The Wallaces

DSLR Cameras and Lense Compatibility: Making Tough Choices

(Posted 4/21/2007) - Amateur photographers have more choices now than ever in the Digital Single Lens Reflex camera market. But there are new risks associated with the traditional strategy of buying lenses and expecting them to be compatible with future camera bodies.

Read one photo-enthusiast's assessment that there are risks in buying 'digital lenses' for the current crop of pro-sumer DSLR's.

A Prologue:
Like many photographer's I used a 35mm format film-SLR camera for (20) years before buying a fixed lense digital camera in 1998. The purchase was prompted by the novelty of immediate gratification. I could take as many photos as I wanted and see the results instantly, without paying for film development. I continued to use my film-SLR camera as well however.

That changed in 2004 when I bought a high quality digital fixed lense zoom camera, the Kodak DX7590. It produced photographs that were comparable (if you weren't trying to make large prints) with those produced using my Nikon film-SLR.

I preferred using the beautiful little Kodak auto-focus camera in manual mode. It easily achieved desired image compositions with its SLR style controls. The Kodak allowed me to set ISO sensitivity, aperture, and shutter-speed on every shot with viewfinder confirmation of focus point and light metering. It also included flash compensation and curtain-sync for creative foreground lighting with long-duration exposures of the background. I put up the Nikon and never looked back.

An interesting side effect of this transition: Freed from film development costs I went from taking a few hundred photos per year to taking a few thousand photos per year. In the following three years I improved noticeably as a photographer (by taking more pictures).

But not all was perfect in this digital paradise. Fixed lense cameras can't change their stripes by attaching a different lense. As time passed I began to long for the ability to use a larger aperture prime, or a wide-angle zoom instead of the tele-zoom lense (a Schneider-Kreuznach design) that was permanently attached to my Kodak.

The shutter lag and inter-shot processing delays inherent in under $500 fixed lense digital cameras resulted in some missed action shots. My Kodak (when pre-focused) exhibited 300ms shutter press lag. Its between shot interval averaged a couple of seconds. In burst mode (emulating motor drive) there was a sizeable delay after a burst before the camera was ready to take more pictures. For all these reasons I kept an eye on the DSLR market, waiting for prices to move into my comfort zone.

A New Generation of DSLRs:
As of 2007 entry level DSLR cameras from Canon, Nikon, Olympus, Pentax, and Sony-Minolta are driving a large DSLR market consisting of two distinct classes of photographers:

• Experienced film SLR users who are switching to their first DSLR.
• Folks who have used point and shoot style cameras (film and digital) and have decided to move to a DSLR.

These two groups have different needs and expectations about lense compatibiliy and camera makers are attempting a balancing act aimed at maximizing revenues as this market evolves. Because of this there are some new pitfalls for camera owners vis-a-vis new lense purchases.

The following section first discusses older lense compatibility with current DSLR bodies. Then the potential future incompatibility of the new breed of digital lenses with full-frame (35mm) camera body sensors is discussed.

Using Older Lenses with a DSLR:
If you've acquired several SLR compatible lenses it would be natural for you to expect that you can connect said lenses to a new DSLR. Basically, this expectation is met with a few caveats.

• All DSLR cameras rely on Auto-Focus (AF) circuitry and on either mechanical or electronic communication between lense and camera body. Older manual focus and auto-focus lenses produced by a given camera manufacturer may not fully communicate with every one of their DSLR bodies (though the lense will attach).
• SLR style split-focus viewfinder screens are not found in entry level DSLR bodies. The manufacturers assume Auto-Focus lenses will be used. That poses a problem when an old SLR lense is not compatible with the DSLR body lense communication protocol. There is no LED or beep tone indication when the camera circuitry detects (maximum contrast point) focus.

  Without focus confirmation the user must rely on keen eyesight to detect focus in a .8x to .9x magnification, 18-22mm wide viewfinder. This is not a happy task in lower contrast light settings.

• Aperture control by the camera body requires that the lense-body communication protocol function. If it does not, then the lense aperture can only be adjusted manually, using the lense aperture ring. Lenses that don't have an aperture ring will not work with that DSLR, except at maximum aperture.
• DSLR light metering may depend upon the lense communication protocol as well. If a DSLR cannot provide exposure information the only recourse when shooting with such a lense is to use an external light meter (usually impractical).

  Note that manual focusing should always be performed at the largest aperture setting of a given lense. Light metering on the other hand should always be done at the f-stop to be used for the shot. This sequence is automated on AF lense-body systems, but must be done by hand on old SLR manual-focus lenses or incompatible AF-lenses.

• There are lense-mount adaptors which allow different manufacturer's lenses to be adapted to mount on your favorite brand DSLR body. The downside is that the adaptors do not normally support the translation of lense to body communication protocol. This means that such things as focus confirmation, automatic aperture control, and / or light metering will cease to function.
• The general rule is that an SLR Auto-Focus lense made by company X will continue to work on that company's DSLR bodies. But exceptions are numerous.

  To determine if an old SLR AF lense will work with the latest DSLR camera body be sure that the focus motor mechanism (lense based or camera-body driven) hasn't changed. Also check that the lense to body communication protocol is the same in the lense and the body.

• If selection of a first DSLR body is biased by the ownership of SLR lenses, the decision should carefully consider whether Auto-Focus (AF) will be possible; whether focus confirmation will be provided for manual focus lenses; and whether correct light metering will be possible.
• Third-party AF-confirmation (chipped) lense adaptors have been introduced to the market, insuring one can take advantage of any DSLR body's focus confirmation circuitry while using the lense of your choice. Since these adaptors don't include AF motor control interfaces the lense must be manually focused, and the f-stop must be manually set (but focus confirmation and metering work).

  These adaptors sell in the $75 - $150 dollar range, so they would be practical only if the lense had superior properties. For lower priced lenses it might be cheaper to just buy a new AF full-frame lense compatible with your DSLR body.

Thoughts on Buying 2/3rds Sized Lenses (aka Digital Lenses):

• Lenses from full-frame (35mm) SLR cameras can be used with DSLR bodies that employ APS-C size image sensors. The 2/3rds sized sensors change the effective focal length of the lense by a factor of 1.5 - 2.0 depending on manufacturer. The old SLR lenses's effective line-pairs/mm resolving power is diminished a bit because of this focal length change. Since most 'good' SLR optics resolve at twice the sensor resolution power in the center of the lense that does not produce a noticeable degredation in image quality.

  Full-frame SLR lenses are focusing on an area that is larger than the current sensor chips, so in a sense they are wasting glass (and dollars to manufactuer).

• Newer so called 'digital lenses' which produce a smaller focal area to accommodate the 2/3rds of a 35mm frame sensor size have been introduced along with the DSLR cameras. This allows construction of lenses that are smaller and lighter, with higher optical quality for a given price point. There is an unspoken downside however.

  As DSLR camera technology advances over the next decade it is inevitable that full-frame 35mm sensors will become available in entry level DSLRs. After investing many hundreds of dollars in 'digital lenses' one would be loath to move to a DSLR camera body that couldn't use such lenses, neh?

Some Conclusions:
It makes sense to buy a $100 digital zoom lense that is light, cheap, and gives optical properties similar to a $200 SLR lense -- you can afford to throw this lense away in 5-10 years along with a well used DSLR body containing an APS-C sized sensor.

If you have some really nice AF primes and Zoom lenses, or specialty macro lenses you should look at reusing them with a compatible DSLR body. In five years these same lenses should be usable with your full-frame DSLR body too.

It doesn't seem reasonable to buy $300 and up digital lenses that will likely be junked in 5-10 years. Look instead to a compatible AF full-frame lense that may cost more but will still be usable with the next generation of full-frame DSLR camera bodies.

Happy shooting!