Colimating dobinsonian 1st go

[LunarRob]

Hi, I have picked up the Orion xs800 plus, used and checked alignment - which was out. I did a school boy error or putting the colimator cap into the Barlow x2 lense and wondered why it was difficult to see

anyhow realised and the best I could get was below. I did the secondary and then got the primary alligned as best I could

but it got a bit too dark then

This is a picture holding my phone to the lense but looking for feedback on it please

Edited October 20, 2023 by LunarRob
Errors in original

[bosun21]

The secondary should always be collimated before the primary. Your secondary isn’t perfectly circular which can be rectified with the three screws on the secondary holder. I can’t see the focuser draw tube to check the centering of your secondary.

[LunarRob]

35 minutes ago, bosun21 said:

The secondary should always be collimated before the primary. Your secondary isn’t perfectly circular which can be rectified with the three screws on the secondary holder. I can’t see the focuser draw tube to check the centering of your secondary.

Thanks for your input it was getting dark I’ll see if I can get a better picture. I did do the secondary 1st but took a bit of messing with the primary. I guess it’s one of those that once you’ve done it a cple times

[Spile]

You need to place a piece of paper behind the focuser and include the focus tube in the image as that is a key reference point.

[LunarRob]

Thanks both edited original as I put the checks in the wrong order and said Robinson lense instead of Barlow (don’t know where that came from)

I’ll do another check with the paper and get a better image

thanks

[LunarRob]

5 hours ago, bosun21 said:

The secondary should always be collimated before the primary. Your secondary isn’t perfectly circular which can be rectified with the three screws on the secondary holder. I can’t see the focuser draw tube to check the centering of your secondary.

I’ve took another picture with paper behind in better light

[bosun21]

1 hour ago, LunarRob said:

I’ve took another picture with paper behind in better light

It's looking much better apart from not being centered with the focuser. Loosen the three secondary screws a little and turn the centre screw clockwise to pull the secondary forward to the open end of the scope. Once it is concentric with the focuser draw tube you only need to use the three secondary screws to make the secondary mirror perfectly round. It's certainly close enough at the moment to be used as is.

[Spile]

This is where the secondary needs to be. Start by moving it away from the primary mirror (centre bolt adjustment as explained in my guide):

Edited October 23, 2023 by Spile

[dweller25]

@Spile

I’m a bit confused - I would have moved the secondary away from the Primary, or is the reflection tricking me ?

Edited October 23, 2023 by dweller25

[LunarRob]

Thanks for your help, I know there are guides but when it’s alien to you sometimes it’s easier to get help with the aid of pictures

ive finally cracked it with assistance from yourselves I’ll post a pic of how it looks now later on

[Mr Spock]

1 hour ago, dweller25 said:

I’m a bit confused - I would have moved the secondary away from the Primary, or is the reflection tricking me ?

Agreed. The secondary needs to move away from the primary.

[LunarRob]

Ok thanks - Here’s the latest colimation, I think it’s much better. Sorry the picture isn’t the greatest holding my phone up to the lense

[happy-kat]

What 5 ratio is your telescope, as depending on that your most inner circles may be off a bit, but what's the f ratio first please

[LunarRob]

4 hours ago, happy-kat said:

What 5 ratio is your telescope, as depending on that your most inner circles may be off a bit, but what's the f ratio first please

Hi it’s f5.9

8”  203mm

 

[John]

The collimation in my 8 inch Skywatcher dob looks pretty much like yours is now. My scope is performing excellently 👍

 

[LunarRob]

2 minutes ago, John said:

The collimation in my 8 inch Skywatcher dob looks pretty much like yours is now. My scope is performing excellently 👍

 

Thanks John good to know I’m on the right track 😀 can you just blow those clouds away 😫

[Spile]

23 hours ago, dweller25 said:

@Spile

I’m a bit confused - I would have moved the secondary away from the Primary, or is the reflection tricking me ?

Senior moment - sorry. You are correct of course - post now edited accordingly. 

Edited October 24, 2023 by Spile

[bosun21]

14 hours ago, dweller25 said:

@Spile

I’m a bit confused - I would have moved the secondary away from the Primary, or is the reflection tricking me ?

No, you are correct. It needs moving away from the primary mirror by a clockwise turn of the centre screw on the secondary mirror holder.

[Spile]

21 hours ago, LunarRob said:

Ok thanks - Here’s the latest colimation, I think it’s much better. Sorry the picture isn’t the greatest holding my phone up to the lense

 

You have sorted the offset error. Just a little tilt/rotation to deal with (three outer screws).

[bosun21]

23 hours ago, LunarRob said:

Ok thanks - Here’s the latest colimation, I think it’s much better. Sorry the picture isn’t the greatest holding my phone up to the lense

I must admit that for your first time collimating a dobsonian you have done remarkably well. Well done 👍.