Long exposures

[Tim Gray]

I want to take some pretty long exposures... 6-8 hours, for a project I'd like to do. Am willing to use any B&W film, but 400TX is my preference since I use a lot of it. I have no real questions to ask, but was looking for some pointers. I took some test exposures, but the room was apparently too dark, and I didn't get sh*t. Does reciprocity failure step in at some point and just end it? I can always light the room a bit more, but I'm worried about extreme overexposure...

Thanks in advance for helping out with such a vague request.

 

[Kevin Caulfield]

Reciprocity failure sure does step in, for some films once you get into the seconds and tens of seconds, and by the time you get into 6 to 8 hours, you could be looking at a correction factor of at least 4 or 5 (or maybe a lot more).

 

[jordanstarr]

what are you shooting that requires a 6-8 hour exposure with 400iso film?

 

[Murray@uptowngallery]

A dark room.

No, seriously, reciprocity failure at 6-8 hours will be far beyond a factor of 4-5 for 400 Tri-X.

I apologize if I misunderstood 400TX as Tri-X if Tmax was intended.

Consider Kodak's reciprocity failure correction chart that only goes to 100 seconds: 1200 is the suggested corrected exposure, a factor of 12.

For longer exposure, there is a chart on the web somewhere; try Googling the following keywords: Lunarlight, Kitathome,mkaz and mkirwan

 

[Dan Henderson]

If reciprocity failure is the issue, consider using Fuji Acros. It does not require reciprocity correction, (at least up to a point, which you may have exceeded.) You may also be shooting in such a dark place that there is not enough light energy present to affect the film, even at these extreme times.

 

[w35773]

I'd be intrigued to know more about your initial experiment. I believe if you could see at all, your 400 speed film would have registered something with an open shutter for 6 hours.

In other words, a very, very dim safe light would fog a piece of film in no time at all. It stands to reason, if I leave a piece of film on the counter all day, it would have to be pretty dark (as in totally) not to fog.

Cheers,
Russell

 

[gainer]

Look in www.unblinkingeye.com for the article "LIRF is Lurking at Your F-stop" by Patrick Gainer. LIRF is Low Intensity Reciprocity Failure. The equation is simple, but logarithmic. The necessary factors are listed for 400TX, HP5+, and some other films. The factor you need for any film is the additional exposure needed to correct for reciprocity at 1 second measured exposure.

The necessary additional exposure is lower by far for the TMax films and many other modern films than for the traditional films when you get out to the hundreds of seconds of indicated exposure.

If the math gives you a headache, take two aspirin and call your nearest math doctor in the morning.

 

[keithwms]

What do you mean, you didn't get sh*t? Was the neg fogged or was there no detail? No density? Too much density? I am very surprised if you got nothing. I haven't done many long exposures but what little I've done, I always got something. I don't know if I would even bother to think about reciprocity past a few hours, the derivative is totally flat out there anyway. Just open up the lens and the shutter and you have to get some density.

 

[Tim Gray]

Alright, so a bit more background is needed. First of all, I didn't try the experiment with Tri-X since it wasn't in the camera at the time. Used some Gekko MW100+. I wasn't too concerned if I didn't get printable pictures because I thought I'd get something. I got nothing. Nothing at all.

I'm taking pictures of people sleeping. Long exposures over the whole night. Testing it on myself. The problem is, my bedroom is DARK. I could always add some light like I said, but I really want to capture it over 6 hours. As a result, I figure it's a bit more complicated than flipping on a lamp, since I'm really looking for a long exposure, and not "just enough" light for an exposure at all.

I'm not particularly sold on any kind of film for this, but merely mentioned Tri-X because I generally like it and have a lot of it.

I know the camera was working, etc., for 2 reasons. First, other shots on the roll came out fine. Second, when I got up in the middle of the night to use the little boy's room, I flipped on a light in the hallway and that portion of the frame exposed fine.

I figured the reciprocity failure wasn't a big deal like keithwms said. Just because I'm opening up the shutter, picking an aperture at semi-random, and just going with it. I mean, how do I even measure the appropriate exposure which I would then adjust for reciprocity failure?

Thanks for the link. Math isn't too scary. I use enough of it in the day job. Thanks for the ideas as well. I think more experimenting is in order; I was really just curious what your guys thoughts. I'm always impressed by the wealth of knowledge here - a great resource for a beginner like me.

 

[Drew B.]

what are you shooting that requires a 6-8 hour exposure with 400iso film?

Now there is a question worth its weight in gold!

 

[Rich Ullsmith]

Even a film like Acros 100 or Tmax 100 will only get you up to about 8 minutes before reciprocity failure. If I was to try your experiment, I would probably do this: light the room with a dim red bulb, like a safelight bulb, and put a 25 red filter on the lens and go from there. At least that way you can get more light to the film and still be able to sleep.

 

[pgomena]

I have a tested reciprocity chart that shows a metered reading for Tri-X of 10 minutes requires an exposure of about 9.5 hours. Tri-X ain't gonna work in this situation.

I used to make pinhole pictures in a darkened photo studio. During shooting sessions there would be light only from several shooting stations plus the odd occasions when all the overhead lights were on. The meter reading (f/180 or more) with the overheads was in excess of 30 minutes. I exposed Tri-X for an entire work-week and got very printable negatives.

Peter Gomena

 

[keithwms]

Ah now I see what you're up to.

How about a low-wattage incandescent black-light bulb, in a lamp off in the corner somewhere. You eyes are rather insensitive to the deep blue/violet/UV light, but most films will see it quite well. RTP2 in particular. Yes, try it with fuji 64T, you might love it. Gorgeous blue colour shift. Should befit the subject.

 

[Tim Gray]

I can actually sleep through just about anything. Not sure if other subjects can... But that's besides the point at this time. I'm really just trying to obtain the right balance of scene lighting and aperture to able to get an exposure over 6 hours. Thanks for the ideas. I'll try some of them out...

 

[gainer]

Choosing a film should be easy if you know the correction for reciprocity at 1 second indicated or estimated time. The failure at any othe time is in the same ratio. Thus, a film that requires a correction of 1 second will have 10 times the reciprocity failure of a film that requires a correction of 0.1 seconds. IIRC, that is about the ratio between Tri-X and either TMX100 or TMX400.

 

[CBG]

Thoughts: You said, "picking an aperture at semi-random..."
Go wide open. Use a fast modern film like Acros. Acros is more tolerant of ling exposures than most other common films, and much more tolerant than Tri-X which is a "venerable" formulation.

In extreme dakness you need days or weeks of exposure. Look up the fellow, Abelardo Morel, who lights rooms with just a small pinhole and then photographs the room from within - great photos and they take many hours or a few days of exposure.

You may need to set up the camera and do cumulative multiple exposures to total a few days if the room is as dark as I think you mean. There has to be a little light to get anything at all. Something.

"Does reciprocity failure step in at some point and just end it?"

Reciprocity doesn't just end it, but it does make the film act as if it loses sensitivity at longer exposures. It is a gradual process of ramping up the compensation for lost "speed". Older film formulations are more prone to losses generally.

Best,

C

 

[Murray@uptowngallery]

OK, I was right, facetious or not. It was a dark room.

http://www.abelardomorell.net/camera_obscura1.html

 

[mark]

Murray, I love those pictures. Thanks for posting them.

I used to turn my classroom into a Camera Obscura every spring and wondered what taking a picture of the picture and projected image in the room would look like.

My Kids used to get such a huge kick out of it.

 

[Murray@uptowngallery]

I really like alot of Abe's work, too.

Inspired by the camera obscura take none step further, I am also stymied by a location/subject matter problem.

But time has passed, I think I found a half interesting location and a sympathetic ear/eye...in fact the person told me they were at a Morell exhibition, so I mentioned my idea...I think the ball is in my court right now.

Re: Acros, see Ryuji Suzuki's extended graphs for Acros, more accurate than the film datasheet. His stuff has been Wikified, so you make have to search a little.

 

[gainer]

From the equation found in the Unblinkingeye article, I compute that an exposure on HP5+ that is calculated to take 6 hrs without reciprocity misbehavior would take 327 hrs. I could not verify the equations beyond a few hundred seconds, but the line I got is headed in the direction of 327 hours. I could photograph my hand on a clear night here in the country by starlight in much less time than that.

The equation needs seconds for input and produces seconds as output, which is reasonable for most mortal photographers. 6 hrs = 216000 seconds. The calculation is:

Total time in seconds = t1*(tm^1.62). Divide by 3600 to get hours.

t1, the correction to be added to a 1 second exposure as measured by a linear meter, is for HP5+ 0.11 seconds from data by Howard Bond.

The symbol * means multiplied and the symbol ^ means "raised to the power"

As you can see, the value of the correction at 1 second is the factor that makes one film different from another. However, even a film that is 10 times better thab HP5+ would still require a 32.7 hour exposure for a a linear 6 hour estimate.

 

[rhphoto]

I've heard that you can somewhat compensate for reciprocity by making incremental exposures of a shorter length, before reciprocity begins to take effect, and adding it up to the total exposure you need. For example, an indicated exposure of 1 minute might yield a reciprociy-adjusted exposure of 3 minutes. So you give 4 or 5 separate exposures of say 20 seconds. I dunno, maybe some genius like PE can weigh in on this.

 

[CBG]

PE knows a great deal more than laypeople like myself on reciprocity etc, but I'm pretty sure I can safely state the solution Robert has heard about won't work as intended. I would be glad were PE or other experts to weigh in with real expertise....

Robert said." I've heard that you can somewhat compensate for reciprocity by making incremental exposures of a shorter length, before reciprocity begins to take effect, and adding it up to the total exposure you need. "

Unfortunately, there is no such easy cure. Robert's solution will lead to the same level of underexposure as the original poster found problematical, or a tiny bit worse due to a second issue called the intermittency effect. It will not bypass reciprocity.

First - To get a sense of what goes on with reciprocity failure, the best layman's explanation I've found is at:

www.camerabooks.com/custom.aspx?id=27

Having read it, reciprocity failure is more comprehensible. There are a lot of erroneous explanations on the net - so if one wanders the net via search engines - please do so with a sceptical eye.

Robert's hoped for solution fails, since breaking a long exposure into several shorter ones must still take into account reciprocity effects and will often introduce another issue, admittedly usually minor, the intermittency effect.

10 two second exposures will generally yield a slightly less exposed image than a single twenty second exposure. I say generally since the intermittency effect is not at all simple to calculate other than by testing for a specific instance.

The intermittency effect is not the magnitude of destructive monster that reciprocity is, so it often goes by unnoticed. Nonetheless it does diminish the total exposure slightly.

I have never read an authoritative explanation of intermittency, and assume it stems from the root causes of reciprocity.

PE??????????????

Best,

C

 

[PaulH]

maybe you need to approach this the other way. if the lens is going to be open for 6 hours, assume that this is the exposure after compensation for reciprocity failure. then back-track to the original exposure based on gadget's calculation.

hope this makes sense.

 

[Tim Gray]

Makes total sense.

 

[CBG]

If I understand the lighting situation, i.e. dark as all get out, the light is waaaay below the threshold of sensitivity of any meter I know of.

Calculation goes out the window at that point. Tests and comparable situations become the way to establish exposure times etc. I'd just open the lens up all the way and try a series of exposures - 1, 2, 4, 8 hours. Then process and see if any show any exposure at all.

If you get some exposure but not enough - either add a little light or use a much faster film or push your processing really hard or try exotic techniques to boost sensitivity and to boost the latent image.

Chapter 10 of my copy of Anchell and Troop's "The Film Developing Cookbook" lists some processes for boosting true film speed and latent image. Astronomers use some of those techniques.

Best,

C