Figure 7-3
A collimated telescope
should appear
7. Once the star image is in the center of the field of view, che ck to see if the rings are
concentric. If the centr
7. Once the star image is in the center of the field of view, che ck to see if the rings are
concentric. If the centr
symmetrical w ith the
central obstruction
centered in the star's
diffraction patte rn.
symmetry of th e star. If you see a s y stematic ske wing of the star to one sid e, then recollim ation is needed.
o accomplish this, you need to tighten the secondary collim ation screw(s) that move the star across the field toward the
irection of the skewed ligh t. These screws are located in the secondary mirror holder (see figure 8-1). To access the collimation
rews you will need to remove the cap that covers the secondary mirror holder. To remove the cap, gently slide a flat head
rewdriver underneath one end of the cap and twist the screwdriver. Slid e the screwdriver underneath the other side of the cap
nd twist until the cap comes off. Make only s mall 1/6 to 1/8 adjustments to the co llimation screws and re-c enter the star by
oving the scope before making an y improvements or before making further ad justments.
o make collimation a simple procedure, follow these eas y steps:
. While looking through a medium to high power eyepiece, de-focus a bright star until a ring pattern with a dark shadow
appears (see figu re 8-2). Center t he de-focused star and notice in which direction th e central shadow is skewed.
. Place your finger along the edge of the front cell of the telescope (be careful not to touch the c orrector plate), pointing
ews, then you will need to adjust the
screw opposite where your finger is located).
. Use the hand control buttons to move the de-focused star image to the edge of the field of view, i n the same direction that
5. While looking through the eyepiece, use an Allen wrench to turn the collimation screw you
direction, so that the star image is moving towards the center of the field of view.
ews by the same amount.
al obstruction is stil l skew ed in the sam e direction, then continue
turning the screw(s) in the sam e direction. If you find that the ring pat tern is skewed in a
Perfect collimation will y ield a s ion
delivers the optimal optical p nce specificat ions that your telescope i s built to achieve.
If seeing (i.e., ai r steadiness) is tu
steadier part of t he sky. A st eadie winkling stars.
pattern.
symmetry of th e star. If you see a s y stematic ske wing of the star to one sid e, then recollim ation is needed.
o accomplish this, you need to tighten the secondary collim ation screw(s) that move the star across the field toward the
irection of the skewed ligh t. These screws are located in the secondary mirror holder (see figure 8-1). To access the collimation
rews you will need to remove the cap that covers the secondary mirror holder. To remove the cap, gently slide a flat head
rewdriver underneath one end of the cap and twist the screwdriver. Slid e the screwdriver underneath the other side of the cap
nd twist until the cap comes off. Make only s mall 1/6 to 1/8 adjustments to the co llimation screws and re-c enter the star by
oving the scope before making an y improvements or before making further ad justments.
o make collimation a simple procedure, follow these eas y steps:
. While looking through a medium to high power eyepiece, de-focus a bright star until a ring pattern with a dark shadow
appears (see figu re 8-2). Center t he de-focused star and notice in which direction th e central shadow is skewed.
. Place your finger along the edge of the front cell of the telescope (be careful not to touch the c orrector plate), pointing
ews, then you will need to adjust the
screw opposite where your finger is located).
. Use the hand control buttons to move the de-focused star image to the edge of the field of view, i n the same direction that
5. While looking through the eyepiece, use an Allen wrench to turn the collimation screw you
direction, so that the star image is moving towards the center of the field of view.
ews by the same amount.
al obstruction is stil l skew ed in the sam e direction, then continue
turning the screw(s) in the sam e direction. If you find that the ring pat tern is skewed in a
Perfect collimation will y ield a s ion
delivers the optimal optical p nce specificat ions that your telescope i s built to achieve.
If seeing (i.e., ai r steadiness) is tu
steadier part of t he sky. A st eadie winkling stars.
To verify collimation , view a star near the zenith. Use a medium to high power ocular — 12mm to 6mm focal length . It is
important to center a star in the center of th e field to judge collimation. Slowly cross in and out of focus and judge the
To verify collimation , view a star near the zenith. Use a medium to high power ocular — 12mm to 6mm focal length . It is
important to center a star in the center of th e field to judge collimation. Slowly cross in and out of focus and judge the
Figure 8-2 -- Even though the star pattern appears the same on both sides of focus, they are asy mmetric. The
dark obstruction is skew ed off to the lef t side of the diffractio n pattern indica ting poor colli mation.
T T
d d
sc sc
sc sc
a a
m m
T T
1 1
2 2
towards the collimation screws. The shadow of your finger should be visible when looking into the eyepiece. Rotate your
finger around the tube edge until its shadow is seen closest to the narrowest portion of the rings (i.e. the same direction in
which the centra l shadow is skewed).
3. Locate the collimation screw cl osest to where your finger is pos itioned. This will be the collimation screw you will need to
adjust first. (If your finger is positioned exactl y between two of the collimati on scr
towards the collimation screws. The shadow of your finger should be visible when looking into the eyepiece. Rotate your
finger around the tube edge until its shadow is seen closest to the narrowest portion of the rings (i.e. the same direction in
which the centra l shadow is skewed).
3. Locate the collimation screw cl osest to where your finger is pos itioned. This will be the collimation screw you will need to
adjust first. (If your finger is positioned exactl y between two of the collimati on scr
4 4
the central obstr uction of the s tar image is skewed.
the central obstr uction of the s tar image is skewed.
located in step 2 and 3. Usually a ten t h of a turn is enough to notice a ch ange in collimation.
If the star image m oves out of the field of vie w in the direction that the central shadow is
skewed, than you are turning the collimation screw the wrong way. Turn the screw in the
opposite
located in step 2 and 3. Usually a ten t h of a turn is enough to notice a ch ange in collimation.
If the star image m oves out of the field of vie w in the direction that the central shadow is
skewed, than you are turning the collimation screw the wrong way. Turn the screw in the
opposite
6. If while turning you notice th at the screws get very loose, then simpl y tighten the other two
screws by the same amount. Conversely, if the collimat ion screw gets too tight, then loosen
the other two scr
6. If while turning you notice th at the screws get very loose, then simpl y tighten the other two
screws by the same amount. Conversely, if the collimat ion screw gets too tight, then loosen
the other two scr
different direction, than simply repeat steps 2 through 6 as described above for th e new
direction.
tar image very symmetrical just inside and outside of focus. In addition, perfect collimat
different direction, than simply repeat steps 2 through 6 as described above for th e new
direction.
tar image very symmetrical just inside and outside of focus. In addition, perfect collimat
erforma erforma
rbulent, collimation is difficult to judge. Wait until a better night if it is turbu lent or aim to a
r part of the sky is judged by steady versus t
rbulent, collimation is difficult to judge. Wait until a better night if it is turbu lent or aim to a
r part of the sky is judged by steady versus t
38