Recently I've Been Photographing With A DSLR; I Now Clearly Remember Why I Prefer Mirrorless Cameras

Nikon D850 which I used for my recent wildlife photography trip.  Using it brought forward
many of the, I believe, disadvantages of using DSLRs versus mirrorless cameras. (Nikon Press Image)

Recently, for a variety of reasons, I found myself photographing with a DSLR.  The experience reinforced why I prefer mirrorless cameras.  To me, using a DSLR is no longer a pleasant experience.  I find it tedious and unnecessarily cumbersome compared to my now multi-year experience with mirrorless cameras.  There are just too many aspects of mirrorless cameras that I've come to appreciate and find an advantage that are absent in DLSRs.  To me, easier, faster and more straightforward are better than being unnecessarily cumbersome and complicated.  Also, I like leveraging existing technology—to a point, to make my photographs better.

Be clear.  I'm not telling you that you need to shoot with mirrorless cameras.  What you use is up to you and what serves your purposes best.  However, for me, mirrorless now serves me better than DSLRs.

Right off the bat the advantage mirrorless cameras have in my view is apparent when you bring the camera to your eye and look through the viewfinder to compose and set your exposure.  When using a DSLR, there is no live view through the viewfinder.  What you see is not necessarily what you are going to get, exposure wise.  With the DSLR I found myself making test exposures then pushing buttons to bring up a histogram on the LCD to assess what I consider the optimum exposure.  As a said above, cumbersome when compared to a mirrorless camera.  This takes extra time and if something quickly happens in front of you, which it often does in wildlife, street and wedding photography, the result can be poor or at least less than optimum exposures of your images.  With a mirrorless electronic viewfinder (EVF) "what you see is what you get."  Your EVF reflects your exposure in multiple ways.  It is instantaneous for determining whether your image will be overexposed, underexposed or optimally exposed.

What about how bad electronic viewfinders are?  Not an issue for me with the latest iterations.  I find them bright, colorful, fast and show highlight and shadow detail.  They also resolve all of the detail in a scene that my eye can see.  It used to not be that way but EVFs have come a long, long way.  One of the tricks to optimizing an EVF is how you have your camera set for JPEGs even if you aren't shooting JPEGs.  Those settings will affect your histogram and how your image is displayed in the EVF.  I predict that in about 5 years you won't find many optical viewfinders so you might as well embrace them.  I don't have any intention of ever going back to an optical viewfinder.  I find no advantage to them any longer.

To go along with that, a DSLR does not show a histogram in the viewfinder, which I use in lieu of the camera's exposure meter.  The histogram, if understood fully, is a godsend for determining optimal exposure.  Also, if you have experience with mirrorless cameras, EVFs and in-viewfinder histograms, you know that the optimal exposure for a JPEG is different than optimal exposure for a RAW file.  All of that is easily seen immediately upon raising the camera to your eye.  

Additionally, there is no preview of white balance with an optical viewfinder.  Same reasons as above.  Getting it right in the camera, especially if you like to make JPEG files, is really an advantage.

However, to me, the most frustrating and biggest issue that arose with DSLRs concerns the accuracy and consistency of autofocus.  That is a function of the phase detect autofocusing system and how it is engineered.

Accurate and precise focusing is more important in digital photography that it ever was with film photography.  Almost without exception, today's sensors far out resolve film.  Negatives and slides do not resolve nearly the detail and sharpness that a modern, high resolution digital sensor does. Not being able to resolve as fine details as digital, there is a certain amount of "fudge factor" with film that can slightly compensate for missing exact focus.  Not with digital.  Couple that with today's lenses being much better than those of the film days, and the situation is even more pronounced.

I won't go into explaining an acceptable "circle of confusion" as it applies to perceived sharp focus and depth of field, but with digital it is smaller than with film due to the ability to better resolve small details.  For example, look at the menu in a Fujifilm X-Series camera.  There are two depth of field settings: one that mimics film (wider) and the other for digital (narrower) for each aperture.  That is Fujifilm telling us that we can better perceive misfocus than we could with film and they are giving you a way to counteract that.

With a mirrorless camera, the image is focused off the front of the sensor itself (now with both phase detect AF and contrast detect AF) just about guaranteeing accurate focus with any lens.  If you didn't already know, a DSLR has a separate focusing sensor mechanism that may or may not accurately focus your lens and is certainly inconsistent in accurate focus.  However, PDAF systems in DSLRs have been generally faster than mirrorless systems.  In some advanced mirrorless cameras, such as the Sony A9II, that is no longer the case.  With most of the latest generation of mirrorless cameras, which have PDAF sites along with CDAF sites built into the imaging sensor itself, the speed just about matches DSLRs.  But I digress.

A DSLR has its focusing system at the bottom of the camera body, below the mirror.  Most of the light that enters the camera body from the lens is reflected up by the mirror into the prism to your eye but some of it is reflected down (with a very small sub-mirror) through a patch of translucency in the center of the mirror to a sensor whose function is to calculate correct focus of your lenses.   Again, it is fast by the design of the system, but inconsistent in achieving accurate focus.  That is why expensive DSLRs include an AF fine tuning mechanism (Nikon AF Fine Tuning; Canon AF Micro Adjustment (AFMA); Pentax AF Fine Adjustment) so you can marry up your individual lenses with your particular camera body.  If the mechanism was like a mirrorless camera, that AF fine tuning mechanism would mostly not be necessary.  

Why would a lens need fine tuning to achieve best focus?  Shouldn't a new lens focus will all cameras just fine?  Sometimes they do and sometimes they don't.  Very simplistically, lenses and camera bodies, as with most products, are manufactured withing certain acceptable tolerances.  Your lens may be within its acceptable factory specification and your camera may be within its acceptable factory specification. They both could be on the plus side within design specification, both on the minus side or one on the plus side and one on the minus side.  They could be dead on perfect or one could be perfect and the other not.  Before you bought the two they had never been together.  If your lens and camera combined are out of acceptable tolerance for accurate focusing, the AF fine tuning mechanism then allows you to bring the two of them into acceptable tolerances by altering the camera's AF system by tiny amounts to achieve accurate focusing.  Sometimes.  But again, DSLR phase detect autofocusing systems with their separate focusing mechanisms, by design, are relatively inconsistent in achieving precise focus repeatedly.  Just because you now have your lens calibrated to your specific camera, the PDAF system can still be a bit inconsistent in nailing most accurate focus.  So how did this affect me?

Last October my annual wildlife excursion was approaching for the mid-December time frame and I did not own a long lens with which to photograph wildlife.  Since I'm not a die hard wildlife shooter, I didn't want to shell out thousands or tens of thousands of dollars to buy a premium lens.  What I really wanted was a used lens of good quality that would allow me to do my wildlife photography for the short term with a lens I don't intend to keep long term.  My future goal (which I may or may not be able to achieve) is to divest myself of the full frame gear and use crop sensor or micro4/3 gear as I've found those smaller cameras and lenses fully meet my needs and requirements for excellent image quality, weight, bulk, cost and ease of use.  But, I needed a lens for the short term.

Tamron 150-600mm f/5-6.3 Di VC USD G2 lens for Nikon mount.

Instead of a very expensive lens I bought an Excellent+ copy of the Tamron 150-600mm f/5-6.3 G2 lens at a very good price from a very reputable company.  This lens has some very good reviews over the years so I felt safe choosing it.  The problem was that when I took the lens out to test it with the DSLR, it would focus sharply at some focal lengths and distances but was off on others.  What was the issue?  I knew the camera was fine so the lens tolerances must have been out at some focal lengths and some distances.  However, it really didn't matter as I needed the focus to be accurate at all distances and at all focal lengths.  When I tried the lens on my Nikon Z7, a mirrorless camera which focuses off the front of the sensor itself, it focused perfectly in the same tests.  The DSLR with its separate sensor focusing mechanism was not able to compensate for any lens variance issues whereas the mirrorless camera could.

Just to be safe, I sent the lens to Tamron USA for a full scale check, clean and calibrate.  When it returned, it still didn't focus as well as I thought it should at some focal lengths and some distances.  Hmmm.  What next?  Calibrate the lens to my camera.

As I mentioned, some cameras allow you to adjust and fine tune autofocusing.  With single focal length lenses (primes) using the in-camera AF fine tuning mechanism is quick and easy and works fine as long as your protocol is exact.  But it doesn't work well with zoom lenses.  Why?  Nikon only allows one AF fine tuning setting for a zoom while Canon allows two—one at the zoom's shortest focal length and one at the longest.  That one or two settings restriction just doesn't work well with the multitude of focal lengths and focus distances of zoom lenses.  There is a lot of glass elements in many groups that shift back and forth when zooming and focusing.  One or two settings just can't compensate for the issues.  This is a real problem.

After my lens came back from Tamron, I also bought Tamron's Tap-In Console lens programming device.  You can read more about it here.  The puck looking device mounts to your lens and connects to your computer with a USB cord to allow you access Tamron software.  This software allows you to reprogram and correct the front/back focus issues of the lens at several different distances and several different focal lengths.  See the chart below.  Also, It solves the problem of only one or two AF fine tuning settings.  That being said, I found it is a real challenge to use as there is no indication from Tamron about how their calibration numbers correspond to your camera's AF fine tuning numbers.  There are calibration numbers associated with the in-camera's AF tuning mechanism, FoCal software, the LensAlign Method, the Dot Tune Method and numerous other ways to fine tune a lens' autofocus.  They all sort of rely on the AF fine tune mechanism in your camera but Tamron never says how the in-camera numbers correspond to the adjustment numbers shown in their software.  This is an issue that shouldn't be an issue.  They should publish data for all cameras that have AF systems that can tuned when using their lenses.

You can see that after calibration with the Tamron Tap-In Console that
the lens needed adjustment at almost all focal lengths and
distances to bring it into accurate focus. But when finished, the lens
was sharp at all focal lengths and all distances.  (click to enlarge)

To make a long story short, I spent about 8 hours over a couple of days working to figure out the best settings to reprogram the front/back focus of the lens.  In fact, I researched and tried three different methods and got three different sets of results at all focal lengths and all distances.  Nothing among the various methods was consistent.  I really struggled with this and just wasn't satisfied with my images.  

I was just about to give up and trade in the lens when I decided that I'm not a quitter and I wasn't going to let a lens get the best of me.  I decided that if I didn't try every which way to get it programmed, I was selling myself short and accepting defeat.  If, after trying everything I could think of and still was unhappy, then I would just trade in the lens for something else.  Luckily after another 3 or so hours of trial and error, I finally got it to the point where I am very happy with the image quality and focusing accuracy of the lens across the board.

There are two things to consider here.  First, the phase detect autofocus in DSLRs, as I said, is by nature inconsistent.  So, test results without any changes to any settings can come out differently, which really can drive you crazy.  Try it sometime.  Make 10 identical exposures with the same settings and you will get a variety of results for adjusting autofocus.  Second, with my mirrorless Z7, no adjustments or testing was necessary.  No matter what inconsistencies are in the lens, the mirrorless focusing system compensates for them by focusing off the front of the sensor itself.  Problems solved with no time wasted.  Again, using a DSLR after using mirrorless is tedious.

In a nutshell.  With a mirrorless camera all of the time and effort outlined in the prior 11 paragraphs would not be an issue.  Grab the camera, attach a lens and you are good to go.  

I know what you are now thinking and would like to ask me—why didn't you just use your Z7?  Although the mirrorless focusing mechanism is more accurate and consistent than in a DSLR, it does not perform as well for tracking flying birds, etc.  Nikons first generation Z7 AF is not quite as good as in the many-generations AF systems in the Nikon D850 or D810.  If I were only shooting static birds, landscapes, travel, etc., no question.  I would have used the Z7.

Another aspect of fast focusing and tracking moving subjects is the number of focus points available in DSLRs and how much of the sensor they cover.  For example, the Nikon Z7 has 493 focus points covering 90% of the screen while the D850 has 153 focusing points covering a lot less of the screen.  I wasn't able to locate the statistic for coverage but see the illustration directly below.

The difference in the number and position of AF points can make all the difference between success and failure.

To be fair, however, the D850's focusing system is faster to lock on than the first generation Z7 focusing system.  But if the sensor points aren't where you need them to be, the result may be not being able to focus exactly where you want.

Enough about focus.  I get frustrated again just writing about it!  LOL

Another issue with DSLRs is mirror slap.  Mirror slap has always stuck its ugly head up in DSLRs and SLRs before them.  As much as the manufacturer tries to dampen that big mirror moving up and down very rapidly, mirror slap seems to occasionally cause blur in image files.  Not an issue with mirrorless.

DSLRs have a slower frame rate than mirrorless.  My Olympus camera can fire off frames with a mechanical shutter at 15fps and with an electronic shutter at 60fps.  My Fujifilm cameras were not quite as fast but still faster than DSLRs.  As far as I know, no DSLR can fire off exposures that fast if and when you may need that speed.

One aspect of mirrorless cameras that really comes in handy is when photographing on sunny days.  When trying to review your images for exposure, focus, sharpness, composition, etc. on a DSLR's LCD, it is almost impossible on a bright, sunny day.  With a mirrorless camera, you simply peer into the EVF and you can see your image clearly in a dark environment for evaluation.  Nice.

These are some of the issues I immediately experienced when recently using the DSLR.  If I had never used mirrorless cameras then they probably wouldn't be issues, but mirrorless cameras and all of their advantages have spoiled me and any disadvantages to mirrorless have, in my view, become minor.

The trend in the industry certainly seems to be going toward mirrorless systems.  That, I suspect, will bring more research and development money to mirrorless which should result in better EVFs, better focus, faster performance, better sensors, additional features and maybe even continued life to the ailing interchangeable camera industry.  Let's hope!

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Thanks for looking. Enjoy! 

Dennis A. Mook 

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