Is there a way to restrict custom column to web application or site collection only?
I did not find any way of deploying the custom field to web applications only. I tried updating the Assembly Deployment Target to "WebApplication" instead of GAC in project properties and the dll got deployed to bin folder in the web application. However, the field did not show up in the web application. Found this info in the msdn
Custom field types are deployed at the server farm-level, using the Microsoft SharePoint Foundation Solution Deployment functionality.