[alma-config] Re: Keto's message

[Bryan Butler]

stephane wrote:

> 
> 1) The spiral array must 2 times larger than the ring to achieve same
>    angular resolution
>         True: but so what ? What we should compare is the brightness
>               sensitivity at a given angular resolution, not the apparent 
>               size of the array (i.e. the maximum baseline)
> 

to which i reply:

this would be fine if we were talking about putting the array in a place
which had unlimited real estate - a very large flat plain, for instance.
this, however, is definitely not the case, and we are presented with some
very real topographic obstacles.  

so, we can ask the question: 

   given a fixed physical size limit, what flavor of array would you design then?

well, if you want the full resolution afforded by that fixed physical
size, then you would end up with a design like the rings/donuts.  if, 
however, you are willing to live with a resolution which is only half of
that achievable from that maximum size, then you might likely end up with
something somewhat more centrally condensed (like the zoom spiral).

now, if you can come up with a ring/donut which has nearly as good an imaging
capability as the more condensed spiral, and that has twice the resolution,
which would you choose?

	-bryan