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8mm soft focus issues with Red one

A

Adam White

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I was curious if folks had ever run into a "soft image" problem with a Red and wide lenses. We shot with a rental house Red and an 8mm prime at 4.5K, images seem softer than the, say, 50mm. I have been told that wider lenses have a much shallower depth of focus than tighter lenses. The rental tech said that some folks have run into that problem with the Red, and that is just a problem with how the Red One sensor processes wide focus imagery. That information, though, came filtered through the Arri rep who was selling the Alexa to them. I just was curious about anyone's thoughts. Solvable, or a Red technology problem?

Thanks
 
RED doesn't have any problems "processing wide focus imagery". Quite the contrary... as evidenced by any of the RED Reels. Not sure what is happening with the lens, back focus, or rental company, but info from a sales rep from another company generating a myth isn't particularly helpful. It appears that you are talking about a Zeiss 8mm but maybe it is a Peleng?

Maybe some of our customers can comment on their experience shooting wide...

Jim

Adam White said:
I was curious if folks had ever run into a "soft image" problem with a Red and wide lenses. We shot with a rental house Red and an 8mm prime at 4.5K, images seem softer than the, say, 50mm. I have been told that wider lenses have a much shallower depth of focus than tighter lenses. The rental tech said that some folks have run into that problem with the Red, and that is just a problem with how the Red One sensor processes wide focus imagery. That information, though, came filtered through the Arri rep who was selling the Alexa to them. I just was curious about anyone's thoughts. Solvable, or a Red technology problem?

Thanks
Click to expand...
 
If a longer lens looks sharper than a wider lens, it sounds like it could need a back focus adjustment. That or the wide lens needs to be looked at.

I've never had any problems with wide lenses on the R1 not being sharp.

Tim
 
Collimation or back focus is far more critical with wide angle lenses than it is with longer lenses. They have great depth of field, but shallow depth of focus so there is far less tolerance for the lens and camera lens mount to be set to the correct distance to focus a sharp image on the sensor.

Bear in mind that the rental house should be collimating all their lenses and their camera lens mount to a common standard. It is possible to collimate a particular lens and camera to match each other, but that's hardly practical for a rental house.
 
Jannard said:
Maybe some of our customers can comment on their experience shooting wide...

Jim
Click to expand...

Red One makes some of the most beautiful wide images I've ever seen. Sharpness is NOT a problem. Quite the opposite - the resolution provides detail that makes wide lenses really come to life.

It is true that the camera's backfocus has to be in correct adjustment for wide lenses to be sharp. On a RED One, it's pretty easy to adjust the backfocus so that it's spot on. Any competent rental house should ensure that this is the case for any camera they rent before it goes out.
 
I thank you for the replies. I am using a Nikkor 8mm as my lens. The house swears they check the backfocus of the cameras on a regular basis, my material had a difference to it between lenses, same location, same day. Here are the two lens...
http://i212.photobucket.com/albums/cc72/lordeggman/32mm.jpg
http://i212.photobucket.com/albums/cc72/lordeggman/8mm.jpg

I'm greatful for the help so far. I just want to make sure my upcoming shoots will go well, when using an 8mm will be very critical.
Thanks
 
What was the stop, did you use any ND's, personally I would never go past T8 on one of those lenses. Lens collimation, camera back focus & any dirt will make a huge difference.
How did you focus the lens?
Take the new Arri / Zeiss 8mm it blows the Nikon away.
Adam White said:
I thank you for the replies. I am using a Nikkor 8mm as my lens. The house swears they check the backfocus of the cameras on a regular basis, my material had a difference to it between lenses, same location, same day. Here are the two lens...
http://i212.photobucket.com/albums/cc72/lordeggman/32mm.jpg
http://i212.photobucket.com/albums/cc72/lordeggman/8mm.jpg

I'm greatful for the help so far. I just want to make sure my upcoming shoots will go well, when using an 8mm will be very critical.
Thanks
Click to expand...
 
Not much to add here that hasn't already been said. The Nikkor 8mm isn't the sharpest of the super-wide fisheye lenses, but it's still a lot sharper than what your image shows. The ARRI/Zeiss 8R is indeed an amazing lens, since others have brought it up, but it's a different animal -- it's rectilinear, so no fisheye. You should still take a look at it if you're not familiar, amazing lens.

Back focus (FFD or flange focal distance) is critical for maintaining sharp focus. When it's off, lenses have trouble hitting infinity focus and your wide focal lengths may end up never being sharp. So there's a pretty good bet here that the back focus is indeed off and/or the lens needs to be collimated.

On these really short focal lengths, you don't want to close your aperture down very far. F8 is even pushing it! And I'm willing to bet that could be another contributing factor here. Given the subject matter, and how it's near impossible to proper ND the glass dome on that Nikkor prime without vignetting, I would not be shocked if you were shooting at F11 or higher. That right there is the most likely gremlin in all of this.

Edit> for future reference, if you can, ND the rear of the fisheye lens before mounting. Some like the Peleng 8mm have screw-on NDs for the rear element. Others on the market take drop-in filters because trying to put an ND in front or even a larger sheet of ND film is just a problem.
 
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If the Nikkor 8mm is your personal lens, then it may be the problem rather than the rental camera. As others have already said, the wide lens is more critical when it comes to back focus. Does the Nikon mount belong to you or the rental house? If it's yours and you are installing after the rental house has collimated for a PL mount, then you will have to adjust the backfocus for the 8mm to be in with a chance. But if your Nikkor 8mm is a looong way out of spec, then you might then find the 32mm having issues then.
 
I have had some CA issues with a 10mm ultra prime. It was a very slight blue shift. Not sure what the problem was but have not had that same issue with the little duclos at 11mm. Flange depth was collimated so it is a mystery to me. This was a couple of years ago so it may be old news.
 
I wasn't aware that a high T-stop would affect it like that. So, to help out with the image quality and focus, being at a T-4 is better than a T-11? I was at a T-11, with no ND
 
Yeah, use ND, most lenses are best at 4 to 5.6. But check back focus again and even once again, it's very critical with wide lenses.
 
Its most likely if not certain back focus and hardly associated with a camera sensor behavior.

An Arri tech trying to sell ALEXA?

Yeah its good he dint say something like oh you cant use other than red primes with red cameras, they are programed to recognize the 3 d party lens and produce distortion images hahahahahaha very funny.
 
Adam White said:
I wasn't aware that a high T-stop would affect it like that. So, to help out with the image quality and focus, being at a T-4 is better than a T-11? I was at a T-11, with no ND
Click to expand...

On short focal lengths, you become diffraction limited at high F numbers (T numbers too, being similar, but they measure light transmission and not aperture size). Increasingly more so on lenses designed to cover larger image areas. So an 8mm designed to cover a 35mm sensor is going to show far more distortion, softness and diffraction at tighter apertures than an 8mm designed to cover a 2/3" sensor area.

But yes, you will do much better at T4~T6 if you can control your exposure in other ways. For still photos, shutter speed is the obvious method, unless you need smeared motion. On motion images, you still need enough motion blur to not look staccato or juddery, but you can cheat it and go faster than a 180-degree or 1/48 shutter. Assuming you were shooting 24fps. As always, test, test, test! Ultimately, you may have to suck it up and find a way to put ND on that lens, even move to a different lens that allows this.
 
Wide angle (short focale length) lenses have their own set of optical abberations. One of which is collimation (back focus) shift with change of stop. While this is not a problem so much on high end newer design cine lenses, it was and can be a problem on less exspensive still camera optics.
 
Sounds like the classic backfocus issue, as many have pointed out. Remember that backfocus is not an absolute standard, but rather a "tolerance from x to y" subject, where different lens-sets can be colimated for different specific backfocus - within that tolerance.

We recently bought a set of Supers and a couple Ultras, and a set of Elites and fun started all over, as our Masters and Elies seem to share the same colimination, but the Supers and Ultras are off in individual ways, the supers more than the ultras, BUT the superspeed set itself and the ultras are share the same colimination.

We're now in the process of standardizing this... while shooting shows with all sets.

Jippeeee!

LOL

Cheers

Gunleik
 
Good post, Jeff, but I would point out an error:

Jeff Kilgroe said:
On short focal lengths, you become diffraction limited at high F numbers.
Click to expand...

That's only true if you use the short focal lengths on smaller formats.

Jeff Kilgroe said:
Increasingly more so on lenses designed to cover larger image areas.
Click to expand...

In fact, it doesn't matter what the 8mm lens was designed for: when you put it on a RED ONE, the diffraction is going to be the exact same as any other 8mm lens.

Jeff Kilgroe said:
So an 8mm designed to cover a 35mm sensor is going to show far more distortion, softness and diffraction at tighter apertures than an 8mm designed to cover a 2/3" sensor area.
Click to expand...

Generally, I agree about the distortion/softness, but not diffraction.
 
Am I missing something? They look equally sharp to my eye. Can you maybe post 100% crops?


Adam White said:
I thank you for the replies. I am using a Nikkor 8mm as my lens. The house swears they check the backfocus of the cameras on a regular basis, my material had a difference to it between lenses, same location, same day. Here are the two lens...
http://i212.photobucket.com/albums/cc72/lordeggman/32mm.jpg
http://i212.photobucket.com/albums/cc72/lordeggman/8mm.jpg

I'm greatful for the help so far. I just want to make sure my upcoming shoots will go well, when using an 8mm will be very critical.
Thanks
Click to expand...
 
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