CustomerGH4
Well-known member
When Im using a 12mm manual lens and it asks the focal lenght do I write 12mm or 24mm??
Cant find in the manual.
Cant find in the manual.
GH4 (GH5) When it asks for focal lenght do I use the native or the 35mm standard?
- Thread starter CustomerGH4
- Start date
Cary Knoop
Veteran
You use the focal length of the lens, in this case that would be 12mm.
Peter Berry
Well-known member
I would assume that in ETC mode (1.4X) this should be factored in. I know a large discrepancy between stated and actual FL will make IBIS unusable, as I found recently after changing the numbers but failing to "set" it, going from a 50 to 135mm prime.
CustomerGH4
Well-known member
Oh okay, but just in theory, what should one write when using a speedbooster + a full frame lens?
Cary Knoop
Veteran
With a speed booster you divide it by the factor. So in case use have an ultra a 12mm would become 12/0.71 which is about 17mm. And 17mm is what you should enter.
CustomerGH4
Well-known member
Thomas Smet
Veteran
You don't write anything. A 12mm is a 12mm no matter what you do with it. What you are asking is the field of view (FOV) or the crop factor. A 12mm lens doesn't suddenly turn int oa 24mm lens it is still la 12mm lens. It is only the FOV that changes.
What exactly are you trying to write down or keep track of here? Unless you are doing some serious VFX work and need to match a virtual camera to a real camera or need to 100% perfectly match another larger sensor camera on the shoot there is really nothing to gain by knowing what the lens would be like on another camera. When you shoot with m43 you should be only thinking of m43 and how your lenses look. You find out what works best for you and don't worry about what a Canon user might use for a certain type of shot.
What exactly are you trying to write down or keep track of here? Unless you are doing some serious VFX work and need to match a virtual camera to a real camera or need to 100% perfectly match another larger sensor camera on the shoot there is really nothing to gain by knowing what the lens would be like on another camera. When you shoot with m43 you should be only thinking of m43 and how your lenses look. You find out what works best for you and don't worry about what a Canon user might use for a certain type of shot.
Cary Knoop
Veteran
If you use a speed booster ultra the focal length of a 12mm lens changes to about 17mm.
It has nothing to do with "what the lens would be like on another camera", it is important to set an accurate focal length for a non-panasonic lens for IBIS to work properly.
Cary, I don't believe that can be correct. IBIS is a mechanical function and it needs the actual focal distance from the sensor to focal point in the lens. This doesn't change with a speedbooster, just the image it is projecting from that distance to the sensor. I'd be interested to see some verification from Panasonic on this one.
Cheers,
Pete
Cheers,
Pete
Cary Knoop
Veteran
You are wrong, a speed booster changes the focal length of a lens.
Thomas Smet
Veteran
No it changes the FOV. Nothing physically changes on the lens. That 12mm is still a 12mm lens. It may have the FOV of a 17mm lens but all other physical characteristics are still 12mm.
Cary Knoop
Veteran
And that is exactly what matters for IBIS.
You need to set the focal length after dividing the metabones factor (which is 0.71 for the ultra), so for a 12mm manual lens you would need to set 17mm (or anything closest to that).
iain.bason
Well-known member
No, it now has a focal length of 17mm. The focal length of a lens depends on how the elements in the lens bend the light. The speedbooster adds an element, and thereby changes the focal length.
Brandon Rice
Distributed Producer
Actually a speedbooster decreases the focal length, so when I put my 35mm on with my speedbooster I type in 24mm. Thank you.
He's talking about when the GH5 prompts your for a focal length for IBIS on manual lenses that don't report this information to the camera. You need to input the proper focal length to the stabilisation will work correctly
This video on the Lumix channel says you'd input the magnified focal length, not the focal length on the lens itself, when using a Speedbooster that doesn't have electronics to pass the info to the camera. For example a 50mm lens on a .71 Speedbooster would input as a 35mm lens for the IBIS to work properly.
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Cary Knoop
Veteran
Yes you are absolutely correct, the focal length shortens instead lengthens!
Indeed you should choose 8 or 9mm.
Interesting and thanks for the link. I still don't believe that is correct as the light coming into the lens crosses (called the focal point) at the lenses focal length. The speed booster simply allows the larger image circle of a full frame lens to be compressed onto the smaller sensor than the lens was designed for. Movement of the sensor to compensate for vibration would still need to be relative to where the focal point is to work correctly. Looks like I'm going to have to test it to see if there is a difference
Cheers for the link,
Pete
Peter Berry
Well-known member
There are many ways to skin the lens design cat, so to speak. You could take a "base" lens design of high quality - say a fine, flat field 50mm/2.0 with a FF image circle - and produce any number of FL variations from this with additional rear elements: think building in the high quality elements of the Speedboosters, or conversely, of a tele-converter, for a 35mm/1.4 m4/3 to a 100mm/4.0. These become fully baked, 35, 50, and 100mm FL lenses, all from the same base, but indistinguishable from native lenses of the same specs.
Cary Knoop
Veteran
I don't understand why this is even a point of contention, a speed booster and a tele-converter change the focal length of a lens.
Optics 101!
Optics 101!