Caveats associated with Vintage Lenses

My vintage lens collection is growing by leaps and bounds.  I have gotten some good results from some of the lenses, and in some cases I find that they equal or exceed a number of currently available (newly manufactured) lenses.

However; not every vintage lens can be used safely on every camera.  I think the old film cameras must have had larger registration distances between the mirror and the rear of the lens barrel.  Certain lenses, when they are focused at some point in the direction of infinity on the focus ring, protrude from the rear of the lens mount.

It doesn’t take much protrusion to hit the mirror on a modern DSLR.  Much over 1 mm will usually do it.   In the list on my vintage lens page is a very nice Yashinon DX 50mm f2 lens.  It is my sharpest vintage lens, and one of the best bokeh lenses I have.  It protrudes between 1 and 2 millimeters behind the screw mount at infinity focus, which runs into the mirror on my Pentax K5.

The K5’s mirror, when in the normal position (i.e, the shutter release is not being pressed) – doesn’t hit anything, because it’s below the lens protrusion at that point.  If the Yashinon is focused to infinity, then when the shutter is released, the mirror will lift up enough to take the picture, but hang on the edge of the rear element of the lens about half way, or a little more than half way, as it goes through its travel.  Thus, by moving the focus ring towards the close-end focus range on the ring after the shot has been taken,   one can cause the mirror to flap back down..

While this allows one to take pictures, the constant banging of the lens element on the mirror edge is not a good thing!  One millimeter must be right on the edge of hitting or not hitting the mirror when using a K5 with a Yashinon DX 55mm f2 lens.

I did this only a couple times before I realized what was going on.  I checked both the lens and the mirror, and there seemed to be no damage to either.

When fitting the same screw mount Yashinon to my Sigma SD14, the mirror doesn’t hit the rear lens element, but it’s for a different reason than the K5.  The Sigma SD14 has the IR filter in front of the mirror (where it is easily removed), whereas most all other cameras have the IR filter close-fitted to the sensor, or even bonded to it.  Of course, the sensor is on the other side of the mirror. So, when trying to focus the Yashinon towards infinity on the Sigma SD14 the rear element runs into the IR filter, rather than the mirror, and this happens before any shot is taken.

This does not make the situation happy, however.  One could damage the IR filter instead of the mirror, and they are not as cheap to replace as one might think.  I checked the filter, and there were no marks (whew!).   The lens is able to focus out to about 4.5 meters or so, on the Sigma, before being stopped in its travel.  I can focus all the way to infinity on the K5, with the problem being that the mirror will hang.  At about 4 meters focus, the lens never hits the mirror on the K5.  But, this is definitely not the way to operate!

So,  if I’m very careful,  I can use my Yashinon on the Sigma, where the travel is a little better.   Even then, I know I take my chances.  Just coincidentally, the mirror registration/alignment on my Sigma got mucked up recently, in spite of the facts that the IR filter prevents any contact to the mirror.  Don’t know what’s up with that.

The mirror is the largest mechanical piece in a DSLR.   It’s also the reason most of us should be thinking about moving up to a mirrorless system.  The mirror on a DSLR carries with it some probability that through its lifetime, it will fall out of calibration due to the constant banging of the mechanical device as it operates (even normally).  How does this manifest itself?

The distance from the eyepiece to the mirror + distance to the lens must exactly equal the distance from the sensor to the lens, or the focus at those two places (sensor and eyepiece) will be different.  When looking thru the eyepiece prior to taking a shot, you are looking at the reflection from the mirror.  When the shutter is released, the mirror pulls up, so that the scene goes straight though to the sensor (mirror no longer in the way).  Vibration can jiggle the distances to be unequal.  Fortunately, the Sigma is somewhat user-serviceable in this regard.  Some mirror adjustment screws are visible from the mirror box opening (seen when the lens is removed) – and this is the case with the Sigma.  Other cameras have the screws on the other side of the mirror box, and require a camera disassembly to fix.

I have a 1.5 mm hex wrench on order, for with to fix this issue.  Currently (this just happened) – I can look thru the viewfinder and adjust the lens until I have a perfect focus.  Then, after the picture is taken, the JPEG shows an unfocused picture.  This is the mirror becoming misadjusted by (whatever it is that happened).  Being somewhat user serviceable is a feather in the cap of the Sigma people.  Unfortunately, the SD14 is far too old to be considered anymore, except by someone who’s been dabbling with the (new-to-me) Foveon sensor type, and (like me) – just wants to see what it does.  The next step for me is definitely mirrorless.  Sigma does have some new mirrorless camera options, and I may be following that route.  They are developing a full frame mirrorless camera, but it won’t hit the street until 2020.

The Fujifilm X-T3 looks pretty tantalizing too.  We’ll see.

Why did the camera companies not just do mirrorless to begin with?  There are two main reasons:

  1.  The basic film camera could be easily converted to digital simply by putting a sensor where the film was, making development cost lower.
  2. The mirror was still necessary because of the cost of electronic LED displays such as what we find on the backs of most cameras these days.  These displays need to have high enough resolution to focus properly.  With no mirror, the focus has to be done with a sensor and an LED display on a mirrorless system.

While the mirrorless cameras, or some of them, have a “viewfinder” – it is really another very small LED display, and not a mirror reflection. Some may count the LED display, and the need to use it for focusing, as a downside of mirrorless systems.  For a near-sighted guy, whose love affair with the viewfinder never happened, this is not so.

The Sigma SD14 is a product of Sigma Corporation.  Sigma and Foveon are their trademarks.  This author and site has no affiliation with Sigma.  The Pentax K5 is a product of Ricoh Imaging Corporation, and is not affiliated with this author or site.

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