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ASI294MM Pro and William Optics GT81 setup: Do I have it right?

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#1 seanboon

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Posted 30 January 2021 - 02:25 AM

My ASI294MM Pro arrived this week and of course the rain rolled in with it and who knows when I will get to use it.   However, I know I need to get the backspace right and think I need some help.  I have the WO GT81 and then attached to that I have the Adjustable Flattener/Focal Feducer Flat 6AIII.   Attached to that I have the M42M-M48F 16.5L piece that came with either the filter wheel or the camera.   Attached to that piece, I attached the 1.25" 7 position filter wheel and then attached directly to the filter wheel I attached the camera.  

 

Did I hook that up correctly?  What should the value be set to the adjustable flattener, assuming I do have it connected correctly? After I get this part correct, I have the autofocuser to install and then hopefully I can start building that dark library to deal with the amp glow smile.gif.

 

Thanks,

Sean

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#2 seanboon

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Posted 30 January 2021 - 02:52 AM

I found this post which suggests I might have been missing a couple of pieces so I have added them in.

 

https://www.cloudyni...ield-flattener/

 

Specifically the T2 Extender 11mm and the m42-m42 adapter male.   So I think that is the right train of components.  I think the flattener is supposed to be set to 7.1.  Do I have that right?

 

Thanks,

Sean

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Edited by seanboon, 30 January 2021 - 03:03 AM.


#3 sg6

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Posted 30 January 2021 - 05:07 AM

I have the WO GT81 and then attached to that I have the Adjustable Flattener/Focal Feducer Flat 6AIII.   Attached to that I have the M42M-M48F 16.5L piece that came with either the filter wheel or the camera.   Attached to that piece, I attached the 1.25" 7 position filter wheel and then attached directly to the filter wheel I attached the camera.

 

Doubt anyone can give a specific answer as the added path of items is not given.

 

The M42M-M48F 16.5L piece (??) what is the 16.5 relevant to. Is it the added spacing ?

What is the added spacing of the filter wheel ? Often seems to be 20mm but not specified.

Does the 294 have the 11mm attachment on it? Guess it does for the filter wheel but cannot recall if it has to be present or not.

 

The WO Flattener has a required separation of 55mm from the attachment face to the sensor - well usually.

 

If the 16.5L piece is the added spacing and if the filter wheel is 20mm and if the camera has the little extension/attachment ring of 11mm and the standard flange to sensor of 6.5mm the all the spacing adds up to 54mm.

 

Meaning the flattener has to be set to 1mm. The filters should mean you will set to 2mm as the glass alters the optical path.

 

However I have had to make too many assumptions and if any 1 is wrong - or the whole lot - then everything is wrong.



#4 Tapio

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Posted 30 January 2021 - 05:15 AM

I looked at WO site and it says like this:

'Adjust distance for DSLR or mirrorless cameras - GT81 - 7.1mm'

 

But ASI294  has different backfocus than DSLR or mirrorless so don't know if 7.1mm applies.

Important is this figure - back focus GT81 62.1mm.

This is the distance you should have between reducer and camera sensor.

Guess you have to try it and see how good stars you get.



#5 pbmazda32

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Posted 30 January 2021 - 06:22 AM

OP, I recently went through this with my GT71, same flattener you have. My setup required 64.1mm if memory serves. I got as close as I could with the extension tubes/spacers, and then used the adjustment on the flattener to fine tune it. Took a couple nights of adjustments on the flattener, but I think I have it dialed in now. Math and measurements didn't solve my problem, it got me close, but the only way I could really dial it in was taking photos and inspecting them and then adjusting again.


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#6 BobE102330

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Posted 30 January 2021 - 06:35 AM

WO gives flattener settings based on 55mm from flattener to sensor. ZWO provides spacers with the cameras to get 55 mm. Follow the ZWO guide. 
 

Remember that the filters subtract about a third of their thickness from the effective back spacing. I added about an extra 1 mm to my flattener adjustment to compensate. I got good star shapes with that, you may need to experiment a bit to find the optimum setting. 


Edited by BobE102330, 30 January 2021 - 06:36 AM.


#7 JStarCN

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Posted 30 January 2021 - 06:41 AM

OP, I recently went through this with my GT71, same flattener you have. My setup required 64.1mm if memory serves. I got as close as I could with the extension tubes/spacers, and then used the adjustment on the flattener to fine tune it. Took a couple nights of adjustments on the flattener, but I think I have it dialed in now. Math and measurements didn't solve my problem, it got me close, but the only way I could really dial it in was taking photos and inspecting them and then adjusting again.

^what he said.

I have never known the spec to be exactly correct. 

Get it close and tweak.



#8 seanboon

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Posted 31 January 2021 - 01:15 AM

Ok, thanks everyone!   We have nothing but rain as far as my forecast goes out, but I did get everything hooked up, including the autofocuser with the ASIAirPro and I'm taking some darks tonight in the garage.   I'm going to see if there is a way I can work on the focus during the day tomorrow if that is possible and also to see if there is a way I can test the coverage of the filters with respect to the sensor.

 

Thanks,

Sean



#9 BobE102330

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Posted 31 January 2021 - 12:00 PM

You should be fairly close with the focuser racked out to 30-35.

#10 Cfreerksen

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Posted 31 January 2021 - 12:58 PM

The proof is in the putting. Do a test shot of at least1 minute and see what your stars look like. follow this guide to getting it as good as possible. With the adjustable flattener you can just unlock the ring and dial in a tiny out or in to get the edges perfect.

 

Chris

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#11 seanboon

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Posted 31 January 2021 - 10:30 PM

It’s another night of darks in the garage.  I did manage to try and focus today on a tree top that is maybe a few hundred yards away with the the blue filter and was at least able to get close with that.  Thanks for posting that graphic above.  I’m assuming that when I get to focus with the night sky, I should do so on the luminance filter?  All of my filters are Astronomiks and the 7 position filter wheel is totally full.



#12 jonnybravo0311

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Posted 01 February 2021 - 12:29 PM

It’s another night of darks in the garage.  I did manage to try and focus today on a tree top that is maybe a few hundred yards away with the the blue filter and was at least able to get close with that.  Thanks for posting that graphic above.  I’m assuming that when I get to focus with the night sky, I should do so on the luminance filter?  All of my filters are Astronomiks and the 7 position filter wheel is totally full.

You're going to have to focus with every filter - not just the L. This is where those lovely auto-focusers are so handy. Without one, every filter switch, you're going to have to manually adjust focus.



#13 seanboon

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Posted 10 February 2021 - 02:08 AM

Finally got first light tonight with the ASI294MM Pro combined with the ZWO EAF Focuser, 7 Position filter wheel and GT81 IV.    I went with M45.  When I fired up the ASIAir Pro I got hit with a dreaded firmware update required.   Then after the update, it failed to move the mount to the correct coordinates.   I shut everything down, untangled all my cables and tried again.  Success.    The autofocuser looks to be the real deal.   I ran Pixinsight subframe selector on it and I"m running between 4-6 FWHM which isn't great, but it's way better than what I was getting my old system of the Nikon D750 and no autofocuser.    I was shooting 30 second frames so maybe that had something to do with it.  I think my backspacing is good.  I don't know if this is a new feature in the ASIAIR Pro update but when you shoot flats now it has an "auto" option for the exposure length and so instead of trying a bunch of different shots in preview mode, it will do the work for you on the Autorun feature.   I was able to tell it to take flats for R, G, B and L in autorun and walk away.   Super happy with the set up.   I haven't actually processed any pictures yet but at least the ones that didn't get hit with clouds look good.    I've already shot all of my dark frames with the rainy nights here.  


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#14 ant-man

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Posted 12 February 2021 - 09:53 AM

Hello! I am thinking about the same camera as you have. In your dark frames, do you have prominent AMP GLOW? Is that a problem at all? Some people say they completely go away with proper calibration. 



#15 seanboon

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Posted 12 February 2021 - 03:38 PM

Yes, there is definitely prominent amp glow in my darks.   The pictures you may have seen of it are definitely similar to what I am seeing.




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