Partial apertures

Online experiments
1

Hi

I want to build a partial circle aperture. For example i want half of a circle or 1/8th of a circle. Is this possible?

thanks

2

Could you have a large flat colour png image with a transparent shape in the middle?

3

Hmmm…I don’t know. I didn’t know where to turn the transparency on/off.But one can create any figure with lines. So that is what i did.