Ian,

That would be very kind of you, the element has a 50mm diameter and is 5mm thick. I'd owe you a favour then.

Ambaker,

Some good news on there and considering the fact that I have to make a ground glass anyway, this now gives me reason to do it sooner rather than later.

Thanks Jonathan and Gerald, I'll be trying that too.
And to you ic-racer, how very dare you, you sir are outrageous