Hi all,

today at 14:30 we had a meeting about the ADC, here in La Silla, with WEC, JAL, and AGI. I'm preparing the minutes.

However, a couple of points of the Fiber Head design were touched as well, so I'll comment on these right away.

1. Alignment of the ferule inside the hole.
If you take a look at WEC drawing with the dimensions (the one with
the wrong 0.130 mm hole), there is a horizontal line that bears two
numbers, 2.35 and 2.50 mm. The first number is the external diameter
of the ferule, the second is the internal diameter of the hole. The
point is, the difference between the two is so small that it turns
out as a single line in the drawing. WEC could make the line thicker,
but in any case, the 0.15 mm space should allow the horizontal
alignment of the rod lens to the sky hole (see also attached fig)

2. The problem of vignetting inside the sky hole tunnel. AGI
reconsidered it, and realized that, although the situation was the
same at the E152, the f/ratio there was f/11, while here we are at
f/8, so the problem is more serious. AGI will come up with some
numbers, but the idea is that there are two effects: 1) for seeing
ca. 1.5 and above, indeed we are going to lose light. 2) for better
seeings, the light loss might be not dramatic, but the marginal rays
are going to graze on the tunnel walls and be reflected back into the
fiber. So after some discussion we came up with this idea: use a
'fresa' (don't know the English word, sorry), to remove part of the
material below the sky hole. The smallest tool has a diameter of
0.5mm, and that's perfect to the job we want to do. The idea is to
operate it manually and with a loupe, until ca. half of the tunnel
lenght is worked out. That looks like a good approximation to a
conical surface. See the second attached figure for having some idea.

--- Ivo

`Dear John,In my view is not that the time issue has become critical now, I thinkthat now we are becoming aware about the multiple details involved inthe practical realization. On the mechanical side the first work estimation was 5 days in 2D and 8days in 3D. After some design work and interactions with AGI an myselfWEC realized that the design time is at least 24 days and he said thathe will need to machine the parts together with the person doing the jobin the machine itself. It is hard to review a design were we cannot evenclearly specify the machining of the parts.On the optical side the first work estimation stated that the opticaldesign was so simple that it was almost nothing, just order the prismsand mount them. This was 2 days maximum including the assembly of theunit. After some design work AGI realized that it is necessary to usecurved prisms due to the in/out function, otherwise we will need tore-focus the instrument every time the ADC is moved in/out. It turnedout that the in/out function is necessary because there is no space forthe calibration mirror and the ADC simultaneously. On the electronicside this requires some hardware interlock to prevent both functions goin at the same time. After AGI found that it is necessary, for complyingwith the requirements, to use the optics of the ADC for correcting thespherical aberration of the telescope and in turn we need a test nightfor characterizing the optics of the telescope and quantifying theactual telescope's aberrations. Finally it also appears to be necessarysome means of adjusting the ADC unit position to bring it in focus.According to WEC there is almost no means to provide the unit with anadjusting mechanism due to the small space available. According to AGIthe adjustment range should be "around" one millimeter...Due to the above mentioned we are still far from a final ADC design, andtogether with the fact that WEC is leaving for holidays between August27 and October 6 and most likely AGI will be very busy with the newfibre head I don't see realistic that we could finish with the PDR andFDR at least until the end of October.SaludosJaime`