Image size to lens size

[Ralph]

Honestly, this is one of the hardest things for me to understand.
I will get to the point where I am totally lost.

Let's say I am after the aftermarket Sigma 100/400mm lens but then I see another lens close to the same number but
this other one is a big beautiful lens. This Is the hard part for me to get my head around and understand it.
Plus I think if you now look at some of these lens where they are under millimeter number like an 85mm lens.
One of the looks to be about the size I was talking about to start of with.

All this has done is made this older person think he has got no chance of understanding all of these lens lengths.
If you know of a good youtube thing that explains it to a dummy like me I would really appreciate it if you
point me to it. As reading it all isn't going to stick in for a while but watching and being told works better for me.

Thank you.

 

[scotty38]

Probably have a look round for "focal length comparison" or something like that as I'm sure you'll find loads that will help.

 

[Ralph]

Probably have a look round for "focal length comparison" or something like that as I'm sure you'll find loads that will help.

Thank you for the point in the right direction.

 

[Uncle Kevriano]

Que?

 

[UncleVanya]

Ignore the fact this is a Nikon link, using this you can see the effect of focal length. The body selection gives you full frame (fx), crop (dx), and 1" sensor (cx).

Nikon | Imaging Products | NIKKOR Lens Simulator