What did we do wrong?

[RFaber]

Hi,

I got my son a Skywatcher 200 Flextube Dobsonian telescope as an upgrade to his 3D-printed Hadley telescope.

He was excited and we went out to try it out in the backyard even if conditions were not optimal (neither the moon nor any planets were up, it was slightly cloudy, and there is some street lights and general light pollution), but we have previously been able to see lots of stuff in his old Hadley.

We started by collimating the telescope with a laser collimator. Researching a bit, I have since found out that the laser collimator needs to be collimated itself, which it certainly wasn't. We didn't have the right hex-tool to collimate the secondary mirror, and it was almost centered anyway, so we only adjusted the primary mirror a bit.

We used the 25mm ocular, found a group of clear stars, located them with the finder scope (the finder scope wasn't aligned with the primary scope), but was completely unable to locate them or anything in the primary scope. No matter how much we searched and tried focusing, we did not manage to get anything but a uniform grey view inside the primary scope. Once or twice we saw a bright shape shaped like the UFO, but I suspect that was just a nearby streetlight reflecting on something.

The plan is to get out in daylight soon, get the finder scope aligned, and retry the collimation, but even with all those done badly, I would have expected us to be able to see something, even if washed out and out of focus. So I suspect we have done something else wrong. Do anyone have any hints on where to start troubleshooting?

Cheers,
Rasmus.

[Cosmic Geoff]

Get it sorted out in daylight with the scope and finder aligned, and focused on a distant landmark. If you were unable to focus on anything, note that a common newbie error with these scopes is to use the wrong setup of extension tubes at the focuser: i.e. not adding an extension tube, or using two extension tubes when you should have used one. 

[dweller25]

It sounds like you have a good plan to first line the finder up with the eyepiece view in daylight, you will need to look at something at least 300mts away for the scope to come to focus.

You may have an extension tube in the focuser that will need to be removed to achieve focus.

The scope will need to be cooled down for at least an hour for best results.

View on grass not hot concrete.

Atmospheric seeing is poor at the moment so that will affect the quality of the views.

Check and adjust collimation on a good night.

Good luck 👍

Edited May 2 by dweller25

[happy-kat]

Hi, I do not have this telescope but have seen written more than once, make sure the right adaptor only for the eyepiece size you are using is in the focuser tube, i'e' don't have both the 2" and 1.25" adaptors both inserted as you wont focus.

[bosun21]

You must use the correct extension piece to achieve focus. The taller slim one for 1.25" eyepieces and the other one for 2" eyepieces. NEVER both at the same time. I wouldn't have adjusted the collimation until you see what you are dealing with as they are generally useable straight from the factory. As has been said align the telescope on a distant object and achieve focus first. Once successful then align the finder scope with the telescope image seen in the eyepiece. Once that is done then you can look at the collimation situation. Walk before you run so to speak.

Edited May 2 by bosun21

[Tiny Clanger]

2 hours ago, RFaber said:

We used the 25mm ocular, found a group of clear stars, located them with the finder scope (the finder scope wasn't aligned with the primary scope), but was completely unable to locate them or anything in the primary scope. No matter how much we searched and tried focusing, we did not manage to get anything but a uniform grey view inside the primary scope. Once or twice we saw a bright shape shaped like the UFO, but I suspect that was just a nearby streetlight reflecting on something.

 

The 'UFO' was probably a very out of focus star, possibly the shape you saw was caused by your attempt at collimation. As bosun21 said,  use just the correct extension tube for the diameter of eyepiece, also ensure the front section of the flextube dob is fully extended and locked in place.

A poorly collimated laser in a stock skywatcher flextube focuser is a recipe for disaster - I know, I have a 250 flextube ! Using the provided extension, the laser (even after being collimated) moves as you touch the focuser, and tilts as you tighten the screws that hold it in place.

This is a good explanation of the various ways to collimate https://garyseronik.com/collimation-tools-what-you-need-what-you-dont/

Gary Seronik also gives the clearest account of how to collimate I've ever come across https://garyseronik.com/a-beginners-guide-to-collimation/

I found the best method with a laser is this  https://www.tomhole.com/wp-content/uploads/2020/12/blaser.pdf a particularly useful thing as it's easy to see the bottom of the barlow and the faceplate you add to it through the open section of the flextube.

[John]

Some good advice on collimation above.

My advice is initially to concentrate on getting the finder scope accurately aligned with the view through the main scope, fully extending and locking the flextube rods and ensuring that the correct adapter is being used in the focuser (earlier posts cover all these things).

 

 

 

 

[JOC]

Astrobabys guide to collimation is the most recommended on sgl https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

It uses a 200p skywatcher as the example so very close what you have.  do it to letter no matter how odd the instructions sound and you won't fail.

I have the same flextube telescope.  I first tried a laser collimator then got a cheap Cheshire and it is much easier with the Cheshire. 

Finally, Just a word to the wise - make sure you draw the flextube apart TWO clicks!  It is very easy to think you are there at the first set of stops, but you must pull it again and get it to the second clickstop to make it long enough to use.  It will not work at the first stop, take it from one that knows!  Oh yes, also make sure you have removed the big plastic cover too, sometimes it gets plonked down on the second stage and you forget to remove it!

Edited May 4 by JOC