Telescope with a pinhole as the Objective?

[Frenemy90210]

Will a telescope work if its front lens (Objective lens) is replaced with a pinhole ? What if both lenses ( Objective and eyepiece) are replaced with pin holes ?

 

[davenn]

Will a telescope work if its front lens (Objective lens) is replaced with a pinhole ? What if both lenses ( Objective and eyepiece) are replaced with pin holes ?

since you labelled you thread with an "I" tag, you should be used to doing research as a undergrad student

so what do you think?
how about trying it out and telling us what happens

Dave

 

[Frenemy90210]

since you labelled you thread with an "I" tag, you should be used to doing research as a undergrad student

so what do you think?
how about trying it out and telling us what happens

Dave

I had tried it a few years ago without much success. Frankly nothing was visible. May be somebody else knows/experienced otherwise.

 

[davenn]

I had tried it a few years ago without much success. Frankly nothing was visible. May be somebody else knows/experienced otherwise.

OK
well I doubt a pinhole at each end will be successful

do you know what a pinhole camera is ?
do a quick google and then have some fun

 

[fresh_42]

Ed. note: I changed the label to "B", so more basic posts are possible.

 

[sophiecentaur]

A pinhole is good for looking at sun spots safely. (Projection method)

 

[russ_watters]

A pinhole is good for looking at sun spots safely. (Projection method)

So, @Frenemy90210, can you tell us what is different between observing the sun and, say, a galaxy, that could make it work for one and not the other...?

 

[sophiecentaur]

So, @Frenemy90210, can you tell us what is different between observing the sun and, say, a galaxy, that could make it work for one and not the other...?

. . . . and why the best and most expensive camera lenses have so much glass on the front?

 

[fresh_42]

A pinhole is good for looking at sun spots safely. (Projection method)

I only want to mention that the emphasis here lies on projection. Just in case: Do not look directly into the sun, pinhole or not!

 

[Khashishi]

The bigger the aperture and the wider the field of view, the more light you will collect. Typically, if you are measuring something dim like a galaxy you will be photon limited. A pinhole doesn't collect much light.

 

[Frenemy90210]

So, @Frenemy90210, can you tell us what is different between observing the sun and, say, a galaxy, that could make it work for one and not the other...?

I can see what you are getting at. Sun emits lot of light and in the other case its not. The reason I asked the question was to know if there is a workaround to that problem. I guess not.

 

[sophiecentaur]

know if there is a workaround to that problem.

The workaround is to use many many pinholes over a large area and arrange the phase delay through each hole to be the same so that a coherent image is formed from all of the holes . That's what a lens achieves for you.

 

[sophiecentaur]

The bigger the aperture and the wider the field of view, the more light you will collect. Typically, if you are measuring something dim like a galaxy you will be photon limited. A pinhole doesn't collect much light.

And a pinhole is so small that diffraction will noticeably affect resolution.

 

[Khashishi]

Another workaround is to use a very long exposure time, though you are going to run into issues with background noise and the rotation of the Earth.

 

[sophiecentaur]

Another workaround is to use a very long exposure time, though you are going to run into issues with background noise and the rotation of the Earth.

That still wouldn't take care of diffraction. Also the actual increase would involve extremely long exposure times (days) for any but the very brightest astronomical objects.
This topic is essentially a practical one and 'in principle' ideas don't necessarily have a place, imo.

 

[Frenemy90210]

A pinhole is good for looking at sun spots safely. (Projection method)

I think it will be great if this statement is re-written/re worded completely from safety point of view. There might be children who are reading this page. Children might be stare at the sun directly through a pin-hole.

 

[sophiecentaur]

I think it will be great if this statement is re-written/re worded completely from safety point of view. There might be children who are reading this page. Children might be stare at the sun directly through a pin-hole.

I agree:
Never try to observe the Sun by looking at it directly unless you are using properly designed viewing equipment.
It can easily lead to blindness.
Navigators on ships, in the past, all went blind in one eye because their navigation equipment was not designed properly.

 

[trainman2001]

Light gathering is the entire challenge. You can take terrific celestial pictures using a standard camera and lens system as long as you can get it stare at one point in the sky long enough. People do this all the time with a standard camera piggy-backed to a well-guided telescope tube. The telescope is only there to provide a star drive based on sighting on a guide star.

Therefore, going the other direction with a pinhole, while it does focus light rays, serves little or no purpose in astronomy simply because it can't capture enough light to make a useful image. Furthermore, "all that glass" in a camera lens is there to adjust for the fact that shorter light rays (blue and ultraviolet) refract at different angles than longer wavelengths (red and infrared) so that all the visible wavelengths focus in one plane. The more elements and the better the glass in the lens determines how well it does compensate for the errors that can occur. Each new major telescope has a bigger and bigger main mirror to do one thing, gather more light. Compare James Webb to Hubble and it's quite easy to see what's going on.

 

[darth boozer]

Therefore, going the other direction with a pinhole, while it does focus light rays, serves little or no purpose in astronomy simply because it can't capture enough light to make a useful image.

A pinhole does NOT focus light rays, as can be seen by moving it relative to the projection screen which only alters the size of the image. The sharpness of the image is better with smaller images, but only because the circle of confusion is smaller as well.