Canon 580/Metz 58 do they adjust for sensor size?

I have the Metz 58 flash. One of the functions I can set is for it to compensate for sensor size if you have a 1.6 crop body like my 30D.

I'm a little confused about this function and I wonder if anyone can help me out. I included the Canon 580 in my title because the Metz is supposed to mimic the Canon, and in my experience Metz has done a great job doing that.

So, when this function is not set, LC screen shows AZoom, meaning auto zoom. When this function is set the LC screen shows SZoom. My question is, in auto zoom is the flash automatically compensating for the chip size? Does the 580 do this automatically or does the user have to manually select it?

I'm confused because with the function off, in AZoom, with my 17-55 lens at 17 the LC screen shows 24 and at 55 it shows 50. But with SZoom on at 17 it shows 16 but at 55 it show 47. So neither function shows the correct focus length for the entire range.

The Metz manual says to consult my camera manual for specific information but the 30D manual doesn't say anything about this.

Thanks for any help you can give me.

From what I can make out, the Metz 58 is behaving nothing like the 580EX when it comes to reporting the head zoom setting when Zoom Size is set to On. On the 580EX, when the custom function is set to take the sensor size into account, the zoom displayed still shows the focal length set on the lens. The difference is in the actual zoom position that's used for the flash head. If, for example, we're using a 24mm lens, the 580EX display will show 24mm along with the rectangular icon which tells us that the sensor size is being taken into account. The actual flash head position, however, will be set at 35mm.

The Metz, on the other hand, doesn't seem to be behaving this way. As a matter of fact, it seems to be doing the opposite. If Zoom Size is set to On, if, for example, I have a 24-105 lens at 105mm, the flash will show S-Zoom as 70mm. If the flash head position were truly set to the 70mm position, the flash would be a lot wider than necessary, even for a FF camera, let alone a 1.6X crop camera.

So, after "reverse engineering" the logic here based on my observation of the Metz's behavior and also reading the first sentence in the manual for Zoom Size:

I've come to the conclusion that the Zoom Size feature really isn't of any practical use to a Canon EOS user since I know of no EOS digital camera that converts the actual focal length of the lens to the crop-factor equivalent before passing along this information to the flash.

I did a side by side test of the Metz 58 AF-1 and the Canon 580EX and, contrary to what I said in my previous post, it does look like the Metz is "correctly" taking the sensor crop factor into account when physically setting the flash head zoom position. I verified this by measuring the light intensity at the "normal" zoom position and the "corrected" zoom position. The corrected zoom position was brighter by 1/3 stop compared to the normal zoom position using a 50mm lens. Interestingly, the 580EX has a 2/3 stop difference using the same lens.

The focal lengths displayed for the zoom positions are obviously out of whack from what should really be displayed but the flash is working the way its supposed to be when Zoom Size is set to On. Metz should be able to fix this bug via a firmware upgrade if they are made aware of this bug.

they both do that.
if you shoot a wall with a full frame camera and the metz set as cropped sensor then you can clearly see the difference: at the bottom of the frame in particular.

then the metz has the extended zoom feature but that doesn't have much to do with the sensor size.

antonello wrote in post #4730826
they both do that.
if you shoot a wall with a full frame camera and the metz set as cropped sensor then you can clearly see the difference: at the bottom of the frame in particular.

then the metz has the extended zoom feature but that doesn't have much to do with the sensor size.

Yes, the physical evidence is very clear. But what's really confusing are the numbers that are displayed on the LCD screen when Zoom Size is turned on. They make absolutely no sense at all.

eheh..
you are absolutely right!

Heh, I remember when I figured that out with my metz, it makes little sense but it works well enough.

It should be possible to adjust the Metz 58 so that it thinks of FF AOV vs. APS-C AOV with any given focal length. For example, it would provide over 45 degree coverage angle for APS-C use, and provide over 65 degree coverage for FF/film use.

In both cases, it still sees 35mm lens or 50mm lens or 105mm lens, but the coverage angle is changed. But I'd have to go home to be sure of the behavior about FL reported.

Still being pretty dense about flashology, the consensus is that setting zoom size to ON is beneficial even though the LC screen readout is confusing? With a house full of young kids I don't have nearly as much free time to experiment and compare as I used to, so the concise answers that I get here on POTN to my basic questions have been invaluable for helping me understand my camera and photography. Thanks again for taking the time to respond.

I just ran a test of the Metz54 behavior on my 20D, with the Metz set to autozoom with APS-C selection of coverage. At minimum it says 20mm unless I pull out the supplementary WA lens which causes it to say 16mm throughout the range. Without the supplementary lens it steps thru the sequence 20-24-28-40-55 with my Canon 17-55mm lens, and all the changeover points are very close to the indicated FL values on the zoom ring.

Wilt wrote in post #4735656
I just ran a test of the Metz54 behavior on my 20D, with the Metz set to autozoom with APS-C selection of coverage. At minimum it says 20mm unless I pull out the supplementary WA lens which causes it to say 16mm throughout the range. Without the supplementary lens it steps thru the sequence 20-24-28-40-55 with my Canon 17-55mm lens, and all the changeover points are very close to the indicated FL values on the zoom ring.

Does the Metz 54 allow you to select between FF and APS-C (we're not talking about the Extended zomm mode here, right)? What Metz 54 model do you have?

PacAce wrote in post #4735695
Does the Metz 54 allow you to select between FF and APS-C (we're not talking about the Extended zomm mode here, right)? What Metz 54 model do you have?

Yes, Metz 54MZ4, and use 3102 M3 module with it for full Canon ETTL flash dedication. The menu allows for normal 135 format cover, E for 'extended zoom' with 135 format, APS-C, 645 format, and 6x6 and 6x7 and 6x9 medium format. Normal 135 format and 'extended zoom' 135 format coverage are different (e.g. 35mm AOV coverage with 50mm lens),

Wilt wrote in post #4735772
Yes, Metz 54MZ4, and use 3102 M3 module with it for full Canon ETTL flash dedication. The menu allows for normal 135 format cover, E for 'extended zoom' with 135 format, APS-C, 645 format, and 6x6 and 6x7 and 6x9 medium format. Normal 135 format and 'extended zoom' 135 format coverage are different (e.g. 35mm AOV coverage with 50mm lens),

Thanks, Wilt. So, since "resizing" for APS-C sized sensors isn't new to Metz, I wonder why they missed the boat when they tried to implement the same thing on the 58 AF-1? Anyway, it's not that big a deal since it does work. It's just the value displayed on the LCD screen that's out of whack.

PacAce wrote in post #4735855
Thanks, Wilt. So, since "resizing" for APS-C sized sensors isn't new to Metz, I wonder why they missed the boat when they tried to implement the same thing on the 58 AF-1? Anyway, it's not that big a deal since it does work. It's just the value displayed on the LCD screen that's out of whack.

Maybe the German Metz engineers were infiltrated by one of the Canon flash engineers who helped them engineer the Canon wireless compatibility! I won't call it 'sabotage', as they were 'helping'...but Canon's flash engineers are not so bright (pun intended!)