OK, I might be having a "stupid" day, but here is what I am trying to figure out:

Is there a way to have an object in the scene (as in within the camera view), which would be invisible, yet cast a shadow onto other objects in the scene?

I know I can disable sadows for an object and I know I could have an object that is invisible, but catches all the shadows, but can I have an invisible oject that casts shadows only?

Thank you and sorry if this is something simple and obvious and I'm just missing it.

Yes, this is possible but it sets limitations on your render.

The one way I know how to do this is to take your object, apply a shader to it with 100% transparency and then in the top tier of the shader, select no light interactions when fully transparent.

Then, in you render options, uncheck the "light through transparency" option.

The object will be fully invisible but will cast a perfect shadow.

You are not the first person to ask this.  It seems to be a common need and this question shows up every once in a while.  What's frustrating is that I can't remember how to do it and have to figure it out again new each time!

However, I can figure it out faster as the years go by.  This is an old trick I figured out way way way back when we were still working with Raydream and transitioning to C.  I was using it for Halloween images.

Wow. Thank you! What an interesting round about way... It wouldn't have occured to me ever...

Unfortunately, this brings me back to the necessity to render my scene twice (since I have transparencies, which need to render properly as such.) Or is there another way around this too?

Another possible alternative: what is a best way to immitate the distant light while using something which has a limited distance range? The spots have an obvious dispercion point, at least within manageable distances. While the whole benefit of the distant light is the parallel direction of rays. Is there a way to fake it?

I was afraid you might have other transparencies That needed formal treatment, hence the limitations I mentioned.  I don't know a way around doing it twice and then combining later.

i also don't know of a way to fake the issue with the lighting you're talking about.  It MIT be something that could be managed by the specific scene you're working on.

Can you explain a little more (maybe).  I don't know if I can help but I'd give it a try.

Thank you again for your help.

Here is my current predicament: I have a rather unusual scene in mind, where only half of the environment seen through the camera is fully lit (as in daylight), while the other half is in the darkness.

I could do it by obscuring the light with something invisible, but the scene has some glass and water and other transparent things, so that doesn't help.

I could also try to limit the range of the lights I'm using, but the best way I know how to do daylight is through distant lights. I might need to go down this road, though.

I could also render it twice, but the scene is complex and my compositiing skills aren't the best. I was also pondering a possibility of a short animation, which with double renders is not going to be possible.

Could you simply put a large plane on one side behind the camera?  Does that mess up the shadows?

Unfortunately, that does not help, because the light is not straight on from behind the camera, but rather from the side. (All the shadows from he objects in the light should be leaning towards the dark side, so the light need to come from the side opposite the dark area.)

The only other thing I can think of (without seeing what you're doing) is to put a semi transparent plane into your camera view and render through it.

There's also those new fangled negative lights which can do some whacko neato things.

I will keep thinking.

Negative lights! I'm an idiot! I clean forgot about negative lights. Thank you so much! I will give it a try. I think if I have a strong negative light of the same colors as my positive ones it should cancel the lights out on the shaded part. I'll try to do it tonight or tomorrow night and see what happens. Thank you again.

Don't thank me yet.  I'd like to see if you can get it to work.  I've struggled a little bit with negative lights but they can be useful.