I often make HDR images by exporting a bracket from lightroom into photoshop via right click>merge to HDR in photoshop. When the dialog comes up it is always a very low resolution preview. When I go to zoom in (cmd +) the resolution remains the same and I am zooming in on a pixelated image and the zoom is very limited. I am working from D3s files so there is plenty of resolution but it just doesn't show up in the preview. Is this simply the way it works or is there a way I can get a higher resolution preview. I'm not worried about rendering times either as I'm on a 8 core with 16gb or ram.
not sure if this is entirely what you want, but there are options in adjusting the preview for a 32bit HDR image. with a 32 bit image you can store the entire dynamic range of the HDR image:
Option for adjusting the preview image for viewing 32‑bits-per-channel high dynamic range (HDR) images on your computer monitor. The slider is available only when the document window displays an HDR image."
hopefully this helps somewhat-
This is "simply the way it works" and there is no way to get a higher resolution preview. I don't remember the exact numbers, but I believe all large images are reduced so that their long edge is 1024 when working in HDR. Once the file has been rendered by clicking OK in the HDR window, your final file is produced using the full resolution version. But this was done due to memory issues.