lundi 15 novembre 2004

Enlarging Lens Test Pick of the Bunch... 50mm f/2.8 El-Nikkor Many photographers spend a considerable amount of money on camera lenses... only to print their films through an inferior enlarger lens. Although it could be said that Nikon users generally know better the question I have often been asked, "Is there a noticeable difference between an independent brand enlarging lens costing £50 and a £150 El-Nikkor... or between that same Nikon product and a premium priced apochromat costing perhaps two or three times as much?" As ex-publishing editor of the UK magazines "Darkroom User" and "Camera & Darkroom," two of only a few specialist darkroom magazines in the world, I saw a lot of handmade prints... and I was confounded and amazed as to why photographers thought nothing of paying for the best to put around their necks but apparently headed for the bargain-basement when it came to what they chose to use in the dark... it was, and is, false economy! When looking at the work of many readers of my own magazines I saw three main problem areas where the quality of their work fell down. Although the negatives their prints were made from had good tonal range and contrast, even-illumination across the entire frame and all important sharpness, the prints they presented had often been printed on a higher contrast paper than I would have judged normal. This of course disguised the struggle they had encountered in their darkrooms... high-contrast prints will always look sharper to the eye than they really are. Admittedly whilst print contrast is largely a matter of personal taste, print sharpness should not be. It was not unusual to see prints with a soft edge and two corners going slightly fuzzy, or the other way around... in fact I dubbed some such prints "lemon drops" after the well-known sweets... soft in the centre and sharp at the edges. Because I knew that the printers who were making them were working with good negatives and was told that both the pedigree of their enlargers was good and their working methods were at least technically and practically competent one had to reconsider the weak link in the photo chain... the enlarging lens. In the early 90's I tested five enlarging lenses for my own use; I had already used El-Nikkors in my various darkrooms for the best part of 25 years previously but wanted to evaluate some of the more recent offerings. At the time they ranged in price from £34 to £250 (the 5Omm f/2.8 N El-Nikkor was about £100 in those days); four were of f/2.8 maximum aperture and the most expensive three examples were six-element lenses. I had a very good and cherished subject for lens testing - a postage stamp. Not any stamp, mind you, but a Great Britain "1929 Postal Union Congress £1." This is a fairly large "line-engraved" stamp which has excellent sharpness of printing and being printed in black has fairly high contrast. My best negative was made with the (then) new and superb AF Micro-Nikkor 60mm f/2.8 camera lens. Readers should note that most modern stamps are of no use as a lens testing subject because they are usually litho printed... their designs look decidedly soft under a magnifying-glass. However, most British Commonwealth George VI stamps (which are plentiful) are line-engraved and will work well for this exercise. The testing procedure was simple being based on visual observations of centre and corner details from 20x enlargements (equivalent to little under a 30x24 inch print size). Small 4x3 inch prints from the centre and a corner of the projected image were made with each lens wide open at f/2.8 and then at their optimum aperture of f/5.6 or two stops down. Although the wide open setting is mainly used for initial focussing that aperture is actually useful when making very large prints in order that unnecessarily long exposure times, with their associated problems, are not incurred. Having made twenty prints from the corner and centre of the negative from each of the lenses I had on test the difference was clear to see. It proved to me that if you are prepared to test you can separate the worst and best. In fact the results from two lenses which were 50% and 100% more expensive than the El-Nikkor did not show any advantage at all in centre or corner sharpness or contrast. One of them did fail when taking corner illumination, or "fall-off" into account... and that was inexcusable for such an expensive optic. Light fall-off is an important consideration with enlarged prints. Whilst there is always some fall-off in illumination at the corners of all lenses (the result of fitting the rectangular 36 x 24mm frame of the 35mm format into an approximately 45mm diameter image circle) the effect of printing any negative which has the resulting lower density in the corners is actually negated by the fact that the enlarging lens also has optical fall-off in the corners - so that it acts almost like "neutral density" and counteracts the original problem created by the taking lens. That may be the basic theory, but the practice is different. Whilst Nikkor camera lenses have minimal fall-off in illumination (an easy test for this is to shoot transparency film of a clear blue sky at different aperture settings and examine the results on a light-box... but not by projecting them which introduces another lens), other marque lenses may be indifferent. And whilst the tested El-Nikkor also had minimal fall-off the other enlarging lenses were worse. In fact much worse was observed. I tested the projected light fall-off on the enlarger baseboard using a digital exposure meter which gave accurate readings to 1/10th of a stop. Choosing the El-Nikkor as the norm, the other four lenses were compared to their marked f/stops, 1/5 to 1/2 a stop darker at both centre and corner of the image. And worse still the fall-off was sometimes variable between corners of the same lens... which indicated off-centre elements. These measurements also showed an inconsistency between f/stops; this may have been due to the number of blades in the diaphragm. Whereas the El-Nikkor had eight iris blades, three others had only six and one had five - the lower numbers not making a very smooth hole when the lens was stopped-down. On the subject of numbers, there was no doubt that lenses with the higher number of elements (six) gave by far the best results. But the big numbers (£ pounds) didn't figure in the final choice. Admittedly, the apochromat may possibly have been better than the El-Nikkor for making large colour prints (where all three colours would have been brought into focus at the same point by the special glass) but I only tested them on black-and-white materials where there was no visible advantage. Possibly the best enlarging lens I have ever used was a 50-year old Focotar matched to an ancient but exquisitely engineered Leitz Focomat IIC enlarger, but whether it exceeded, was the equal of, or was surpassed by my own 63mm f/2.8 El-Nikkor is a moot point... (I believe that the Agfa films I was using at the time were particularly suited to the German optics, but that's another story!). Unsurprisingly both of these enlarging lenses are made by camera manufacturers - an important factor which influenced my choice both times. Interestingly, when I recently published a highly detailed lens testing and evaluation feature entitled "The World's Best Enlarging Lenses" by Ctein (one of the most knowledgeable American photojournalists and one of the few remaining master printers of dye-transfers) he nominated five El-Nikkors in his "Top Twenty" listing out of over 90 enlarging lenses rigourously tested during a six-month period. They were the 50mm f/2.8, 63mm f/2.8, 105mm f/5.6, 135mm f/5.6 and Apo-El-Nikkor 105mm f/5.6... that's right, there was a 105mm Apo El-Nikkor; it was made for scientific use plus the American space program and became an instant legend according to those who were fortunate enough to use one. In his article Ctein said, "The 105 Apo was arguably the most perfectly made enlarging lens available, and priced accordingly. There were no detectable aberrations of any type... and it was the one true Apo on the market." On another occasion in "Darkroom User" he stated, "If you need the ultimate in colour correction this lens provides it; it costs thousands of pounds, assuming you can find one! I don't own one and you probably don't need one, but I thought you should know just in case." So if any reader knows where this traditional photographer and printer can buy an example of the legendary 105 Apo-El-Nikkor please let me know... but without telling anyone else! The nearest I have come to one was when I spoke to a well-known American photographer who now lives in Las Vegas. He has two - but one is entombed in a block of clear resin and used as a paperweight. Boy, I'll bet that paperweight even produces sharp prints! BTW: If you want the most up-to-date Nikon news, reviews, tests, downloads, folios and opinions Nikon Links will have them listed and checked out. 9:23:02 PM    comment []