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hz Feb 29, 2008 11:03 PM

I am trying put the SB-25 flash on my D40. It looks like the camera and the flash don't talk to each other. The pictures are way over exposed. The manual says SB-25 can be used on D40 in non-TTL auto and manual modes. But there is no auto at all. Anyone has some experience? Thanks.

ReneB3 Mar 1, 2008 5:57 AM

How are you using the auto mode? I use several older flashes both Nikons and non-Nikons and they work fine. Maybe with some fine tuning but still close.

Make sure you have the camera set to the correct iso, shutter speed and aperture for the flash in the auto mode.

Most of my auto mode flashes assume 1/60 for shutter speed and they have an iso table (max 400) for setting the correct aperture for the working distance. You can figure out higher iso's from that table.

In the auto mode the flash detects it's own output and shuts down when it has the correct exposure. In Manual it just fires at full power. Also make sure the sensing port (small hole in the front of the flash) is not covered. I don't have a SB 25 to test or a d40 for that matter, but it should work.

JimC Mar 1, 2008 10:13 AM

hz wrote:

I am trying put the SB-25 flash on my D40. It looks like the camera and the flash don't talk to each other.
They don't (other than for triggering purposes). This flash is not designed to be compatible with Nikon dSLR models.

But, as already mentioned, you can still use it's Auto or Manual power settings. Simply use manual exposure on the camera and set the camera to match what the scales on the flash show you for aperture and ISO speed.

Shutter speed doesn't make any difference in how much light from the flash is seen by the camera, as long as you're within the camerea's sync speed limitations (1/500 second with your D40).

That's because the flash burst is very short (usually running between about 1/10000 second to 1/1000 second with a typical flash). Since it's faster that then shutter speeds you'd use, the camera sees the same amount of light from the flash, regardless if you're shooting at 1/60 second or 1/500 second.. Higher power settings will use a longer flash burst, and lower power settings will use a faster flash burst.

Shutter speed is used to dial in the amount of ambient light (light sources other than the flash) you want in the image for a given ISO speed/aperture setting with flash. Use slower shutter speeds to allow more ambient light, faster shutter speed to allow less. That can let you dial in the mood of the image as desired (for example, brighter backgrounds with slower shuter speeds, or a darker backgrounds with faster shutter speeds to help isolate the subject).

I'd probably use around 1/100 second for starters and adjust from there.

hz Mar 1, 2008 11:06 PM

Thank you both ReneB3 and JimC.
By manually match the ISO, aperture and zoom values between the flash and camera, the exposure seems ok.
I tried different speed there is not much difference. So JimC is right.

My other question is about the non-TTL auto. Nikon says D40 can use SB-25 in non-TTL auto mode. I assume "auto" means the camera and flash communicate so the flash knows the camera's current setting such as speed, aperture, ISO and zoom. The flash will automatically adjust the output for the correct exposure so I don't need to manually match the settings. The only problem is the flash does not consider the camera's throuhg the lens exposure information.

However, the flash knows nothing except that the shutter is released and it simply fires.

What am I missing? I just want to get some degree of "auto" Nikon promised. Please comment. Thanks again.

JimC Mar 2, 2008 7:00 AM

To repeat the first part of my last post, that flash is *not* designed compatible with a DSLR. They do not communicate other than for triggering purposes. ;) It's an older flash model, and is not supposed to work with it.

Nikon changed the flash prototcol with Digital to what they are calling i-TTL. Older flash models don't understand it.

If you want a flash that understand the camera's settings, you'll need to buy a dedicated flash model that's compatible with your model (the SB-25 is not). In Nikon models, look at the SB400, SB600, or SB800.

You can still use your SB-25 in non-TTL Auto (it's A mode). But, you'll need to set the camera and flash to match for ISO speed and aperture.

I couldn't find an SB-25 manual online. But, if you look at this SB-28 review, you'll see some steps on how to set the Mode, ISO, and Aperture speed on the flash using it's A mode.

Your SB-25 should be set in a similar manner. Then, use manual exposure on the camera and set it's aperture and ISO speed to match.

That's as "Auto" as it gets trying to use an older flash like this with your Nikon DSLR. The "Auto" part is because the flash has a built in sensor that is measuring reflected light during the exposure. When it sees enough reflected light for the ISO speed and aperture set, it terminates the burst.

IOW, it works the same way as most non-dedicated flash models would work that have Auto modes with a built in sensor. You set the camera and flash to match manually, since they do not communicate with each other (except to trigger the flash).

hz Mar 2, 2008 3:49 PM

Now I understand. D40 tells SB-25 nothing but the fire command. the non-TTL auto means if I manually set the flash to match the camera's settings, the flash automatically adjust its power based on the reading from its own sensor.

BTW, I posted a question to Nikon support and got the similar answer.

I appreciate your help.

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