What does THAT button do? (FM3A flash comp)

[david_rifkind]

I'm trying to understand the flash compensation button on the FM3A. The reason I want to understand it is that I'm trying to decide whether to buy a Nikon dedicated flash; I have a Vivitar 285 HV. I do very little flash photography, and when I do (and care about the results) it's almost always fill flash.

 

If you read some of the descriptions carelessly, it sounds like the flash comp button is a magic "fill flash" button. But unless my thinking about how TTL metering works is wrong, that doesn't seem possible. What I think of as "magic" is that the camera does the calculations you'd do for fill flash--measuring the subject distance, doing the guide number division, then reducing the output by the fill ratio. This seems impossible unless the flash can read the len's distance setting, or TTL metering is capable of doing really subtle things.

 

Anyway, since I don't believe that, I *think* what's going on is that the flash comp button just sets the TTL metering logic for a 1 stop underexposure, and that's based on the assumption that your subject is a small part of the picture and the standard 60/40 metering would overexpose it by overmetering the background.

 

I wonder if anyone could clarify this for me. I also wonder a few other things. One is, does magic fill flash exist? That is, if I buy the latest, most automatic equipment, can I just set it for -1.5 stops of fill and have everything done for me, or am I going to be doing flash calculations for the rest of my life?

 

Second, is this what "3D metering" on the Nikon D lenses is about? You can't do fill calculations without knowing the subject distance. Do D lenses tell the camera where they've focused so the flash can do the figuring automatically?

 

Oh, and last. Forgetting all the theory, are the benefits of TTL metering and the comp button enough to get a dedicated flash?

[jonathan_ratzlaff]

TTL flash is the best thing since sliced bread as far as flash photography is concerned. Because the flash output is metered off the film during exposure you don't have to worry about the flash exposure quite as much. The flash compensation dial will allow you to control the ratio of fill flash to the metered exposure of the camera.

The D function of the lens gives the camera an idea of what distance the lens is focused at. For example if the lens is focused close, the flash meter thinks that the main subject is close to the camera and will set the output of the flash accordingly. Otherwise a small object in the field may get too much light because the area of the object is too small to affect the output of the flash otherwise.

[henry_c]

>I wonder if anyone could clarify this for me.

 

 

See, FM3a has a 60/40 center weight meter. The TTL works with that. So whenever the center weight meter thinks it's enough light, it will cut the flash. Therefore the TTL on FM3a has the same problem with any other Off the Film TTL flash combined with a 60/40 center weight meter. That means, if your subject is on the edge of your frame, be sure that it will be misguided by the background. I am not sure if setting the A mode and use AEL works to lock the TTL though.

 

>I also wonder a few other things. One is, does magic fill flash >exist? That is, if I buy the latest, most automatic equipment, can I >just set it for -1.5 stops of fill and have everything done for me,

 

 

Pretty much. If you buy the latest the metering will be so advance that it will take a lot of things into consideration and the thing you have to learn is WHEN and HOW will this latest bells and whistles get fooled and dial in your compensation and whatnot to adjust. But for the most part when shooting print film, just DON'T worry too much about it.

 

 

>or am I going to be doing flash calculations for the rest of my >life?

 

If you are worry about camera being fooled, GN calculation and manual dialing in flash power is still the safest way to do it, but it takes more time.

 

 

 

>Second, is this what "3D metering" on the Nikon D lenses is about? >You can't do fill calculations without knowing the subject distance. >Do D lenses tell the camera where they've focused so the flash can >do the figuring automatically?

 

Yes. The D chip tells the flash the subject is at whatever distance and it will know when to cut flash. This works when the camera is on the matrix mode. But Nikon has this autmatic balance formula so I am not sure if you can dial in compensation while you set the flash on matrix flash and camera on matrix mode. But for the most part, it's fairly accurate and I haven't had any problem with it. If you have shot canon and nikon like I do, then you will bless the 3-d matrix and distance infomation with Nikon system.

 

 

>Oh, and last. Forgetting all the theory, are the benefits of TTL >metering and the comp button enough to get a dedicated flash?

 

For FM3a, yes and no. See, if you get flash with TTL that works with FM3a, most likely that's all that you need. A lot of the newest features on a SB80 or Sb28 won't work on the FM3a. None of the 3d matrix TTL works with the Fm3a. The thing is, if you are thinking that you will ONE DAY be using an autofocus Nikon camera, then plaese do get a dedicated flash so in the future you can just hook that flash on the AF camera, and you will love yourself more.

 

 

Also, FM3a is pretty new, a lot of the non-nikon flashes might and might NOT work with it since Nikon is quite secretive about the FM3a TTL compatibility (it's annoying). By getting a Nikon flash you know that it will work, and that's a good thing.

[graham_wilkins]

I use an SB28 with an F5 and an FM3A. 3D matrix TTL flash works with the F5 (due to the chip in the AFD lens providing the distance infomation). TTL flash is the highest option possible with the FM3A. The SB28 is a good flash unit, although possibly a little over the top for the FM3A unless you also have a second Nikon AF body like the F80, 90X, 100 or F5.

[amauri_nunes]

>>What does THAT button do? (FM3A flash comp)<<

 

When you press and hold "THAT" button while shooting, the FM3a will underexpose the flash output by one stop. You can test it out by using a flash exposure meter. This button is a welcome addition on the FM3a because you can't set the flash exposure separately on those earlier TTL-Flash cameras (FE-2, FA, FG, F3). Newer cameras, N6000 and up, allow flash exposure compensation to be set on the flash itself. I've used my FM3a with several Nikon flashes; SB-15, SB-24, SB-26, SB-27 & my new SB-80dx, also a Metz MZ54 w/Nikon module. All exposed correctly in TTL mode.

[richard_cochran]

<cite>What I think of as "magic" is that the camera does the calculations you'd do for fill flash--measuring the subject distance, doing the guide number division, then reducing the output by the fill ratio. This seems impossible unless the flash can read the len's distance setting</cite>

<p>

You're right, that would be impossible without distance information.

(As an aside, it would also need aperture information, and

information about what filters are on the lens. Further, it would

need to know the flash power in order to do GN calculations. None of

these bits of info are available to the FM3A.)

But TTL flash on the FM3A doesn't work that way. It works very

similar to old-fashioned auto flash, except that instead of

having the light sensor out on front of the flash unit, there's

a light sensor inside the camera, watching the light reflected

off the surface of the film. When the sensor sees that the

film has received enough light from the flash to produce an

average exposure, it tells the flash to shut off (quench).

Because it's measuring the light that's actually hitting

the film, it naturally accounts for aperture, distance,

filters, etc. without having to know these things individually

and do any calculations.

<p>

"THAT" button just tells the camera to send its quench signal

a bit earlier, so it will give the film a little smaller than

normal dose of light from the flash.

[mark_jacobson1]

So does that mean that with the FM3a you should take a meter

reading and set your aperture accordingly (in aperture priority

mode), allow the camera to set the default speed to 1/250 and

hope for the best (using TTL)? Or is it a matter of knowing the

camera/flash and how to adjust them?

 

When I bought my FM3a and SB-50dx I thought, and understood

from the manual that you do what i asked about above. But I''ve

read conflicting things.

 

Also, when I am in aperture priority mode, the manual says it will

default to 1/250 but the meter does not indicate that. Should it?

 

Thanks for your help.

 

Mark

[jim_gifford]

<<Also, when I am in aperture priority mode, the manual says it will default to 1/250 but the meter does not indicate that. Should it?>>

 

Nope. The meter will keep telling you the shutter speed for exposure using just the ambient light. But you can HEAR that the shutter is not, for example, taking 1/4 second to open and close when you use flash. So you know all is working as it should be.

 

Have fun,

[mark_jacobson1]

OK, then how do I judge what the right exposure should be?

 

Thank you,

 

Mark