D shaped stars sw 200pds

[alacant]

4 hours ago, andrew s said:

rotate the camera say 30 deg

Hi

The pattern retains its relation relative to the diffraction spikes.

Substituting the camera also results in the same image with the same spikes. It's only the 200pds which produces these pronounced spikes. Other Newtonians are fine.

My conclusion to this test is that it's the telescope producing the effect, not the camera.

Thanks

Edited May 19, 2020 by alacant

[alacant]

Just before I finally take the hammer to it...

The spikes are the same with and with out cc and with and without filter.

Cheers

[andrew s]

Unfortunately  rather looks like one or other of the mirrors . 

Regards Andrew 

[Captain Scarlet]

Turned edge on the primary? I'm currently trying to deal with a suspected case on my 300p. Easy to test, just make a cardboard edge-mask and see if that makes a difference.

 

Edited May 19, 2020 by Captain Magenta

[Merlin66]

A simple Ronchi screen will quickly show any issues.....

[Peter Drew]

Mirror defects should show up in the out of focus star image, I don't see any?    Very puzzling.      🤔 

[andrew s]

15 minutes ago, Peter Drew said:

Mirror defects should show up in the out of focus star image, I don't see any?    Very puzzling.      🤔 

I certainly defer to your greater experience.  Looking at the out of focus image made me consider it looked a bit rough but it is very difficult to  separate roughness and seeing.

Regards Andrew 

 

[Ricochet]

23 hours ago, alacant said:

Exactly the same awful spikes

No, not exactly the same. Look again:

Left is with mirror clips, right is without. The clips don't create spikes, they prevent them in some areas (but this is more complex than the standard 120 degree shadows normally seen).

1 hour ago, Captain Magenta said:

just make a cardboard edge-mask

This is exactly what you need to do. I think everyone should do this, no matter the make or model being used. Even if the mirror arrives in perfect condition, over time the coatings will degrade and the edge of the coating will be the first place to go, creating spikes like this. A few mm off the aperture is a small loss compared to the tighter star images.

12 hours ago, alacant said:

When I change the secondary, the spikes change too. 

Unfortunately, if changing the secondary changes the spikes, you may also need to mask the secondary.

[Peter Drew]

2 minutes ago, andrew s said:

I certainly defer to your greater experience.  Looking at the out of focus image made me consider it looked a bit rough but it is very difficult to  separate roughness and seeing.

Regards Andrew 

 

I think the out of focus star image is par for a 200P.  I certainly have plenty of experience with deformed stellar images due to obscurations in the light path, to produce a D shaped star would normally need a significant bite out of the out of focus disc.     🤔

[andrew s]

1 minute ago, Peter Drew said:

I think the out of focus star image is par for a 200P.  I certainly have plenty of experience with deformed stellar images due to obscurations in the light path, to produce a D shaped star would normally need a significant bite out of the out of focus disc.     🤔

Fully agree, regards Andrew 

[Dan13]

6 hours ago, alacant said:

Hi

OK. Here is Vega out of focus left and right and in focus left-centre-right.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hi, what program is this please?

[alacant]

1 hour ago, Dan13 said:

what program

siril

[alacant]

1 hour ago, Peter Drew said:

to produce a D shaped star would normally need a significant bite out of the out of focus disc

Hi

This issue was solved by cutting off the focuser tube which was intruding into the light path.

The current issue is the pattern surrounding bright stars.

Anyway, I've yet another secondary mirror on order from TS. If that fixes it, good. If not, time to give up!

Thanks everyone for your time and patience.

 

[tooth_dr]

26 minutes ago, alacant said:

Hi

This issue was solved by cutting off the focuser tube which was intruding into the light path.

The current issue is the pattern surrounding bright stars.

Anyway, I've yet another secondary mirror on order from TS. If that fixes it, good. If not, time to give up!

Thanks everyone for your time and patience.

 

Please update your results. Very interesting thread. 

[Dan13]

41 minutes ago, alacant said:

siril

Thank you 

[alacant]

23 minutes ago, tooth_dr said:

Very interesting thread

Unless you're on the having-to-sort-out-non-existent-skywatcher-quality-control end. LOL.

It's not the first time I've banged my head against this. But it will certainly be the last!

It's such a pity as it produces lovely images. So long there are only very faint stars in the fov. Even then...

Cheers 

Edited May 19, 2020 by alacant

[alacant]

11 minutes ago, Dan13 said:

Thank you 

Sorry. Didn't include the link.

[tooth_dr]

3 minutes ago, alacant said:

Unless you're on the having-to-sort-out-non-existent-skywatcher-quality-control end. LOL.

It's not the first time I've banged my head against this. But it will certainly be the last!

It's such a pity as it produces lovely images. So long there are only very faint stars in the fov. Even then...

Cheers 

I image with the same scope as you, a blue tube 250px, I know the issues you speak of.

[alacant]

Just now, tooth_dr said:

a blue tube 250px

 

So do we. A lovely old reliable instrument.

The newer sw stuff just seems to be thrown together.

Cheers and thanks for your interest.

[CedricTheBrave]

my 200pds looks similar i have ordered some flocking material to see if that helps

[alacant]

43 minutes ago, CedricTheBrave said:

my 200pds looks similar

Thanks for posting and please do report back re the blackening.

Cheers

[CedricTheBrave]

1 hour ago, alacant said:

Thanks for posting and please do report back re the blackening.

Cheers

It arrived today so let the fun begin!!!

will keep you informed

[CedricTheBrave]

this is my image of Vega 3min exposure 800 Canon 1300d Skywatcher 200P-DS

after flocking the scope, 

due to me being a dumb ass i forgot to take a before shot

no processing apart from jpg conversion

 

 

Edited May 27, 2020 by CedricTheBrave

[philhilo]

Very interested in this thread as I have a 200PDS with all of the above issues - has to be said this isn't a £1000 or multiple ££££ OTA, more like £200, so giving it a hard time seems a little unfair. However, I have all of the above issues, D shapes, ugly spikes etc. Am considering if it is worth spending ~ £400 on upgrading it, flocking, focuser, dew/light shield, clip cover, cheshire collimater (I have a laser but it rocks about in the aperture which makes it useless).  Other option would be a better OTA, but I don't see any options that give me the reach or speed (live in Bortle 8 so need speed if images are going to be done in less than a week of good weather!) at less than a snip under £2k?

[alacant]

12 hours ago, philhilo said:

Am considering if it is worth spending

Hi

I think only you can decide that but if you're an ap and want to fix the aberration and allow the telescope to hold collimtaion:

-remove the mirror clips

-remove the main mirror and 'glue' in place with neutral weather sealant silicone

-loosen the mirror cell locking bolts and add strong passive springs to them. Leave the locking bolts loose.

-add m6 washers between the mirror cell and the main spring adjusters. The idea is to obtain greater spring compression.

-replace the secondary mirror with this one and blacken its edge

-replace the dovetail bar with a 50cm long Losmandy version

-tie the top of the the tube rings with strong aluminium box section. We used 4x2x60 2.5mm wall aluminium window frame stuff.

-remove the focuser and bolt and glue a 0.6mm blackened aluminium sheet around the tube. A paper template helps. Inside the tube is elegant but we gave up and went outside.

-affix a 30cx30cm square of black canvas(?) -sorry, forgotten what it's called in English- inside the tube opposite the focuser. Double sided tape is good.

-fit a proper focuser

-decide you've had enough of sw products for ever and make a big loss on the resale, just to see the back of it.

 

The only alternative I can find which may work out of the box is the priced-like-a-small-refractor cr ontc.

Please note that i am not an expert on this stuff and must credit @laser_jock99, our resident Newtonian modification expert, for the influence on the above.

Cheers and HTH but do tell us what you decide to do.

 

Edited July 2, 2020 by alacant