Data sheet: Tamron Auto 28 mm f/2.8 (adapt-a-matic)

Pekka Buttler, 07/2025

Specifications

The table below summarises the lens’ key specifications (measurements based on pictured sample with Canon FD adapter):

Brand:	Tamron	Lens name	Auto 1:2.8 f=28mm
Focal length(s) 1	28 mm	Angle-of-view 2	75°
Maximum Aperture	f/2.8	In Production	1972-73
Lens mounts (native)	Tamron Adapt-a-matic	Other lens mounts	See Adapt-a-matic article
Length 3	56,7 mm	Diameter 4	67,5 mm
Filter ring diameter	58 mm	Weight	280 grams
Lens element count	7	Lens group count	7
Aperture blades (S/R/C) 5	5 S	Focus throw	180 °
Minimum focusing distance (measured)	24 cms	Maximum magnification (measured)	1:5,5
Has manual aperture ring	YES	Has manual focus ring	YES
Aperture mechanism type	Automatic	Aperture click stops (on preset ring) 6	2.8•4•5.6•8•11–16

Further notes:
• This is a wide-angle lens manufactured for the Tamron Adapt-a-matic mount.

Versions

There are at least four different versions of the Auto Tamron 28 mm f/2.8 with the adapt-a-matic mount:
– versions 1 and 2 are significantly longer (59 mm or more, including adapter ring) and have a 62 mm filter thread while versions 3 and 4 are shorter (58 mm or shorter, including adapter ring) and have a 58 mm filter ring.
– Versions 1 through 4 all feature a 7 elements in 7 groups design, but apparently the lens’ optics was redesigned between versions 2 and 3.
– Version 1 is the only one to feature a metal focus ring, version 4 is the only one to have detents on the aperture ring to enable aperture ring coupling (which was however never implemented on the adapt-a-matic mount).

Adapting

Given that this lens uses an intermediate mount, there are several ways to go, depending on what your intention is

To film SLRs or dSLRs?
You’re in luck, because there used to be Adapt-a-matic adapters made for pretty much every mainstream SLR system available before the mid-70s, (including at least⁷: Canon FD, Exakta, Konica AR, M42, Minolta SR, Miranda, Nikon F, Olympus OM, Pentax K, Petri FT). What you need to do is head to your favourite online classifieds platform and procure an adapter (adapters for dSLR mounts are still available new).

To Mirrorless
Again, not a challenge. If you do not yet have a Adapt-a-matic adapter to an SLR mount, you can buy any combination of an Adapt-a-matic to SLR and SLR to mirrorless adapter.

Footnotes

1. Focal length is (unless stated otherwise) given in absolute terms, and not in Full-frame equivalent. For an understanding of whether the lens is wide/tele, see ‘Angle-of-view’. ↩︎
2. Picture angle is given in degrees and concerns the diagonal picture angle. Rule of thumb:
   > 90 ° ==> Ultra-wide-angle
   70–90 ° ==> Wide-angle
   50–70 ° ==> Moderate wide-angle
   40–50 ° ==> ‘Standard’ or ‘normal’ lens
   20–40 ° ==> Short tele lens
   10-20 ° ==> Tele lens
   5-10 ° ==> Long tele lens
   < 5 ° ==> Ultra-tele lens ↩︎
3. Length is given from the mount flange to the front of lens at infinity. ↩︎
4. Diameter excludes protrusions such as rabbit ears or stop-down levers. ↩︎
5. S=straight; R=rounded; C=(almost)circular at all apertures. ↩︎
6. Numbers equal aperture values on aperture ring; • intermediate click; – no intermediate click. ↩︎
7. This list will only contain adapters that we at JAPB have witnessed.  ↩︎