What is the largest field of view achievable by a magnifying lens system when the observer is not peering through a peephole?

You just described a basic view camera. Light comes through the lens and is projected upon a glass freznal at the rear.

The angle of view is determined by the lens choice on the front.

This technology has been adapted to film and digital. When one is ready to actually take a picture, the glass freznal is replaced by a film back or digital back.

See some incredibly detailed images from the Gigapixel Project where an old view camera was given a full 8×10” digital chip. Click the images to see the incredible detail. These images are 2–6 gigabyte each.

@RealEyesRealizeRealLies I see! ok…so, easy enough I suppose. I wonder if there is a bigger display field then your basic camera. I will check it out, though.

I thought it might be good for a football game.

What you want is a camera obscura. You don’t even really need a lens as the first ones were designed around the pin-hole concept. It just depends upon how large you can get the freznel lens on the rear. There have been some absolutely huge ones made in the past. Some require an entire air hangar to be converted into a camera.

Oh… forgot to mention, the image seen on the freznel is always reversed and upside down. That’s one reason why single lens reflex (SLR) cameras were invented to shoot the light off a mirror and up through a three angle prism to reverse the image back to normal. But it’s still just glass and light.

@RealEyesRealizeRealLies That’s Fresnel lens. I pronounced it “frez-nell” myself for many years before learning the dude was French & it’s “fray-nell”. Anyhow I’m not sure a Fresnel can invert an image rather than simply magnify or minify it. Besides in lighthouses, they’re most often seen as stick-ons for the rear windows of buses and other large motor vehicles to give a wide-angle view.

Thanks for the correction. I’ve never had to actually spell the word out and it’s been a very very long time since I’ve even entertained these topics.

The reason the image is reversed and upside down is not because of the fresnel, it’s because of the lens inverting the light path. The fresnel is simply the medium which the light lands upon. It could be film or digital back, the lens still inverts the light.

The reason it doesn’t happen on the vehicle variety is because in that case, the fresnel and lens are combined into one substrate. It’s not a lens projecting upon a fresnel.