[jrd104]

Is there an adaptor and an app for the Nexus 7 that allows downloading and editing photos from a digital SLR camera?

[EvilMonkey]

Not sure, but you could always go through a PC and just copy the files onto your Nexus or go through Dropbox or another cloud service to get them onto the tablet. There's lots of photo-editing apps available (I personally would use Photoshop on a PC for serious photo editing though).

[jg12899]

You could use Google+ as a kind of file dropzone. Upload them there and you will be able to see them, add captions, edit, etc. from your Nexus.

[Adamsberg]

If you really don't want to use PC and cloud for the transfer then you might try to connect your SLR via USB OTG cable to your N7.
Or the SLR's SD card via USB card reader and USB OTG cable to connect to your N7.

For to use USB OTG on an unrooted N7 you'll need the app 'Nexus Media Importer' from Play Store.
So your photos on the SLR's SD card will be readable on your N7 ... but truthfully, I don't know for sure if you can copy the photos.
Maybe worth a try.

[wildaho]

I use a Transcend WiFiSD card in my camera. The associated app on my tablet makes it easy to transfer the files wirelessly. I use Photoshop Touch to do my editing once the files are there.