfadJVnA
http://www.youtube.com/watch?v=Fo4Byk_rGDo
and while we are at it- Optimators- DeLuxe and Pro
http://www.youtube.com/watch?v=tF022NkUeOw
http://www.youtube.com/watch?v=TKSKCdZdoyE
Don't worry- we'll figure this out- a lot of big brains on this forum:wink:
 
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