Testing film speeds indoors?

[menglert]

I would like to do some film speed tests for new films I purchased, but the weather is rather dreary here, rain and snow. So, I was wondering if I could do these test indoors under normal room lighting?

Regards,
Martin

 

[Roger Hicks]

I would like to do some film speed tests for new films I purchased, but the weather is rather dreary here, rain and snow. So, I was wondering if I could do these test indoors under normal room lighting?

Regards,
Martin

Dear Martin,

Speeds to tungsten light and daylight may vary insignificantly (1/6 stop or less) or significantly (1 stop or more for ortho) so a lot depends on the film. Or, of course, gel your tungsten lights to daylight values.

Cheers,

R.

 

[Lee L]

I use 5000k flourescent lamps (available in spiral bulbs, straight tubes, PL style) and a white diffuser (Expodisc) for a full frame tone or the same style lamp and step tablets (MacBeth color checker, Fotowand gray scale card, Kodak Q-13, etc) for indoor testing of film, including speed point. This avoids the tungsten balance / spectral response problem Roger mentions.

Lee

 

[MurrayMinchin]

This is probably a bit whacked...but it works for me

What I've done in the past is to point the camera towards a window, making sure to include a good piece of the wall below the window. If you're lucky, you can place a building or some textured surface outside on zone VIII and then find a blanket to tack to the wall that falls on zone I. Then I cover part of the blanket with something really dark, so that I can tell which film speed gives the proper zone I seperation from zone 0. If you're really, really lucky the zone VIII and zone I will both be right on the same negative, but if not, it gives you enough information for your next test.

Murray

Added later; I do this during daylight hours, with the indoor lights off.

 

[Michel Hardy-Vallée]

You know that the color of the object you're shooting has no importance? If it's not sunny enough outside, use a white card instead of a grey one, and meter as usual: straight meter reading will give you a Zone V, etc.

 

[menglert]

Will issues with reciprocity failure come into effect when I'm testing inside?

 

[Helen B]

Possibly. You need to make sure that the exposure times you are using are clear of the reciprocity failure region.

I prefer testing indoors with filtered incandescent light - it provides a repeatable method and light intensity can be adjusted.

Best,
Helen

 

[Lee L]

Will issues with reciprocity failure come into effect when I'm testing inside?

When testing with a full frame tone and a diffuser over the lens, I move the camera to an appropriate distance from the daylight lamp so that the exposure time falls within the range where reciprocity holds.

If you have Ansel Adams' books, look for the pre-exposure device he shows. It's made of two white diffusion plastic pieces spaced for inserting filters between them. This, with the proper conversion gel filter for your light source inserted would work, and would allow you to get the correct distance from a light source to avoid reciprocity failure levels. You'll get single tone frames. Focus on infinity to avoid an extension factor. Move either the camera or the lamp to adjust light levels.

Lee

 

[menglert]

Will I need a diffuser? I'm only working with b&w films.

I was thinking of setting up my cams on a tripod and bringing the light source close enough, so then I can avoid reciprocity failure. Then filling the frame with either a gray or black card, and focus at infinity. If I do this, do I still have to worry about a diffuser or the type of bulb I'm using (not daylight balanced)?

Thanks for all the help so far.

Regards,
Martin

 

[fschifano]

A diffuser will help even out any hot spots, and that's important for obvious reasons. And even though you are testing only B&W films, color tempertature could have a significant effect. Some films, like orthochromatic emulsions or even panchromatic emulsions with a weak red response, will show a considerable speed loss under standard tungsten lamps due to these lamps relatively low output of light in the blue/green part of the spectrum.

 

[Lee L]

Sorry if I've introduced some confusion. The diffusion material I've been talking about is placed right against the lens like a filter, then backlit and exposed out of focus to give even coverage across the frame.

Any evenly lit neutral surface, gray card, white wall, matt board etc. should suffice for a front lit full frame tone. A non-specular surface is easier to deal with. Look for references on copy lighting (for flat artwork) if you want to know how to evenly light a surface.

Lee

 

[ZoneIII]

I would avoid reading off of a target of saturated colors. Reflected light meters often really do have spectral response problems. I found that my (original) Gossen Ultra Spot produced exposures with variations of up to 4 or 5 stops (!!!) when reading off of colored papers or through colored filters. I was in touch with Gossen designers and, believe it or not, they told me that I should "Never meter off of colored objects at all because I am shooting black & white'"!!!??? Then then told me that I should always meter off of gray cards which, of course, is the equivalent of just taking incident readings and totally ignores the whole point of Zone System readings. (I am not making that up!) I switched to a Zone VI modified meter which gives me nearly perfect densities as claimed. However, I can't claim that meters other than my (original) Gossen meter are that bad. (Gossen finally did admit that they had a problem with the meter and it may have been improved with the second version.) I was surprised to find that my in-camera 35mm meters were far more accurate than the original Ultra Spot.

Anyway, my point is that you should do your testing off of neutral colored targets to be safe.

You should definitely avoid reciprocity during testing for obvious reasons.

I always try to use a target that will produce exposure settings that are fairly normal for my "real" shooting. In fact, the other day I did testing inside myself inside. The daylight in the room was even but low so I used a target that was just about 18% gray. But I avoid white targets and even 18% gray targets if I am testing in "normal" outdoor light so that I can nearly simulate exposure settings that I would normally use outdoors. For example, when I do Zone I (film speed) testing, I use a dark target or I put a medium gray target in deep, even shadow. You should not read off of a white target in bright sunlight and place it on Zone I. If you do, your exposure settings will be very high shutter speeds and/or tiny apertures. After all, when would you place an 18% target on Zone I when it is in brightly lit? The bottom line is to try to have test conditions that closely match your most common actual shooting conditions. If your exposure settings are pretty normal for your real shooting, then you are in the ball park. Again, you should not use targets that produced extreme exposure settings.

An option for indoor testing if daylight entering the room is not enough is to use blue (daylight balanced) photofloods but be sure that they produce uniform readings across the entire target.

When I tested film the other day, the natural light in the room was even but low. (It was raining outside.) To me, that's an ideal testing environment for film speed tests because Zone I readings will be made on similar things under similar conditions. Zone I readings - in real shooting situtions, are taken off of dark things in shadow. But because it was relatively dim in the room, I used an 18% gray card instead of a darker one. As a matter of fact, I have more testing to do today and I think I will do it in my garage using with an 18% gray card. I will place it back in the shadows simulating a real shooting situation as much as possible.

For development tests, I use a white card in daylight, again simulating as close as possible realistic shooting conditions and exposure settings.

 

[ZoneIII]

BTW, if you are getting into reciprocity when doing your film testing, then something is definitely wrong with your testing methods. Ideally, your Zone I film speed tests and your film development tests should use identical or nearly identical exposure settings. Remember, when you photograph a real scene with a wide subject brightness range, you are possibly recording everything from Zone 0 to Zone X (or higher) with a single exposure. Your single camera settings produce the full range of densities with a single exposure. If it didn't, there would be no photography! Using an 18% gray card in open shade or sun for Zone I or Zone VIIII (or whatever zones you target) is not the best idea because the exposure settings will not be as they would be in a real shooting situation. Think of what you would place on Zone I and Zone VIII in real shooting. Zone I might be the dark trunk of a tree in deep shade or the shadowed side of a dark rock. Zone VIII might be the white paint on a house in full sun. Try to simulate those reflectances as nearly as reasonably possible when you do your testing. If you are getting into reciprocity when testing, you are not even coming close to simulating normal shooting conditions unless you almost always shoot in low light with slow film with tiny f/stops or in extremely bright light with large f/stops. The first scenario is more likely, of course and if you do that, you should be using a film with better reciprocity characteristics.

 

[jstraw]

I try to avoid looking at images where values higher than Zone X are recorded. I'm afraid I'll damage my eyes.

(sorry, couldn't resist)