Paper Exposer App

Your new mobile darkroom for analog film to paper printing.

Paper Exposer will help you develop black-and-white prints with your mobile device and turn your film camera into an enlarger within just three simple steps. From 35mm and smaller up to 8x10 inch negatives.*

The app turns your phone into a handy tool for exposing negatives on photographic paper – without taking any of your creativity during the whole process.

* Depending on screen size of used device.

Paper Exposer App - Quickguide.

Learn the process and how to make your first prints with the Paper Exposer App.

Darkroom for 35 $.

If you want to know how to build your own darkroom and start printing for less than 35 bucks - here you go!

Large format with Paper Exposer App.

Print your first large format negatives with the Paper Exposer app on photographic paper.

Paper Exposer Hardware.

Here you can download .STL-files for the hardware you need for free. The holder is consists of parts usually.

Baseplate for attachment on your camera, the negative carrier bottom and negative carrier top and device carrier.

If you wish to find your hardware here, feel free to contact me. I do my best to update and add many more holders, but it is very time consuming and there is a lot of data needed. If you have a specific request, send me technical details of your camera, so I can create the 3D objects.



Hasselblad V System

This holder is compatible with all Hasselblad V models (500C - 503CW)

Download .STL here:

Complete Hasselblad 500 - iPhone XS (holder version1)


Negative carrier top

Negative carrier bottom

iPhone XS carrier ( works with every other device smaller 75mm x 147mm)

Press & References

Pascal on usage with a Praktica MTL5 with stunning results

“I have kept myself quite strongly to the videos of Jakub while building my enlarger.

A Praktica MTL 5 including an Pentacon 50mm f1,8 from ebay for 12 Euro is the base of my solution. Since I only want to use the camera as a enlarger I completely removed the backcover. As in Jakub's video I used thick foam boards to build a holder for the negative and for my smartphone (Galaxy S8+). Very helpful was the black fabric tape to attach the holder and as a hinge for the negative cover. I used simple glue to connect the foam parts. After this was done I started to make the easel. An old white Ikea board serves as a solid base.

On it I taped the mask, made of thick black cardboard. Also here the black fabric tape was very helpful again. At the end there are two rubber bands around the holder and the phone so that the negative don't slip and everything keep together very well.”

Pascal Schubert, Starnberg, Germany

click here for Pascal´s Instagram & Website


Paper Exposer - Mobile Darkroom App Disclaimer (ENG)

Jakub Kotrc
Schlüterstraße 56
10629 Berlin

Telefon: +491736905892


The following applies for all versions on Android or iOS devices, no matter if smartphone, tablet or other.


The application is direct purchase in Apple App Store and in-app purchase in Google Play Store. Prices might change through time and due to changing exchange rates.

Intention | App Basics

The App “Paper Exposer” is used as controlled light source together with the devices display. It is not intended by the developer the app to be used for reason or functionality.

The basic functionality is a consecutive illumination of the devices display. The illumination can be controlled by the user as much as the software allows. Color is changed through RGB channels and the devices pixels and brightness by usually the backlight illumination. The times pre- and mid illumination, as the illumination time itself can be controlled by the user as well.


The Device, working as light source being controlled by the paper exposer app is placed above a photographic transparency film. This is then projected through a lens onto photographic paper in absolute darkness, or safelight conditions. Make sure, the device is in secured position and secure from falling down on the ground or into liquid. Make sure you don’t wet your device with chemicals or other liquids du to subdues lighting or darkness conditions. The correct hardware usage is in users responsibility only. Correct usage of hardware is not under developers control and therefor developer can not be held liable for that.


The amount of light of certain wavelength over time will provide exposure to photographic paper. This might differentiations between devices. No consistency is guaranteed between devices. The possibility of using remote triggering through headphones is not guaranteed for all devices, especially those which do not come with genuine headphones and using type-C connector. Though the app still can be used properly.

Data | Permissions

The application itself does not collect any personal data for itself or for the developer. There is no intention by the developer to use any personal data. No data is asked for through usage such as creating an account.

Datatransfer for purchase or in-app purchase with Apple App Store or Google Play Store and datatransfer between user and Apple App Store or Google Play Store for crash reports and advertisement etc. is not under developers control and therefor developer can not be held liable for that.

The application might ask for system-permission (WRITE_PERMISSION) to be allowed. This is mandatory for correct brightness and lighting control.


If user finds any issues in usage, has ideas about additional function etc. the developer will appreciate any information send to the email-address stated above.


The Paper Exposer App is an invention by Jakub Kotrc.The Paper Exposer App Logo, functionality, design is under copyright by Jakub Kotrc.

Thank You

To everyone who helped to make this possible.