I’ve been developing film at home for a while now, and I’ve done everything that I can to get my money’s worth from my chemicals. Using the recommended 2% per roll time extension methods from Cinestill, I’ve been able to extend my chemistry’s life to the point where I’m spending just a couple of bucks a roll for development, which really adds up if you shoot a lot.

While I have been utilizing that method for a while, my math wasn’t always correct when computing the proper time on the fly in the darkroom, which resulted in some mistakes here and there.

I made a chart to help me out while using CineStill’s C-41 Quart Kiand I no longer have to second guess my work. Well, I’m sharing that with you.

I would like to test these numbers a bit further, just to see if any tweaks need to be made, but the last roll that I developed using an exact time yielded positive results (my 8th roll of film developed with the chemicals and it was push processed 1 stop). Here’s the table, scroll past it to see the results I’ve obtained.

Push +1
(2x ISO)
Push +2
(4x ISO)
Push +3
(8x ISO)
Pull -1
(½ ISO)

Results time! Here’s the first roll I ever developed back in 2018. I severely screwed up the development and blix timings and did not monitor the developer temperature. There’s still an image (of me) but it’s not pleasing whatsoever.

Me Laughing from the first roll I ever developed back in 2018
Me Laughing from the first roll I ever developed back in 2018

Moving to the four samples below, all the films I developed using roundabout timings that were pretty close but not precise. This resulted in some minor color and exposure issues that were somewhat manageable in Photoshop but generally yields decent results.

At this phase of my understanding in extended chemistry times, I was still just doing math on my phone and incorrectly calculating the times. I wasn’t taking notes and generally just shooting from the hip.

Here’s a frame from the first roll that I processed using the precisely calculated times in the table above. Pushed +1 stop to 800, 4th roll processed with the chemistry.

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7th St, Alvarado
7th St, Alvarado

More examples using my calculated times. Both were pushed +1 stop to 800, rolls 10 and 11 (respectively) processed with the chemistry, which at this point is now 3 months old.

People ask me why I develop my own color negative film. When I got into shooting film back in 2013, I just kept shooting and shooting and shooting but never got the film processed. I stacked up something like 15 rolls of film that had not been processed, so I started looking up places to get it done. What I came to find out was that it was going to cost me something like $150+ to send my film to some darkroom for processing, or I could spend that same amount of money and buy the bare minimum amount of equipment to do it at home myself.

Since I’ve always been an industrious DIY tinkerer-type person, I went with the latter. I bought a black film changing bag, a double-spool Paterson developing tank, some chemical storage bottles, and a box of fresh powdered chemicals. I tossed a lamp with some red lighting gel in my bathroom and bada bing bada boom I had a darkroom. I experimented with different powdered chemicals for a little while before I settled on the liquid C-41 kit that Cinestill offers. It’s a good price and I get pretty satisfying results consistently.

It took me a little bit of time to really dial in the science of developing film at home, and after making this table, I feel like I am definitely working on a better level than when I started. I feel that I can now confidently develop any C-41 film with these chemicals because of the math, which was the lesson I needed to learn.

I hope that this data helps other people too, because there is no better feeling — as a photographer — to defy the odds of failure and perfectly develop a roll of film that may or may not have the coolest once-in-a-lifetime shot on it and you know that you had a hand in every step along the way; it’s why my Instagram handle is Celluloid Junkie 🙂

Thanks for reading!

~ Aric

About the author

Avatar - Aric Abraham

Aric Abraham

I'm a 34 year old camera nut living in Los Angeles and have been working in the film and tv industry for 8 and a half years now, with 4 and a half years of those as a Camera Assistant, and I often take a camera with me to work for behind-the-scenes photos...


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  1. How long do you think the storage life of Cinestill is? I bought a year ago and developed about 4 rolls. I have about 10 more rolls to develop and wanted to do them myself again. Do you think its still good or should I restart fresh?

  2. Super useful info! Yesterday, I developed two rolls in the Cinestill kit and for the first time it completely failed. I wasn’t keeping track the proper way and was only tracking how many times I developed so if I did two rolls at one time I only counted that as one roll. I really don’t know why the heck I decided to do that, but around 8 rolls in I decided to count properly. A really rough guess is that I was at 26-28 rolls when it finally failed me. I noticed the final few rolls that worked had poorly developed spots around the edges of the film, but it wasn’t extreme. Yesterday’s rolls were completely blank. Lesson learned though and thankfully it was just two casually shot rolls that didn’t have anything special on them.

    Very handy to have the chart you created! I’m definitely saving it for future use.

  3. There was a really interesting and well-researched article about how much film you could develop using a 1 Liter C-41 kit from Unicolor. I have linked to the article below. The author really did a practical set of tests to develop an equation that you can use to determine dev time using this kit based on the number of rolls of film you’ve already developed. In general, this has worked out very well for me developing at home and I have easily been able to develop 20-25 rolls using the 1 Liter kit and this equation. I don’t usually shoot enough color film fast enough to go through an entire 1 Liter kit before 6-8 months, so I’m likely to just mix up a fresh kit once it gets to that point. http://120studio.com/film-dev/c41-capacity.htm