Helicon Soft Forum

What are my options to use Helicon Remote to control a Nikon D810 from an iphone or ipad to focus stack? Thanks in advance.

You need Wi-Fi, so Nikon WT-4 or WT-5. I don't remember if WT-4 supports D810.

Are there any other alternatives that work with Helicon? Are wifi cards only one way?

Yes, these are the only alternatives. Wi-Fi memory cards do not grant you remote control of the camera, they can only transfer photos.