Curious about Tamron adaptall 270-150mm (20A)

[seany65]

Some members may know that the tamron 20a is marked as having a maximum aperture of f3.5, but it is in reality f4. It says this on the blurb for that lens on the adaptall 2 website.

If this is true I'd like to know what aperture is the lens actually at when the ring is set to f4? I've looked carefully and I can just about see the iris blades come into view when moving from f3.5 to f4.

Any help would be much appreciated.

 

[randy stewart]

Tamron aperture

Tamron aperture

From your own description, it looks like f4.0 marked is probably f4.0 in fact. I have the highest regard for the Tamron SP lenses of this era, owning and still using a number or them, but this is one of Tamron's budget offering with nothing special to offer. My reaction was, "why care"?

 

[seany65]

I was just curious. As I said in the original post, according to what I've read the lens is not an f3.5 but actually an f4 that is marked as f3.5, so not only was I wondering what the f4 setting actually is, I'm also wondering if the f3.5 is nearer to that setting than what I've been led to believe.

Curiosity usually gets the better of me and makes me ask questions that others wouldn't.