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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Soft Focus Problems

R

Ryan Nichols

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I just received my RED One on Friday and have been doing a lot of testing. I’m loving it but I just cant seem to get a 100% sharp image. I’m using the RPZ 18-85. I have the 300mm as well but cant seem to get it on point either.

I’ve I figure it’s one of three things: Myself, backfocus, or possibly, that using the support ring that I’m off just a hair on the height and that’s causing soft focus.

I don’t think it’s myself because I’m usually on focus and I have shot things with such a wide range of depth that something should be in focus but nothing is.

Any help is GREATLY appreciated.
 
Sounds like your backfocus is off. Especially since you are having the problem with two different lenses.

Are you having trouble finding minimum focus? Is the problem achieving focus to infinity?

Is the soft focus occurring evenly across the focal plane?
 
It’s soft pretty evenly across the plane. It seems from about 6-12 feet the focus is a little sharper but still off.

I’m going to do a backfocus check tomorrow. I’ve seen it suggested that a 50mm or 85mm prime should be used for backfocus. Is that a strict rule or is it possible to use the zoom? I didn’t do a check because it’s so new. Is the bf ring loose when you take off the screws? Should I be careful not to bump it when retightening it?

Also it happens at every focus. I haven’t pulled but maybe one almost sharp still.
 
If you're going to do a backfocus check, it should be done with a trusted prime lens and a backfocus chart. Don't use a zoom lens to check your backfocus if at all possible.

Another good solution to check the backfocus would be to use the Null Lens and Target.

image.php


... or the Optimator Pro.

optimator3.jpg


Ryan Nichols said:
Is the bf ring loose when you take off the screws? Should I be careful not to bump it when retightening it?
Click to expand...

Oh yes. You should not completely take off the screws. :nonod:

Even when you set the backfocus with a tool, you should be extremely careful not to throw it out when you tighten the ring down. When I use the Null Lens, I keep the target up on the monitor as I tighten the screws to make sure that there is no slight shift.
 
Before you go to all this trouble, do yourself a favor and make sure its really out. Record and export a frame and look at it full size. You can also go 1:1 on the viewfinder or LCD.

You can technically do the backfocus with any lens, but the best lenses to use are the wider lenses. The wider the lens, the narrower the depth of focus (focus behind the lens). So you can get it more precise with wider angle lenses. Of the lenses available to you, Id stick the zoom on, and line it up at the 18mm, with a chart at 3'. Make sure your lens it wide open (adjusting your shutter to get a usable image) and set the lens to 3'. Open up the 2 screws and have at it. Once you are on at 3', check 6' and infinity, then check other focal lengths, before locking it down.

The thing to remember is that because of the design of the backfocus ring on the R1, the backfocus will shift as you tighten it down. Ive found the way around that is to find out how far it is off, then aim for it the other way. For example, you have your chart at 3' and you lock it down, and check again. Now it comes up as 3'2". Unlock and set your lens to 2'10" and readjust the backfocus and lock. Now it should come up right about at 3'. The distance and direction it will go off depends on the last move you did on the backfocus ring. So make your last move on the backfocus ring always in the same direction. It takes some time and theres a bit of zen to it.

Or you could just take your R1 and lenses to a rental house.
 
BTW, there are two schools of thought on the subject, which is why the advise given by Peter and i seem to differ a bit. The first school of thought is that everything should be to spec. You should always use the tools to make sure your lenses/cameras/whatever are at spec. I think the problem with this is that although my camera is at spec by using the null target or the optimator, I dont shoot my film with the null target. I shoot it with a lens that has its own characteristics. So the second school of thought is that you should do your backfocus with the lenses that you are using. Certainly if you are out in the middle of the desert and find your backfocus off without a null target lying around, you are going to use the second theory. Of course the problem with that is when you change lenses or change cameras (first/second unit, etc) then you will have backfocus issues.
 
Thanks for the help. I would totally take my R1 to a rental house if there were any here haha. All the stills seem to be a touch out.

Exibit A:
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[/IMG]

Is the 5.6 lcd adequate enough to proper backfocus?
 
R3D Data said:
BTW, there are two schools of thought on the subject, which is why the advise given by Peter and i seem to differ a bit. The first school of thought is that everything should be to spec. You should always use the tools to make sure your lenses/cameras/whatever are at spec. I think the problem with this is that although my camera is at spec by using the null target or the optimator, I dont shoot my film with the null target. I shoot it with a lens that has its own characteristics. So the second school of thought is that you should do your backfocus with the lenses that you are using. Certainly if you are out in the middle of the desert and find your backfocus off without a null target lying around, you are going to use the second theory. Of course the problem with that is when you change lenses or change cameras (first/second unit, etc) then you will have backfocus issues.
Click to expand...

This is a really good point.

As a disclaimer, I am by no means a lens tech. Just a camera owner who likes to keep my focus tack sharp.*

*Except when working with Cybill Shepherd. :001_smile: ("Moonlighting" joke)

Fortunately, I have had very few backfocus issues. When it has come up, it's been with other people's gear and it's usually been an inability to achieve sharp focus at infinity.
 
No, a 5.6" LCD is not adequate, you should be looking at a 17" monitor or larger... but the other thing is that you should be shooting line charts at measured distances to judge backfocus, not macro shots with shallow depth of field. If not charts, something like a city skyline in direct sunlight with fine lines in the frame, a natural grid pattern. It's really in wide, distant shots where backfocus problems are more obvious, like when you set the lens for 60' for something 60' away but the focus looks like it was set to 20'.

Also, keep in mind that Red frames have no electronic sharpening added to them unless you add it later.
 
David, I’m judging by the 4k file at actual size on a 1080 monitor.

So if I backfocus to the zoom I’m going to have problems with my 300mm? This sounds like it’s going to be an expensive fix. I was hoping to make money with the camera to buy these things first. I guess I’ll just have to shoot a chart tomorrow.
 
David, thanks. I just pulled a random still to show. Everything I have is soft though it doesn’t matter where the focus is or how wide or tight. Even after sharpening most of them are in the acceptable focus range but not tack sharp.

For lack of money, until I make more with the camera, if i do an output to my 50” HDTV with a zoom can it be done properly...or do I really nee the null lens and a production monitor?

I just took delivery on Friday, after all.
 
Well backfocus problems are more of an issue with wide-angle lenses and zooms (when you zoom in to set focus and zoom out and have the focus go out), most focusing on telephotos is done by eye.

The thing is that a backfocus problem is not quite the same thing as soft softs, if there is a backfocus problem, often it means that the focus is falling on the wrong place, though it's so critical with wide-angle lenses that nothing in the frame may be falling into the misplaced plane of focus. But with longer lenses, you can still get a sharp shot, it just may mean that your eye focus doesn't correspond to the actual distance of the object. In other words, the object looks in focus when the lens is set to 15' when the actual distance is 30', that sort of thing.

We also don't know what stop you are shooting at, a lens' optimal stop is often two-stops closed from wide-open, so I assume you aren't trying to judge sharpness based on stuff shot wide-open on the zoom.

When encountering problems the first thing is to reduce the variables.
 
Well the focus seems to be better in the shorter range. The wider I go the harder it is, and anything past about 25 feet is very soft. If i go wider with the zoom I can barely get it acceptable. I know that if you go to either extreme of a zoom you typically get a softer shot that a little ways in. Also yes, I try not to shoot wide-open ever for sharpness. That being said, it could very well be my eyes.
 
Also, I haven’t done a black shading calibration since I’ve gotten the camera. I know that probably doesn’t have anything to do with a soft image but I will do that as well. Are there any other variables that I may not have thought about?
 
Forget back focus for a while and try this:

- Set up a proper target, if you don't have one you can download this one and print it out (as large as possible) :
www.graphics.cornell.edu/~westin/misc/res-chart.html

- Put it up rectangular to the camera in a few feet distance and focus by eye with the 1:1 display activated at open aperture

- Close the aperture down two stops and check the result.

If it's still soft, it's not the backfocus, but something else. BTW, black shading has nothing to do with it.

I hope you rendered the images in full quality, did you?
 
Please please please stop looking at round objects and trying to decipher focus. The first thing any professional AC will do when theres any mention of there being a focus issue is throw up a chart. Please buy a chart, or even print one out at a good resolution, set it at a specific distance from the film plane (marked on the camera body with a O and a line through it, right above the on/off button on the side of the camera). Use the Red's 1:1 function (found in the menus and assign it to a button on the side). This will "zoom into" 4k and take 720 pixels from the center. Then you can use any good monitor and judge focus. Make sure the lens is wide open @18mm, and put the chart specifically 3' or 4' from the mark on the camera. Rack focus until you are sure its as sharp as its going to get. If the footage mark is within a line of the witness mark on the lens, thats tolerance (i.e. just barely off). Anything else means something isnt right - the lens, the camera or both.

Remember that the backfocus tolerance is smaller on wide lenses. So you will find that the 18mm on the zoom has much less tolerance than the 300 does. As you zoom in from the 18mm, you'll see things get sharper. This is also what David is explaining above - wide vistas have a much more critical backfocus. So it very well could be that once you set your backfocus for the 18mm, and verify it throughout the range of the zoom, the 300mm will be in that tolerance. Thats why in the field Ill always use the widest lens available to me to judge the backfocus, using the method above. It could be that both the lenses are spot on to where they need to be, and the camera is off, so if you set the camera to the 18mm, the 300mm will fall in line.

Black shading wont make a difference here, except for apparent contrast.

Also its important to note that RedcineX has its own detail settings, and if you have the rocket the detail is disabled. So software renders will appear sharper than rocket hardware renders. Im not sure what your path is, but this can make a difference also.

One last point - everything in filmmaking is expensive. I dont think this has to be... yet.

EDIT: was typing while Uli posted, glad we gave the same advise..... :)
 
Thanks guys, I’ll do both of these things today and see what’s going on there. It’s not just in the round objects but in everything, I guess I threw up a bad sample, sorry about that. I’m not using a rocket at all. I’ll try the 1:1 first. I didn’t know about that yet, that’s pretty cool. Whatever it takes to get it done-I’m not discouraged! I will let you know the results when I’m done!
 
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