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Webcam Modding: Why Remove The Lens?


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Hi, sorry if this is a stupid question but can anyone explain why it is better to remove the lens from a webcam that is used for imaging? I guess there is a bit more light reaching the chip without a lens in the way but is there more to it than that?

Regards

Hugh

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Webcam lenses are made to focus at close range but the objects you're imaging are many millions of miles away. All the webcam lens is doing is magnifying what you've focused on with the scope. Generally webcam lenses are low quality and have their own inherent deformations of light. Some are even plastic.

It's better to focus using just the prime focus of the scope, and if you still want to magnify the image then use an astronomy lens for a clearer image with less deformations, or use software to zoom in. But I doubt you'll need to cos a perfectly acceptable image can be had with the scope alone and no lens. Hth :)

Edited by brantuk
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It is a bit strange and relies on the "fact" that a scope with an eyepiece in should not produce an image on the output side of the eyepiece. Your eyeball does that not the scope.

A scope is basically collimated light in, collimated light out, but no image out.

Collimated light being the term for light that come from infinity, or as close as makes no difference.

A webcam lens does the same as the eye - the eye takes the collimated light and focuses it down to an image on the retina (sensor).

So you could leave the eyepiece in and then put the webcam+lens on the output side of the eyepiece.

It does form an image (afocal imaging) but as said the quality of a webcam lens is generally low so the resultant image is poor.

The "simple" solution is to remove the webcam lens, throw the eyepiece at a cat and put the webcam sensor (no lens) where the eyepiece would have been = at the focal plane of the scope objective, and just put this internal image formed by this straight on the webcam sensor.

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  • 3 years later...

Carrying on needing simple information, it would seem to me that some object, like Mars, would be too small (without eyepiece magnification) to get any reasonabe resolution to the image.

Sensor pixel size must have an effect on small objects that processing would not be able to cope with.

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9 minutes ago, Unklewhale said:

Carrying on needing simple information, it would seem to me that some object, like Mars, would be too small (without eyepiece magnification) to get any reasonabe resolution to the image.

Sensor pixel size must have an effect on small objects that processing would not be able to cope with.

There's a balancing act between getting enough light on each pixel that it operates efficiently and resolving as much detail as possible.  What detail you can resolve however is limited by the size of the objective lens or mirror.  It's possible to calculate those limits and what focal ratio is required to achieve them with your specific camera sensor, then adjust the optical train accordingly using a barlow for instance.  If you're not getting sufficient light falling on each pixel of the sensor at that point then you have to start making compromises.

James

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I used an SPC900 myself for quite some time with a 127 Mak.  With that camera you probably want to be trying to get the focal ratio somewhere over f/30 as long as the image is still bright enough.  I used to use a Revelation 2.5x barlow with the kit Skywatcher barlow (with the lenses removed) as a spacer between it and the camera to get a bit more focal length.

With the small sensor of the SPC900 it can be a real pain to get a planet on the sensor at all, especially once you've ramped up the focal length.  I used to start with an eyepiece with a reticle, centre the planet, then add the barlow and recentre, then add the spacer and recentre again and finally switch to the camera (with the barlow and spacer).  It's a bit of a faff, but the sensor is only about 3.5mm x 2.5mm so it's easy to miss.  It can help to turn up the brightness and gain on the camera until you have the image on-screen, too.  Sometimes if you have them too low you just can't see the image.  You can always adjust them back down again later.

These were captured five or six years back with the 127 Mak, SPC900 and the barlow/spacer arrangement described above.  It's a transit of Io.

io-transit.png

The planets aren't ideally placed for imaging at the moment, but you do have another 3" of aperture so you should be able to get more detail when the seeing is good.

James

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39 minutes ago, Unklewhale said:

My other major problem is changing focus from eyepiece to camera. If you used that webcam, do you have any tips on that ?

If I was only imaging then between sessions I'd leave the focuser where it was for imaging.  For getting the target centered I never cared about focus, so didn't change it when using an eyepiece for that.

If you're switching between visual and imaging then it might perhaps be useful to focus on the Moon with an eyepiece, swap to the imaging setup and then count the number of turns of the focuser knob (and in which direction) to get in focus again.  That should at least get you somewhere close when you're swapping around in the future.

James

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Noted the Sky's the Limit 3x barlows are a bit longer than the norm, which from your comments JamesF, may be a slight advantage. Not a bad price, and some reviews suggest it isn't a bad lens.  I already have an Astro  Revelation 2x barlow,  so would it be worth getting the 3x, or will I notice little operating difference compared to the 2x when using a 8" SCT and the SPC900 ?

If I get another barlow, was considering maybe making the lens and webcam a semi permanent arrangement (dust protection for the sensor if nothing else).

 

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A couple of tips: The earlier idea of modifying a webcam for astro use now seems obsolete, as you can buy a Chinese made astro video webcam (probably not a very good one) for under £10 on Ebay, and good ZWO cameras cost not much over £100.

To focus, I always focused my SCT with a 25mm eyepiece pulled out by around 5mm, which I had determined by trial and error to be the correct distance, and then dropped in the ZWO camera.  This got the focus accurate enough so the blurry planet could be found on screen. (With a Startravel refractor you can pencil mark the focuser barrel).

I did not have much joy with Barlow lenses, finding that on the whole they just made the blur bigger, what with bad seeing and/or low planets.

A couple of days ago I got a good result with a x2 Barlow element screwed into the 1.25" nosepiece of the ZWO camera.  With Mars at over 40 degrees attitude.

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