Sigh...Half Rant, Half Question

[Pawlowski6132]

Ever have a photography nut you just can't crack?

I'm trying to expose 8x10 film in simple studio light environment and cannot figure out why images are underexposed.



I know I can simply get the exposure I want by opening the aperture but, all my instincts are telling me I should get the correct exposure from my calculated exposure. I've been racking my brains trying to figure out what 's going on.

In case anyone cares to try to crack this case, here are the facts. Just the fact's.

• Film: TXP
  Size: 8x10
  Lens: 210mm Convertible
  Lights: Two - Fill & Main 4:1
  Background: White
  Composition: H&S
  Incident Reading: 1/30, f22
  Bellows Length: Approx 16"
  Exposure: 1/30, f11
  Process: PMK Pyro, Brush Method, 14 Minutes

Image contact prints are too dark on Ilford FB Warmtone at #2 Filtration developed in Dektol 2 Minutes. Exposure is for 18 seconds. Tanned olive skin (Polish & Italian mix) is printing around ZIV.5 approximately.

Prints OK but, still a little dark at #3 Filtration for 15 seconds.


Questions I'm asking myself:

1. Am I measuring "bellows extension" wrong? From tip of front element to film? ONLY actual bellows length? Does a couple of inches matter either way?
   Is my development time correct? Anything longer than 14 minutes seems too long.
   Is there something in my print process that's kooky?
   Is my shutter aperture openings really accurate for these cells?
   Is my meter correct? I'm pretty sure it is.
   Will I have more success taking a spot meter off the face? Why would it matter?
   ISO in meter is 160 from 4x5 testing. Should it really be 80?? Seems way too low.
   Does convertible lens and cells impact bellows extension calcuation?
   Does it matter how much ambient light I have in the room?

[Jim Galli]

I've often heard or read that tungsten light would cost you about 1/3 stop. So 160 would become 125 or less perhaps. Bellows extension roughly to the aperture of the lens. Instead of messing with formulae, try just measuring the real aperture in mm and divide into the real length from glass to aperture in mm. ie. you've got 15mm hole and 300mm extension, you're at f20. This always works perfectly for all of my weird set-ups.

Do you have some good cheat sheets for reciprocity failure? I keep some good ones in my wallet at all times.

[Pawlowski6132]

Thanx Jim. Yes, I was actually going to measure the aperture diameter tonight but, didn't get around to it. I do keep a list of things to not have to remember with me in my camera bag (filter factors, reciprocity failure info, etc.). I assume my Alien Bee lights are daylight color?? No?

[Vaughn]

How can the images be under-exposed? If they are too dark, it sounds over-exposure to me. How are the negatives is the question. If you don't have detail in the shadows where you want detail, then they are under-exposed.

If they are underexposed, expose a stop or two more -- process the negatives and pick the neg that has the shadow detail you want. Figure out how to jiggle your exposure determinations to arrive at the exposure of your best neg. and use it from now on...or until experience leads you elsewhere. Then fuss with your development to give the negs the contrast you want.

Then while you are looking at a good negative, ponder things like aperture accuracy, ISO's, and how to make a good print from the neg.

Heavy on the right-brain today...

Vaughn

[Jim Galli]

Thanx Jim. Yes, I was actually going to measure the aperture diameter tonight but, didn't get around to it. I do keep a list of things to not have to remember with me in my camera bag (filter factors, reciprocity failure info, etc.). I assume my Alien Bee lights are daylight color?? No?

Yes, the alien bees should be daylight, and at 1/30th there's no recip failure, so I didn't help much.

[Pawlowski6132]

Hi Vaughn. Thanx VERY much for your input. Not enough light hitting the film so...under exposed is my take. I hear what you're saying but, want to be able to trust my equipment and technique. Right now, they're telling me that 1/30 f11 should give me skin at around Zone VI. It's below Zone V? Why? When I can figure that out I can move on with my life!!

[Jim C.]

Just checking to see that when you mean incident light readings
that you're using a flash meter for that reading and not regular incident light meter ?
Something doesn't sound right with your exposure of 1/30 @ f11 using studio strobes like AB's

[Pawlowski6132]

Just checking to see that when you mean incident light readings
that you're using a flash meter for that reading and not regular incident light meter ?
Something doesn't sound right with your exposure of 1/30 @ f11 using studio strobes like AB's

Specifically, I'm using the Sekonic 508. So, yup, flash meter.

For what it's worth the I'm using an AB800 with a large, baffled Softbox and an AB400 with a shoot through umbrella. Both are pretty close to the subject.

[Jim C.]

Sorry if this sounds dumb, but is your meter set to flash readings ?
I've made the mistake sometimes on my 558, which is similar to
your 508 a combo flash/incident/spot meter, when I switch from
tungsten to my AB's and forget to check the LCD on my meter.

[Vaughn]

My best guess is that the way you are metering is not representing the real world. Perhaps something in the set-up and how/where you hold the meter does not allow for the round dome of the meter to approximate the way the light actually hits the subject.

For some reason the meter thinks that there is more light than there actually is? Perhaps you are measuring light hitting the subject at such a steep angle that it does not bounce back towards the lens, but still reads on the meter?

vaughn