Speed boster for Nikon DLSRs?

Is there a speed booster for Nikon APS-C cameras? Couldnt find any.

I don't think there is one. You're out of luck. Both full frame and DX cameras have the same flange distance so there is no room for the adapter.

That means its available only for 4/3 cameras?

There are speed boosters available for APS-C mirrorless systems with a shorter flange distance (and smaller image circle) than the native lens - other manufacturers are available, but have a look at metabones.com and their products list. Metabones support mounts for micro 4/3 (and BlackMagic), Sony E, Fuji X and (bizarrely) Pentax Q. I imagine it should be possible to do the same for Leica M, Nikon CX or Samsung NX, but I doubt the demand is there. I've not yet seen anything for the Canon EF-M, but I suspect it's a matter of time (complicated by the electronics). The situation may change if Nikon produce a large-sensor mirrorless body with a shorter flange distance.

 

I suspect it should be possible to produce a speed booster for a medium format lens (several have a larger flange distance than Nikon and a larger imaging circle). I'm not sure how many lenses it would actually be worth adapting - the depth of field advantage of the larger format is usually cancelled out by medium format lenses not getting to the f/1.4 aperture relatively common in 135. With the possible exception of the Pentax SMCP-67 600mm f/4 (which might be easier to find than Nikon's own 300mm f/2? I don't know) there aren't many medium format lenses for which an equivalently fast 135-format lens doesn't already exist. (Yes, the Schneider 150mm f/2.8 Xenotar that covers 5x4 could be adapted to be a faster-than-f/1 50mm equivalent, but that's a bit esoteric. And you might run into the limitations of the F mount radius.) There are certainly (non-optical) adaptors that use medium format lenses to support shift (and possibly tilt), though - I believe that's essentially how my Hartblei super-rotator came about.

 

TL;DR: don't hold your breath for adaptors for DX until (and if) Nikon make an APS-C mirrorless body. If anything, that's an argument why Nikon should go full-frame with their mirrorless, when and if they do it: otherwise people might buy a crop body with a focal reducer/speed booster as an alternative to a more expensive full-frame body.

Speed boosters work by focusing the image on a smaller area, increasing the light intensity in the process. The adapter takes care of the increased flange distance, but it only works if the image circle of the lens will cover the image area. That means a FF lens might only cover a 4/3 or APS-C sensor. Since only a simple lens is used, the image quality may suffer.

The adapter takes care of the increased flange distance,

 

Does it? I need to read up on my optics, but the only speed boosters I've seen are for cameras with short flange distances. I'll believe you if you tell me they're effectively retrofocal (moving the rear nodal point farther from the sensor) elements, though - but I'd have expected them to appear for APS-C DSLRs by now if that were the case.

 

but it only works if the image circle of the lens will cover the image area. That means a FF lens might only cover a 4/3 or APS-C sensor.

 

That rather suggests there's no reason not to provide one for a DX DSLR, for which FX lenses are available, doesn't it? I've not found time to learn as much about lens design as I'd like, but I assumed there was a good reason nobody had made one for the F mount. Given that Nikon once produced an electronic camera with a focal reducer in it (for a tiny sensor) attached to the F mount, I'd have thought they'd have offered such a thing for the F mount in the days before they had an FX sensor if it were doable.

 

Since only a simple lens is used, the image quality may suffer.

 

I thought they were fairly multi-element, but there's certainly a limitation to the available optical corrections. On the other hand, those producing these things have tended to point out that the output of the lens is effectively shrunk relative to the sensor. In other words, optical aberrations from the original lens, near the middle of the image, tend to be less visible - it effectively increases quality (in the same way that a full-frame sensor with the same pixel count as a smaller one is less sensitive to optical aberrations just because its pixel density is lower, except not quite as good because of the additional optics). On the other hand, you're now seeing the edges of the imaging circle, which were previously beyond the limits of the crop-sensor image - so you're seeing the same worse corners that a full-frame sensor of the same resolution would tend to see. You win some, you lose some.