Josh Mitchell-Frey
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I know the subject of speed boosters for RED is a contentious one. I've read a lot of forum posts where responses range from "it's impossible, there's not enough room" to "why would you bother?".
Well, it is possible. I've designed a custom CNC machined mount that houses a Metabones Speed Booster and achieves focus at infinity (without removing the OLPF or adjusting the back focus).
Here are a few images:
So, there are a few limitations.
The first is that this was only possible with medium format lenses - in this case, Zeiss Jena Pentacon Six mount lenses. These were cheap & plentiful for me to test with, and also had one of the longest flange focal distances (74.1mm). Based on this prototype, it should also be possible to design a working speed booster mount for Hasselblad (74.9mm FFD) and possibly Pentax 645 (70.87mm FFD) lenses.
However, as has been stated in other forums, this isn't possible with PL, Canon, Nikon, or other lenses with an FFD much shorter than 70mm.
The second main limitation is that there are vignetting issues at 6K, depending on which lens is used. Strangely, I've found that longer focal length CZJ lenses (the 120mm Biometar & 180mm Sonnar particularly) are most prone to vignetting, especially at minimum focus. I can't be certain, but I suspect this vignetting is caused by the Metabones Speed booster, as it's not designed to cover a sensor larger than APS-C.
Third limitation - the mount consists of three components - the glass from a Metabones E-mount speed booster (not BMCC), the CNC machined housing, and a Pentacon Six to Nikon mount adapter bolted together. I don't have the mechanical knowledge to design the P6 mount mechanism, so instead a P6>Nikon adapter is bolted into the front of the CNC machined housing with M4 grub screws. It's fairly strong, but if it were designed all together as one piece, it'd be rock solid.
What's the point?
This setup isn't practical for the vast majority of shoots. The widest Zeiss Jena lens for P6 is a 50/4, which becomes a 35/2.8 because of the speed booster. And as to be expected, these lenses aren't razor sharp, and some are extremely prone to flaring.
I acknowledge all of the above, but I still think these lenses have a very attractive quality to them, and for some projects, that "character" may be the right thing.
In addition, I'm hoping that this serves as proof of concept — if I can hack together this mount, a company like Metabones may be able to purpose-build a speed booster mount with an optic that covers the new 8K Weapon sensor - capturing the full image circle of these medium format lenses, competing with Alexa65. I think there's a market out there for medium format to full-frame speed boosters, Metabones & similar companies just don't know it yet.
I didn't create this mount to make money, but if anyone is interested in one, I can look into the costs involved to get a batch machined. Also, if anyone is interested in collaborating, with mechanical or optical design knowledge, I'd love to further improve this mount beyond what I'm capable of alone.
Thanks for reading. Feel free to share your thoughts, but again, I pre-emptively acknowledge that this isn't for everyone. If you can't see value in this, you are free to go back to your Master Primes
Test footage:
(Quick & dirty test to demonstrate the range of focus. 6K FF 5:1 compression, DC2 RG4, 320-640ISO, STH OLPF, Tiffen 4x4 Pola, all lenses are wide open, no sharpening or post adjustments. Made no attempt to rack focus smoothly.)
50mm Flektogon f/4 (equiv 35mm f/2.8)
https://vimeo.com/170758509
80mm Biometar f/2.8 (equiv 57mm f/2) (This lens is unusually soft, I think it's a bad specimen. Also, reflections in the top right corner are caused by a gap between the lens and the mattebox & pola filter. Not caused by the focal reducer)
https://vimeo.com/170758521
120mm Biometar f/2.8 (equiv 85mm f/2)
https://vimeo.com/170758529
180mm Sonnar f/2.8 (equiv 128mm f/2)
https://vimeo.com/170758566
Well, it is possible. I've designed a custom CNC machined mount that houses a Metabones Speed Booster and achieves focus at infinity (without removing the OLPF or adjusting the back focus).
Here are a few images:
So, there are a few limitations.
The first is that this was only possible with medium format lenses - in this case, Zeiss Jena Pentacon Six mount lenses. These were cheap & plentiful for me to test with, and also had one of the longest flange focal distances (74.1mm). Based on this prototype, it should also be possible to design a working speed booster mount for Hasselblad (74.9mm FFD) and possibly Pentax 645 (70.87mm FFD) lenses.
However, as has been stated in other forums, this isn't possible with PL, Canon, Nikon, or other lenses with an FFD much shorter than 70mm.
The second main limitation is that there are vignetting issues at 6K, depending on which lens is used. Strangely, I've found that longer focal length CZJ lenses (the 120mm Biometar & 180mm Sonnar particularly) are most prone to vignetting, especially at minimum focus. I can't be certain, but I suspect this vignetting is caused by the Metabones Speed booster, as it's not designed to cover a sensor larger than APS-C.
Third limitation - the mount consists of three components - the glass from a Metabones E-mount speed booster (not BMCC), the CNC machined housing, and a Pentacon Six to Nikon mount adapter bolted together. I don't have the mechanical knowledge to design the P6 mount mechanism, so instead a P6>Nikon adapter is bolted into the front of the CNC machined housing with M4 grub screws. It's fairly strong, but if it were designed all together as one piece, it'd be rock solid.
What's the point?
This setup isn't practical for the vast majority of shoots. The widest Zeiss Jena lens for P6 is a 50/4, which becomes a 35/2.8 because of the speed booster. And as to be expected, these lenses aren't razor sharp, and some are extremely prone to flaring.
I acknowledge all of the above, but I still think these lenses have a very attractive quality to them, and for some projects, that "character" may be the right thing.
In addition, I'm hoping that this serves as proof of concept — if I can hack together this mount, a company like Metabones may be able to purpose-build a speed booster mount with an optic that covers the new 8K Weapon sensor - capturing the full image circle of these medium format lenses, competing with Alexa65. I think there's a market out there for medium format to full-frame speed boosters, Metabones & similar companies just don't know it yet.
I didn't create this mount to make money, but if anyone is interested in one, I can look into the costs involved to get a batch machined. Also, if anyone is interested in collaborating, with mechanical or optical design knowledge, I'd love to further improve this mount beyond what I'm capable of alone.
Thanks for reading. Feel free to share your thoughts, but again, I pre-emptively acknowledge that this isn't for everyone. If you can't see value in this, you are free to go back to your Master Primes
Test footage:
(Quick & dirty test to demonstrate the range of focus. 6K FF 5:1 compression, DC2 RG4, 320-640ISO, STH OLPF, Tiffen 4x4 Pola, all lenses are wide open, no sharpening or post adjustments. Made no attempt to rack focus smoothly.)
50mm Flektogon f/4 (equiv 35mm f/2.8)
https://vimeo.com/170758509
80mm Biometar f/2.8 (equiv 57mm f/2) (This lens is unusually soft, I think it's a bad specimen. Also, reflections in the top right corner are caused by a gap between the lens and the mattebox & pola filter. Not caused by the focal reducer)
https://vimeo.com/170758521
120mm Biometar f/2.8 (equiv 85mm f/2)
https://vimeo.com/170758529
180mm Sonnar f/2.8 (equiv 128mm f/2)
https://vimeo.com/170758566
