Nikon SB 28 & SB 80DX under exsposure

[nick_brown3]

Has anyone experienced what I am finding with Nikon flashes that when

used indoors on straight TTL they under expose by 2 full stops? I

have tested my SB28 and SB80DX with 2 minolta flash meters side by

side and the results are consistent. The testing involved different

colored backgrounds to see if that was the reason why they were

underexposing but the results were the same regardless. I also varied

the time of day to see if the level of ambient light played a part

but it didn't, test times varied from noon to night. (I shoot on TTL

inside for candids as opposed to Matrix TTL).

 

Thanks, Nick.

[ellis_vener_photography]

It sounds like your meters are reading the preflashes, not the actual flash that is used to expose the image. Have you tested with film? Can you post the results?<P>I always use TTL-flash Matrix metering, have for years, and haven't seen any exposure problem using either of my two SB-28dx Speedlights with Nikon F5, N90s film cameras, or Nikon D1x, D100 or Fuji S2pro digital cameras.

[rick_gray]

Hmmmmmm! I'll have to think about this. The SB80 DX is a precision flash - it delivers everything asked of it and more ...it almost makes breakfast for me. I have not had the problem as described. Perhaps someone else can provide clarity.

Rick Gray

[ray]

I have both the SB-28 and the SB-80DX. They have never underexposed for straight TTL shots (which is what I use for indoor receptions/weddings).

 

Are you getting underexposure on film or just the flashmeter? I suspect that the flashmeter is picking up the preflashes and not the main flash. Set the head angle to something other than Zero (-7 degrees or a positive angle). That will cancel the preflashes (I think).

[hal_bissinger]

First off you can't meter TTL flash. Second, you probably should not be using straight TTL though that may or may not be your problem. You don't say what body and lens you are using, but I'll bet you should be using 3DMBFF and matrix metering on the body. Read your SB-80DX or SB-28 manual and check the chart in front for your body and lens type. There is usually only one mode for any given combination and that's what you should be using. <p>

When you get all of this straightened out then shoot a roll of slide film and look at the results. If you still have underexposure problems have the body looked at. I would say that a consistant problem involving two different flashes would make me want to take a look at the body anyway.

[jeff_plomley1]

On my F5, both of my SB-28's underexpose by 1 stop in total flash mode using either Spot or 3D-matrix metering. To compensate, I simply dial in +1.0 on the SB-28 unit.

[hellobob]

this might sound totally sophomoric, but do you have both flahes set to -2e.v.?

why do you use ttl indoors for candids as opposed to matrix?

rob

[nick_brown3]

Thanks everyone for your speedy responses. Here is some further info how I was testing which might help. I used 2 F100 bodies and the results were consistent across both flash units and both bodies, so I'd bet that rules out any equipment issues. I use TTL inside (dark reception halls) as opposed to TTL Matrix for the same reasons as Shourya probably uses TTL inside too - but that's another discussion and one I'd be happy to talk about but I know it's probably a split camp on that point.

 

I tested using film in the camera and I think this is the problem, as Ellis pointed out, I think it is measuring the pre-flashes. So I tested it again just now without film and it's perfect (presumably it only pre flashes with film in the camera). Problem solved? well, here is the dilema, I turned the pre-flashes off with film in the cameras, tilting the heads up and it still underexposed on the meters by 2 stops. According to the SB80DX instructions, on Page 74, it says that in standard TTL there are no pre-flashes and with the head up there shouldn't be any pre flashes so I can't understand why it shows on the meters as underexposed, am I missing something?

 

Further background info, the photos do look fine but this was me just tinkering around with the meters and flashes trying to fine tune my compensation for indoor flash shots, I was expecting them to slightly off but not by this much. I shoot negative film and it's hard to see if something is slightly off due to printing compensation and the forgiving nature of print film.

 

I guess the only real way to test this is with slide film but it sort of defeats being able to use two perfectly good meters.

 

Any more thoughts or should I just go and have a beer and stop worrying about it.?

 

Nick

[hal_bissinger]

Ergggh! Now it's TWO cameras and TWO flashes eh?? When are you going to figure out it's YOU not the gear?<p>

Forget about preflashes. Forget about having film in the camera. YOU CAN'T METER TTL FLASH! Period! End of story!! <p>

Go put some damn slide film in the camera, set it to the proper mode ACCORDING TO THE MANUAL and then see how it works! That's the ONLY way you will know if everythings working.

[nick_brown3]

OK Hal, keep your hat on. I was just trying to get some feedback and you had asked about what equipment I was using so I gave you more details.

 

I will test with slide film as suggested and thanks for that advice. However, I don't understand why you think you can't meter TTL flash with the pre flashes turned off. If I set the camera to manual F8 and 1/60th sec in straight TTL why wouldn't it give F8 on the flash meters if everything was working properly and the subject was middle grey and in flash range? Apologies if this is straightforward to you but I'm just trying to understand what the camera and flash are doing to lead to apparent underexposed flash meter readings and to get a clear idea of how accurately TTL flash works inside over different conditions so I can dial in the necessary compensation to adjust it if needed.

 

TTL vs Matrix TTL for inside shooting is another debate and there are a few even sided discussions on this forum about that subject but I'm talking about just TTL, which is what I use. Outside I use Matrix TTL at -0.7 to -1.7 depending on what effect I'm looking for and I'm happy with that.

 

Jeff - you mentioned that your SB28's underexpose in TTL inside by 1 stop, did you find this out by slide testing?

 

Thanks again everyone for your advice.

 

Nick

[hal_bissinger]

<i>...I don't understand why you think you can't meter TTL flash with the pre flashes turned off.</i><p>

I and most other people except those who, about every two months, ask this same question usually because they have too much time on their hands.<p>

A flash meter is designed to measure the illumination from a studio strobe. A studio strobe simply fires at a power level you set and naturally decays. <p>

TTL controlled flash, on the other hand, is a complex closed loop system that relies on real time feedback and microprocessor control. You actually discovered one of the intricacies when you noted the difference in flash output with film and without. This is because the flash illumination is monitored on the film itself and the color or reflectance of the film is a critical factor. The difference you saw is because, without film, the system saw the black backing plate. <p>

Preflashes, which are not discernable from the main flash because they are so closely spaced, give the system a kind of "heads up" for what it can expect. The microprocessor then probably determines things like whether it should fire at full power then throttle back or fire at something less. With or without preflashes, the system has control of both the flashtube power and duration and constantly monitors and adjusts these during the exposure according to the metering off the film plane and some programmed algorithm. <p>

Now, obviously preflashes are going to trip up your flash meter by triggering it prematurely. But, absent the preflashes, a flashmeter isn't designed to make sense of a power and time modulated flash impulse that a TTL flash system generates. That's the reason for the error.

[nick_brown3]

Thanks for the detailed response Hal, now you've explained it I can understand why the meters are showing different values to what is actually happening for the end exposure.

 

Slide testing it is, but, I don't however, have too much time on my hands (I wish), just a desire to know how accurate my flash will be in automatic modes in certain situations which I feel is important.

[bruce_rubenstein___nyc]

"...a flashmeter isn't designed to make sense of a power and time modulated flash impulse that a TTL flash system generates. That's the reason for the error"

 

 

This is gibberish. All flashes put out light power over some period of time, and a light meter integrates intensity over time to calculate the total amount of laght that came out of the flash. Modern power meters should have no trouble integrating different discharge/time curves regardless of how the flash is controlled.

[jeff_plomley1]

Nick:

 

My 1 stop underexposure with the F5/SB-28's was tested with slide film. I have been compensating +1.0 on the SB-28's for over 2 years now with good results. As an aside, this is just one of many Nikon quirks which has caused me to slowly migrate to the EOS 1vHS and IS lenses. But that is a whole other can of worms not worth getting into...