Finderscopes

I have a Syntafinder 6X30. it has an aperture stop, so I would estimate it to a 10-15mm. Why is this so, I mean the 30mm lens is there, why not make use of it`s full aperture.
Had a closer look at my 8X50mm finder (Japan) which sits on my Cave 8" from -73. Same thing there; aperture stop so I think the finder is working at 30mm!
Has anyone out there an explenation?
Clear Skies,
Magnus

It's a baffle, it sits downstream and hopefully doesn't cut the light cone.

Dmitri

A decent finder (or refractor of any kind) will have one or more baffles that get smaller as they get closer to the eyepiece. These aren't aperture stops: they are just outside the light cone and prevent stray light from entering the eyepiece.

An aperture stop like you sometimes see on really cheap scopes is right up against the objective lens. It really is there to stop down the lens, to make up for lousy optics, and to artifically increase the f-ratio so that the eyepiece specs aren't as stringent.

Tim Iafolla