Chucker2000

Hi all.
I recently bought a new Tamron 90mm G2 f2.8 macro lens.
When set to Aperture Priority, my D850 sometimes does not go down to F2.8.
It can be wound down to say F4, but no lower.
I have tried other lenses to same settings and have no problem (for example using the 24-70 G2 I can set it to f2.8 no problem).
Has anyone experienced this type of thing with that lens?
I am stumped as to why I cannot get the maximum aperture out of this lens particularly when shooting in low light and close up.
Any thoughts would be appreciated.
Thank you.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

My guess is that you might be at or close to minimum focus distance and the lens is fully extended. If this is the case, it's perfectly normal.

amfoto1 Loc: San Jose, Calif. USA

I am not sure I know what lens you're talking about. There's no such thing as a Tamron 90mm "G2", that I can find. They have 15-30mm, 24-70mm, 70-200mm and 150-600mm "G2" lenses... but no 90mm.

AFAIK, there are currently two Tamron SP 90mm f/2.8 Macro lenses available in Nikon mount:

1. Tamron 90mm f/2.8 SP AF Di Macro that sells for around $449.
2. Tamron SP 90mm f/2.8 Di Macro 1:1 VC USD that costs about $649.

The difference between them is that the first is an older design that's not internal focusing (i.e., it extends longer as it's focused closer), doesn't have image stabilization and uses a slower micro motor focus drive. The second lens is a newer model with some optical tweaks in addition to being internal focusing, having "VC" image stabilization and using a faster ultrasonic type focus drive motor.

The first lens is model #272E (imprinted on the side of the lens). The second is designated model #F017 (not imprinted on the lens, AFAIK).

The non-internal focusing version of the lens will definitely change aperture as the lens is focused closer and the barrel extends. This is in part because of light fall off, as it has to travel farther through the lens.It also may be due to changing relationship between the physical aperture and the optical elements of the lens. As Gene51 said, it's fairly normal. A really extreme example of this occurs with the Canon MP-E 65mm Macro lens, which is a non-IF, manual focus 1:1 macro lens at its minimum and nearly doubles in length as it's focused to its maximum magnification. The smallest selectable aperture of that lens is f/16. But a chart in the user manual for it indicates that at max magnification... 5:1... that setting becomes an effective f/96!

The internal focusing version also might change effective aperture as the lens is focused closer, even though the barrel doesn't extend. I don't really know why this would be the case. I do know that IF lenses change effective focal length as they are focused closer, particularly 1:1 capable macro lenses due to their extremely close focusing ability.

Maybe the D850 is designed to reflect this change in effective aperture?

You might ask Tamron or see if there's any info about it on their websites.

The Tamron SP 90mm Macro lens has a long legacy... Counting both autofocus and manual focus, there were eight previous versions dating back to the 1980s.

Chucker2000

Thank you all.
It is the newer SP model.
When I attach the Tamron 24-70 G2 the Aperture priority, I can always set it to f2.8 and higher.
But when I attach the new 90mm SP it does not go down to f2.8, just now it went to f3, earlier it went down to f4 only. So it appears to be intermittent.
I have tried focussing close to minimum and also further at 1m and further again.
Still cannot get it to go down to f2.8.
Help?

Chucker2000

I contacted Tamron to ask about the issue and they replied as shown below.
I must accept what they say to be true unless someone can advise differently.
So it appears I don't really have a problem.
Thank you all for assisting.
(Please see below their reply)

Dear Charlie,
This is normal, with a macro lens the maximum aperture is (2.8) when the lens is focused at infinity as you focus closer the lens moves further from the sensor which spreads out the light and makes the image darker. The effect aperture is reduced even though the physical aperture has not changed, until at 1:1 you have lost 2 stops, this is known as bellows effect (The light that passes the lens is diluted to a bigger area),this is physics not a problem with the lens.

These 2 links will give you some additional information. https://www.cambridgeincolour.com/forums/thread1358.htm and
https://www.dpreview.com/forums/post/61281835.

Let me know if you require any further assistance.

Regards.
Nigel.

Manglesphoto Loc: 70 miles south of St.Louis

You just bought a fantastic and to me expensive camera, Why get a fantastic lens to match? Nikon has two great macros/micros, well they have more, but the 105 macro and the 200 macro to me are the best.

Don, the 2nd son Loc: Crowded Florida

Lens extension for minimum focus is equivalent to adding an extension tube, thus f/2.8 = f/4.0 wide open.

Howard5252 Loc: New York / Florida (now)

This is normal. I asked Nikon about it when I noticed it on my Nikon lens. It has to do with the actual amount of light that will get through the lens. I really cannot explain it properly but do not be concerned about it.

davesit Loc: Media, PA

This happens with Nikon macro lenses too, so have no worries. And for folks who disdain non-Nikon lenses, you should look at these new Tamron and Sigma lenses. They oftentimes equal and sometimes outperform Nikon lenses. I have the Nikon 60mm, 105mm, 200mm and the Tamron 90mm (F017) macro lenses. I find myself using the 90mm and 200mm the most.

JeffDavidson Loc: Originally Detroit Now Los Angeles

Shooting with the macro lens usually is affected by the distance. The same thing happens with Nikon macro lenses.

Grahame Loc: Fiji

Yes.