Skywatcher 200p focusing

[Kidbriar]

Hi guys hope someone can help me. I have a Skywatcher 200p on a Dob mount which I haven't used for about 10 months because of an eye problem I had (thankfully everything is now ok) and it has been stored upright in my dining room.

Tonight was the 1st night I've been out with it and so I attached my Canon DSLR with the t ring attached to the 2" eyepiece, got the moon in the cross hairs of the finder scope, but I couldn't get focus at all

[Kidbriar]

just to say folks, it wasn't the 'F' word I used which was removed .....

[Alveprinsen]

...so I attached my Canon DSLR with the t ring attached to the 2" eyepiece, got the moon in the cross hairs of the finder scope, but I couldn't get focus at all . ...

Did you remove that long eye-piece holding thing? (I don't know what it is called).

You need to remove all extension tubes etc. from that focusing tube so that the DSLR is as short distance from the secondary mirror as possible.

I am using a modified Canon EOS 600D as well as a regular unmodified Canon EOS 700D - and they both achieve focus just fine. I got the Canon T2 threaded ring attached directly onto the coma corrector, and the coma corrector connected straight into the focusing tube. No extensions in between.

[Kidbriar]

Yes I did remove it. All I had was the T ring attached to my DSLR and the 2" eyepiece 'thingy' attached to that ...

[Alveprinsen]

Yes I did remove it. All I had was the T ring attached to my DSLR and the 2" eyepiece 'thingy' attached to that ...

you want your DSLR connected directly to the focusing tube itself. The aluminum part. Like, there's a thin black ring with two thumbscrews mounted directly on the aluminum tube. You want your T ring to go straight onto that.

That lower part is just a hole with the two thumb screws going through though, so you'll need the T-ring to be connected to something threaded that can slide down into the hole and be attached with the thumb screws. In my case, its a Baader Mark-III Coma corrector.

Setting it up like this, I actually have to extend the tube a little to get focus.

Edit: Note that I have the 200PDS though. I ripped this image off google. But the focusing tube length should be the same.

[Marky1973]

On my 200p Dob I remove the 1.25" eyepiece holder from the focussing mechanism. The 1.25" tube unscrews from the disc that slips into the focusser and is held in by the grub screws.

The ring then screws into the t-ring and those two items connect to the camera minus lens.

The whole thing can then be slipped into the focusser and secured in place.

There is no need for the 2" adapter.

If you still don't get focus, I guess there might be a problem with collimation, but can collimation get so bad that you can't focus?

Does the image change at all when trying to focus? If not, is the locking screw on the underside of the focusser loose? If it is tight, you might be turning the focusser but not getting any/much travel in the tube? Very unlikely, but worth checking?

[Uhwaz]

i have 200P and i have to have all tubes off to get it in focus. DSLR goes strait on MPCC with about 0.5cm wiggle room from lowest point on focuser

[Charic]

Kidbriar..........Hi, when I store my 200P its a habit, but I nip-up, tighten all the knobs on / around the focuser. The fact that you can't  get focus even with eyepiece suggests you have locked the focuser ( grubscrew - its underneath the focuser) if this is too tight, the focuser wheels will appear to turn, but the focuser  tube will not extend from the focuser assembly. Loosen this lock nut and try again?

[acey]

I had occasional issues with my 200p not reaching focus visually, and in my case found 2 causes:

1. The upper cage had not been fully extended (the poles were very stiff)

2. The primary had been moved significantly forward during collimation, leaving insufficient back focus at the focuser.

Collimation in itself has no effect on focus, but reaching focus depends on being able to put the eyepiece at a correct distance from the primary (measured in two steps via the secondary). The position of the secondary itself is irrelevant in this instance (though obviously not in general): all that matters is the total path from primary to eyepiece.

Establish whether what you need is more focus in the outward (longer) or inward (shorter) direction. If you need a longer path then try screwing in the eyepiece at a low point on its barrel, thus moving it further out. If that is insufficient then an extension tube could be used (e.g. unscrew the tube of a barlow). If you need a shorter path then inspect the focuser and see if there are any adapters you can remove to accomplish this. If not, try adjusting the primary bolts, screwing in close to their limit of travel, so that the primary is moved forward. Then recollimate the scope. Or else try extending the upper cage to less than its full height. Again you will need to recollimate.

If focuser adjustment does not make the image larger or smaller then the focuser is not working: it is slipping and needs retightening using the central socket on the underside plate. That would be the first thing to check.

[Kidbriar]

Thanks for all your replies. I figured it out in the end and it is exactly as Charic suggests - the screw under the focuser was too tight!

[BranocsSky]

Thank you all for this, I found this post whilst searching for focusing remedies for my Nikon D3300 DSLR (I have been trying to get Orion's Nebula in focus to no avail), I will try all that you have suggested and will keep you informed.