Manual Focus Lenses Forum

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

Following on from my tests of a Fujinon-TV 50mm f1.4 c-mount lens, this is a report on a 25mm f.14 lens. It is much smaller than the 50mm.

The rear needed a deep step machining to get infinity focus.

Now the results of my (new) test chart. The chart was 1.25 m away.

First, the full picture at f1.4 and then crops at all stops (f1.4 to f16). Bear in mind the focus was set in the centre and the chart is not going to be exactly square to the camera. At f1.4 the lens is really very good in the centre, but both edges of the chart look a bit soft. The lens rapidly becomes very sharp indeed when stopped down - really excellent at f2.8.

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

Some pictures where I work, taken at f5.6 and f8. These show the vignetting is restricted to the very corners at these apertures but is still severe. it does reduce slightly from f5.6 to f8.

rbelyell · Expire: 2014-01-31

nice mark. i just got one in silver and it doesnt focus at all. but reading what you said about needing to machine it, im wondering if my lens is not defective, as i had thought, but needs machining to focus. what are your thoughts/suggestions?

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

I doubt the lens is defective. The focus is just moving the entire optical assembly back and forth. As long as it is moving, there is not much to go wrong (unless someone has disassembled the helicoid and put it together wrong). One possibility is that the lens is a CS mount version, in which case it is pretty much useless on m4/3.

You should be able to find a focus somewhere. Mount the lens on the camera, set it to infinity and, starting at about 1m away from an object, move towards it. You should come into focus before you collide with the object. Laughing

Another thing to do is remove the rear ring on the lens (the bit I machined, with the lens name written on it). It is held on with three small screws - you can see I machined very close to them. Be careful though, this ring carries the steel ball that gives the aperture its click stops. Disassemble over a tray in case the ball falls out. This ring also holds the aperture ring in place, so without it the aperture ring will flop about but it can still be used. The c-mount is actually screwed to the back of the lens on this lens (at least it is on mine!) and so you can still screw the lens into the adapter. You will now be able to screw it much further in. The picture below shows how far the back of the mount should protrude from the adapter.

If you can get it screwed in this far, you should be able to focus properly.

The rear ring needs to be machine to fit inside the well of the adapter, see below. You can see the rub marks where the machined face has contacted with the adapter. Exact machining is not too critical as it is easy to get minor infinity correction on these lenses by loosening and turning the focus ring. (Big adjustment is not possible as the pin that controls the aperture will foul on the body of the lens if you try and screw the lens too far past the nominal infinity position.)

I hope this helps.

Mark

Nordentro · Expire: 2015-01-29

very good test, and nice craftsman's work!

I also have this lens, and like you, I needed to remove a pretty big chunk of metal to make it fit. No more serial number on mine:-)

Her is my test

rbelyell · Expire: 2014-01-31

thanks so much mark, much appreciated!
tony

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

fatdeeman · Joined: 13 Jun 2009 Posts: 780 Location: UK

I have no machining facilities so with my copy I removed the back ring and then pressed one of those foam spacers from a box of blank cd's around the end of the mount till it sits in the groove which keeps the aperture mechanism in place and gives a nice clickless aperture! The foam thing needed trimming around the edge but after that the adapter screws all the way and gives infinity, it doesn't look too good but it's a nice non destructive alternative until I can find the means to have it machined.

I'll post a picture to give a better idea if I remember!

SXR_Mark · Joined: 12 Jun 2010 Posts: 506 Location: England

pat donnelly · Fri Apr 22, 2011 10:19 am

Wonderful tests! Thanks for sharing.

Now the price will be forever out of my grasp! Laughing