GH4 (GH5) When it asks for focal lenght do I use the native or the 35mm standard?

A teleconverter makes the focal length longer by putting the focal point further away from the sensor. A speed booster sits in the exact same focal length from the focal point to the sensor and only with a lens that allows the speed booster to fit in between some flange to lens mount. They are totally different things.

With all that said, it doesn't appear it makes any difference between 35mm and 50mm setting on a 50mm lens. The first one is with is set to 35mm the second is with it set to 50mm on my Metabones SB 0.71x and a vintage OM 50mm f?1.4

https://vimeo.com/215118710

Cheers,
Pete
 
A Speedbooster changes the focal length of the lens. The focal point is a theoretical point based on a conceptual single lens element, which is of course not what is actually used. The Speedbooster alters the position of this focal point.

With a standard Speedbooster (,71x inverse-magnification) a 50mm lens is transformed into a 35mm focal length lens. The image is also made brighter because the same amount of light is striking a smaller area. So in this case the correct focal length to input into the IBIS correction control menu is 35mm. For the example of a 12mm lens with a Speedbooster, the correct focal length would be 8mm.

A lens is a lens is a lens, until it is optically transformed into another lens.
 
Cary Knoop said:
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!
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It's been fun watching this thread! You can tell who really knows their optics and who doesn't!
 
c3hammer said:
A teleconverter makes the focal length longer by putting the focal point further away from the sensor. A speed booster sits in the exact same focal length from the focal point to the sensor and only with a lens that allows the speed booster to fit in between some flange to lens mount. They are totally different things.

With all that said, it doesn't appear it makes any difference between 35mm and 50mm setting on a 50mm lens. The first one is with is set to 35mm the second is with it set to 50mm on my Metabones SB 0.71x and a vintage OM 50mm f?1.4

https://vimeo.com/215118710

Cheers,
Pete
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Of course an SB and a TC are totally different things: the former brings a compressed, brighter image to the focal plane (the sensor); the other an expanded, dimmer image likewise focused on the sensor. If a TC brought the "focal point further away from the sensor" as you claim, it would be out of focus!

Some 2X TC's, like Canon's current EF vIII measure 2" flange-to-flange, whereas my old Quantaray 2x EF Canon TC measures half that. But the different internal optics do the same thing with any EF mount lens on it - double the FL, with 2 stops aperture loss and the same expansion of the image circle, focused on the sensor. And I presume that a slimmer or thicker Speedbooster of the same 0.71X factor could likewise be achieved with different optical formulas.

I just tested IBIS with my Nikkor 85mm/1.8 with a plain adapter at 35mm, 50mm, and the correct 85mm input FL's. No effect at all at 35mm, only mild effect at 50mm, and rock solid at 85mm with excellent images at 1/15 sec. repeatedly. It makes a difference!
 
Cary Knoop said:
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).
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Sorry didn't know the OP was talking about IBIS or using a Speed booster. Thought they were just talking in general using lenses on the GH5.
 
Mitch Gross said:
A Speedbooster changes the focal length of the lens. The focal point is a theoretical point based on a conceptual single lens element, which is of course not what is actually used. The Speedbooster alters the position of this focal point.

With a standard Speedbooster (,71x inverse-magnification) a 50mm lens is transformed into a 35mm focal length lens. The image is also made brighter because the same amount of light is striking a smaller area. So in this case the correct focal length to input into the IBIS correction control menu is 35mm. For the example of a 12mm lens with a Speedbooster, the correct focal length would be 8mm.

A lens is a lens is a lens, until it is optically transformed into another lens.
Click to expand...

Mitch breaks it down exactly. His A Lens Is a Lens is a Lens video is the first thing I think of when I see questions like this. Anyone with questions about the differences between focal length and field of view should definitely give it a watch.

Actually, you should probably watch it even if you think you've got it all figured out ;)
 
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Finally figured it out! A speedbooster is about 15mm shorter than a dummy adaptor. The focal point in the lens is still in the same place in the lens, but it is moved closer to the sensor, thus the shorter number. I had always assumed the adaptor and SB were the same length and all you folks were full of it :)

Thanks for the education

Cheers, Pete
 
c3hammer said:
Finally figured it out! A speedbooster is about 15mm shorter than a dummy adaptor. The focal point in the lens is still in the same place in the lens, but it is moved closer to the sensor, thus the shorter number. I had always assumed the adaptor and SB were the same length and all you folks were full of it :)

Thanks for the education

Cheers, Pete
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Pete, I think you're way over-thinking this, and hung up on focal point distances "in the lens". Since the lens has to focus on the sensor, that's it's focal point, or "focal plane". And the physical thickness of a focal reducer behind the lens, or a tele-extender for that matter, is entirely dependent on the optical formula used to bring the reduced or expanded image to focus on the sensor.

As I previously explained above with two TC's for Canon EF lenses I have of the same 2X power, one is 1" thicker flange-to-flange than the other - and both bring identical images focused on the sensor, with necessarily different optical formulas.
 
Peter Berry said:
...the physical thickness of a focal reducer behind the lens, or a tele-extender for that matter, is entirely dependent on the optical formula used to bring the reduced or expanded image to focus on the sensor.
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+1

I believe the SpeedBooster "S" is physically thinner than the "Ultra", but both provide the same .71x focal reduction.

A Focal Reducer (e.g. Speed Booster) is also known as a Telecompressor, & just like a Teleconvertor (aka Tele-Extender) optically alters the focal length, & therefore the f-stop, of any lens it's attached to.
 
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So moron question here - but if using a native panny 14-140mm i assuem the camera does it automatically? Also lens is at firmware 1.2 anyone know if a newer one is coming?
And last - so if using a speedbooster I multiply by .71 to get the right number to input?

Thanks
 
Harry Pallenberg said:
So moron question here - but if using a native panny 14-140mm i assuem the camera does it automatically? Also lens is at firmware 1.2 anyone know if a newer one is coming?
And last - so if using a speedbooster I multiply by .71 to get the right number to input?
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If using a Panasonic m4/3 lens the GH5 automically optimizes the IBIS settings. Imagine the same applies to Olympis m4/3 lenses, but not certain.

As Mitch explained a Focal Reducer (e.g. Speed Booster) optically changes the focal length of the lens, so you need factor the .71x reduction when setting the GH5's IBIS.
 
Bern Caughey said:
If using a Panasonic m4/3 lens the GH5 automically optimizes the IBIS settings. Imagine the same applies to Olympis m4/3 lenses, but not certain.

As Mitch explained a Focal Reducer (e.g. Speed Booster) optically changes the focal length of the lens, so you need factor the .71x reduction when setting the GH5's IBIS.
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Can confirm that Olympus lenses will work the same as Panasonic m4/3 lenses with IBIS. The camera should be able to detect the focal length automatically.
 
I'd like to revive this thread again briefly if I may. I understand how to select the proper focal length when the camera asks, but what I can't figure out is what focal length to use when attaching a non-native zoom lens. Do I use the short (wide) end focal length, the long end focal length, or something in the middle? On the one hand I can see using the shorter focal length to ensure sensor coverage throughout the full range. On the other hand, image stabilization is more demanding/critical at the longer end of of the lens. Any insights?
 
asergi said:
I'd like to revive this thread again briefly if I may. I understand how to select the proper focal length when the camera asks, but what I can't figure out is what focal length to use when attaching a non-native zoom lens. Do I use the short (wide) end focal length, the long end focal length, or something in the middle? On the one hand I can see using the shorter focal length to ensure sensor coverage throughout the full range. On the other hand, image stabilization is more demanding/critical at the longer end of of the lens. Any insights?
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I don't have a solid answer but I did see some videos recently of somebody that used a Nikon 80-200mm lens and they used the long end of 200mm and it still worked at 80mm. I think the reasoning behind that is that the lens will shake more at 200mm so setting the IBIS to that should compensate for the wider angles which will not shake as much.

It may not be optimal and really you should reset the value every time you adjust the zoom lens for perfect results but this particular user seemed to be happy with the tele value method.
 
Thanks, Thomas. I'm still left with some doubts/questions, but I suppose the best thing to do is test each lens in advance and find what works. Just wouldn't want to compromise stabilization effectiveness by not using the optimum setting.

Anyone out there from Panasonic care to offer some insight??
 
asergi said:
Thanks, Thomas. I'm still left with some doubts/questions, but I suppose the best thing to do is test each lens in advance and find what works. Just wouldn't want to compromise stabilization effectiveness by not using the optimum setting.

Anyone out there from Panasonic care to offer some insight??
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There are no optimized settings when dealing with a adapted zoom lens. The GH5 has the ability to enter the focal length for a reason and when dealing with a zoom lens there is no single focal length. The optimized and correct way to handle an adapted non OS zoom lens is to go into the menu and adjust the focal length every time you change the lens. Yeah its a major pain but it is what it is. Thats why it is really important to use zoom lenses that can communicate that information to the body.

The Metabones EF Speedbooster does communicate some information to the body so the IBIS at least knows what the heck is going on. With dummy adapters you have to do it all manually. Not a big deal for primes although you have to change it every time you swap lenses.

If you want the most out of the IBIS on the GH5 you use adapted primes and enter the focal length, Use native lenses or at the very least use Canon EF mount zooms with an adapter that supports electronic communication between the lens and body. If you don't want to go the Metabones route, Fotga makes a EF straight (non focal reducer) adapter with electronic EF control for $120. It seems to work well with some Canon lenses although autofocus seems to be a bit hit or miss. I'm not sure how well it works with IBIS.

Nikon users are SOL I'm afraid. Nobody has ever managed to make an adapter that can provide electronic control of Nikon lenses. Sometimes that can be a plus since the EF control with adapters can be a bit hit or miss. With Nikon you don't get any features but that also means nothing can ever go wrong. Just sticks the lens to the body and thats it really. I would love if the things could at least provide power to Nikon lenses so the optical stabilization would work but we can't even get that.
 
Well put, Thomas! Again, thank you! Ultimately, it is mostly academic for me anyway--I use native Panny lenses, Sigma on Metabones EF or primes for most of my work anyway. I was just kind of thinking in advance in case I ever needed to use a non-native, non-communicating zoom lens (I have an old Tokina FD mount zoom I'm fond of). Thanks again.
 
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