frame width and focal length, looks far or close, please help

function

Had asked a similar question 2 years ago, got some answers, and I thought I understood it. But no, recently I found I didn't fully understand.

Below picture was got from here or somewhere else, I tried many times but can not achieve the Background 'looks far or looks close' effect.

My problem is, in DAZ Camera settings, the default frame width is 36mm and focal length is 65mm, if enlarge them in Same ratio, say 360mm and 650mm, or reduce them to 3.6mm and 6.5mm, this can keep the figure in same size, then I got the Same render result (100% same picture), no matter open or close the Depth of Field, the DOF only affect blur, so I can not find a way to get the 'far, close' effect.

How to get below picture's background looks far or looks close effect with a same size people? Please help.

kpr

Setup scene and lights with figure visible (make sure you have no background in "Environment and Scene tabs")
Do a render <-- Your "original"

Hide "scene"
Do a render of just the figure (1)

Hide figure & Unhide Scene
Move the "scene" (set) closer or further away
Do a render of just the scene (2)
Move the "scene" (set) closer or further away
Do a render (3)
Move the "scene" (set) closer or further away
Do a render (4)

Combine (1) + (2) in your image editor (Photoshop / gimp etc)
Combine (1) + (3) in your image editor (Photoshop / gimp etc)
Combine (1) + (4) in your image editor (Photoshop / gimp etc)

Place The-Orignal plus the 3 combines on one canvas in your image editor (Photoshop / gimp etc)

You'll get what you're after

... at least, that's what it looks like has been done on the image you attached?

felis

You should only change one parameter. For a normal photographer you would change focal length.

But when you change focal lenght you will also have to change the distance to the character, so you will have to move the camara to maintain character size. But be aware of with a different focal length the character will also change proportions. If they are posing rather flat, it will be less obvious, than if the pose is dynamic.

Padone

You use lens compression, that is, as Felis said you change the focal length (or "zoom") then the distance from the subject. There may be some formula to tell you how to exactly change the distance to maintain the same size, I guess if you double the zoom then you also double the distance ? Or you can just eyeball.

https://www.iphotography.com/blog/what-is-lens-compression-in-photography/

function

Yes, I got it. Thanks @felis, thanks @Padone and @kpr .

My mistake is I didn't know it needs to move the camera, so I just adjusted the camera parameters within the same camera position.

Now when I moving the camera, that picture's effect appears, but, totally contradict to that picture, the lower value of frame width (say 24mm) makes the picture more flat, and bigger value makes the background far away, anyway, it works now.