Upgrading to a cooled mono cam

[Space Oddities]

I saved a bit of money and I'm thinking of upgrading my DSLR. After a lot of research on the zillion cameras and brands available, I figured the cooled ASI183MM was the best fit. But since it's quite an investment, I wanted to discuss it first with more advanced users! 

 

First, mono vs color. The M word sounds a bit scary for the beginner, but from my readings I understand that mono is easier to process in heavy light pollution (which is my case). And that you'd actually need more subs with a color camera to rival what a mono image can do, so the fact that you need to do 4 separate images (LRGB) isn't actually a disadvantage.

I plan on using my camera with short focal lengths. My imaging rig includes a TS Optics 60mm f/6 refractor, as well as a Canon 200mm f/2.8 for wide field. I also have a lovely SW 130P-DS, but I use it for visual only. There's also my Samyang 135mm, which I love, but it's the mirrorless version and I can't adapt it to anything.

According to the calculations I did on astronomy.tools (thanks FLO, very cool tool! ), I understand that I would need small pixels. So in the end, I came up with 2 sensors that might work: the IMX178 and IMX183. 

I saw very cool images done with the IMX178, but the IMX183's 20 megapixels can be cropped to give similar results. And it would allow me to do more wide field AP, with my Canon 200mm. And I can bin 2x2. So it appears that the ZWO ASI 183 is the best candidate   I've considered the QHY as well, but I have found less reviews about this camera, so I figured ZWO was a safer choice.

In terms of targets, I image from my balcony, which is facing east. So I have a ~120° view between NE and SE, with plenty of big nebulae in summer  Also M42, the Rosette in winter, the Pleiades in Autumn, and some big galaxies like M31/M33. Which means I'll mainly do narrowband on rather big targets, and occasionally LRGB. I tested the ASI183 with my 60mm refractor and Canon 200mm on Stellarium, and it seems to have the right FOV for these targets. For smaller targets, I guess I can crop!

My mount isn't very sophisticated, since my space is limited. I'm using a Sky-Watcher AZ-GTi in EQ mode, controlled and guided via Stellarmate. So a fairly lightweight setup, but that worked well so far with my DSLR.

Do you think it's a good match, given the gear I'm already using and the targets I have in mind? 🤔

 

I also have a question for filters. Since they are quite expensive, I'm being careful. I already own a pair of 2" Ha and OIII filters, both in filter drawers from Baader. So I don't think I need a filter wheel for those, I'm fine with manually switching them. And they work with my DSLR too.

For LRGB though, I'm a bit confused. There are 1.25" filters and 31mm unmounted filters. Does it make a difference when mounted in a filter wheel (like the one from ZWO)? 

 

Also, my Baader filter slider has a M48 mount on the camera side. Will I be able to mount it to an ASI183? I saw on their website that it comes with a T2/M48 adapter, but it's hard to tell with product pictures...

 

Thank you for your feedback!  

Edited June 23, 2019 by Space Oddities

[Stub Mandrel]

This is the camera that tempts me, but it is quite a lot smaller than a DSLR sensor.

I would like the ASI1600 sized sensor - as that is the biggest that works with 1.25" filters and I already have a filter wheel and filters (but not narrowband ones) for planetary. But it is even more expensive and there are horror stories of strange things happening to bright stars.

That said, at £1000 it's still a lot to invest when my biggest purchase so far has been a secondhand HEQ5 at a third of that.

[Stub Mandrel]

The ASI294 looks good... but not available as mono!

[Space Oddities]

It does look like a great camera, pity that it doesn't come in mono... This being said, I don't mind a slightly smaller sensor, since I'm working with short focal lengths! Perhaps a 1" sensor is a good compromise?

[MarsG76]

I'm with Stub about the sensor size.. if anything I personally would go for the 1600.. 

[Space Oddities]

40 minutes ago, MarsG76 said:

I'm with Stub about the sensor size.. if anything I personally would go for the 1600.. 

I'm a bit confused, the general consensus seems to be that a camera like the 183 is more adapter to short focal lengths (<400mm), which is my case. What would make the 1600 a better choice?

[vlaiv]

Both these cameras (1600 and 183) will suit you well for the gear that you have and plan to use.

1600 has a larger sensor and therefore it will record more of the sky in a single go, but also has larger pixels, which is beneficial for your case. You work with small apertures and mount that you are using is very basic. This means that you won't be able to resolve high detail even if atmosphere is playing ball.

Although you have short focal lengths and 183 with smaller pixels is better suited for picking up detail on shorter focal lengths - your gear will not provide that detail. Maximum sampling rate that I would think using in your case would be somewhere in range of 2-3"/px. We say that those are medium resolutions and you should not worry about not getting close up with some targets. For that, you would need some serious kit. What you have will be plenty of resolution to enjoy.

Both 183 and 1600 will need specific approach depending on scope / lens you will be using it with, so non is at distinct advantage there.

Take for example 60mm f/6.

it has 360mm focal length, so 183 will have sampling rate of 1.38"/px - this will in my view be oversampling for your setup. 1600 will have sampling rate of 2.18"/px - which is excellent sampling rate for this scope, however, 1600 sensor is large enough that you will want to use flattener - and you can use one that is reducer as well. In that case sampling rates change. If you put x0.8 FF/FR on that scope, you will have 288mm FL and respective sampling rates will be 1.72"/px and 2.72/px.

183 you can bin x2 to get different resolution (you can do that with 1600, but for your setups there probably won't be a need for that).

Similar goes for 200mm lens - both cameras will provide you with good resolutions. Both of these cameras will work with 1.25" filters.

In the end only difference is in size of the sensor - and if you are willing to pay extra to have more sky recorded in each session (1600) or you want to go with cheaper (but only because it is smaller sensor) 183.

Longer the FL - odds are that you will need to bin x2 183 as resolution provided by it will be too much - keep in mind this if you plan on using 130PDS for imaging in the future (will require more serious mount).

 

[DaveS]

One thing to watch out for, the 183 has horrendous amp-glow which can be a pig to calibrate out, while the amp-glow in the 1600 is relatively benign, and calibrates out easily.

[Space Oddities]

Thank you @vlaiv for the thorough answer and additional information, it's very helpful  

I didn't consider the ASI1600 initially, as it seemed more expensive and less adapted to my gear. But on the other hand, FLO and other providers are selling interesting bundles with the EFW and LRGB filters, and the price difference is about 60€ with the same accessories. I'm not sure ZWO filters are the best, I was actually more inclined to chose Baader's LRGB, but those sold with the ASI1600 seem good enough for the time being.

Perhaps the ASI 1600 also gives the advantage of be more forgiving as well, and more future friendly (especially with the 130P-DS). I don't think I'll get a more robust equatorial mount in a near future, at least not before I own my own garden or a bigger balcony... but that's not going to happen anytime soon  

I do have a 1x flattener for the TS 60mm, however I haven't heard of any reducer compatible with that scope. Could be interesting indeed, f/6 is quite a slow aperture.

And thanks for the info @DaveS, I read a lot about the horrendous amp glow on the ASI183. Good to know, indeed.

[vlaiv]

2 minutes ago, Space Oddities said:

I do have a 1x flattener for the TS 60mm, however I haven't heard of any reducer compatible with that scope. Could be interesting indeed, f/6 is quite a slow aperture.

Hm, compatibility is an odd thing - sometimes its there when you don't expect it to be, and sometimes it's not quite there even if manufacturers claim it

This one might work?

https://www.teleskop-express.de/shop/product_info.php/info/p5965_TS-Optics-REFRACTOR-0-79x-Reducer-Corrector---APO---ED---2--connection.html

But I would advise you to browse the internet and see if anyone actually tried this FF/FR with the scope you have and what results they obtained.

(TS page for this product - that is no longer in stock but can be ordered? under reviews section has example of it being used with TS photoline 60mm F/5.5 - not your exact scope, but it does suggest that it might work).

[Space Oddities]

Thanks for the link, I'll look into it! Fortunately this scope isn't rare, with WO and AT having similar versions. Perhaps there's a compatible reducer out there! 

[sloz1664]

The focal reducer mentioned by Vlaiv is also a WO clone

Steve

[geordie85]

I wouldn't worry too much about the 183 amp glow. 

I use both, a qhy183m and qhy183c and the amp glow calibrates out perfectly fine with correct calibration frames

Of you're interested in the 1600 now, I notice there is one in the classifieds section on here for £800

Edited June 25, 2019 by geordie85

[Adam J]

On 23/06/2019 at 09:42, Space Oddities said:

My imaging rig includes a TS Optics 60mm f/6 refractor, as well as a Canon 200mm f/2.8 for wide field. I also have a lovely SW 130P-DS, but I use it for visual only. There's also my Samyang 135mm, which I love, but it's the mirrorless version and I can't adapt it to anything.

According to the calculations I did on astronomy.tools (thanks FLO, very cool tool! ), I understand that I would need small pixels. So in the end, I came up with 2 sensors that might work: the IMX178 and IMX183. 

I saw very cool images done with the IMX178, but the IMX183's 20 megapixels can be cropped to give similar results. And it would allow me to do more wide field AP, with my Canon 200mm. And I can bin 2x2. So it appears that the ZWO ASI 183 is the best candidate   I've considered the QHY as well, but I have found less reviews about this camera, so I figured ZWO was a safer choice.

 

At those short focal lengths I would recommend a IMX183 based camera. You do have to take care with pixel scale with very short focal lengths though as they tend to be associated with small aperture optics and so the diffraction limited resolution of the optics and exceed the pixel scale with very small pixels. 

When combined with the 130PDS the IMX183 will be surprisingly good at galaxy imaging. However, not quite so good as the IMX178 with its lower read noise and higher dynamic range via its 14bit A/D as opposed to the 12bit A/D used in the IMX183. On the other hand the difference is not too big and the larger sensor of the IMX183 makes it more useful across a range of targets and focal lengths and will work very well with your Canon 200mm lens and 60mm refractor. 

Other people here are suggesting the ASI1600mm pro and that is another good option that will provide you with wider views due to its larger and slightly more sensitive sensor. However its is more expensive and be warned, prior to going down that path look up something called micro lens diffraction pattern as associated with the ASI1600mm pro and other cameras using that sensor. If you can live with it then sure, get the ASI1600mm pro. If you cant live with it or the additional cost then you are best off getting a IMX183 based camera. 

Hope that helps. 

Adam

[Adam J]

On 23/06/2019 at 14:30, vlaiv said:

In the end only difference is in size of the sensor - and if you are willing to pay extra to have more sky recorded in each session (1600) or you want to go with cheaper (but only because it is smaller sensor) 183.

I would say that the lack of micro lens diffraction effect on the 183 against its presence on the ASI1600mm pro is a significant difference to consider between the two chips too. Different people have different views on it based on personal preference. 

[vlaiv]

29 minutes ago, Adam J said:

I would say that the lack of micro lens diffraction effect on the 183 against its presence on the ASI1600mm pro is a significant difference to consider between the two chips too. Different people have different views on it based on personal preference. 

I think that this micro lens diffraction thing can be managed. I had several discussions and found that some people believe it is there regardless of actual optical setup - that is not what I've found. There is plenty of evidence that it depends on several factors - mainly speed of beam and other reflective surfaces in optical train (any sort of correctors and filters used). If one comes across it, I think it can be managed with some effort to rearrange spacing of these elements (usually moving filter to different position as moving correctors will introduce aberrations)

[JamesF]

1 hour ago, vlaiv said:

I think that this micro lens diffraction thing can be managed. I had several discussions and found that some people believe it is there regardless of actual optical setup - that is not what I've found. There is plenty of evidence that it depends on several factors - mainly speed of beam and other reflective surfaces in optical train (any sort of correctors and filters used). If one comes across it, I think it can be managed with some effort to rearrange spacing of these elements (usually moving filter to different position as moving correctors will introduce aberrations)

It would be good to get a better understanding of this.  It's probably the one thing that puts me off buying a 1600 at some point this year.

See for example this image posted today:

James

[vlaiv]

I was about to quote that example as well.

I noticed that Rodd has issues even with RGB filters, R being particularly affected.

On the other hand I noticed on my ASI1600 that I don't get them with RGB imaging on a small scope (80mm F/6 reduced to F/4.8), for example this image:

Maybe effect is there but so subtle that it is masked by seeing blur (and my less than perfect processing).

I don't get them with large scope 8" F/8 in most filters, but I do get them in narrow band (very slight effect)

For example, examine these two very close wavelengths - Ha and SII

This is Ha and we can argue if effects is there at all (maybe, just maybe there is some of it).

This is SII sub - it is definitively there, but again subtle. OIII on the other hand shows it more clearly:

But pattern seems to be somewhat different.

How are they formed in the first place? Well light has to constructively interfere with itself to produce that pattern - it needs to bounce off micro lens and then bounce back of something in imaging train. Phase shift will depend on distance traveled to bring light back to sensor and wavelength of that light, and of course effect will depend on how much light bounced back towards sensor from some surface (filter or corrector). This distance changes with position but also with F/ratio of beam (angle light travels at). F/ratio also impacts spread of light and therefore intensity of it.

From above you can see that even small shift in wavelength is enough to throw the phase off (Ha vs SII) and decrease this effect. Changing position of elements for even small value will have similar effect - have an issue in Ha? shift filter or other element by as small distance as difference between Ha and SII wavelengths and you will reduce or eliminate effect. You can do this for all filters, but best of course is to avoid any reflective element (good AR coatings on other elements in optical train).

 

[Space Oddities]

4 hours ago, Adam J said:

At those short focal lengths I would recommend a IMX183 based camera. You do have to take care with pixel scale with very short focal lengths though as they tend to be associated with small aperture optics and so the diffraction limited resolution of the optics and exceed the pixel scale with very small pixels. 

When combined with the 130PDS the IMX183 will be surprisingly good at galaxy imaging. However, not quite so good as the IMX178 with its lower read noise and higher dynamic range via its 14bit A/D as opposed to the 12bit A/D used in the IMX183. On the other hand the difference is not too big and the larger sensor of the IMX183 makes it more useful across a range of targets and focal lengths and will work very well with your Canon 200mm lens and 60mm refractor. 

Other people here are suggesting the ASI1600mm pro and that is another good option that will provide you with wider views due to its larger and slightly more sensitive sensor. However its is more expensive and be warned, prior to going down that path look up something called micro lens diffraction pattern as associated with the ASI1600mm pro and other cameras using that sensor. If you can live with it then sure, get the ASI1600mm pro. If you cant live with it or the additional cost then you are best off getting a IMX183 based camera. 

Hope that helps. 

Adam

Thank you Adam. I wasn't aware of this issue. Indeed, not very cool!

I had selected the 183 initially because it seemed to be more versatile than the 178, which I also considered. My goal would be to use this camera for hunting galaxies, with the 130P-DS, once I have a better mount. And that can be used in the meantime with smaller scopes, like my 60mm.

It's hard to choose!  But that might be too soon too. I realize I have enough on my plate right now, and I don't want to over complicate things and end up frustrated. But I like thinking ahead and having the next step in mind; your answers will definitely help define that next step  

Thanks everyone!

[Stub Mandrel]

I am agonising about this.

The ASI 183 is better suited to small DSOs with a pixel scale very well matched to my scopes, and offers potential for binning while still keeping a decent final image size. The smaller sensor means any residual worries about field curvature with my frac evaporate; I could also use my 0.5x reducer to get a wider FOV so it could effectively frame anything the ASI1600 can.

The ASI1600 has a bigger FOV but will undersample and would not suit tiny targets.

But these differences are marginal.

The issue seems to come down to the amp glow of the AS!183 versus the microlens artefacts of the ASI1600.

Any purchase is some way off, but I like to have an 'end in view' and a decent cooled CMOS mono cam is pretty much where my upgrade path can end -aside from finding better skies...

It is an agonising subject to debate.

 

[vlaiv]

2 hours ago, Stub Mandrel said:

The ASI1600 has a bigger FOV but will undersample and would not suit tiny targets.

What scope(s) do you plan on using it on?

Or rather, why do you feel it will undersample?

[Stub Mandrel]

ED 66 66mm x 400mm

130PD-S 130mm x 590mm (with coma corrector)

150PL 150mm x 1200mm

Using the f/3.6 rule, I get optimum pixel sizes of  1.68, 1.26 and 2.2um.

If I use a 0.5 focal reducer these pixel sizes halve.

The ASI 183 has  2.4um pixels and the ASI1600, 3.8um, to me the ASI183 seems better match?

I know there are other ways of calculating the optimum pixel size and it depends on seeing & guiding as well. On all but the 150PL my RMS guiding on a good night is <=1 pixel with the ASI183.

With 150PL I'd  experiment with binning in processing.

Edited July 27, 2019 by Stub Mandrel

[vlaiv]

31 minutes ago, Stub Mandrel said:

ED 66 66mm x 400mm

130PD-S 130mm x 590mm (with coma corrector)

150PL 150mm x 1200mm

Using the f/3.6 rule, I get optimum pixel sizes of  1.68, 1.26 and 2.2um.

If I use a 0.5 focal reducer these pixel sizes halve.

The ASI 183 has  2.4um pixels and the ASI1600, 3.8um, to me the ASI183 seems better match?

I know there are other ways of calculating the optimum pixel size and it depends on seeing & guiding as well. On all but the 150PL my RMS guiding on a good night is <=1 pixel with the ASI183.

With 150PL I'd  experiment with binning in processing.

I'll give you my view on this - it might be useful to you.

At 400mm in case of ED66, ASI1600 is going to give you 1.96"/px. In my view this is almost optimal sampling rate for 66mm scope. You can expect to get more than 3" FWHM stars with such scope (for example 3.2" FWHM in 1.5" seeing and 1" RMS guide error).

We can say that FWHM / 1.6 is optimal (or close to optimal) sampling rate, so 3.2" FWHM means 2"/px sampling rate.

Therefore ED66 and ASI1600 is very good match for wide field shots. You can even add flattener with reduction factor and you won't be undersampling much if at all (in just a bit poorer seeing you will be at optimum again).

With my 80mm at F/4.75 (~380mm FL, F/6 native with x0.79 reduction) I happily use ASI1600 and I don't feel images are undersampled at all - results look very good.

With 130PDS at 590mm you will be 1.33"/px. This will actually be closer to oversampling in most circumstances than undersampling. You need ~2.13" or less FWHM in order not to oversample. In same conditions as above - 1.5" seeing and 1" RMS guide error, at this aperture size you are likely to get around 2.9" FWHM stars. To utilize 1.33"/px to full potential at this resolution, you would need either 0.5" RMS guide error in 1.5" seeing, or perhaps 0.8" seeing with 0.8" guide RMS. With 1" RMS guide error it is virtually impossible to reach 2.13" FWHM regardless of the seeing at 130mm aperture.

With 150PL and 1200mm focal length, you will be at 0.65"/px. If you bin x2 you will be at 1.3"/px - just look at above to see if that is undersampling. I would argue that if you have worse guiding results with such a long scope, you will be still oversampling by quite a bit. With this scope I would rather go for x3 binning than x2.

You might say - what would be the purpose as you already have setup that does 2"/px (ED66), but these two approaches will be rather different. ED66 is going to do wide field stuff, while 150PL is going to be really fast in comparison to ED66 (when binned x3) but will be of a quite narrow field - so suitable for small targets.

This is good example how slower scope can be "faster" than fast scope. If you observe these two setups in different way - aperture at resolution way, you can see how much 150PL will be faster. You have 150mm vs 66mm both sampling at 2"/px. That is more than twice aperture by diameter (more than x4 light gathering area) and in terms of SNR, 150PL will be at least twice as fast.

 

[Stub Mandrel]

Thanks @vlaiv that's useful food for thought.

 

[Space Oddities]

If that helps: I went for the ASI1600. It's a proven camera, and despite being more expensive than the 183, the deals with the filter wheel and LRGB filters made it more attractive.

Also, as someone said above, it's a more forgiving camera for the beginner that I am  It leaves me some room for improvement, and should be good enough for most situations and scopes that I own.