420 EX Guide Number?

[rmpcanon]

Just purchase a Digital Rebel XT, and had planned to use an existing Sunpak 433AF/CA, but it won't work (it fires OK, but apparantly only @ full strength -- no TTL metering apparant).

Accordingly, am planning to purchase a Canon 420EX, but am wondering about the relative lighting power between the two (don't want to spend money to get a weaker flash). The GN for the Sunpak is 120 @ ISO 100 (as I understand -- illuminates to 120 ft. w/ISO 100 film). I have seen the 420EX rated at everything from 42 to 138 -- what is the 420EX's GN @ ISO 100?

Dick P.

[CyberPet]

I have the 420EX and I'd be dishonest if I would recommend it, unless you want a pretty "dumb" flash. It's not bad when it comes to output, but it has no manual settings at all. Which is pretty bad. So I rather recommend you to buy a 550EX or the 580EX. I'm going to save up for the 580EX and use the 420EX as a slave, which it's great at, as I'm told.

[Curtis N]

The GN for the Sunpak is 120 @ ISO 100 (as I understand -- illuminates to 120 ft. w/ISO 100 film).Only if your lens will open to f/1.0.

You need to divide the guide number by the f/ stop to get the distance.

According to Canon's website page on the 420EX:
Maximum Guide Number 138 at 105mm setting; G.N. 101 at 35mm setting.
Approximately 1/2-stop less powerful than 550EX.

Guide numbers are tricky on zoom flashes. They will advertise the maximum GN which you only get when it's zoomed in all the way.

But I agree with Petra. You will soon wish you had a flash with more features.

[rmpcanon]

1. Dooh!! Regarding the GN variance, I just realized that one was in meters, the other in feet. Double-Dooh <slap>

So if apples-are-to-apples, the 420EX would seem to have approximately the same power as the SunPak. But from above, apples-may-not-be-to-apples. But do you think they are RELATIVELY equal, or does one company rate agressively and the other conservatively?

2. I'm confused regarding the comment that the 420EX does not have manual controls -- what would I be missing? On my old camera, I used the flash for hand-held bounce-light for portraits, still lifes, and other interior shots. My camera previous to that (20-years ago) had no TTL flash metering, and all bounce shots had to be laboriously calculated. When I was able to purchase a camera with TTL flash metering I truly thought I'd gone to heaven. Why would I want manual controls -- what would they be used for?

Dick

[Curtis N]

Why would I want manual controls -- what would they be used for?For when you want to take control of the shot and not let the camera decide what is the "correct" exposure. Or for controlling how much fill flash you want relative to the ambient light. Or for use off-camera as part of a slave setup. The more creative you want to be, the longer the list grows. And having a digital camera really lends itself to creativity. You will find yourself trying things that you never would have before because you didn't want to "waste" film.

[robertwgross]

Manual flash controls? Yes, it can be a big deal. Or not.

If you take only ordinary snapshots of ordinary subjects, then you might get by with a camera and flash combination that you use "straight" and automatically.

On the other hand, if you ever shoot weddings, then "straight flash" does not cut it. On one shot, you will have the bride in a white gown and the groom in a black tuxedo. On the next shot, you may have the bride only, and on the next one, it is the groom only. You probably will not get all three of those right if you shoot "straight." You really need to do some type of flash exposure compensation, turning it up for white and down for black.

Now, in some cameras, you can control that. In some flashes, you can control it. But you better get it one place or the other. I prefer to be able to control it in the camera and in the flash.

---Bob Gross---

[CyberPet]

If you want to use fill-flash instead of anything else, you have more control to be able to step down the flash output on the flash instead of in camera (FEC). I find it cumbersome to control the 420EX when it has no controls at all to at least step up or down the flash a few steps.

[tim]

I have the 550EX, the only switch I ever use is the power switch. I use FEC on the camera body, which works well.

[PacAce]

If you want to use fill-flash instead of anything else, you have more control to be able to step down the flash output on the flash instead of in camera (FEC). I find it cumbersome to control the 420EX when it has no controls at all to at least step up or down the flash a few steps.
I find the opposite to be true. I'd rather be able to control the FEC via the camera with my eyes looking through the viewfinder instead of having to pop my head up to see the flash just the change the FEC. But I guess different strokes for different folks, eh? ;)

[DavidEB]

Dick --

The difference between FEC and manual flash operation is like the difference between shooting in Av mode with exposure compensation and shooting in manual mode. Using FEC means you're likely going to shoot a test shot and adjust the amount of flash up or down with FEC. Often the test shot comes out right on the first time. Using manual flash controls means you're going to do a bunch of calculations and then take your shot, and if you're like me, it will be wrong, so you'll adjust anyways. I use this formula:

F-stop = D / GN + S

where D=distance, GN= guide number, and S is the screw-up factor, ranges from -2 to +2 stops.



I still use manual flash setup for macros, because I can trigger my sigma 500 super with the on-camera flash, but for everything else, I love E-TTL. It changes flash exposures from a nightmare to relatively straightforward.

[steve547]

David, Your algebra needs refreshing. It's f stop = GN/distance +S

[PacAce]

Dick --

The difference between FEC and manual flash operation is like the difference between shooting in Av mode with exposure compensation and shooting in manual mode. Using FEC means you're likely going to shoot a test shot and adjust the amount of flash up or down with FEC. Often the test shot comes out right on the first time. Using manual flash controls means you're going to do a bunch of calculations and then take your shot, and if you're like me, it will be wrong, so you'll adjust anyways. I use this formula:

F-stop = D / GN + S

where D=distance, GN= guide number, and S is the screw-up factor, ranges from -2 to +2 stops.



I still use manual flash setup for macros, because I can trigger my sigma 500 super with the on-camera flash, but for everything else, I love E-TTL. It changes flash exposures from a nightmare to relatively straightforward.
Funny, but I can set my flash on manual mode and, without doing any kind of calculation, short of acurately measuring my flash to subject distance, I can determine my apeture value and nail the exposure dead on. The trick is to let the flash do all the work for you. See that little distance scale on the back of the flash? Use it to your advantage. ;)

[DavidEB]

Steve ---

THAT's why my screwup factor is so large. thanks for catching my goof.

[robertwgross]

Funny, but I can set my flash on manual mode and, without doing any kind of calculation, short of acurately measuring my flash to subject distance, I can determine my apeture value and nail the exposure dead on. The trick is to let the flash do all the work for you. See that little distance scale on the back of the flash? Use it to your advantage. ;)

The thread is on the 420EX, and it has no distance scale display.

---Bob Gross---

[PacAce]

The thread is on the 420EX, and it has no distance scale display.

---Bob Gross---
Yes, I know and it doesn't have manual controls either but that didn't prevent your from discussing it here, did it? :confused:

[steve547]

To get back to Dick's original question. If the guide # is 101 at 35mm(wide angle), you can shoot up to 25 feet at f4 or 50 feet at f2 apertures. That's more than enough power for 99.9% of us. So don't even make that a consideration. You will always have enough light! So just keep the flash at 35 mm setting all the time. Also remember that all advertized guide numbers are grossly inflated sometimes by a 100%. So just stay within 20 feet and that should be fine. Unfortunately, you can never calculate the true guide # of the 420 if it has no manual setting. I think that's the dumbest thing Canon ever did. Even the cheap old fashioned automatic flashes had manual settings.

[Curtis N]

Yes, I know and it doesn't have manual controls either but that didn't prevent your from discussing it here, did it?The person who started the thread specifically asked about the benefits of manual controls.

[PacAce]

Well, I guess I owe everybody an apology. From now on, I'll make it a point to only address and answer the original poster's questions or comments and ignore everybody else.

Sheesh, get a life, people. I don't know what the big deal is here. :confused:

[robertwgross]

Yes, I know and it doesn't have manual controls either but that didn't prevent your from discussing it here, did it? :confused:

Exactly. That is because some people need to understand the advantage of a 550EX or 580EX over the 420EX. For some types of subjects, it is a big deal, and that was the topic of the thread, and that is what I addressed.

Now, are you still confused?

---Bob Gross---

[Curtis N]

Unfortunately, you can never calculate the true guide # of the 420 if it has no manual setting. I think that's the dumbest thing Canon ever did. Even the cheap old fashioned automatic flashes had manual settings.I agree.

However, with respect to flash power, if you need to stop down to f/16 to get the DOF large enough (a group portrait, for example), or if you bounce the flash, or both, you could run out of light real quick unless you bump up the ISO.

[robertwgross]

However, with respect to flash power, if you need to stop down to f/16 to get the DOF large enough (a group portrait, for example), or if you bounce the flash, or both, you could run out of light real quick unless you bump up the ISO.

I believe the rule of thumb is that you increase your effective flash range by a factor of two by increasing your ISO by two stops (e.g. increase from 100 to 400). The trick is in getting the happy compromise between better ISO, better aperture, and better shutter speed to make everybody happy in the color noise department and the depth of field department. That is why it can be tough to be stuck with a rig with no controls.

---Bob Gross---

[BCAPhoto]

I certainly wished I'd found this site months ago... My Digital Rebel/420EX has been underexposing my bounce shots so bad I'm seeking another flash unit to use as a slave for more light. You'd think the 420 would adequatly light a subject 8 feet away bounced off an 8' ceiling!
I've gone thru various adjustments on the camera and even at 1600/4 the portrait is still too dark.
Any "in camera" ideas on adjustments would be warmly welcomed!

thanks........b

[tim]

Can you show us a sample photo? The 420 should have enough power for that, it could perhaps be metering modes. Are you on ETTL?

[steve547]

Underexposing is what the 420 was designed to do. We're supposed to correct for that with our editing programs later. The 20d can be set to overexpose flash shots, but I dont know if the rebel can. You're better off just fixing the picture with your editing program and not try to make the flash do what it wasn't disigned to do. I think the 550 and 580 flashes can be set to manual (full output). That lets you get consistently good exposures by picking the right f stop (f stop = guide# divided by distance). Good luck.

[tim]

Underexposing is what the 420 was designed to do. We're supposed to correct for that with our editing programs later. The 20d can be set to overexpose flash shots, but I dont know if the rebel can. You're better off just fixing the picture with your editing program and not try to make the flash do what it wasn't disigned to do.

That doesn't sound right to me. The logic of how bright the flash should go is in the camera, the flash is reasonably dumb. The 420 should work almost exactly the same as the 550 or 580, just a bit less powerful. I never touch the manual controls on my 550.

You shouldn't underexpose the fix in software, you should get it right in the camera, for reasons of time in your workflow and picture quality. Perhaps you mean the camera exposes for the highlights, which is true, but you compensate for that with FEC if you want to. The camera's dumb, you have to be smart to use it.

[steve547]

You shouldn't underexpose the fix in software, you should get it right in the camera, for reasons of time in your workflow and picture quality. Perhaps you mean the camera exposes for the highlights, which is true, but you compensate for that with FEC if you want to. The camera's dumb, you have to be smart to use it.

What I was trying to say is that it's better to have an underexposed photo which you can fix with software, than an over exposed one where the highlights are blown and can't be retrieved. So I think all the speedlite flashes were designed to give under exposures and that's good. Even my outdoor shots are underexposed on the 20d, and I think that's done by design to preserve the highlight details. The problem with the automatic speedlite is that it exposes for the object 3 feet away that it thinks is important and may underexpose the object 6 feet away that you're trying to photograph. So you need to put the flash on manual, and choose the f stop that will expose the object 6 feet away properly. That f stop is the guide # divided by 6. That's often more efficient than hoping the flash reads your mind and guesses correctly.

[tim]

Like I said, flash metering is handled within the camera, not within the flash. Some 20Ds underexpose more than others, according to what i've read, though mine's about spot on under normal circumstances.

You don't need to put the flash onto manual for the situation you talk about, just use flash exposure compensation and your histogram. If you have experience with manual flash it might be easier for you to do it that way, but it won't be for everyone.