Dumb question about ISO and f-stops

[thorsten]

Hi everybody,

I am planning for today to test the combination of Tri-X in Xtol for my Zeiss Ikon to find out the real sensitivity and developing time for this combination. Since I lately got a densitometer from ebay, I want to shoot a grey card in zones I, II, V and VIII for ISO-settings in 1/3-steps (ISO 125, 160, 200, 250, 320, 400, 500, 640, 800). So if my ZI's meter tells me at ISO 400 to use f/8 at 1/250sec for zone V, I would have to use f/32 for zone I, f/22 for zone II and f/2.8 for zone VIII (all at the same shutter speed).

So here's my question and I hope you could read over it and tell me, if I am wrong or if this is correct: Since the Zeiss Ikon only offers shutter speeds in full stops and aperture settings in 1/3-stops, it would be wrong to meter the grey card again, when shooting at an ISO-speed 1/3 away from ISO 400 (let's say ISO 320), because if I set f/8 again, it would show me the same shutter speed (since shutter speeds are only available at full stops). So I plan to stay with 1/250sec and only change the aperture by 1/3-steps. For ISO 320 it would be: f/5.6 + 2/3 for zone V, f/22 + 2/3 for zone I, f/16 + 2/3 for zone II and f/2 + 2/3 for zone VIII.

So I would try to only change the apertures at 1/3-steps for the different iso-settings. In ranges, where the aperture-settings aren't enough (e.g. at ISO 125 at the given example), I would change aperture and shutter speed for one full step and go on with the rest.

At the moment I am completely not sure, if this is correct. So what do you think?

Thanks for any help,
kind regards,

 

[SolaresLarrave]

Thorsten... photography is not that complicated. I think you're twisting yourself like a pretzel on this. While I cannot say anything about the developing, I will advice you to trust the old adage: with B&W film expose for shadows (meter dark spots) and let the highlights hit where they may. You're dealing with print-film, which is, by its own nature, very tolerant to under and over exposures. In othe words, trust your meter and develop according to the book. To be quite honest, I fail to understand the use of the zone system with a metered body, but then, somebody will have a different opinion...

Follow the meter, enjoy taking pictures with your new kit and don't forget to post some later! 🙂

 

[jlw]

Solares is right in saying you don't need to overcomplicate this, but it can be worth going through the exercise for a film/developer combination you plan to use a lot -- especially if you're going to be doing your own printing.

And the good news for you is that, even though your ZI can only be set to full-step shutter speeds in manual mode, it DOES set shutter speeds continuously in auto mode. Since you can set ISO speeds in one-third-step increments, you can use this feature to vary shutter speeds by exactly one-third step.

When making exposure tests, it's probably somewhat more accurate to do it this way than to use the lens aperture, since by keeping the aperture constant you rule out possible slight variations caused by vignetting, miscalibration, etc.

Here's a rough outline of how you'd do it: Set up your camera on a tripod under conditions where the light will stay completely unchanged during the entire duration of your test. Position it so your gray card fills all or most of the frame. (With an RF camera, you may need quite a large gray card because the minimum focus distance tends to be only 1 meter or so.) Choose a moderate lens aperture of, say, f/8. Set the ISO dial to 400 and make your initial exposure.

Now, leaving the aperture unchanged, continue to make a series of exposures, changing the ISO dial by one increment (one-third step) each time, going all the way down to ISO 25 and all the way up to ISO 3200. You'll wind up making 22 exposures (it's good to leave the first and last frames blank to rule out the possibility of their being light-struck during loading or unloading, and throwing off your results) so a 24-exposure roll works well for these tests.

If you want to test different development times, repeat this procedure for as many rolls as you need for all the times you want to test.

As Solares says, you don't want to overcomplicate this. For example, remember that the pure version of the Zone System assumes you'll be using sheet film and can adjust the developing time for each individual exposure; obviously that's not practical for 35mm film!

So, here's a procedure that can simplify your test and give you just as much useful information: Instead of exposing just a gray card, put a "step tablet" (target with values from black through a series of grays through white) in the middle of it. You can buy a step tablet from graphic arts dealers and dealers in photo supplies for technically-obsessed "Zonies," and there's also one along one row of a Macbeth ColorChecker.

What you do with this simplified procedure is make your series of exposures and developments, then examine the negatives and print them. (Your densitometer won't be of much help at this stage; remember, the object of the game is to get negatives that will print easily! The densitometer will be more useful later, when you're trying to compare negatives made with different film/developer combinations against your "standard" negative.)

What you'll be looking for is the combination of ISO setting and development time that clearly separates the darkest patches of the step tablet, but also provides enough density to give a clean white on the lightest patch of the step tablet. This will tell you the exposure/development combination that gives the most easily printable results for your particular equipment, metering technique, and preferences. You'll want to save the frame that produces these results as your standard negative.

Once you've got this dialed in, you'll be able to print most of your negatives similarly to the standard. You'll be able to reserve different contrast filters and printing techniques only when needed to produce different creative interpretations or deal with "difficult" subjects or lighting conditions.

For anyone else reading this, note that you don't necessarily have to go through this entire procedure to optimize your exposure/development combination. A fairly experienced printer can simply look at the shadow and highlight areas of negatives and say, for example, "The highlights are generally too dense; next time I should cut back my development time by about 10%" or "There's not quite enough shadow detail; next time I should try using a lower ISO setting." By changing in small increments this way, you can gradually creep up on your optimum settings, without much risk of making completely unusable exposures.

 

[kmack]

Does the ZI have an electronically controlled shutter? I would still stick to changing aperture rather than shutter speed. Less chance of variance with the lens aperture than with the shutter.

You really only need to run a Zone I test for personal EI. You would run a zone VIII test for determining development time for n+/- 1..3. If you are really picky you can also run base fog tests.

You do testing to get a total grasp on the process. Shooting the test film is only a small part of the process. Make doubly sure that every phase of your development process is reproducible. That means you have a good thermometer, use it to calibrate a second thermometer for verification. Use water baths to control temperature. Pick an agitation scheme and stick to it. Use distilled water etc. etc. etc.

 

[ampguy]

my .02

my .02

Unless you're doing this purely for a science experiment, I would recommend that you read the John Shaw Amphoto books, and maybe Les Meehan's Creat Exposure Control books first.

No matter how accurate your developing process is, your optimal exposure for great photos is rarely going to be what is metered with your built-in camera meter.

Hi everybody,

I am planning for today to test the combination of Tri-X in Xtol for my Zeiss Ikon to find out the real sensitivity and developing time for this combination. Since I lately got a densitometer from ebay, I want to shoot a grey card in zones I, II, V and VIII for ISO-settings in 1/3-steps (ISO 125, 160, 200, 250, 320, 400, 500, 640, 800). So if my ZI's meter tells me at ISO 400 to use f/8 at 1/250sec for zone V, I would have to use f/32 for zone I, f/22 for zone II and f/2.8 for zone VIII (all at the same shutter speed).

So here's my question and I hope you could read over it and tell me, if I am wrong or if this is correct: Since the Zeiss Ikon only offers shutter speeds in full stops and aperture settings in 1/3-stops, it would be wrong to meter the grey card again, when shooting at an ISO-speed 1/3 away from ISO 400 (let's say ISO 320), because if I set f/8 again, it would show me the same shutter speed (since shutter speeds are only available at full stops). So I plan to stay with 1/250sec and only change the aperture by 1/3-steps. For ISO 320 it would be: f/5.6 + 2/3 for zone V, f/22 + 2/3 for zone I, f/16 + 2/3 for zone II and f/2 + 2/3 for zone VIII.

So I would try to only change the apertures at 1/3-steps for the different iso-settings. In ranges, where the aperture-settings aren't enough (e.g. at ISO 125 at the given example), I would change aperture and shutter speed for one full step and go on with the rest.

At the moment I am completely not sure, if this is correct. So what do you think?

Thanks for any help,
kind regards,

 

[kaiyen]

I agree that you should adjust aperture if you can, though I don't personally know how hard it is to reliably and accurately set 1/3 stops with the aperture ring on the ZI lenses. I'm presuming that you can't set the aperture electronically as well?

As Kevin mentioned, if what you're after right now is just your EI, then you don't need to care about anything other than Zone I. If you're going the densitometer route, make a couple of exposures with the lens cap on so you can get a base fog reading. Then read that. Then move along until you find a frame that reads .10 above base fog. If that frame was shot at ISO 25, and it's supposed to be Zone I for a 200 ISO film, then your film requires 1 full stop more exposure to reach Zone I than box speed, meaning your EI is 100. I think I got that right.

And fill the VF with the card. Forget about focusing. Just fill it.

allan

 

[jlw]

I don't want to turn this whole discussion into another full-blown Zone War (have been in too many of those already) but if you base everything on Zone I, the density range variation of your negatives is going to be about as wide as the brightness range variation of your subjects -- not a pleasant situation if your goal is merely to simplify your life in the darkroom (which, IMO, is the only good reason to pursue this kind of testing instead of spending your time making pictures!)

Keep in mind that the whole point is just to find a meter setting and developing time that make most of your negatives reasonably easy to print. The way you do that doesn't have to be complicated.

I won't get into the question of whether it's better to vary the exposure via the aperture control or the shutter speed control, other than to say that the ZI lenses (being made for M-mount cameras) do NOT have electronically controlled apertures. They do have third-stop clicks, so it should be fairly easy to set them repeatably. However, that doesn't address the problem of the fact that the actual light transmission at various apertures may not have an exactly linear relationship to the marked f/stops, so you can't really be sure that opening up the lens, say, three stops is giving exactly three stops' more exposure. That's one reason that formal sensitometric testing usually is done by varying time, and an electronically controlled shutter is probably accurate to a few percent throughout its range, so there's no reason not to use it.

 

[thorsten]

Thank you all for your comments and helpful advice. This afternoon, I shot one roll of Tri-X and one of Neopan 1600 with the wonderful topic "grey card". ;-) I also decided not to get too scientific, 'cause I only do this whole procedure to determine my EI and my developing time to make sure, that "bad negatives" are my fault and not the fault of a wrong ISO-sensitivity set or a wrong developing time. Other than posted before I tried to mostly change the aperture, 'cause the ZI has an electronically controlled shutter, which should be pretty accurate. Only in the range of nearly full closed apertures, I didn't make 1/3-aperture steps but prefered to change the shutter speed. Unfortunately I didn't have time to develop the rolls and also my densitometer didn't arrive today (as I thought it would). 🙁

Until now I thought it went pretty well, but now I read Allan's answer and noticed that I didn't take shots with the lens cap closed... too bad! But: I only shot about 28 exposures per roll, so there must be some unexposed frames... can I also use these for reading the base fog?

Thanks again,

 

[kaiyen]

unexposed frames will be the same, yes. it'll still have the base fog.

jlw - I have no interest in a zone war, either, but I think you misconstrued my post. I was not suggesting that you get your zone I/shadow exposure/EI and then be done with it. I was just saying that the testing for EI doesn't require shooting for zone VII, just Zone I. Testing for development absolutely requires Zone VII, and one should absolutely get _both_ dialed in.

allan