How come a wideconverter doesn't exist?

It would not be cost effective to attach a front and back element on an already made lens.

>>3000720
google "speedbooster"

>>3000720
Because the image isn't there.

a tc just enlarges the centre of the image circle, if you want a wide angle converter it has to go on the front of the lens. These are available, but unless it's one custom designed from the ground up (as with the 20mm adapter for the sony 28mm f2 lens) they give shite image quality and are larger than a prime lens.

>>3000728
For the reasons I've stated above, speedboosteers only work with full frame lenses on crop sensors, and again, image quality massively suffers.

>>3000731
>>3000720
I've seen wide-angle converters which go on the front of lenses but never used them personally. Also image quality difference with a good quality speedbooster is relatively negligible, especially when you consider the extra stop and magnification you get.

>>3000720
fujifilm x100 wide converter.
sony e mount wide and fisheye converter for 16mm and 28mm fe.
ching chong wide converter.
it exist.

>>3000839
But those you put them on the front of the lenses.

>>3000728
That's what I was looking for.
But they don't make them the same way as teleconverters. There is not a single one for the same mount in-out.

>>3000953
> There is not a single one for the same mount in-out.
Well yea, they physically occupy the space difference in flange focal length between the camera system where they are used and the camera system they're adapting+focusing on a different size sensor.

>>3000956
But then how is a teleconverter possible?

>>3001020
In the case of the TC they kinda grab a centered section of the image, enlarge it in the lens, and project it out ~the same way as it just exited from before the TC, I guess?

Also, just to show it's simple "information-wise": You can crop an image in post, too, right? It's virtually the same thing but done in software rather than with hardware.

>>3001024
Then why can't the oposite be done by using a FF lens on a APS-C body with the same mount.

It is the same thing as a TC with a different ratio.

>>3001024
PS: Not saying at all that the thing you envision is not feasible at all.

But it might be much bulkier and less economically viable to have a same-system focal reducer.

And then why would people STILL use it rather than just plain old FF...?

>>3001028
No because the image isn't there in the first place to be made wider. They could put a front element on the lens like those fisheyes you put in your phone but it has to be designed to do it beforehand to not lose image quality.