Most photographers using flash are leaving performance on the table — not because they’re doing anything wrong, but because they don’t fully understand what the numbers on their kit actually mean. In this episode, Marcus unpacks the physics of flash in plain English: what wattage really tells you, why flash duration is the spec that actually freezes movement, and how your choice of modifier is quietly affecting every shot you take.
If you’ve ever wondered why your flash feels slow, why your action shots aren’t as sharp as they should be, or whether spending more on a higher-watt unit is actually worth it — this episode will change how you think about your kit.
00:00.57
Sam Hollis
Hello Marcus, how are you doing?
00:02.68
Marcus Ahmad
ah I’m very well, Sam. How are you?
00:04.92
Sam Hollis
Yeah, excellent, excellent. Dedicated to the show, as video listeners can see, I’m in a park trying to keep cool, but still here recording for you.
00:12.98
Marcus Ahmad
Yeah, you’re you’re in Holland, you said.
00:12.80
Sam Hollis
for the
00:16.59
Sam Hollis
Netherlands picking up my…
00:17.37
Marcus Ahmad
Netherlands.
00:18.30
Sam Hollis
on the way back, back to the…
00:20.09
Marcus Ahmad
Nice. And it looks equally as hot there as it does here.
00:21.37
Sam Hollis
at
00:24.54
Sam Hollis
ah Yes, very, very similar.
00:26.89
Marcus Ahmad
Oh, yeah, yeah, yeah.
00:26.81
Sam Hollis
um So Marcus, I think you’re going to be talking to us today, aren’t you? What what are you going to be talking about today?
00:32.91
Marcus Ahmad
I’m going to dive into the technical side of Flash. So a little bit of numbers and physics and that kind of thing. So going to, you know, this is probably aimed at more intermediate advanced Flash users.
00:47.10
Sam Hollis
Okay, and I’ll run my physics mind over the numbers for you.
00:50.21
Marcus Ahmad
That’s what I thought.
00:50.54
Sam Hollis
You’d be really pleased pleased with that.
00:51.96
Marcus Ahmad
Yeah.
00:52.46
Sam Hollis
And then you’ve got a webinar coming we up in flash as well, haven’t you, that’s kind of related.
00:55.32
Marcus Ahmad
I have. Yeah, that’s right. That’s coming up on ju on July the 6th. It’s coming up. You can sign up. There’s going a little um voice promo coming up during the show about when it is. but But that will be covering more basic Flash.
01:08.48
Marcus Ahmad
In fact, on that webinar, I’m going to be covering the six principles of Flash. I’ve distilled everything I know about Flash into six sentences, Sam.
01:14.20
Sam Hollis
Okay. Okay.
01:18.20
Sam Hollis
Cool. And then how do people sign up?
01:20.47
Marcus Ahmad
Yeah, it’s at marcusalma.com at flash hyphen slash slash fundamentals.
01:29.37
Sam Hollis
Okay, let me just do that one again. marcusarmed.com forward slash flash hyphen fundamentals. Yeah.
01:36.09
Marcus Ahmad
Something like that. I think there’s there’s an ident coming There’s a voice promo coming up on the show, isn’t there?
01:43.22
Sam Hollis
Yeah, the only thing is I wasn’t sure we’re going to do it if we talked about it first, Marcus.
01:46.90
Marcus Ahmad
okay. let me get let me
01:48.25
Sam Hollis
Anyway, it’s fine.
01:48.89
Marcus Ahmad
like Okay, I was going to get this. The name is marcusahmad.com forward slash flash hyphen fundamentals.
02:00.38
Sam Hollis
Perfect. Excellent.
02:01.14
Marcus Ahmad
Wow, we got there in the end.
02:01.34
Sam Hollis
So that’s it.
02:02.50
Marcus Ahmad
I have to apologize.
02:03.33
Sam Hollis
Let’s start with…
02:04.57
Marcus Ahmad
The heat is getting to me.
02:04.79
Sam Hollis
That’s right.
02:05.57
Marcus Ahmad
The heat is getting to me a bit, Sam, today, I must admit.
02:07.48
Sam Hollis
The heat is on. So Marcus, tell us about, in this lack of light environment we have right now, do tell us about Flash.
02:14.53
Marcus Ahmad
that’s perfect Yeah, so this is going to be called What’s the What Got to Do With It? So I’ve sureve got a double but double pun going in there, if you might recognize. So what’s the what? So what is a what, first of all? then this says You see this um on the side of some flash units, WPS or what seconds. And it’s basically, as you well know, so actually I’m going to hand this first question over to you because you probably know it better than me.
02:42.87
Sam Hollis
Well, watts is a unit of power, and power is just energy used per second.
02:44.95
Marcus Ahmad
Yes.
02:46.89
Sam Hollis
So it’s how much NE have you got, and you can use it per second.
02:47.51
Marcus Ahmad
Exactly. Exactly. Which is different to how we some flash guns measure it. Some flash guns, mainly speed lights, measure it as a guide number.
02:58.73
Marcus Ahmad
And that’s how much the actual light comes out of the flash, as opposed to the wattage.
03:02.84
Sam Hollis
OK.
03:05.56
Sam Hollis
Yeah.
03:06.68
Marcus Ahmad
So different flashes, different they range roughly, like for a speed light, might be 100 watts, for example, but it can go up to a studio light. Could be something in the around region of 3,000, 4,000 watts per second.
03:19.74
Marcus Ahmad
four thousand watts per second
03:21.60
Sam Hollis
Well, you could be cooking someone under that.
03:23.61
Marcus Ahmad
You could. And there’s a reason for that, Sam. um And this is what vi is we’re going to dive into first. the The first reason is when you put a modifier on a light, you’re going lose power. Some modifiers more than others, like a beauty disc, for example, which is like a silver line beauty disc, is going be quite a hard reflective surface. You’re not going to lose too much power.
03:47.67
Sam Hollis
Yep.
03:48.31
Marcus Ahmad
But ah um a massive six foot octabox, double line, double diffused, you know, with the flash pointing, not straight out, but into the actual brolly, you’re going lose maybe half the power that, you know, I’m guesstimating here, but going lose a lot of power.
04:03.16
Sam Hollis
Yeah, yeah. But you’re going to lose a lot. the more The more stuff you put in front of the flash, the more going to lose light, aren’t you?
04:08.80
Marcus Ahmad
Exactly. If you’re bouncing a flash, you’re going to be losing light. And what I mean by bouncing is off a ceiling or of ah ah ah for a scrim or for bounce board or something like that.
04:14.28
Sam Hollis
Yep.
04:21.19
Marcus Ahmad
And there you’re going to maybe be losing one or two stops of light ah as well. as So you you can soon chip away to those figures. um And if you’re using like a 100-watt flash gun bounced off a ceiling,
04:37.69
Marcus Ahmad
and you’ve got it at one-to-one power, i.e. full power, it’s going to take ages for that flash to recycle. And when I mean ages, it could be between two and five seconds, which is not a lot.
04:50.87
Marcus Ahmad
But in the world of photograph photography, it’s a lot.
04:51.30
Sam Hollis
I guess it depends what you’re doing is whether that’s ages doesn’t if you’re doing something like an event that could be you need to bang bang but you could be doing something that’s quite slow and it doesn’t matter
04:53.02
Marcus Ahmad
Yeah, exactly.
04:56.60
Marcus Ahmad
Oh, yeah.
05:00.50
Marcus Ahmad
Yeah, I mean, again, when I, you know, back in the studio shooting fashion, it’s all bang, bang, bang, really, really. I thought, you know, you fire very quickly. Every frame with a good good model, every frame is different. So you don’t want to be lagged behind by um this recycling time.
05:15.79
Marcus Ahmad
So the way around it is by going for a higher wattage unit in the first place. Yeah.
05:21.75
Sam Hollis
A flash or of battery or both?
05:23.93
Marcus Ahmad
ah Well, the the flash, the flash unit, you want to hire, you know, that’s where the 2000, well, sorry, let’s just say the 800 watts per second up to the 2000, 3000 and start to come in.
05:26.97
Sam Hollis
Okay.
05:35.49
Marcus Ahmad
Because what it means, you’ve got a lot of headway there, and you can shoot at maybe quarter of power, which I tend to do.
05:42.41
Sam Hollis
Oh, okay. So then if you’re shorting at quarter power, the batteries it come with will have no problem keeping up because they’re designed to cope with the full the full flash.
05:50.04
Marcus Ahmad
Exactly. So you might think, worst what’s the point of paying for the extra? But soon as you get that and you start using it, you’re going to think, oh, why didn’t I just go for those maximum watts? So that’s a a really a good way of thinking about it, recycling time.
06:01.75
Sam Hollis
Okay.
06:03.76
Marcus Ahmad
Now, obviously, yes.
06:04.31
Sam Hollis
And then, sorry, quick question. so if Do you get a choice of battery with flash? So could you get like ah a lower power flash with a higher power battery so it has a shorter recycling time?
06:14.27
Marcus Ahmad
That…
06:13.91
Sam Hollis
Or do they tend to just come together?
06:16.09
Marcus Ahmad
Now, you can get different powered batteries, the watt-miller amp, isn’t it, that it will give you more, ah like, will hold the power better. yeah That is a very technical question, Sam. I don’t know about batteries. Let’s just say i don’t think so.
06:32.02
Marcus Ahmad
yeah I don’t think so.
06:32.44
Sam Hollis
Okay, so basically you buy it as a other thing and it the flash comes to the battery.
06:36.31
Marcus Ahmad
Yeah, you can’t replace the batteries on flashes anyhow.
06:39.13
Sam Hollis
Okay.
06:39.91
Marcus Ahmad
They’re really heavy units. And I’m going to talking a little bit more about that in a minute.
06:41.56
Sam Hollis
Yeah.
06:43.59
Marcus Ahmad
So um so high wattage is great if you’re go so you can keep it down the power down.
06:44.06
Sam Hollis
Okay.
06:50.35
Marcus Ahmad
But and another thing you could do these days, of course, is you can shoot at higher ISOs. ah
06:56.73
Sam Hollis
Yeah.
06:57.34
Marcus Ahmad
back in the day, you know, you be you were limited by what film stock you had, and in a studio you’d be at 100 ISO, maybe 64.
07:02.58
Sam Hollis
Yeah, yeah
07:04.10
Marcus Ahmad
These days, you could be shooting at 400 on a full-frame sensor, and it’s not going to be much grain, and the contrast still holds.
07:11.96
Sam Hollis
yeah.
07:12.50
Marcus Ahmad
So that’s another way around it.
07:12.32
Sam Hollis
Yeah, the the noise is getting less and less all the time, isn’t it?
07:15.51
Marcus Ahmad
Yeah, but I have to say this on a what we call a monoblock, which is basically the flash um is separate to the ah power source where you can separate those two out and it’s on full power. You know, I really with lots of watts per second going on. It’s got a very satisfying sound to it when it pops off.
07:36.63
Marcus Ahmad
It makes all the difference.
07:36.52
Sam Hollis
Excellent. Most important thing.
07:38.46
Marcus Ahmad
Yes. Okay. So that’s the, the, that’s the, uh, what the watch is and what that, the importance of that. Um, another thing that we might need a lot of power is when you’re shooting outside, like on ah a day where you are, Sam, if you want flash to overpower the sunlight, when you’re outside,
07:57.21
Sam Hollis
that Then you need a pretty powerful flash.
07:59.10
Marcus Ahmad
but you need really a high-powered flash. It’s quite surprising. Your speed light will not cut it outside on a sunny day.
08:07.93
Sam Hollis
Yeah, well I guess you’ve got a lot of background light, haven’t you? So yeah, ah getting equivalent to that, you’re goingnna you’re going to need your own little son.
08:11.30
Marcus Ahmad
A lot to overcome there.
08:14.68
Marcus Ahmad
You are get exactly right. So, you know, you can bring it in close and stuff like that, and I talk about these kinds of things in my workshop, but you still need lots of power. Okay, the next um thing we’re going to talk about is the T number.
08:23.05
Sam Hollis
Yeah.
08:28.70
Marcus Ahmad
The T number.
08:29.19
Sam Hollis
Ooh, never heard of that one.
08:29.82
Marcus Ahmad
hey No, T ranges from one to five.
08:31.51
Sam Hollis
Go on.
08:34.35
Marcus Ahmad
And it’s really what it is. It’s a flash duration. How long the flash is flashing for. And it can vary. A slow T number would be something round about maybe two hundredth of a second. A fast T number would be something in the tens of thousands of a second, probably even beyond that with some specialized lighting units for physics. So why does that matter? Well, to do if you’re photographing something that’s got movement,
09:03.38
Marcus Ahmad
um And let’s go to an example. There’s a really famous photograph of a bullet going through an apple that was photographed in the 1940s.
09:10.78
Sam Hollis
Yeah, yeah. Yep.
09:12.10
Marcus Ahmad
You know it.
09:11.80
Sam Hollis
I know the one.
09:12.58
Marcus Ahmad
Most people know this.
09:12.48
Sam Hollis
Yeah, yeah.
09:13.62
Marcus Ahmad
Now, the way that was done, it was not with the – obviously, the shutter wasn’t able to capture it at that speed. It was done in a darkened room, which triggered a flash.
09:19.83
Sam Hollis
Okay.
09:23.48
Sam Hollis
So, and then are most flashes working that way. yeah yeah Your kind of speed is shutter speed isn’t that quick, but actually the flash is, and that’s kind of what, that’s key.
09:35.13
Marcus Ahmad
Well, that’s exact that’s how that picture was taken, that photograph was taken.
09:38.08
Sam Hollis
Yeah.
09:39.09
Marcus Ahmad
So to stop the bullet going through the apple, which is an amazing shot, that you would have need you would need a shutter speed at that time would have been possible. But you would probably, I don’t know what it would be, Sam, something like above the tens of thousands to to freeze a bullet.
09:48.63
Sam Hollis
Yeah.
09:53.17
Sam Hollis
Yeah, which certainly with a manual shutter, it’s just not possible, is it?
09:56.34
Marcus Ahmad
Not at all. So um movement matters for your two number. Now, obviously, we’re not all going out there photographing apple bullets going through apples. But a common usage is photographing like movement like ballet in a studio or people jumping, jumping around.
10:10.22
Sam Hollis
Yeah.
10:11.66
Marcus Ahmad
And, you know, if you haven’t got ah a high T number, you’ll notice blur on your flash where it’s not frozen in it.
10:17.62
Sam Hollis
Yeah. yeah
10:20.89
Marcus Ahmad
So you that’s something that needs to bear in mind. And when you buy a flash, if you dig deep down, it will give you the T number. So you can make evaluations on that.
10:29.05
Sam Hollis
Okay And then how relevant that presumably depends on what you’re photographing
10:33.66
Marcus Ahmad
Yeah, that’s right. I mean, ah you know i my the Godox flashes I use have all got good T numbers. They’re quite fast, so I’ve brought that in mind.
10:39.75
Sam Hollis
Yeah
10:41.02
Marcus Ahmad
Now, there is a way around this, and speed lights, the ones that go in your camera, they have very high T numbers. They’re really good at capturing movement.
10:49.14
Sam Hollis
Okay.
10:50.26
Marcus Ahmad
I don’t know what it is, why that is, but they they are.
10:55.90
Marcus Ahmad
Yes, so any questions on that, Sam, before I move on?
10:58.94
Sam Hollis
No, I think that all kind of makes sense. um So even with normal flash, you were saying you have a relatively long um exposure time, but then the flash is just kind of capturing that thing quickly.
11:09.21
Marcus Ahmad
Yes.
11:10.87
Sam Hollis
Yeah. Okay.
11:11.83
Marcus Ahmad
Yes. Okay. So what else can we talk about with Flaps? Well, we’ve talked about the wattage, we’ve talked about the modifiers, we’ve talked about the tea time. and Those are some of the more advanced um things that you’re going to think about.
11:27.67
Marcus Ahmad
um Maybe if going to start using grids, which is like a honeycomb honeycomb on your modifier, you really need to think about positioning of the light in a very critical way.
11:40.73
Marcus Ahmad
Because what a honeycomb or grid does to the light, it’s like a crisscross arrangement. And it’s a bit like this thing in front of me so on my microphone, um the pop filter. It actually directs light into, to go to it doesn’t spread out, it goes straight ahead.
11:58.04
Sam Hollis
So it focuses the beam. So instead of it spreading, you’ve got a much…
12:00.15
Marcus Ahmad
It focuses.
12:01.88
Sam Hollis
So presumably it can actually go further because you’re going in a straight line rather than it’s spreading out.
12:06.59
Marcus Ahmad
Ooh, now there’s a question, Sam. That’s a do… Does it go for… I don’t know.
12:10.92
Sam Hollis
It should do.
12:12.06
Marcus Ahmad
theory, yes.
12:11.70
Sam Hollis
It should reach further because normally further away, you’ve got the problem the light spread out more. If it’s if it’s not spreading out, it should remain quite powerful.
12:16.02
Marcus Ahmad
That’s right. In the same way that the aperture, you get a sharper image at that at the smaller at the higher numbers, the smaller aperture, because beam is more focused, that gives you ah a greater depth of field, because the light is travelling faster.
12:31.78
Marcus Ahmad
um So…
12:32.63
Sam Hollis
The light is definitely not travelling fast to market.
12:34.39
Marcus Ahmad
Not faster, sorry, sorry, no.
12:34.75
Sam Hollis
It’s definitely all going at the same speed.
12:36.59
Marcus Ahmad
It’s it’s it’s based more focused, the beam is more focused, making appear like it’s, yes.
12:38.36
Sam Hollis
Yeah, yeah, yeah. It is.
12:40.79
Marcus Ahmad
So um so if you’re using a beauty disc, sorry, a honeycomb or grid, you need to be really careful about placing your light on the subject because the beam can be very focused.
12:40.79
Sam Hollis
Yeah,
12:52.51
Marcus Ahmad
You get different size of grids. They vary by the degrees. I think it’s like 20, 40, 60, if my memory serves me right. Basically, the holes get bigger. The bigger the hole, the less focused the beam.
13:04.84
Marcus Ahmad
So if you’re photographing like a still life or product shot and you want the beam really narrow on like a label or a letter or on a wine cork card or whatever, you’re going to use a very narrow honeycomb.
13:04.86
Sam Hollis
yeah Yeah, that makes sense.
13:18.29
Marcus Ahmad
And that’s got to be positioned very carefully. And really, the best way of doing it is by putting a modeling light on. which is a little light that comes on on the beam, on the flash gun.
13:25.85
Sam Hollis
Okay.
13:30.27
Marcus Ahmad
and And that gives you a rough idea of what the light’s hitting. So yet again, when you’re buying your lights, it’s worth looking for one that’s got a modeling light.
13:34.60
Sam Hollis
that makes sense.
13:41.30
Marcus Ahmad
The higher end ones do tend to have a modeling light.
13:42.36
Sam Hollis
Okay. Yeah. So effectively you can see where the light’s going to end up. It’s like, you know, a kind of very dim version of what the flash would be like.
13:48.47
Marcus Ahmad
Exactly, exactly.
13:49.62
Sam Hollis
Yeah.
13:50.03
Marcus Ahmad
Okay, so the the last thing going to talk about is I sort of mentioned it earlier, this idea of you get… I think this is terminology. A monoblock is where the light and the battery power are separate.
14:03.91
Marcus Ahmad
Oh, no, sorry, I put it wrong. It’s the other way around. the The monoblock is where the light and battery are in one unit, and it makes a very heavy unit. um And especially if you’re putting that on a C-stand and it’s high up, I’ve actually seen it bend.
14:12.95
Sam Hollis
Okay.
14:17.72
Marcus Ahmad
Well, it it bends the metal rods. So yes, and it becomes very dangerous.
14:20.02
Sam Hollis
Oops.
14:22.40
Marcus Ahmad
If that lands on someone’s head, um that is not a good thing to happen. So,
14:26.84
Sam Hollis
so that So generally avoid those unless you’ve got a very sturdy studio setup, presumably.
14:31.54
Marcus Ahmad
well, what you can do, Sam, you can either, again, with these Godox light, you can buy an accessory where you separate the battery and the head with a big nice big thick cable and you get about 10 foot or maybe a little bit more.
14:42.05
Sam Hollis
Yeah.
14:44.22
Marcus Ahmad
So you can position in the light, just at the flash head, which is then very light, away from the battery.
14:44.50
Sam Hollis
Yeah.
14:49.08
Sam Hollis
Yeah. Yeah, sounds like a good plan.
14:52.15
Marcus Ahmad
or you buy a dedicated monoblock, which, you know, are very expensive. um You know, you’re looking at two to three thousand pound, even for Godox one, more for a Profoto and their separate light and head.
15:06.56
Marcus Ahmad
the the Just one but on that, just to finish, start wrapping up the program.
15:07.36
Sam Hollis
Yeah.
15:10.84
Marcus Ahmad
The advantage of those bigger blocks, I believe, I’ve never experienced it myself, but I believe the advantage is it gives you a much constant, more constant color temperature.
15:22.20
Sam Hollis
Okay. Interesting.
15:24.22
Marcus Ahmad
I’ve been being a portrait photographer primarily. I was never really worried about color temperature too much. But if you’re doing, ah again, still like product shots where you might be doing focus stacking or you might be doing layering, you really want to make sure every frame is at the right color temperature.
15:30.29
Sam Hollis
Yeah.
15:41.44
Marcus Ahmad
Guys, Sam, you’ve gone in complete silhouette. I’m just looking at silhouette of you.
15:45.05
Sam Hollis
There we go.
15:46.39
Marcus Ahmad
You look like Mickey Mouse. Okay. yeah
15:49.21
Sam Hollis
Thank you. Yes, well, know I’m going to have to do now, Marcus? I’m going to have to update my guide to photography. So I was sharing with Marcus, wasn’t I? Because I’ve just been moving house, and you go through all that stuff in the loft. And I found it, I showed Marcus some pages, my guide to photography that I wrote, I think for GCSE English.
16:04.74
Sam Hollis
Did you like the diagrams on it, Marcus?
16:06.14
Marcus Ahmad
Yeah, no, the excellent.
16:06.62
Sam Hollis
Maybe have to share that on LinkedIn or something.
16:07.93
Marcus Ahmad
That was A-level photography, I believe.
16:08.53
Sam Hollis
Yeah.
16:10.40
Marcus Ahmad
but Was it not A-level?
16:10.90
Sam Hollis
No, no, no. That was just GCSE English.
16:11.88
Marcus Ahmad
It was above.
16:12.70
Sam Hollis
It was like English, so you had to write about, so explain how something worked.
16:13.14
Marcus Ahmad
Okay.
16:16.50
Sam Hollis
I think. I mean, it’s a long time ago now, Marcus, but I definitely didn’t do A-level photography.
16:20.56
Marcus Ahmad
Well, look, as you know from this conversation we’ve just had, Sam, photography, lighting can get very technical. You know, and I’m not ah a super technical person. You’ve got a physics background. You understand these things better than me.
16:36.38
Marcus Ahmad
But that’s why I’ve come up with this idea of just the six core principles. There’s really six sentences. I know I’ll keep going on about this, but it takes a lot of thought and effort to get it narrowed down to really something that everybody can understand.
16:49.34
Marcus Ahmad
And we’ll be talking about that in the webinar.
16:49.69
Sam Hollis
Perfect. And quick reminder, Marcus, to can you go through the address again to sign up to the webinar?
16:54.66
Marcus Ahmad
Oh, you’re making me do this on purpose, Sam. It’s marcusahmad.com ah forward slash flash hyphen fundamentals.
17:06.83
Marcus Ahmad
um That is the…
17:07.58
Sam Hollis
Excellent.
17:08.19
Marcus Ahmad
that is
17:07.86
Sam Hollis
Thank you, Marcus. And if you notice, any time we promote the podcast website, it’s always me that say it. Because if we try get Marcus to say it, it could take us all day.
17:14.97
Marcus Ahmad
Yes, I don’t like it it’s Too much information. and But you can sign up to it there. It’s free. It’s going to be the five evenings. It’s going to be 20 minutes. I’m going to get my students to take some photos as well.
17:27.67
Marcus Ahmad
going work I’m going to do that. But it’s going to be a good fundamental.
17:29.91
Sam Hollis
Amazing.
17:30.59
Marcus Ahmad
And that that’s the reason why I’ve called it Fundamentals. It’s going to be fun.
17:35.35
Sam Hollis
Perfect, Marcus. Sounds amazing. So get signed up to that um and enjoy that. And Marcus, I’ll see you next week.
17:42.64
Marcus Ahmad
See you next week, Sam. Thank you.
17:44.22
Sam Hollis
Cheers.
