Weird question - this happen to anyone else?

[cornfedkiller]

I don't know how to explain this real well, but hopefully its good enough that if someone knows what I'm talking about, they can expand on it.. I asked Doug if he could explain why this happens, but he doesn't know what I'm talking about...

I have a 15-45x65mm spotting scope, and when I zoom the eyepiece in, once I get to about 35x, when I keep zooming, it doesnt seem to do much for the image. It seems like the field of view shrinks and maybe the "field" gets closer to me, but the actual object I'm looking at doesnt seem to get any larger, or it doesn't really show me any more.. if Im trying to read a road sign at 3/4 mile, once I hit a certain point of zoom, it doesnt seem like the letters on the sign get any larger or any easier to read.

Anyone experience this or have any idea what I'm saying?

 

[rhusby28]

As you go up in magnification the picture gets distorted. Your best picture will be somewhere between the bottom and backed down from the top of your highest magnification. So when judging animals at a very long distance it’s better to back down the magnification. For this reason is why some people buy fixed magnification rifle scopes.

 

[willfrye027]

There are probably some good technical answers to exactly why this happens. I bet the bird forum guys could spend hours talking about that.

Basically your ability to resolve details is limited by a lot of factors...glass quality and exit pupil size especially. If you had the same scope in an 80mm objective, this effect would be less/minimal. Same scope in a premium offering, less effect. My experience is that beyond an exit pupil of about 2mm (30x on a 60mm objective), you need high quality glass and coatings with a good sized objective lens or the image goes south quickly. I read somewhere this has to do with longitudinal chromatic aberration which can be corrected with fancy coatings and fluorite glass...but that’s going beyond my knowledge really.

Oh and atmospheric conditions are a huge factor too. If it’s hot you’re gonna have a tough time seeing much. Cold, clear, crisp day you can see what your scope is really capable of.

 

[sneaky]

Sounds like your eyepiece is screwed up. Is it a removable eyepiece? I could take mine off and see that the element was not moving as I adjusted it. This came after letting someone else use the scope. They'll never lay hands on any of my optics again btw.

Sent from my SM-G955U using Tapatalk

 

[kevlar88]

I think you did a fine job explaining whats happening. I've researched this before and if I remember correctly it was referred to as "tunneling".

 

[Brian Fahs]

Sounds like your eyepiece is screwed up. Is it a removable eyepiece? I could take mine off and see that the element was not moving as I adjusted it. This came after letting someone else use the scope. They'll never lay hands on any of my optics again btw.

Sent from my SM-G955U using Tapatalk

Good optics are like honey holes for hunting.
Better kept to yourself and not shared.

 

[cornfedkiller]

I think you did a fine job explaining whats happening. I've researched this before and if I remember correctly it was referred to as "tunneling".

I did some reading and even watched a couple videos on "tunneling" and I don't think that is what I'm seeing. I'll have to look again, but I don't believe I'm seeing increased black area around the outside of the image.