I'm only kidding—I understood everything perfectly—you have a knack at explanations soap :^)

Whoa - none of those flashes are instant-film specific.

Break it up you two! ;^)

Look at how much I learned though—there are three types of polaroid flashes: ones with thyristors, ones with fill flashes, and ones with windows. Thanks for the lesson you two! ;^)

Ha Ha way to "cover your tracks" soap but make up your mind about PMing me if your going to reply here. Choose one.

I accept your "apology". Now go get me a breakfast bagel or something. :^)

Since you continue to edit your post, I will reply.

My initial observation on the area under the main head of the article's flash has been well explained in the thread. I included photos with annotations, and an explanation of what I thought I was seeing. I also included photos of another potato masher _without_ a fill flash, yet a similar looking area. I think my words speak for themselves, and I apologize for using the word "window" which clearly has you chasing a mental tangent unrelated to the point I was making.

Did you even click the link I put up? IT'S A FILL FLASH! Not a freakin' "window"?!?

Explain why there would be a "window" on a flash? A window to what?

PM me

If you don't find the black dot in gray field pattern matches the what I circled on the flash from the article, I can't help you. LOL

EDIT - I thought this was a dead horse - why do you keep posting?

I don't see a "window" on your photo there soap. LOL

But whatever dead horse moving on...

Looks like this:

as well, which isn't a fill flash, it's a thyristor in a fancy plate.

That's all fascinating soap but as usual you over complicate things. It's not a "window" it's a fill flash! It looks like a Metz model.

http://www.metz.de/en/photo-electronics/mecablitz-models/sca-flash-units/mecablitz-45-cl-4-digital/product-information.html

Mind you - not all thyristor flashes were user variable power. Film exposure has enough latitude that many ones just went for broke - made a lot of assumptions and let the photo lab sort it out.

Oh, so the ND filter is like flash compensation? That makes a lot more sense—thanks soap :^)

The thyristor is the shirt-button-sized eye I believe I circled in blue in the photo above. (Not 100% that's a thyristor flash).
(and if that's not confusing enough, I circled in red in the photo below) ;)

The thyristor is an electronic eye on the flash unit which controls the flash's power by shutting off the flash tube itself once enough (reflected) light reaches the thyristor. In a nutshell if you want the thyristor to shut off later (giving you a brighter image) you fake out the thyristor by covering it with a ND filter, so less light gets to the thyristor and it keeps the strobe on to make things brighter.

Oh, did you have a typo before jonny with an "e' instead of an "o"? That's what I saw and I thought that was the difference. Let me try the correct spelling:

thyristor

You were right!

Thanks jonny.

Still don't understand the ND card thing. The thrysitor thing has it's own flash inside? I don't get it.

I did understand the card thing though :^)

I'm just going by your screenshot crop:

alphanikonrex said:

But I did jonny!

ND filter thing:
The thyristor eye triggers at a specific light level. You can't change that. If you want the thyristor eye to trigger at a higher light level you "fool" the eye by putting a ND filter in front of it, so it takes more light to trigger it. On my 285 this is what the control dial does - it just dials in different ND filters.

The card thing:
You're solving for three variables. A handy X/Y chart can only show you a solution for two.
So you have multiple cards. Think of the separate cards as single steps on the Z axis.

I'll bet your spell check wouldn't bother you if you spelled it thyristor and not thrysistor, alpha. ;-)

You explained it well, soap, it's just me failing to understand. Maybe I'm just tired as well.

Like I didn't get the ND filter thing. Or the card thing. But otherwise I just barely understand how the thing works. Kind of.

alphanikonrex said:
OK, thanks soap. I think I kind of grasp the idea, but it's too old for me to really understand how to use.

What part did I fail to explain clearly enough?

It's a relatively dumb auto mode. It doesn't work nearly as well on digital as it does on film because of film's softer shoulders - film is much more forgiving when it comes to exposure.

OK, thanks soap. I think I kind of grasp the idea, but it's too old for me to really understand how to use.

A thyristor is simply a light-sensitive transistor.
When you say "thyristor" in the context of flashes you're talking about the entire system.
A system which would quench a flash tube's light mid pulse once a predetermined amount of light hit the thyristor.

Flash tubes vary their power by varying the pulse length - the length of time the tube is "glowing".

So, on a thyristor flash unit you typically had either a set of reference cards, or a mechanical calculator (as the math problem to be solved had three variables - aperture, ISO, distance (shutter speed isn't a variable because even at full power the typical electronic flash tube is illuminated for fractions of the shutter open time)
So you dialed in your distance, your ISO, and your aperture, and the calculator (or reference card, (typical X/Y chart with two variables, cards themselves being the third dimension)) told you how to "dial" in the thyristor.

Since the thyristor itself was a dumb static thing (it only knew one light level) you would put a series of ND filters over it, to "fool" it into triggering at different light levels. This is what the calculator helped you choose.

Basically, the effect was to have the flash turn off when enough light _returned_ to the camera/flash (through the window) to indicate properly exposed film.

A seasoned photographer could use tweak this dumb auto mode by saying "hmm, the subject appears 2 stops darker than the backlight, I'll lie to the thyristor by two stops so it doesn't quench the strobe early."

EDIT:
PS:
This is what TTL flash metering replaced. Through The Lens instead of "through the flash's eye". More accurate and allowed for multiple "eyes" to be used in combination with Matrix metering and it's ilk.

PPS: A little more explanation: Distance is an important variable to account for (though it may not be immediately obvious) because you need to account for the light falloff on it's way /back/ from the subject.

PPPS: Zoom head flash units (The classic Vivitar 285, for example) had four variables to solve for, as the zoom head position also needed to be accounted for.

poster said:
I was on a shoot for Planet Green during the annual Coney Island Polar Bear swim. He was there. He was a bit rude and condescending to me. Whatever.

I see. One of my old math teachers is a Coney Island Polar Bear. Not sure how they do that stuff, but they just do it.

soap said:
I called the area under the strobe's reflector a "window" because it looked like one. It appears (now that I have zoomed the image) to be the thyristor, either behind a plastic window (as many were) or surrounded by a metal badge (likely saying "THYRISTOR" in big lettering (as many other earlier models had)).

Nothing to do with aiming a flash, lol. You are aware of what a thyristor is, no?

Thanks!

alphanikonrex said:
No, I have no clue what a thrysistor is. LOL, neither does my computer's spell checker:

Lol. I don't know either.

No, I have no clue what a thrysistor is. LOL, neither does my computer's spell checker: