Mosaic Fail and hotspot woes

[Notty]

Hello everyone, I was hoping for some advice. I dug the equipment out yestarday for the first serious attempt at a full disk using my TAL100 PST Stage 1 which I obtained late season last year, and took what I thought looked on the PC to be some excellent captures.  I took about 30 sets of 1000 to ensure I captured everything (and I still missed a small chunk doh), gave it a small sharpen in Paint.net and fed it into the Autostitch, but I couldn't get more than a half disk.  So I went to first principles and tried to work out if it was a problem with my manipulation of the Autostitch settings, or whether there really was an issue with the images.  I manually pasted them next to each other to look, and from what I can see the hotspot is causing huge gradients to the bottom right edge such that the edges are all different contrasts.  I tried playing around in curves to even it out but had no success.  I know gain compensation can help but not it seems this much.  I see the lastest version of autostitch seems to have simplified the settings, which I wonder is taking away some of the flexibility.  Do you think the shade gradient is causing the problems?

My question, assuming I haven't got a rubbish PST to start with that makes that hotspot unmanageable, how do you all deal with this?  Do you accept it and do something clever post processing or should I be looking at tuning it differently?  At the moment I tune for the maximum detail ie Ha contrast.  Presumably if I tune for a flatter contrast I will lose all the lovely detail.  Frustrating as the sun isn't going to shine not for another month where I live.

Any opinions very gratefully received.

[smerral]

Have you tried taking a flat by centring the disc and defocusing?

[Notty]

No I haven't... can you explain please?  

[smerral]

When I do my PST mosaics I always take a flat frame - it gets rid of the uneven illumination.  It can't entirely get rid of the sweet spot effect but it can go a long way towards it if you make sure you have plenty of overlap and can crop each image somewhat.  Centre the solar disc and defocus until the details vanish,  Then take a capture of 50 frames or so.  You can then use this in either registax or autostakkert to create a flat field which you can apply to your captures when stacking.

[Notty]

Very interesting, thanks for that. Through the TAL my magnification is quite high, and I only get something like 20% of the disc area. Do you think I would need to take one of these before each sub-capture I do?

[smerral]

No, one should be sufficient.