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EAA for Meade ETX 125

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9 replies to this topic

#1 Brian.J.

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Posted 05 August 2020 - 12:53 AM

Looking for recommendations for an EAA for my Meade ETX 125 (1900mm f/15) telescope. Was looking at the ZWO ASI290 or 462 WC, any thoughts on what would work best or better options ? Not stuck on the ZWO line. Have no idea on how to calculate best EAA specs for my telescope.

 

Appreciate any advise.



#2 GazingOli

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Posted 05 August 2020 - 01:39 AM

1. question: which of the two threads you opened do you wish to continue wink.gif

 

2. You sure you want to stick to that scope?

 

if so then check for a reducer and a camera with small pixels and highest sensitivity

 

CS.Oli


Edited by GazingOli, 05 August 2020 - 01:40 AM.


#3 chilldaddy

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Posted 05 August 2020 - 01:20 PM

Brian,

 

Check out this FOV calculator, https://astronomy.to...field_of_view/ 

 

Plug in your scope and try different camera/focal reducer combinations on various objects to get a good feel for what to expect.

 

You'll definitely want a focal reducer.  A long focal length and small FOV is a challenging way to start.  Consider larger sensor cameras if your budget allows and at least a F/6.3 reducer/flattener or a cheap .5X reducer to get started.

 

Greg


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#4 GSBass

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Posted 05 August 2020 - 02:21 PM

Here is the tool, it really helped me, put your numbers in and use different combinations, the 462 has 2.9 pixels https://astronomy.to...ccd_suitability

Looking for recommendations for an EAA for my Meade ETX 125 (1900mm f/15) telescope. Was looking at the ZWO ASI290 or 462 WC, any thoughts on what would work best or better options ? Not stuck on the ZWO line. Have no idea on how to calculate best EAA specs for my telescope.

 

Appreciate any advise.



#5 GSBass

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Posted 05 August 2020 - 04:02 PM

I’m using the qhy462 with a 7” mak, it’s 2700 f15, I chose the camera based on mathematics for ideal sensor size, the website above lets you input your data and show the results. In my case under good seeing my mak and sensor was a perfect match, however as you adjust the numbers for less than perfect seeing then you had to add a focal reducer to get back in the range of perfect. So I ordered a focal reducer to cover all my bases. I’m not going to be able to image really large stuff but there is a lot of small stuff to go after for us mak users, I’ve only imaged one night but I have a few Planet and moon captures if you want to search my post, the moon capture is full frame so you can see the narrow field of view at this fl



#6 GazingOli

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Posted 05 August 2020 - 07:46 PM


a camera with small pixels and highest sensitivity

 

 

nonsense, of course - sorry. Big focal length needs big pixels... I mixed it up.

 

CS.Oli
 



#7 GSBass

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Posted 05 August 2020 - 08:15 PM

No you were right the first time, long fl = small pixels, at least when your talking prime focus on a f15 mak

nonsense, of course - sorry. Big focal length needs big pixels... I mixed it up.

 

CS.Oli
 


Edited by GSBass, 05 August 2020 - 08:18 PM.


#8 GazingOli

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Posted 05 August 2020 - 08:39 PM

don't they say that the image scale should be between 1 and 2 arcsec / pixel?

 

Image Scale = Pixel Size / Focal Length * 206

 

With 1900 mm focal length and 6.3 reducer you are roughly at 1200 mm focal length which requires 6 micron pixels to reach 1 arcsec per pixel...

 

I know that this is just theory and I am getting reasonable results with my C8 and 3.8 micron camera but I can see the difference when using a 6 micron camera and the 6.3 reducer.

 

This is M57 with C8 f/10 and ASI 224 camera:

 

M57.jpg

 

looks more pixelated than this one, also C8 at f/6.3 with Atik Infinity

 

M57InfinityCrop.jpg

 

CS.Oli


Edited by GazingOli, 05 August 2020 - 08:47 PM.


#9 GSBass

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Posted 05 August 2020 - 08:49 PM

I can’t express knowledge, I’m just using this tool https://astronomy.to...ccd_suitability

the results vary by what you input for seeing conditions


Edited by GSBass, 05 August 2020 - 08:50 PM.


#10 GSBass

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Posted 05 August 2020 - 09:08 PM

Running some numbers, it does appear for your example the recommended pixel size does go up as seeing quality goes down, I did buy my camera to give highest resolution in perfect seeing but this tool taught me I should use a focal reducer when seeing was lower, which is often of course but still works out good for me because my field of view is so small the focal reducer does make some object possible to fit on sensor, I’m just starting out with a .5 gso to experiment, gotta say though deep sky is secondary, on those rare nights when seeing is perfect I will be getting the highest resolution possible with the 7” and 462 combo at f15 prime focus on planets and moon, mathematically anyway


Edited by GSBass, 05 August 2020 - 09:09 PM.



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