Opinions are like... (Rating B&W film speeds)

[smo2]

Sorry about the attention getter - at least the attempt.

Here is my question - WHAT is the benefit of underexposing films? If the box says 400, why not shoot at 400? If you do underexpose, do you change your development times? If so, aren't you just pulling the film? I ordered several rolls of TRI-X (400) that I wanted to try but all I see is conflicting opinions. Most seem to say shoot it at 250 or 200. WHAT is the benefit one is trying to achieve by doing so - getting a "better" negative? If so - what does better mean - more contrast, finer grain, etc. etc?

Also, I purchased Ilford HP5, Fuji Neopan 400 and Ilford Delta. Any details on these films as well? I shoot film in 120 mostly and started developing myself recently with TMAX developer. From what I read D-76 is the best for Tri-X. Is that good for these other films as well?

Let's have some opinions! And Facts (just opinions more people share)!

Also, I know there are MANY threads on this but nobody seems to answer the why.

Thanks.

 

[Peter De Smidt]

The benefits of underexposure? By that, you mean giving less exposure than rated? With slide film that can lead to greater color saturation and a lessening of the chances of burning out the highlights. With negative film less exposure gives slightly more sharpness and finer grain, all things being equal, but you quickly lose shadow separation, which is usually a bad thing.

Pulling a film means giving it more exposure but less development. Pushing means giving less exposure and more development.

 

[smo2]

Sorry...

I meant shooting at 250 ISO when the film says 400.

 

[David A. Goldfarb]

Please use a descriptive title when you start a new thread.

Rating film at a lower speed increases exposure. Doubling the film speed rating would produce underexposure.

Usually the reason for rating film at lower than the box speed is to improve shadow detail.

Take a look at an Ilford data sheet for any of their B&W films, and it will explain what the tradeoffs are with different film/dev combinations, and they will generally apply to Kodak and Fuji B&W films as well. Different developers might give you better or worse grain, acutance, speed, highlights, economy, ease of use, etc. There are a lot of options, and it's up to you to decide what's important for your work and your photographic vision.

 

[Nick Zentena]

Some people don't trust the box speed and over expose out of habit.

Others test the film in our own cameras and developers to see how it reacts to our process. That gives us an EI that we know works for us and not for how the guys in the ANSI testing lab do things.

With negative film it's safer to give more exposure then to not give enough. So if you have to risk you risk that way.

 

[Lee L]

... and to be a bit more explicit, a film will often have different effective speeds with different developers, or with changes in agitation routines. So experienced people will rate a film differently depending on the developer and agitation method they use. Some do this in a "seat of the pants" way, judging by eye and repeated experience with the characteristics of their negatives and prints, and others do it by careful measurements of negative densities with very accurate instruments. These two methods of arriving at film speed adjustments often end up in the same place, especially with experienced photographers.

It's not really about overexposure, it's about learning what the proper exposure is given your choice of metering method, developer, agitation, equipment, etc.

I shot a lot with one brand of SLR for half a dozen years with Kodachrome 25 rated at EI 32 to get correct exposure and saturated colors. Then I changed to another brand of SLR and had to shoot it at EI 25 to get "equivalent" results.

Lee

 

[smo2]

Dev Times

What does underexposure do to your development times? Do you develop at the reccomended time? I have been using the massive dev chart thus far and seem to get decent results. Do you shorten it at all?

 

[Peter De Smidt]

Ok., giving more exposure with negative films, say rating an ASA 400 film at 200, moves the shadows up the toe of the film. In other works, you'll get better shadow separation. This is especially true of long toe films like 320 Tri-X.

 

[Peter De Smidt]

I would not change development times. To be clear, you should run film/developer tests to determine your exposure and development for a giving SBR (Scene Brightness Range.) As a result, you're neither over exposing nor under-exposing. You'd be giving the proper exposure for your needs.

 

[smo2]

Up the Toe????

Not sure what that means - can you explain it in english? I am not an expert developer - please be patient.

So, change the ISO - and keep the development times. I shoot Tri-X at 200, then develop with the time used for 400 ISO from the massive dev chart or somewhere else. Correct?

 

[David A. Goldfarb]

Take a look at the data sheet for your favorite film (they are available at the manufacturer's website) and there will be a "characteristic curve" rising from left to right with the log of the density on one axis and exposure on the other axis. The area on the left with the least exposure and least density is called the "toe" and the center is usually a more or less straight line, and the area at the top of the curve is called the shoulder, because ultimately you can give the film more and more exposure, but you won't get more density in the highlights, because you are approaching the maximum density the film is capable of (Dmax).

The film speed rating determines where the shadows will fall on that curve. If the film has a long toe like Tri-X 320, then you might want to increase exposure (not "underexpose" as you've been saying, but the opposite) to get the shadows on the straight line portion of the curve, and that will produce better tonal separation in the shadows.

Development time will not affect shadow detail as much as it affects highlight detail, so once you determine your film speed, you want to adjust development time to give you negatives of good contrast for the paper, enlarger, print developer, etc. that you are using.

This is all explained in many books. I recommend Ansel Adams' _The Negative_.

 

[Peter De Smidt]

The "toe" is part of the characteristic curve for a film/developer combo. It is a representation of what film densities you get for given exposures. The toe is that part of the curve where the film first responds to exposure. At that point it takes relatively large changes in exposure to get significant changes in film density, i.e. there's not much tonal separation. The middle part of the film curve is called the straight line section. In this area a given change in exposure gives the greatest change in film density, and so there's very good tonal separation here. Finally, the shoulder of the film is when there's so much exposure that the film reponds less to changes in exposure. So again, like with the toe, on the shoulder of the film curve the film needs big change in exposure to get a different density.

Another way to say this is that the toe and shoulder are low contrast areas of the film, and the straight line section gives the most contrast.

This is a generalization. Some films are pretty much all straight line, like TMY in Xtol, and some films are mainly toe and shoulder, like XP2.

Basically, film and developer combo has it's on characteristic curve, and this determines the tonal qualities of the film.

Getting back to film and development. Exposure mainly determines the densities of the shadows and development mainly determines the densities of the highlights. So you want to give enough exposure to get the shadow separation that you want, and you want to develop enough to give the midtone and highlight rendition that you want.

With negative film, it's better to overexpose and underdevelop than to underexpose (which give detailess shadows) or overdevelop (which give bigger grain and hard to print highlight detail.)

 

[Lee L]

First off, I should probably not have mixed comments about color transparency film with B&W negative films. That was only an instance of equipment variation, not a way of equating behavior between two very different materials.

You're probably asking larger questions than you realize, but that's a good thing. I'd suggest that to answer your questions in full, in a systematic way, an online forum isn't the best format. A good book would be better. There are several that I know of that would be a good starting point for reading about the topics you're interested in, and could give the basics without overwhelming you with heavy B&W sensitometry discussions. Les McLean's "Creative Black and White Photography" and Henry Horenstein's "Black and White Photography" have clearly written and illustrated chapters on determining film speed and development times. There are threads here on APUG about good beginners' books that recommend others. Check the library, book store, etc for the recommended ones that suit your style.

In the meantime, try part IV of Mike Johnston short primer at http://theonlinephotographer.typepad.com/the_online_photographer/a_simple_system.html That discussion of the ring-around might give you some grasp of the factors involved, although he assumes a bit more than beginning level.

Hope this helps.

Lee

 

[Area51Resident]

Up the Toe????

Not sure what that means - can you explain it in english? I am not an expert developer - please be patient.

So, change the ISO - and keep the development times. I shoot Tri-X at 200, then develop with the time used for 400 ISO from the massive dev chart or somewhere else. Correct?

There are two basic reasons for exposing your film at a different ISO than what is printed on the box.

1) Your meter or the way you use it may be slightly off the mark and measure high or low. The only way to know this for sure is to have it tested against a calibrated light source. If you meter is new it is probably OK.

2) Most people do not like the shadows in their photos to be solid black or so dark you can't see any details. A solution to this is expose the film 1/3, 2/3 of a whole stop below the ISO rating on the box. For Tri-X 400 1/3 less is 320 ISO, 2/3 is 250 ISO and 3/3 (one whole stop) is 200 ISO. By lowering the rating you are telling your meter that the film is less sensitive to light and to give it more light. This lightens the shadows and will show more details in the dark areas when printed/scanned.

By lowering the ISO/increasing the amount of light hitting the film also means that the light areas will get lighter which may not be a good thing. The usual solution here is to adjust development time, make it shorter, to reduce development of the film and stop the light areas from being too bright or solid white when printed or scanned. What works to your advantage here is that changing the development time doesn't have a significant effect on shadow areas of the picture.

To summarize:
Lower film ISO to increase shadow details
Reduce development time to increase details in the highlights.

As mentioned previously you can measure an exact "personal" ISO if you have the testing equipment or by making test shots at different ISOs, make carefull notes on which frame is which and see what works best for you. It is important to make sure you have a consistent developing process (developer dilution, temperature and agitation method) otherwise you will never get the same results twice. Even mundane things like the differences in your tap water is enough to make a difference, so you have to work out the development process and time yourself. What works for me may not work for you. "Been there, done that (wasted a lot of film)" using other people's dev. times.

I hope that helps.

Jason...

 

[DeanC]

smo2,
I think part of your confusion might be about which direction is under exposed and which is over. If you expose a 400 speed rated film (400Tri-X, say) at 200, you're actually OVER exposing it relative to what Kodak rates it. To under expose it, you would have to rate it at a higher number (800, 1600, etc).

Many of us have found through testing our films, developers and development methods that the speed on the box isn't exactly right for how we work. Film speed for any given film can vary based on how you develop (intermittent agitation, constant, semi-stand), how long you develop for, which developer you use and how dilute you use your developer. Add to that the fact that the level of contrast a film exhibits also varies by all of the above factors and you have a fairly complex system.

I'd recommend picking up either a copy of Ansel Adams' "The Negative" for a (somewhat) simple description of what's going on or Phil Davis' "Beyond the Zone System" for a much more detailed version.

Good Luck!
Dean

 

[Steve Smith]

Have a look here: Dead Link Removed



Steve.

 

[nworth]

There are very strict standards for determining film speed, and using the ISO speed will usually give acceptable pictures. But not always. The problem is usually in the shadow details. The way film speed is measured, you have very little tolerance for error in the shadow areas. But most modern films have considerable tolerance for overexposure. Rating a film speed lower than the ISO value is really a sort of insurance.

Development mostly controls contrast. If your negatives print well on normal paper, your development is OK. If your negatives tend to be harsh, whether or not you adjust the film speed, you need to decrease the development. Development depends a lot on the technique you use, and consistency is important. Almost everyone needs some sort of adjustment here. When you use a film speed lower than the ISO speed and develop normally, you will get a more dense negative. This is not a big worry, as long as the highlights do not block up. It just means that you will have to expose the print longer.

Barry Thornton said that most people underexpose and overdevelop their negatives. ("Edge of Darkness", Amphoto, 2000). The result is excessive contrast and poor shadow detail. Thornton's explanation of the effects is pretty long and complicated but well worth studying. The bottom line is that you have to find a film speed that works for your kind of shooting, and that speed is usually a third to a full stop less than the ISO speed.

 

[Steve Smith]

Although I read the article to which I posted the link, I did not actually do the tests myself.

Most articles and information I found ended up with an EI rating of about half the film's rated ISO and development time of about 75% of the suggested time for full ISO development.

So I just tried that (HP5+ @ EI 200) and decided that I liked it. I have stuck to that since.

I also use PAN F but as I like the results I get using it at its rated ISO 50, I have not thought about experimenting with this film.


Steve.

 

[Donald Miller]

If you will go to the Kodak site (since you are speaking of a Kodak product) you will find a link to spectral characteristics. At that link you will find a characteristic curve for the film that you mention. You will notice, when looking at that curve that the curve is not a uniform gradient. In the lower left portion of the curve you will find a lower gradient. This is called the toe of a film. In this flatter gradient you will have less tonal separation than you will in the middle of the curve.

The upper right hand portion of that curve is called the shoulder of the curve and you will notice that the curve also flattens again and this leads to less tonal separation.

When you overexpose a film (what you are describing even though you are saying underexposing) you are moving the exposure point to the right and more rapidly onto the straight line middle of the curve. This will give better low value tonal separation. One must be careful, however, that you do not exceed the straightline portion of the curve to the point that you push your
higher tonal values onto the shoulder of the curve.

All films and papers have a characteristic curve that shows their performance characteristics. You can learn a great deal by studying these when you choose a given material. It should be noted here that while shadows reside in the toe region of the curve with films that the opposite is true with papers. That is because film is negative, ie...it produces lower densities in the regions that a paper, being positive, will produce the greatest densities.

Hope that this helps.

 

[smo2]

OK

I had a mental block - I thought that we were underexposing it by shooting 400 @ 200. We are OVERexposing the film. Now that I have that straight - we just develop it as 400 film shot @ 400 even thought we actually overexposed it by shooting it at 200.

 

[Steve Smith]

Now that I have that straight - we just develop it as 400 film shot @ 400 even thought we actually overexposed it by shooting it at 200.

Some people do that, others, like me, develop for less time. I use 75% of the ISO 400 time when using ISO 400 film at EI 200.


Steve.

 

[DeanC]

Go shoot a roll and try it...

The times in the massive dev chart are submitted by people who feel they got decent results. If you shoot @ 200 but use the developing instructions for 400 my guess is you'll wind up with good shadow detail in your negs but that they'll be a little on the contrasty side. BUT, they'll probably print fine and you might like the way they look, and that's really all that matters. On the other hand, if you do think they're a little too contrasty, try the shot @200 dev instructions the next time (or just knock 20% off the 400 time) and see what those look like.

One of the enjoyable (and really frustrating) things about B&W photography is that there's no one "right way". If your negs are too contrasty, you can always use a soft paper, if they're soft, use a contrasty paper. Try different things and see what you like...

 

[smo2]

Thanks for all the advice

I am going to try to write down all my exposures and see what happens. I had been disappointed with my results so far. I love the detail and richness that I see in some other black and white shots. I am not sure what richness and detail mean exactly. I really like the "Ansel Adams" sharpness. That may sound stupid considering he was a master and I am not. But I think if I can get the "right" combo of development, film, exposure, etc. that I should be able to get that "look" even if artistically the photo would not be as good. It seems like HP5 and Tri-X are some favorites so I will start there.

 

[PHOTOTONE]

I had a mental block - I thought that we were underexposing it by shooting 400 @ 200. We are OVERexposing the film. Now that I have that straight - we just develop it as 400 film shot @ 400 even thought we actually overexposed it by shooting it at 200.

You can do that and with some films get very good results, however most serious photographers who also develop their own film, tend to work out their own personal exposure and developing times to get results that give THEM the best negative for their style of photograph and printing techniques.

As a general "catch all" rule, if you expose generously (for the shadows) then you "usually" need to cut back on the developing time a little bit in order to not allow the brightest parts of the picture (the highlights) to get too dense in the negative. The goal is to have a developed negative that will print a full tonal range image on the photo paper of your choice with the least amount of dodging and burning.

 

[dpurdy]

re this issue of box speed vs actual speed I think there is another variable and that is the metering method. I have always used a spot meter and based my exposure on shadows. So for me there is no question or opinions I just do a film speed test and find zone 1 and it basically always indicates almost a stop slower than box speed. However if you are using an averaging meter and generally metering out doors and lots of skylight then box speed will probably be about right most the time.