Technical dark room.........
This is an LPL 7452 enlarger head
that we use in the dark room.
These are medium format 6 by 6 and 6 by 7 negative holders with a medium format lens (green ring) and attaching ring.

This is a large format negative holder with a large format lens and attachment ring.
This is a 35mm lens and negative holder, what i used to print from my 35mm film.
This is the correct way that a lens fits into the holder.

The lens fits into the enlarger head with the aperture sign facing towards you so that you can see what aperture you have set your lens to. Then you tighten the screw on the side to hold it in place.
A 35mm negative holder.
Put the negatives in the holder shiny side up and upside down so when projected on to the board at the bottom the photo appears the right way up.
Pull the leaver down to lock the holder in place, it is then safe to turn the enlarger light on. If the leaver is not pulled down then the light will spill across the room and fog any paper that is out.
The controls on the side of the enlarger, the one nearest to the wall can be loosened to adjust the height of the enlarger and the one nearest to you focuses the photo.

The filtration, Cyan, yellow and magenta, the controls are on the right hand side of the enlarger and the leaver on the front turns the filtration on and off.
My dark room double exposures
This was done on F8 and exposed for 25 seconds after doing a teat strip.

I did this on F8 and exposed it for 23 seconds
This was done on F8 for 28 seconds.
This was set to F8 and exposed for 22 seconds

This was also set to F8 and exposed for 25 seconds.