Figure 2 – Absolute efficiency curve of two 600 grooves/mm gratings, maximum efficiency peaks at 300 nm (orange) and 500 nm (blue).

If you find your high-power views look blurry, or galaxies look way too dim, or you just can't find what you're looking for, it's got nothing to do with collimation. If you find that out-of-focus stars in the centre of the field of view aren't circular then it might be a collimation issue.

As grating diffracts the incident radiation, it does not do so with uniform efficiency. The overall shape of the grating efficiency curve (a plot of absolute or relative diffracted efficiency as a function of the diffracted wavelength) shows normally a single maximum, at the peak of maximum brightness (or blaze wavelength) and is generally a rather complex function of wavelength and polarization of the incident radiation and depends on the groove density, plane of polarization, shape, and angle of the grooves and the reflectance of the coating material.

Diffraction grating

A collimator is a device, often a piece of plastic with hole in the center of it and crosshairs to help collimate the telescope. Other collimators use a precision laser that is put into the focuser and then shines a laser at the secondary mirror, then at the primary mirror and back. The goal is to get the laser that has bounced back centered with the collimator itself, which usually has a bullseye type marking on it. Collimating is essential for optimum telescope performance, both for visual and astrophotography. Here's a collimator from Orion.

What collimation achieves is simple. Think of your telescope like the lens of an SLR camera. At the focal plane of the SLR lens there's the film or CCD chip. Imagine what would happen if the focal plan and CCD weren't parallel with eachother: you would never be able to focus properly. It's the same thing with your telescope. You align the optics in order to ensure that the focal plane of your eyepiece is coincident with the focal plane of the telescope objective. Here's some reading: http://www.physiol.ox.ac.uk/~raac/collimationLinks.shtml

If the focal length of two lenses is the same, the lens with the larger diameter will be brighter. For example, if the focal length is 50mm and the lens ...

The "problem", if that is the correct term, is that optical settings need to be fairly accurate, when a beam is reflected any error is doubled. There are 2 mirrors in the path of a newtonian.

A question not asked enough by observers (especially those with fast newts) is "Does my scope need any collimation adjustments?" And the answer is simple - do a star test that takes only a few seconds. No scope can be perfectly collimated but doing a star test will tell if you are as near to a perfect collimation as is practical. How often should my scope be adjusted? a simple star test will give you the answer every time you go out to observe.

From what I understand, collimation is necessary for all scopes, even fracs, but due to their design, newts and cassegrains need a tad more care and attention. From this, I've wrongly or rightly concluded that collimation in the latter type scopes is an absolute necessary and must be done on a regular basis - how often I'm not sure, but I guess if you treat your scope well, not that often.

Sarspec uses regularly three types of gratings in its spectrometers depending on the purpose of the application and required specifications. A brief description of Ruled, Holographic, and Blazed Holographic grating can be found within the following sections.

It says a 'cheshire collimater' used for the primary mirror (so no lazers at all here then). Not knowing precisely what such a gizmo is, I wonder if anyone can suggest even a 1/2 decent way to collimate the primary w'out the realtive added expense of a cheshire or a lazer gizmo? (perhaps therefore good enough for the humble 'budget' 1st scope type 130EQ. Im sure it doesnt warrant the most precise collimater as a costly beastie would after all).

All spectrometers manufactured by Sarspec are equipped with fixed diffraction gratings that can be selected by the user according to the wavelength range of interest. The two key parameters when choosing the right grating for your spectrometer are the groove density which allows you to set the operational wavelength range and optical resolution and the grating groove efficiency for the selection of the wavelength range where your system sensitivity is at its maximum. Detailed information about these two parameters can be found in the following sections.

Echelle grating

3) removed the cards, and checked that the 3 retaining clipss (look like small black clips against the primary mirror background now) are equally spaced, if one off or not same the its corresponding allen bolt needs a tweak 9you'll figure out which).

In ruled and ruled holographic gratings, changing the groove angle (the angle created by the longer side of the groove and the plane of the grating) moves the diffracted radiation along the spectral region and changes the blaze wavelength. When selecting the best grating for your spectrometer, take into consideration the grating efficiency – its maximum will, normally (also depending on the efficiency curve of the detector), correspond to the maximum sensitivity of the operational wavelength range (see Figure 2).

A "good" scope could very easily be one where the assembled items are checked and set up better. If the main mirror is checked to be central, and tweeked so it is perpendicular, if the secondary is attached so it is at 45 degrees and central and not just close enough, if the focuser is seated so that it is more accurate then that scope will perform better. Nothing there other then a little extra attention.

1) mirror2 is perfectly central to the EP tube (if off LH ar RH the centre screw needs a tweak, ie move mirror2 in a fraction in or out).

Holographic gratings are produced by interfering with two laser beams to create a sinusoidal pattern on the surface of the substrate, then coating it with a highly reflective material, see Figure 4.

An anti-reflective (AR) coating for glasses is a specialised optical coating applied to the surface of eyeglass lenses to reduce reflections and glare.

Diffraction grating formula

The advantages of both ruled and holographic gratings can be combined into the so-called blazed holographic gratings. The grooves on a blazed holographic grating are produced by applying a two-laser-beam-interference method, which is the same method used to produce conventional holographic gratings. Then, the ion-beam etching technique creates the standard “sawtooth” design that is used in conventional ruled gratings.

Ruled gratings are produced by physically forming a series of triangular grooves onto the surface of a substrate, using a diamond tool mounted on a ruling engine. The slope of the triangular groove is usually adjusted to improve the brightness of the grating at a specific wavelength. Once the triangular grooves have been formed, the substrate is coated with a highly reflective material, see Figure 3.

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The groove density or groove frequency is usually expressed in nm/mm and determines the range of wavelengths that are dispersed by the grating into the detector. The increase of the groove density (grooves (or lines)/mm) results in an improvement of the optical resolution for a certain slit width. On the other hand, groove density also defines the operational range of wavelengths of the grating, being that a higher groove density will generate shorter operational ranges for your spectrometer. Increasing the groove density leads to a higher optical resolution but also to a shorter wavelength operational range (see Figure 1).

Get a film cannister cut the btm 1" off and put a precise pin hole in centre, pop in EP tube (make sure fit perfect 1st/ no droppings thru!). Then with OTA flat, & twd a light area, put a primary mirror cardboard 'stopper' (a bit of card bent into a T to gently put in to block mirror1) and a blue bit of card/ red whatever behind/ below mirror 2 for a blue even background (ie not black). Check:

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Collimation in terms of a reflector is setting the mirrors and eyepiece all in line and setting the secondary at the correct angle.

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Having set these 2 correct then the main mirror has to be both centered and perpendicular to the optical axis, they tend to put a small marker on the mirror to aid in this. You adjust the main mirror to get this accomplished. If the main mirror is not perpendicular to the optical axis then you get coma - little egg shaped stars.

Others will be able to inform you a lot better than a simpleton-frac user I am, but for now, I think you'll find this guide a great read and help.

Transmission grating

It's not as complicated as it looks. Enjoy your scope and pick away at the collimation until it's good. It'll all come together in the end. You'll get reasonable views of most objects even if it's misaligned.

The diffraction grating is the main element in the optical system of a spectrometer that separates incident polychromatic radiation (white light) into monochromatic radiation (light of one color). It consists of a series of parallel grooves, equally spaced and formed in a reflective coating deposited onto a glass substrate. The distance between each groove and the angles the grooves form with the substrate influence both the dispersion and efficiency of a grating.

Hi there, Im new to the game and have the same 130EQ. I collimated the secondary mirror without a lazer which I have a hunch might be 'good enough' for our humble scopes (I may be wrong and a precise collimation of primary mirror 1 with lazer gizmo is essential too, but I think with care this might be ok).

I bought my astromaster 130 and was to think it was set up and ready to point it up. Oh no iv gone and done some reading ( i know stupid me) and i have heard if collimators. what does it do?

The thing about collimation is that you can check it and worry about it on cloudy nights or in the daytime, using tools that are in some cases quite expensive. This can make it a fatally attractive subject for people who don't get enough dark time.

diffraction grating中文

in telescope terms, collimation is just the proper alignment of the mirrors and other components to ensure they perform well. it's a simple process once you 'get it' and now takes me about a minute max. it's often a case of checking it and not doing anything as nothing is out of alignment.

LightSmyth

Because there is no need for mechanical ruling, the periodic structure errors found in conventional ruled grating are no longer present, and that ensures less amount of stray light and ghosting. Owing to their high efficiency and minimal stray light and ghosting, blazed holographic gratings are the ideal optical components to be used in instrumentation that require extreme efficiency and resolution and are included as standard in our UV/Vis, UV/Vis/NIR and Vis/NIR configurations.

The drawback of ruled diffraction gratings is that due to the nature of the production process, they have defects that can occur in the form of periodic errors, surface irregularities, or spacing errors. As a consequence of these defects, ruled gratings have increased stray light and ghosting effects.

While ruled gratings offer higher efficiencies at a particular wavelength (blazed wavelength), they suffer from periodic errors in groove production, therefore generating high amounts of stray light. With holographic gratings, these errors are strongly reduced. The drawback of holographic gratings when compared to blazed gratings is reduced efficiency.

Take a lens, tilt it around in front of your eye, and you'll see that the best view is when it's exactly square to your eye. The same applies to the reflection in a curved mirror. Collimation just means ensuring that the components are properly squared or aligned. The effect of not being properly aligned is in most cases very small and to a beginner probably not noticeable at all. So the advice to any beginner is not to start by worrying about collimation, but start by looking at stuff.

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collimation is akin to tuning a guitar. you can still use a guitar and broadly get a tune out of it if not in tune but it will not perform as well as if it were properly adjusted. continuing the analogy, the more often you tune your guitar, the easier and quicker it gets.

There is nothing requiring vast knowledge and experience or an optical test bench. An understanding of what you are aiming at accomplishing is useful otherwise you are going through a set of actions without knowing why and that means things do not get performed correctly.

The link below includes how to do such a test as well as lots of other info on the subject. As for collimating equipment, you don't need any to get very good results. Most times the primary mirror only may need adjustment during a star test.

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Blazed grating

A collimator is simply a tool to check the alignment of all the bits, and if they are not accurate then the best collimation cannot be achieved. A laser collimator needs to be checked that the laser is itself centered. Fairly easy but a necessity. Seems to be 2 main types:- Laser and Cheshire. There are I suspect others, think FLO have a Catseye unit that operate differently.

2) mirror2 is a perfect o and not a 0 for eg, ie aligned- if a slight 'rugby ball' then mirror2 needs a tweak around, where it is).

Diffraction grating experiment

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Back to an earlier point if the eyepiece cannot be held perpendicular to the main tube then you have a problem, as other then taking it off and putting it back on correctly they is nothing that can be done.

Assuming it is then the secondary has to be positioned at 45 degrees to the eyepiece optical path and such that the centre of the secondary is also on the optical axis.

Small scopes hold their collimation very well and the factory setting is most likely fine, or at any rate good enough for enjoyable views. If you don't enjoy the views then the first things to think about are light pollution, using excessively high magnification, and various other faults. Eliminate those before worrying about collimation.

If your telescope is out of collimation then the views will be blurry. There can be a vast difference in planetary views. Your telescope is f/5, which is a fairly fast focal ratio. Telescopes with faster focal ratios need more careful collimation.

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