How does a webcam magnify?

[dazzst]

So you remove the EP, insert your webcam without its lens and fire it up. How does it magnify the image?

[Bizibilder]

It doesn't. You simply focus the image on the webcam's chip. The webcam chip is tiny - maybe 5mm square or thereabouts. You look at the image on a computer screen that is maybe 10cm by 8cm, or similar, so it appears much bigger.

[Ags]

It doesn't. The telescope objective forms an image on the sensor. The scale of the image is proportional to the focal length. The same principle applies to camera lenses (so a 55-250mm zoom gives 'x5 zoom'). A scope with a focal length of 1200mm gives much greater scale than even the biggest telephotos.

[LukeSkywatcher]

The scope acts as a lens which magnifies the image. Same with using a DSLR.

[dazzst]

The scope acts as a lens which magnifies the image. Same with using a DSLR.

Without an EP, how does the scope magnify. I've very confused.

[Ags]

The scope IS a big lens... You have to ask: "magnify what?" The EP magnifies the image formed by the scope. In contrast, the webcam simply records the image formed by the scope onto its pixels.

[Cubemaster]

The chip on the webcam can see. The focusing tube acts as the eyepiece and the mirrors on the scope magnify the image

[dazzst]

But different EP's give different magnifications!

[Ags]

But different EP's give different magnifications!

Yes, but you only get one image scale with the webcam, unless you use barlow lenses or reducers to change the focal length of the scope. If you put a x2 barlow in front of the webcam, then Jupiter (or whatever) will be twice as big.

[Cubemaster]

But different EP's give different magnifications!

The webcam gives one magnification.. Simples

[Probablynot]

Thank you, Dazzst, for asking a question that puzzles me too. I did ask in another thread a few days back but got no replies.

From replies here so far, I guess the chip must have a VERY wide focusing field, and just ignores the fact that there's no EP between the primary lens and itself.

And 'magnification' in these circumstances isn't magnification as we know it, but just a spreading-out of pixels on our computer screens?

I have supplementary questions.

[1] If I just position a (good) webcam so that it looks through a (good) ep, will it be able to take (good) pics?

[2] Can I mount a DSLR camera on the focusing tube, using adaptors, without any of its lenses attached, and expect good results? (I have a Pentax K-x)

[3] Or as [2], but WITH lenses attached?

Regarding the webcams, I suppose I'm just asking whether I have to go through the agony of 'modding' it at all!

[JamesF]

At some point in the focus tube of your scope there's a plane (think of it as an imaginary "screen" if you like) where all the light "gathered up" by the primary lens or mirror from a specific point on the target is brought back to a single point. Every different point of the object you're viewing has the light it emits brought back to a corresponding point on that plane. The size of the image on that plane never changes and may in fact be only a few millimetres on a side. The production of this image on the "image plane" is what the primary optics are for.

The webcam will be in focus when its sensor is in the same position as that plane. Because the webcam sensor is also small, the image can appear to fill most of it.

When you put in an eyepiece instead, it takes the light reaching that plane and "spreads it out" again. Long focal length eyepieces "spread it out" less than short focal length ones. That "spreading out" is the magnification you experience.

That's a bit (ok, a lot simplistic, but I don't think it's an unreasonable first pass at explaining what's going on.

James

[rowan46]

Thank you, Dazzst, for asking a question that puzzles me too. I did ask in another thread a few days back but got no replies.

From replies here so far, I guess the chip must have a VERY wide focusing field, and just ignores the fact that there's no EP between the primary lens and itself.

And 'magnification' in these circumstances isn't magnification as we know it, but just a spreading-out of pixels on our computer screens?

I have supplementary questions.

[1] If I just position a (good) webcam so that it looks through a (good) ep, will it be able to take (good) pics?

[2] Can I mount a DSLR camera on the focusing tube, using adaptors, without any of its lenses attached, and expect good results? (I have a Pentax K-x)

[3] Or as [2], but WITH lenses attached?

Regarding the webcams, I suppose I'm just asking whether I have to go through the agony of 'modding' it at all!

no the webcam is in effect the eyepiece it would be like putting 2 eyepieces together you wouldn't be able to get focus, you can use a barlow or tele=extender to magnify the image or a focal reducer to shrink the image not an eyepiece.

2 yes if you get the correct t-mount and t-adaptor you can take photo's this way it's called prime focus.

3 you can image through an eyepiece using a camera and lens google digiscoping or afocal imaging

[Cornelius Varley]

Thank you, Dazzst, for asking a question that puzzles me too. I did ask in another thread a few days back but got no replies.

From replies here so far, I guess the chip must have a VERY wide focusing field, and just ignores the fact that there's no EP between the primary lens and itself.

And 'magnification' in these circumstances isn't magnification as we know it, but just a spreading-out of pixels on our computer screens?

I have supplementary questions.

[1] If I just position a (good) webcam so that it looks through a (good) ep, will it be able to take (good) pics?

[2] Can I mount a DSLR camera on the focusing tube, using adaptors, without any of its lenses attached, and expect good results? (I have a Pentax K-x)

[3] Or as [2], but WITH lenses attached?

Regarding the webcams, I suppose I'm just asking whether I have to go through the agony of 'modding' it at all!

1. Yes. Look in the imaging section, especially the lunar and planetary sections. Lots of images taken using a webcam.

2. Yes. this is called prime focus photography.

3. Yes. Afocal imaging, camera + lens taking photos through the eyepiece, or eyepiece projection, camera body attached to telescope eyepiece.

Modding (long exposure mod) is only requires for DSO imaging.

Peter

[LukeSkywatcher]

Here's an image i took a couple of yrs ago of Jupiter just using my Canon 450D on a fixed tripod (single image) using the 10X zoom. Imagine how much better it would be if i had attached my camera to a scope. If i got this much magnification with a simple 18-55mm lens on the 450D............

A scope can and will only do better. Webcams though are best for imaging planets.

[Probablynot]

Thanks for that Peter. It answers all my questions.

The 'modding' I was talking about is the conversion of a MS Lifecam Cinema webcam, for which superb instructions have been posted in another thread. It doesn't (apparently) have a long exposure option. Yet.

However, I think you've given me sufficient courage to start vandalising!

[ollypenrice]

There are some very wrong answers here, and some very right ones!

The best way out of this is to remove the term 'magnify' because it is very misleading.

A telescope doesn't really 'magnify,' it focuses light onto a plane. It looks out into space and creates an image on that plane. Now how wide a field of view is it going to embrace in the image it forms on the plane? That depends on its focal length. It may embrace Jupiter and its moons and half a degree of sky each side. (Short focal length.) Or it may just embrace Jupiter and its moons. (Longer FL) Or it may just embrace Jupiter (Longer still FL). It hasn't really 'magnified' anything along the way, rather it has just restricted its own view. The image of Jupiter has been getting larger on the chip because, if you like, the area around it has been selected out by increases in focal length. But the scope has not 'done anything' to the light from Jupiter. It has just brought it to focus.

As said early on and very well, this image is tiny as is the webcam chip it sits on. Make the image 'actual size' on the screen it will be the tiny size of the webcam chip.

This is where the term 'magnification' first becomes meaningful. You hit Control Plus in Photoshop and magnify it!

The proper professional term in astrophotography is plate scale. This turns arcseconds on the sky into mm on the plate (chip.) Forget 'magnification.'

Olly