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Saturday, 29 December 2018

Zeiss Contax 18mm f/4 Lens Hood - part 2

I managed to get a few example images of the lens with and without the hood.

This one is indoors with the sun coming through a window and falling onto a plain wall. I folded the hood back then just angled the camera until I saw the flare, took one picture then pulled the hood forward - flare gone.

This second example was taken outside. I did the same procedure as before.

The second pair of pictures have another area of flare that wasn't removed by the hood. It's not obvious so I've ringed it in the next picture.

 I could also get the lens to produce some more obvious flare even with the hood in place so it's not a 100% solution, but hoods never are. But I think it's a worthwhile addition.

I also wanted to add a note to say that the lens I have is an MM type with a serial 72*****. There was, apparently, an earlier version of the 18mm which may behave completely differently.

Friday, 28 December 2018

Zeiss Contax 18mm f/4 Lens Hood

The 18mm f/4 doesn't have a filter thread. It takes 70mm push-fit accessories and Zeiss made a 70mm to 86mm ring to take 86mm filters and which they also suggest will act as a hood. The problem now is the difficulty in finding one and then the probably extortionate cost you'll have to pay for it. At the time of writing, there is one on ebay with a buy-it-now price of $110 with shipping from Japan so, in the UK at least, there will also be VAT and import duty etc. to pay on top - no thanks.

As I've found the 18mm is a bit prone to flare, I thought I would look for an alternative. What I found was a hood for a Mamiya 45mm lens for the 645 system. It is a 70mm push fit hood and fits perfectly straight onto the 18mm. I paid about £20 for mine including postage. This seems a typical price. The only problem is is that it's a bit deep so I took a knife to it and cut it back (rather badly as it happens).

The hood has a square section on the front. Not  a lot of use with the 18mm as the front of the lens rotates so it's impossible to keep the hood square. Some experimentation suggested the whole square section needed removing anyway to stop vignetting on the 18mm so that's what I did. You end up with a round hood so it doesn't matter that it rotates.

Here's a few pics.

Some testing afterwards showed there was a tiny amount of vignetting in the corners so I trimmed another, maybe, 3mm off it which cleaned up the cut edge and got rid of the last bit of vignetting.

Being such a wide angle lens, a hood is never going to be very effective but it's better than nothing. I'll see if I can get some example shots with and without the hood to show the difference.

Just one thing of note, there is a Mamiya hood available that is said to fit the 645 45mm lens and also the 65mm RB67 lens. This is not the correct hood. The original version of the 45mm had an 80mm diameter front and that hood is for the original version lens. Check what is written on the side of the hood. It should be as shown in my picture above. If it mentions RB67 lenses, it's the wrong one.

(Edit: There is now a second part to this post with some examples).

Thursday, 27 December 2018

The Contax/Yashica Bayonet

This might seem a particularly boring subject to write a blog post about but it's intended to be the first of a few posts regarding the information that get's passed to the camera body from the lens. This has been prompted by some questions I had and which I'm in the process of doing some investigation of. Also, the suspected incompatibility between some lenses and camera bodies suggested by some forum posts but yet to be confirmed.

Rather than try and cover everything in one long post I thought I would split it up and start here with a general explanation of the linkage between lens and camera.

Besides the bayonet itself, there are, up to, four points where the lens and body couple together. Earlier AE lenses had three then a fourth was added to MM lenses to tell the camera a MM lens is attached. The diagrams show the points of contact on the body and the lens with a description of each below.


Aperture Linkage Pin/Lever. The pin on the lens rotates as the lens aperture is changed and couples to a lug (described as a lever in the diagram) on a ring that rotates around the camera lens mount and which, in turn, couples to a device that converts the position of the ring into an electrical signal. On earlier cameras this was done using a potentiometer (variable resistor) which was part of the metering circuit. On later cameras, the potentiometer was replaced by an encoder that outputs a digital code.

The value passed to the camera represents the number of stops that the lens has been stopped down from maximum. It doesn't represent an actual aperture value.

Aperture Scale Coupling Pin/Lever. The 'pin' on the lens may actually be a lever or a shaped lug depending on the lens. It is in a fixed position that represents the maximum aperture of the lens. It couples with a lever on the body to transfer this information to the camera so that it can display the actual aperture in use. On earlier cameras a mechanical system, that linked the maximum aperture information and the number of stops the lens has been stopped down, was used to display the aperture in use. On later cameras with electronic displays it is done electronically.

The Contax S2/S2b and some Yashica cameras that don't have an aperture display in the viewfinder, don't use this feature.

Automatic Diaphragm Action Pin/Lever. This lever is driven from the camera and causes the lens to stop down to the selected aperture. On later MM cameras when used in shutter priority or program modes, this lever will move just the correct amount to stop the lens down to the required aperture.

AE/MM switch (not shown on diagram). On MM lenses, an extra lug was added which extends just beyond the bayonet mount and engages with the switch on the camera. The switch is a three position switch. The first, default, position is for AE lenses (AE lenses don't have the extra lug so the switch doesn't move). The third position is for MM lenses but there is also a mid position which I intend to be the subject of one of my following posts.