6 years ago I designed and constructed a large spectroscope and I am also in possession of a small hand-held double Amici prism professional spectroscope, which was bought 10 years ago.
As far as I am concerned my design plans were correct for the larger spectroscope (bottom of page). Collimation is also correct and has been tested extensively. The device performs excellently.
Does anyone have any idea why on both my prism spectroscopes the images of emission lines appear more "curved/bowed" as you go towards the purple part of the spectrum? This effect can be seen on pictures I've taken with both my large spectroscope and my small one.
Here are some spectra photos with both spectroscopes. Note that as one moves towards the purple Mercury lines, the lines curve more. The effect is visible on the small spectroscope as well, but is less pronounced, because it has much smaller resolution. (Photos which show the whole spectrum are taken with the small spectroscope. Photos which show part of the spectrum are taken with the large one).
I know lower wavelengths are bent more, but what *exactly* is the optics explanation for the fact that the lines appear "bowed" more towards lower wavelengths?
It looks to me like the optics of the telescopes is what is causing the bowing of the lines. The thing here is that the pictures of the lines don't always have the same amount or direction of bowing.
-- Why do penguins walk so far to get to their nesting grounds?
> It looks to me like the optics of the telescopes is what is causing the > bowing of the lines.
There are no telescope components in the small spectroscope, except one lens to collimate the slit:
slit--lens--amici prism--eye
> The thing here is that the pictures of the lines don't always have the same > amount or direction of bowing.
The different direction is because collimation is slightly off and the telescopes are not EXACTLY centered on the optical axis. The problem is still unexplainable to me.
> -- > Why do penguins walk so far to get to their nesting grounds?
"Ioannis" <morph...@olympus.mons> wrote: >6 years ago I designed and constructed a large spectroscope and I am also in >possession of a small hand-held double Amici prism professional >spectroscope, which was bought 10 years ago.
>As far as I am concerned my design plans were correct for the larger >spectroscope (bottom of page). Collimation is also correct and has been >tested extensively. The device performs excellently.
>Does anyone have any idea why on both my prism spectroscopes the images of >emission lines appear more "curved/bowed" as you go towards the purple part >of the spectrum? This effect can be seen on pictures I've taken with both my >large spectroscope and my small one.
>Here are some spectra photos with both spectroscopes. Note that as one moves >towards the purple Mercury lines, the lines curve more. The effect is >visible on the small spectroscope as well, but is less pronounced, because >it has much smaller resolution. (Photos which show the whole spectrum are >taken with the small spectroscope. Photos which show part of the spectrum >are taken with the large one).
>I know lower wavelengths are bent more, but what *exactly* is the optics >explanation for the fact that the lines appear "bowed" more towards lower >wavelengths?
> 6 years ago I designed and constructed a large spectroscope and I am also in > possession of a small hand-held double Amici prism professional > spectroscope, which was bought 10 years ago.
> As far as I am concerned my design plans were correct for the larger > spectroscope (bottom of page). Collimation is also correct and has been > tested extensively. The device performs excellently.
> Does anyone have any idea why on both my prism spectroscopes the images of > emission lines appear more "curved/bowed" as you go towards the purple part > of the spectrum? This effect can be seen on pictures I've taken with both my > large spectroscope and my small one.
> Here are some spectra photos with both spectroscopes. Note that as one moves > towards the purple Mercury lines, the lines curve more. The effect is > visible on the small spectroscope as well, but is less pronounced, because > it has much smaller resolution. (Photos which show the whole spectrum are > taken with the small spectroscope. Photos which show part of the spectrum > are taken with the large one).
> I know lower wavelengths are bent more, but what *exactly* is the optics > explanation for the fact that the lines appear "bowed" more towards lower > wavelengths?
"Charles Attends" <inco...@cette.adresse> writes: > The bowing of spectral lines is absolutely and entirely normal. > Will give you an explanation later. > It occurs with prisms or gratings.
I've seen monochromators where the slits were curved.
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>>It looks to me like the optics of the telescopes is what is causing the >>bowing of the lines.
> There are no telescope components in the small spectroscope, except one lens > to collimate the slit:
> slit--lens--amici prism--eye
Unless the lens has mutiple components to correct for chromatic aberration, the col;imation is not done well at all wavelngths, which will cause what you see. Most spectrometers use front-surface mirrors.
>>The thing here is that the pictures of the lines don't always have the
> same
>>amount or direction of bowing.
> The different direction is because collimation is slightly off and the > telescopes are not EXACTLY centered on the optical axis. The problem is > still unexplainable to me.
>>-- >>Why do penguins walk so far to get to their nesting grounds?
> >>It looks to me like the optics of the telescopes is what is causing the > >>bowing of the lines.
> > There are no telescope components in the small spectroscope, except one lens > > to collimate the slit:
> > slit--lens--amici prism--eye
> Unless the lens has mutiple components to correct for chromatic aberration, the > col;imation is not done well at all wavelngths, which will cause what you
see.
Sorry, doesn't make sense to me. It's true that the small spectroscope has a single lens collimator, but it produces less bowing than the big spectroscope which has two element objectives on both the collimator and viewer.
If what you say were true, then a two element lens would collimate better, thus the big spectroscope would have displayed less bowing.
> Unless the lens has mutiple components to correct for chromatic aberration, the > collimation is not done well at all wavelngths, which will cause what you see. Most > spectrometers use front-surface mirrors.
The bowing of spectral lines is inherent to the use of prisms. Collimation has very little if anything to do with it.
Charles Attends wrote: > "Marvin" <physc...@cloud9.net> wrote
>>Unless the lens has mutiple components to correct for chromatic
> aberration, the
>>collimation is not done well at all wavelngths, which will cause what you
> see. Most
>>spectrometers use front-surface mirrors.
> The bowing of spectral lines is inherent to the use of prisms. > Collimation has very little if anything to do with it.
Absent collimation, not all of the light of any wavelength follows parallel paths through the prism. The smaller spectrograph presumably has a lower f-number, which tends to exaggerate problems like this. Prhaps some ray-tracing will convince you.
