Imaging with the 130pds

[Adam J]

1 minute ago, alacant said:

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...

I am assuming that you have looked to ensure that the focuser itself is square with the optical axis?

[richyrich_one]

3 minutes ago, alacant said:

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...

One last time...

Have you checked the mounting screws either side of the tensioning screws?

[alacant]

1 minute ago, Adam J said:

focuser itself is square

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

[Adam J]

Just now, alacant said:

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

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

So in my case with a laser colimator the position of the reflected spot would change as I racked the focuser in and out, if its parallel then it would remain in the same place irrespective of focuser position. 

[alacant]

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...

[alacant]

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...

[Stub Mandrel]

Last night I focused on Arcturus with a  bahtinov mask, got it spot on, tightened the lock screw half a turn so that turning the focuser knobs made no difference to focus.

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

[alacant]

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...

[Stub Mandrel]

48 minutes ago, alacant said:

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...

Single raw sub from last night stretched carelessly in Raw Therapee.

Might be a tiny bit of coma in the very top right corner, or it might be because the scope was pointing straight up.

[alacant]

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.

[alexbb]

Glad you sorted it out. And yes, it should apply to reflectors too.

On another note, my focus routine for the last 3-4 sessions was just to place the bahtinov mask and check the focus. But, on the other hand, the ASI 1600 + the manual filter wheel are lighter than other camera combos.

And one more iteration of the Veil, this one with almost 3.5 hours of O3. I shot last night one more hour of O3, but it's not processed yet. The seeing was not very good when I shot the O3 so the image is resized to half and even the small stars look pretty big. I won't put much effort though in processing until I have all the data I want. I plan to gather at least 5-6 hours on both Ha and O3 before I switch to something else, but it seems that the weather does not allow this soon.

Clear skies and thanks for looking,

Alex

[alacant]

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

[Adam J]

4 minutes ago, alacant said:

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

You can shift the primary up the tube on its adjustment screws, it pushes out the focus tube a little and prevents it getting so badly in the way.

[alacant]

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.

Edited May 24, 2017 by alacant

[alacant]

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

[alexbb]

Same as Adam, I pushed the primary up the tube, but I also changed the screws with longer ones. The focuser still pops in the light path, but just a little.

[Stub Mandrel]

I cut the end of my focuser and glued on a stop so it doesn't wind right out.

[alacant]

1 hour ago, Stub Mandrel said:

cut the end

How much needs to be removed? TIA.

[spillage]

You can cut a wide slot out the the focus tube from front to back and this allows full movement of the focus tube and is less restrictive.

[Stub Mandrel]

I lopped off about 1/2

I like  Spillage's idea, however, I think cutting out some shallow arcs as well as lopping the end off.

[alacant]

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

cut the end of my focuser

Hacksaw?

[spillage]

If I get 5 mins I will post a photo of my focuser. I think a dremel type tool would make things easier.

[Stub Mandrel]

17 minutes ago, alacant said:

Hacksaw?

Well I parted the end off in a lathe, but Hacksaw is fine, if you mark a line with tape to cut too and tidy it up with a file afterwards ;-)

[Adam J]

18 minutes ago, alacant said:

Hacksaw?

Like someone else said just make sure you glue a stop on to the end of the tube to stop it falling out if you move it out too far. 

[alacant]

Thanks everyone. Done it. No protrusion. Perfectly round star halos right across an evenly illuminated field.

As I removed the focuser, I noticed more seemingly undocumented screws around the focuser; the three sets of push pull screws at 120° around the barrel which look suspiciously like tilt adjusters. One set however cannot be accessed because it is directly beneath the focus knob. Anyone? TIA.