I have been reading a lot lately about the sharpness of some "legacy" lenses - ie those made for 35mm film cameras - on modern digital bodies. Having just sold a load of my old 35mm lenses to pay for a "new" camera, this is obviously of some interest to me! When I bought into the four thirds system in 2006, I was partly influenced by the prospect of being able to use some of my old 35mm equipment on the new digital bodies, with all the concomitant advantages of instant results / computer processing and so on. In fact, Olympus were touting this to the extent of giving away an OM to four-thirds adaptor with their early E1s.
Unfortunately, as is often the case with me, I neglected to find out enough about the drawbacks before pitching in. The key issue is that the smaller size of the 4/3rds sensor compared to 35mm means that only part of the image formed by the 35mm lens is used. Known as the "crop factor", this effectively doubles the focal length of the lens - so a 28mm wide angle operates as a 56mm, the 50mm "standard" lens becomes a 100mm and so on. Depth of field is not affected, which can be an issue. A "genuine" 100mm would have a much narrower plane of focus than the "doubled" 50mm, limiting the amount to which the photographer can use aperture to throw the background out of focus. On the other hand, longer lenses benefit from having a wider depth of field (the 300mm OM becomes a 600mm in terms of field of view, but retains the 300mm's slightly wider field of sharp focus), giving slightly more latitude in focusing.
This phenomenon is not unique to four-thirds: most DSLRs have a "crop" sensor, with most being around 1.6 times the original focal length. There are a few "full frame" models around, but these tend to be high-end cameras like the Canon 5D. Not that all high-end cameras are full frame: there are advantages to the smaller sensor size, so some professional models also have crop sensors. Olympus's E3 comes to mind, although whether this is a professional or "prosumer" model is moot.
What this meant for me was that my favourite wide angle lenses were virtually useless. My prized 21mm became a nearly "standard" 42mm, my standard 28mm - on my camera almost all the time - a 56mm and so on. My 18-28mm zoom becomes a 36-56 - nearly wide angle... but only just. These are all pretty useless focal lengths from my point of view. Furthermore, tests by John Foster reported on his invaluable Biofos website showed that most of these lenses, excellent on 35mm, were quite disappointing on the new Olympus cameras. The longer lenses, such as the 135mm and 200mm were better, but of course are much more critical to focus.
That brings us, then, to the problem of focus. My eyesight is not the best, requiring a sufficiently extreme prescription to correct that I haven't paid for eye tests for over 10 years! This has always made critical manual focusing a chore, especially in poor light. It was helped in 35mm by the split image viewfinder available in all OM cameras - but even then, was far from foolproof. Autofocus, then, has been a huge step forward for me. However, it is obviously not available with legacy lenses, nor is there any means by which it could be accomplished. It is suggested that Olympus could - if they chose - implement a focus confirmation system with legacy glass, giving a "beep" and focus confirm light when focus is achieved. They haven't yet. Such a system is available from a third party manufacturer, but involves buying either a special chip to be fixed to an OM adaptor or a special adaptor including the chip. While these have been widely reported on DPReview, I have yet to see examples from their use.
There is a ray of hope in that Olympus's latest firmware upgrade for the E510 and E3 includes a system for allowing image stabilisation with legacy lenses. This suggests they are aware of an issue, though whether they care about legacy to the extent of including focus confirm remains to be seen. I'm not holding my breath.
I was sufficiently determined to get some use from my remaining OM lenses that I invested in a special Katz Eye focus screen soon after buying my E500. This gave me back my split-image focusing for manual use, and was a joy. I loved just watching the image snap into line with AF on my newer lenses too. Unfortunately, transferring it to my E510 was only possible at the expense of losing the focus confirmation indication, so I decided to sell it. One of my Flickr friends bought it and loves it!
Getting my new E1 has made me think about this again. The viewfinder is noticeably bigger and brighter than the E500 and E510, but experiments with my old 50mm lead me to think that manual focus is not going to be any easier. This would be a shame, as the old Zuiko 50mm f1.8 is extremely crisp, has a really wide maximum aperture, and weighs next to nothing. Other manual lenses, like Konica's Hexanon 50mm f1.7 and 57mm f1.2 are even sharper (some say among the sharpest ever made, for any camera) and cost peanuts.
So, today, I've taken the plunge and ordered a split image focusing screen for the E1. This time, I've opted for a Chinese-made clone of the Katz Eye, sold by a company called "Virtual Village" on eBay. The Katz costs $95 plus shipping and customs duties - the VV is under £18 all in - so no contest! A number of people on DPReview and Flickr have them and they seem fine - with the bonus that the E1 is designed to have the focus screen user-replaced (like the OM film cameras), so there's less risk.
I hope that when this arrives, I'll be able to get some use from my legacy lenses. The E1 looks quite smart with them mounted, so that's a start!