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OAG: Loadestar X2 or other?

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#1 Hawkdl2

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Posted 31 March 2020 - 04:04 PM

I've had good luck ASI1600mmm-c imaging through my RC10 with a solidly mounted 80mm guide scope and a QHY5Lii-m guide camera.  I usually get guiding in the range of 0.5 to 1arc sec. - typically 0.7-0.8.  I suspect my guiding is seeing limited, but it's time I see if I can improve guiding with an OAG.  I bought a ZWO OAG and plan to upgrade my guide camera. I had researched this and concluded the Lodestar X2 was the best option, then read a thread recently that said one of the ZWO cameras is better with OAGs.  So, I'm back to square one of which camera to buy.  Time to give up solo-researching and ask for opinions and advice from anyone who's familiar with the Lodestar X2 and the ZWOs.



#2 Gene3

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Posted 31 March 2020 - 04:33 PM

I had the QHY5Lii and then the Lodestar X2. I then switched to the SX-Ultrastar (Lodestar X2 big brother) and it made an incredible difference in my ability to find and use a suitable guide star. I do not have any experience with ZWO.



#3 FlankerOneTwo

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Posted 31 March 2020 - 05:20 PM

I have the Lodestar X2 and it is significantly more sensitive than the other cams that I've used for guiding (QHY5III 174 and 178, ASI 290). Having said that, I've not yet had a problem finding guide stars with those other cams and still use them for guiding in some of my setups. But I suppose in particular areas of the sky the increased sensitivity would be an advantage.



#4 APshooter

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Posted 01 April 2020 - 12:01 AM

I too have the lodestar X2.  Used it reliable for hundreds of hours  for narrowband imaging.  I have 4 ZWO cams but haven't tried them on the OAG.  Shooting at F6 with the 5" refractor I never felt the need for something more sensitive.  ZWO cams would probably work well and are significantly cheaper .



#5 james7ca

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Posted 01 April 2020 - 01:03 AM

The Lodestar X2 has 8.3um pixels (actually 8.4um x 8.2um)  which will give it some advantage in terms of effective sensitivity. Compare that to another good sensor for OAG applications, the IMX174 that has 5.86um pixels. Now take the square of both of those pixel sizes to estimate the difference in photon gathering potential for each sensor:

 

 Lodestar: 8.3^2 ≈ 69

 IMX174: 5.86^2 ≈ 34

 

Thus, a 2x advantage for the Lodestar.

 

However, the IXM174 is a larger sensor than the Lodestar so that COULD be an advantage if your OAG has a large enough prism to cover the entire sensor (which I suspect would NOT be the case for the ZWO OAG). The respective area of both sensor is as follows:

 

Lodestar: 6.52mm x 4.89mm ≈ 32 square millimeters

IMX174: 11.3mm x 7.1mm ≈ 80 square millimeters

 

Advantage definitely to the IMX174.

 

But, as I mentioned earlier I doubt that the ZWO OAG could take full advantage of this particular difference.

 

Then, you'd have the possibility of binning the IMX174 which would probably provide near equivalence in terms of photon gathering and sensitivity to the Lodestar. But, that's going to halve the image scale of your guiding which could become an issue. Given your 10" RC (f.l. 2032mm) and with a binned IMX174 you'd have a guiding image scale of 1.19 arc seconds per pixel which I think would be fine, so no issue even when binning. However, if you used a scope with a much shorter focal length then the "fit" (when binned) would not be as good.

 

You could also bin the Lodestar and that would result in a scale of 1.69 arc seconds per pixel. Note, that with the ASI1600 you'd have a primary image scale of just 0.39 arc seconds per pixel and I certainly wouldn't want to go to a guide scale over 2 arc seconds per pixel with that combination. So, in terms of guiding scale the binned IMX174 is probably somewhat better than the binned Lodestar (but both are still okay, even when binned).

 

So, it may come down to an issue of cost and driver support where the IMX174 is cheaper and where driver/software support MAY be somewhat of a "wash" (I don't know if compatibility and stability would favor either the Lodestar or the ZWO ASI174).



#6 Hawkdl2

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Posted 01 April 2020 - 02:34 PM

Lot's of great input.  Thanks!   It looks like I could go either way, so price and availability might be the deciding factor. 




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