Conversion mp4-DNxHD-mp4 Files too large

Hi
I hope, I'm in the right forum for this question. I'm just starting my video editing career (well, not really ) and also thanks to this forum, I can do some nice color grading of my diving videos. I often use a cheap camera (and will likely get the next model soon), which only records in mp4/h.264. Then, with streamclip, I convert these files to DNxHD. As expected, the filesize explodes, no problem. Then some cutting and grading in resolve and finally, I convert these files back to mp4/h.264 with the same software. Now, my expectation was, that I would get similar file sizes, which is already a lot. However, the recorded video is around 100MB per minute, while the converted mp4 stands at around 800. Does anyone here have experience with the streamclip software? Or has a tip for any other free conversion software? I hope, it's just a wrong setting, but ultimately, it would be nice to go back to the small file size. Not only, but also, to be able to upload some vids to youtube.

Thanks in advance!

Edit: I'm really a beginner, so, I found in the mean time, that I can limit the bitrate for the conversion. This helped a lot and the quality seems to be similar. Now, I'm only at 300 MB instead of 100. I guess, the rest is knowing, how low I can go with these settings and finding out, what the "quality" button does.

Streamclip is a very good application that I have installed on all of my systems used for video capture and transcoding. It's a bit slow (although it's old, now) but I find it offers more control than - say - Handbrake. I recommend that you seek out a free plugin called "x264" and install it on your machine. When selecting H.264 encoding options you'll see it crop up in the menu. x264 is very good because it compresses files to as much as half the size with little effect on the quality. It's very good indeed.

Thank you so much! This is exactly what I was looking for. With this, I get close to the size of the original video.

Edit: Problems, problems, problems... There are only a few programms with a GUI, that can convert DNXHD to x264. Such as Handbrake. I'm on a windows machine... Well, handbrake gives an error with the source file (no valid source). Same for others, such as staxrip. I've been searching a lot, but didn't find any solution. So, right now, I'm still sitting on the large files. If I find out more, I'll write it here - for the next poor soul that googles the same problem.