Welcome to our community

Be a part of something great, join today!

Log in
  • 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 :)

Red back focus

Matt, always ready to assist.
 
jimhare said:
I followed Doug's method, but now a lot of users are saying to set the back focus based on infinity, not 3 feet.

Haven't gone back to try it again but I'm definitely getting mixed results so far.
Click to expand...

I would set a lens up at infinity back focus. And if the footage scale is off I would correct that afterwards.
 
most critical

most critical

First of all the widest lens at lowest aperture and closest distance is most critical. No urban legends, just simple physics, DOF and such..
The problem is making sure that the lens is setup correctly, callibrated so the back focus matches nominal distance at the nearest focusing distance.
And I have the solution for this.
Jacek Zakowicz, OptiTek-dot-org:thumbsup:
 
Matthew Duclos said:
In addition to other topics, I've been considering a creating a short vid detailing what back focus is and why its important. Maybe include some of the many options for tools available for helping obtain proper back focus. Not only for the RED camera but for lenses as well.
Interest?
Click to expand...

Definitely interested.
 
Jacek Z. said:
First of all the widest lens at lowest aperture and closest distance is most critical. No urban legends, just simple physics, DOF and such..
The problem is making sure that the lens is setup correctly, callibrated so the back focus matches nominal distance at the nearest focusing distance.
And I have the solution for this.
Jacek Zakowicz, OptiTek-dot-org:thumbsup:
Click to expand...

Me too:thumbsup:
 
Matthew Duclos said:
In addition to other topics, I've been considering a creating a short vid detailing what back focus is and why its important. Maybe include some of the many options for tools available for helping obtain proper back focus. Not only for the RED camera but for lenses as well.
Interest?
Click to expand...

That would be a nice resource
 
Matthew Duclos said:
In addition to other topics, I've been considering a creating a short vid detailing what back focus is and why its important. Maybe include some of the many options for tools available for helping obtain proper back focus. Not only for the RED camera but for lenses as well.
Interest?
Click to expand...

I am definitely interested!
 
Matthew Duclos said:
In addition to other topics, I've been considering a creating a short vid detailing what back focus is and why its important. Maybe include some of the many options for tools available for helping obtain proper back focus. Not only for the RED camera but for lenses as well.
Interest?
Click to expand...

Really interested in anything you got Matt!
 
I've been putting together a little webpage for me to dump my rants.
I figure this would be a good place to write a little bit and possibly host videos and whatnot on the topics people want to know about.
I'll let everyone know when I actually get it to a decent viewing point.
 
Great stuff Matthew. Look forward to it!

Eric
 
When I was at Schneider Optics, I was the project engineer on their HD Collimator, which is a self-illuminated star pattern, focused at infinity.
To use it, set your fastest lens (more important than focal lg.) at infinity on the camera, place the collimator in front of the lens, and watching your monitor, dail it in.
Of course, double check marks, if the footage does not check out, the lens backfocus is out or the lens infinity mark is not accurate.
Here is a link to Schneider (who I do not work for);
http://www.schneideroptics.com/ecommerce/CatalogItemDetail.aspx?CID=1098&IID=1069
 
What Matthew said.

As for his last paragraph about adjusting the camera flange focale depth to accomadate a misadjusted lens, this is true for a fixed focale length lens. It is not true for a zoom lens. If you set up the back focus on the wide angle end of a zoom and it does not agree with the telephoto end (front focus) your lens will not hold focus as you zoom it.
 
chuck colburn said:
What Matthew said.

As for his last paragraph about adjusting the camera flange focale depth to accomadate a misadjusted lens, this is true for a fixed focale length lens. It is not true for a zoom lens. If you set up the back focus on the wide angle end of a zoom and it does not agree with the telephoto end (front focus) your lens will not hold focus as you zoom it.
Click to expand...

Correct. Compensating by adjusting the camera will only make things worse with a zoom. I was referring to primes.
Don't get me wrong.. The part about both needing to be adjusted independently, and PROPERLY stays true no matter what kind of lens or camera you're using.
 
Let me just say that some things are easier said than done and others are easier done than said. I and other technicians here at Abel have used various collimating tools, wide angle lenses and such to set the RED One as well as other Digital Cinema cameras. This can be extremely difficult in even the most controlled circumstances. For instance the Schneider HD Collimator Ken mentioned will put out a tiny focus target when used with a wide angle lens on a RED One. This makes it quite difficult to judge accurate focus. On some wide angle lenses there can be enough slop or play in the focus ring as to make it impossible to lock the focus point, at least to the degree of precision necessary to set back focus.

Every one who tries the RED Null finds it to be stunningly easy to use and incredibly accurate. We have tried some of the other new devices out there and some appeared helpful while others had their own issues. I'm not going to "Dis the competition" as we'll leave it up to the community to decide what items they prefer, but I do urge you all to get some form of proper, dedicated device to do this job. It really is that important.
 
Mitch is right, using a WA with Century's HD Collimator (or the Zeiss SharpMax), the star can get very small. The thing to keep in mind is that at infinity (where these things work), lens speed is the important factor. A f2 50mm is going to be just as accurate as a f2 18mm. And a f1.4 50mm is going to more accurate than either. That is because the depth of focus equation uses magnification factor, not focal lg. in it's equation. So you can use a longer lens (up to 75mm in Centurys case), as long as it is as fast as your other lenses.
 
You must log in or register to reply here.
Back
Top