One of the toughest jobs a beginner has to learn is Newtonian telescope collimation.
This needs to be carried out relatively frequently on Newtonian Reflector type telescopes and
it can be a very scary and/or frustrating experience for a beginner using a collimator.
This guide will take you through the various steps towards perfect collimation.
I have included both diagrams to show you the ideal as well as pictures showing how it will actually look
as beginners are often confused between the idealised views of a well collimated telescope and the views
they are seeing with their own equipment.
The scope being collimated in these pictures is a Sky-Watcher 200P with an aperture of 200mm and a focal
length of 1000mm (Focal Ratio f 5).This is a common enough fast reflector and the collimation process is
essentially the same for any Newtonian telescope. Where there are differences between a fast scope and
a slow (high f number) scope I have provided text and pictures to highlight the differences.
Fast telescopes are typically of around f5 to f3 or even faster.
You can calculate the focal ratio of your own telescope by the simply dividing the focal length by the diameter
of the primary mirror. The Sky-Watcher 200P has a focal length of 1000mm and a primary mirror diameter of 200mm
so 1000 divided by 200 = 5 ( focal ratio ). Slow telescopes are usually at f6 – f7 or slower.
To accurately collimate with this guide you will need a Cheshire collimator and a collimation cap.
My own collimation cap is made from a focuser blanking cover with a small hole drilled through the exact centre.
You can make a collimation cap from a 35mm film container or buy them ready made.
I have not covered collimation with a laser because my own experience has been lasers seem to create more problems than
they solve as they also require collimation which isn’t always possible with some low cost lasers.
Lasers generally only work well in telescopes which have a high quality focuser with minimal ‘slop’.
The average mass produced telescope very often has a focuser that is too imprecise to make use of a laser.
This guide may look scary – if you take it one step at a time its not that hard.
In order to cover off all of the issues the guide is somewhat larger than some others on the web – many guides
omit various details which can lead to confusion and frustration in the beginner.
To collimate the telescope it should be aimed towards a bright but not glaring surface such as a well lit pale painted
wall or fabric in order to get a good image in the telescope and the Chesire should be arranged so that its
shiny angled surface gets a good light. Cheshire @ Amazon
Rule 1 – Before starting collimation don’t assume that anything is out of kilter and check each element before
adjusting anything. About 90% of collimation errors are down solely to the primary mirror so don’t jump in and
start meddling with the secondary unless you are sure that there is a problem.
Each stage of this guide will show you how to check the various elements – only if they are out of alignment
will you need to make adjustments.
Rule 2 – Make sure you have all of the tools you require ready to hand.
Some telescopes will require Allen keys and a screwdriver.
You don’t want to be looking for tools when you halfway through collimation.
Rule 3 – Make sure you have budgeted for enough time. Collimation can be a very time intensive process for a beginner. It can be carried out over successive sessions if you need to but don’t plan on collimating on a night when you want to be observing. It will lead to a rush job and frustration – TAKE YOUR TIME and you will be rewarded with good collimation and better viewing through your telescope.
Rule 4 – Do not over-tighten nuts and adjusters.
They need to be firm and tight – they DON’T need to be tightened until the threads pop.
建议4 - 不要过度拧紧螺母和调节螺丝,只需上紧即可,切勿拧到螺纹极限。
Rule 5 – Whenever you are working on a telescope ALWAYS work with the telescope tube in a horizontal position.
If you drop things into the tube you don’t want them to impact on the primary mirror.
I also wear cotton gloves when I am working to make sure I don’t damage anything with sweat from my hands.
Collimation Step 1 – The Spider Vanes and Secondary Mirror Holder 校准步骤1 - 蜘蛛架和副镜座
Before attempting to collimate the secondary mirror it’s essential to get the mirrors holder central to
the tube and the primary mirror. Some scopes allow adjustment of the spider vanes.
If your scope has this facility you need to check whether the secondary mirror holder is held perfectly central
by the spider vanes.
Note: Some scopes require the secondary mirror to be offset from the centre of the tube.
This in itself raises questions. Some telescopes will have the secondary offset on its holder
in which case the centre of the vanes should be centred to the tube while other manufacturers
will opt for the vanes centre point being off centre. The offset on most scopes will be in millimetres and
wont affect collimation by much. You should check whether your telescope requires offsetting with the manufacturer
or supplier. If you cannot get an answer assume that the mirror holder is to be central to the telescope tube.
There are two methods to accomplish getting the mirror holder central to the tube.
The first is relatively simply which is to measure the distance between the tube and the secondary mirror holder
along each of the vanes. The distance should be identical for each vane.
If the vanes are not equal than adjust them using the vanes attachment / adjustment screws.
The cross head on the central screw makes an ideal reference point.
The second method for aligning the mirror holder is a little more complex but more accurate and easier once
the initial work is done.
Cut a piece of card out which is the same diameter as the telescope tube and drill a small hole in its centre.
To find centre on the circular piece of card fold the card into quarters.
The point where the folds cross is the centre. Now look through the hole and the central screw on the secondary
mirror holder should be exactly underneath. If it isn’t adjust the spider vanes until it is.
This provides a simple and reliable method of getting the mirror holder central and once you have made
the piece of card future centering of the vanes will be easier.
To adjust the vanes you will need to slacken the screws and then slowly tighten them in turn to pull
the mirror holder to the centre.
The hardest stage of collimation is the secondary mirror alignment.
This is almost always very time consuming but once done should not need readjustment unless the scope is
severely shaken or dropped or the vanes and the secondary are removed for any reason.
The easiest method to align the secondary mirror is with either a collimation cap or a sight tube.
With my Sky-Watcher 200P I find a collimation cap is the better solution as a sight tube or my Cheshire do not
allow me to see the very edges of the secondary mirror through them.
The first object of secondary mirror alignment is to get the secondary mirror directly under the focus tube and
appearing as a circle. The secondary mirror is an elliptical shape but when presented to the focuser at
the correct angle will appear as a perfect circle.
副镜对齐要做的第一件事是将副镜置于调焦筒的正下方,且通过调焦筒看为一个圆。副镜虽为椭圆形状,但是通过调焦筒从正确的位置观看时,
其呈现为完美的圆形。
Many people find the reflections in the mirrors confusing and in truth it can make this stage of the process quite
hard as your eyes can be confused by the multiple reflections between the secondary and primary mirrors which can
create a kind of optical illusion which can make it hard to assess whether the view is circular or elliptical.
A simple solution is to use a piece of white card or paper to block the primary mirrors reflections.
Simply insert a piece of white paper into the telescope tube between the secondary and the primary mirrors.
This will create a view of the secondary as just a white circle. Another tip here is that it’s often quite hard to
see whether the secondary is presenting as a circle against the black background of the tube.
I insert a piece of coloured card or paper behind the secondary which allows my eyes to more readily detect whether
the secondary is appearing as a circle and is centred to the dark circle created by the edge of the focuser.
If the secondary is not centred under the eyepiece you will need to adjust it using the centre screw of
the secondary holder.
在视场中,如果副镜不在中心,则需要通过副镜座中间的调节螺丝进行调整。
This is shown below. You are advised to have the telescope tube near the horizontal position
while you carry out this work in order to ensure that if there is an accident the secondary doesn’t fall down
the tube and into the primary mirror. Keep a hand holding or supporting the secondary mirror holder without
touching the mirror surface itself. Proceed with great care and caution and take your time.
The adjuster screw is quite coarse and the mirror will move quite a lot with each turn.
Be careful not to loosen the screw too much which will cause the secondary to disengage from its holder and fall off.
Adjusting the secondary mirror centre screw
调节副镜中心螺丝
The centre screw adjusts the secondary mirror both up ( away from the primary mirror ) and
down ( towards the primary mirror. To adjust this you may have to loosen the screws or Allen keys which control
the tilt of the secondary mirror. These are also visible in the picture to the left.
Be careful not to apply too much force and go slowly.
Then use a collimation cap in the focuser to force your eye central to the focus tube and rack the focuser tube
as far out as possible.
Now move the mirror up or down the tube using the central adjusting screw on the mirror holder until you have
the secondary mirror centred.
You will also need to rotate the mirror until it presents as good a circle in the focuser as possible and adjust
the tilt screws to to achieve a good circular shape on the secondary.
You should eventually get to a view which is similar to that shown on the left – this view is not perfect as it
was taken with a small digital camera but it should serve as a rough guide as to how things should be looking
if you have adjusted the secondary correctly.
Once the mirror is aligned correctly under the focuser lightly tighten the tilt screws.
Aligning the secondary mirror to the primary is easily the hardest task. Still using the collimation cap in the
focuser you now align the secondary using its tilt adjusters and occasionally a slight amount of rotation on
its main centre screw ( you may need to loosen the screw tightly and twist the secondary mirror round by grasping
its holder – DO NOT TOUCH THE MIRROR ITSELF ) to get the secondary centred onto the primary.
This process is covered in the pictures below.
First remove the coloured card and the white ‘baffle’ card in the telescope tube.
Now look into the collimation cap and using the tilt screws get all of the primary mirrors retaining
clips into view and at the edge of the secondary mirror. IGNORE ALL OTHER VISUAL INFORMATION !
All you are trying to do at this stage is get the secondary mirror centred on the primary mirror.
This diagram shows the classic view of the mirror clips showing in the secondary mirror which are equally spaced
and equally proud. Not all scopes will have three mirror clips – larger scopes maye have 6 or even eight.
It may be that to achieve this view the tilt screws alone may not be enough and you may have to
apply a small amount of rotation to the secondary mirror by slackening slightly the centre screw and
applying a small amount of rotation to the mirror.
Don’t worry about this as it may just show that your visual check was ‘off’ by a small amount.
In the diagram above there is a circle marked in yellow. This is the likely extent of your view
if you are using a Cheshire eyepiece at this stage.
I personally prefer a collimation cap which provides a slightly wider view of the secondary.
This photograph shows what the actual view should be like at this stage of the process.
Note the three mirror clips are all visible and are all equally close to the edge of the secondary mirror and
the secondary is showing round and centred to the focuser tube ( the dark area at the edges of the picture)
You may need to move your focuser in or out to achieve a good view but the image should be very similar to
this photograph.
这张照片展示了本阶段调节过程中的实际视场。注意三个主镜固定爪都可见且等距且靠近副镜边缘,
而且副镜显示为圆面且位于调焦筒(照片边缘的黑色区域)中间。你可能需要结合调焦以获得一个好的视场,但是不管怎么样,
看到影像应该非常类似这张照片。
When all three clips are in view (and some scopes may have more clips) and shown at the edge of the secondary mirror
with equal space around them this part of the collimation process is complete.
Tighten down the tilt adjusters and take a final check.
The tilt adjusters can be set quite tight but be careful not to apply too much force and bend the spider vanes.
As with the previous step its best to have the telescope horizontal during this step in case an Allen key is
dropped into the tube.
Once the primary mirror clips are shown reflected in the secondary and the tilt screws have been tightened
take a final check using the procedures in stage 2 that the secondary still shows as centred and circular.
If the secondary has shifted then you will need to realign using the procedures in stage 2 and then run through the procedures in stage 3 again. Its not uncommon for some rotation error to creep into the mirrors position while the tilt screws are adjusted. Take your time, be patient and continuously go back over your work and make sure all is well at each stage before continuing.
When you are satisfied that the mirror is centred and true as in step 2 AND all the mirror clips from the primary are in view as per step 3 you can now tighten the adjusters down, these need to be firm but do not apply so much force that you strip threads. A standard Allen key is best rather than an Allen headed screwdriver or a multi tool as it will limit the force you can apply. Take care also that you do not apply too much force and cause the spider vanes to bend.
Now you should check using a small mirror that the secondary adjustment is more or less equal and that
no one screw is causing the mirror to be canted too far over as per the diagrams below.
The final step in collimation is the primary mirror. This is relatively simple to carry out and the cause of
most ‘in the field’ collimation errors.
校准的最后一步是主镜校准。这一步相对简单但也是多数校准误差的根源。
At the rear of the telescope you will find three pairs of screws.
These are the primary mirror tilt adjusters and their respective lock nuts.
在望远镜的后端有三对调节螺丝。它们是主镜的倾斜调节器以及相应的锁紧螺丝。
Note: Some telescope manufacturers (Sky-Watcher for instance) cover the collimation adjusters with a steel plate.
This will need to be removed before collimation can proceed.
注意:某些望远镜生成商(例如信达)会用一块钢板盖住校准调节器,因此,在开始校准之前将其移除。
For this stage you will need the Cheshire collimator. Insert this into the focuser and take a look
through the collimator. You should see a pattern similar to the one shown below right – this is from
a telescope that is in collimation.
It may be that that the pattern is offset and will show the cross hairs as being adrift from the central
circle created by the Primary Mirrors centre spot and that the centre spots are adrift.
If this is so then you will need to adjust the primary mirror.
可能你看到的模式已发生偏移,十字丝与主镜中心点对应的圆环已发生偏移,这时就需要调节主镜。
If collimation of the primary mirror is required loosen the lock screws off and adjust the primary mirror
using its adjuster screws until you see a pattern as per the diagrams and pictures below.
如果需要调节主镜,松开锁紧螺丝然后调节主镜调节螺丝直到看到如下所示的图片。
Take care when using the adjuster screws that you do not allow the mirror to come too far forward on
adjustment as the screws may disengage and also take care that the collimation screws and lock screws
aren’t tightened down to a point which may cause the primary mirror to become ‘pinched’ or distorted.
They should be finger tight only.
调节时防止螺丝脱落或锁紧螺丝过紧导致主镜变形。锁紧螺丝只需用手拧紧即可。
Bear in mind the collimation pattern may be slightly different depending on the f ratio of your scope.
For more information see below.
望远镜焦比的不同,校准模式会有轻微的不同。详见以下内容。
A note on spider vanes in the view…………
视场中的蜘蛛架:
When collimating the spider vanes, apart from the inistial stage of making sure they are holding the secondary mirror central, are not relevant to the collimation procedure. Ignore them – you should only be looking at the Cheshires cross hairs and making sure that the cross hairs intersect the primary mirror centre spot.
You should note that fast scopes of f5 and above are less tolerant of collimation errors and
they also show slightly offset collimation patterns. These are shown below as a guide.
焦比为5甚至更快的望远镜对光轴校准误差更为敏感,且校准模式有轻微的偏移,如下图。
This photograph shows what the actual view should be like at this stage of the process.
Note the three mirror clips are all visible and are all equally close to the edge of the secondary mirror and
the secondary is showing round and centred to the focuser tube ( the dark area at the edges of the picture)
You may need to move your focuser in or out to achieve a good view but the image should be very similar to
this photograph.
This is an actual photograph taken through a Cheshire and shows a near perfect collimation pattern for a fast (f5)
Newtonian. It is in fact my own Sky-Watcher 200P Note that the centremost circle is made up of the primary mirrors
centre ring and its associated reflection. The cross hairs exactly intersect the centre circle.
Note also the offset typical of a fast Newtonian.
[本段描述的似乎还是关于快镜的,感觉作者是不是写错了!!]
When collimation of the primary has been achieved and the Cheshire pattern is correct tighten down the
locking nuts and recheck. Do not over-tighten the lock nuts. They should be firm but do not require massive
amounts of pressure. I usually feel for them coming into contact with the mirror cell and then add a small amount
of pressure.
Replace any protective plates and remove the Cheshire collimator.
移除任何保护板和Cheshire校准器。
When this step is completed and all of the alignment patterns shown in this guide are true then the telescope
is collimated to within the limits of what you can achieve with a Cheshire and you should find the telescope
is perfectly well collimated for use.
You may wish to carry out a ‘star test’ to verify this and/or to make any fine fine tuning adjustments.
Star testing is simple enough to carry out and there is a section below which will explain this and show
the most common problems.
你可能还希望进行一次星点测试以确认是否还需进一步微调。星点测试非常简单,下一节将详细展开。
So – get it as good as you can but do not overly worry if there is some small element which isn’t perfect.
My own collimation via a Cheshire is always a little ‘off’ – star testing confirms the scope as being spot on
so bear this in mind.
尽你最大的努力进行校准,但是如果还有些小的偏差也不用担心。我自己的校准也经常会有一些小偏差。
Star Testing Your Telescope
星点测试
When collimation is complete you may wish to carry out a star test which will confirm the collimation or
show small errors which can be fine tuned out.
当校准完成后,你可能希望进行一次星点测试以确认校准精度或进行微调。
To star test you will need a bright star and good seeing conditions. Polaris is the best star to test on
but almost any bright star will do. You will need your telescope to have cooled down to the ambient
temperature and also to be away from obstructions such as houses which may cause air thermals.
Get the star centred in your view using a low power eyepiece. Now use a very high power eyepiece
( or the highest powered you have available) and defocus VERY slightly. You should see a classic Airey disk
as shown in the pictures below. Ideally the Airey disk will be perfectly formed for both sides of the perfect
focus (Extrafocus and Intrafocus) but in reality most telescopes wont do this perfectly owing to slack within the
focus mechanism or atmospheric turbulence but you should see an Airey disk on at least one side of the perfect
focus position.
The optimum magnification for star testing is at 25x per inch of aperture to start with and then fine tune at 50x
per inch if seeing permits – you will need a very stable sky to get maximum magnification.
If you are not seeing an Airey disk this then there are several reasons why. This may be due to faulty
collimation or other conditions which may not be correctable.
一些原因,例如,校准失败或其他一些未考虑到的条件,可能会导致看不到艾里斑。
A list of common conditions and their corrective responses are shown in the tables below.
下表列举一些常见的情况以及对应的现象。
Be aware that in UK skies atmopsheric turbulence will be very often the pattern you will see.
Unfortunately the typical turbulence pattern is very similar to the pattern you will see with a badly
damaged mirror. Unless you have reason to believe the mirror IS damaged then there is no need to panic.
Even a turbulent atmosphere pattern will allow you to see whether the circles are concentric or whether
they are off centred and non-concentric.
完美星点:
Airey disk shows neat concentric circles. The innermost are dark due to the telescopes central obstruction caused
by the secondary mirror.
艾里斑完美同心。最内层的黑色区域是由于副镜带来的中心遮挡导致的。
校准偏差:
Results such as these suggest the primary mirror is not well aligned. This is simple to correct in the field by
adjusting the primary mirror collimation screws. Small adjustments only are needed.
这样的星点表示主镜没有完全对齐。这种情况只需微调主镜调节螺丝即可。
大气扰动:
The air around the telescope and in its line of sight is being disrupted by rising heat or by higher altitude
turbulence. You cannot star test with this present.
望远镜周围及镜筒所在光柱存在大气扰动,这种情况下不能进行星点测试。
过渡锁紧:
this is the classic ‘heart’ shape indicating the primary mirror has become stressed. Initially check that the
collimation adjusters are not over tight.
If the problem persists you will need to remove the primary mirror cell and make sure the clips holding the mirror
to the cell have not been over tightened.
Another common cause of ‘pinching’ is often over tight tube rings.
这是经典的心形星点,表示主镜承受的压力过大。首先检查主镜调节螺丝是否过度锁紧。如果问题继续出现,可能需要将主镜从镜筒取下以
检查主镜固定爪是否过度锁紧。还有可能是镜筒过紧。
望远镜冷却:
the telescope has not cooled sufficiently to the outside air temperature.
Allow the telescope more time to cool down.
望远镜冷却不充分,花点时间继续冷却。
像散:
Astigmatism can be caused by poor collimation but also by poor quality optics.
Secondary mirrors which are not flat either because of bad collimation or bad polishing are typical causes.
像散可能由校准失败导致,也可能是望远镜光学组件质量太差,例如副镜表面不平。
Zonal Error:
Usually caused by incorrect figuring of the primary mirror.
This cannot be corrected by the user. It indicates faulty optics in the mirrors design or production.
通常是主镜形状不正确导致。这种情况无法校准。表示望远镜的光学组件有缺陷。
Optical surface damaged:
These show typical patterns for mirrors with poor optical surfaces.
This may be caused by roughness of the mirror caused by poor polishing or damage from poor cleaning.
This is not correctable.