[Brightcolours]

Actually it is not at all like a FF with a 35mm f2.  The exit elements are much larger than a 35mm f2 to accomidate the light transfer of a F1.4.

You do not understand lens design then. It is a 23mm lens, that is why the elements are larger for one. But also, compare a Canon 50mm f1.4 and a Sigma f1.4, they show things are more complicated than that.

 

About "light transfer".... You do agree that with both the 23mm on your APS-C and the 35mm on FF the sensors collect light from the same angle of view, right? Ok. Now calculate the aperture size for a 23mm f1.4 and a 35mm f2:

23 / 1.4 = 16.4mm, 35 / 2 = 17.5mm.

The 35mm f2 FF combo collects light from a slightly larger hole. The image gets formed with a bit more light.

Also I have shot with a Canon 35mm f2.  It is a crappy lens.

I have shot with the Canon 35mm f2 lens. It is not a crappy lens, it actually is quite a nice lens. And the new Canon 35mm f2 IS USM is a very good lens.

  A comparison to the 24mm f 1.4 is more akin. 

Of course it is not, a 24mm on FF gives a much wider view than a 23mm on APS-C.

I agree with Klaus this is apples to oranges. 

 

You are forgetting that although the bokeh might resemble that of an f2 lens,

You are mixing up bokeh with blur. The blur will be similar. Maybe the bokeh too, but bokeh is the character of blur, not the quantity.

in actual shooting conditions it allows the exposure control of a 1.4.  For street photography this often makes a huge difference.

You are not using equivalent ISO settings. f1.4 does not say how much light gets captured (a smaller sensor captures less light than a bigger sensor), it just describes the focal length/aperture ratio. Exposure also depends on exposure duration, and (which you are forgetting) signal amplification. On APS-C with smaller sensels on smaller sensors, the signal gets amplified more. If you use similar amplification (equivalent ISO settings) you get similar results, also for street photography.

So for instance, if you find it important to get similar exposures next to similar FOV and similar DOF, do the following.

On your X series APS-C camera with  your nice 23mm at f1.4, you for instance shoot with ISO 400. To get a similar image with similar exposure on my 6D, use a 35mm (23mm x 1.5) at f2 (f1.4 x 1.5). That makes for a similar FOV, and similar DOF. Now set an equivalent ISO for a similar amount of signal amplification: 400 x 1.5 x 1.5 = ISO 900. You can't really set ISO to 900, so choose between ISO 800 and ISO 1000 and you are close enough.

 

Now you do not only have an equivalent focal length with a similar FOV and an equivalent f-value with similar DOF, but you also have an equivalent ISO setting with similar amplification of the signal and similar noise (well, maybe not exactly the same noise, but then we restarting to compare different sensor technology and not lenses on different sensor formats, a whole different discussion).

 

Everything similar, All apples.