How to use Delta

The 2022 edition was made possible with the assistance of Mr.Cad – Europe’s largest dealer of used cameras. For all things analogue film photographic, get in touch with Alex Falks, whose “time in the business began roughly when Elvis joined the army”. Mr.Cad carries permanent stock of enlarger lenses and offers knowledgeable and approachable service. We would also like to acknowledge the pioneering ninety-sample enlarger lens test program of Ctein in the late 1990s and John Jovic’s articles and 472-entry Big Enlarger Lens List at photocornucopia, as well as the invaluable editorial assistance of Johannes and others.

Modern lenses tend to suffer sample variation because they’re highly-strung marvels of nano-tolerance manufacturing. Enlarger and projector lenses in circulation vary because they’re old and beaten up; they’ve worked hard and are now being eaten by fungus. They operated in damp environments and weren’t moisture-sealed. Most have been dismantled and reassembled. So in many cases, we cleaned and tested multiple samples and only recorded the best results. If we were unable to find a pristine copy, it was noted. Even so, given the wide variation in sample quality, it’s hard to state categorically that lens A was – or is going to be – better than lens B. 

Tests were conducted intermittently with several cameras over a ten year period, but a final ‘mark out of 10’ was awarded by comparison with Sigma Art (50mm and 105mm) reference lenses on Lumix S1R and G9 cameras in 2021/22. Tests are ongoing. A mark of 10 is only awarded if a lens is considered to fully resolve the sensor. The ‘full-frame’ 47.3MP S1R has a pixel pitch of 4.27µ and therefore demands of a lens 105 lp/mm resolution* across the frame. To better differentiate lenses that seem to resolve > 100 lp/mm, a shift adaptor on a Lumix G9 subjected Zones 1-3 to the scrutiny of a 3.3µ pixel pitch sensor. Fully resolving a 20MP M4/3 camera requires a lens capable of projecting 136 lp/mm*. 

At peak apertures, unless they are ancient or broken, most lenses deliver ‘acceptably sharp’ results centre frame (Zone 1) but fully resolving a sensor at near and far distance in Zones 2 and 3 is rarely possible. Unlike ‘portrait’ lenses of their day, industrial, enlarging and projection lenses were designed for flat-field, corner-to-corner consistency (though not usually at 100 lp/mm) and this, as much as the absence of a focusing mechanism, distinguishes lenses in Delta from conventional taking lenses. However, the purpose of Delta is more than the creation of ‘sharpness league tables’: many overlooked gems in the archive offer unique ‘looks’ despite lacking the Nth degree of per-pixel crispness – a quality many shooters (especially videographers) claim is over-rated.

Please note Delta is based on their practical ‘in the field’ performance as taking lenses and doesn’t reflect on or attempt to evaluate their performance in the darkroom, or for print-making. Tests were made at 50-80cm distance and 10-15m distance using full-frame SLR and mirrorless cameras of at least 42MP resolution. In certain cases – to better separate closely performing lenses – tests were made using a more demanding 20MP Micro 4/3 camera with the enlarger lens mounted on a shift adaptor. Good quality samples were collected and CLA’d over a ten year period. Where I felt there was a question mark over sample variation (where results fell below expectations) or visual inspection revealed flaws, multiple copies of certain lenses were used and only the best samples entered into the database. Real-world performance of these old lenses is uncommonly sample dependent, which generates statistical noise that inevitably compromises analysis. However, given that none of these lenses are still in production, the somewhat anecdotal nature of our survey fittingly reflects the real-world lottery of using vintage enlarger lenses. It’s not an exact science. Such practical limitations made it hard to include, for instance, more than one, token Kowa/Computar DL lens. However good these lenses once were, by now most have suffered from terminal separation; or, if they haven’t yet, they’re destined to fail imminently and can’t be recommended.

Using and Understanding Delta

Each column heading (ManufacturerFocal Length (mm)Minimum Aperture (f), etc.) can be selected to sort in ascending or descending order and combined with keyword search for more targeted results. For instance, you may want to ask the database to show all lenses with circular apertures, or display all Componons. You may only be interested in lenses produced in the 1950s, or those faster than f4. Perhaps most usefully, selecting the column headings for sharpness creates a league table of test results for averaged performance across the frame, and (on scrolling right) specific performance at each aperture and part of the frame (see below).

There is a broad correlation between the number of Elements and image quality. Generally (with noted exceptions), triplets (three element lenses) are cheap, low-quality optics that don’t resolve well in their outer image circle. Not every four and six element lens performs to a high standard, but all the best enlarger optics have a minimum of five elements. 

The Aperture Type column shows both the number and geometry of aperture blades, which influences the lens’ drawing style. Circular apertures (common to most enlarger lenses made prior to 1980) tend to produce smoother bokeh and a more pleasing focus transition, and render circular ‘bokeh balls’ at all stops. The shape of the aperture (stopped down) naturally dictates the shape of the bokeh balls: straight-sided hexagonal apertures render straight-sided hexagonal bokeh balls. Enlarger lenses have rather less predictable aperture shapes than normal taking lenses – sometimes changing shape unexpectedly as you stop down. Where this is notable, we have noted it.

The shape of the aperture also influences when (or whether) the lens produces Stars: spokes of light radiating from in-focus point light sources. Some photographers find these attractive, so we have rated and noted each tested lens’ ability to produce them, awarding high marks (out of 10) for a lens that can generate stars at wide apertures. We have defined ‘good’ stars as having minimal flare and maximal definition, without reference to the number of light-spokes produced.

When we have tested a lens it receives a Sharpness percentage rating for Near Distance (typically 40-80cm) and Far Distance (10m-infinity), as well as marks for Contrast, Colour, Focus Shift and Flare. The ratings appearing in columns 7 and 8 are averaged sharpness across the frame at apertures f5.6 and f8. By comparison with reference lenses (Sigma Art DG primes) you will note that most enlarger lenses suffer performance lag at longer distances. However, at the short working distances typical of copy work, product and food photography (for instance), they match or exceed the average resolution of conventional taking lenses. Delta’s reviews do not delve into the 1:2-and-above realm of macro photography, for which use-case enlarger lenses are well documented elsewhere. If you scroll right, at the end of the table you will find the full breakdown of each tested lens’ performance from apertures f2.8 to f11. in Zone 1 (centre frame) and Zone 3 (outer image circle), and another Sharpness rating that averages performance across the frame using a more demanding benchmark of f4 to f8.

Don’t take for granted that a good enlarger lens will be sharp at every setting: commonly they are narrowly optimised for a specific aperture (typically two stops down) and the widest aperture intended only for focusing – which always was a questionable practice because many have quite pronounced focus shift. Meopta Meogon lenses, for instance, are relatively poor performers wide open, but generate some of the highest resolution figures at appropriate apertures. Conversely, Schneider Apo-Componon lenses and certain orthometars like the EL Nikkor 80/5.6 N give optimal Zone 1 rendition wide open, and the only purpose of stopping down is to raise Zone 3 to same level.

As touched on above, enlarger lens Bokeh is a contentious topic, and these lenses vary greatly. The rating awarded is inevitably somewhat subjective, but we have aimed for an empirically sound comparison based on prioritising  smoothness, consistency fore and aft of the focal plane, and absence of distracting artefacts. We also give kudos to a lens’ power to defocus, privileging longer and faster designs. The bokeh rating specifically penalises the manifestation of soap bubbles, onion rings, cat’s eyes and swirling; and marks down ‘edginess’ or ‘vibration’ – noted in Bokeh Characteristics.

However, projector lenses in particular are now sought-after for exactly these ‘technically incorrect’ qualities – particularly those that generate ringed bubbles from defocused specular highlights. Note that the same rendition is seen wide open in many triplet enlarger lenses, too. At wide apertures most lenses oblate these bokeh balls into rugby/football or cat’s eye shapes that vary in distortion and orientation with distance from the centre of the image circle. This effect tends to go hand-in-glove with bokeh swirl, which can be effective when framing a central subject. Because both effects are proportional to the size of the image circle, be aware that the best way to achieve pronounced swirling is to choose a lens whose image circle only just covers your sensor. For instance, a 100-120mm projector lens may generate strong swirl on a medium format sensor in parts of the image circle that aren’t visible to a 35mm sensor. Shifting such a lens on a 35mm body will show swirling with apparent radial asymmetry. To achieve frame-filling swirling on a smaller sensor requires a smaller image circle – typically that of a 60-80mm lens on 35mm and 40-50mm on APS-C or M4/3.

Marks and notes for Colour, Contrast, Focus Shift, Weight (in grams), Used Value (in £GBP), Front / Rear Threads, Years of Production and observed ranges of Serial Numbers (from lowest to highest) are self-explanatory.

Screw mount fittings have varied frustratingly over the century+ spanned by the Delta project. To simplify as far as possible, all 39mm fittings are here treated equally and marked M39 (yes, even the Imperial-thread lenses), as they are practically interchangeable – unless they aren’t, in which case it is noted. For the record, Leica’s hybrid metrimperial Screw Thread (LST, also known as Leica Thread Mount (LTM) and L39) is an Imperial pitch (26 turns per inch). It is not identical to M39, which is 1 turn per 1mm. However, Leica’s Imperial 1 turn per 0.971mm is usually close enough for the handful of turns required by 39 > 42mm adaptors – depending on the machining accuracy of the adaptor in question.

Delta also includes true Imperial thread lenses such as C-Mount (1″), RMS (Whitworth 0.8″ x 36, Wollensak (1 5/8″) and Wray (1 1/4″) mounts.

Finally, columns marked FFD (recording the focal-flange distance of the lens) and, to avoid confusion, Extension (the distance between the lens flange and camera body flange (AKA flange distance) when focused at infinity) aid in finding the correct helicoid and/or adaptor for your lens. Extension is the minimum helicoid you need to achieve infinity focus (minus the depth of the mount adaptor).

Note that Extension figures are calculated for Canon RF and L-Mount cameras that have a body focal-flange distance (the distance between sensor and lens mount) of 20mm. For other cameras, the following adjustments are necessary: Nikon Z: +4mm; FujiFilm X: +2.3mm; Sony E: +2mm; Canon EF-M: +2mm; Micro 4/3: +0.5mm; Canon EF: -24mm; and Nikon F: -26.5mm

To give a worked example: a Nikon EL-Nikkor 50mm f2.8 N has a 43mm FFD. According to the chart, achieving infinity focus on a Panasonic S1 requires a helical/adaptor extension of 23mm. This lens therefore hits infinity at 27mm extension on a Nikon Z6 (+4mm); 25.3mm on a Fuji X-Pro 3 (+2.3mm); 25mm on a Sony A7 (+2mm), etc. Infinity focus isn’t possible when mounting the 50/2.8 on an old-school DSLR camera like a Canon 5D: that would require a helicoid/adaptor of -1mm depth.

M42 helicoids are commonly available in extensions of 10-15mm, 17-31mm, 22-55mm and 35-87mm. M42 mount adaptors are around 1-2mm thick. Tilt and shift mechanisms tend to be 25-35mm deep. In practice, then, a lens must have at least 42mm extension to give infinity focus and movements on Canon RF/Panasonic S bodies. Typically, most 75mm+ lenses fit the bill. As an extreme case, a slim adaptor and the smallest helicoid would enable a Nikon Z user to deploy a lens with a FFD of just 29mm.

The F-FD of a lens is usually similar to its focal length but, as Delta shows, there is considerable variation: among 50mm lenses we find early Rodagons hitting infinity focus with 28mm extension, and a late Vega 11U with 18mm. Rear element protrusion also varies much more than the tidy backsides of conventional lenses. And with regard to fitting lens mounts to projector barrels (which are either smooth or feature wide proprietary helical threads) the extension will vary like a trombone, depending on placement of the adaptor.

Not Included

Undertaking a wide-ranging survey of screw mount lenses deployed via M42 helicoids or bellows, it was tempting to include the spectrum of Leica LTM rangefinder lenses, large format lenses in Copal shutters (to which many of these lenses are closely related) industrial lenses, projector lenses, microscope lenses, scanner lenses, et al – all of which are all viable in the same rig and share many of the drawbacks and benefits of enlarger lenses. However, ultimately we made four rules for inclusion in Delta:

1) No internal focusing mechanisms
2) Adaptable to M42
3) Image circle > 25mm at infinity focus (to be useable on mirrorless cameras with a body flange-focal distance of c20mm)
4) No large format taking lenses (that would otherwise qualify under rules 1-3)

These rules allow us to include some scanner and microscope optics via RMS > M42 adaptors; V-Mount lenses, and many interesting bellows, projector, X-ray, repro and process lenses that are worthy of consideration – and not just for macro applications. I’m waiting for the first digital indie film to be shot entirely on Printing Nikkors in gratifying coming-full-circle homage to Stanley Kubrick (who insisted on using these lenses for film duplication at Pinewood).

Inevitably many lenses are absent simply because we haven’t located them yet. Such a catalogue can never be complete. However, if you spot something we’ve missed, or can send samples or examples (lenses or photographs), please get in touch – especially if you can cast any light on lesser-documented Russian, Indian, and Chinese designs.

Image Circle Considerations

Not all enlarger lenses (particularly below 40mm) have image circles large enough (> 43mm diameter) for full frame digital cameras at infinity focus. Such lenses are included with a caveat specifying their image circles. However, lenses with a 30mm image circle are still fully useful on cameras with sensors smaller than APS-H, and stopped down, or shooting certain aspect ratios, you may even get some utility from them on Super 35. Lenses with a 25mm image circle can only be used with Micro 4/3 and smaller sensors.

Having said that, some 12-35mm enlarger lenses with < 25mm image circles can be used in the macro range where the increased distance from the sensor naturally widens their image circle. Some also throw larger image circles when reversed – the natural orientation for certain applications. 

Ultimately, a key benefit of so many of these ‘alt’ beauties is that they throw big image circles. Broadly speaking: the longer the focal length, the bigger the image circle. Most enlarging lenses cover a full-frame sensor with room for shift and tilt movements (at infinity focus) by 60-75mm. Put another way, most 60mm enlarging lenses cover medium format sensors by less than 75mm, and by 100mm most enlarging lenses cast a big enough puddle for medium format sensors to shift about in. Fast projector lenses (very cheaply) provide medium format users with shallow DOF unattainable by native or conventional lenses, but be aware that they tend to have more constraining FFDs: the shortest focal length projector lens that covers a 645 film frame properly is around 110mm, and the move up to 6×7 requires around 140mm, depending on the required presence or absence of vignetting and corner aberrations.

Within this archive is a vast playground of ‘looks’: novel ways of shooting stills and moving images; powerful macro lenses and every flavour of bokeh. All these worlds are yours (except Europa). Use them wisely. Use them in peace.

  • The Nyquist limits for sensors with 4.27µ and 3.3µ pixel pitches is theoretically 117.1 and 151.5 lp/mm. However, real-world limits are dictated by other issues – here, primarily, that photosites are not contiguous. The Kell Factor (originally calculated in 1934 at 0.64, commonly averaged at 0.7, and continuously upwardly revised) is therefore applied when converting microns to line pairs. For the Lumix S1R a Kell Factor of 0.7 gives: 1/0.00427/2*0.7 = 81.97 lp/mm. But the Kell Factor is guesswork, flagging a need for specific information – of particular relevance here: gaps between photosites. Testing lenses that reportedly resolve 80 lp/mm against lenses that demonstrably outperformed them, setting an information ceiling of 81.97 lp/mm for the S1R just feels wrong. Indeed for CMOS sensors, the appropriate factor is typically 0.9, and rising as sensor technology improves. For the purpose of the article we have therefore assumed a Kell Factor of 0.9.  

Leave a Comment

Your email address will not be published.