Data sheet: Tamron 300 mm f/5.6 BBAR MULTI C. (adaptall)

Pekka Buttler, 09/2026

Specifications

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

Brand:	Tamron	Lens name	1:5.6 f=300mm BBAR MULTI C.
Focal length(s) 1	300 mm	Angle-of-view 2	8°
Maximum Aperture	f/5.6	In Production	1976–79
Lens mounts (native)	Tamron Adaptall	Other lens mounts	See article on Adaptall
Length 3	161,5 mm (without adapter) 166,6 mm (with Pentax K adapter)	Diameter 4	66,7 mm
Filter ring diameter	58 mm	Weight	544 grams (without adapter) 606 grams (with Pentax K adapter)
Lens element count	4	Lens group count	4
Aperture blades (S/R/C) 5	9 S	Focus throw	180 °
Minimum focusing distance (measured)	238 cms	Maximum magnification (measured)	1:6,6
Has manual aperture ring	YES	Has manual focus ring	YES
Aperture mechanism type	Automatic	Aperture click stops (on preset ring) 6	5.6•8•11•16-22

Further notes:
• This lens was designed to use the Tamron Adaptall/Adaptall2 intermediate mount
• Tamron has always had its own coding scheme for lens designs. This coding scheme is extremely useful to discern between two (or more) lenses that have the same mainline specifications (focal length and maximum aperture). According to the Tamron coding scheme, this lens is “Model CT-300”.
• This lens replaced the previous Tamron 300mm f/5.6 that was made for the Adapt-a-matic mount.
• The focus ring is wide and grippy. The aperture ring is narrow but does have a rubber grip.
• Sadly – as with many lenses from this age of Tamron lenses – the rubber rings have swollen somewhat and are no longer a tight fit.
• When focusing the entire front of the lens (including the filter threads) rotates.

• The lens features a decent-sized pull-out lens hood.
• Next to the aperture ring there is a switch for choosing between manual and automatic aperture.

Versions

There seems to be only one variant of the Tamron Model CT-300.

Adapting

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

If you intend to adapt your Tamron Adaptall lens to a dSLR…

There are original Tamron Adaptall adapters to both Pentax K and Nikon F (Ai) available. These adapters allow you to use the tamron Adaptall lens as if it was a native (manual focus) lens (including aperture and aperture priority exposure automation). There are also modern adapters available from several adapter manufacturers, but – in general – these adapters are dumb adapters and do not allow aperture control.

If your dSLR is a Canon EF or Sony/Minolta A and Four thirds camera, you can get an aftermarket dumb adapter, but will have to manually control aperture.

To film SLRs?
You’re in luck, because there used to be Adaptall/Adaptall-2 adapters made for pretty much every mainstream SLR system available before the mid-70s, (including at least⁷: Canon FD*, Contax/Yashica*, Fujica X†, Konica AR*, M42 (several variants⁸), Mamiya Z°, Minolta SR*, Miranda°, Nikon F° (Pre-Ai and Ai), Olympus OM*, Pentax K (K° and A† versions), Praktica B†, Rollei QBM° and Topcon RE° (Exakta). 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).

Notes:
* Available both as Adaptall 1 and 2 (with different features)
° Available only as Adaptall 1
† Available only as Adaptall 2

To Mirrorless
If you already have a number of adapters from the typical SLR mounts to your mirrorless camera (e.g. Canon FD / M42 / Nikon F / Olympus OM / Pentax K …) your best choice is to either:

• get an original Tamron adapter from Adaptall to whatever your most favoured SLR era lens mount is or
• get a modern Tamron adapter to mirrorless adapter from one of the contemporary adapter manufacturers (K&F Concept seems to offer dumb adapters for Adaptall to most mirrorless mounts)

Of these, the earlier option is likely to be cheaper and the later less finicky.

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.  ↩︎
8. There were both adaptall adapters to vanilla M42 mounts as well as some of the M42 variants (such as Fujica M42, Mamiya M42, Praktica electronic M42). For details, see the JAPB article on the m42 mount.
   
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