An F-mount to LTM lens adapter on a Canon 7

Following my recent clear out and acquisition of the Canon 7 and the Russian lens, posted recently, I also purchased an adapter that would allow my Nikon F lenses to fit the Canon for manual focussing.

The adapter

The adapter I bought is well made for its very reasonable price. The T-mount style adjustable thread mount to adjust for scale alignment was slightly oval, however. The three grub screws had been unevenly tightened and it was binding initially before I evened things out.

The lenses

I have three F-mount lenses, a 55mm Micro Nikkor, Tamron 17mm Adaptall 2 and a Tamron 28-200 AF zoom, potentially giving me a wide range to go at. The 17mm has to be guessed at for composing but keeping both eyes open and centering the rangefinder spot on the estimated frame seems to be close to my peripheral vision so I am roughly taking what I see.

In use it must be remembered that, whatever the lens focus setting, the finder frame remains at its closest focus position. Parallax compensation must be allowed for by eye but in the reverse direction to normal, i.e. from rather than to 4o’clock.

When using the 55mm Nikon set to 3’ for close work, like my test shot below however, the finder is accurate with the USAF target nicely placed in the centre.

When using the zoom at 28mm this allows the whole finder frame to be used but now parallax must be allowed for conventionally. This is in contrast to using other focal lengths covered by the finder frames as mentioned above.

The examples shown here are of the tests with the 55mm and show how I tested, at a measured 3 feet and at Infinity. Exposures were 1sec and 1/1000th sec respectively at f5.6. All the F-mount lenses were tested with the same set-up and exposure. There is a handy power line as a target on the horizon at the centre of the image at infinity.

Results showed that the short throw focus calibration on the zoom isn’t sufficiently precise for manual focus. Ultimate precision when using autofocus with a consumer lens on an AF SLR would not be given highest priority of course with the scale being too cramped at longer distances for spot on focus.

The 55mm looks to focus perhaps a little “short” at close range, the mirror frame in my test shot being slightly sharper in front of the target which the inset enlargement shows is a little soft. The Industar will be preferred at this focal length in any case for general work. An SLR would be used with the Micro close up. So maybe the adapter is just that touch out at closer range when it becomes more critical. Not that surprising given its low cost.

So of the lenses I tested the 17mm and the zoom locked on 28mm or set to 35mm for a moderate wide angle would probably see the most use. Longer focal lengths if used would have to be at smaller apertures for safety.

On the camera focus calibration is good when checked at the gate with the Industar. Altogether perfectly useable and supports my close work conclusion with the adapter.

Practical results

I tried these combinations out on some of my favourite subjects using the 17mm and the zoom locked at 28mm. I didn’t think it was worth trying the longer focal lengths based on my earlier tests.

This series below gives an idea of the range covered compared to the standard 50mm.

The finder seems to be very accurate so that my usual tight crop has in fact been too tight in this case using the Industar which is slightly longer than 50mm.

The 17mm opens up some interesting options, especially like this one of the Queen Victoria memorial in Dunedin. A step back and a little to the right plus more care with the verticals will make a good composition taking in all the base and more of the “exploding” tree in the background.

Convergence with the 17 can be alarming, especially when one of the buildings has a façade that is already angled outward.

The 17 does allow the whole of subject to be included when necessary.

Final comment

As a very inexpensive stop-gap, these combinations can fill in for infrequent use or until a dedicated prime can be sourced. The 17mm really grabbed my attention as you may gather. I must practice more to be able to visualise the coverage, and I might try a portrait focal length with the zoom in due course.

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