Speed Boosters - Thoughts, Ideas, usage

TaoTeJared

I enjoyed the artice on the blog (Here) about the review of the Metabones Speed Booster for Nikon lenses on Fuji x-mount camera and thought I would start this to see if anyone is finding them usefull or thoughts about them.

shawnino

Your analogy to burning ants with a magnifying glass might be the most illustrative I've read this year. Well done.

heartyfisher

Like you said in the main blog its just a 0.67 X TC .. sigma, tamron, nikon, anyone could make one for the DX cameras ! Would make a 50mm F1.4 FX into a 35mm F1.0 DX

Ade

No, it's not practical for DX cameras.

TaoTeJared

Your analogy to burning ants with a magnifying glass might be the most illustrative I've read this year. Well done.

Who would have thought the temporarily misguided demonic pyromaniac child could ever utilize that knowledge for good?

I think it is practical for any format of lens design. Just like any lens or teleconverter you have to know it's limitations and weigh the tradeoffs.

Say make a 50mm f1.4 (designed), which would be a small sized lens. Add an integrated speed booster and turn it into a 34mm f1.2 lens in a compact design. That could be a boon for low light shooting. Flipside, if you could put that on existing lenses for DX, you could turn a 2.8 zoom to f2.

As we all know in difficult low light situations anytime you can gain a stop of light that is a good thing.

Ade

Umm, all SLR wide angle lenses (including the 35mm DX/FX) are already designed in this way.

The issue is the mount-to-sensor distance required to accommodate a moving mirror. A "true" 35mm lens would have to sit so close to the sensor that it would interfere with the mirror.

So a 35mm F-mount lens is actually a longer lens (around 45mm) with a "speed booster" (focal reducer) built-in. This is what's called a retrofocus design. Using a longer lens allows clearance from the moving mirror. Attaching a focal reducer widens the lens to the desired focal length.

The requirement for retrofocus design for wide angle lenses is a limitation of all SLRs, and is what makes adding another external "speed booster" not practical on these types of cameras. Longer lenses don't need them. Shorter lenses already have focal reducers within them, and cannot be "speed boosted" anymore for the specific flange-to-sensor distance.

Having a mirrorless camera removes this limitation. That's why it's possible to adapt a longer DX/FX lens and "speed boost" it to match the short mirrorless flange-to-sensor distance. Rangefinder cameras can similarly use shorter lenses before resorting to a retrofocus design.

Msmoto

Ahhh...yes, my argument for the line of mirrorless bodies which will accept "F" mount lenses. And, we will see a new breed of very sharp wide angle non-retro focus lenses which will blow us away.....it is my understanding the difficulty of avoiding distortions, etc., with retro focus is fairly significant, and doing away with this like on a view camera lens will be very nice.

PB_PM

@Msmoto Having an F mount mirrorless camera would not solve the problem. Due to the design of the F mount, the lenses still need to maintain the current distance from the sensor. Just look at the Nikon 1 FT-1 adapter for the reasons why.

Ade

There are at least two possibilities:

1) Design the new mirrorless camera with a new optimized (short-distance) electronic mount. F-mount compatibility has to come via an adapter (with or without a focal reducer). The Nikon 1 system takes this approach; it is the most straightforward approach for a new system and allows for the most compact camera possible.

2) Design the new mirrorless camera with a new electronic mount (let's call it a F Plus mount for the moment) having full F-mount "backwards compatibility". The F Plus flange-to-sensor distance has to be the same the regular F-mount. This provides 100% compatibility with existing F-mount lenses. However, it also allows creating a new series of F Plus non-retrofocus lenses which have rear elements "recessed" in the mount (with reduced distance from the rearmost lens element to the sensor.) These new F Plus lenses cannot be mounted on existing F-mount cameras.

Pros/cons of either approach are left as an exercise for the reader.

heartyfisher

I like both ideas :-) Maybe type 1 for a new range of DX CoolpixA (with interchangeable lenses) type lenses. and Type 2 for some new pro level FX mirrorless camera .. but having a set of Nikkor (R)ecessed lenses could be confusing :-) ... nah type 2 is just too "messy" ..

PB_PM

Just what Nikon needs, another line of lenses they cannot keep in stock.

heartyfisher

in the other thread Ade provided a link to a whitepaper on the gadget.

One section listed the advantages of the thing. As expected the "boost" in aperture was mentioned. However, there was another interesting "boost". We all know TC degrade IQ but that is due to the magnification of the imperfections of the original lense. With the 0.71X magnification of the boost (Ie image reduction) you also get an increase in IQ! and an improvement of the MTF numbers !

heartyfisher

what about a SB device for the Nikon1 system? would be interesting if it had a 0.4 or even just a 0.5 "boost". Thats a 2+ stop boost ! :-) Stick an 85 1.8 on a nikon 1 + the boost and .. I dont even know how to calculate the F stop !

Ade

I don't now if there's enough room for a good quality 0.5x magnification. 0.71x seems to be the magic number for now.

The downside of the CX format is the very high 2.7x crop factor.

A 35mm/2 FX lens mounted on an APS-C mirrorless (like the Fuji X) becomes the equivalent of 37mm/1.4, so you get the 1-stop "boost" while maintaining the almost same equivalent field-of-view.

But on a Nikon 1, that same 35mm/2 FX lens becomes the equivalent of 67mm/1.4. You get the speed but you lose the wide-angle, so it's not as attractive. Still better than using the FT1, I guess!

heartyfisher

I am confused ... those numbers are not adding up...

Ade

Why not?

On APS-C (DX) with 1.51 crop factor, the lens has equivalent PoV of 35 * 0.71 * 1.51 = 37.5mm

On CX with 2.7 crop factor, the equivalent PoV is 35 * 0.71 * 2.7 = 67.3mm.

The aperture is the same for both.

Msmoto

Some of us remember the Hasselblad with the wide lens which had to be a separate camera as the lens was not retro focus. Also, the early 8mm fisheye for the "F" bodies required the mirror to be locked up. As I remember, the fisheye stuck back into the body nearly a centimeter. ANd, of course, all these problems go away with no mirror.

In a previous post, I was referring to the idea as Ade mentioned, a mirror less body which would accept "F" mount lenses, albeit with an adapter, but would be ready for all the non-retro focus lenses from about 50mm and shorter, used directly. Although, if the body had the same mount to sensor distance, the new lenses could simply project into the body as in the old days. Either case would give us higher quality wide lenses, IMO.

heartyfisher

:-) Thanks for your calculations Ade :-)