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Author Topic: Photographing an O'scope screen  (Read 3772 times)
W8JX
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« Reply #15 on: March 03, 2011, 10:02:37 AM »

This is really pretty simple as to a solution. You have to be able to put camera is manual mode for shutter speed and set it to 1/30th of a second or so. You will also have to control exposure (aperture) for correct exposure. If you can get  auto to work here you are lucky. The human eye has "persistence" so that you see things that the quick eye of a camera will not record. (example with old analog TV when you take a picture it is usually garbled some unless you us a slow shutter speed.) Try this, if you can set ISO to 400 or 800 and shutter to 1/30 and play with aperture until you get a good picture. You might even have to go slower to 1/15th of a second.
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K8AXW
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« Reply #16 on: March 03, 2011, 11:20:48 AM »

All:

I think I am beginning to get a handle on this problem.  I've taken various suggestions presented here, analyzed them and came up with this possible solution.

I obtained a large cardboard box, painted the inside flat black.  I then cut a 5"H X 6"W hole in one end to accommodate the scope screen.

I then cut a round hole in the opposite end to accommodate the camera lens.  I attached the box to a short tripod with duct tape and tilted the box down and moved it in towards the scope.  I found it was necessary to remove the tubes from the overhead fluorescent lights to prevent light from entering the large hole in the box.

I left a 2" gap between the box and the scope so that when I took the shot I had part of the scope as well as the screen.  This gave meaning to the pictures.  In other words, I didn't have just a black square with illuminated 'dashes' as with a square wave.

Since the box was so large, it was necessary to use the zoom feature to get a full sized picture of the screen.  I left the camera on AUTO.  The results were encouraging. 

The pictures have the scope trace without reflections.  The trace was fairly sharp and leaving part of the scope in the picture gave the pictures meaning.

My next step is to find a more suitable box somewhat like the scope hood that KE4DRN sent a photo of. This will make the setup more manageable.

I think the key to this is leaving a gap between the box/hood and the scope to leave some light reach the scope face.

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AC5UP
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« Reply #17 on: March 13, 2011, 08:06:35 PM »

This is actually very simple once you learn how to control the lighting and exposure balance...

Adjust the scope brightness for a normal display. No bloom or flare in the bright portions but bright enough to show detail in all portions of the trace. Position the camera on a tripod (or Jerry rig) such that it's parallel and square to the face of the CRT. Turn off the flash and darken the room as needed to eliminate stray reflections on the graticule. A dark cloth draped above and around the 'scope and camera can act as a light shroud if necessary.

Check the user guide for your camera and choose a program or manual setting that gives you a slow shutter speed at an ASA equivalent of 50 or 100. The goal here is for the exposure to be long enough to cover several trace refreshes on the CRT at a sensitivity low enough that the camera doesn't try to lift the dark areas on the CRT above black / dark grey. Use the self timer feature so you won't jiggle the camera. 1/15 of a second exposure should give even brightness from left to right. If not, try a slower shutter speed.

Finally... Shoot a bit wider than what you need and crop the image with a photo editor like GIMP. You can also tweak the contrast and color balance so that if you didn't get it exactly right in the camera you can dial it in on the computer.
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K8AXW
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« Reply #18 on: March 14, 2011, 09:39:10 PM »

AC5UP:  Thank you for your response.  However, I have to disagree with you about it being "easy."  Your long paragraph that follows this "easy" statement points this out exactly.

So far I've found that it's beneficial to show part of the scope screen bezel to give the photo more meaning.  And therein lies part of the problem.  Once you back away from the scope to show the bezel then reflections on the scope screen start to show.

What I mean by "meaning" in the above statement is this.  If you turn off the room lights, get in close to the screen with a black cloth hood or whatever.... adjust the camera parameters so that you don't have "bloom" and you are photographing a square wave, all you will see in the photograph is a black background with two or more horizontal dashes.  If the scope has an illuminated graticule then this pretty well eliminates the problem but my scope doesn't have this feature.

I am still checking and reading any posts here about this problem.  Thank you one and all.  Please continue to "bring 'em on!"
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W7SMJ
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« Reply #19 on: March 14, 2011, 10:52:52 PM »

I have never tried this, but it would seem to me if you're using a tripod at a fixed distance you could take a picture of the scope in bright flood light to capture the graticule.  You then take your picture of the waveform in no light conditions.  Then take these two pictures and stack them so you have the graticle and waveform.  Since your tripod is fixed the overlay should be relatively easy to do.

I'm intriuged and might try this tomorrow night...

73,
Scott
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K8AXW
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« Reply #20 on: March 15, 2011, 08:28:28 AM »

SMJ:  Interesting thought.... but think you have seriously complicated an already somewhat complicated problem.  Using a digital camera, how do you "stack" pictures?  OK, you print them out and then "stack" them....... "overlay"?
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W7SMJ
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« Reply #21 on: March 15, 2011, 09:18:05 AM »

SMJ:  Interesting thought.... but think you have seriously complicated an already somewhat complicated problem.  Using a digital camera, how do you "stack" pictures?  OK, you print them out and then "stack" them....... "overlay"?

Not complicated at all.  I have seen "stack" and "overlay" used interchangeably with regard to digital images, although maybe they're different...  Anyway, there are several image packages that are easy to do this with.  I would suggest paint.net, it's free and not overly complicated.  I think it was developed by some MIT students...

If you use paint.net, paste one image in it (scope trace), add a layer, paste the graticle image on top of it, then adjust the opacity of the graticle image.  Done!

Works pretty slick and not complicated at all...

73,
Scott
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KG4RUL
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« Reply #22 on: March 15, 2011, 05:44:50 PM »

Many years ago I was using an oscilloscope to photograph the output waveform of electric fence chargers under development.  I was using a Tektronics scope with their camera mount and a polaroid back.  With the graticle not illuminated, I would open the shutter and use a single, triggered sweep to make the exposure then close the shutter.  I would then turn on the graticle and do a normal exposure using the shutter release.

One day I was working with the first pack of a fresh batch of polaroid high speed, panchromatic film.  I noticed that I was getting the graticle but NOT the trace!  I confirmed that the sweep was appearing by using the view port to observe it.  Not being able to figure out what was going wrong, I removed the partially used pack and put in into a normal camera. 

Shots taken of various scenes looked strange and an outside shot showed the grass in a strange way.  I then took a shot of a color wheel and discovered that the film appeared to have no sensitivity to green, the color of the scope trace.

So, I called the polaroid folks who put me into contact with their QC lab.  They made a quick check of other film packs from that same run and discovered that what I had observed was in fact true!  That resulted in a large recall of film packs.
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W7SMJ
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« Reply #23 on: March 15, 2011, 09:16:08 PM »

This actually wasn't too hard at all.  I have a five year old relatively inexpensive Canon A540 camera and it worked great with a tripod...

Here's my first image, just a picture of my scope in normal light:
http://www.flickr.com/photos/60621738@N05/5531263854/

That seemed to look OK and probably would work as-is...


Here's a picture of the trace I took dimmed down in low room lighting:
http://www.flickr.com/photos/60621738@N05/5530678723/

Here's a picture of the scope turned off in bright light:
http://www.flickr.com/photos/60621738@N05/5531264296/

I then copied the images into paint.net and then edited using the rectangle select tool to get only the screen of the dim trace and the scope turned off.  Using layering and adjusting the opacity I ended up with this:
http://www.flickr.com/photos/60621738@N05/5531263940/

I think it came out OK, although the trace looks slightly out of phase.  This was because I cropped both pictures before doing the overlay and i was slightly off in the dim trace pic.  As you can see it's hard to tell in the picture where the screen starts.  This could have been avoided by doing the crop AFTER the overlay.

Anyway, it really wasn't hard to do and really didn't take more than 5 minutes.  Give it a try!

73,
Scott
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K8AXW
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Posts: 3722




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« Reply #24 on: March 15, 2011, 09:31:08 PM »

SMJ:  Frankly, I though you was blowing smoke up my $ss but after looking at your results, I'm impressed!  This process is definitely worth a try.  I've never used paint.net..... or anything similar.  While I use and I'm able to upgrade, modify, repair computers, when it comes to software I'm as dumb as a coal bucket.

But, will check this out.  Many thanks for another path to investigate.

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