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Is anyone running a coma corrector, filter wheel and an OAG?


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I have an MPCC Mark III coma corrector which is attached to my ZWO manual filter wheel (20mm thick). The other side of the filter wheel attaches to the ZWO 1600 and I have a ZWO OAG to add into the chain. If I put it in front of the coma corrector I cannot get enough 'in focus', is this something that has been overcome by anyone?

 

image.png.e30e6211669382606b020981a4ff62c3.png

 

James

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7 hours ago, tooth_dr said:

Can you set it up like below?

 

7B1136CE-C642-46EB-B836-06A1E06CFC30.jpeg

You’ve missed off the coma corrector! I have the same problem, which is why I’ve had to revert to a separate guidescope when capturing with my 200mm Newt.

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19 minutes ago, lukebl said:

You’ve missed off the coma corrector! I have the same problem, which is why I’ve had to revert to a separate guidescope when capturing with my 200mm Newt.

No it goes on the end left side 

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1 hour ago, tooth_dr said:

No it goes on the end left side 

I know it does, but that's the whole problem.

Your illustration doesn't show a coma corrector, which is the very thing preventing focus. At least in my case.

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4 minutes ago, lukebl said:

I know it does, but that's the whole problem.

Your illustration doesn't show a coma corrector, which is the very thing preventing focus. At least in my case.

Is that a 2” drawtube?  The CC goes inside it.  

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1 hour ago, JSeaman said:

Thanks all, I could put the coma corrector into the draw tube and then the OAG I guess, will have a play - thanks!

In the first photo it looks like the OAG has a 2” nosepiece attached and is inserted into the drawtube?

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Oh ,sorry, the OAG has an M42 male thread rather than a nosepiece

The 1600 is 17.5mm (with the included 11mm ring) then 20mm for the FW and ~18mm for the OAG = 55.5mm, should be just about right hopefully!

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On 06/12/2021 at 09:59, tooth_dr said:

Is that a 2” drawtube?  The CC goes inside it.  

I appreciate that the CC goes inside the drawtube, but the problem is still an inability to focus in far enough. However, I found that the problem was with a Skywatcher Coma corrector. Using a Baader Coma Corrector I can reach now focus.

UNFORTUNATELY, there is another problem I hadn't forseen in that the CC is over 80mm from the focal plane, rather than the corrrect 55mm, resulting in terrible coma. In fact, worse coma than without a CC at all!

This all arose because I downized recently (now deeply regretting selling my RC8 and Atix428ex camera) and am just left with a 200mm Newt and an Atik 383L. I think that basically, It's just not possible to use a CC, an OAG (even a slimline one), and the Filter wheel with an Atik 383L and 200mm Newt.

Unless someone can prove me wrong.

This is the current unsatisfactory setup.

51739798484_58bf779a2b_b.jpg

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35 minutes ago, lukebl said:

I appreciate that the CC goes inside the drawtube, but the problem is still an inability to focus in far enough. However, I found that the problem was with a Skywatcher Coma corrector. Using a Baader Coma Corrector I can reach now focus.

UNFORTUNATELY, there is another problem I hadn't forseen in that the CC is over 80mm from the focal plane, rather than the corrrect 55mm, resulting in terrible coma. In fact, worse coma than without a CC at all!

This all arose because I downized recently (now deeply regretting selling my RC8 and Atix428ex camera) and am just left with a 200mm Newt and an Atik 383L. I think that basically, It's just not possible to use a CC, an OAG (even a slimline one), and the Filter wheel with an Atik 383L and 200mm Newt.

Unless someone can prove me wrong.

This is the current unsatisfactory setup.

51739798484_58bf779a2b_b.jpg

 

I'm going to say that this is entirely possible, in fact 100% it works, because at one point I used an Atik 383L+, EFW, OAG and MPCC with a range of SW newts (200, 250, 300), only one of which was the PDS version, the others were the visual versions.

Firstly regarding your measurements above: the backfocus of the camera is 17.5mm, and if you are using the M48 threads then the backfocus you need to the MPCC shoulder is 57.5mm.    You have some sort of additional adapter between the OAG and the MPCC, I cant really tell what is going on with that photo.  I'm not sure how simply swapping from a SW flattener to an MPCC added 25mm to your back focus?

Looking at the photo, you have 40mm space to use up between the camera face and the MPCC to get the correct backfocus.  If your OAG + FW measure more than 40mm then you need to address this separately, and this is nothing to do with focuser. Based on the photo above I cant see how you are over 85mm from the CC, unless of course you are measuring from the end of the CC rather than the shoulder, or measure the distance to the CCD plane incorrecly.

This is my set up - ignore the fact it's a QHY9 - this is the same camera as the Atik 383L, but I just dont have a photo of that to post. You can see I went one further and added a Baader clicklock - this actually takes up about 10mm more that the standard focuser, and I still was able to get enough inward travel.

You havent posted what brand of 200mm scope you are using, but certainly if it's one of the main stream cheap ones like my SWs, then all of the above is relevant.

IMG_2542.thumb.jpeg.473585cc63c01e9b1c75980d9dea4bbf.jpeg

 

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37 minutes ago, tooth_dr said:

I'm going to say that this is entirely possible, in fact 100% it works,...

Thanks for that. It certainly sounds more promising!

I'll have a look more closely at the connectors and see if I can get something more slimline. I was measuring the CC from the wrong point, so the distance was closer to around 72mm but still too much. My current connector also separates the Atik from the filter wheel by about 6mm so it's not flush like yours.  I'll see if i can reduce that.

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1 hour ago, lukebl said:

Thanks for that. It certainly sounds more promising!

I'll have a look more closely at the connectors and see if I can get something more slimline. I was measuring the CC from the wrong point, so the distance was closer to around 72mm but still too much. My current connector also separates the Atik from the filter wheel by about 6mm so it's not flush like yours.  I'll see if i can reduce that.

And the next problem is getting the old connector off the camera. It is stuck fast, and as you can see I've somewhat wrecked it in my attempts to remove it (although the camera's fine).

There are no end of discussion threads about this on various forums (using mole grips, rubber shoe soles, etc), but I haven't found anyone with a satisfactory answer. Sorry, I seem to have hijacked this thread!

51740311890_805442fed1_b.jpg

Edited by lukebl
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43 minutes ago, lukebl said:

And the next problem is getting the old connector off the camera. It is stuck fast, and as you can see I've somewhat wrecked it in my attempts to remove it (although the camera's fine).

There are no end of discussion threads about this on various forums (using mole grips, rubber show soles, etc), but I haven't found anyone with a satisfactory answer. Sorry, I seem to have hijacked this thread!

51740311890_805442fed1_b.jpg

Nightmare! I’d try holding the camera downwards and pushing against a hard rubber surface and turning it that way. 

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50 minutes ago, lukebl said:

And the next problem is getting the old connector off the camera. It is stuck fast, and as you can see I've somewhat wrecked it in my attempts to remove it (although the camera's fine).

There are no end of discussion threads about this on various forums (using mole grips, rubber shoe soles, etc), but I haven't found anyone with a satisfactory answer. Sorry, I seem to have hijacked this thread!

51740311890_805442fed1_b.jpg

As weird as it sounds, in a similar situation, I had good success with a jar opener tool  - effectively a grip with a rubber insert to grip the thread.

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  • 4 weeks later...

I finally got a chance to try this and it worked well with the MPCC in the draw tube. I then had two problems:

1. The stock focuser kept falling down, I have just finished fitting my Steeltrack to test that later

2. The guiding using the 1500 focal length was crazy, it just didn't work at all. I have reverted back to the ED80 as a guide scope for now

 

As for removing the stuck fine pitched threads, I favour upside down on a rubber glove pushing down and twisting. Sometimes you need to pinch the corners with mole grips too

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