Wide Rolleiflex lenses

[Humphrey]

I will try again with a photocell. I found audio an easier way to get the results - the photocell is very slow when trying to get the adjustment correct at the same time. Stay tuned.

 

[AgX]

Those are pretty ugly but not beyond salvation. Strange as it might sound, I'd take a black fine-tip Sharpie to the scratches and fill them in. Get a lens shade for it, and use it. At this point, you got the camera for free, so what's the harm in trying? Look around APUG for an old classified ad/discussion thread Jim Galli had posted about a lens that was old, rare, and literally cracked all the way through. It still worked. The scratches on yours are ugly, and certainly harm resale value, but if you keep the sun out of the frame and have the front element well-shaded, you should still be able to make good images.

One might even try a patch over all that scratched area.

 

[BrianShaw]

Depending on the type of shutter and which speed, the accuracy varies from a decent approximation to useless.

The function of a shutter is to control the duration of admission of light to the film; measuring the duration of the sounds the shutter makes will only work - albeit not really well - at the very slowest speeds. With a focal plane shutter, the results I got were utterly useless at any speeds above the full-gate speed.

I was looking for an example; some data. Let's restrict the example to leaf shutters since a Rollei is the topic of discussion in this thread.

Is the difference you have measured greater than 1/3 stop, which is approx. the nominal max tolerance?

 

[E. von Hoegh]

I was looking for an example; some data. Let's restrict the example to leaf shutters since a Rollei is the topic of discussion in this thread.

Is the difference you have measured greater than 1/3 stop, which is approx. the nominal max tolerance?

I didn't keep notes of the results. At the slower speeds, say up to 1/25, if you picked the right peaks to measure between the discrepancy was not terrible, within your tolerance anyway. After that it was increasingly difficult to find the reference points - and remember I had a simultaneous trace from the photocell to guide me.
But, what is the use of a calibration instrument that itself is only good within 33%? Could you diagnose a dysfunctional electronic circuit with a volt/ohm meter that was good only to 33% fullscale?

 

[BrianShaw]

So... are you trying to say that you don't know for sure? Nothing wrong with that. Or are you trying to say that the difference between a sound card reading and a photocell reading could be similar if one knew how to accurately read the sound card waveform?

 

[E. von Hoegh]

So... are you trying to say that you don't know for sure? Nothing wrong with that. Or are you trying to say that the difference between a sound card reading and a photocell reading could be similar if one knew how to accurately read the sound card waveform?

Well, my premise is that looking at the waveforms of the sounds a shutter makes as a means of measuring how long it lets light hit the film is a poor method. The sonic waveform is messy, it's hard to know which spikes represent what event. As I said, the higher the shutter speeds the less useful.
On my setup, which was for the purposes of comparing the two methods, the photocell - phototransistor actually - gave unambiguous results, not so the contact mike. I think I've seen a circuit somewhere that allows the use of a photocell with the Audacity program- that really would be the way to do it, since the circuit had I think three components and a 1.5v AAA cell.
Personally, I'm not going to waste my time with such a method as using a microphone, it isn't much better than comparing the shutter in question with a known good shutter against a white wall.

If I can find that circuit I'll post the link.

 

[Humphrey]

Here
http://www.baytan.org/prak/shutter.html
I used this one myself, but found too many spikes compared to the audio.

I can show you the difference tomorrow.

 

[E. von Hoegh]

Here
http://www.baytan.org/prak/shutter.html
I used this one myself, but found too many spikes compared to the audio.

I can show you the difference tomorrow.

The spikes might be due to your light source - I use a somewhat similar circuit, with a phototransistor, with an incandescent light source and get clean waveforms, essentially a squarewave.

edit - that circuit isn't as similar as I thought, it feeds a pulse through the 4300pf capacitor when the phototransistor turns on, then another pulse when it turns off.
Mine gives a signal as long as the phototransistor is "on", then goes back to zero when the transistor goes dark hence the squarewave. The voltage of the signal is adjustable with a pot. If I can find a way to scan it I'll post it, but beware it was intended to work with a scope the circuitry of which will amplify DC - the soundcard will likely not pass dc.

 

[Humphrey]

My scope is far too basic to be of any use, so I used Audacity, available on the net. I then went on to use Audition which worked better.
The results with the phototransistor and audio editor were very close to the microphone results.

I tried an online scope but have never understood how to use them.

 

[Bill Burk]

I did a series of shutter tests on my Retina I and I wrote about the experience here...

(there was a url link here which no longer exists)

I used a graycard and took photographs in daylight and measured the densities.

I took photos including a record-player spinning at 78 RPM and measured the arc.

And I used a photocell-based electronic timer.

I found that graycard provided best estimates of shutter speeds 500, 250, 100 and 50.

The record-player gave best estimates for shutter speeds 25, 10 and 5.

And the electronic timer gave the best estimates for speeds 2 and 1.

 

[E. von Hoegh]

I did a series of shutter tests on my Retina I and I wrote about the experience here...

(there was a url link here which no longer exists)

I used a graycard and took photographs in daylight and measured the densities.

I took photos including a record-player spinning at 78 RPM and measured the arc.

And I used a photocell-based electronic timer.

I found that graycard provided best estimates of shutter speeds 500, 250, 100 and 50.

The record-player gave best estimates for shutter speeds 25, 10 and 5.

And the electronic timer gave the best estimates for speeds 2 and 1.

Testing a leaf shutter has to take the efficiency of that type of shutter into account.

 

[Bill Burk]

Testing a leaf shutter has to take the efficiency of that type of shutter into account.

This is where the gray card test excels. My test compares expected vs actual density of an in-camera graycard exposure... The negative has a step wedge exposed on it by sensitometer, so I have a graph of the actual characteristic curve... Mark the x-axis under the expected exposure based on the exposure calculator dial on the meter... And another mark on the x-axis under the actual density. The difference is the deviation from nominal marked shutter speed.

Granted, it includes any error of f/stop marking and also includes flare. It also includes deviation due to spectral difference between the light used on the graycard and the light used on the sensitometer. But it gives me the best estimate I could get.

 

[BrianShaw]

Testing a leaf shutter has to take the efficiency of that type of shutter into account.

Isn't leaf shutter efficiency a function of the aperture rather than the type of shutter?

 

[Bill Burk]

Isn't leaf shutter efficiency a function of the aperture rather than the type of shutter?

Right you are BrianShaw

I had overlooked evaluating the exposure deviation at various (wide open vs mid vs stopped down) f/stops for the higher shutter speeds.

 

[E. von Hoegh]

Isn't leaf shutter efficiency a function of the aperture rather than the type of shutter?

Both, but primarily aperture for leaf shutters. There is of course a huge difference in the efficiency of leaf vs focal; plane shutters.
There's a reason that, the bigger the (leaf) shutter the lower the top speed.

A pretty good primer on shutters - http://collectiblend.com/Library/Photographic_Shutters_Neblette.php

 

[BrianShaw]

Both, but primarily aperture for leaf shutters. There is of course a huge difference in the efficiency of leaf vs focal; plane shutters.

Right. But we're talking about leaf shutters in this thread.

 

[E. von Hoegh]

Right. But we're talking about leaf shutters in this thread.

True. But, the thread was originally regarding scratches on the front glass...

 

[BrianShaw]

Yes of course... but a scratch on a lens in a leaf shutter. ... and a German scratch too.

 

[E. von Hoegh]

Yes of course... but a scratch on a lens in a leaf shutter. ... and a German scratch too.

I still bet he can fill those gouges with India ink and use the lens without trouble. Blacking them might even improve the efficiency vs aperture curve at higher speeds...