Introduction: How to Digitize 35mm Negatives

About: I am a physicist working in research, Making things and sharing the experience with others, helps me in many ways.

One of the best ways to preserve old photos is to copy the negatives with a digital camera and then use image processing software to "develop" the photo.

I built a setup for digitiziation with a DSLR to process my old negatives some of which have a sentimental value.

Since I do not have a macro lens, I combined an SLR lens with a couple of cheap adaptors. The rest was improvised from pieces of wood, cardboard , PVC and even meccano parts.

NOTE: Check out a recent update of this instructable!

Step 1: About Film Negatives

Image formation
  • Film photography is based on the sensitivity of  silver halides (AgBr, AgI etc) to light. The upper layer of the film is a coating of gelatin containing crystal grains of silver halides.

  • When the film is exposed to light, some Ag+ ions are excited to higher energy states and a few combine with electrons to form Ag which will act as nucleation centres in the development stage. At this point the latent image is formed .

  • When the film is developed with chemicals,  an oxidation - reduction reaction takes place. The silver ions in the exposed regions are reduced to neutral silver atoms which coagulate to form metal grains. This is a negative image since the film becomes non transparent in the exposed regions.

  • Colour photography is based on a variation of this process with the addition of organic coloured dyes coupled to the silver halides. The film coating  has three layers for the three basic colours (see photo).
Deterioration of negatives
  • Black and white negative images consist of silver grains which are stable over time. The supporting gelatin is sensitive to humidity and temperature but if stored properly B/W film can last for hundreds of years.

  • On the other hand the colour negatives are more sensitive to environmental factors because of the organic dyes they contain. The cyan dyes fade away faster and the negative becomes reddish. Exposure to light causes the magenta dyes to fade also, due to  ultraviolet  light.

Step 2: How Much Detail Is Recorded on Your Negative?

  • The resolution of the image recorded on the negative depends both on the quality of the film and the camera used. Suppose you have been using several cameras of different qualities as I did. We need an estimation of how much detail has been recorded  in each case.

  • The figure of merit here is the resolving power of the camera lens which depends upon the size of the lens and the wavelength of the light source. The resolving power R of a lens of diameter D  is given by the following simplified formula which is based on wave optics:
                                            R (measured in arcsec)=120/D (measured in mm)

         A specific example
  • A 58/2 lens  has a focal distance of 58mm and a diameter of 58/2=29mm.  The resolving power is R=120/29=4arcsec. The viewing angle through the camera is about 30 degrees which covers the 36mm  length of the negative. The minimum  sizeof a dot(or line width)  that can be  recorded on the negative is 36mm x 4 arcsec / (30 x 60 x 60 arcsec) =1.3micrometers.

  • Such a camera fully exploits the potential of a  good quality film with a recording capability of about 350 line/spaces per mm.
  • If you repeat this calculation in the case of a low end cheap camera the minimum feature size may become 10 times larger. Such a camera cannot take full advantage  of even a mediocre negative.

Step 3: How Much Resolution Do You Really Need ?

Since the resolving capability of even a normal film usually exceeds your commercial digital camera or scanner the direct answer is :

                                                                     As much as you can get.

Here is a brief justification of the above statement:
  • Standard consumer  films are capable of  recording dense line/space patterns in the range of   50- 150 lines/ mm  ( for example see the  data sheet of  Agfapan 100). Let us workout the lower value.

  • A pattern of 50 lines/mm corresponds to  100 pxls / mm . If you intend to use  a scanner to copy them , you need at least 100 dots *25.2 / inch=2520 dpi.

  • If you intend to use a digital camera , the 36mm x 24mm negative format requires 36*24*100 *100pxls=8.64Mpxls. A 10Mp camera is sufficient.

  • If you repeat the calculations for the upper 150/mm limit the corresponding numbers are 3x2520=7560 dpi and 3x3x8.64=77.8Mpxls !

  • This simply demonstrates the potential  of the film as a  recording medium. It is not a surprise that films are still used for specific applications such as aerophotography.

Step 4: Design of a DSLR Setup

Now, after this lengthy  introduction - which I hope was useful to some people - it's time to get practical.

These are the parts of the setup:

1. Your DSLR.
2. A macro lens capable to frame exactly  the 36x24mm negative. This can be substituted with a common SLR lens and adaptor rings .
3. A film holder that you can make yourself.
4. An opaque plastic screen
5, A light source. I have used two different slide projectors for this as well natural light by aiming on a white wall outside the house. Everything works including a tungsten filament lamp .

Since I needed to have good control of the distance between the film holder and the lens in order to fit the frame exactly, I made a useful x-stage out of meccano parts . You can substitute this with something simpler, but  the stage proved to be useful..

Step 5: I Suppose You Don't Have a Macro...

If you do have one, lucky you, go on and use it.   I used a 2/58 SLR lens.

To mount this on the camera I used an adaptor for M42 (42mm metric threading) for my specific camera and and two M42 extension rings.

I already had these for other applications. I use them to mount other lenses on the  camera as well as to mount the camera on telescopes.

The M42 extension rings come in sets of three sizes and I saw them on e-bay for less than 10$.
I have a pair of such sets that I got from a flee market a long time ago. Never regretted that buy.

Please do not use any other method to mount a lens on your camera (PVC , cardboard ).
Remember that damaging the interior will cost you much more than a set of adaptors.

Step 6: The Optical Bench

I used a 30cm board for the basis of the whole construction and I mounted the camera on a higher platform.
This setup is easy to work with and can be useful  for other similar projects involving the camera.

Step 7: The Meccano X-stage

The purpose of the x-stage is to control exactly the distance between the lens and the negative in order to cover the whole camera sensor width with the image.

No pixels should be wasted!

Of course you can do this by a sliding stage made out of wood, plastic or any other material.

However I needed an excuse to use the meccano of my childhood.

The platform slides between two vertical guides and it is controlled by a 4M screw of 6cm length.

Step 8: The Film Holder

After fooling around with many designs involving springs, plastic, metal etc, , I selected the simplest solution: cardboard .

The film holder is made out of cardboard and it is supported by a thin plywood piece.

A plastic slide part from a slide is the ideal window which must be aligned to the camera lens .

Step 9: The Finished Setup

A cardboard tube completes the setup.

Everything can be disassembled and stored in a box, when not used.

Step 10: Try Different Light Sources

There are two basic methods for illumination

1. Natural sunlight.

You may work outside , set the camera for sun illumination and aim the device towards a white wall.
It works very well for colour negatives.

2. A lamp source

Use a filament lamp combined with an opaque screen, Set the camera for lamp illumination.
I use two different slide projectors I have.

Step 11: Now Shoot!

A few tips for the camera:

1. Exposure time selection.

I prefer to overexpose by a couple of stops. The range of exposure times is from 1/100s to 1/250s

2. Focusing

A DSLR has the very useful feature of magnifying the image x10 times and focusing on a detail.

When doing this I prefer to focus on a regular pattern if there is such on the photo. Otherwise select a region with an edge with a clear separation  line from light to dark.

Step 12: In the Digital Darkroom: Black and White

Black and white is magic.
We have a 3D coloured perception of the world. B/W reduces what we see into pure form and tonal quality .
In photography as well as in painting it is important to balance these elements.
This is what you have to do in the digital darkroom.

Camera settings
The negative was photographed  using  a slide projector as a light source (200W lamp) at 1/250 sec exposure speed.
The projector was 60cm away from the opaque screen.
The camera lens was set at F/8 for less distortion and more depth of focus.

Select a clear pattern for fine focusing.
In this case I selected the chair pattern which was focused by setting the camera in "live view" and  used the feature of magnification x10 times on a detail for focusing. This is a very useful feature of most DSLRs.

Digital develpoment
I used Photoshop 6.0 . The terminology is similar for any other software.

1. The initial shot needs croppingrotating and colour inverting .
2. Then the colour scheme is turned to grayscale This results in  a faint image which needs further balancing of tones.
3. The challenge here is to preserve the  details as well as the gray scale  (e.g.  in the model's hair)  when you try to increase the darks. I strongly prefer to adjust the tone levels instead of using the common brightness/contrast tool.
4. If it is necessary to smooth the tones add some limited blurring (Gaussian Blurr with a range smaller than 3 pixels).
4. Finally you may have to frame the theme by cropping the picture.

About this photo:
I took this shot with a humble SMENA camera back in 1979 using a FP4 Ilford B/W negative which I developed myself. I like the gradation of tones  and the relation of the three people involved here: the photographer/viewer, the painter and the model. One  of my favourite photos over the years.

Step 13: Colour Negatives

This specific negative is 15 years old. The colours have been preserved.

Camera settings

Essentially the procedure is the same as for B/W.
The negative was photographed  using  a slide projector  at  a speed of 1/200 sec.
 The camera was set for  tungsten illumination.


1. The initial shot needed cropping and rotating .
2. Then the colour scheme was inverted.
3. The challenge here is  to balance the colours and tones. I prefer to work by adjusting the tone levels for each colour separately and then make overall adjustments of the whole colour scheme. I avoid using the  brightness/contrast tool.
4. The next step is to control the colour hue/saturation in order to obtain a natural colour scheme. As a rule, the blue colour will need desaturation.

Step 14: Old Colour Negatives Can Be Tough

As discussed  in step 1, when the colour negative gets older, the blue dyes tend to fade away. Therefore the negative becomes reddish and when the colours are inverted,  blue and green tones dominate.

It may prove difficult to restore colour balance. In such cases I work with each colour separately adjusting the range of tones, hue and saturation. I repeat this procedure 1-2 more times.

The photo shown here is from a 30 year old negative. The best I could do after playing around with colours and levels was to trust the "variations " option of Photoshop 6.0. This resulted in a much better balance than that I could obtain manually. Still it does not look natural. Compare the two photos.

Step 15: Conclusions

1. The setup was worth making, it proved to be stable , versatile   and effective . Lighting and focusing are  controlled very well.

2. There was no problem with B/W processing, I processed 34 years old negatives. The contrast was excellent.

3. If a coloured negative is less than 20 years old probably there should be no problem. However treating colours one by one is not trivial.

4. Older negatives may appear as "overpainted " when processed. Probably one could overcome this by treating colours and contrasts in different layers. If it fails you can always turn to B/W.

5. You cannot save everything.  You may have to let go  overexposed,  underexposed or unfocused negatives.

6. This method is faster than  a scanner and it offers much more control of the illumination used and the contrast. It offers the additional possibility to use sunlight (by pointing to a wall outside).
Overall,  judging from the  results obtained so far (more than 200 photos)  I intend to continue using it for the rest of my negatives, as well as for those  supplied by friends!