DIY Lens

This is an excerpt from my Personal Investigation Project for Photography A Level

  1. Introduction

In this essay I will describe the process and outcomes as well as the reasons for building a camera lens. We live in a time where it’s possible to get digital camera setup for under £20, and a working quality film SLR (second hand) for under £10. On the other end of the spectrum some lenses for the epic red film cameras run at over £30,000. This begs the question: is it still possible to make a working lens from easily available parts. And produce quality prints? Well that depends on the definition of quality print. If to you a high quality print is a razor sharp, high contrast and undistorted image of a sporting event, then this is unlikely, as the technology required to make a lens that is sharp at wide apertures with little distortion is very precise. But it is certainly possible to get a very distinctive style of image with easily available lenses. Images taking with non-achromatic glass will result in chromatic aberrations (more on that later). And lenses that aren’t very precisely ground will not focus properly, and produce spherical aberration in images. The other simple method to make a lens is to use camera filters and adapters mounted in sequence onto a camera mount. This has the advantage of consisting of mostly achromatic lenses and will be securely and accurately mounted (via screw thread). It is very possible to create very high magnification images using this technique.

Figure 1 Image taken using the lens shown below and a 2x multiplier.

(Swierzbin, Untitled, 2009)

Figure 2: method 2 of creating a lens; stacking filters and lens modifiers.

(Swierzbin, homemade 75 mm lens and paper diaphragms, 2009)

Update: I have decided that I cannot easily source the components for the above lens. So will use the internals of an old lens instead, these will be mounted on a small bellows designed as a macro extension. Similar to the image below

Making your own lenses also allows for more experimentation with the light capture itself, such as making custom apertures (similar to using a Bokeh). Except that the aperture is not limited by the internal aperture, this means that wider aperture could be used and more light may be captured.

Figure 3: A macro extension bellows, and some custom aperture diaphragms

(Swierzbin, DIY soft focus lens: The Imagon Clone, 2009)

  1. The theory:

Photography uses the principle of an aperture to focus light onto a plane where the light is either stored on film or digitised by a camera sensor. Placing curve glass between the subject and sensor allows the light to be manipulated in a range of ways. It allows sharper images at larger apertures, and lenses to be shorter than their effective focal length. Using glass also means that some of the image will be out of focus, while a pinhole has an infinite focus. This is because when light enters glass from air at an angle other than 90 degrees it refracts (an effect of it slowing as it passes from one substance to another) and this angle depends among other things on the distance from the lens to the subject.

Chromatic aberrations occur when light of different wavelengths is refracted a different amount, and therefore not focussed to the same point on the film, this can result in purple-blue halos on one side and red/orange rim around the other. In modern lenses this is corrected by passing the light through different glasses or films which handle different wavelengths differently, with precision this allows all the light to be reformed precisely on the focal plane(on the sensor). As light passes through a modern lens is broken up as it passes through and then corrected before it comes out at the other end.

Spherical aberrations occur when a lens is not focussing on one point because it is ground unevenly. This could mean the light that enters at the edge of the lens is focuses closer or further away from the lens than light entering at the centre.

This causes halos of light around bright objects. This effect can be reduced by stopping down the aperture to a smaller diameter.

A lens (in the physical sense) has a fixed focal length, this is the distance from the lens to here beams of light entering in parallel would join up to form a point. This is important because beams of light from an object would never be traveling exactly parallel to each other. This is because the object can never be infinitely far away. So as the subject gets closer to the lens, the lens has to be moved further away from the focal plane because the rays of light have to be refracted further to focussed to form the image.

Figure 4: diagram showing constant angle of refraction in lens.

(Selter, 2013)

Figure 5: diagram showing effect of moving subject closer to or further away from lens.

(eloch, 2012)

Figure 6: A diagram showing how spherical aberration is caused.

(Swierzbin, Spherical Abberration in the anti pinhole, 2009)

The aperture of a lens defines how wide the narrowest point that the light has to pass through is. This has the effect of limiting the amount of light entering the camera. The narrower the aperture the less light reaches the camera and the longer the shutter has to be open for to achieve the same level of exposure. This is why lenses with large maximum apertures are referred to as fast lenses. There are two main types of aperture diaphragms: external and internal. External diaphragms are placed in front of the first glass element. And internal ones are placed as close the focal point inside the lens as possible.

Figure 7: diagram showing effect of moving plane forward, without changing focal length

(eloch, 2012)

DOF is affected by aperture because of the difference in angle of incidence on the focal plane. When the aperture is wide open, the angle of incidence varies greatly meaning that even a slight change in distance will result in a large change of focus. The smaller the aperture the more accurately the light will be focussed on the focal plane. This means that if the glass has spherical aberrations they are not as obvious as the light has to pass through a narrower aperture.

Figure 8: effect of aperture on angle of incidence and hence DOF

(eloch, 2012)

Figure 9: The internals of a modern zoom lens, showing different types of glass to reduce the splitting of the light and therefor chromatic aberration.

(Tamron, 2005)

  1. Modern lenses

Modern lenses are made up of a myriad of different elements which are arranged in groups.

Figure 10: Images showing a selection of modern lenses as seen by x-ray.

(Viner)

  1. The plan:

I plan to make a series one with glass obtained from an old rear projection TV, or glass taken from an old lens mounted on a bellows from an old camera, or a homemade bellows. And the other lens with assorted lens adapters. The other lens will be made from the internals of an old photography lens.

The TV lenses have a very short focal length in their current configuration. They also have noticeable chromatic aberrations around the edge of the image.

Images planned. I plan to take a few sample shots with each lens, covering most of the major fields: portraiture, landscape, and macro, to test the capabilities of the product. Then as final prints I will depict various aspects of the farm I live on using some of the lenses I built.

I am expecting some very soft, dreamy images from the TV lenses. I hope that this will work well with macro photography as in these

Examples:

The above images have a very dreamy feel about them possibly because the edges are all blurred and in soft focus.

(Swierzbin, Untitled, 2009)

(Beswick)

  1. In Practice

A log of what I did to make the lenses.

  1. Disassembling the lens (135mm f/3.5)

(A. Schacht Ulm 219515 Travenar)

Disassembling a lens requires an exceedingly tiny screwdriver and a lot of patience, not to mention fine motor skills.

Figure 11: Starting top left a fully functional 135mm lens that I have to disassemble, I would like to state here that it hurt me a little inside taking it apart

(Selter, 2013)

First the screws at the back of the lens are removed; this reveals more and more of the internals of the lens. When back of lens is stripped as far as possible, a little screw in the outside of the front has to be loosened. This releases the screw fitting of the front element. This is then removed by gently tapping the lens on the table. The second element should follow without too much encouragement. This is where I hit a little snag and can’t separate the last two elements from the aperture diaphragm.

Time taken to this stage: 4 hours, this was because I was trying to maintain the integrity of all the parts, as if I was going to put them back together. I see this as practice for the next one which needs cleaning, and hopefully will be reassembled to full functionality.

  1. Disassembling the lens (projection TV)

I couldn’t find a way to non-destructively open this lens so I took a hacksaw to it and opened it this way, the inside layer(shown in image) was kept mostly intact and is used to hold the lenses to avoid scratching them.

Figure 12: projection TV lens open to elements

(Selter, 2013)

Figure 13: comparison of exposure and sharpness using two different aperture disks. Left small, approx. 5mm, right about 1cm

(Selter, 2013)

  1. Bellows & front element

The first basic set up will be the front element from the 135mm lens I disassembled, mounted onto the macro bellows these are then attached to my Nikon via an adapter ring. Using a digital camera allows me to quickly and easily test the lens rig without having to buy and develop film. In hindsight this setup allowed for a huge amount of very fine control over focus and ensured that the lens was mounted correctly. So even when the lens is used wide open the image is surprisingly sharp (see first picture of Mabel)

Figure 14: large macro ring with small aperture diaphragm.

(Selter, 2013)

Figure 15: parts of bellows lens with front element, showing two aperture diaphragms used during testing.

Figure 16: image of lens mounted on Nikon d60.

(Selter, 2013)

I later experimented with distance of the aperture disk to focal plane and front element. For this I used a variety of macro extension tubes to hold the diaphragms as well as using the camera body mount directly.

Using a paper aperture diaphragm meant that the aperture cannot be easily changed in comparison to using the diaphragm from the original lens. But this would have brought a whole other set of complications trying to build the aperture assembly into the mount.

Figure 17: first image of Mabel using bellows lens. (Unprocessed)

(Selter, 2013)

  1. TV lenses mounted on Pringles tube (the thinnest lens)

The lenses that came out of the TV lens set are too large to mount on the bellows properly (the slider bar gets in the way, and the lens would be mounted of centre. This resulted in a very shallow depth of field (because it was used wide open, without an aperture disk).

On the second attempt I used my macro tubes as a “mount” for the Pringles tube. This made for a more stable attachment for the lens, and allowed for more reliable adjustments of distance of lens from camera.

Mark III includes an aperture disk cut from paper that is inserted 36mm from the camera body diameter of aperture is approximately 3mm. As the aperture size is increased even slightly the sharpness falls off greatly.

Figure 18: image showing the lighting fixture used to demonstrate this lens, and some example shots free lensing without macro tubes as holder.

Figure 19: top left: wide open Pringles tube lens,
top right: stopped all the way down all the way to 3mm,
middle and bottom: aperture opened to about 5mm.

  1. Free lensing TV middle element

Using the same aperture card mounted in a similar fashion I was able to use the middle element from the TV as a much more powerful lens. For this I again used the macro tubes to mount the aperture disk onto the camera. For this simple experiment I simple handheld the lens in front of the macro tube as this allowed a quick test of its capabilities. Mounting this large lens presents a number of difficulties, such as the large weight of such a thick lens. As well as the trying to find a jig to mount it suitably would provide a significant challenge. And I think that my efforts are better spent further experimenting with the lens that works more effectively and easily.

  1. Using lenses (the simple glass) as effect filters for a standard lens.

Another way to use the lenses acquired from the TV is to use them as an effect filter on an existing lens. The front and back elements are more suited to this as they produce a high degree of distortion. If the glass is held about a foot from the front of the lens, a good degree of distortion can be achieved. The effect is somewhat similar to that of a fisheye lens. For this experiment I mounted the lens onto the end of a Pringles tube with masking tape. I then slid the other end of the tube over the body of my kit lens. This results in a very narrow focal range of about 1.5m. These examples were shot using an 18-55mm kit lens. If a longer lens were used there would probably be a lot less vignetting caused by the Pringles tube.

Figure 20: images showing distortion of text on screen, holding lens about 30cm from front of kit lens. Top images show using smallest element from TV, bottom using larger lens.

(Selter, 2013)

Note: There is a significant difference in focus from the centre to edge using this lens.

  1. Postponed:

I have decided that I will postpone building a lens from filters and adapters as this will involve a substantial cost, as well as a lot more time than I have available.

  1. Conclusion

Over the duration of this project I learned a lot about the principles of lenses and photography. I believe that this will help me enhance my photography even if I do not use the lenses I built after this project is complete, as I now have a more complete knowledge of which factors of lens design play into the final image. As long as the aim is not to get a perfectly sharp image it is perfectly possible to make a useable lens; as the following images demonstrate. I think that they have a very nice Lomo effect which is not simply a filter. All images below are only minimally processed to improve contrast and brightness.

When using the bellows the lens even has a reasonable ease of use, allowing quick and easy focusing of the lens, all these images have a wonderfully vintage feel that I am pleased to know does not originate simply from a filter applied later, but from the lens itself.

  1. Appendices

    1. Glossary

Free lensing: using a lens without attaching it to the camera by its mount, holding it freehand. This allows for creative albeit unreliable effects.

Wide open: aperture at its widest setting. In DIY lenses without aperture diaphragm.

Lens: either a shaped glass disk used to refract light. Or a lens assembly used in photography.

Focal length: the distance from lens that an image is formed (on focal plane). (Theoretical, actual will be longer as no object will be infinitely distant.

Focal distance: the distance at which a lens is focussed

Focal plane: a plane equidistant from centre of lens at which image is formed.