How to compare Flash Power (against others)?

**UncleVanya** · 10-14-2018, 11:54 AM

Originally posted by mcgregni

Yes, but with the 105mm flash setting we could light up something a lot further away, something that might look very small through that 28mm lens.

I suppose I was trying to avoid us giving the impression to the OP that GN was somehow related to the lens on the camera, as it isn't. GN is affected by changes to flash zoom settings, as the longer settings throw light' further along a narrower pathway. Guide number can be calculated even without any lens.

On Pentax flashes the zoom is automatic in p-TTL can you disable it? I know you can override when you are on manual mode, but I'm away from my gear.

photoptimist · 10-14-2018, 12:15 PM

If worth noting that the guide number is a non-linear value -- power goes with the square of the guide number. Based on the numbers people have found, the Cactus RF60x puts out double the light (1 stop) of the Metz M400 flash. And the numbers people have found seem to imply that HSS for 1/500 shutter speed is maybe 1/8 the light of a normal flash (3 stops).

Thus, you can simulate the Metz M400 flash HSS @ 1/500 second shutter speed with the Cactus RF60x fired normally at 1/16th power. And if you want to simulate rapid cycling see if the Cactus RF60x @ 1/64 is enough light.

Overall, HSS requires a lot of power to get a fast shutter speed.

**UncleVanya** · 10-14-2018, 12:35 PM

This is why some methods rely on using a lot of ganged flashguns to get enough light.

mcgregni · 10-14-2018, 01:10 PM

Regarding the question about Pentax flashes auto zooming in P-TTL mode .... Yes, the Manual flash zoom button overrides things, allowing a manual setting to be fixed even when focal lengths are changing in P-TTL mode.

angerdan · 11-04-2018, 02:54 AM

angerdan · 11-12-2018, 12:07 PM

Originally posted by BruceBanner

How can I get an idea of what the M400 will be like, in terms of power output?

I mean it's a smaller more compact flash (which is great for the purposes I want), however that should mean it's quite a bit weaker than the RF60x I'm imagining... but in real terms by how much?

Like the Metz M400 does HSS, but is it pretty bad at it?

Why not go for the AF 360 FGZ II ?

**BruceBanner** · 11-12-2018, 12:42 PM

Originally posted by angerdan

Why not go for the AF 360 FGZ II ?

I did in the end, as well as nabbing a AF201. I was just curious to see the difference of power vs weight/bulk of the M400 vs 360II but now that I own the 360II I am very happy, it's actually way more compact and lighter than the 540II which I did not like at all.

**UncleVanya** · 11-12-2018, 01:28 PM

Originally posted by BruceBanner

I did in the end, as well as nabbing a AF201. I was just curious to see the difference of power vs weight/bulk of the M400 vs 360II but now that I own the 360II I am very happy, it's actually way more compact and lighter than the 540II which I did not like at all.

I have the version 1 of the 540 and 360 and agree - the 360 is quite a bit smaller.

**BruceBanner** · 11-12-2018, 01:35 PM

Originally posted by UncleVanya

I have the version 1 of the 540 and 360 and agree - the 360 is quite a bit smaller.

Yeah I really felt the weight and stress of the 540II on the K-1 (let alone KP!). I hate hotshoes in general and have seen images of the Hotshoe plate come away from the K-1! It's a weakness in design imo, so for longevity the lighter and smaller the thingy you dock into it is prolly a good idea.

I'm just unsure how much power I am losing however from using a 360ii vs 540ii. I do shoot through my ring flash thingy for example.

**UncleVanya** · 11-12-2018, 01:43 PM - **1 Like**

Originally posted by BruceBanner

Yeah I really felt the weight and stress of the 540II on the K-1 (let alone KP!). I hate hotshoes in general and have seen images of the Hotshoe plate come away from the K-1! It's a weakness in design imo, so for longevity the lighter and smaller the thingy you dock into it is prolly a good idea.

I'm just unsure how much power I am losing however from using a 360ii vs 540ii. I do shoot through my ring flash thingy for example.

Understanding Camera Flash Guide Numbers, plus GN Calculator

The AF540 is guide number 54, the AF360 is guide number 36. These assume ISO 100 and 85mm zoom. The AF540 at 1/2 power is about guide number 38. This means the 360 is just under half the power.

This should also help: Pentax AF360FGZ II Flash Review - Specifications | PentaxForums.com Reviews

**BruceBanner** · 11-12-2018, 02:03 PM

Originally posted by UncleVanya

Understanding Camera Flash Guide Numbers, plus GN Calculator

The AF540 is guide number 54, the AF360 is guide number 36. These assume ISO 100 and 85mm zoom. The AF540 at 1/2 power is about guide number 38. This means the 360 is just under half the power.

This should also help: Pentax AF360FGZ II Flash Review - Specifications | PentaxForums.com Reviews

Thanks!

**UncleVanya** · 11-12-2018, 03:43 PM

Originally posted by BruceBanner

Thanks!

Happy to help.

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10-14-2018, 11:54 AM	#16
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,400	Originally posted by mcgregni Yes, but with the 105mm flash setting we could light up something a lot further away, something that might look very small through that 28mm lens. I suppose I was trying to avoid us giving the impression to the OP that GN was somehow related to the lens on the camera, as it isn't. GN is affected by changes to flash zoom settings, as the longer settings throw light' further along a narrower pathway. Guide number can be calculated even without any lens. On Pentax flashes the zoom is automatic in p-TTL can you disable it? I know you can override when you are on manual mode, but I'm away from my gear.

10-14-2018, 12:15 PM	#17
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,122	If worth noting that the guide number is a non-linear value -- power goes with the square of the guide number. Based on the numbers people have found, the Cactus RF60x puts out double the light (1 stop) of the Metz M400 flash. And the numbers people have found seem to imply that HSS for 1/500 shutter speed is maybe 1/8 the light of a normal flash (3 stops). Thus, you can simulate the Metz M400 flash HSS @ 1/500 second shutter speed with the Cactus RF60x fired normally at 1/16th power. And if you want to simulate rapid cycling see if the Cactus RF60x @ 1/64 is enough light. Overall, HSS requires a lot of power to get a fast shutter speed.

10-14-2018, 12:35 PM	#18
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,400	This is why some methods rely on using a lot of ganged flashguns to get enough light.

10-14-2018, 01:10 PM	#19
mcgregni Veteran Member Join Date: Sep 2012 Location: Surrey, England Posts: 2,603	Regarding the question about Pentax flashes auto zooming in P-TTL mode .... Yes, the Manual flash zoom button overrides things, allowing a manual setting to be fixed even when focal lengths are changing in P-TTL mode.

11-04-2018, 02:54 AM	#20
angerdan Pentaxian Join Date: Feb 2015 Photos: Gallery \| Albums Posts: 2,639	I do recommend these sources: Normal Power - Pentax P-TTL Flash Comparison Guide Numbers - Pentax P-TTL Flash Comparison Pentax hotshoe flash options \| Recommended old flashes for P? \| Flickr Blitze für Pentax \| Flash offerings for Pentax DSLRs compare? \| Karl Knipser \| Flickr Leitzahlen \| Leitzahlen als Formeln ausdrücken \| Karl Knipser \| Flickr

11-12-2018, 12:07 PM	#21
angerdan Pentaxian Join Date: Feb 2015 Photos: Gallery \| Albums Posts: 2,639	Originally posted by BruceBanner How can I get an idea of what the M400 will be like, in terms of power output? I mean it's a smaller more compact flash (which is great for the purposes I want), however that should mean it's quite a bit weaker than the RF60x I'm imagining... but in real terms by how much? Like the Metz M400 does HSS, but is it pretty bad at it? Why not go for the AF 360 FGZ II ?

11-12-2018, 12:42 PM	#22
BruceBanner Site Supporter Join Date: Dec 2015 Posts: 5,404 Original Poster	Originally posted by angerdan Why not go for the AF 360 FGZ II ? I did in the end, as well as nabbing a AF201. I was just curious to see the difference of power vs weight/bulk of the M400 vs 360II but now that I own the 360II I am very happy, it's actually way more compact and lighter than the 540II which I did not like at all.

11-12-2018, 01:28 PM	#23
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,400	Originally posted by BruceBanner I did in the end, as well as nabbing a AF201. I was just curious to see the difference of power vs weight/bulk of the M400 vs 360II but now that I own the 360II I am very happy, it's actually way more compact and lighter than the 540II which I did not like at all. I have the version 1 of the 540 and 360 and agree - the 360 is quite a bit smaller.

11-12-2018, 01:35 PM	#24
BruceBanner Site Supporter Join Date: Dec 2015 Posts: 5,404 Original Poster	Originally posted by UncleVanya I have the version 1 of the 540 and 360 and agree - the 360 is quite a bit smaller. Yeah I really felt the weight and stress of the 540II on the K-1 (let alone KP!). I hate hotshoes in general and have seen images of the Hotshoe plate come away from the K-1! It's a weakness in design imo, so for longevity the lighter and smaller the thingy you dock into it is prolly a good idea. I'm just unsure how much power I am losing however from using a 360ii vs 540ii. I do shoot through my ring flash thingy for example.

11-12-2018, 01:43 PM - 1 Like	#25
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,400	Originally posted by BruceBanner Yeah I really felt the weight and stress of the 540II on the K-1 (let alone KP!). I hate hotshoes in general and have seen images of the Hotshoe plate come away from the K-1! It's a weakness in design imo, so for longevity the lighter and smaller the thingy you dock into it is prolly a good idea. I'm just unsure how much power I am losing however from using a 360ii vs 540ii. I do shoot through my ring flash thingy for example. Understanding Camera Flash Guide Numbers, plus GN Calculator The AF540 is guide number 54, the AF360 is guide number 36. These assume ISO 100 and 85mm zoom. The AF540 at 1/2 power is about guide number 38. This means the 360 is just under half the power. This should also help: Pentax AF360FGZ II Flash Review - Specifications \| PentaxForums.com Reviews

11-12-2018, 02:03 PM	#26
BruceBanner Site Supporter Join Date: Dec 2015 Posts: 5,404 Original Poster	Originally posted by UncleVanya Understanding Camera Flash Guide Numbers, plus GN Calculator The AF540 is guide number 54, the AF360 is guide number 36. These assume ISO 100 and 85mm zoom. The AF540 at 1/2 power is about guide number 38. This means the 360 is just under half the power. This should also help: Pentax AF360FGZ II Flash Review - Specifications \| PentaxForums.com Reviews Thanks!

11-12-2018, 03:43 PM	#27
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,400	Originally posted by BruceBanner Thanks! Happy to help.