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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 :)

OLPF change affecting back focus?

That's right David,
I mean with setting focus, you should use a test chart like Putora or something like this. And I strongly feel you should set focus with the stop you're shooting at.
Even on 720P you can set focus pretty good with a chart. But I agree it is very difficult to see. A 1:1 zoom in would be defintly the thing to have.

Sebastian
 
yes - this is a really good point (which goes against prior knowledge) - set focus at the stop you are using rather than opening up to set focus. weird.

1:1 is what we need.

still not sure about the uneven focus / improbably short depth of field business with the master primes......

cheers,

david
 
It may hurt some of you to hear this, as you glance over at your cases of Nikons or antique PL mount lenses.

An OLPF is necessary in front of a digital sensor. These filters are made of layers of crystal, alternately oriented north/south & east/west, so that they do not astigmatically reduce sharpness (meaning that they do reduce sharpness evenly). That's fine & dandy for the center of the image, but as one moves off to the corners, the path of light on non-telecentric lenses becomes increasingly oblique, or at an angle. This means that the light is passing through the OLPF at an angle and therefore passing through more of the filter. How much more does this diffuse the light? Depends on the grade of OLPF needed for the sensor size and design and of course the angle of said light. But this is what RED is referring to with their "optimized for digital" lens designs.

I can tell you from my experience with RED and other Digital Cinema cameras that generally this is really not an issue or an incredibly minor one at best. And this is with testing on optical benches and various metrics charts. And I can also tell you that it should have little to no bearing on why popping one lens on comes up soft while the next appears soft. This would effect corner to corner (edge fall off) sharpness only.

Superspeeds are not the way to judge this based on their now-outdated mechanical design. Wanna have fun? Mount up a wide Superspeed and give a little push/pull on the focus ring towards and away from the lens mount. Watch the whole image slop in and out of focus. The way to set a superspeed is (on a collimator) to roll it back & forth between close focus & infinity quickly at least three times, ending it at infinity and calling wherever it lands that particular lenses natural resting spot. Then shim from there. If the play becomes too large there is some mechanical work that can help, but after a point there's nothing that can be done for old, old mechanics. And for most still lenses, just breath near the focus ring and watch it shift many microns. There's a number of reasons we don't like certain lens solution, and the fact that one option I won't name can slop around 80 microns or so (our tollerance is +/- 5 microns) is certainly one of them.

This is the real reason for your focus problems. That and maybe your cameras are heating up and expanding things during the day.
 
Mitch Gross said:
It may hurt some of you to hear this, as you glance over at your cases of Nikons or antique PL mount lenses.
Click to expand...

hi mitch,

yes i take your points, but the problems we had were with a top-notch set of master primes.

there was much head-scratching....

and i suspect there will be a lot more head-scratching on my part at least.

cheers,

david
 
ready2roll said:
That's right David,
I mean with setting focus, you should use a test chart like Putora or something like this. And I strongly feel you should set focus with the stop you're shooting at.
Even on 720P you can set focus pretty good with a chart. But I agree it is very difficult to see. A 1:1 zoom in would be defintly the thing to have.

Sebastian
Click to expand...

What is a 1:1 zoom? Wouldn't that be a single focale length and therefore a prime lens?
 
We ment a 1:1 digital closeup of the sensor on the 720p out, to see a small portion of the 4K image.
 
I think you mean pixel-for-pixel.
 
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