[Shiraz (Ray)]

Interesting info Robert - thanks for posting.

I don't think that amateurs are anywhere near in this league - we cannot do better than this survey, except to maybe provide a little bit of variable quality data from outside of the VPHAS+ region.

To illustrate the problem for amateurs, a well heeled one may have a 0.5m scope, so will collect about 1/25 times as many photons as the 2.6m scope. Using the biggest affordable high QE CCD, the amateur system will cover about 1/10 as much sky as the 268mpixel VST in each exposure. So, allowing for different sampling, QE and the overlap problem of the VST array, the amateur will need to image for maybe 100 times as long as the VST to cover a chosen patch of sky to the same depth and at lower resolution. VST is going to take about 1000 hours to cover the limited survey region, so the amateur would take maybe 100,000 hours to do the same job. Big survey scopes have huge exposure time advantages and can do things that are totally out of the reach of amateur systems.

I wouldn't be concerned that the Ha exposures are only 2 minutes long - the VST gets to better than mag20 at 10sigma in this time, so the survey will be pretty deep. I guess that the depth that can be obtained must involve a tradeoff between sensitivity on dim targets and total loss of data on brighter objects as the sensor saturates - in this case apparently at about mag14. The resolution will be seeing limited at about 1 arcsec (better than Australian conditions) and all data will be calibrated to 0.05mag and 0.1arcsec, which is much better than amateur standards. Looking forward to seeing results, but of course there will be 11TB of data to wade through.

Maybe there is a good case for an additional low resolution amateur survey of the gaseous regions beyond VPHAS+ or follow-up deep imaging of regions of interest. These activities could be carried out by coordinating and combining the resources of a number of amateurs so that the regions are covered efficiently at a consistent resolution, linearity and depth. Not sure how one would go about coordinating amateurs though, we seem to be a bit of a disparate bunch with widely varying equipment, opinions and egos.

Regards Ray