Which QHY camera for DSO?

[Orion1]

I'm getting rid of my dslr and thinking about getting a cooled QHY CCD camera with medium size sensor for DSO photography with my Canon 200mm f2.8 (which I already have).

My options are 183C (1"), 163C (4/3"), 165C (APS-C) or 168C (APS-C 14 bit)

What is the benefit of mono - sensitivity only?

 

I would like to hear what you think

 

[ollypenrice]

I don't know these cameras but I'll comment on the advantages of mono.

1) You can shoot narrowband using all of the pixels of your camera. This opens up moonlit nights for Ha imaging, very important for emission nebulae.

2) You can shoot colour in the right proportion rather than shooting twice as much green as red or blue.

3) You can shoot luminance, which means you shoot all three colours at once (though without distinguishing between them. You do that with your colour layer.) This saves time.

None of this means that OSC isn't good, but you asked about the mono advantage so that's my opinion. I've used both with great enjoyment and concluded, in the end, that mono was more productive. Others might come to a different conclusion.

Olly

[Orion1]

10 minutes ago, ollypenrice said:

I don't know these cameras but I'll comment on the advantages of mono.

1) You can shoot narrowband using all of the pixels of your camera. This opens up moonlit nights for Ha imaging, very important for emission nebulae.

2) You can shoot colour in the right proporition rather thashooting twice as much green as red or blue.

3) You can shoot luminance, which means you shoot all three colours at once (though without distinguishing between them. You do that with your colour layer.)

Thanks for your input. I'm currently reading up on the subject but it sounds like mono is the way to go. I'm just afraid it will be much extra effort to get color data and filters are quite expensive?

[ollypenrice]

15 minutes ago, Orion1 said:

Thanks for your input. I'm currently reading up on the subject but it sounds like mono is the way to go. I'm just afraid it will be much extra effort to get color data and filters are quite expensive?

Certainly it is cheaper to buy the filters as part of the chip (OSC) but you don't have any control over them. You get red, green, green, blue and that's that. If you put an Ha filter in front you'll get perfectly good Ha but only on a quarter of your pixels (those under the red filters). It can be done but only a used car salesman could pretend that it was an advantage to do so...

As for the extra effort, I've never been convinced and I've done a lot of both. Yes, capture is a bit easier with OSC but the real work in natural colour imaging comes when you try to remove colour gradients, preserve good and accuate star colour and balance the three colour channels. None of these tasks is easier from one shot colour data than from mono with filters. In fact I'd say the reverse, if anything.

Olly

[Orion1]

3 minutes ago, ollypenrice said:

Certainly it is cheaper to buy the filters as part of the chip (OSC) but you don't have any control over them. You get red, green, green, blue and that's that. If you put an Ha filter in front you'll get perfectly good Ha but only on a quarter of your pixels (those under the red filters). It can be done but only a used car salesman could pretend that it was an advantage to do so...

As for the extra effort, I've never been convinced and I've done a lot of both. Yes, capture is a bit easier with OSC but the real work in natural colour imaging comes when you try to remove colour gradients, preserve good and accuate star colour and balance the three colour channels. None of these tasks is easier from one shot colour data than from mono with filters. In fact I'd say the reverse, if anything.

Olly

Very interesting. It's indeed difficult to edit colors in post...

37 minutes ago, ollypenrice said:

3) You can shoot luminance, which means you shoot all three colours at once (though without distinguishing between them. You do that with your colour layer.) This saves time.

How is this done practically?

[ollypenrice]

20 minutes ago, Orion1 said:

Very interesting. It's indeed difficult to edit colors in post...

How is this done practically?

You shoot through a luminance filter, which passes the full visible spectrum (red and green and blue) while blocking the non-visible wavelengths the camera can record but which might defeat the efforts of your optics to focus.

In post processing you process your RGB for strong colour, low noise and low resolution of fine detail. You process your luminance for high resolution of fine detail and visibility of very faint signal and then you 'illuminate' the RGB in the light of the luminance layer. Skilled one shot colour imagers may do something quite like this, extracting a synthetic luminance for processing differently from the colour layer, but they don't have the same signal strength they'd get from real luminance. 

Olly

[RichLD]

16 minutes ago, ollypenrice said:

You shoot through a luminance filter, which passes the full visible spectrum (red and green and blue) while blocking the non-visible wavelengths the camera can record but which might defeat the efforts of your optics to focus.

In post processing you process your RGB for strong colour, low noise and low resolution of fine detail. You process your luminance for high resolution of fine detail and visibility of very faint signal and then you 'illuminate' the RGB in the light of the luminance layer. Skilled one shot colour imagers may do something quite like this, extracting a synthetic luminance for processing differently from the colour layer, but they don't have the same signal strength they'd get from real luminance. 

Olly

+1

[Adam J]

3 hours ago, Orion1 said:

I'm getting rid of my dslr and thinking about getting a cooled QHY CCD camera with medium size sensor for DSO photography with my Canon 200mm f2.8 (which I already have).

My options are 183C (1"), 163C (4/3"), 165C (APS-C) or 168C (APS-C 14 bit)

What is the benefit of mono - sensitivity only?

 

I would like to hear what you think

 

 

You say that you want to use a 200mm F2.8 canon lens. So I am assuming you want to do some nice wide field work. What mount are you thinking of? 

One thing to consider is how are you going to use filters with your lens / adapter. I have seen a few systems that incorporate a filter draw into the lens adapter. But I am not an expert in that so you would do well to get advice before jumping for a mono that would need filters. 

The next thing is, to me if you are wanting a nice wide field setup (possibly with a non goto mount???) then you may not want to sacrifice too much sensor size in going for a mono over a OSC camera. Small sensor with short focal length lenses are at odds to your objective if you ask me. If you dont have a goto its also probably a pain to do multiple tiles with a smaller sensor. 

With your lens I would be looking at the QHY163m for mono or the QHY168c for color. 

Take a look at lens adapters / filter draws / focusing aids before making choices. 

Also almost forgot, you are unlikely to get 1.25 inch mounted filter to work with 4/3 sensor or larger when imaging at F2.8 so you would be forced to stop down the lens or use larger filters adding to the cost. 

 

[Thalestris24]

Hi Orion

Ditto Adam's post. I can't see any real advantage in swapping out a dslr for an astro camera of any sort if you're just going to use it with a fast lens. How has your lens + dslr (presumably a Canon) performed? Are you unhappy with the results? What mount are you using? How has your dslr+lens been attached to your mount? What has driven your desire to spend a lot of money on another camera?

Louise

[Orion1]

8 hours ago, Adam J said:

 

You say that you want to use a 200mm F2.8 canon lens. So I am assuming you want to do some nice wide field work. What mount are you thinking of? 

One thing to consider is how are you going to use filters with your lens / adapter. I have seen a few systems that incorporate a filter draw into the lens adapter. But I am not an expert in that so you would do well to get advice before jumping for a mono that would need filters. 

The next thing is, to me if you are wanting a nice wide field setup (possibly with a non goto mount???) then you may not want to sacrifice too much sensor size in going for a mono over a OSC camera. Small sensor with short focal length lenses are at odds to your objective if you ask me. If you dont have a goto its also probably a pain to do multiple tiles with a smaller sensor. 

With your lens I would be looking at the QHY163m for mono or the QHY168c for color. 

Take a look at lens adapters / filter draws / focusing aids before making choices. 

Also almost forgot, you are unlikely to get 1.25 inch mounted filter to work with 4/3 sensor or larger when imaging at F2.8 so you would be forced to stop down the lens or use larger filters adding to the cost. 

 

I have a Celestron AVX mount.

I want to get the biggest sensor I can get. With QHY the biggest mono is 4/3. I will get a bigger lens or scope later. But the 200mm is what I have right now.

Thanks for the heads up. The filters and wheels are quite expensive...

[Orion1]

5 hours ago, Thalestris24 said:

Hi Orion

Ditto Adam's post. I can't see any real advantage in swapping out a dslr for an astro camera of any sort if you're just going to use it with a fast lens. How has your lens + dslr (presumably a Canon) performed? Are you unhappy with the results? What mount are you using? How has your dslr+lens been attached to your mount? What has driven your desire to spend a lot of money on another camera?

Louise

I’ve come to the stage where I want to modify my dslr. Modification is expensive and the clip in filters a expensive. Plus cooling would help to keep noise to a minimum.

doing astrophotography it makes sense to use a dedicated camera that are made for the exact purpose (I think)

[ollypenrice]

7 hours ago, Thalestris24 said:

Hi Orion

Ditto Adam's post. I can't see any real advantage in swapping out a dslr for an astro camera of any sort if you're just going to use it with a fast lens. How has your lens + dslr (presumably a Canon) performed? Are you unhappy with the results? What mount are you using? How has your dslr+lens been attached to your mount? What has driven your desire to spend a lot of money on another camera?

Louise

I think there are advantages. When the idea is to shoot large swathes of sky you'll be shooting objects dominated by Ha. A mono camera can record that Ha on all pixels, rather than a quarter of them, and it will record Ha with higher contrast and more structural detail than a modded camera's broadband red filters. (The important aspect of an Ha filter is not so much what it passes as what it blocks.) Also there is the thorny business of star size in widefield imaging. Small apertures create large stars and these can dominate widefield vistas. Narrowband filters give much smaller stars which is of particular interest in widefield.

Adam's point about fiters for fast F ratios is sound though. 

Olly

 

[Orion1]

Can anyone chime in on the QHY cameras. To me they look well engenieered with sealed cool chamber and built in heater.

[Thalestris24]

22 minutes ago, Orion1 said:

Can anyone chime in on the QHY cameras. To me they look well engenieered with sealed cool chamber and built in heater.

Hi

If I was going to get one (and I might!) I'd go for the cooled QHY163M. But I'd be using it with a 115mm APO. I think you probably want to make a comparison of various camera options via a fov calculator or your favourite planetarium program and work out the arc secs/pixel. 

Louise

[Adam J]

38 minutes ago, Orion1 said:

Can anyone chime in on the QHY cameras. To me they look well engenieered with sealed cool chamber and built in heater.

 

Well, I have not heard any complaints about the new range of QHY CMOS based cameras, people used to have issues with some of their stuff a generation or two back but from what I have read the new stuff is well engineered.

Put it this way, its ZWO who are having to offer an exchange scheme on the ASI071mc not QHY on their QHY168c.

It seems to me that QHY take the approach of not adding any bells and whistles to their cameras that are not strictly required in order to keep the price down. So you wont get the fancy shiny red case that ZWO use, or the useful but not 100% necessary USB hub incorporated into the camera body. What you do get is working dew control and on board DDR memory from the get go.......

I heard whispers about diver issues, but to be honest its not something that is consistently reported and so I would take it with a pinch of salt.

I dont speak from personal experience, just been researching this for a long time and it will be a while longer before I can afford one. You could go on astro bin search for the camera and then ask some people about their experiences.

 

[Thalestris24]

2 hours ago, ollypenrice said:

I think there are advantages. When the idea is to shoot large swathes of sky you'll be shooting objects dominated by Ha. A mono camera can record that Ha on all pixels, rather than a quarter of them, and it will record Ha with higher contrast and more structural detail than a modded camera's broadband red filters. (The important aspect of an Ha filter is not so much what it passes as what it blocks.) Also there is the thorny business of star size in widefield imaging. Small apertures create large stars and these can dominate widefield vistas. Narrowband filters give much smaller stars which is of particular interest in widefield.

Adam's point about fiters for fast F ratios is sound though. 

Olly

 

Hi Olly

Of course, I don't disagree! I took some nice Ha shots with my cooled mono 550d and 200mm F4 Takumar (before the camera broke). I front-mounted the 2" Ha filter via an adapter and it worked fairly well though did get annoying reflections/halos on some bright stars. It was either that or splash out on a clip filter and I didn't want to go that route. I'm not sure how things would perform at F2.8 though - I've never had anything so fast! Mind you, I expect the lens would perform better stopped down. I don't think a camera/lens setup would be practical for rgb - not impossible, I suppose, but I reckon I'd soon get fed up with swapping filters around... Um, it's not strictly true that only the 'red' pixels respond to Ha filtered light, others do too, albeit to a lesser extent, but, yeah, mono is best! Anyway, I was just checking that Orion1 was sure about what he was doing before parting with >£1,000!
 

Louise 

[Adam J]

What is it you are wanting to do? What do you actually want to take images of?

[Thalestris24]

ps - obviously with a dedicated astro camera you could probably squeeze in a filter holder of some sort between lens and sensor but you'd have to check your spacing and options carefully. I use a filter drawer on my 115mm apo between the flattener and dslr that I currently use.

[ollypenrice]

1 hour ago, Thalestris24 said:

Hi Olly

 Um, it's not strictly true that only the 'red' pixels respond to Ha filtered light, others do too, albeit to a lesser extent, 
 

Louise 

I've just had a quick gleg at the RGB bandpasses of several popular Bayer matrices and none of the ones I found had any significant transparency in G or B at 6500 nanometres, the Ha line. I'd have thought, then, that the imager would strip out the G and B entirely. Isn't that what people do when shooting Ha with an OSC camera? I've never done it so I don't know the process. That would mean literally 'red only' in the final image.

Olly

[Thalestris24]

8 minutes ago, ollypenrice said:

I've just had a quick gleg at the RGB bandpasses of several popular Bayer matrices and none of the ones I found had any significant transparency in G or B at 6500 nanometres, the Ha line. I'd have thought, then, that the imager would strip out the G and B entirely. Isn't that what people do when shooting Ha with an OSC camera? I've never done it so I don't know the process. That would mean literally 'red only' in the final image.

Olly

Hi Olly

It's just my experience. Thinking about it, it's probably light from non-Ha sources that's making it through the filter and lighting up the green and blue pixels. In that case, the end result is essentially noise + red pixels. Probably at a dark site (with no Moon!) only Ha emission light would get through -> B and G pixels would then be ~black, as expected. The Glasgow LP has corrupted my thought processes! 

Louise

[Stub Mandrel]

When I made my first try (I've only had two so far) at Ha imaging using a DSLR and 7nm Baader filter. The results aren't very good as it was also my first attempt a guiding and even so the subs are only 2 minutes, but it was really a learning exercise.

I've gone back to one of the raw stacks  it was done using Bayer Drizzle in DSS so each channel is JUST what was on each of R, G and B with no debayering. I aligned the histogram peaks for R, G and B and applied an aggressive and crude stretch. Ignore the fact the data is crap - it was a warm night (18 June) and camera temperature was 25 degrees! This data is what convinced me to cool my DSLR to sub-zero temperatures so the next attempt should will not have so much noise!

The red channel does have more data and more subtlety, but I think the G & B channels could be combined and processed as a denoised mask layer to help bring up the nebulosity.

Red:

Green:

Blue:

 

 

 

[Thalestris24]

16 minutes ago, Stub Mandrel said:

When I made my first try (I've only had two so far) at Ha imaging using a DSLR and 7nm Baader filter. The results aren't very good as it was also my first attempt a guiding and even so the subs are only 2 minutes, but it was really a learning exercise.

I've gone back to one of the raw stacks  it was done using Bayer Drizzle in DSS so each channel is JUST what was on each of R, G and B with no debayering. I aligned the histogram peaks for R, G and B and applied an aggressive and crude stretch. Ignore the fact the data is crap - it was a warm night (18 June) and camera temperature was 25 degrees! This data is what convinced me to cool my DSLR to sub-zero temperatures so the next attempt should will not have so much noise!

The red channel does have more data and more subtlety, but I think the G & B channels could be combined and processed as a denoised mask layer to help bring up the nebulosity.

Red:

Green:

Blue:

 

 

 

Interesting - lots of crosstalk, apparently! Maybe the rgb bayer matrix in a dslr isn't particularly good at blocking particular wavelengths? Certainly, all the matrix lets through infra-red with a full-spectrum modded camera. I've taken lots of IR images

[Orion1]

3 hours ago, Thalestris24 said:

Hi

If I was going to get one (and I might!) I'd go for the cooled QHY163M. But I'd be using it with a 115mm APO. I think you probably want to make a comparison of various camera options via a fov calculator or your favourite planetarium program and work out the arc secs/pixel. 

Louise

According to the Telescope Capabilities at astronomy.tools (FLO) the smallest sensor (QHY 183C with 1" sensor) is the best match for short focal length 200-400mm) and my DSLR (APS-C) being the absolute worst. But I'm not sure if these numbers apply for wide field work.

[Stub Mandrel]

The bayer matrix is designed to mimic the eye, so the sensitivity curves for each colour are curves, this means any one wavelength produces a certain ratio R:G:B which gives the great subtly of colour we see with our eyes and expect in photos.

LRGB imaging uses filters with very 'square' edges to the curves and minimal overlap. This gives maximum sensitivity but it means, for example, that any monochromatic light will simply show up as red, green or blue.

This doesn't matter too much with 'black body' radiation as produced by stars, for example, has a curved profile so the exact colour will impact differentially even through hard-edged filters.

Such RGB filters won't distinguish well between closely spaced colours and not at all between, say, monochromatic deep red and orange, wile a DSLR would clearly show the difference.

This is probably why RGB imagers say they find processing easier - their colour data should give very strong colours, but with less subtly than DSLR data.

It should be possible to see more subtle distinctions in nebula colour in DSLR data while LRGB data should make bold distinctions like that between OIII and Ha starker.

[ollypenrice]

1 hour ago, Thalestris24 said:

Hi Olly

It's just my experience. Thinking about it, it's probably light from non-Ha sources that's making it through the filter and lighting up the green and blue pixels. In that case, the end result is essentially noise + red pixels. Probably at a dark site (with no Moon!) only Ha emission light would get through -> B and G pixels would then be ~black, as expected. The Glasgow LP has corrupted my thought processes! 

Louise

Your debayering algorithm will try to interpolate the missing signal and 'fill in' the blank pixels so I guess that's where some of your G and B data is coming from.

Olly