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Underexposure problem with flash diffuser


john_horvath1

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I shoot black and white film, and recently I started to use flash with a LumiQuest Mini Softbox diffuser. I always use my lightmeter when shooting with flash, and somehow even this way some of the pictures came out a bit underexposed, despite the fact that I compensated one stop for my black and white filter.

 

What could be the problem?

 

On the box of the diffuser the manufacturer says that there's one EV loss of light, but if I meter with an incident light meter, then I don't have to compensate - right? Or even a meter it's better to compensate one stop?

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When you use a flashmeter it ought to be giving you a "correct" exposure; there should be no need to compensate for any "modifier" on the flash unit itself.

 

Of course there can be special situations that require "interpretation" of a meter reading. Same situation as with non-flash readings. But I'm guessing this is not such a case since you did not mention anything along these lines.

 

Are you perhaps using an "auto" mode for the flash? Where you might have metered in one auto-flash situation, but perhaps the flash varied its power for the actual film exposure?

 

My first guess would be that the problem is more likely related to whatever filter you used, and the exposure compensation for that. But without any more info about the problem it's hard to be sure. If you have previously used the same filter/film combination with success, using a spectrally similar light source (ie, "daylight") then I would rule this out.

 

Have you also considered the possibility that the film processing may have been off?

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Some electronic flashes aren't 100% charged when the ready light comes on. They may be only 70% to 90% charged. You can find out by shooting a test picture immediately after the ready light comes on, then shooting another picture at the same settings after waiting a full minute after the light comes on. If the second shot is noticeably brighter, the ready light is premature. But I would expect the difference to be less than a full stop of underexposure.
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You do need to confirm a few things some have already been mentioned :

 

You’re using an INCIDENT FLASH METER and that meter is accurate and good battery.

The Flash is NOT on an AUTO SETTING

You have confirmed that the FILTER FACTOR is accurate for the FILM type and LIGHTING type (i.e. NO Lighting Filters) that you’re using.

You’ve double checked the ISO Setting on the Flash Meter to match the Film

Your Developer is fresh and the Temperature and Development time are your ‘typical’.

You’ve double checked the Aperture that you used

The Flash has fully charged before firing

 

Assuming all that is OK, then my guess is the Filter Factor suggestion of the filter that you used, is inaccurate.

 

WW

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Hi John

 

When you say “ black and white filter” exactly what do you mean? Is it a green filter which can cause people to have a tanner appearance. Filter factor determination is far from an exact science. I have 2 or 3 flash meters & I've found that they can vary from one to another. Are entire frames underexposed or are just parts? Are entire rolls underexposed, or just some frames? I have a small diffuser that doesn't always stay properly aligned. Also it's easy to bump the “F” stop ring. If this post & the above haven't answered your question, then please post all of your variables. My guess for the most likely cause is lack of recycle time as tom_halfhill said.

 

Now I have a question that I haven't been able to find the answer: How do I make an original post on Photo.net? I have been able to in the past, but I've forgotten or something.

 

I would really appreciate an answer, Jonathan

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Thank you very much for all these informative answers. After considering all these factors, I assume it must be a combination of a not fully charged flash as well as problems with the film processing. Or just one of these two.

 

Some additional info: I use a simple yellow filter and a Minolta IVF lightmeter.

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. . .

Now I have a question that I haven't been able to find the answer: How do I make an original post on Photo.net? I have been able to in the past, but I've forgotten or

something.

 

MAIN PAGE of each Forum at the Top Right there is a Banner Link [+ Post New Thread]

 

Click on this [LINK] to open the MAIN PAGE of this "Beginner Questions Forum" as an example.

 

WW

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Test original post

jonathan_mcgraw

MAIN PAGE of each Forum at the Top Right there is a Banner Link [+ Post New Thread]

 

Click on this [LINK] to open the MAIN PAGE of this "Beginner Questions Forum" as an example.

 

WW

How could I have missed that? I guess that I've started looking after I've opened the page.

 

Thank you so much, Jonathan

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Thank you very much for all these informative answers. After considering all these factors, I assume it must be a combination of a not fully charged flash as well as problems with the film processing. Or just one of these two.

 

Some additional info: I use a simple yellow filter and a Minolta IVF lightmeter.

John

 

I'm curious, are entire rolls underexposed or is it individual frames or part of individual frames? Also what is the reason(s) for using a yellow filter? It's one more variable going into the total exposure. You do realize that if you shoot an object (person, statue) in an empty field & expose correctly for the object, that most of the rest of the negative is going to clear or almost clear.

 

Regards, Jonathan

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On the topic of a Yellow Contrast Filter in general –

 

Typically used for Outdoor B&W to bump (contrast of the) sky relative to the general scene.

 

However as the OP describes the use of Flash, it seems that this work would be indoors, likely a Portrait Studio or similar setting.

 

We’d regularly use a “Yellowish” Contrast Filter for B&W (Pan Emulsion) Studio Portraiture for two main purposes:

> bump the (relative) Skin Tone of typical Caucasian Skin

> hide minor skin blemishes.

 

Specifically we usually use a Yellow-Green for these purposes.

 

Using a B&W Contrast Filter correctly, does not of itself add another ‘variable’ to the exposure if the Filter’s Filter Factor is known.

 

WW

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I found out the hard way that Flash diffuser manufacturers grossly understated the EV loss of their difussers. Usually if you are using one of those diffusers that uses some type of material that sits in front of the flash you are going to get any where from -1, -2, -2.5 sometimes even -3 loss of light depending on the situation. If you are using this diffuser to shoot cheezy portraits and you have the flash set on Manual, this might not be so much of a problem, but if you are using Automatic Flash where light hitting the sensor determines the flash output, then get ready for some erratic, if not frustrating results.

 

Not only are you going to get under exposed photos, but discolored ones too which are extremely hard to fix in Photoshop. You might take two pictures one after the other of the same subject from the same distance and with exactly the same shutter/iso/aperture settings and get two different pictures. One exposed correctly and the other underexposed. I'm telling you this from someone who has tried to shoot weddings and other events with these so called diffusers. On the other hand, bounce diffusers are not that bad because you can estimate the flash-to-subject distance and adjust the power setting of your flash accordingly.

 

The trick is if you are going to be using one of these mini soft box diffusers (which a lot of photographers use), then set your flash and camera to Manual. Try taking a few pictures around the house under varying lighting conditions and check your results. Sooner or later you will get an idea of what settings to use under what conditions.

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On the topic of a Yellow Contrast Filter in general –

 

Typically used for Outdoor B&W to bump (contrast of the) sky relative to the general scene.

 

However as the OP describes the use of Flash, it seems that this work would be indoors, likely a Portrait Studio or similar setting.

 

We’d regularly use a “Yellowish” Contrast Filter for B&W (Pan Emulsion) Studio Portraiture for two main purposes:

> bump the (relative) Skin Tone of typical Caucasian Skin

> hide minor skin blemishes.

 

Specifically we usually use a Yellow-Green for these purposes.

 

Using a B&W Contrast Filter correctly, does not of itself add another ‘variable’ to the exposure if the Filter’s Filter Factor is known.

 

WW

 

Thank you for explaining it way better than I ever could. Yes, that’s the reason.

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I found out the hard way that Flash diffuser manufacturers grossly understated the EV loss of their difussers. Usually if you are using one of those diffusers that uses some type of material that sits in front of the flash you are going to get any where from -1, -2, -2.5 sometimes even -3 loss of light depending on the situation. If you are using this diffuser to shoot cheezy portraits and you have the flash set on Manual, this might not be so much of a problem, but if you are using Automatic Flash where light hitting the sensor determines the flash output, then get ready for some erratic, if not frustrating results.

 

Not only are you going to get under exposed photos, but discolored ones too which are extremely hard to fix in Photoshop. You might take two pictures one after the other of the same subject from the same distance and with exactly the same shutter/iso/aperture settings and get two different pictures. One exposed correctly and the other underexposed. I'm telling you this from someone who has tried to shoot weddings and other events with these so called diffusers. On the other hand, bounce diffusers are not that bad because you can estimate the flash-to-subject distance and adjust the power setting of your flash accordingly.

 

The trick is if you are going to be using one of these mini soft box diffusers (which a lot of photographers use), then set your flash and camera to Manual. Try taking a few pictures around the house under varying lighting conditions and check your results. Sooner or later you will get an idea of what settings to use under what conditions.

 

Thanks, Joseph! Yeah, I was thinking about using a two stop compensation (one for the filter, the other one for the softbox) after the metering, just in case.

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