alacant

On 2017-5-24 at 10:43, Stub Mandrel said:

cut the end of my focuser

Hacksaw?

1 hour ago, Stub Mandrel said:

cut the end

How much needs to be removed? TIA.

cc comparison Here are my 2 markarian chains with different ccs solving to 648mm and 588mm respectively. Which is best for the 130? TIA.

7 hours ago, Adam J said:

shift the primary up the tube on its adjustment screws

Hi. Thanks. Unfortunately not enough. Hence, I suppose the uneven stars and illumination on one side of the field. Other coma correctors retain the same focus position. SkyWatcher's not.

Dunno. The design doesn't seem to have been thought about much.

Hi again. OK, the next problem is the intrusion of the focus tube into the light path, especially problematical with the cc that sw seem to recommend. It looks like it needs around 2cm chopping off. 

Has anyone any guidelines? I'm thinking of a brute force and ignorance policy of removing the focuser and getting out the hacksaw. 

TIA

8 hours ago, Stub Mandrel said:

Single raw sub

Thanks. Yep. I think I've got it; camera hanging toward the ground and no shift. The adjustment seems to have done it. Just hoping it will hold in real life. I wonder if the tilt from the lock screw is associated with the maladjusted focuser? Thanks for your time and help.

31 minutes ago, Stub Mandrel said:

IMHO I think that proves it is possible to get the stock focuser set up right.

Hi. How was the coma at the edges? Did it tilt the camera? TIA.

*Am almost there with the adjustment to obviate the need for the lock...

1 minute ago, Adam J said:

you would find that the collimation would change as you move the focuser in and out.

Ah, OK. That's a good one to check. It seems fine no matter where the focuser is, but I use a Cheshire with cross hairs rather than a laser. I think however it should amount to the same end...

4 minutes ago, richyrich_one said:

checked the mounting screws either side of the tensioning screws?

Hi. Yes. I'm proceding according to these instructions. Nearly there...

1 minute ago, Adam J said:

focuser itself is square

I think so. Would it collimate if it were not? TIA.

59 minutes ago, Adam J said:

if you really cant adjust the tension to prevent it from slipping you may have a duff focuser... 

Hi. Thanks. It's only a matter of time, trial, error and a few cloudy nights before I get the right combination of twisting and turning to get the focuser o hold! The main issue is that the focuser lock tilts the field. If I can take the latter out of the equation, I think the issue will have been solved. Until...

55 minutes ago, moise212 said:

 

I think this can explain what happens:

 

Hi. Thanks for the link. Yes, it looks like that on the right of the image. That's why I think the focusing lock is tilting the field.

That discussion was for field flatteners on refractors. Does the same apply to coma correctors on newtonian reflectors?

Hi everyone. Here's a light frame with the field deliberately tilted with the focus lock screw. It's distorting the stars, but not producing coma. Strange. This much tilt on my faster f3.9 and it would be coma city. Does anyone know what this effect is called? TIA.

8 hours ago, TareqPhoto said:

I think Cheshire or something like that collimator.

Hi. Yes, a Cheshire is all you need, one with cross hairs is even better. There are a lot of idealised diagrams in the guides which look nothing like the real thing. Here's what it actually looks like through a 130pds looking through the focuser with and without the Cheshire.

1. Get the secondary more or less centred just by looking at it.

2. Insert a Cheshire with cross-hairs.

3. Use the secondary screws to make the cross-hairs intersect with the centre of the of the primary.

4. Adjust the primary to centre everything else.

5. Now go out and look at an out of focus star. Adjust the primary again tiny amounts to make it circular.

Forget all that. Just make it look like this:

22 hours ago, Stub Mandrel said:

the locking screw doesn't need to be so tight

Hi. I had a go at the tension but unless the telescope was pointing overhead, still couldn't get it to stop slipping . Even the slightest turn on the lock screw -not even trying to lock anything- and it tilts. You can't see it so much in a stacked image, but here's a light frame from the same; alas with the lock screw tightened...

8 hours ago, TareqPhoto said:

I hope i can figure out about collimation

Hi and welcome. It's easy. As soon as you get to do it on a telescope, you'll see it's intuitive and will wonder what all the fuss was about. Some guides make a simple one-minute task seem horrendously difficult. So have a quick Google, but don't read too much about it before you try!

FWIW, I already had a 200mm telescope and got the 130mm because of the wider field of view. If you have a choice of which to get first, I'd recommend the 130mm.

Good luck and clear skies...

2 minutes ago, Uranium235 said:

you dont need to use the locking screw

Excellent. I think you ought to write the pds guide for removing the out of box nightmares. 

7 minutes ago, Uranium235 said:

no clear instructions from SW

Yeah. Even more surprised. They don't seem to have anyone on the ground, in the cloud or anywhere. If I have a problem with my Bresser, I send an e-mail to ES and they get back to me that day. Maybe I'm not comparing like with like but SW don't seem to do it like that(?).

Anyway, it's clear again tonight so I'm gonna stop feeling sorry for myself and go and take some snaps! 

8 minutes ago, Stub Mandrel said:

you lock it with the lock screw

That's the problem; tighten it and it tilts the focus tube and/or changes the focus. The only way I could keep it flat was by trial and error between adjusting the two screws which hold the camera-cc combination in the focuser tube to 'anticipate' the tilt before I turned the locking screw.

Am going to try your adjustments to see if I can get the focuser to hold without having to tighten the lock screw. Thanks for posting. There is hope...

3 hours ago, Atreta said:

Are you using a cc? I'm waiting for my spacers to arrive so i can use mine.

Hi. Yes, there's a cc. Maybe try without the spacers? Unless you have the Baader, I don't think it'll matter much. HTH.

2 hours ago, Uranium235 said:

get a dovetail bar for the top as well

Hi and thanks for the tips. Here's the state of play ATM. Oh, and the spring which pushes on the secondary seems too weak; unless you collimate vertically, the spring isn't strong enough to respond. Apart from the third screw, is there any cure for the focuser? It just doesn't seem capable of -or was designed to- carry a dslr.

First light: Markarian's Chain. Having got used to 208mm f3.9, the first thing that strikes you is how much longer you need to get anywhere near... but hey, just look at that FOV...

Stuff that is gonna need fixing: the focuser, the springs on the primary, the secondary allen key adjusters, the flimsy dovetail, the tube... The latter is a bit of a flashback to those awful blue skywatchers from the 90's; breathe too heavily and it /bent/flexed/dented and went out of collimation. I thought that by now they'd have done something about that. Aluminium perhaps? At least something that doesn't make that awful tinny sound when you drop the allen key down the tube.

But these are minor quibbles. For what it cost, it's amazing. I'm gonna read through the whole thread and see if I can pick up any hints.

Any comments/hints/tips most gratefully received. Clear skies and thanks for looking.

1 hour ago, Stub Mandrel said:

Do you have the 0.9x Skywatcher CC ahnd an APS-C

Hi. The latter yes. The cc, not sure. It's an unbranded Chinese affair. It plate solves to less than the quoted focal length, but exactly how much... Anyway, thanks for the framing hint, and yes, I can get the whole of the curve of the chain with room to spare. On snap 10 as I write....

1 hour ago, Thalestris24 said:

thumbscrews

Hi. Thanks for the link. It states m4 so should be easy to get bolts long enough. 

Just joined the club officially. After the 10 kilo 8", the little 130 is refreshingly lightweight. I put some proper dovetails on it and struggled with the secondary. How I hate Allen key adjustments! Is it possible to put thumbscrews on the secondary I wonder? Size if so?  The only thing I'm missing is the screw which holds the focusing knob. M3 and M4 don't fit. Any ideas anyone? Anyway, first light with it I'm planning Markarian's Chain; should be able to fit it in easily now. TIA.

On 2014-3-10 at 19:19, Uranium235 said:

Skywatcher will owe us commission for pushing up 130pds sales

Hi. I've been trying to source one for the last week. All European middle-men are out of stock until September and it seems impossible to deal direct with SW. I've an offer of secondhand from the sgl wanted section. Is there anything I should look out for? Any weaknesses or bits that wear? TIA.