Flash stupidity question

Lukey · 09-12-2017, 07:33 AM

Ahoi,

So i'm a bit daft with flash units and truly have only ever used them for fill lighting at best.

Looking for something with a bit more power, basically just want to buy once and not find myself wanting more power down the line. Helping out with a not for profit and will need a flash for the event, limited space inside and group photos will be impossible with faster primes (which is what I prefer to use). So figured time to bite the bullet and learn some more.

The thing i'm not really sure about is the whole 'zoom' aspect of the units. For example the Metz 64 is 24-200mm whilst the Pentax AF540 is only 24-85mm. Does that mean I can't use most of my 70-200mm length for example with the Pentax? Or does it simply mean the TTL will stop working and i'll need to adjust manually? Or does it mean something completely different?

And yes, I know both those models are probably overkill but basically I just want something I can use for whatever I want to do with them. Plenty of times I have thought i'd have loved to have a flash with me whilst using the 70-200 at the upper end of the range for a little fill lighting (to for example remove a shadow), so i'm sure I will find uses for it.

Appreciate any help/advice!

Oh and FWIW, camera gear in Canada is apparently stupidly expensive when you account for taxes... So looking at $440 for the Metz or ~$600 for the Pentax, before 15% tax (assuming you can even find stock).

pschlute · 09-12-2017, 08:25 AM

The zoom on the flash is there for efficiency. So if you use a 85mm lens the flash narrows the beam meaning it can fire further because it doesnt need to fire as wide as if you were using a 24mm lens for example. So if you use a 200mm lens the Pentax flash will simply be sending the same width of beam as if you were using 85mm.

The AF540 at 85mm (in FF terms) will have a P-TTL maximum range of 27m at f2; 19m at f2.8; 13m at f4

Lukey · 09-12-2017, 09:00 AM

Ah ok I think I understand now. Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose? Or does it increase power to compensate for this? And if it does compensate, wouldn't the maximum range be -extremely- reduced as a result?

Not that i'd be shooting at 200mm very often, but I definitely would be @ 135mm.

bdery · 09-12-2017, 10:20 AM

Originally posted by Lukey

Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose?

It depends on the distance.

Originally posted by Lukey

Or does it increase power to compensate for this? And if it does compensate, wouldn't the maximum range be -extremely- reduced as a result?

The flash can tune its power, and it can focalize its beam (zoom). The most power is reached at the longest "zoom" position. See it this way : if the output power is fixed (say, max power), and the beam is spread over a smaller area (zoomed to max), then each surface element gets more light.

When you use a 200mm lens with a flash set to 85mm, a lot of light is lost (outside the field of view of the lens) but if the distance to subject is right (Guide Number adequate) then you won't get underexposure.

On the other hand, a flash with its max guide number given at 200mm might in fact be much less powerful than one whose GN is given at 85mm. It's useful to compare GN at similar focal lengths.

**RKKS08** · 09-12-2017, 10:47 AM - **1 Like**

Setting the flash zoom for wider than what the lens focal length would suggest can sometimes have a positive effect.

Inside, specially in smaller rooms, there will be more light bouncing from walls and ceiling, which may produce a less flat appearence of the picture. Whether this will improve the result, will depend on many things.
You should experiment with it a bit, to get a feeling of when to use this effect, and when better not.

pschlute · 09-12-2017, 10:54 AM - **1 Like**

Originally posted by Lukey

Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose?

No. P-TTL will set the correct exposure for the subject. It fires a preflash...measures the light reflected back from your subject....then calculates the flash power needed based on the aperture, ISO, and camera to subject distance. You would only get an incorrect exposure if you tried to photograph a subject outside of the available flash-to-subject distance range. These are in the manual and are also helpfully displayed on the flash unit display.

**tduell** · 09-12-2017, 03:34 PM

Originally posted by Lukey

Ah ok I think I understand now. Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose? Or does it increase power to compensate for this? And if it does compensate, wouldn't the maximum range be -extremely- reduced as a result?

Not that i'd be shooting at 200mm very often, but I definitely would be @ 135mm.

If you want to shoot with flash with long lenses, a BetterBeamer or similar can help quite a lot.

Cheers,
Terry

automorphism · 09-12-2017, 09:39 PM

In terms of zoom, I really don't think it matters too much unless your're shooting direct flash. I try and avoid this as much as possible because of the harsh "flash" look that gives. For a cramped venue, direct flash may not be necessary if you have some good walls for bouncing.

bdery · 09-13-2017, 05:20 AM

Originally posted by RKKS08

Inside, specially in smaller rooms, there will be more light bouncing from walls and ceiling, which may produce a less flat appearence of the picture.

True, although usually not applicable. In small rooms you're lucky enough to be able to bounce on a wall or ceiling. I don't think I've ever used direct light inside with my flashes.

Originally posted by automorphism

In terms of zoom, I really don't think it matters too much unless your're shooting direct flash. I try and avoid this as much as possible because of the harsh "flash" look that gives. For a cramped venue, direct flash may not be necessary if you have some good walls for bouncing.

Lukey · 09-14-2017, 09:47 AM

Thanks for the info everyone, understand it a little better now. Although seems mostly pointless unless Pentax has put support for longer than 70mm zooms into their firmware for the K-1? I'm unsure if they have or not but did read through the Metz thread explaining the K-1 refuses to communicate any focal length beyond 70mm and thus the Metz would have to be put into manual mode in that regard anyway.

Really torn, locally I have a place selling the Metz for $440, whereas the Pentax is $600+ anywhere I look (CDN$). Found one on forums, but having Paypal issues due to moving countries. I would like the WR, but honestly I rarely shoot in the rain and if I did i'd probably just slap a sandwich bag over it anyway (i'm not one to stand in the rain if it's bucketing down). Bit of a long shot, but has anybody used both and have some recommendations? Aha.

09-12-2017, 07:33 AM	#1
Lukey Forum Member Join Date: Aug 2008 Location: Newcastle Posts: 76	Flash stupidity question Ahoi, So i'm a bit daft with flash units and truly have only ever used them for fill lighting at best. Looking for something with a bit more power, basically just want to buy once and not find myself wanting more power down the line. Helping out with a not for profit and will need a flash for the event, limited space inside and group photos will be impossible with faster primes (which is what I prefer to use). So figured time to bite the bullet and learn some more. The thing i'm not really sure about is the whole 'zoom' aspect of the units. For example the Metz 64 is 24-200mm whilst the Pentax AF540 is only 24-85mm. Does that mean I can't use most of my 70-200mm length for example with the Pentax? Or does it simply mean the TTL will stop working and i'll need to adjust manually? Or does it mean something completely different? And yes, I know both those models are probably overkill but basically I just want something I can use for whatever I want to do with them. Plenty of times I have thought i'd have loved to have a flash with me whilst using the 70-200 at the upper end of the range for a little fill lighting (to for example remove a shadow), so i'm sure I will find uses for it. Appreciate any help/advice! Oh and FWIW, camera gear in Canada is apparently stupidly expensive when you account for taxes... So looking at $440 for the Metz or ~$600 for the Pentax, before 15% tax (assuming you can even find stock).

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09-12-2017, 08:25 AM	#2
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,222	The zoom on the flash is there for efficiency. So if you use a 85mm lens the flash narrows the beam meaning it can fire further because it doesnt need to fire as wide as if you were using a 24mm lens for example. So if you use a 200mm lens the Pentax flash will simply be sending the same width of beam as if you were using 85mm. The AF540 at 85mm (in FF terms) will have a P-TTL maximum range of 27m at f2; 19m at f2.8; 13m at f4

09-12-2017, 09:00 AM	#3
Lukey Forum Member Join Date: Aug 2008 Location: Newcastle Posts: 76 Original Poster	Ah ok I think I understand now. Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose? Or does it increase power to compensate for this? And if it does compensate, wouldn't the maximum range be -extremely- reduced as a result? Not that i'd be shooting at 200mm very often, but I definitely would be @ 135mm.

09-12-2017, 10:20 AM	#4
bdery Pentaxian Join Date: Mar 2008 Location: Quebec city, Canada Photos: Gallery Posts: 9,363	Originally posted by Lukey Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose? It depends on the distance. Originally posted by Lukey Or does it increase power to compensate for this? And if it does compensate, wouldn't the maximum range be -extremely- reduced as a result? The flash can tune its power, and it can focalize its beam (zoom). The most power is reached at the longest "zoom" position. See it this way : if the output power is fixed (say, max power), and the beam is spread over a smaller area (zoomed to max), then each surface element gets more light. When you use a 200mm lens with a flash set to 85mm, a lot of light is lost (outside the field of view of the lens) but if the distance to subject is right (Guide Number adequate) then you won't get underexposure. On the other hand, a flash with its max guide number given at 200mm might in fact be much less powerful than one whose GN is given at 85mm. It's useful to compare GN at similar focal lengths.

09-12-2017, 10:47 AM - 1 Like	#5
RKKS08 Site Supporter Join Date: Mar 2010 Location: Frankfurt am Main Posts: 1,241	Setting the flash zoom for wider than what the lens focal length would suggest can sometimes have a positive effect. Inside, specially in smaller rooms, there will be more light bouncing from walls and ceiling, which may produce a less flat appearence of the picture. Whether this will improve the result, will depend on many things. You should experiment with it a bit, to get a feeling of when to use this effect, and when better not.

09-12-2017, 10:54 AM - 1 Like	#6
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,222	Originally posted by Lukey Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose? No. P-TTL will set the correct exposure for the subject. It fires a preflash...measures the light reflected back from your subject....then calculates the flash power needed based on the aperture, ISO, and camera to subject distance. You would only get an incorrect exposure if you tried to photograph a subject outside of the available flash-to-subject distance range. These are in the manual and are also helpfully displayed on the flash unit display.

09-12-2017, 03:34 PM	#7
tduell Loyal Site Supporter Join Date: May 2015 Location: Melbourne Posts: 1,517	Originally posted by Lukey Ah ok I think I understand now. Wouldn't that mean if it's firing a beam width for 85mm and I was actually using 200mm it would consistently underexpose? Or does it increase power to compensate for this? And if it does compensate, wouldn't the maximum range be -extremely- reduced as a result? Not that i'd be shooting at 200mm very often, but I definitely would be @ 135mm. If you want to shoot with flash with long lenses, a BetterBeamer or similar can help quite a lot. Cheers, Terry

09-12-2017, 09:39 PM	#8
automorphism Veteran Member Join Date: Jun 2015 Location: Ontario, Canada Photos: Albums Posts: 791	In terms of zoom, I really don't think it matters too much unless your're shooting direct flash. I try and avoid this as much as possible because of the harsh "flash" look that gives. For a cramped venue, direct flash may not be necessary if you have some good walls for bouncing.

09-13-2017, 05:20 AM	#9
bdery Pentaxian Join Date: Mar 2008 Location: Quebec city, Canada Photos: Gallery Posts: 9,363	Originally posted by RKKS08 Inside, specially in smaller rooms, there will be more light bouncing from walls and ceiling, which may produce a less flat appearence of the picture. True, although usually not applicable. In small rooms you're lucky enough to be able to bounce on a wall or ceiling. I don't think I've ever used direct light inside with my flashes. Originally posted by automorphism In terms of zoom, I really don't think it matters too much unless your're shooting direct flash. I try and avoid this as much as possible because of the harsh "flash" look that gives. For a cramped venue, direct flash may not be necessary if you have some good walls for bouncing.

09-14-2017, 09:47 AM	#10
Lukey Forum Member Join Date: Aug 2008 Location: Newcastle Posts: 76 Original Poster	Thanks for the info everyone, understand it a little better now. Although seems mostly pointless unless Pentax has put support for longer than 70mm zooms into their firmware for the K-1? I'm unsure if they have or not but did read through the Metz thread explaining the K-1 refuses to communicate any focal length beyond 70mm and thus the Metz would have to be put into manual mode in that regard anyway. Really torn, locally I have a place selling the Metz for $440, whereas the Pentax is $600+ anywhere I look (CDN$). Found one on forums, but having Paypal issues due to moving countries. I would like the WR, but honestly I rarely shoot in the rain and if I did i'd probably just slap a sandwich bag over it anyway (i'm not one to stand in the rain if it's bucketing down). Bit of a long shot, but has anybody used both and have some recommendations? Aha.