IMac connect to Sony HD tape recorder

If you tell us eactlly what year model the iMac is?

Identify your iMac model - Apple Support

Then perhaps we can connect you up with the correct adapter(s) to make a FireWire connection.

Identify the ports on your Mac - Apple Support

About Apple Thunderbolt cables and adapters - Apple Support

Do you have the cameras micro FireWire to FireWire 400 cable?

If you do, then all you need is three other adapters.

a USB-C (Thunderbolt 3) to Thunderbolt 2 adapter to plug into the iMac.

https://www.apple.com/shop/product/MMEL2AM/A/thunderbolt-3-usb-c-to-thunderbolt-2-adapter?

a ThunderBolt 2 to FireWire adapter to plug into the first adapter.

https://www.apple.com/shop/product/MD464LL/A/apple-thunderbolt-to-firewire-adapter

a FireWire 800 to 400 adapter to plug into the second adapter.

https://www.amazon.com/UCEC-Firewire-Adapter

then plug the FireWire 400 to micro FireWire cable to plug into FireWire adapter and hope it works.