c8 edge collimator

[iwols]

can anyone recommend me the above cheers

[Grotemobile]

Have a look on U tube.  I used a star @ night time.This might help you.

 

[alanjgreen]

Firstly, buy some stainless steel bobs knobs to replace the dodgy collimation screws, you dont want to be messing about with a screwdriver in the dark - FLO sell them.

https://www.firstlightoptics.com/bobs-knobs-collimation/bobs-knobs-celestron-8-edgehd-collimation-knobs.html

Then (and only when you C8 is properly cooled - after at least an hour outside) do a STAR TEST using minimum x200 magnification by defocus a medium brightness star - Polaris if you can see it - and check the circular diffraction rings...)

- if they are circular and concentric then you are collimated (make sure the STAR IS IN THE CENTRE OF THE EYEPIECE)

- if they are not concentric then you need to TIGHTEN the screw opposite the tightest patch of rings by a TINY AMOUNT (one eighth or one tenth of a turn)

- recheck the results of the tiny adjustment IMMEDIATELY (make sure you re-centre the star before checking the results). If its improved then go a bit more, if its worse then undo what you did and try another screw!

- if the star is not in the centre then the results will be inaccurate!

 

Here is a guide:    https://www.astromart.com/reviews-and-articles/reviews/beginners/show/eds-guide-to-sct-collimation

 

Buy the Bobs Knobs now but only fit them when you have confirmed that collimation is needed via the star test. If its okay then leave the knobs "in stock" until you need them

When replacing the three collimation screws do them ONE AT A TIME and make sure the C8 is HORIZONTAL so nothing can drop on the primary mirror. You also have the option to REMOVE the secondary assembly from the scope then nothing can drop onto the primary. Fit the knobs while having plenty of soft bathroom towels underneath in case of any drops!

 

Once you have collimated for the first time, then its easy!

1. Just make sure you finish with all three screws/knobs TIGHT.

2. Only do the collimation when your scope is properly cooled.

3. Make sure you use an eyepiece that provides at least x200 magnification for the best results.

 

HTH, Alan

 

PS. A visual check of SCT collimation state can be done in the daytime. If you lock the scope horizontal then remove the front cover. Now stand back 5 meters and get your eye level with the centre of the scope. Look into the front of the scope and you should see nice concentric circles like this...

If not, then you can do a ROUGH COLLIMATION by turning the knobs to get the concentric pattern seen above!

[newbie alert]

I use a peg and a 90degree bend peice of cardboard to locate the right screw then slacken or tighten it which ever way it needs to go..i use my capture program and go either side of focus..my tube holds collimation fairly well but worth a check..this isn't 100% but will correct it when I have more time

[iwols]

does a sct make things unfocusable when collimation is slightly out

[Tim]

19 minutes ago, iwols said:

does a sct make things unfocusable when collimation is slightly out

No, but the chances of sharp detail on planetary objects is reduced, star shapes are wierd, and, well, it's just not right

[Tim]

The Hotech SCT collimator is very good btw

[alanjgreen]

1 hour ago, iwols said:

does a sct make things unfocusable when collimation is slightly out

Make sure your sct is property cooled. Set up early and let in acclimatise before you use it (especially if you store it in your warm house). Image quality is affected by warm air inside the tube.

- I had a scope coat that I used to put over mine in case of a shower or birds! FLO sell TeleGizmos scope covers for SCTs.

- then you can get setup before dark and leave it to cool.

 

Dont go mad with magnification. UK atmosphere affects image once you get over x230 ish usually.

If fine focusing is an issue consider upgrade to a feathertouch micro focuser with two speed focusing (best accessory I ever bought for my c11). If you go for external Crawford focuser as an alternative then remember the extra weight at the back will impact balance. A Micro focuser will not impact balance.

Alan