return link

Sunday, 21 July 2019

Zeiss -v- Yashica ML lenses - 200mm f/4

I've had the opportunity to do a side by side comparison of a couple of Zeiss and Yashica lenses. It's not the sort of thing I normally bother about but one of the lenses is the Yashica 200 f/4 ML C (compact) which has an excellent reputation and I was interested to see how it compared to its Zeiss equivalent. The other comparison is between the Yashica 50mm f/1.7 ML and its Zeiss equivalent. That will appear in another post (eventually).


Zeiss                                     Yashica
The two lenses are very similar in size and weight. Here's the specifications for both:


Elements/Groups
Angular field
Min. Focus
Aperture range
Size (mm)
Weight
Zeiss
6/5
12° 40’
1.5m
f/4 – f/32
66.5 x 122
550g
Yashica
5/4
12° 30’
2.5m
f/4 – f/22
64 x 113.5
535g

The Zeiss has a filter size of 55mm, the Yashica 58mm.

This is not a scientific comparison, just a few shots on each lens compared against each other. I attached the lenses to my Sony A7II and photographed the roof of a nearby house putting the corner of the roof alternately in the middle of the frame and in the corner of the frame. I took photographs at f/4, f/11 and f/22.

I also took photographs of some out of focus highlights and also of a blank wall to check for vignetting and another wall to check for distortion.

The last photographs of the wall (not shown here) showed both lenses have slight pincushion distortion with nothing to choose between them. What they also showed was the focal length of the  Yashica is about 95% of the Zeiss. This is contrary to what the specification suggests. I'm not able to measure the exact focal length but just did a comparison of the two.

Vignetting at f/4 was very similar with both lenses.
YashicaZeiss










The images of the out of focus highlights are similar.

Zeiss

Yashica


Here's the rest of the images to compare for sharpness and contrast. All the images are 100% crops.

Yashica centre f/4
Zeiss centre f/4

Yashica centre f/11

Zeiss centre f/11

Yashica centre f/22

Zeiss centre f/22

Yashica corner f/4

Zeiss corner f/4

Yashica corner f/11

Zeiss corner f/11

Yashica corner f/22

Zeiss corner f/22
Both lenses are showing chromatic aberration when used on my Sony A7II. More so towards the edge of the images as is usual. I don't think there's any significant difference between the two lenses though.

One area of difference between the lenses is their compatibility with converters. Zeiss made x1.4 (Mutar III) and x2 (Mutar II) converters specially matched to some of their lenses including the 200/4. These converters can't be used with the Yashica as they are mechanically incompatible. But other converters can be used including the Zeiss Mutar I x2 converter. I took some more photographs using the Mutar I and Mutar II converters. The images are 100% crops.

Yashica f/4 Mutar I

Zeiss f/4 Mutar II
Yashica f/8 Mutar I

Zeiss f/8 Mutar II
My conclusion is that there is negligible difference between the two lenses. Yes, you could say one is better than the other in some instances but it's not always the case that the Zeiss is better than the Yashica which is what might be expected. In normal use, I would be happy to use either based on these results.

Sunday, 21 April 2019

FX-3 Super 2000 - spot the difference

Can you spot three differences between these bodies? (click on the images for larger versions).



So what's the difference and why.

The top one is the earlier version of the FX-3 Super 2000 (I call it the mk1), the bottom one is the later version (mk2). The visible differences are the strap lugs, the badge and the finish on the grip - the mk2 has a moulded finish to the grip while the mk1 has a stick on, leatherette, cover that matches the other covers.

There are a few internal differences as well but they are pretty insignificant. A few changes to the cover mouldings to reduce the part count mainly. I did replace the shutter in the top one of the two examples shown and found a slight difference between the one fitted and the spare one I had which may have come from a later camera. But it only required the swap of one gear to make it compatible.

I don't know why these changes were made. The later one appears slightly simpler in construction so it may have been a cost saving exercise to make assembly easier and quicker.

Anyone looking to buy an FX-3 shouldn't have any concern about the differences - they make no difference to the function or the reliability of the camera.

Note: In calling these two versions 'earlier' and 'later' or 'mk1' and 'mk2' I'm making assumptions about their age. I might be wrong. It's possible what I consider to be the later one might be the earlier one. But as the mk1 is more similar to the earlier versions of the FX-3 I'm assuming that one came first. It's also possible they were made in parallel but in different factories. If anyone has any information, I would be interested to see it.

Wednesday, 17 April 2019

Documents update

I've just added the Yashica FX-D repair manual to my documents page.

One useful item in it is a clear description of how to align the viewfinder LEDs. This is just as relevant to the 139 and as I always end up turning the wrong screw in the wrong direction, I'll be keeping a copy of this somewhere to hand.




Wednesday, 13 February 2019

Is your 139 locked up? This may help.

The Contax 139 is an electronically controlled mechanical camera. 'Mechanical' in that all the physical operations are driven directly by operating the film advance lever or by springs that are tensioned by the same action. Those springs subsequently drive the mirror up, rotate the shutter main shaft, drive the shutter curtains and return the mirror back to its normal position - in that order. Without any electronic control, all the steps in the sequence will still happen if manually triggered. The electronics just introduce a delay between the release of the first and second curtains by blocking the release of the second curtain with an electro-magnet and so controlling the period the shutter is open for.

Sometimes the sequence might not complete, or maybe fails to start, leaving the camera in a blocked condition where it's not possible to operate the film advance lever and the shutter release does nothing. Here's some tips on identifying where the problem could be and what might be done about it.

The first step is to identify if the sequence has started and, if so, at what point it has stalled. This is done by inspecting the position of the mirror and the shutter curtains. Check if the mirror is up or down. Also check if the shutter is open or closed and, if closed, whether it is still cocked or not. The following two pictures show the shutter in both cocked and released condition looking at the back of the shutter.

Shutter cocked
Shutter released
Possible scenarios:

1. Mirror is down and shutter is still cocked.
The sequence hasn't started. Watch the data back LED located at the bottom left of the shutter (visible in above pictures) and press the shutter release. If the LED flashes, the most likely fault is the release magnet is stuck. The release magnet is a permanent magnet which holds the mirror mechanism in its cocked condition. To release the mirror, an electro-magnet, wound around the permanent magnet and in opposition to it, is energised so cancelling the permanent magnet field and releasing the mechanism. The face of the magnet can become contaminated causing the release lever to stick to it even when the magnetic field is cancelled. The solution is to clean the magnet and release lever faces. There is more information on this on my DIY page. If the data back LED doesn't flash, the release signal is not getting through to the magnet driver circuit. Most likely cause is the transfer switch but there could be other reasons. More investigation is required.

2. Mirror is up and shutter is still cocked.
When the mirror reaches its up position, the mirror mechanism triggers the shutter. See the bottom of the page for a description of the couplings between the mirror mechanism and the shutter. With care, it is possible to manually trigger the shutter.

Triggering shutter
If the shutter triggers, the shutter is not at fault and the problem is with the mirror mechanism. Most likely cause is the lever of the mirror mechanism that contacts the shutter release lever is seized due to corrosion of the snap rings holding the lever onto its pivot.

Corroded snap rings
If the shutter doesn't release even when manually moving the release lever, there is a fault with the shutter. It's possible something is blocking the shutter, such as a piece of broken film, so it's worth trying to blow any debris out of the shutter with a can of compressed air. Other than that, the shutter needs removing for investigation.

3. Mirror is up and shutter is open.
The first shutter curtain opens immediately the shutter is triggered. The second curtain is held by the shutter magnet. If the second curtain fails to close the magnet may be contaminated and the lever that releases the curtain is stuck to it. This is easy to check visually. See the 'Triggering shutter' picture above. The white plastic lever that is held in position by the magnet is clearly visible. In the picture, the lever is in its released position. If the magnet has released the lever but the second curtain doesn't close, there is a fault with the shutter. See previous scenario.

4. Mirror is up and shutter is closed but not cocked.
In this instance, the first thing to check is if the shutter has fully closed. Compare the shutter with the 'Shutter released' picture above. There may only be a millimetre of difference in the position of the shutter blades but that is enough to cause a problem. If the curtain isn't fully closed, it may be pushed upwards by pushing against one of the rivets. This may close the curtain and release the mirror. If this happens, the problem is likely to be the second curtain brake which can become seized, or very tight, and prevent the curtain from fully closing. There is information on my DIY page about this issue. If the shutter is fully closed but the mirror hasn't returned then the problem is likely to be with the mirror mechanism again as in 2 above.

5. Mirror is down and shutter is not cocked.
The sequence has completed normally.

Mirror box/shutter couplings

These pictures of the shutter and mirror box show the two points of contact between them. The green arrows show the coupling used to trigger the shutter and the red arrows show the coupling used to lower the mirror.



Saturday, 9 February 2019

Does your 139 over expose?

If your 139 has never been serviced or had its meter adjusted, chances are it will over expose.

Almost every 139 I've seen has had a degree of over exposure. Usually between a half and one stop but sometimes more. Recently I had a 139 that overexposed by a couple of stops and decided to investigate further. This lead to me discovering that the meter sensor had become cloudy. Checking the sensors in some other cameras I found nearly all of them were cloudy to some extent and this seems to be the reason why 139s generally over expose. Looking closely at the sensors, there is a glass filter fitted over the sensor and the cloudiness is under the glass. It's impossible to remove. The glass filter is very thin and is stuck down and any attempt to remove it results in its destruction. Under the glass is a clear compound - could be silicone or something similar. It seems it's this which is going cloudy.

Here's just three I picked at random from my collection of donor cameras. You'll see two have cracked filters also although I don't think that's a problem.




To compare, here's a clear one.


In a few cameras where the cloudiness has been quite bad, I've replaced the sensors but I only had ones removed from donor cameras and they were also cloudy to some extent. What I needed was a new replacement and, amazingly, I seem to have found one.

The sensor I found is mechanically identical and has the same glass filter on it. The specification says it's sensitive to the visible spectrum with the filter removing an extended sensitivity into the IR region. As I had no specification for the original, the only way to find out if the new sensor was a good replacement was to try it. I removed a sensor from a working camera, having first done some exposure checks, then replaced it with the new one. Repeating the exposure checks gave almost identical results but probably half a stop less exposure which would be about correct as the original sensor I removed was cloudy.

For anyone who wants to replace their own sensor, the replacement I found is part number VTB8440BH from Excelitas Technologies. I bought mine from RS-Online (UK).

Edit: Couldn't resist adding this picture of a sensor removed from a 159. The 159 clearly also suffers the same problem. This one was over exposing by one stop.


And in case anyone is wondering if the flash meter sensor also has the same problem, it seems it doesn't. The flash meter sensor appears to be the same, or a similar, sensor but there is no filter on it and the ones I've checked are perfectly clear.

Wednesday, 30 January 2019

Some Zeiss/Contax lenses under expose by half a stop!

This is a continuation of a previous post on how the Contax lenses communicate to the camera body in which I mentioned I was doing some investigation into some questions I had and also some forum posts that suggested some lenses had compatibility issues with some Contax bodies.

To deal with the second issue first - I've not been able to duplicate any of the problems I've seen mentioned that might suggest some incompatibility between some lenses and bodies. I suspect these problems were due to individual lenses or bodies that had one or more faults.

I have, however, determined that the information passed from the lens to the body differs between lenses and that means, in some cases, certain lenses will cause a half stop under exposure.

The questions I had were raised by references in a few different Contax body service manuals to a feature called 'theta compensation'. This is something that appeared to relate only to some lenses. I initially tried to discover what theta compensation was but have been unable to find anything. Even an email to Zeiss was unproductive with Zeiss saying all the information was passed to Yashica. So I took a different approach and started to look at individual lenses that appeared to have theta compensation to see if I could find a difference between them and other lenses.

I was able to identify two lenses in my collection that have theta compensation. I was able to do this because those lenses have a different tab that couples to the AE/MM switch on the body. The AE/MM switch on the body is usually referred to as the 'theta switch' in the service manuals and it has three positions. The first, normal, position indicates an AE lens is fitted, the third position indicates an MM lens is fitted, but there is a second, middle, position that indicates an MM lens with theta compensation is fitted. So lenses that have theta compensation have a narrow tab that only moves the switch to the middle position.

Here's a couple of pictures of two of my lenses that show the difference. I've outlined the tag on the lens in red and the switch lever in green so their shapes and positions are more clear. The first is a 85mm f/2.8 MM lens. Note the tag is pushing the switch all the way to the end of its travel.



The second is a 50mm f/1.7 MM lens. Note the tag on the lens is notched and it only pushes the switch half way.



Besides the 50mm f/1.7 MM, I also found the 18mm f/4 MM had the same shaped tag so that is the second lens I have that has the feature.

To try and ascertain if there were any differences between lenses with and without theta compensation, I set up a test rig using the mirror box from a 139. The mirror box has the lens mount attached and the various couplings to the lens and has a potentiometer (variable resistor) directly coupled to the aperture stop down ring of the lens mount. By measuring the resistance of the potentiometer with various lenses attached and at all apertures, I was able to plot graphs of resistance against the number of stops the lens was stopped down. Here's a picture of the rig and the results.



The X axis is the number of stops the lens is stopped down. The Y axis is the measured resistance.

What is clear from this is there are two distinct groups of results with one group shifted by half a stop from the other. Two of the lenses in the group shifted to the right are the 50mm f/1.7 MM and the 18mm f/4 MM which had previously been identified as having theta compensation. Surprisingly, the third lens in this group is a 50mm f/1.7 AE lens. This is surprising as the AE lenses were designed and manufactured before MM cameras were brought out and before there was any method of detecting that such a lens had been fitted to the body. As a check that this wasn't just a fault of the individual lens, I tested a second 50mm f/1.7 AE lens and got identical results.

The second test I did was to check the position of the maximum aperture lever for each lens. In the 139 the lever is coupled mechanically to the aperture display so there's nothing that could be measured other than physical position but it was clear that the lenses that exhibited the half stop shift in the aperture stop down lever, also had a half stop shift in the position of the maximum aperture lever.

Here's the inside view of the maximum aperture lever (arrowed). You can see the black marks on the chassis where I've recorded the position for different lenses.



My first thought was that these two half stop shifts would cancel each other out so there would be no effect on the metering but it's not that simple. In the 139, for instance, the maximum aperture lever plays no part in the metering, it is only used to display the correct aperture in the viewfinder. The metering is done purely from the potentiometer coupled to the aperture stop down ring. So, not unsurprisingly, lenses that have theta compensation under expose by half a stop when used on a 139. This is easily confirmed by metering a scene with a lens with theta compensation then again with a lens that doesn't. The half stop difference in the meter reading is quite obvious.

With other MM bodies I thought the exposure error might not happen but I tested an RX, RXII and a 167 and it does happen and in all metering modes.

Conclusions

In the 167MT service manual there are some tables that show the aperture associated with each position of the aperture stop down lever and the maximum aperture lever. The tables have two different values, with a half stop difference, for lenses with and without theta compensation. This effectively confirms my findings that the physical position of these levers differ on lenses with theta compensation. Or, put another way, any particular position represents a different value on lenses with theta compensation to ones that don't.

You would think, therefore, that the MM bodies would carry out a different exposure calculation depending on the position of the AE/MM switch. I have tried manually changing the position of the switch but it makes no difference to the meter reading. Either my expectations are inaccurate, or the bodies don't have the theta compensation feature fully implemented.

Clearly I'm not able to test every combination of lens and body in every metering mode - I don't have examples or the time - and it may be that the half stop change in metering only affects a few lenses, but the phenomenon definitely exists. Whether it's a problem is for individuals to decide. Does half a stop error in metering matter? In the days when I used to use transparency film, I would have said it does.

If anyone has anything to add to this I would be very interested to hear from them. If you have seen the issue with particular lenses then which ones and with which bodies and in what metering mode? Also, if you find any lenses that display the wrong aperture in the viewfinder when other lenses are OK, I would be interested in the same information. And, finally, if anyone has any idea what theta compensation is (specifically related to the lenses under discussion), please let me know.

(Edit)

There was one other test I did which I failed to mention above, probably because it produced no useful information at the time. However, on reflection, the fact it showed no difference between lenses with theta compensation and those without is relevant. The test was to attach the lenses to my A7, digital camera, and check for differences in meter readings. The A7 has no connections to the lens and simply measures the light passing through it. The result was there is no difference in the light transmitted between lenses with, or without, theta compensation. This is significant because, if the lenses with theta compensation did transmit a half stop more light, the apparent half stop under exposure would be correct and make all the above rather inane.

Sunday, 27 January 2019

The Bitser

Bitser (Bitzer): "A thing that is made from parts that originally did not belong together."

I acquired another 139 parts camera recently. These are cameras that have too many problems to make it economical to repair. They end up in my 'parts camera' drawer and get regularly picked over when I'm in need of a part to repair another camera. I have nine or ten I guess, some of which are little more than a chassis with a few parts left attached. As I was adding the most recent one to my collection, I thought about the possibility of making a complete, working, camera out of the various bits and pieces.

Always up for a challenge, I picked out the best chassis I could find as a starting point. The chassis had a shutter, which tested as OK, along with the film advance mechanism, which had a problem, and the electronic PCB. A mirror box with a clean viewfinder came from another camera. The top plate and all the other parts came from several other donors.

With the film advance issue resolved, I assembled all the parts onto the chassis, cleaning and lubricating etc. along the way. I wanted to fit a base plate with a serial number that was of the correct period for the modification level of the camera. The chassis I used had the last version of the transfer switch and the mirror box had the later version of the release magnet and associated mechanism, so I needed a base plate with a high(ish) serial number. I found just one that fitted the bill. It was a bit bent and dented but a couple of blocks of wood and a hammer got it into shape and soon fitted.

The final thing, after a full function and film test, was to add some covers. I had some freebies supplied by Aki-Asahi and, in the spirit of using up what I had, I fitted those. I actually think they are OK though not a colour I would normally use. I also had some matching winder covers and so a winder I acquired with a camera recently got a quick overhaul and new covers fitted to complete the look.

I'm not sure I'm going to give it much use but I like how it looks and find it satisfying to have built a complete camera from spare parts. It will sit on the shelf for a while until I decide what to do with it.