The globular cluster Terzan 6 was discovered by Terzan (1968)
with Schmidt plates obtained at the Haute-Provence Observatory.
The cluster is also known as
GCL B1747-3115, HP5, BH249 and ESO455-SC49.
The coordinates are
,
15' 44'', and it is located at
, 
.
By means of the bright giants method, Webbink (1985) estimated an horizontal
branch level of 
, and a reddening of E(B-V) = 1.46 from the
modified cosecant law, deriving a distance from
the Sun of d = 12.8 Kpc.
Using integrated near-infrared spectroscopy,
Armandroff & Zinn (1988) derived
[Fe/H] = -0.61 from CaII triplet lines, and E(B-V) = 2.93
from the interstellar
band at 8621 .
Fahlman et al. (1995) presented JHK photometry of Terzan 6,
deriving a reddening E(B-V) = 2.04, distance modulus
(m-M) = 20.53 and distance to the Sun 
kpc,
and they conclude that the metallicity would be similar to that of M71
([Fe/H] 
, Zinn & West, 1984).
The cluster structure is very concentrated, with
c = 2.50, and it presents
a post-core-collapse
morphology (Trager et al. 1995). An X-ray source is present
(Predehl et al. 1992).
In the present paper we analyse CMDs of Ter 6 in the V, I and Gunn z passbands. In Sect. 2 we describe the observations. In Sect. 3 we present the colour-magnitude diagrams. In Sect. 4 the cluster parameters are measured. The conclusions of this work are given in Sect. 5.