New Camera QHY5 178

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Umair Asim
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New Camera QHY5 178

Post by Umair Asim » Wed Aug 17, 2016 6:55 am

Hi all, I have LUNT 152 and an 127mm APO awarded by CBSAP. I have been using DMK21 (old version) for years. Now is the time to upgrade the camera. This one seems really nice. What are your thoughts about it.

http://www.qhyccd.com/QHY5III.html
https://www.telescopi-artesky.it/qhy-cc ... usb-3.html



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Re: New Camera QHY5 178

Post by Montana » Wed Aug 17, 2016 2:27 pm

I have no idea about that particular camera but there are some interesting comments in this post viewtopic.php?f=4&t=17660&p=170130&hili ... ch#p170130
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Re: New Camera QHY5 178

Post by marktownley » Wed Aug 17, 2016 3:41 pm

I personally think the pixels are rather small. You won't be able to ramp the focal length up too much without oversampling.


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Re: New Camera QHY5 178

Post by Umair Asim » Sat Aug 20, 2016 7:54 am

Thanks Alexandra for sharing the link.

Mark, Smaller pixel will allow me to avoid barlow, which should result in a bright image (unlike using a barlow). Don't you think that will be better?



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Re: New Camera QHY5 178

Post by GreatAttractor » Sun Aug 21, 2016 8:54 am

Umair Asim wrote: Mark, Smaller pixel will allow me to avoid barlow, which should result in a bright image (unlike using a barlow). Don't you think that will be better?
Nope, it's not the case. Consider a camera with 1 µm pixels (Cam1) and another with 2 µm (Cam2). For a given telescope, to obtain the same image scale (arc seconds/pixel) on both cameras, you'd need a 2x Barlow for Cam2. Such a Barlow creates a 2 times larger image with 4 times less surface brightness, however Cam2 has 4 times larger pixels than Cam1, so the captured image brightness (photons/pixel) is the same as in Cam1.

The questions of smaller vs. larger pixels can be important if you have a setup with very large effective focal length, e.g. a Quark. In such case it's better to have big pixels, so the image is not oversampled (and not too dark). For small pixels with such a setup you'd have to use a focal reducer, which is much less reliable (possible optical aberrations, uneven brightness) than using a Barlow.

On the other hand, having large pixels and a short focal length telescope is not a big problem, you just use a Barlow (which usually doesn't introduce significant image problems) to enlarge the image to optimal scale.

From my experience, for 3.75 µm pixels a focal ratio of f/11.2 gives appropriate sampling. For 2.4 µm, as in e.g. QHY5III178, this would be ~f/7.2, so close to Lunt 152's f/8. However, I cannot say anything about QHY's performance in Hα.


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Re: New Camera QHY5 178

Post by PDB » Sun Aug 21, 2016 11:23 am

2.4 µm is indeed small for longer focal lengths. I have the ZWO 178 (same chip as th QHY) and if i use that for solar i use 2x binning which brings appropriate sampling at around f/15. (Actually bought that camera for primary focus work at f/10 with my C8) I used the camera for Hα and the only problems i got were interference rings (which dissapeared wit focal reducer, 2x binning or camera tilt). But of course this was the ZWO model.


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Re: New Camera QHY5 178

Post by Umair Asim » Fri Aug 26, 2016 9:43 pm

hmm. thanks for the help guys. I actually have been using DMK21 for years now and desperately need to upgrade it. What do you think i should look at for Lunt 152 telescope?



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Re: New Camera QHY5 178

Post by Montana » Sun Aug 28, 2016 10:50 am

I would PM Pedro Re, he has a Lunt 152 and has trialled a lot of cameras on it, I think he would be a good person to recommend one. Gabrieli is another 152 owner with many cameras you could try.

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Re: New Camera QHY5 178

Post by marktownley » Sun Aug 28, 2016 7:05 pm

I'd go for something with 4-5um pixels.


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Re: New Camera QHY5 178

Post by Umair Asim » Tue Aug 30, 2016 6:16 pm

Dear Alexandra, cant find Pedro Re here.



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Re: New Camera QHY5 178

Post by Montana » Mon Sep 12, 2016 11:05 am




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