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Converting the camera to prime focus

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Offline RaduP

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Converting the camera to prime focus
« on: 17 / May / 2008, 17:56:59 »
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A while ago, I came up with the idea to remove the lens from a P&S camera so that I can put it directly to my spotting scope or telescope.
I had some mixed results with this.
The cameras with fixed focus (no lens controls) work the best, because the camera won't complain about not being able to move its lens.
However, only the CMOS cameras with no shutter (electronic shutter only) seem to work properly. A CCD camera that I tried, a Samsung Digimax A503, will not work very well with the shutter removed, because on long exposures it would do dark frame extraction (which doesn't work without a shutter), and on short exposures the CCD lines do not have the same exposure (3 interleaved lines with different exposure).

Now, CHDK could fix some of those problems (turn off the dark frame), but I am curious if there is a way to make the camera not complain about the lens being removed.
One other question that I have is, can the Canon P&S cameras use only an electronic shutter, so no additional exposure happens during the sensor reading phase?
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Offline Microfunguy

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Re: Converting the camera to prime focus
« Reply #1 on: 17 / May / 2008, 18:42:11 »
I have removed the lens from a number of Vivitar fixed-focus non-zoom cameras in order to attach them to microscopes and telescopes.

I had to make fast acting mechanical shutters, normally from pager motors.
If the light is not very bright, they close sufficiently fast after the exposure.
Otherwise, they do not and you get the interlacing effect.
On a microscope, the simple soloution (with my setup) is to use flash.

I was thinking exactly the same as you today about the A460.

It is inexpensive and gives very nice results.

The thing that puts me off is the mechanical shutter needed for outdoor use and the various fedback signals the DIGIC processor expects as it turns on, zooms and focuses.

It is easier to use afocal projection and retain the lens.


David
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #2 on: 17 / May / 2008, 19:48:45 »
I'm glad to see that someone else tried that too ;)
I think some CCD chips do have an electronic only shutter, basically what they do is transfer all the information in an area of the chip that is not exposed to light, where it can then be read without further exposure from the light.

With the lens, do you think there is no way to make the camera just ignore the errors? Isn't there somefunction that checks different sensors, and if it detects an error it just complains and shuts down?
If this is the case, perhaps bypassing that function (or put a ret at the beginning or something) should take care of it.

The reason why I am not so happy with afocal coupling is that:
1. You lose some light.
2. Assuming you have a very good microscope/telescope, the camera lens will get in the way and add distorsions, chromatic aberations, etc.
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Offline Microfunguy

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Re: Converting the camera to prime focus
« Reply #3 on: 18 / May / 2008, 07:49:12 »
Quote from: RaduP on 17 / May / 2008, 19:48:45
I think some CCD chips do have an electronic only shutter
Hybrid cameras (such as Aiptek) seemed to be like that.
I added C-mount to the DV5700 (I think) and even moved the screen to the other side on one so that I could get a pair nearer together for stereo.

Problem was, at the time, I had no manual control over exposure.


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the camera lens will get in the way and add distorsions, chromatic aberations,

Yes, the distortions are quite bad.

Probing the firmware is a very time-consuming business that may lead  nowhere.

May be worth looking at hybrid cameras again to see if the features now include better control of exposure and white balance.

I have to say that I was very pleased with photos taken on the microscope with the lensless Vivicam but the shutter motor is rather bulky.

Did not need any electronics, the Vivitar shutter signal drove it directly.


David
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Offline Psychokitty

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Re: Converting the camera to prime focus
« Reply #4 on: 18 / May / 2008, 08:36:32 »
The non-electronic shutter is part of the lens assembly?
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Offline Microfunguy

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Re: Converting the camera to prime focus
« Reply #5 on: 18 / May / 2008, 09:19:04 »
Quote from: Psychokitty on 18 / May / 2008, 08:36:32
The non-electronic shutter is part of the lens assembly?

Yes.

On the Vivicam, a brief pulse is applied to some coils to rotate a tiny armature that carries very thin lightweight vanes.
When the pulse is finished, a weak magnet keeps the vane in its current position.

A pulse of opposite polarity(on the same two wires) then swings the vane back to the open position.

The mechanism is tiny, does not have to move far and can move very fast.

It is extremely difficult to scale that up to a larger size, it is too slow.


David
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Offline DataGhost

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Re: Converting the camera to prime focus
« Reply #6 on: 18 / May / 2008, 16:29:42 »
Can't you just break the glass out of the lens assembly so the camera's lens still 'works' and the camera doesn't notice anything? Else it'll probably complain with the famous Exx error messages. Still then, those can be bypassed (of course) but it'll be difficult. I already bypassed the assert function in my camera's firmware, it'll ignore an error and not shut down when something bad happens (instead, it'll show me where the error happened and then stop working partially). Maybe this is also possible with Exx errors.. heck, maybe they use the very same function. Fact remains that I hooked the assert function because it was loaded in memory somewhere (read: Canon developers put in a bypass functionality) which might not be the case with the Exx errors.

CCD readout might be acceptable on long, lowlight exposures but as you said, you'll notice changes in exposure. This is just because of the way a CCD works, at least the ones in Canon cameras, I believe. It's possible to quickly discharge a CCD before shooting (that's why the shutter doesn't have to be closed before shooting) but not to prevent charging without a shutter. I have no idea how those 'hybrid' cameras work but I think you can be sure it requires the shutter if it has one.
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #7 on: 18 / May / 2008, 19:01:17 »
Breaking the lens it's not so easy, because there are a lot of them, and doing so might damage the sensors the camera uses to see if the lenses are OK.
Also, even if you break then and get away with it, the whole for the light is too narrow (since the lenses focus the light through a small opening), so you will get severe vignetting.
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Offline Microfunguy

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Re: Converting the camera to prime focus
« Reply #8 on: 19 / May / 2008, 04:49:14 »
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Offline RaduP

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Re: Converting the camera to prime focus
« Reply #9 on: 19 / May / 2008, 05:12:05 »
Quote
The Canon powershots do not use the shutter in movie mode (I assume).
I don't think any consumer camera uses that.
They just skip the lines, so only the lines with proper exposure are used. This sucks, because it would have been much nicer if the video mode actually took the whole sensor data then resized it to 640x480 (so much better noise reduction and image definition).

I have a DSLR camera that I do use with my spotting scope, but the advantage of a P&S is that the pixels are much smaller so in the crop factor is bigger. Of course, you get more noise, but sometimes the tradeoff is acceptable.
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