Pixiq

REVERSING LENSES – WHY BOTHER ?

Most lenses (other than macro lenses) were traditionally optimised for a scale of reproduction of 1:10 though many modern designs now have internal lens groups that move to provide better close-focus correction.

Reversing a lens gives better performance in the macro realm – it works like this:

• In ‘normal’ use, the subject is larger than the on-sensor image and most lenses are designed and corrected for this.
• In the macro realm the image on the sensor is larger than subject  reverse the lens and the biggest item is closest to the larger lens surface:

The corrections work better in reverse especially for non-symmetric lens design where front and back elements (e.g. wide angles) are very different.

Even 1:1 macro lenses can show distinct  improvement when you start using them beyond about 2x life-size

Reversed lenses with bellows and extension tubes

Stacking was covered in the last post but another good way of getting magnified images is by reversing a lens (using a reversing ring) directly onto extension tubes or bellows. And for this you can use a whole range of lenses with great results.

• First, you need an adapter ring – a reversing ring - which has a filter thread on one side and lens mount on the other. The suppliers mentioned in a previous post are a good place to start.
• By the way body caps, T2 mounts (see the suppliers listed) and old Tamron Adaptall mounts can, with a little bit of ingenuity be used to create adaptors.
• Mounting a lens in this way does not involve any extra glass which should reduce the chance of image deterioration compared with stacking on a prime lens.
• Nikon have always recommended that its users employ the technique of reversing. They suggest using their wide-angled lenses reversed on bellows and provide extensive magnification tables showing exposure corrections for given bellows extensions.

Bellows are not easily used in the field although the lightweight and beautifully engineered Novoflex bellows can be used by those with patience. But this technique really works and there is little if anything to choose in image quality between a good reversed wide angle and the more exotic offerings that cost an arm and a leg (and more…) as long as you take every precaution to cut vibration.

Effective aperture: reversing a wide-angle lens on to a bellows provides excellent image quality though you have to be careful with setting the diaphragm because with added extension the marked aperture becomes an effective aperture: the exposure needed is changed by a factor of M…the magnification (see the end bit of this post ‘for nerds’).

As a rule of thumb… I find that it is it is better to keep the effective aperture to around f16 - f20 and not stop down more: a rough mental calculation working backwards is what is needed i.e. divide 16 (or 20) by the magnification…it means with some wide angles you will have to use them wide-open anyway.

 DRAWBACKS

Coupling with the camera (autofocus, auto diaphragm) is lost though many of the upmarket SLRs will allow manual metering of the stopped-down variety and some will allow you more. This is not exactly convenient  but some manufacturers have an old accessory in their lists that used to be called a “Z” ring that fits onto the lens bayonet and allows stop-down by means of a double cable release that also fires the shutter.

A Bonus for Canon Users

The ingenious people at Novoflex have produced a very useful gadget (EOS Retro) for Canon users (why nothing for Nikon people?) that allows them to reverse a zoom lens and retain full control between camera and lens: it consists of a specially made body mount that enables you to reverse the lens and this is connected electrically to an adaptor that fits on the lens mount.

There is also nothing to stop you increasing magnification further by adding an extension tube between camera and reversed lens. With the Canon EOS 28-105 mm zoom lens in reverse position, you get a range of image ratios from 1:7 with focal length 105 mm to 2.8:1 at 28 mm. The rrp is around  £299.00

Three Cheers for Live View

With true macro lenses and reversed wide-angles the image becomes very difficult to focus if you stop-down to check depth of field because the light is spreading out and its intensity gets less. This is a huge bonus for me (and many others) – for example, with the D300 and its superb LCD (and image intensifier) the live-view function allows me to get crisp focus. 

With 20:20 vision for the first four and half decades of my life that slight deterioration that comes with ‘middle age’ was something that had me in denial for a while. It was those twin points on the ends of a crescent moon that signaled astigmatism as well as myopia! And, for those feeling smug in their youth...time will tell.

This same live-view function has made it much easier to use the venerable Zeiss Tessovar I have (I shall post on this at some stage for curiosity’s sake if nothing else) whose working apertures tend to be around f/45 wide open and go down to f/128 – f/256. Focusing this is a trial. It is possible to use the video feed on such cameras to a TV screen though an AC power adaptor needs to be supplied since batteries loose power quickly. 

Bellows lenses, enlarger lenses etc

• You can try anything reversed in this way – some zooms work, most not but try…then there are enlarger lenses, wide-angles, large format lenses and old cine lenses such as the Switars (25mm) made for Bolex 16mm cameras…incredible in reverse as high-power macros.
• Microscope manufacturers such as Olympus, Leitz and Zeiss have, in their time, produced series of special lenses corrected for use over specific ranges of magnification: they are sometimes referred to as ‘true macro’ lenses. In fact, the Leitz Photars and Zeiss Luminars represent extraordinary image quality but at a price to match.

• Nikon also made some Macro Nikkors for its Photomacrographic “Uniphot” as opposed to what we consider its ‘macro lenses’ for general use they called those micro-Nikkors…and I have some Zeiss Jena lenses for the same purpose that I bought for $ 10.00 each….two decades ago no-one wanted them.

• Generally, these are lenses for use in the lab – only Olympus, with their level of ‘macro creativity’ designed and marketed a variable extension tube (65-115mm) that made use of their ‘true macro’ lenses (20mm, 38mm 80mm and 135mm) and was practical in the field. With a macroflash mounted it was light and portable

• If you want to move into realms of higher magnification then microscope lenses (achromats and planachromats) with image stacking can give astonishing results and not break the bank (more soon)

Be reasonable…rein in your demands

If you have a set of bellows and are an experimenter then you can press all sorts of lenses into use and get results that surprise you. The important thing (and here I am as guilty as sin) is to view images properly…I sit in front of a 24” Mac screen using Lightroom at 100% (and I have even taken to using 200% just to see).

If you do the same then stop for a minute and think. 100% means each pixel is revealed at screen resolution of 72dpi which with a file width of 4288 pixels equates to 59.5” a ‘tad’ under six feet wide. Or, in metric units 1.51m…which is a pretty big print and it is typically being viewed from 30- 40cm away. This is far more critically than we ever appraised prints on a wall…and it looks good with no sharpening at all. So, just how spoiled are we?

It is important to make assessments on the basis of ‘realistic’ expectations so would there be obvious differences -  if we take something with a Zeiss Luminar and also with a reversed “Switar” 25mm focal length lens meant for a Bolex, 16mm format cine lens? If your technique is good, vibrations eliminated and you have mastered the lighting to create ‘relief’ then, with a bit of unsharp mask (USM) and prints to A3+, I would contend that you will see differences only if you want to…