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OAG camera selection...

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12 replies to this topic

#1 krockelein

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Posted 21 May 2019 - 12:28 PM

Hey, ya'll, here's the situation:

 

I am trying to go OAG instead of a guidescope so I can eliminate football shaped stars caused by flexure.  I picked up an inexpensive Orion OAG to pair with my Orion All in One camera.  But, due to noise and what I assume to sensitivity issues I have only once been able to pick up a star to caliberate PHD2.  Even with the bad pixel map and new dark library I still have a multitude of hot pixels.  So, I am looking around for a dedicated guide camera and have been leaning towards QHY5L-II, or the ASI120.  So, here's the question:

 

They all have the same sensor!!  Shouldn't I expect to get similar performance from the QHY and/or ASI?  If so, then I need to find a camera with a different sensor, right?  And if not, what factors influence the performance of the sensor that might differ between brands?

 

As always, thank you for your assistance!



#2 happylimpet

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Posted 21 May 2019 - 01:21 PM

I use the ASI120MM, and occasionally have trouble finding guidestars. If I were buying a new guidecam, id get the zwo asi290mm mini. More sensitive and lower noise.


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#3 BetaDraconis

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Posted 21 May 2019 - 01:44 PM

I use the ASI120MM, and occasionally have trouble finding guidestars. If I were buying a new guidecam, id get the zwo asi290mm mini. More sensitive and lower noise.

I second the ASI290MM-mini for OAG.


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#4 pgandy

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Posted 21 May 2019 - 04:17 PM

I third the ASI290-mini. I started out with the 120mm that I already had then switched. The 290 is amazing by comparison, it locks on to even questionable SNR targets and sticks. Don't have experience with your other possibility mentioned.

 

Paul



#5 TinySpeck

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Posted 21 May 2019 - 04:55 PM

Here's a fourth, from someone who also just switched from ASI120 (albeit MC) to ASI290MM mini.  It's about the same sensor area but smaller pixels.  With the smaller pixels you can reduce the guide cam focal length and still have good star resolution for guiding.  I have a separate telecompressor on my guide cam, so I get a bigger FOV (and smaller stars) in my guide cam than I would if I were compressed the same as my image.  This provides more opportunity for the guider to find stars.  You can use a cheap $35 0.5x 1.25" compressor for your guide cam.  Mine is a GSO from Agena Astro, but others are available too.



#6 cfosterstars

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Posted 21 May 2019 - 05:06 PM

HEre is a fifth. The only reason to consider the ASI174MM-Mini is if you have a large prism. Most OAGs have at most a 8mm prism and you gain no advantage over the ASI290MM-mini and it costs significantly more. The ASI290MM-mini is a good camera. I am just now trying out OAG and I am trying out both an ASI290MM-Mini and a ASI174MM-mini since i have both the QHY-M (8mm prism) and the Celestron OAGs (11mm prism). 



#7 freestar8n

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Posted 21 May 2019 - 06:01 PM

I have a 12mm prism and I don’t think it is that uncommon nowadays. If you have a 174 in 1.25” format and you can get it close to the prism it will receive a good amount of light with only slight vignetting. I use it with edgehd 11.

Frank
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#8 telfish

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Posted 21 May 2019 - 06:55 PM

Here is a sixth for the 290 mini. Very sensitive, good size chip.



#9 krockelein

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Posted 21 May 2019 - 08:31 PM

wow, there seems to be a definite consensus here!  alright, i will start saving my money and watching the classifides for the asi290 mini.  I was worried that the small chip size would lead to a loss of sensitivity, especially when paired with the 1600mm focal length on my main telescope, but apparently not going to be much of an issue given the OTAs you all have.

 

Once again, CN has proven to be the online home of champions!!  Thank you all!!



#10 james7ca

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Posted 21 May 2019 - 09:22 PM

There are a number of past threads on guide camera selection that should probably be referenced if you want to make a fully informed choice.

 

Here is one, that has some interesting graphs to compare various sensors:

 

  https://www.cloudyni...t/#entry6941285

 

All that said, if you are looking specifically for something to be used with an OAG and you have an OAG with a large enough prism then the ASI174 mini is hard to beat. However, the OP's "inexpensive Orion OAG" probably doesn't warrant using a chip as large as found in the IMX174.

 

As for the ASI290 Mini, that's a good guide camera but for an OAG you'll probably want to bin the pixels.



#11 freestar8n

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Posted 21 May 2019 - 10:53 PM

If you have a big enough prism and can illuminate the sensor, the 174 has 4.5x the area of 290. And that translates to 4.5x the odds of a good guidestar in view.

But if you are able to find guidestars easily enough with 290 then larger may not be needed.

New oag users may find challenges with guidestars and a larger field of view helps.

Frank

#12 ChrisWhite

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Posted 22 May 2019 - 08:09 PM

I use the 290mini and it's great.  I've never had a problem finding guidestars even at 920mm FL.  I usually have 10 to 20 or more to choose from. 

I was a beta tester for this camera and you can find that thread here: https://www.cloudyni...ta-test-thread/

#13 baron555

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Posted 22 May 2019 - 08:27 PM

Lodestar X2




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