Wow, great pic of the milky way
9 exposures of 300 seconds
What is the mod on your 5d2, did you remove UV/IR filters in it ?
Yes, 9*300s; a moderate (number of frame)/(exposure time) ratio, I already did more on Milky Way
This 5D2 is not full spectrum, there's an Astrodon Inside filter in place of the Canon IR-cut filter who gives 400>700nm @99% with fluorite substrate, very nice product.
I will buy an Ioptron SkyTracker V2, it can handle 300mm @ 150 sec well (i'm mainly interessed in astrolandscape, i don't need such precision ), can be powered by 4 AA battery (~24h@20°) and is LIGHTWEIGHT (i love to go on the mountains). And it is cheap ~300€.
Do you have some hint on a good Skytracker?
You know, 150s @300mm with this kind of device is 'marketing'. I think you could use up to a 80mm, more you will see stars trails because the device has ~40" of periodic error in tracking. <50mm it will be easier, specially at the beginning. But <=80mm will be far enough for Milky Way, look at my previous link where it was 50mm.
For the power source, with AA batteries maybe it will be enough for a couple of hours but it could be expensive (?). An other solution could be to use a external source (9~12V, 500mA), like from a car lighter if you have your car close to you.
In the same budget there's the Skywatcher Star Adventurer travel mount, two times heavier but stronger and more precise. Plus you could use an auto-guiding system, later. It depends if you want a very light device or not, for 300€ and 0.5kg the Ioptron is the one on the market I think.