I think I see what's going on. I'm using a full resolution top/bottom stereoscopic format EXR with the project set to the single eye resolution, not the entire double height resolution top/bottom. There must be a scaling up going on, then scaling back down or something like that. Because I see it also when loading and rendering TIFFs. So I think my workaround is to split the top/bottom EXRs first before loading into Vegas, because the top/bottom isn't staying 1:1.

I was about to say something similar. When importing still images into Vegas, one must manually set the project dimensions to exactly match the image, otherwise blurring will occur. Sorry, I cant help with your 3d project bc I have nothing to test.

There may be a workaround; if you can provide an original exr sample to test.

I did download a high resolution EXR image and compared it to a Vegas screen capture at source / project resolution. There is a very slight loss of detail in Vegas capture, which further testing in Photoshop revealed to be dither noise. Unfortunately, very little you can do about that. EXR on top, Vegas PNG capture on bottom.

Here's a jpg link and a raw EXR top/bottom for those who want to try. Remember, first set your project into stereoscopic "top/bottom (full)" mode, then you can try rendering a frame both in the 1080 then 2160 height resolution.

Your links are being blocked here. We suggest uploading to Drive or Dropbox, thanks.

New link to Google Drive Vegas folder HERE.

OK...I remember running to this before & put together an example.

When you set up a 3D project your project settings should be the same as the individual left or right image dimensions. When you render it, the dimensions should be the size of the combined pair---a square image if TBF.

If you render a top bottom full project using the individual image dimensions in the render settings then Vegas will adjust the display aspect ratio so it displays properly, but with a loss of resolution.

Project settings for my example:

Media parameters for the still image i used:

Render settings and media info, rendering using the individual image dimensions:

Render settings and media info, rendering using top/bottom full dimensions:


In other words...if you render a top bottom full image using the individual image dimensions you get a top/bottom half image and the display aspect ratio is adjusted.

I hope this is what you are noticing.

I'm glad you know what you're doing -- the double height preview was driving me crazy!

Stereoscopic video is a dead format because you can't find proper display (and its hardware/graphiccard driver) anymore for watching. 
OK, this aside. 

The industrial standard 3D-video has always 2streams in the container. 
And this to the side, too. 

The none standard 3D-video canbe full or half of sidebyside/topandbottom, depending on which one your 3D-monitor can display. 

Assuming you have a 3D-monitor that can display full topandbottom as your 2nd monitor. 
And the main one is just normal for running VEGAS, your project must set firstly as the following to arrange source materials. 

There's no internal scaling issue with any kind stereoscopic material. But there're 4 kind of them you should know: 
1, 
clip with 2streams can direct go to timeline. 

2, 
clip with 2 separate files must be paired  in mediapool firstly then go to timeline. 

3+4, 
clips in full or half of the SideBySide and TopAndBottom go direct to timeline, but must be adjusted accordingly.

After the Arrangement you can edit them as you like.

The finished editing can be estimated by change your project and watch in the 2nd monitor.

The last, rendertemplate:

LOL. I got Vegas specifically to edit 3D, FWIW.

You can change the preview mode. I actually downloaded your image to use as an example, but displayed it in difference mode and didn't see any 3D differences so used one of my 3D 360 VR images.

I repeated the experiment using Carbo3D's jpg image. (Vegas can't read the other file directly, AFAIK.)

The image is 1970x2160 pixels...not sure why it isn't 1920, but I used it as is.

Project settings: Media properties:

Case A: Rendered at 1970x1080:

Render settings: Media info: Resulting video:

Case B: Rendered at 1970x2160:

Render settings: Media info: Resulting video:

I repeated the experiment using Carbo3D's jpg image. (Vegas can't read the other file directly, AFAIK.)

The image is 1970x2160 pixels...not sure why it isn't 1920, but I used it as is.

Quick tip for importing EXRs: change the Import Media drop down to "All Files" instead of the default "All Project and Media Files". Then you'll see the EXRs show up to choose.

The odd size 1970 will ultimately allow me to crop down to the delivered 1920; I have the renders oversized on the horizontal so I can readjust convergence and still have pixels to work with.😎

I downloaded your sample T/B renders and they do indeed have the same resolution softness. So at this point I will take the extra step to pre-split the raw T/B frames into individual L/R frames.

BTW, this is for a stereoscopic theme park project opening in the next couple of months; for simplicity the VFX company is delivering as full-res stereo T/B EXRs. The imagery at the venue is being projected on several large IMAX-sized screens so there is no room for any soft focus issues...

I was unable to download the examples I posted above to double check, but when I play them above they do look pretty much the same. I'm guessing they are being processed when uploaded so may not be a good comparison.

Let me share one more case and draw some conclusions, then I'll upload them to a google drive if you still want me to.

There several tabs to the render settings menu: Video, Audio, System, and Project. In my examples above I varied the image size settings in the Video tab and let the rest default. Specifically, in the Project tab I let the Stereoscopic 3D Mode: to Use Project Setting.



For my third case, case C, I explicitly render the image as a top/bottom half file:

Here are the Video and Project settings and resulting video;



Now, let's put all three videos back into Vegas:

Project settings

Media properties for each of the clips, A, B, and C, respectively:

 

Render settings and resulting video

Note how much smaller clip A ends up: I believe that Vegas is shrinking the video to fit the entire over/under image into the frame size (1080) before rendering AND adds the 2:1 (1.85:1, in this case) display aspect ratio adjustment. The result is the image is shrunk by half in both the x and y directions!!!! If so, this appears to be a bug, IMHO. I believe someone recently suggested correcting this in the pan/crop tool, but that still leaves you with a top/bottom half file (like case C).

The second clip, clip B, fills the 1970x2160 frame and has a 1:1 (0;912 in this case) display aspect ratio which is full resolution!

The third clip, clip C, fills the 1970x1080 frame it was rendered into and also has a 0.912 display aspect ratio so, as expected, it has half the vertical resolution.

You can render the left and right views separately and combine them later with FFMPEG---I have many times and probably have an FFMPEG input to share---but that won't improve the resolution over simply spedifying the TOTAL combined image size in the render settings as I have done in the B case.