Very Basic Flash Question

[vgoklani]

Hi,

 

I am using a Nikon F4 with an SB-23 flash. At night, regardless of

which aperture I choose, the flash syncs to 1/60 (which I believe is

the longest duration of the flash). But this is regardless of

whether I choose f/8, f/5.6, or f/1.4? How can this be, ie: how

will the film get exposed correctly.

 

Thanks,

 

Vishal

[majid]

Your speedlite is a so-called TTL (fully automatic) flash. The camera has a circuit that

observes how much light is coming in (reflected off the surface of the film!) and cuts

the flash when the exposure is right. The aperture and shutter are used to control

how much light comes from ambient lighting, TTL controls how much light comes

from the flash. In fill flash situations, controlling this precisely is quite

important.<p>You can read NK Guy's excellent <a href="http:/

/photonotes.org/articles/eos-flash/">flash tutorial</a>, it is for Canon EOS

systems, but the basics are the same for Nikon, such as the explanation for why your

<a href="http://photonotes.org/articles/eos-flash/index2.html#xsync">X-Sync</a>

speed is less than your maximum shutter speed. As a high-end professional camera,

you should be able to get X-Sync speeds to 1/250s, however.

[vgoklani]

Thanks! I guess the balance between Ambient light and TTL light is what makes flash photography so complicated. I would like to see a collection of shots, where someone took multiple photos of the same image, but varied the TTL and Ambient Light settings. okay, I should probably do this by myself.........

[angel_o.]

Vishal,<br><br>

in addition to Fazal's comment, the flash duration is very short. According to the manual of the SB-28, the flash duration of this flash varies between 1/8700 sec and 1/830 sec. I don't know the specs of the SB-23 but the flash duration will be much shorter than 1/250 sec. Therefore, slower shutter speeds have only an effect on the ambient exposure and not on the flash-exposure. <br><br>

Regards,

[el_fang]

This is the stupid thing about the automatic modes on the Nikon. The F100 I used to have did this also. There won't be a problem with flash exposure because of TTL, but your background may or may not be exposed to your liking (as mentioned by another poster, shutter speed affects background exposure), and will likely be too dark. At night with flash, I always used the camera in manual mode only, so I could adjust the shutter speed slower than 1/60, usually 1/15 to 1/4 with ISO 100 film, to burn in some background detail.

[el_fang]

<i>"I guess the balance between Ambient light and TTL light is what makes flash photography so complicated."</i>

<p>It's actually pretty simple - all you have to do is always keep in mind two limitations: 1) your camera's x-sync, and never set the shutter speed faster than it, and 2) your flash's maximum range. Keeping those in mind, then you decide which (of ambient or flash) will be the main light, and which will be the fill light. Most people prefer that the fill light be 1 to 2 stops below the main. I find it easiest to do this manually, although I recall my F100 and SB-28 did it pretty well when I wanted outdoor fill (main=sun; fill=flash) and set the combo to 3D-matrix with flash -1.7 below ambient. As long as I was in the flash's operating range, this worked well for me. For indoors or night, I set the camera to manual with spot metering (to selectively meter and expose for the background) and took the flash out of 3D and into regular TTL at no compensation (as the main light to expose a foreground subject).

[chien_shih]

I think it also has something to do with the lens you have, if you use NIKON F4 in (P)rogram mode or (Ps) Program Shutter mode, and your lens is capable of lock down to the maximum aperture ( most of the AF lens), you will be able to have multipe choice for shutter speed range from 1/250 downward automatically selected by F4. if your lens is AIS or older, you can only have 1/60 if you use TTL with (A)utomatic mode.