Issue with Photomerge in CS5

[rlriii13]

I was fiddling around with CS5's Photomerge operation yesterday and ran across an issue. In Lightroom 3, I selected 6 RAW files from my 60D and chose Photomerge from the menu. CS5 opened up and I proceeded to kick off the operation. Once Photomerge was finished, I was left with something I didn't want, especially with the blending. You could clearly see where each image stopped and the next one began. It was as though the shots were taken at slightly different exposures, which is not the case. All shots were taken at the exact same exposure settings.



If I stopped there, there are a million questions you could ask me to try and diagnose this issue. But, the other big piece of evidence is that when I do the same exact steps with only 4 of the images, the Photomerge image looks great.



Things get slightly better if I run the test with the same 6 RAW files from within Photoshop (without using Lightroom), but still not acceptable.



And again even better if I use 6 JPEG files from within Photoshop, but no where near as good as the 4 shot image.



Does anyone know why doing additional images is limiting Photomerge's performance? I would initially wonder about scratch disk space and RAM. I've got about 70GB of empty SSD scratch space and I'm using 4GB of RAM on a 32-bit Windows 7 machine. Of the 4BG of RAM, Photoshop is allowed to use 1192 MB of the total 1633 MB available. I've read about people doing 60 shot merges in Photoshop. Why can't I get 6? Not enough RAM? Isn't that what the scratch disk is for?

Also, I did my usual Googling to see what I was doing wrong and I found this thread. The second post shows the results I'm seeing. The original poster's solution was restarting. I'm continuing to get that result even after a restart. It seems quite repeatable with either RAW or JPEG files.

http://forums.adobe.com/message/2903101

Anyone have any ideas?