Hey,

Can any of you explain how a doughnut (gobo sharpener) works?

I look forward to reading the inevitable "Its a fried lump of dough" replies

Thanks!

Actually your not far off the mark.Doughnuts work by increasing the sugar levels in the focuser's blood,leading to an increase in energy,the more energy you have the longer you can spend focusing individual lanterns .The type and flavour of the doughnut will have a major impact on the time you spend focusing,for example a plain jam doughnut covered in sugar will give a good boost of energy. Certain flavours may however have a negative effect due to the niceness factor,causing the focuser to spend more time eating dough nuts than focusing the rig .To much niceness may eventually lead to the person being unable to focus the rig due to fatbastard syndrome

It is the same principle as a pinhole camera.

Hippy is, of course, correct The doughnut is a practically universal foodstuff, the origins of which have been lost in the mists of time. A wide variety of local variations can be found across the world, although they go by almost as many different names.

In stage lighting, the homophonic donut refers (as stated) to a device used to sharpen the beam edge of profile spots and in this context is correctly spelt using the americanised version. In America, National Donut Day is celebrated on the first Friday of June each year, having originally been started in 1938 as a fund raiser for the Chicago Salvation Army.

There appears to be little information on how lighting donuts work and the Truth is probably filled with the kind of mathematical hieroglyphics, which sent you diving for a theatrical career in the first place However, this post on CB gives a small clue...

...which is possibly about as much as any of us need to know IMO

See I have always knowen a doughnut to be a ring gobo that is basicaly a solid iris. I have one for a cantata, no idea why though I didnt buy it. I have used them for spotting down on to mirrorballs.

Nothing to sharpen a gobo.

Have I been wrong all along or is this another variation?

Donuts live in the colour frame plane of the beam, not in the gobo gate.

Donut
Reduces flare in template projections

Source- etcconnect.com

I guess it masks flare from the lens Jack.

And yes, a Donut lives in the gel-frame holder not in the gate

Yes you definately don't want to be putting donuts in the gate of a lantern, for risk of creating a sticky mess. Nice smell though, mmmm caramelised sugar! The colour slot at the front is much cooler than the gate, and this is where donuts belong.

As to how they work. It's the same principle as an iris (aperture) in a camera. Remember the camera is the opposite to a profile lantern. So the iris in the camera is between lens and film/sensor. In a camera, a small hole in the iris creates more depth in the image in focus and also makes the image a bit sharper.

The colour slot in a lantern is usually close the the optical centre of the beam, ie. where the beam crosses over (why you put gobos in upside down). So a donut in a lantern works much the same as a camera iris by only letting through the nice sharp bit in the middle of the lens and cuts out the fuzzy bit towards the edge. It does this with the loss of some light output though.

I hope this vaguely makes sense!

Forgot to mention...


...Which IIRC is also why axials are said to be "better" for gobo projection - because the alignment of the filament better approximates a point source in one plane. Axially-aligned discharge lamps do it even better - especially ones with very short arcs

Some argue that the ideal aperture for the donut hole is 80% of the lens diameter; in which case the standard ring doughnut from your local bakers is going to be little use in anything larger than, say, a 650 Watt profile, as it will cut the intensity too much (and get burnt more).

Well jack a doughnut can come in many varieties,

Sugar,
Ring,
Custard,
Apple,
Cream.

The list truly does go on and on.

Here is a link to further your interests.

http://en.wikipedia.org/wiki/Doughnut

I have always known the ring gobo or solid iris as masks which can be seen on some patt 23 documentation below.
http://www.strandarchive.co.uk/lanterns/do...23_explode1.pdf
I think I have also heard masks called "shovels" in the past.

- and of course as any young inspiring technician may or may not know, the easiest and quickest way to make a donut is to use blackwrap!!

or, goto krispie kremes!!

As ocfe says, that is a mask, not a Donut. You'd struggle to get a true Donut into the gate of a profile.

And with my Mod hat on - I think we've covered the Donut / Doughnut jokes now so unless it is truly funny please refrain.
Thanks

T

So at risk of taking OT what is it I have been calling a Doughnut? Is it as simple as a gobo?

Well it's hard to know what it is you've been calling a Donut, without seeing it our selves.
However, if you read the rest of the thread, and in particular click on the link that ocfe provides, you may find it's called a "MASK".