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130PDS Coma Corrector


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2 hours ago, Jamgood said:

a baffle to the primary mirror to block the mirror clips

Excellent images. If ever anyone needed... 

As an alternative to the baffle and one which retains the full diameter, simply remove the clips and fix the primary using three small helpings of neutral silicone sealant, sufficient and placed so a little oozes up the side where the clips were when the mirror is re-seated. Push down lightly to distribute then leave for 24 hours on a level surface. This method has the advantage of retaining collimation at all imaging angles and between sessions. 

Cheers

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On 22/10/2021 at 11:27, alacant said:

Excellent images. If ever anyone needed... 

As an alternative to the baffle and one which retains the full diameter, simply remove the clips and fix the primary using three small helpings of neutral silicone sealant, sufficient and placed so a little oozes up the side where the clips were when the mirror is re-seated. Push down lightly to distribute then leave for 24 hours on a level surface. This method has the advantage of retaining collimation at all imaging angles and between sessions. 

Cheers

There is an interesting thread that highlights removing the primary clips will only introduce more diffraction spikes from the primary mirror edge, and that the shadows from the primary mirror clips are in fact blocking some of those diffraction spikes.

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On 21/10/2021 at 19:08, alacant said:

Hi

We tried four CCS.

Assuming affordable is important...

If you want corner to corner over aps-c out of the box, the GPU. The GSO comes a close second with the added advantage of not needing the focuser barrel cutting, the disadvantage being that it increases the focal length to over 700mm. 

Then comes the sw 0,9 which widens the field to a nice 585mm with the Baader the least satisfactory and prone to astigmatism.

No theory. Just our hands on.

HTH

On an older post you attached a graph showing the working space for the GPU, which concluded to be 52.5mm for the fl of 650mm on the 130P-DS.

Can you reference where you got that graph, and how did you get the spacing right with an aps-c sensor?

The distance to my sensor (Canon 800D) is 44mm and if I use this recommended adapter, it bumps that working distance up to 55mm. Which going by the graph, 55mm would be required for a fl of 850mm.

Edited by Pitch Black Skies
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44 minutes ago, Pitch Black Skies said:

you attached a graph

?

But anyway...

You'll be given the correct spacing along with the cc.

Lose your adapter. We use a 1mm optical path t-adapter and an 8mm extension ring.

 

Edited by alacant
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1 hour ago, alacant said:

?

But anyway...

You'll be given the correct spacing along with the cc.

Lose your adapter. We use a 1mm optical path t-adapter and an 8mm extension ring.

 

Thanks, I've amended that hyperlink now.

Are they easy to source? I'll have at look on FLO and Teleskop-express.

Edit: I didn't receive any spacing or paperwork with mine, the Skywatcher Aplanatic from FLO.

I found this and this. They should work yeah?

@Jamgood Are you getting results with just this?

Edited by Pitch Black Skies
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  • F=600mm, working distance = 51.66mm
  • F=800mm, working distance = 53.66mm
  • F=1000mm, working distance = 55.0mm
  • F=1200mm, working distance = 54.66mm
  • > 1500mm, working distance = 54.60mm

 

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6 minutes ago, alacant said:
  • F=600mm, working distance = 51.66mm
  • F=800mm, working distance = 53.66mm
  • F=1000mm, working distance = 55.0mm
  • F=1200mm, working distance = 54.66mm
  • > 1500mm, working distance = 54.60mm

 

Cool, where are you getting that from? Also, it doesn't marry up with the graph you shared before.

Going by the above figures,

F=650mm, working distance

=52.16mm

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On 27/10/2021 at 20:57, Pitch Black Skies said:

where are you getting that from

Google;)

A search confirms what it says in the box. Pragmatism is however IMO by far the best approach.

On 27/10/2021 at 20:57, Pitch Black Skies said:

F=650mm, working distance

We use 53mm for the 130 and 55 for the 200.

But just try it. You may not notice any difference; The correction still works. All that happens is that the stars get fatter.

1.thumb.jpg.ccb71316a7179bd3a16dea21dd53299f.jpg  2.jpg.7d0b43c5939147dcca0c5c432289fdb8.jpg  3.thumb.jpg.5eda28c7088a79c3c7c36a952608cb34.jpg  4.jpg.19fdf803f69b9cf9a73fc901dc0aa53d.jpg

 

Edited by alacant
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40 minutes ago, Pitch Black Skies said:

@Jamgood Are you getting results with just this?

I don't use one of those adapters as I have a dedicated camera but my back focus with the TS-Optics GPU is set at 55mm and works perfectly.

Recommended for the TS-Optics GPU is:

♦ Focal length up to 600 mm - working distance 53 mm
♦ Focal length 610 mm and more - working distance 55 mm

I went with that.

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Right 🤣

 

So on the latest figures we have:

52.16mm

On that old graph it was:

52.60mm

You use:

53mm which I agree is very close to the above figures.

But now Jamgood has thrown a spanner into the works with TS recommendation at 55mm 🤣 

It would be interesting to see an image with same camera set at 53mm and then 55mm.

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32 minutes ago, Pitch Black Skies said:

 

The prescription changes. Ours is an old Hungarian model. The mass produced Chinese varieties may give different results. YMMV.

The only way is to...

11 minutes ago, Pitch Black Skies said:

It would be interesting to see an image with same camera set at 53mm and then 55mm

Correct. Do post your findings.

Cheers.

Edited by alacant
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I have this one already ordered from a few days ago. If it seems okay I will keep it, but if not I will order the ones you mentioned and definitely do a comparison. I suppose what works for one might not work for all though. Thank you again for sharing your knowledge and experience.

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Just try and see....

I purchased the SW Aplanatic and I assumed it was 55mm and set my rig to this - even though it is a 600mm FL (I have not checked what the images plate solve to though). It gave good results but I have actually had to increase by about 0.25mm to get 'perfect' results. At 53mm my stars would be pretty poor.

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23 hours ago, Elp said:

it's not on GSOs website

It looks quite dated. For example, there's the m42 cc which may never have made it out of Taiwan. But anyway, I don't think they do retail. 

Cheers

 

 

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