How to read an exposure calculator on a flash?

Discussion in 'Beyond the Basics' started by Garbz, Dec 2, 2004.

  1. Garbz

    Garbz No longer a newbie, moving up!

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    Good morning from down under. After scrwing around with my camera the other day I finally got my old speedlight to work. (and wasted 12 photos cause my dad advanced the film constantly out of pure habit).

    The camera is a fantastic little no nonsense Nikon FE, and it's older then I am as far as I know. It's the best camera I've ever used (what's autofocus). But it does have 1 problem which apparently plagues a lot of photographers with this camera and that is it doesn't have a TTL flash metering. As such I'm stuck with (may not be a bad thing) the Nikon SB-10 Speedlight.

    [​IMG]

    And that's it there. The SB-10 is dedicated to the FE's hotshoe because it not only has a flashsync contact but also a flash ready contact which can be seen through the eyepiece, but I digress.

    The FE is capable of syncing with the SB-10 in it's Auto setting (locked at 1/90th), every manual locked setting under 1/125th, the M-90 battery independant setting, and the fully mechanical and manual B setting. For simplicity sake it won't be taken of Auto or SB-90.

    The SB-10 has 3 modes. 2 "Automatic" modes (marked with a red line, and a blue line) and a "Manual" mode where the flash will always fire it's full brightness for the duration of the shot.

    the question is how do the auto modes and manual modes relate to the exposure calculator?

    It's easy enough to say a subject is 5m away, set the calculator to ASA100 and you end up wih a f5.6 for the lense. No problem. But where do these auto and manual modes come into play.

    I'm not sure if it's significant or not but the auto modes appear 2 fstops appart. e.g. at ASA100 the calculator shows f4 under the red mode, and f8 under the blue mode.

    So can someone please enlighten me how this antiquated piece of maths works so i'm not limited to daytime photography :D
     
  2. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    The flash has a guide number (GN), which is usually listed at full power in ISO 100/feet (or meters).

    GN divided by flash to subject distance equals f/# for "correct" exposure at ISO 100

    The exposure calculator is just a piece of plastic to help you do the math without actually having to do the math. Adjusting the exposure calculator has no effect on the output of the flash.

    I prefer to use the flash in manual if I have the time to fiddle with the camera as I change my distance to subject, but if I'm moving too quickly then I'll use an auto mode. The auto modes are not as accurate, but are "good enough" for some subject matter. When I'm on auto I'm relying somewhat on the exposure latitude of neg film.

    The reason you have 2 auto modes is just to give you some choice. One for less DOF, one for more, one for close up shots, one for farther distances, and also it may affect recycle time.
     
  3. Garbz

    Garbz No longer a newbie, moving up!

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    Yes i'm aware that the calculator is just a piece of maths.

    It's the modes i'm confused with.
    Ok given the picture above assuming that the subject is 3m away from me I set the lens to f8 and the flash to manual. The flash fires at full brightness and the fstop should keep the light in perfect control to illuminate a subject at 3m. If that's the case why the auto modes at all. Subject 10m away I set the lens to f2.8. Furthermore how do the 2 modes differ. If I read it correctly then M being manual and full flash is the correct measurment for the wheel.

    So what is the result of switching it to blue or red? The flash metres the light of the subject, but even so it doesn't know the fstop of the lens which is the short comming of cameras without TTL flash metring.

    So how do I use the flash in either of these auto modes. As in how do I set the fstop of my lens?
     
  4. Hertz van Rental

    Hertz van Rental TPF Noob!

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    The red mode would appear to be lower power (2 stops difference). Lower power allows the flash to recycle quicker.
    If it has an Automatic mode then there should be a little sensor just below the flash - if it is not capable of TTL mode. This sensor reads the reflected light and quenches the flash to adjust for objects closer to the camera. It just means that you don't have to keep measuring the distance and changing your f-stop. The red and blue work as above.
    Set the film speed - see what f-stop the red or blue line gives - choose and set that on the camera - make sure the subject doesn't go beyond the max distance. Help you?
     
  5. Garbz

    Garbz No longer a newbie, moving up!

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    kindof I imagined that they do something like that.

    However if Manual fires the flash at max, what does the blue setting fire it at to require 2 fstops higher?

    Also the calculator calculates independently of the setting. I.e. even with it set at blue which points to f8 at 3m, I should still be able to set it to f4 at 6m. That's what confuses me!
     
  6. Hertz van Rental

    Hertz van Rental TPF Noob!

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    You should find that in automatic mode you usually need to be nearer the subject - that is how the blue setting can appear to be kicking out more power than Manual. It isn't really.
    If you have it on Auto mode and do not use the indicated aperture you will find the exposure will be out. The aperture/distance thing is only for Manual. Some flashes have a test button and light to indicate if your subject is in range - but it doesn't look like yours does.
     
  7. Garbz

    Garbz No longer a newbie, moving up!

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    Ok so manual requires very detailed calculation, but the automatic modes simply allow some play.

    So say the subject is between 2 and 4 metres away or is moving around and I can't get an exact distance, I set the aperature to f5.6 or f8 the flash to blue and shoot and pray

    And conversly if he is 5-10m away set it to f2.8 or f4, and red and shoot.

    Is this roughly the idea? With manual there's no play on the settings at all and I need to follow the calculator religiously but I have a bit of play either way with the automatic modes.

    Or the other posibility I just thought of is keep the aperature at f5.6 at all times and if the subject is close go for blue, and if he is further away go for red?
     
  8. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    If you are going to be adjusting the aperture each shot, you might as well use the flash on full manual. It'll be a lot more accurate. It's not really very difficult, the dial makes it easy, and if you do use it a few times, you'll find that you'll have the calculator dial almost memorized pretty soon.

    The auto modes are added because many folks value convenience over accuracy. Convenience has it's place, but if you have the time, go for accuracy.

    Also, just another thing to worry about. I've used dozens of different flash units, and only one so far (a Vivitar 285HV) has been what I consider accurate (less than 1/2 stop off) to the GN/calculator. I test all new flashes with a flash meter and a few test rolls to make sure I know what they can deliver. Often I find that they are slightly underpowered compared to what the manufacturer claims, at least with my style of shooting.
     
  9. Hertz van Rental

    Hertz van Rental TPF Noob!

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    You've got the basic idea. Try shooting off a test roll and play around with the flash during (making a note of settings) so that you can get a feel for it. Auto is usually fine for most occasions.
    I have always used top-end Metz and found them accurate to within a fifth of a stop on auto. Manual dials are only approximate - but accurate enough for most use. If you want accuracy then you buy an expensive flash meter or use a tape measure and a calculator. But you sacrifice speed.
    As most manual film SLRs can only be adjusted in at best 1/2 stop increments anyway.....
     
  10. Garbz

    Garbz No longer a newbie, moving up!

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    Thanks both of you. You've been very helpfull.

    I'm just an amature so no fancy gadgets like a flash metre etc. but then I love playing with things a lot so I'll probably be using it in full manual anyway.

    At least now I'm not limited to long exposures when it's dark.
     
  11. airgunr

    airgunr TPF Noob!

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    From "The Nikon Flash Guide" by Thom Hogan

    Setting Automatic Flash Exposure

    1. Move the Auto/Manual switch on the front of the SB-10 so that the white indicator line adjacent to the dial is opposite either the orange(f/4) or blue (f/8 ) marker.

    2. Set the ISO film speed value in the white cutout labled ASA at the bottom of the dial located on the top of the SB-10. The ISO value of the film you're using should align with the small arrow under the ASA label. The distance listed on the top dial adjacent to the aperture you selected (f/4 or f/8 ) is the maximum range for which the flash can provide exposure. Subjects at any distance between the minimum (2 feet/0.6 M) and this maximum will be correctly lit by the flash.

    3. Set the aperture on the camera to the value you set in Step 1 (either f/4 or f/8 ), and make sure that the shutter speed is within the sync range of your camera.

    4. Turn the flash unit ON. When the ready light glows, you can take the picture. Note thatt if you are shooting near the range limit of the flash (19.6 feet [6m] for f/4 or half that for f/8 ), you should wait a few seconds after the ready glows before taking a picture, as the light comes on before the flash is fully charged.

    Setting Manual Flash Exposure

    1. Move the Auto/Manual switch on the front of the SB-10 so that the white indicator line adjacent to the dial is opposite the white M marker.

    2. Set the ISO film speed value in the white cutout labeled ASA at the bottom of the dial located on the top of the SB-10. THe ISO value of the film you're using should align with the small arrow under the ASA label.

    3. Focus on the suject and note the distance. On the top of the dial on the back of the SB-10 not the aperture that corresponds to that distance (the outer values are apertures, the next ring is the distance in meteres, and the small numbers in teh innermost ring are distance in feet). For example, at ISO 100 and 9.8 feet (3 m), the aperture is f/8. if in doubt, choose the larger aperture (f/5.6 in this example), especially if outdoors.

    4. Set the perture calculated in Step 3 on your camera, and make sure that the shutter speed is within the sync range of your camera.

    5. Turn the flash unit ON. Wait several seconds after the ready light first glows, then take the picture (the ready light flows before a full charge is available; in manual flash mode you may get underexposure if you fire the flash the moment the ready light appears).

    SB-10 Usable Apertures and Flash Range in Automatic Mode (ISO 100)

    Color of Markers------Aperture-------Range in FT------Range in Mt.__________________________________________________________

    Orange---------------------f/4-----------------2-19.6----------0.6-6
    Blue-------------------------f/8-----------------2-9.8-----------0.6-3
    _________________________________________________________


    I hope that helps you. :) (sorry for any misspellings)
     
  12. Garbz

    Garbz No longer a newbie, moving up!

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    wow thanks a lot.l

    If in doubt pick red and f4, if you know they are close enough pick blue and f8, and when you have the time manual :D

    I've seen that book a few times around the net while looking for the SB-10 manual, thanks for the copy. :D
     

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