filming with K30, 50mm f1.7 + wide angle adaptor?

hello,
I am using my camera to film these days (some music covers), and it's really dark in the music studio. I've filmed with the K30 with the 50mm f1.7 at 800 ISO and the results are decent. The only problem is the 50mm on APS-C sensor is pretty zoomed in. So I am considering the cheap £20 wide angle adaptor (0.45x).
I don't mind the distortion at all, all i need is a wider angle without spending the £300 to get the 30mm f1.4.
So questions is:
- has one of you tried for video? (guessing it's not great for taking pictures but this is for video only)
- will the light entering the lens be the same? with 1.4x and 2x we lose stops, but with 0.45x will the lens stay a f1.7?
If you have any other techniques for filming in low light? I always see these amazing videos with no noise and haven't been able to get any close, above 800 ISO there is too much noise, maybe people do some post production noise reduction but i currently don't own a good video editing software.
thanks!

Bouncing ideas around:

What about an older manual lens, like a 28mm f2.8 or something?

Convert to black and white and call the noise film grain?!

Can you introduce more light into the studio?

Get a Vivitar 24 or 28mm f/2.0 (MF).

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thanks for your advice
my lens is already an old lens (50mm A f1.7), hmm i've already use the black and white trick previously.
i am already adding some extra light (led) but better to capture the real light otherwise it doesn't look as nice.
the 24mm/28mm vivitar arent easy to find nor cheap otherwise i would have gone for it.

Ideas #2

I mention the 2.8 model for that reason, I found one pretty cheap. I don't much like it, but for video work it could be good.

Most of the pro video setups have significant LED lighting on the rig. Seriously I was at one wedding where everyone was close to squinting when the camera first turned up in their face. However, the results were awesome so you can see why they would do it.

Video is an interesting one for me, in that (due to cost obviously), people make do with very basic editing software, akin to using Microsoft Pain for photo correction. Inside Adobe Premiere, for example, you can essentially do the same main corrections you'd see inside Lightroom. So if you have colour issues from LED lighting then say the Fast Colour Corrector tool will soon fix that.

here's a quick 4 minute tutorial link

From here you're starting to enter the realm where full frame, or mirrorless with focal reducers will start to help you also. Pentax obviously doesn't offer anything in this range unfortunately. Adding more light yourself seems the easiest option? Oh and also, ensure you are using a low frame rate, go for 24fps, as higher frame rates mean less exposure time per frame.

A really wide aperture does let a lot of light in, but it starts to create a really narrow depth of in focus field, which means focussing becomes critical and you have to do that in low light. Pentax doesn't offer any continual autofocus in video modes, so frankly you'd want to look at manual focus control lenses anyway. To help nail the focus you might look at rear screen loupe covers which magnify the rear screen and remove side lighting glare etc.

Hopefully some of the above is applicable/useful/interesting for you? Good luck and please share the results also

thanks for your comment.
I have the tammy 17-50 f2.8 so would use that instead of buying another lens - i never thought about the 24fps, that's a very good point. i actually dont know what setting i am using but i will check.
the focusing isnt so much of an issue because the camera is on a tripod, and i dont move in distance (playing the drums so sat down).
i will have to invest in a good software at some point...