Film speed and backscatter

[louisianadiver]

Hi all. I noticed some confusion in another post, where one shooter proposed that faster film speed increased backscatter. I hope to clear that up. Film speed is created by designing an emulsion to produce an 18% gray image at a "standard" (machine) development and temperature. Light meters measure a scene to produce an 18% gray image at a specific film speed (ISO) setting. Therefore, an image taken with different film speeds will result in the same 18% gray exposure and development, so backscatter will not be highlighted by faster film. However, since the faster film will produce the 18% gray image at a smaller aperture, a faster shutter speed, or a combination of both, backscatter may possibly be more apparent with faster films due to increased depth of field or to a faster shutter speed's ability to "freeze" moving particulate that might otherwise blur into oblivion. Backscatter is mostly a strobe effect, though, and film speed doesn't matter nearly as much as strobe placement. Faster films produce more grain and slightly higher contrast than slower films. I shot 50 speed film (Fuji Velvia) for macro for many years, but the high-end 100 speed films (Proviaf) have such fine grain that the difference is negligible. I now shoot Proviaf-100 for both wide angle and macro. I do use Proviaf-400 for dirty water. To see the difference, have a look at the 100 speed shot at http://claycoleman.tripod.com/id148.htm and the 400 speed shot of a manatee in turbid water at http://claycoleman.tripod.com/id103.htm

 

[Scubatooth]

clay

i see what you mean in the image, with the 100 speed all of the tones are smooth and contnious, but with the 400 you start to see the grain alittle bit(or that maybe jpeg compression artifacts) and the colors arent as saturated as the first shot.

as for the backscatter, i didnt quire follow you at first but then i did get your point and it make much more sense

thanks for the lesson

tooth

 

[louisianadiver]

Scubatooth: The color and saturation of the faster film should equal that of the slower film (the water in the example photo was green and there wasn't a lot of color). The main difference is in the grain, which you can see in the water behind the manatee. Because of the larger grain, the tonality of the photo is not as smooth as with the slow film. Are you familiar with the concept of 18% gray? -Clay

 

[Scubatooth]

yes im familair with it, in the color calibration process of digtal pre press, with photo it has taken me a little longer to get up to speed. but yes all meters in cameras are always looking for 18% gray to make a exposure as this is the middle tones in the color scale(close to) so that there is a complete tonal range in the negative or positive..

ok so that was grain and not jpeg artifacting i saw inthe image.

currently on land i mainly used 400 speed BW(As this is what i use for my school assignement) for shooting as im mostly indoors and in low light situation(and some 1600 and 3200 for fun and for real low light situations were i would be running in to massive recoprocity failure problems because of long exposures), except for this weeknd in that i will be using some tmax 100 and illford Pan F 50 in a bright outdoor native american pow wow that im attending.

for me for on land and using negative nothing really beats some Fuji NPS or NPH (if exposure is dead on) i dont shoot much slide but i do like th fujichrome series as i have had to many consistency problems with kodak slide films as of late (5 rolls from the same batch and no two were the same in color saturation, balance, etc)

Favorit films
B&W
Kodak TMAX ,100 ,and 400 (everyday use, and with flash) 3200 in real low light

Ilford HP5, XP2 (these two are my main films i usebecause of there great tonal range and sharpness even at speed or pushed a stop) also delta 3200 is some good stuff.

i want to try some fuji B&W but havent gotten a chance yet, but i want to try it out

for color i am mainly a fujiite NPS, NPH, NPZ are all my favs even though from time to time will use some kodak Portra NC 400 or 800)

Tooth

 

[louisianadiver]

We're drifting rather radically from the initial subject, but if you shoot and develop your own b&w, then you are aware that a film's speed is not set in stone. Most b&w shooters I know tweak film speed and development times/temps to get the negatives they want. For example, I shoot Tri-x 120 film, which is officially rated at ISO 320. I expose at ISO 200, which overexposes the film a bit. I then cut the development time to compensate. The negs look right to me and I save some time in the darkroom. Many people shoot Velvia at ISO 40 instead of the rated ISO 50, feeling that the film is actually slower than rated and that the faster rated speed of 50 was done to exaggerate color saturation. Plus, of course, films can be "pushed" to higher speeds by overdeveloping. -Clay

 

[Scubatooth]

clay bary intresting im just shooting at rated speeds right now and bracketing, but was wondering what you think the various ISOs are for the various kodak B&W films
TMAX 1,4,3200, Tri-X 400, etc.

im just a first semester photo student and learning all of this darkroom stuff as i came from a pre press enviroment were i was just doing color editting work and printing not the start to finish im doing now.



also clay do you have any books that you reccomend on black and white shooting and devolpment (IE pulling)and how to get negs that a balance through the frame .

clay question do you devolp your own B&W film and print it or do you send it out. also in that example of tri-x what is the reccomended devolpment time and then what time do you use in the pull ?

heres one for you give a reccomendation on, i normally shoot t-max 400 (what school requires forthis semster, will change when i finish testing films) and develop in 68 deg with HC 110 Dil B (1:7) for 6 minutes. the packaging on the box says this combonation should be around 320. from time to time i find that in printing i find the grain rather big and dont really care for it as i would like it smoother (i know go to a slower film) but for cloudy conditions 100 is to slow for hand hold in situations where a tripod is not allowed.

Tooth


also what med format camera do you use ?
tooth

 

[louisianadiver]

I don't have much experience with any of the 35mm films because I could never get grain under control with 35mm negs. I know the T-max films are better for grain, but I never got around to shooting any. I bought an old Mamiya C220 TLR 6x6cm (2 1/4x2 1/4) camera for $150 and it has served me very well. It's a totally manual camera, of course, and I use a variety of light meters with it--usually a Minolta meter that I use in incident mode. I develop the Tri-x 320 shot at ISO 200 in a 1:1 dilution of D-76, 68 degrees, 9 minutes with a full inversion and return every 30 seconds. The development time is 12 minutes if shot at ISO 320. I use tap water for my stop and wash, and during the summer the tap water is 80 degrees or higher down here. The hot water can "pop" the grain due to the rapid expansion, so my summer negs are not as good as my winter ones. Pulling the film gives me better grain and a bit less contrast in the negs. I dial contrast back in with a Beseler dichro head printing to polycontrast paper and develop the paper in a 1:2 dilution of Dektol. It's been awhile since I've done any darkroom work here, and my darkroom is starting to fill up with junk. I learned from advice from friends and trial and error. I'll bet the Internet is full of information on ISO exposure/developments for all kinds of film if you look around. You're definitely on the right track learing photography by doing your own black and white. Once you get the hang of it, you'll have a good understanding of what the automatic cameras are trying to accomplish.