I want to reproduce the 35mm format in Photoshop. How do I set the image size for this affect?

Answer 1

A 35 mm slide measures 35 mm x 23.3 mm in the mount. Crop to some multiple of that and there you go.

In inches, this would be 1.378" x 0.917", so a multiple would be about 10" x 6.65". I used to get "full format" prints and they were pretty close to 12" x 8". The 6" x 4" is the closest commonly available print that will give the full format of a 35 mm negative.

Answer 2

35mm was a measure of the frame size on the film for those cameras. The lenses were then engineered to deliver an image the right size to fit the 35mm frame. After developing, the negative could be used to make larger or smaller prints.

I do not think there is a particular image size that would correspond to 35mm. There are various opinions on what digital resolution corresponds to 35mm negatives. (I have seen opinions ranging from 12MP to 20MP.)

In any case, resampling a smaller digital image to a higher resolution will not give you what you want. The resampling process just creates new, additional pixels based on the characteristics of surrounding pixels. If you increase resolution significantly, the images just gets fuzzy with blurred edges and colors. Whatever 35mm images have that you like, it comes directly out of the camera.

The closest thing I can think of is to get a d-SLR camera with a "full frame" sensor (same physical size as a 35mm frame), and resolution 12MP or greater.

Good Luck