Wednesday, 22 May 2013

Legacy lens adapters

In the course of collecting these old camera, I have also collected a number of old lenses, some of which are very good.

My Olympus OM10 camera has a Zuiko 50mm, f1.8 lens which six elements in five groups and a Vivitar zoom lens (75-205mm) which has a very good reputation.  I also have another Vivitar zoom lens (20-200mm) which doesn't have quite the same reputation as the other Vivitar but performs very well nonetheless.

My Zenit E came with the famous Helios-44 which is a superb copy of the Carl Zeiss Biotar (six elements in four groups) and my Praktica LT3 came with a Meyer Optiks Domiplan which is a triplet - so not in the Zuiko or Helios-44 league but a good performer when stopped down.

When thinking about a 50mm prime lens for my Canon DSLR, it occurred to me that I already had several good  50mm prime lenses and was there any point in buying another?

With this thought in mind, I looked into buying an adapter so I could use one of my old prime lenses (it would seem that these  have morphed into legacy lenses while i wasn't looking).

First, I looked into buying an adapter for my Olympus OM lenses.   There are a number of these available and they are quite cheap.  These range from simple metal rings with an OM female bayonet on one side and an EF male bayonet on the other - these cost £2 to £3 each - to more complex adapters with electrical contacts and a chip.  this is then one I bought and it cost me £12.99 including postage.

The adapter ring is very well made out of brass which has been chrome plated.  The EF bayonet fits smoothly into the Canon digital camera and, similarly, the Olympus lenses fit smoothly into the female side of the adapter.

When the lens, adapter and camera are all fitted together, the result is snug and secure.  There is no significant play, even with the heavy and long Vivitar zoom.    The electrical contacts make contact and the camera recognises the adapter.

The point of the contacts and chip is so that the focal length and aperture of the lens can be stored in the Exif data of the resulting digital file.  th achieve this it is necessary to programme the chip on the adapter.  t5rhis is actually quite easy - but not simple as it involves quite a few steps. Once the adapter is programmed for a particular lens, it is necessary to manually set the aperture on the lens and then separately set the aperture on the camera - this aperture is then stored in the Exif data.

If accurate Exif data is important to you, this process will be worthwhile (and will be necessary to repeat for each lens you use with the adapter) but I routinely ignore Exif data so I do not bother with the process.  If, like me, you want to be simple, you just focus the lens, set the aperture (you need the camera to be in Av mode) and let the camera select the shutter speed.

The adapter works well so long as you remember the lens is entirely manual - you need to focus and set the aperture for each shot.  Given that I use fully manual cameras a lot of the time, this should be second nature, but as soon as I pick up my digital DSLR I forget to worry about focus and exposure.

My next adapter is for M42 lenses (also known as Pentax fit, although developed by Zeiss Ikon in Dresden in the 1940s).

I had two M42 lenses when I bought this adapter - the Helios-44 Biotar copy and the Meyer-Optik Domiplan.  Both screwed nicely into the adapter but there is a problem with the Domiplan lens in that it is an automatic lens - there is a pin on the lens that must be depressed by the camera just before the shutter is released in order to close the diaphragm. The adapter leaves this pin alone so the Domiplan can only be used wide open.  

Actually, while trying to get this lens to work with the adapter, I noticed that the lens has a significant fungal growth on one of the inner glass surfaces.  This lens is now in the dustbin!

The Helios-44 lens worked well.  This adapter is a simple aluminium disc with no contacts or chip sop there is no need to set anything up.  The same working method as with the OM adapter is required - focus with the lens diaphragm wide open, stop down the lens to the required aperture and let the camera sort out the shutter speed.  As there are no contacts, no lens details are stored in the Exif data.

Both adapters are easy to use and work well.  Not being interested in the Exif data, I would have been better off buying a cheaper and simpler OM adapter, but the one I did buy was certainly cheap enough.

Theoretically, as the camera is metering the light through the lens it should give the right exposure regardless of the lens used.  It has been suggested to me that TTL meters do not cope well at low light levels so will give poor exposure at small apertures.  I have not found that.  Initially, using the OM adapter with the Zuiko 50mm lens, the camera consistently overexposed at all apertures with the highlights clipping in all photographs.  The cause of this is that I was not setting the aperture on the camera as well as on the lens so the metering system assumed - incorrectly - that the lens would shut down when I pressed the shutter release.

Repeating my OM test exposures with the camera set to f1.8, the exposures were fine with the histograms coming up well to the left with no clipping.  This setting of the aperture on the camera as well as on the lens is only a problem with chipped adapters - or you can do as I now will and keep the camera set to its smallest aperture.

When using the Helios-44 with its simple adapter, the exposure histograms were well to the left and without any clipping so giving usable photographs.  This is regardless of the aperture set on the lens.  With this adapter, it is not possible to set an aperture on the camera as the absence of contacts makes the camera default to f00

Test pictures:  first, the same scene at different apertures (after these, a focal plane test).

OM adapter with a Zuiko 50mm, f1.8 lens.

 
aperture f16
aperture f5.6

aperture f1.8
M42 adapter with Helios-44 58mm, f2 lens.

aperture f16

aperture f56.
aperture f2

Focal plane test:  in order to focus on infinity, it is necessary that the focal node of the lens is the right distance from the film/sensor.  For a 50mm lens, this distance is 50mm (in some designs, the node might be in front of the physical lens).  This distance is split in two.  The first part is the film/sensor to mount distance (obviously, this never changes) and the second part is the mount to node distance.  This second part is susceptible to being changed by the adapter.  If the mount is too thin, the lens will still focus on infinity but its near focus point will be further away than intended.  If the mount is too thick, the lens will focus on nearer objects ok but will not be able to focus on infinity.  It is this last that I want to check.  I am not too bothered if I cannot focus on an object two feet away but I am very bothered about not being able to focus on infinity.  To be clear, I had better define 'infinity' - for this purpose, it is anything over 50metres away.

First the OM adapter.  The first picture is a standard scene in Lincoln.  The second picture is an enlarged crop from the centre to critically check the focus.



detail from the centre

Now the M42 adapter.


detail from the centre
You can see by comparing the two details that the Zuiko is performing better at a distance.  I think I can safely say that this lens adapter is correctly placing the lens in the mount.  The detail from the Helios-44 photograph is a lot less clear - but I cannot say if it is down to the adapter or the lens performance.  It is certainly good enough to use.