Hasselblad Zeiss 80mm T* Shutter Accuracy - is this sort of OK?

[Geoff Bartlett]

So I recently bought lovely 500 C/M with an 80mm T* lens. Out of curiosity and too much time on my hands, I built a little rig to tim the shutter. To get right to it...

I'm sure my results could be challenged on technical and methodological grounds, but the same test on my 1963 Nikkormat returned more consistent and accurate actual times across most of the range.

So my questions are:

1. is this inaccuracy to be expected in the lens?
2. Is it tolerable (probably, as it amounts to roughly .25 of a stop)
3. could I expect a service to the accuracy?

Thanks

---------------------------
If anyone is interested, I built my test rig using an Arduino microcontroller and a couple of infrared LEDs. I could optimise my code to reduce response lag, but really the Arduino works in tens of micro-seconds so there's not much error at the more moderate shutter speeds

 

[shutterfinger]

This is my go to http://www.flutotscamerarepair.com/Shutterspeed.htm
1/3 stop either side of nominal is acceptable. CLA when speeds are 1/2 stop off for the most reliable shutter speeds.

 

[itsdoable]

That would be within the original manufacturer's tolerances, although they often came better. 50% at the top speed was not unusual.

There are also some variations in the exposure with leaf shutters at the top speed - the over all exposure wide open would be cumulatively shorter than stopped down, this is because the center of the leaf shutter opens first. At the top speed, the leaves open and close without a delay, so the periphery gets less exposure than the center. Integrating the light at the focal plane gives a better measure of the exposure corrections than just timing at these shutter speeds.

 

[Philippe-Georges]

With these speed variations, a Tri-X exposed at box speed and processed in X-Tol 1+1, wouldn't show a problem under 'normal' light conditions...

 

[Scott Micciche]

With the C or C T*, that 1/500s always seems slower than the prontor-shutter CF and later. I believe there is either a stronger spring or a secondary spring for that specific speed. I remember speaking with Hasselblad in Los Angeles about it when I had the lens in for a CLA. I would expect within 30% +/- to be ok, as long as you are aware of those timings and make the necessary adjustments, especially at f/8 and higher.

 

[Geoff Bartlett]

That would be within the original manufacturer's tolerances, although they often came better. 50% at the top speed was not unusual.

There are also some variations in the exposure with leaf shutters at the top speed - the over all exposure wide open would be cumulatively shorter than stopped down, this is because the center of the leaf shutter opens first. At the top speed, the leaves open and close without a delay, so the periphery gets less exposure than the center. Integrating the light at the focal plane gives a better measure of the exposure corrections than just timing at these shutter speeds.

Thanks for your thoughts. I had to think about this one for a while. A hypothetical ideal shutter would open and close instantaneously. But even my less that ideal shutter should still illuminate the entire frame evenly, otherwise wouldn't it vignette at high f stops?

Error from stated shutter speed aside, my lens also exhibited a wide degree of variation at each speed. Oddly enough, 1/125 was pretty much spot on.

 

[Geoff Bartlett]

With these speed variations, a Tri-X exposed at box speed and processed in X-Tol 1+1, wouldn't show a problem under 'normal' light conditions...

Thanks. I was thinking that any exposure error should be addressable at the printing stage anyway. It's been interesting to read the responses. I've never had much cause to look into the operation of my shutters, I just assumed they did their thing more out less in line with the age of the camera. I would not have though that a 20%-30% error was common even for good shutters.

 

[Geoff Bartlett]

With the C or C T*, that 1/500s always seems slower than the prontor-shutter CF and later. I believe there is either a stronger spring or a secondary spring for that specific speed. I remember speaking with Hasselblad in Los Angeles about it when I had the lens in for a CLA. I would expect within 30% +/- to be ok, as long as you are aware of those timings and make the necessary adjustments, especially at f/8 and higher.

Living in a place that can be quite sunny, 1/500 is a useful speed to have working properly. The lens is getting a bit of a clean up and tending to. Not through Hasselblad - would they even look at something that old now? - but I hope that it at least settles into a consistent error.

 

[Philippe-Georges]

It's rather simple to test a camera shutter your self, what you need is a smartphone, a 'PhotoPlug and the appropriate app.
The PhotoPlug, which is rather affordable, can be bought in Germany, look here: www.filmomat.eu/photoplug.

 

[Geoff Bartlett]

It's rather simple to test a camera shutter your self, what you need is a smartphone, a 'PhotoPlug and the appropriate app.
The PhotoPlug, which is rather affordable, can be bought in Germany, look here: www.filmomat.eu/photoplug.

True, but build your own is always more fun

I do wonder about the accuracy of a smartphone application at high shutter speeds (1/1000). A smartphone is doing many things concurrently and sampling the microphone port might not be its highest priority. While my microcontroller is much slower that a smartphone CPU it has only one thing to do. Even the less that ideal polling technique I used, I think I'm within 100 micro-seconds response time. I could make it quicker by recoding to use interrupts, but then I'd rather be taking photos

 

[Philippe-Georges]

The only thing I want to 'built' right now is replacing the broken waterboiler in my darkroom, so I can go on with my photography project, that's all...

 

[MattKing]

But even my less that ideal shutter should still illuminate the entire frame evenly, otherwise wouldn't it vignette at high f stops?

Leaf shutters don't vignette at any f stop. The light hitting the film just cycles through the available intensities - starting at none, increasing from low to the maximum, staying at maximum for a defined time and then decreasing again to none.

 

[Grim Tuesday]

Leaf shutters don't vignette at any f stop. The light hitting the film just cycles through the available intensities - starting at none, increasing from low to the maximum, staying at maximum for a defined time and then decreasing again to none.

That's exactly right. It helps me to understand it when I remember that the shutter is in the middle of the lens, so as it's moving it is like changing the f-stop. Unlike a focal plane camera, where the shutter is directly covering up parts of the film.

 

[Jim Kilroy]

So I recently bought lovely 500 C/M with an 80mm T* lens. Out of curiosity and too much time on my hands, I built a little rig to tim the shutter. To get right to it...

View attachment 271609

I'm sure my results could be challenged on technical and methodological grounds, but the same test on my 1963 Nikkormat returned more consistent and accurate actual times across most of the range.

So my questions are:

1. is this inaccuracy to be expected in the lens?
2. Is it tolerable (probably, as it amounts to roughly .25 of a stop)
3. could I expect a service to the accuracy?

Thanks

---------------------------
If anyone is interested, I built my test rig using an Arduino microcontroller and a couple of infrared LEDs. I could optimise my code to reduce response lag, but really the Arduino works in tens of micro-seconds so there's not much error at the more moderate shutter speeds
View attachment 271608

20%+/- on speeds from 1 second to 1/125 and 35%+/- on speeds 1/250 and 1/500 are the acceptable tolerances (according to ANSI when the C lens was manufactured). A properly tuned lens will be pretty much right on with the exception of 1/500 which is usually between 1/375 and 1/450. Every once in a while I’ll see a leaf shutter Zeiss lens (C, CF, CB etc.) that will go 1/500 or over. Unusual though. Cool tester you built there!

 

[john_s]

At least the OP knows what adjustment to make in selecting exposure settings, if it matters. I wonder if with more use the lubricants might ease up a bit and change the effective speeds? I have experienced this with a different type of MF camera (focal plane shutter in SL66).