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Do you think that Nikon SB-26 flash unit would be a good start for my Nikon D50 for professional use?
No, I would not. The D50 uses the i-TTL Creative Lighting System compatible with only a few flashes like the SB-800 or SB-600. To use an SB-26, which will waive all TTL flash metering. Essentially, you only manual mode and auto flash mode, possibly. In manual mode, you have to take the flash guide number (from specifications techniques) and divide by the distance to get the opening to set the camera. In automatic mode, you set the camera aperture based on the flash setting. For professional use, I recommend that you get a TTL (through the lens) flash metering. Try SB-600, which is very powerful and flexible and is fully compatible with the D50.
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