Flash crop factor.

jwkwd · Jan 1, 2008

Maybe hell froze over or it's a new year or possibly an alien abduction, but I got a digital camera. What my question is, if you have a crop factor of 1.5 and your lens is 35mm, would a flash with zoom be set to 52mm? (50mm). TIA

table1349 · Jan 1, 2008

jwkwd said:
Maybe hell froze over or it's a new year or possibly an alien abduction, but I got a digital camera. What my question is, if you have a crop factor of 1.5 and your lens is 35mm, would a flash with zoom be set to 52mm? (50mm). TIA

No. a crop factor is just that, a crop factor. You are getting the center of the field of view of the lens on the sensor. It is not magnifying anything. Thus your 35mm lens on a crop sensor camera gives the sensor the field of view that a full frame would see on a 50mm lens.

The flash puts out the light needed for the focal length of the lens at the angle needed for that focal length. A 35mm lens is a 35mm lens. That never changes.

jwkwd · Jan 1, 2008

Well thank you, that seems simple enough.

Garbz · Jan 2, 2008

Well that being said if you use a 50mm lens you can manually zoom your flash to 75mm to get a bit extra power out of it without vignetting.

Think of it as reverse crop factor. It works per normal and you get to crop it down rather then the other way round

Big Mike · Jan 2, 2008

That's right.

The zoom settings on the flash are calibrated for a 35mm film FOV....so if you are using a crop factor camera and matching the zoom on the flash head to the focal length, the flash will give you more light coverage than the lens sees...thereby wasting some light/power.

However, the newest cameras/flashes have been programed to compensate for this when mounted on crop cameras...and set the zoom on the flash head to a longer setting.

table1349 · Jan 2, 2008

Big Mike said:
That's right.

The zoom settings on the flash are calibrated for a 35mm film FOV....so if you are using a crop factor camera and matching the zoom on the flash head to the focal length, the flash will give you more light coverage than the lens sees...thereby wasting some light/power.

However, the newest cameras/flashes have been programed to compensate for this when mounted on crop cameras...and set the zoom on the flash head to a longer setting.

While that is true, I don't believe that it registers as such on the flash display. It still is putting out the needed amount of light for the focal length/distance to the subject, just narrowing the beam of light for the crop, thereby saving power. Ain't that about right Big Mike?

jwkwd · Jan 2, 2008

What would show up in the display of the flash is what made me think of crop. I did not know if even with auto this and thats on the flash, if I would have to shoot on manual. However, when using flash I generally bounce it with a Lumiquest 80/20 or supersoft attached to the flash so the extra bit of light that the flash thinks it needs might actually work better. Other than that, I would compensate 1 - 2 stops for the diffuser. Thank's, Garbz, Big Mike and Gryphonslair99. I think that you are all right, and after shooting film for 30 years, regardless there is going to be a learning curve when holding a digital. I know that you should never say never, but I really did not think I would get a DSLR unless a good deal fell into my lap and I could still use all the older lens' that I have. A D1, that's cutting edge isn't it?

Sideburns · Jan 3, 2008

The newest E-TTL and I-TTl and whatever flashes automatically sense they are on a cropped body, so they narrow the beam(zoom in more).

Garbz · Jan 3, 2008

How new do you have to get? The SB-800 doesn't.

gryphonslair99 you're right about that it still puts the needed light out. The point is that it is zoomed out slightly compared to what it needs to be. The difference then happens in the marginal cases where the flash fires full power and under exposes by half a stop may be saved by manually changing the zoom from 75mm to 100mm. But I wouldn't do it in any setting where automatic and speed is critical.

jwkwd · Jan 3, 2008

I don't think that I am going to worry about "new" stuff. If this camera was manufactured in '99 or so, it is by far the newest thing that I have. The SB-25 and the couple of AF lens' that I have been using on my F4 are compatible with a D1 and that's all I care about.