# Do you need to buy a specific flash depending on the lens?



## duarted (Sep 23, 2015)

Hello everyone!

I was about to buy this flash NEEWER NW680 speedlite flash E-TTL II and I saw on the description this:

GN(m ISO 100): 58m/190ft(ISO 100, 105mm)
Flash Coverage: 24-105mm(14mm with wide panel)

Does it mean that it's only usable starting with a 24mm lens? 

I have a Canon 17-40mm, does it make sense to buy this flash?

Thank you!

Duarte


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## Derrel (Sep 23, 2015)

No, the 24-105mm refers to the flash's ability to wide the beam to cover a 24mm lens's angle of view, or to restrict the beam's spread so that it covers the rather narrow angle that a 105mm lens "sees". This refers to what is called a flash with a *zoom head* system. Most of these zoom head system flashes use a small, internal motor to automatically adjust the beam's output for the length of lens in use, or for the setting that a zoom lens has been zoomed to.

With 14mm is an ultra wide-angle setting, and most all flashes use a small, slide-in or clip-on type attachment to greatly broaden the flash beam to handle such a wide angle lens's wide, ecompasssing angle of view.

The 24-105mm is almost assuredly for FX or FF aka full-frame digital, or traditional 35mm film lens angles; your camera's built-in CPU ought to send the right information to the flash automatically. I would not worry about buying the Neewer flash.


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## Overread (Sep 23, 2015)

Derrel covered it really - you should be fine with that flash.

Note that if you use the flash off-camera it will have a default head position that it will most likely spend most of the time in and you'll use light modification devices (like umbrellas or softboxes) to further modify the light angles. 

As a point of interest yes if you start using longer lenses you can end up using Frensel lens (Better Beamer is a popular brand choice) which angles the light to focus it into a tighter beam; again to allow a better coverage and less wastage at longer distances.


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## ak_ (Sep 23, 2015)

duarted said:


> GN(m ISO 100): 58m/190ft(ISO 100, 105mm)



Seems they are quoting the maximum guide number claimable by stating it for 105mm (i.e with the flash head at full zoom).


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## Derrel (Sep 23, 2015)

ak_ said:


> duarted said:
> 
> 
> > GN(m ISO 100): 58m/190ft(ISO 100, 105mm)
> ...



YES, this has become *the new normal way* to make flashes appear more powerful. It is somewhat deceptive, however, but a lot of the flash makers are following this practice these days.  For example; with the flash zoomed all the way to maximum telephoto, the 105mm position, the 190 Guide Number in Feet would yield an exposure of f/19 at 10 feet. ( 190 GN in Feet, divided by a 10-foot flash-to-subject distance = 19, or f/19 on the camera, at ISO 100 sensitivity). However...if you wanted to take a photo at 10 feet, and needed the 17mm end of the 17-40mm Canon L zoom,you would likely have a much lower Guide Number with the flash zoomed to the wider-end of the zoom range; you'd PROBABLY get an exposure of around f/8.5 to f/9, I would estimate, roughly; I have not looked at the Guide Numbers Neewer has published, but even published numbers are often optimistic (meaning, exaggerated) coming form many makers.


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## ak_ (Sep 23, 2015)

Yes, I would guess at about half that GN for wide. I have a book for the SB24 - I will take a  look at what it says.


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## ak_ (Sep 23, 2015)

Nikon SB-24: 24mm 30m (98ft); 85mm 50m (164ft)
Cobra 700AF: 28mm 25m; 85mm 38m

I have an Osram S440 also ('potato masher' type, with a bracket -non zooming, 80/20 diffusor screen) - the spec-sheet is less clear: 25ASA 8m; 1000ASA 50m; 40x54 degrees (40mm+), 60x78 degrees (24mm)


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## duarted (Sep 24, 2015)

Thank you for your tips everyone! I will order this flash


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## WayneF (Sep 25, 2015)

duarted said:


> GN(m ISO 100): 58m/190ft(ISO 100, 105mm)
> Flash Coverage: 24-105mm(14mm with wide panel)
> 
> Does it mean that it's only usable starting with a 24mm lens?
> ...




It means the angle of the flash covers a full frame sensor with a 24 to 105 mm lens.   A lens shorter and wider than 24 mm would show dark corners (on a full frame camera).

Except of course, cameras with an APS cropped sensor are a smaller frame (cropped), so the  same flash should cover and fill 17mm too.   Because the smaller sensor only shows a cropped smaller area of the flash coverage.




Derrel said:


> YES, this has become *the new normal way* to make flashes appear more powerful. It is somewhat deceptive, however, but a lot of the flash makers are following this practice these days.



Agreed, advertising only the maximum zoom guide number seems to be the new Chinese way to do it.  That is  rarely where the flash would be used.   But there should be a Guide Number chart in the user manual (sometimes can be downloaded) that shows guide numbers for every zoom.

In the old days (Japanese flashes), it was a common standard to advertise the guide number for 35 mm zoom, considered a typically useful value (mild wide angle for full frame cameras).  Today for APS cropped sensors, that same interest would be more like 24mm zoom.  But that 24mm Guide Number would be a smaller number, does not advertise as well.


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## duarted (Sep 26, 2015)

WayneF said:


> duarted said:
> 
> 
> > GN(m ISO 100): 58m/190ft(ISO 100, 105mm)
> ...






But then if I have a Canon 6D (Full Frame) this flash is not indicated for me since I have a 17-40mm lens right? I don't want black corners on my photos while shooting at 17mm


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## Derrel (Sep 26, 2015)

Put the supplied 14mm diffuser in place when you want the widest possible flash coverage. So, when shooting below the 24mm focal length range with the 17-40mm lens, you will likely want to use the supplementary diffuser device. You should be just fine. This is all very normal stuff.


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## duarted (Sep 27, 2015)

Well ok! Thanks for the tips again


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## beagle100 (Nov 9, 2015)

duarted said:


> WayneF said:
> 
> 
> > duarted said:
> ...



you won't have "black corners" with the 17-40 lens   
also look at the Yongnuo flashes


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