Analysis Paralysis - ZWO vs QHY & Filter Options

[upahill]

I've been tearing my last few hairs out trying to make the call between a few different camera options and filter options but just not sure which way to go. Ideally I want to get into some narrowband - 99% sure I want mono over OSC. Undecided between CMOS and CCD options though. To begin with it will be used on the TS65mm Quad, but want to ensure whatever I get can be used with a larger newt/frac etc too in a year or two.

FLO have the package deal for the ASI1600mm Pro + Filter Wheel - this comes with 3 filter size options to which I was leaning towards the 31mm or 36mm after reading there can be issues with the 1.25". I am at f/6.4 right now but wanted to leave a bit of room should I get a faster newt.

The other alternatives were the QHY163M, which is the same ballpark price as the ASI1600 - I cant discern any major differences between the two units other than very tech figures regarding noise. Any advice on a comparison between the two units? Bintel says Good sampling at 1.87" /pixel for this and the ASI. If I go for this option I would still need to source filters/wheel etc so looking at closer to

The other contender was the QHY10 - CCD, 16bit over 12, larger pixels - Bintel suggested this camera would slightly undersample with a resolution of 2.97" /pixel

Filterwise there are two options in my price bracket - ZWO or Baader. There isn't much between the prices on any of these options:

Any suggestions, curveballs or tips appreciated, its kind of all melded into one thing in my head right now.

 

[david_taurus83]

What's your usual seeing conditions? FWHM values? With the QHY at that focal length you run the risk of blocky stars. Personally I'd go for smaller pixels at 420mm. My WO 71 is 420mm. See below an example of a 30s sub with the ASI1600. The average FWHM value for the picture was around 3". With a longer exposure I'm sure tracking errors and seeing would probably increase this value but if the pixels were larger the smaller stars wouldn't look good at all. I suppose it depends on how much your going to pixel peep!

[upahill]

Currently DSS reckons my FWHM is anywhere between 3 and 5 if im understanding it right.

Im not looking for exacting standards when it comes to pixel peeping - but dont want to miss out on finer details that I could otherwise get by making a different choice. This camera needs to last me a few years but anything is going to be a step up from the noisy 1200d im using right now I guess.

I was worried about the slight undersampling on the QHY10 - but its the only 16bit CCD option compared to the other two 12bit CMOS cameras. Or am I barking up the wrong tree with CCD being preferable perhaps?

I still have my fingers crossed that I might snap up a bargain on the second hand market which could well sway the decision regardless 😂

[geordie85]

You may be slightly under sampled with the qhy 10 but if you end up getting a longer focal length newt or frac later on then this will bring your sampling down and not be over sampled. 

[rickwayne]

The consensus seems to be that practically speaking, unless money is no object CMOS wins out over CCD these days. 12-bit readouts aren't as much of a limitation as you might think, at least not if you're stacking.

There's a current discussion going over at the CN beginning/intermediate forum that's mostly on point for that, Jon Rista notes:

The main benefit of 14 or 16 bits over 12 bits is that the gain at which quantization error becomes effectively meaningless is lower. Lower gains have more dynamic range, and thus you can potentially better-utilize the DR the sensor hardware has to offer with higher bit depths. With lower bit depth cameras, we can recover DR by stacking more subs. With lower read noise, we can use shorter exposures than with higher read noise, and since lower bit depths and lower read noise generally come in pairs, bit depth in practice (assuming you are processing in 32-bit float or higher precision), need not be a primary concern. A 12-bit camera might not be the best choice if you want to acquire very long exposures and stack only a few subs...but if you are stacking 90 subs or more, I would not really be concerned about bit depth.

[JamesF]

In another thread it was recently posted that (if I recall correctly) CCDs don't really produce 16-bit data anyhow, as a number of the lower bits are really just noise.

James

[rickwayne]

As someone who often agonizes about this kind of thing, I note that if you miss one night of imaging because you can't decide, you're already likely behind the curve of total satisfaction over time. You can't go very far wrong with these choices, right? Otherwise it wouldn't be hard to decide.

[upahill]

2 minutes ago, JamesF said:

In another thread it was recently posted that (if I recall correctly) CCDs don't really produce 16-bit data anyhow, as a number of the lower bits are really just noise.

James

Interesting, and if like rickwayne says the benefits of the 16bit can be achieved by stacking more subs then maybe the smaller pixel cmos option is ultimately better.

1 minute ago, rickwayne said:

As someone who often agonizes about this kind of thing, I note that if you miss one night of imaging because you can't decide, you're already likely behind the curve of total satisfaction over time. You can't go very far wrong with these choices, right? Otherwise it wouldn't be hard to decide.

This is a good point, and I have lost plenty of nights fighting with the canon too. If I was going OSC I wouldn't agonise about it as at least the upgrade can be staged, camera, then a while later filters/wheel etc. With mono I have to kind of do it one go and that makes the decision just that little bit scarier

4 hours ago, geordie85 said:

You may be slightly under sampled with the qhy 10 but if you end up getting a longer focal length newt or frac later on then this will bring your sampling down and not be over sampled. 

Good point, I ran the calculator for some other scopes and the QHY10 undersamples on my TS65 but is fine for most others. If I understand it correctly oversampling can be solved by binning on very long focal lengths. That would make the ASI options the best all rounders on that metric.

 

[JamesF]

I have been tempted by the 1600MM myself, though I still want to get my head around some of the issues.  For me those are probably:

1) There have been some issues with strange shape stars, possibly due to optical effects within the camera itself, but these may only occur in specific conditions and I don't know what those are and if they'd be likely to affect me.

2) Some of the CMOS sensors have what often seems to be called amp glow, but actually seems to be "pollution" from (IR?) light sources close to the sensor.  Some camera models appear to be far worse than others.  I want to understand what I'd be letting myself in for in that respect, how hard it is to calibrate out and what side-effects there might be as a result.

James

[upahill]

14 minutes ago, JamesF said:

I have been tempted by the 1600MM myself, though I still want to get my head around some of the issues.  For me those are probably:

1) There have been some issues with strange shape stars, possibly due to optical effects within the camera itself, but these may only occur in specific conditions and I don't know what those are and if they'd be likely to affect me.

2) Some of the CMOS sensors have what often seems to be called amp glow, but actually seems to be "pollution" from (IR?) light sources close to the sensor.  Some camera models appear to be far worse than others.  I want to understand what I'd be letting myself in for in that respect, how hard it is to calibrate out and what side-effects there might be as a result.

James

Hmm I had heard of the first problem but not the latter. I also want to see if anyone has issues with condensation. I noticed that FLO sell a heater strip so this could be a potential issue?

[geordie85]

29 minutes ago, JamesF said:

 

2) Some of the CMOS sensors have what often seems to be called amp glow, but actually seems to be "pollution" from (IR?) light sources close to the sensor.  Some camera models appear to be far worse than others.  I want to understand what I'd be letting myself in for in that respect, how hard it is to calibrate out and what side-effects there might be as a result.

James

When I used to image with an atik 383L I'd always have an issue with frosting on the window and would need to wait for it to "melt" before I could start imaging. 

With the qhy183c I've never had this problem or any condensation problems and I do cool it quite quickly. 

My qhy183c does have amp glow on the right hand side that looks quite scary when just the lights are stacked, (it's definitely not "pollution" as no matter how the camera is oriented, it's always in the same place) but it completely calibrates out when using the correct calibration frames. I've never had a problem with any remaining amp glow after correct stacking. 

Hope this helps. 

Edited June 2, 2019 by geordie85

[JamesF]

7 hours ago, geordie85 said:

My qhy183c does have amp glow on the right hand side that looks quite scary when just the lights are stacked, (it's definitely not "pollution" as no matter how the camera is oriented, it's always in the same place)

I was using "pollution" in the sense of being a contaminant, not light pollution from outside the imaging system.  From what I've seen I think it's possible that some sensors have something in their design that causes an effect similar to amp glow, but isn't actually amp glow.  Because it's in a fixed position relative to the rest of the sensor, it will always be in the same place in the image frame.

What I've yet to get my head around is whether these things do genuinely calibrate out, as I feel sure that even doing so must compromise the available dynamic range, in some cases very significantly.

James

[david_taurus83]

8 hours ago, JamesF said:

I have been tempted by the 1600MM myself, though I still want to get my head around some of the issues.  For me those are probably:

1) There have been some issues with strange shape stars, possibly due to optical effects within the camera itself, but these may only occur in specific conditions and I don't know what those are and if they'd be likely to affect me.

2) Some of the CMOS sensors have what often seems to be called amp glow, but actually seems to be "pollution" from (IR?) light sources close to the sensor.  Some camera models appear to be far worse than others.  I want to understand what I'd be letting myself in for in that respect, how hard it is to calibrate out and what side-effects there might be as a result.

James

Your talking about the microlensing effect on the Panasonic sensor. Any other camera that uses this sensor may exhibit the same artifact on bright stars. Though it may depend on your optical system of how well its controlled. See my image of the Horse and Flame. 16 x 15 minute subs in Ha. Optical configuration is WOGT71, Idas D2 LPS in front of Flat 6A II reducer, spacers, filterwheel and ASI1600. See how well Alnitak is controlled compared to other images. Though I would say this is a lucky configuration..

 

I've not heard of the second issue. Sure, it suffers amp glow on the top right and bottom right hand side but calibrated out just fine. Again, below is a stack of 15 minute subs and all the amp glow has been removed.

[david_taurus83]

8 hours ago, upahill said:

Hmm I had heard of the first problem but not the latter. I also want to see if anyone has issues with condensation. I noticed that FLO sell a heater strip so this could be a potential issue?

No issues here with condensation and have been cooling to -25. The ZWO design intends that the excess heat from the heat sink acts like dew prevention on the sensor window. Though you do need to run the cooler/fan hard enough to generate the heat in the first place.

[JamesF]

17 minutes ago, david_taurus83 said:

Your talking about the microlensing effect on the Panasonic sensor. Any other camera that uses this sensor may exhibit the same artifact on bright stars. Though it may depend on your optical system of how well its controlled. See my image of the Horse and Flame. 16 x 15 minute subs in Ha. Optical configuration is WOGT71, Idas D2 LPS in front of Flat 6A II reducer, spacers, filterwheel and ASI1600. See how well Alnitak is controlled compared to other images. Though I would say this is a lucky configuration..

This is one of the things that I need to get a better handle on.  I'd prefer not to drop that much on a camera only to find out that I had one of the "unlucky" configurations.

James

[david_taurus83]

24 minutes ago, JamesF said:

This is one of the things that I need to get a better handle on.  I'd prefer not to drop that much on a camera only to find out that I had one of the "unlucky" configurations.

James

That's understandable but it is usually on exceptionally bright stars it occurs. There are many many people happy with the ASI1600. It's a lot of sensor for the money.

[Adam J]

19 hours ago, upahill said:

Any suggestions, curveballs or tips appreciated, its kind of all melded into one thing in my head right now.

 

You talk about both 31mm and 36mm filters in the case of the QHY163m you wont be able to use both in one filter wheel.

My choice would be for 36mm unmounted filters all round with the QHY camera and 1.25 inch mounted or 31mm unmounted filters with the ZWO camera.

Also there is not such thing as a ZWO 7x31mm wheel, they do either 7 x 36mm or 8 x 1.25inch / 31mm.

For me the baader filters are superior to the ZWO filters.

Adam

 

Edited June 2, 2019 by Adam J

[upahill]

36 minutes ago, Adam J said:

Also there is not such thing as a ZWO 7x31mm wheel, they do either 7 x 36mm or 8 x 1.25inch / 31mm

Doh, mis-read that then, I think 7x36 is going to be the most future proof

[upahill]

So FLO had a deal on a set of ex-display 36mm baader narrowbands So that's the decision made on filter size if nothing else and the ball is now officially rolling.

I am leaning more towards the ASI now, considering holding out til a second hand unit comes up but they appear to be few and far between. Anyone nearing upgrade time? 😁😉

[JamesF]

19 minutes ago, upahill said:

Anyone nearing upgrade time? 😁😉

Wait until the new ZWO cameras come out later this year :) (I think)

Though price-wise they may be in a bit of a different bracket to the 1600.

James

[david_taurus83]

^^^Not going to get much imaging time now as we roll into June so don't rush to buy one. If they release a new model then that may also open up the used market.

[Adam J]

15 hours ago, david_taurus83 said:

^^^Not going to get much imaging time now as we roll into June so don't rush to buy one. If they release a new model then that may also open up the used market.

I think your talking some serious money for the models coming out. I dont see them as a direct replacement for the ASI1600mm pro.

[david_taurus83]

1 hour ago, Adam J said:

I think your talking some serious money for the models coming out. I dont see them as a direct replacement for the ASI1600mm pro.

It's easy to part a fool with his cash in this hobby! 😂😂😂

[upahill]

2 hours ago, Adam J said:

I think your talking some serious money for the models coming out. I dont see them as a direct replacement for the ASI1600mm pro.

Any rumors on the prices? specs? They will no doubt be out of my leauge but interesting anyway.

[Adam J]

9 minutes ago, upahill said:

Any rumors on the prices? specs? They will no doubt be out of my leauge but interesting anyway.

The one I have seen is a full frame mono sensor with 60mp 3.75um, just over 1e read noise and a 16-bit A/D, no amp glow. Expect about £5000 and thats without the 50mm square filters that would be required and wheel to put them in. 

So you are looking at £7000 minimum without thinking about a scope capable of covering that sensor with a flat field. 

Adam