I'm weighing on deciding on getting a a7iii or a7iv modded to Visible + H-Alpha filter, a 420nm to 1200nm filter, or go for the gold for full spectrum. Ideally, I want capture more reds for astrophotography and IR for b&w landscapes. Is there a compelling reason why I should not go with full spectrum to achieve both targets? My understanding is that WB correction is straightforward in any of the options. So is there anything else I should consider when making this decision?
I don't believe you would lose anything going for the full spectrum. But you need to check that the sensor can capture the range you desire. I know some sensors are not full spectrum, which makes the full mod a waste of money. If your's is full sensor, then I would go for full spectrum. Just don't forget to buy filters for shooting normal when you need it.