flash exposure / focal lenght in 10D

[Sendide]

About adjusting the flash exposure in 10D
my question is : if the 10D reports the normal focal lenght of the attached lens to the flash (as mentionned by Slin100), the flash coveraget will be wider than needed (wich does not matter) , but will it be stronger than needed? should we than adjust it (whitin the 550EX or the 10D if the 440EX is used)?
I read once in this forum that the 1.6 factor for the 10D is actually about reducing the width not increasing the focal lenth is the strict meaning of the word, if this is true , means that the flash exposure needs no adjustment at all!1 am I right ?

[DaveG]

About adjusting the flash exposure in 10D
my question is : if the 10D reports the normal focal lenght of the attached lens to the flash (as mentionned by Slin100), the flash coveraget will be wider than needed (wich does not matter) , but will it be stronger than needed? should we than adjust it (whitin the 550EX or the 10D if the 440EX is used)?
I read once in this forum that the 1.6 factor for the 10D is actually about reducing the width not increasing the focal lenth is the strict meaning of the word, if this is true , means that the flash exposure needs no adjustment at all!1 am I right ?

Yes the flash's cone is too wide for the "asked for" focal length. 99% of the time it doesn't mean anything since the wide cone doesn't affect exposure unless your subject is some distance away and at the edge of the flash's power. A more concentrated cone of light would be more effective there, but it's unlikely you'll run into this problem very often.

You may have to bias your exposures, but not because of this.

Have you increased the focal length with a 50 mm lens on the 10D compared to the same lens on an ELAN II? Yes and no.

Yes, you have "cropped out" the equivilent of 80 mm with the 10D, so effectively you have an "80 mm" lens aboard.

No, because focal length doesn't mean magnification.

Before the 1.6 conversion digital stuff there were three main types of cameras: 35 mm, medium format and large format. A 50 mm lens on 35 mm was normal; "normal" technically being the diagonal of the negative, but more or less what you eye sees. A 50 on medium format would be a moderate wide angle lens, while on large format (4"x5") a 50 would be a super wide angle. It's all affected by the size of the negative, or in this case the CMOS.

Because the 1.6 conversion is so new, the lenses are still for full 35mm format, and (I hope) that the whole 1.6 thing is transitional; there hasn't been a mind set change. If I'm talking about a 55 mm Mamiya 645 lens I know that it's a wide angle and so does anyone familiar with MF. But I still convert the 35 mm lens to "80 mm effectively" with DSLR so I'm clear. If the 1.6 conversion was an industry standard and around for years then you would just know that a 50 mm lens was a short telephoto for portrait shots, just like I know that an 85 is the same thing for 35 mm, a 150 for MF and a 300 for large format.

[Sendide]

it's always instructive to ask questions over here!
thanks for the information, than another one if you don't mind, far away may be from the first one, just that I do not know what the word means :
I've been told once that the 12-24 Sigma is not bad but might present some "vignetting" problem!! what is vignetting?!!!
thx
Kh

[Jim Larson]

I read once in this forum that the 1.6 factor for the 10D is actually about reducing the width not increasing the focal lenth is the strict meaning of the word, if this is true , means that the flash exposure needs no adjustment at all!1 am I right ?

Not 100%. The 1.6 factor means that the 10D sensor is smaller than a 35mm frame by a factor of 1.6.

With a standard lens, some light falls outside of the range of the sensor. In part, you are not fully utilizing the lens.

On the canon flashes, the flash head zooms to better cover the lens. Strictly speaking, since fully covering a lens that is too big for the sensor is slightly silly. Zooming the flash a bit further based upon sensor coverage would be better. This is a bug.

BUT as long as you have enough flash power, the width is irrelevent. The camera will call for "the right power", and will not underexpose the image. The zoom error just means that the flash has to work a bit harder. If the flash is powerful enough, there is no issue.

Frankly, you are best off buying a diffuser ($20) to spread the light FURTHER. This bounces light around and makes the image look more natural. With a diffuser attached, the zoom setting is actually irrelevant.

[Sendide]

is this diffuser the same one mounted onto the 550EX?
do they fit any flash ?

[Jim Larson]

There is a chinsy flip out diffuser built into the 550EX head.

I bought a Stofen Omni Bounce for $16 from B&H. The diffuser should be fitted for the flash.

I have heard many say a index card attached with a rubber band (when the flash is pointed to a ceiling) works just as well.

[DaveG]

There is a chinsy flip out diffuser built into the 550EX head.

I bought a Stofen Omni Bounce for $16 from B&H. The diffuser should be fitted for the flash.

I have heard many say a index card attached with a rubber band (when the flash is pointed to a ceiling) works just as well.

The difference is that the built in diffuser widens the flash's cone. Both the Stofen and a fill card act in concert with a bounce. If you are in a room with a low white ceiling then you would be OK with the Stofen/card approach. But this technique significantly weakens the power of the flash, so the flip down diffuser is the tool to use when you want very wide light but with the flash tube pointed directly at the subject.