If I put a lens in front of a camera can I take picture of the virtual image formed by the lens without having the lens projecting an image on a ground glass?
Intriguing question! Thinking back to dimly-recalled school physics lessons, I would say yes. Presumably you would need to use an SLR camera to view and focus the virtual image ?
Ah, yes, "aerial" is the correct term. My physics lessons were too long ago ! (IIRC, a similar situation occurs in the optics of a microscope, where the eyepiece produces an aerial image from the objective lens, so that the eye can focus it (sort of a "photograph" by the eye....) ? )
I think that to focus an aerial image there's a line or cross hair that's needed to focus your eye.
If your remove the focus aid can you still focus on an image at the same distance?
I certainly don't know but have my suspicions...............
An aerial image is a real image formed by rays that converge to a point "in the air" at the focal point of a lens or mirror. If you focus a view camera and take away the ground glass the image is still there as an aerial image. A virtual image is formed by diverging rays that appear to come from a point, like the image you see in a garden gazing ball. You can see and photograph both.
Somewhat on a tangent: the Polaroid SX-70 (SLR 680, 690) is a SLR camera where the image you see in the viewfinder is an aerial image: there is no groundglass as with other SLRs.
Well, if you think about what the image really is, it certainly seems possible. It is really just a bunch of photons that are aligned in a specific way to make the image. If you can direct those photos to your film, while keeping them focused, then you should be able to capture an identical image. Exposure time may be tricky, but you could certainly experiment. Of course, a flash would not work since there is nothing to illuminate.
And if you want to inspect the image without having to photograph it, you can use a loupe to inspect it.
The only problem working with the aerial image like this is that you will only see (or photograph) a small area near the center of the image. If you stop down the lens, this area will get really small. This issue can be overcome by placing another lens, called a "field" lens, near the image plane. This field lens must have a diameter at least as large as the image you want to photograph, and have a carefully-selected focal length. The general idea is that the field lens captures light rays near the outer parts of the image that would have completely missed the second lens, and bends them back towards it.