Not sure, I'm new to futzing with dosbox conf files.

I was reasonably happy setting the aspect=true in the [render] section of the dosbox_st25.conf file. but I would prefer to have it just full screen with double the res with black borders all around.

(I have a 1680x1050 monitor)

Maybe you have to edit you conf-file manually. The following parameters are important:

[sdl]
fullresolution=0x0
output=opengl

[render]
apsect=true
scaler=none

If your graphic card doesn't know to fill 640x480 with additional information to the left and right for it to look correct on a 16:9, 16:10 or 5:4 display it will look stretched, no matter the "aspect=true" setting. With both Nvidia and AMD graphics cards there's a GPU scaling setting, that you can set up so the GPU scales the incoming resolution to the native resolution of your display using the correct aspect ratio.

Adding the

fullresolution=0x0

line Tomy mentioned together with the

aspect=true

line, makes Dosbox do this by itself. The 0x0 tells Dosbox to output fullscreen to the resolution of your desktop while the aspect=true makes dosbox add the correct black borders. Personally, I prefer the correct resolution of my monitors (using the 0x0 line in the .conf file) to the rather blurred results you get by using GPU scaling but you can't argue about taste. Try what you like most. Additionally, I like using a CRT-shader that comes with a Dosbox SVN build that makes the output look close to the real thing.

[sdl]
fullresolution=1680x1050
output=opengl

[render]
apsect=true
scaler=normal3x

This is what worked for me:

[sdl]
fullresolution=[your native resolution]
output=overlay

[render]
aspect=true
scaler=normal3x

NB: Setting 'output' to 'overlay' is really crucial, otherwise it won't scale properly.

How do I edit any of this?

I used the DOSBox Configuration tool and set it to my screen resolution, overlay and keep aspect ratio, but that gives me small resolution with giant black borders. I tried editing the dosbox_st25.conf fire in the ST25 folder with your settings and saved it in notepad. I then used the Launch Star Trek shortcut. This still gives me whatever I put into the Dosbox Configuration tool, and anything I manually put into the dosbox_st25.conf gets ignored.

I'd like a fullscreen game with correct aspect ratio and not a totally blurred blown up resolution.

"Personally, I prefer the correct resolution of my monitors (using the 0x0 line in the .conf file) to the rather blurred results you get by using GPU scaling but you can't argue about taste. Try what you like most. Additionally, I like using a CRT-shader that comes with a Dosbox SVN build that makes the output look close to the real thing."

yeah I guess that's what I'm looking for.

Try output=direct3d

aspect=true