I'll put the conclusion at the front and then defend it like some kind of thesis. In conclusion I love everything about this film. I love the cost, I love how it behaves, I even love developing this film. Fomapan 100 is for me the best 100 ISO film that I can get my hands on and I'll shoot on it until it's gone or I'm broke. Now let me explain why.
First lets look at what Fomapan 100 is. Fomapan 100 is a slow and very unforgiving black-and-white film that has a somewhat unique timeless look when shot right. 100 ISO isn't as versatile as you might think, lending itself to either sunny days or long exposures. This film is panchromatic with a fine grain that resolves detail extremely well. The film base is cellulose triacetate(I'll come back to this in a minute) which is oldschool and perhaps it could be responsible for the timeless look of the film. The film base isn't plastic, its oldschool. Hailing from the Czech Republic this film is to my eyes as sensitive as the famous Tri-X film from Kodak. However this film seems to feel as if it's older and somehow less sterile and perfect if that makes sense. Some reviews of this film are negative and I don't understand why, it seems the reviewers don't understand how to shoot slow film like this and get disappointing results.
An oldschool film for oldschool photography.
The real problem is, Foma is old in it's formulation and how it behaves. There are "better" films out there, by that I mean more modern and more accurate. However Foma shines in that while it has fine grain, it's grain is still visible and lends itself to a sort of softness that feels like it came from many years ago. Now in some cases I guess that's bad, but in my opinion having a timeless looking film lends itself to artistic creative possibilities that more modern films can't contribute to.
What this film therefore also lends itself to is old cameras and old style shooting. If you've got your dads old camera and wanted to try creating something that looks like it was shot 50 years ago, this is the film to put in that camera. If you want to try shooting like a photojournalist back during WWII, this film can do that too. The bottom line is that you need to be aware of what this film is and the character it has so that you can capitalize on it's strengths rather than it's weaknesses, and woah nelly is this film unforgiving.
Foma 100 has some of the most insane reciprocity failure that I've ever found in a black and white film. Normally black and white is somewhat forgiving, however this film has reciprocity dive off a cliff. What that means is that underexposing doesn't just lead to dark images, it leads to ruined pictures, especially in low light. Unfortunately most of us have become spoiled by the latitude of newer film stocks combined with amazing scanning, or digital. With Foma 100 you absolutely must get your metering at least in the ballpark if you want a decent image. What can be a creative decision can become a curse in an instant if you forget what film you're shooting. However the rich tones diving into inky shadows can sometimes add to your images.
Shooting at night with this film is stupid and could take hours. The falloff curve with this film creates a cliff-like situation for your exposure times. 30 seconds metered is 347 seconds with this film. Want to do a 2 minute exposure? That'll cost you 27 and a half minutes of your life that you will never get back. Even with perfect exposure the film will return murky results. However, why let that stop you? Do something stupid! Go try this and get some very interesting results unlike almost any other modern film. I did and got this picture. I had to sit in my car reading a book for half an hour but hey, it's interesting.
Developing this film.
Development of this film is possible with a lot of different techniques. Personally I just use Kodak D-76 because I'm lazy and get good results with it. I buy two gallons of distilled water and mix my solution directly into the jugs while drinking a glass of tasteless water to replace the added volume. Personally I like the near lack of colored anti-halation layer on this film.
You'll want to stay close to your prescribed development times however I have found this film very forgiving. In one case I accidentally left the film on the counter for 10 extra minutes and still recovered acceptable images. This longer development time may annoy some people who are used to shorter development times such as C-41, however being forgiving can be a strength for a film, especially for people developing at home for the first time. One thing I've noticed is that if I let my scanning software scan for color I will get varying hues of brown akin to sepia tones found in old images.
Holy cow this film is cheap and that's reason enough for you to buy it. If you shoot no other black and white film then consider this film. This film is constantly at the top of the list if you sort by price with the lowest being first. This is also a great selling point for testing on old cameras since you aren't throwing expensive film away. A bag of D-76 developer and a gallon jug of water is all you need to develop at home which further lowers the cost. Foma has done a wonderful thing here by giving us a high-quality cheap-as-dirt film. If you cannot afford to shoot another film then this filmstock may be your saviour. The cost of only about $3 a roll simply cannot be beat.
"Vinegar syndrome" and why this may not be good archival film.
As I mentioned previously this film has a base that consists of cellulose triacetate. What that means is that this film like any other with a base like this will probably suffer from what is known as "vinegar syndrome." What that means is in a nutshell is that moisture, heat, or acids, will break acetyl groups loose in the film base itself releasing acetic acid. As the film base breaks down there will be a vinegar smell and eventually the film will degrade enough to be ruined. How long this takes is up for debate but even under near ideal conditions it appears as though the process can take as little as 70 years. Furthermore some of my earliest film has this characteristic smell and that's in less than 10 years. Therefore you'll probably want to digitize your film and not rely on the negatives for too long.
Is any of the above true? I don't know, I'm just reporting what I've seen and what Wikipedia says.