GH4 Rokinon Cine DS lens tests

DotKomrade

DotKomrade

Member
Hi all, I got a set of Rokinon primes for my GH4 this week and started out by testing how each lens looks at each T stop. I've compiled those into a video here: https://www.youtube.com/watch?v=yM-wo80Bn3E

If anyone is interested in specific shots, let me know and I'd be happy to post links to the original media for any given lens/aperture combo.

All shot on GH4, Portrait mode (-2 -2 0 -3 0), with a speedbooster, at 5600K on a shaky tripod.

Please disregard colour shifts - I had a variable ND filter on for wider apertures and also the sunlight was coming and going behind clouds. I was more interested in sharpness and the DOF look.

I was worried that the lenses would be softer than they are, so I'm quite happy with the look. Looking forward to some practical applications soon.

This has raised one or two questions for me. The main one is: on a lens + speedbooster combo, how is the focus distance affected? I noticed that the focus scale doesn't correlate with the actual distance from the focal plane on the camera to the subject. If this is the case, would I use the lens + SB combo to calculate for DOF? EG, instead of specifying a 24mm at T2 would I specify a 17mm at T2 in a DOF calculator?

The other thing is that with the Speedbooster none of the lenses stops down past T16. The 85mm only goes to T11. I guess I should google it, but is there something that needs to be set on the SB to solve for this?

Matt.
 
I don't know if this will help, but the instructions on my speedbooster said to stop down both the lens aperture and the speedbooster's aperture ring all the way down before mounting. Then to use the speedbooster to open it back up.
 
Thanks for the video :)

It might be good to do another set of shots without the variable ND filter, as it could introduce additional image errors. Just use the shutter speed to compensate accordingly.

To answer your questions:

Focus distance isn't affected at all, but the lenses are cheap, so the markings aren't likely to be accurate (and the barrels turn beyond infinity). If you need the markings to be accurate, put tape around the barrel over the existing markings and mark out actual, measured distances for your lenses. Then they'll be much more accurate.

DoF should be calculated for a Super35 (or close enough) image circle. That said, true DoF doesn't change at all, only apparent DoF. A 50mm is a 50mm is a 50mm, as they say. So calculate for the lens length and f-stop it's set at, at the lens itself. You will gain a stop of light T-stop wise, hitting the sensor itself, but for the lens characteristics the lens is creating the images based on its focal length and f-stop onto the Metabones lens, which is then compressing the image circle down to the m43 sensor circle.

The Speed Booster reports the T-stop as hitting the sensor, so it will show f16 even though the physical lens itself is stopped down fully to its f22 position. Where this differs is that any lens with f1.4 or greater real world f-stop, the Metabones shows the lens's true f-stop to prevent camera errors from having indicated f-stops of 1 or less. So there's nothing to set, just be aware that's it's indicating differently depending on the lens.

HTH!

Cheers from Berlin,

Paul :)
 
Hey Zak, thanks for the advice. That doesn't help unfortunately. It looks like the lever in the SB doesn't push back far enough to stop the lens down fully.
 
In simple terms, your aperture scale slides down a full stop. This is why f/1.8 becomes f/1.2 on the wide end. The same is true on the narrow end: f/22 becomes f/16.
 
refocusedmedia said:
In simple terms, your aperture scale slides down a full stop. This is why f/1.8 becomes f/1.2 on the wide end. The same is true on the narrow end: f/22 becomes f/16.
Click to expand...

The SB concentrates light and increases it's intensity by about a stop at the sensor, right? My problem is that the irises in my lenses don't stop down all the way when attached to my speed booster. So the iris contracts all the way to T16 but doesn't contract any further after that. Off the SB it contracts further without any trouble though.. Does that make sense?

Edit: Sorry, I realised I never mentioned that they're Nikon mounts..
 
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I have the same issue! Only my 35mm and 85mm only goes to f/8. I tested this by making sure the speedbooster is at 8 (yes I have the first version of the speedbooster. The new one goes up to 7) and changed the aperture ring on the Rokinon lenses until I saw the ring wasn't doing anything anymore and it stops becoming useful a tiny tiny bit past F/8.
I have a newer version metabones adapter (with 7 markings) for my other camera (a7s) and it works up to f/16 not up to f/22 which is what the lens is capable of but that's expected as these manual rings are suppost to control 8 stops (counting wide open as 1).
What are your thoughts about the lens set so far? I was thinking about getting the Sigma arts instead?
 
Zak Forsman said:
I don't know if this will help, but the instructions on my speedbooster said to stop down both the lens aperture and the speedbooster's aperture ring all the way down before mounting. Then to use the speedbooster to open it back up.
Click to expand...

Doesn't matter, Rokinon are fully manual.
 
kastel07 said:
I have the same issue! Only my 35mm and 85mm only goes to f/8. I tested this by making sure the speedbooster is at 8 (yes I have the first version of the speedbooster. The new one goes up to 7) and changed the aperture ring on the Rokinon lenses until I saw the ring wasn't doing anything anymore and it stops becoming useful a tiny tiny bit past F/8.
I have a newer version metabones adapter (with 7 markings) for my other camera (a7s) and it works up to f/16 not up to f/22 which is what the lens is capable of but that's expected as these manual rings are suppost to control 8 stops (counting wide open as 1).
What are your thoughts about the lens set so far? I was thinking about getting the Sigma arts instead?
Click to expand...

Sheez, I can live with T16, but 8 is a bit hectic!

I really like the lenses so far but haven't had much opportunity to shoot properly yet. I have a job this weekend so will get a better idea. I really had to toss up between the sigmas and these as well. I also considered a mixed set (18-35mm, 50mm and 85mm). But I'm happy so far :)
 
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