On 6/3/2018 7:42 AM, Paul Carmichael wrote:
On 03/06/18 06:01, android wrote:
On Sat, 02 Jun 2018 10:01:22 +0200, Paul Carmichael
wrote in :

On 01/06/18 19:09, android wrote:
On Fri, 01 Jun 2018 18:33:36 +0200, Paul Carmichael
wrote in :

On 01/06/18 17:39, android wrote:
On Fri, 01 Jun 2018 11:30:25 -0400, nospam
wrote in lid:

In article , android
wrote:

Why does my macro lens (Tamron SP90) open up to 2.5?

Does it ? as it seems to state f2.8 on the web.

It could be that the firmware of the camera has access to the lense
T value in its database. PC uses a fairly modern EOS 6D mark II,
IIRC. There is according to DxO Mark two different Tammies 90SP one
T/3.0 and the other, newer T/3.3. The latter would be more like 2.5
rather than 2.8 if the former is used for reference... HTH!

or it could actually be f/2.5
http://www.adaptall-2.com/lenses/52B.html

Sure. But that would not be reported from lense to camera.


I chipped the adaptall. So yes, it is.

Then you would need to program the chip to report that that you want it
to report...


Well obviously. And knowing that the lens is 2.5-22, that's what I
programmed it as.

You were kind enough to post a link to a picture with the full exif, and
it does not seem to be programmed at all:

I don't get your point. Do you know how these chips work? The chip tells
the camera that it's a 90mm lens. I have to tell the camera the aperture
setting. It won't let me go below 2.5 or over 22 (I "programmed" the
chip to know it's a 90mm lens with aperture between 2.5 and 22). What I
tell the camera is what's reported in the exif. Obviously the chip can't
know what I've set the aperture to. Also, the chip enables focus
confirmation. They are generally sold as "focus confirmation chips".

Exif:

Â*Max Aperture Value - 2.5


Could something similar to this be your problem
https://www.dpreview.com/forums/thread/2248343

--
PeterN