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For anyone who's chosen to use legacy lenses on digital bodies, the initial lens choices would likely be any of the zillions of manual focus 35mm full frame types. They are plentiful, cheap (compared to their 'digital' versions), and have mounts that can handle cross-branded lens adaptions with matching adapters readily available. Whether these lenses were passed down from family or tucked away from previously owned film cameras, or something newly sought out from online sites or garage and yard sales... they are familiar to most of us and the obvious first choice. They are however, not the only choice.

By that, I mean that lenses available for conversions with off-the-shelf adapters aren't limited to just this one well known every-family-had-one film format. Although the overall production numbers may not be as high as 35mm lenses, Medium Format (MF) glass can be had for modest prices, and their optical qualities can equal or exceed anything in the 35mm family. Remember that these lenses were primarily used by commercial photographers for weddings, advertising work or other types of commercial endeavors; and are generally a notch or more above the quality found in most 35mm consumer lenses. I've read any number of articles and forum postings that suggest there's no real benefit to using these larger format objectives - that it's only a waste of time/effort/money. My response? RUBBISH!

My reasons to adapt medium format lenses are pretty simple and you might see some value in doing the same.

• If you already own medium format lenses, why not use them if you can?
  This is the initial reason I started to investigate the possibility. The investment in one suitable adapter alone can be considerably less than the cost of a single adaptable lens of good quality in 35mm format. If you currently have multiple focal lengths in MF, you gain the use of them all for the cost of that one adapter. You may have a huge chunk of money invested in old MF lenses, and have no reasonable way to recoup that cash outlay in today's used gear market - and then turn around and buy all-new lenses in various sizes and of ANY type, without loosing a few bucks in the process.
  
  I started with an inherited adapter after I purchased the Bronica 100-210mm zoom lens it was attached to. It was designed to adapt to a Nikon F-mount body, and not directly to a digital/mirrorless camera. This allowed me to pair my lenses to standard Nikon film or digital bodies, and it attaches to every ETR series lens I have without issue. I can additionally stack a Nikon-F to E-Mount adapter behind it if I choose to mount any of those same lenses onto my NEX-F3. Infinity focus is preserved with one or both of these adapters in place, since the film to flange distance is additive with the combination. Slightly rolling past infinity can be a possibility with some of the adapters at the 35mm end when their tolerances aren't as precise as they could be (in other words - the really cheap ones). The only caveat that matters in my case - it won't accommodate fitting either of my ETR teleconvertors between the adapter and the lens because of a protruding linkage lever on the 1.4x and 2x convertors. Annoying, yes - but certainly not a deal breaker. If your digital body is also Nikon F-Mount based and you'd prefer using the same method with Bronica lenses, the cost is under $75 for that exact same Fotodiox Nikon AI adapter [ available at Amazon ].
  
  An example of using the Bronica 100-220mm while adapted with the Bronica to Nikon, and Nikon to E-Mount pair of adapters, and shot on various digital bodies are posted in the galleries.
  
  Remember that if you're still shooting film, you can immediately gain a fresh set of adapted lenses to use for standard 35mm film cameras if there's a matching mount for your body. If it's the same mount that's natively used or adaptable on your digital bodies, you get a one-time purchase bonus by not having to buy 2 or more adapters. If you don't currently shoot film - but want to at some point - superb film bodies are still cheap and plentiful, and I'd suggest you investigate any matching mounts that would work for MF adaptions, and buying one adapter would suffice for you as well. Even if you wouldn't be wanting a film body right away, you'll have an idea of what your options would be for later.
  
  
• If you are the creative type who prefers to use whatever tool you need - and at a reasonable cost - you'd use it without giving it a second thought.
  If the results you seek can be achieved or enhanced by choosing a less common tool, why wouldn't you? It's the results that matter, not just the method or the tools. As one example, a UK photographer has pulled his gear out of storage and successfully adapted some of his old Mamiya C 645 manual focus lenses for use in his architectural photo business. They are now used as tilt and/or shift lenses on a Canon EOS-1Ds [ Keith Cooper / Northlight Images ]. In this case, his lenses were also repurposed by the tilt/shift functionality added by the adapters themselves so they can now create something that wouldn't have been possible with the original lenses. More bang for the buck AND new tricks at the same time.
  
  
• If you aren't afraid to experiment outside the obvious choices (no matter what others think), you can expand your toolset.
  Keep in mind that you wouldn't be the only one interested in choosing this larger format lens family for adaption. After all, it took a considerable investment for companies to make these mass produced devices in the first place, and in fact there are several mount types from several manufacturers, so there's clearly a need that's been filled very well... and the offerings available continue to expand.
  
  
• You can gain a nearly equivalent focal length (via a nearly equivalent Field of View) that more closely matches those designed for your cropped sensor body.
  The mathematical reason might be overlooked, but is still as valid as any other. Legacy lenses produced in full frame 35mm formats were obviously never designed for a cropped sensor's smaller frame size so they work more like tele-converted versions of themselves. Medium format lenses can coincidentally be closer to an equivalent field of view that translates well in place of native non-adapted cropped lenses. Essentially the result can be a near-cancellation of crop factors when using some of these adapted MF lenses.
  
  That's not to say that a you get back a 50mm lens as measured natively on digital, from an adapted 50mm medium format lens. What you can end up with is an adapted lens to fit into those voids at the wider end that aren't available from most other legacy formats in a comparable field of view. You're also likely to gain the quality of glass you might prefer to have with the wide, normal and mid-telephoto ranges too. Long range ultra-telephoto framings won't necessarily be feasible with MF adaptions, but there are plenty of suitable lenses in 35mm formats to take care of the longer focal lengths.
  
  
• A minor concern - apart from maybe lens weight/size - might be how the aperture controls work on your lens.
  Bronica lenses in the PE model line have a toggle-type D.o.F. slide switch to temporarily hold the aperture into stopped-down preview mode. The E/EII and MC lens models have a momentary push-down lever instead. Once the PE versions are slid into preview they still need sideways pressure to stay in position, while the others require a downward push. Something like a rubber band can be added as a hands-free slide button holder or pressure helper - or - you can choose to just press to hold them over/down before taking each shot. I'd caution against using the latter technique on longer lenses (both physically and focally) because of camera shake, so rubber bands are a quick/easy/cheap fix that don't require modifying the actual lens hardware, or add complexity or weight.
  
  One remote but unlikely possibility for me: With the large number of Nikkor/Nikon lenses I have, it would be nice to find a Nikon-F to E-Mount adapter with a built-in iris and aperture control like those I've seen available for Canon EF mounts intended for adapting their G type (Gelding) lenses. I doubt there's anyone making a Sony E-Mount adapter that's a direct-to-Bronica setup with it's own aperture and control ring, but that would certainly forgo any need for rubber-bands on Bronica models (or other adaptable brands that would require a similar approach, if similar adapters exist). If your lens collection includes a fair number of Canon EF lenses that you'd also want to adapt to Sony E-Mount, you could make use of the simple Bronica to EOS-EF Mount adapter currently available [ at Amazon ], along with the EOS-EF to NEX E-Mount adapter to gain the use of its iris control and bypass the aperture issue entirely [ also at Amazon ].
  
  If your intent is not to cover a mix-n-match of multiple mounts as I've done, there are certainly adapters that marry an adaptable medium format lens directly to a digital body with ease and precision, and all in one single and cohesive device. An example of a Bronica to NEX adapter for roughly $85 USD is available [ on Amazon ].
  

Calculating lenses for adaption

The following table contains calculations for some selected medium format lenses - with approximate lens equivalencies relating to other film/sensor formats. The various crop factors as they come into play would allow you to get close to the angle of view that are comparable to many common lens lengths that a cropped sensor body would use natively. The corresponding focal lengths (as calculated) can provide an approximate subject framing as shown at the film/sensor plane, in the same way you would expect from a non-adapted lens.

I should state for clarity that I won't quibble over terms here when it comes to "equivalent" and "focal length", but basically these digital adaptions can always be compared to the horizontal angles of view provided by the adapted lens. In other words, no matter what the stated numbers on the adapted or native lenses happen to be, the unarguable truth is that 49 degrees is always 49 degrees, and the XXX mm focal length of any lens doesn't actually get magically modified regardless of any other factors to suddenly become a new focal length. The field of view on any lens - when converted - becomes the equally compared value. Any differences to the image circle acceptable for your sensor/film format (the tube of transmitted light used to reflect the scene as an image) and the focal plane's flange distance to the lens is automatically rectified when using the correct adapter... and as I've done - you can stack adapters if needed. They would be passive and won't be altering any optical properties or have physical clearance issues at the body end.

I can't speak to the suitability of using anything termed as 'smart' or an optically modifying glass-assisted adapter, wherever they might be available, so you'd have to research that on your own and it's outside the scope of this article. One source of medium format 'Turbo' 0.7x style convertors I have seen, would be those from Kipon in China - designed by IB/E Optics in Germany - and marketed as the Baveyes format reducer. One of these adapters, designed for ETR lenses, would set me back about $495 USD. Thanks, but no... I'll pass on purchasing one of those for now.

Lenses chosen for comparison

The choice of 645 lenses and the 35mm/Cropped focal lengths used in this table are based on my own adapted gear... a fair set of Bronica ETR series PE lenses, as well as target lenses for both of the Nikon based formats I have (full frame 'FX' in film and 'DX' for digital); along with the nearly identical-to-DX crop size from my Sony NEX-F3. I should also note that I use NO native lenses on the Sony, and I've never owned any. I've also included the values calculated for Micro Four/Thirds as an added comparison to yet another common interchangeable lens format where easy 645 lens adaption is also possible. Cross format adapters for Hasselblad, Mamiya, Pentax 67, Kiev 66 / Pentacon 6, Fujifilm, and others are available - and all these same basic principals apply to them whenever a 'dumb' adapter is used.

There is one additional aspect to these calculations that I've chosen to exclude from the data, and that is the differences reported as the supposed maximum aperture for a given lens at conversion. The math used to obtain these results would modify what the indicated f-stop value becomes once all the collected light is passed to the film/sensor that's recording it. Simply put, the amount of reflected light transmitted through the lens elements will increase or decrease in intensity by a factor of X, where the value of X is entirely dependent on the focal length of the lens.

To me the theory itself sounds reasonable on one level, but practical application doesn't seem to bare it out, nor to be a terribly accurate assumption to me. Yes, there will undoubtedly be some light-loss and falloff beyond the capturable image circle, and a certain amount of reflected/refracted light that may not get collected at the 'film plane' - but - I think a doubling (or more) of light output that greatly modifies f-stop values this way just isn't realistic without using additional glass elements to refocus and then incidentally boost the light output like a turbo/boost adapter provides. I haven't seen anything in my limited testing to convince me that there's actually a noticeable increase with glass-less adapters, only a slight loss, if any. I have no reliable way to measure it for raw comparison, so I can only go by the metering results presented from the body that's in use and what I read in the EXIF data - plus, my gut instinct and what I see and know from past experience.

645 Lens Comparison Data

NOTE: These results are compiled with various camera/lens data sets reported from the pointsinfocus.com calculator, and using an aperture setting of f/1 with a subject distance of 10 feet, as measured to a generic 645 size standard to produce an approximated set of values. There's no such thing as a 250mm f/1.0 645 medium format lens with a given framing size of 6.0 cm x 4.5cm of course, but using these somewhat arbitrary values will insure there's no oddities or out of range results with differing lens specifications within each focal length's calculations.

If you want to compare your own formats, the calculator also provides variables for anything from a Super 8 movie frame - up to sheet film 8x10 view cameras. You can run the calculations with whatever focal length lenses you wish to, and modify the related options to get precise numbers to fit your chosen setup. There are several other calculators online that can provide similar results if you'd prefer to search for them on your own, but I found them to be a bit harder to use (with too many variables, or too few), or they don't contain a broad enough range of film/sensor formats to evaluate against.

Conclusions

Adapting Medium Format lenses isn't going to be a fit for every situation with every photographer. There won't be a full set of focal lengths at the extreme telephoto end if that's where your needs are. It is, however, a possibility that warrants some consideration. Once you investigate the potential and weigh the pros and cons, it might be a viable solution for you too. You can gain some outstanding optics at bargain prices too.

UPDATE: After writing this article, I acquired a Sony A7R mirrorless body, and now use the same technique explained here to capture photos onto a full-frame digital sensor. This produces even better results with it's higher resolution capabilities and greater dynamic tonal range. What's not to like about vintage MF lenses that keep on giving?

I've also added MF Projector lenses into the toolbox, to further expand on what Medium Format glass can add when adapting lenses for film, digital, and multiple capture formats.