1. Is there less potential for Moire issues with the P30+?
You can get moire in anything and unless you shoot both cameras side by side in the excact conditions it's almost impossible to answer. I've seen more moire from the p30+ but I've used it more than the p21+.
There is also a lot of types of moire, pattern, colour, a combination. The best test is the blue shell top or a men's grey small plaid jacket. Women's patterned hoisery also will pattern moire.
2. Is there an advantage to the 9 micron pixel size on the p21+ over the P31+ smaller pixel size.?
What I think is an advanage is probably a negative to some others. It depends on what/how you shoot. The p30+ has amazing detail for that size of sensor and the price, but it is smoother and for me sometimes too smooth. The p21+ has more texture when worked deep in post so I guess you could say a little more grain. I like that, some others may not.
These really are two different digtial films and can be made to look very different. Once again it depends on what you shoot. The upside to the p21+ is it has more texture, shoots much faster and is 1/2 the price of the p30+.
The downside is if you send your image to outside sources for retouching, or one of those images that goes through 10 rounds of correction, you may hear that the p21+ is a small file given that uninterpolated in processing it's much smaller than the p30+.
Still, for 98% of what I do I can shoot either back and if they are rezzed up or down to the same size nobody says anything or knows the difference.
3. Which back will produce a cleaner 400 ISO image under outdoor, low light, shaded conditions?
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As far as iso, once again it depends on what you shoot, how it's lit. Soft even light at 400 iso the p21+ doesn't show much noise, in fact it shows little at all.
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Harsher, or more backlit, 3/4 lit with darker subjects you will see more noise, underexposed even more, but it depends on what you shoot.
I would not say in general that the 30+ is a full stop better than the 21+, maybe 1/2 a stop but it depends on what you shoot.
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And it depends on how you light and the ambient conditions.
Overall in shaded light, like open shade under a tree or awning, the phase backs, most medium format in general, is very ambient color sensitive. If the grass is green you will get a lot of yellow green in the subject, blue sky, lot of blue. For this type of lighting the Canons really are nicer in overall look and seem to be a little more color dumb.
The backs are very sensisitve to ambient color and obviously need some new color presets written for the software, though Raw Developer handles skin tone color better than almost any 3rd party processor.
Still, for a medium fomat back I believe the 21+ has as good, if not better color response of any back I've used.
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I think the 21+ is the deal of the century if you must have a digital back as the cost is low, the shooting speed is great and it is good up to 400 iso.
All of the phase backs (at least my two) are very strong and sturdy really dependable though the physcial design of the back is starting to look a little dated, compared to the new hasselblad and Sinar backs, but they are built like a tank.
After 400 iso I haven't owned any digital back that really performs that well. You can use them all at 800 iso but you start to see a lot of detail loss, to the point the image begins to look like a much lower detailed camera.
All of medium format really does need a lot of external light.
You really need to try them side by side in the conditions you shoot to and if you have the opportunity try them next to a 1ds3.
JR
