Photographing a CRT Oscilloscope Screen Outdoors under shade

Hi!
First, let me say that I found your tutorials on photography among the best on the Internet. Thank you for providing those they are of great help.

I am an absolute beginner to photography. 2 weeks ago I didn't know what ISO, f stop and shutter speed meant. After reading your tutorials, I'm at least somewhat familiar now with those.

So today I was trying to photograph the face of an anolog oscilloscope to capture the waveform moving across it's screen (CRT) with a refresh rate of approximately 100ms

I was outdoors but in the shade under a tarp canopy. Bright sunshine.

The problem I encountered today was with Brightness. I had a very difficult time finding a combination of settings that gave me a dark enough image. I ended up with the following settings....ISO 80, f8.0, 1/30 shutter speed.
The camera was approximately 18 inches from the screen. I tried normal and macro modes.

This is a Canon SX20is Digital camera.

I found it very difficult to get the image dark enough. I ended up draping a towel over the subject and the camera just to get it down to a reasonable light level. I could not understand this.

Since the CRT image was refreshing at approximately 100ms I tried to set the camera shutter speed to just below 1/10 of a second, but adjusting the shutter speed any lower than 1/30 cause the image to be over bright and wash out.

The lowest ISO for this camera is 80. Smallest aperture setting is F8.0

Did I do something obviously wrong? Or is this simply a limitation of the camera?

Thanks in advance.
Randy

You're trying to deal with a lot of variables, without much experience or knowledge.

Outside? Lots of light. Slow shutter speed? Lots of light. You have to deal with balancing the subject with ambient light, and needing to use a long shutter duration just makes it worse.

Here's where you have to use ND filters, to cut down the overall amount of light entering the lens. ISO will only get you so far, as you've discovered, and so now you need to use other techniques. Shade is not a bad thing, but it's not enough, as you've discovered.

You probably need to start with a 6-stop ND filter, but that's just a guess (3 stops isn't a lot). You don't mention aperture, but f/8 will help, too. Then, you can compute the number of stops you need to cut by working from an acceptable exposure in your environment. Given a starting point, and given a target, you can figure out a filter strength.

One presumes the display will be bright enough to capture, since it can be seen in daylight.

In the old days, photographers used to through a black cloth
over their head so to shield them from incoming daylight as
they were looking at the ground glass on the back standard
of their camera.

Making a black paper cone to fit snuggly around the lens and
the oscilloscope's screen will simply and efficiently solve your
problem.

Dear OP:

In an effort to provide you with more clues about what to research in order to enhance your knowledge and skills, let's start with the Sunny 16 rule, which we use for shooting in bright, open daylight:

1/100s @ f/16, ISO 100.

You need 1/10s, at minimum, for your shot to record the entire pattern, if it cycles at 100 ms (10 Hz). 1/30 won't do it, by the way; it's not long enough for the entire pattern.

Let's adjust only the shutter speed to figure out how many stops away you are from your goal:

1/100 -> 1/50 = 1 stop
1/50 -> 1/25 = 1 stop
1/25 -> 1/13 = 1 stop
1/13 -> 1/10 = 1/3 stop.

You are 3.3 stops away from what you need. If you go on to 2 cycles, that's 1/5s, another 1/3 stop.

Changing your ISO from 100 to 80 only helps by 1/3 stop less. Your aperture, going from f/16 to f/22 (if your lens allows), would give you one less stop of light, so moving in the right direction.

There's too much light in your environment.

All that said: bare minimum, you are still 2 stops away from your goal. You need to remove two stops of light from entering the lens. Wrapping the entire setup in a thick, dark blanket might get the job done (you will need to eliminate light from every angle, not just above), but an ND filter will be a lot more convenient.... if you can even use one on that camera. Also: tripod. Forgot to suggest that.

Have you considered shooting at dusk, or at night? You haven't explained what you're hoping to accomplish (or even why a scope is outside?) so the only advice is, change up your environment, or change up your equipment.

I ordered an N2 - N1000 variable ND Filter
However, after reading the above post, I may also order a 6 or 10 stop filter.
Thanks for the assist

BlurredLines wrote: I ordered an N2 - N1000 variable ND Filter
However, after reading the above post, I may also order a 6 or 10 stop filter.
Thanks for the assist

I think a 6 stop is probably your best bet, but the variable will come in handy. The 10 will let you get multiple tracings of the pattern, which might also come in handy.

Note that some variable ND filters, at strong settings, create a "X" pattern due to the diffraction gratings interfering with each other. Usually usable at modest settings, however.