New ASI 482MC / 485MC - Do I Sell My ASI 178MM and go OSC?

[Ags]

I see this on FLO today:

https://www.firstlightoptics.com/zwo-cameras/zwo-asi-485mc-usb-30-colour-camera.html

For about the same money as my ASI 178 MM, you get twice the sensor surface area? My partner has suggested selling the 178MM and upgrading, but would it be an upgrade as it would be a switch from mono to OSC? I have Bortle 8-9 skies and do EAA, planetary imaging and short sub DSOs (max 20 seconds). Is this camera coming out in a mono version? 

I prefer the 485 over the 482 because it is a better match for my SCT when doing planets, but I guess thebigger pixels of the 482 would be much better for EAA and DSOs.

 

Edited September 8, 2021 by Ags

[Ags]

I have already changed my mind - the 482 is better all round. For planetary, I would simply add a barlow to get to around F20.

[vlaiv]

2 minutes ago, Ags said:

I have already changed my mind - the 482 is better all round. For planetary, I would simply add a barlow to get to around F20.

Actually - maybe still consider 485

It appears that these two cameras are really the same except for pixel size and it might well be that it is similar case to ASI294 which had double pixels.

ASI485 has 2.9µm and ASI482 has - exactly double that 5.8µm

ASI485 has 13K FW and ASI482 has 51K FW. 13 * 4 = 52

ASI485 is quoted as 0.7-6.4e of read noise while ASI482 has 1.5-12.9

0.7 * 2 = 1.4

6.4 * 2 = 12.8

In another words - you get ASI482 from ASI485 if you bin your data in software. You can easily bin in software - but you can't really divide pixels in software.

[Ags]

That's good info, I thought OSC binning was difficult. Do I understand you correctly that I can bin from SharpCap, or only in post-processing? 

[vlaiv]

4 minutes ago, Ags said:

That's good info, I thought OSC binning was difficult. Do I understand you correctly that I can bin from SharpCap, or only in post-processing? 

I think that you can bin in drivers - so you can choose binned format with any software that uses ASCOM drivers. Possibly that native drivers support binning as well.

[Ags]

One issue with the 485MC is the odd shape of the sensor - the aspect ratio is nearly 2. Personally, I find squarer sensors more practical as a high aspect ratio just pushes the corners to the edge of the image circle.

Edited September 9, 2021 by Ags

[vlaiv]

14 minutes ago, Ags said:

One issue with the 485MC is the odd shape of the sensor - the aspect ratio is nearly 2. Personally, I find squarer sensors more practical as a high aspect ratio just pushes the corners to the edge of the image circle.

I think it is standard 16:9 isn't it?

Same as for 482MC and similar to other models that have ~1920 x 1080 (actually other models like 462, 385, 290 are 1936 x 1096 but that is just 16 extra lines for calibration that have been "unlocked").

I guess that best EEVA "small" sensor is still ASI183 - but it is also more expensive then other models (although by size - it is quite close to these two new models 1" vs 1/1.2").

[Ags]

4 minutes ago, vlaiv said:

I think it is standard 16:9 isn't it?

Yes you are right, I  misread the dimensions. Still, I  would prefer it to be squarer...

[Ags]

Still no reviews of this exciting camera. It seems to have a good blue sensitivity, which is very attractive. With my current blue filter, the ASI 178 MM is almost immune to blue light!

[Andrew_B]

QHY launched their version using the same chip earlier this year as the QHY5III485C. Only found this one review but it's better than nothing!

[vlaiv]

9 hours ago, Andrew_B said:

QHY launched their version using the same chip earlier this year as the QHY5III485C. Only found this one review but it's better than nothing!

Yes, except that is for 462 model so really marginally better than nothing

[Ags]

Still not sure I go OSC. Does the larger size of the 485MC counterbalance the greater sensitivity of the smaller 178MM? Selecting targets that fill each sensor, the 485MC is nearly like having a triple rig of 178MMs with RGB filters...

[Andrew_B]

4 hours ago, vlaiv said:

Yes, except that is for 462 model so really marginally better than nothing

That's annoying. I was sure that was for the right camera and it was one of the first results when I searched for reviews of the 485C model. The perils of skim reading!

I notice the 462 uses 2.9 micron pixels and has very similar characteristics - perhaps the same basic pixel architecture so the 485 might in practice be like a scaled up version of the 462.

[vlaiv]

6 hours ago, Ags said:

Still not sure I go OSC. Does the larger size of the 485MC counterbalance the greater sensitivity of the smaller 178MM? Selecting targets that fill each sensor, the 485MC is nearly like having a triple rig of 178MMs with RGB filters...

One of the things that you need to be careful with comparing two different sensor sizes is that you need to pair them with different scopes in order to fully understand benefits.

Best way to do it would be to match FOVs with similar type scope just larger FL and aperture (If you are matching them by using 130PDS - then look at 150PDS and 200PDS as OTAs to match with).

Once you have similar FOVs - then bin as necessary and then compare sensitivity - taking into account aperture size and also any bayer filters.

3 hours ago, Andrew_B said:

I notice the 462 uses 2.9 micron pixels and has very similar characteristics - perhaps the same basic pixel architecture so the 485 might in practice be like a scaled up version of the 462.

I think that 462 is quite unique as it is designed to be very sensitive in IR part of spectrum:

That puts sensitivity in blue somewhere around 0.5 or so (since peak at 800nm is likely to be around 80% absolute QE so each reading from above relative chart should be multiplied by 0.8 - peak in blue is 0.67 * 0.8 = 0.536).

It is good choice for planetary imaging (especially IR and Methane bands), and there have been models like that previously - although not as sensitive. I have one like that ASI185 that I use for guiding:

It also acts almost as monochromatic sensor for wavelengths above 800nm - but no where near as sensitive as ASI462

[Ags]

3 hours ago, vlaiv said:

One of the things that you need to be careful with comparing two different sensor sizes is that you need to pair them with different scopes in order to fully understand benefits.

Well... I am looking at buying a new camera, not an new telescope and a new camera 😀 

My thinking is that the camera would let me capture larger targets, so it effectively offers more (RGB filtered) light gathering than the 178 MM. I wouldn't attempt the same targets with the 178 MM because I don't get enough time for a mosaic, the most I can manage is a couple of hours now and then...

In an ideal world I would keep both cameras and have an ultralightweight dual imaging setup with camera lenses!

Edited September 13, 2021 by Ags
spelling

[vlaiv]

5 minutes ago, Ags said:

My thinking is that the camera would let me capture larger targets, so it effectively offers more (RGB filtered) light gathering than the 178 MM. I wouldn't attempt the same targets with the 178 MM because I don't get enough time for a mosaic, the most I cam manage is a couple of hours now and them...

Still not convinced that there would be speed benefit from this camera. I really do think that we need to crunch the numbers in order to get the idea.

If you don't like doing mosaics - well that is fair enough, but here is fun fact:

"Any scope, what ever it's focal length, can act as same F/ratio scope with integer fraction of its focal length - with any given camera".

In another words - if you say have C6 - which has 1500mm of FL - you can make it work as 750mm (1500/2), 500mm (1500/3), 375 (1500/4) and so on F/10 scope with your ASI178.

Say you want to do 500mm image in 2 hours. Instead of imaging single field for two hours - you image 9 panels, each one for 800 seconds. That will total to 7200 seconds or two hours. Then you take each panel and bin x3 effectively reducing pixel count to ~1000 x 700 (instead of ~ 3000 x 2100), but when you stitch back 3x3 mosaic you will again have ~3000 x 2100 (or just a bit less due to overlap, maybe 2800 x 1900).

Although you imaged each panel for 1/9 of two hours - you binned it x3 which improves SNR by factor of x3 - same as stacking x9 more subs - or imaging for two whole hours

There you go - you created image of wanted FOV - in wanted amount of the time, same as if you actually had same F/ratio scope of smaller FL and used it for same amount of time with the same camera.

 

[Ags]

Witchcraft I say! It is a very interesting idea, and one I will try on the next clear night! If I can get this to work, then I can get a smaller and much cheaper RGB camera and mosaic. The obstacles I see are simply leaving gaps, and dealing with gradients, which I expect get worse the wider the field.

Thank you for the clear explanation. Can you recommend a good (free) mosaic stitching program?

[vlaiv]

6 minutes ago, Ags said:

Witchcraft I say! It is a very interesting idea, and one I will try on the next clear night! If I can get this to work, then I can get a smaller and much cheaper RGB camera and mosaic. The obstacles I see are simply leaving gaps, and dealing with gradients, which I expect get worse the wider the field.

Thank you for the clear explanation. Can you recommend a good (free) mosaic stitching program?

It won't work on smaller sensor. I mean it will - but it will always provide you with equivalent of that sensor with shorter focal length - and not same scope with "larger sensor".

Say you get ASI224 - above approach will always produce 1300x900 pixel image - as if using that same ASI224 with smaller scope. This is because the need to bin to recover SNR for each panel. You can't add panels to create larger (more mega pixels) image of the same SNR - for that you need to spend more time because you can't bin if you want more mega pixels.

9 minutes ago, Ags said:

Thank you for the clear explanation. Can you recommend a good (free) mosaic stitching program?

I used ImageJ/Fiji - it has few plugins that can stitch images for you. Yes, gradients are a pain and you need to remove gradient from each panel (sometimes not easy) before stitching. Imaging software like Nina, APT (I think) and SGP have mosaic  planners/generators which will help you plan your mosaic.

Alternative is to use Stellarium to plan mosaic. It is easy to do with custom markers (shift + click to place, ctrl + click to remove if I'm not mistaken - look up key assignment under F1/help).

Here is B174 planned with ASI178 and 80mm F/6 reduced to F/4.5.

I set first marker at the center of the target - then I move FOV so that marker ends up in corner. I eyeball distance of marker to corner (marked with arrows in above image). After I'm happy with placement of FOV - I add custom marker in center of the FOV at that position (markers 2, 3, 4 - and ready to add final marker).

After that I can select markers and get exact RA/DEC coordinates for each of these custom markers - which can be then used to direct mount on the target (plate solving is good to have here).

Here is an example of mosaic I did some years ago:

This is 500mm scope with ASI185mc camera. I used ST102 and stopped down aperture (to tame chromatic blur). I did not do flats at that time - but that helps to see panels in the final image. Image does not go deep due to stopped down aperture and LP conditions it was shot in - but I think it is something like 2h of exposure divided in 9 panels.

[Ags]

OK, so I still need the bigger sensor 😀 The native resolution of the ASI224 is just too low. I think the sensor size of the 485MC would be more practical with my C6, even when it is reduced to 945mm focal length.

 

[vlaiv]

4 minutes ago, Ags said:

OK, so I still need the bigger sensor 

Again, I can't really tell if you do.

Pixel wise, ASI485mc and ASI178mm are very similar - 3840x2160 vs 3096x2080 - you are really only getting about 800px in width and 80px in height.

If you want larger sensor just for the FOV - then with above trick you can extend FOV of ASI178 to larger size and still have 3096x2080px (mind you - you could do some hybrid approach when doing mosaics - if you put 3x3 panel mosaic for example - you'll end up with roughly 9000 x 6000 px - you could bin that x3 as described above or maybe even x4 and end up with 2250 x 1500px image in the end - gaining a bit more SNR in the process - not many people have displays to show 2250x1500 without resizing).

If you want ASI485 for "speed", well, we need to do calculations - 2.9µm pixel size with 1/4 getting red, 1/2 getting green and 1/4 getting blue vs 2.4µm some sort of LRGB imaging with full pixel usage - for example you could do LRG. You really don't need to do full LRGB to get proper color - since we are using luminance that collects all three color bands at the same time thus increasing SNR for given imaging time and since luminance is more important visually then chrominance and since we need only 3 components to get color - you could do something like 3/4 of lum and split 1/4 of time between Red and Green.

Which one would be faster in that case, Color camera or mono + filters? It is very hard to tell if we don't do the math (and even then we would need exact color matrices in order to calculate things properly - that is if you want true color rendition).

If you want ASI485 for "novelty factor" - time to get new gear, then maybe consider getting cooled version of some camera instead?

There are cheaper and better alternatives as well. How about APS-C sized mirrorless camera? If you mod that by removing IR cut filter - you'll get very good 6000x4000 large sensor camera that is essentially the same for DSO (it won't be as good for planetary).

We touched up on that subject in another thread (might be interesting read):

 

 

[Ags]

Yes, I know... my curse is a always get distracted by shiny new things. At least I hardly ever translate my over-enthusiastic shopping into over-enthusiastic buying 😀 There are many advantages to getting a mirrorless camera (conventional photography, aside from anything else, but also milky way and astro landscape shots), the main disadvantage to me seems to be the small batteries they come with (and I don't know any options to provide offboard power). But it is an option I am considering. I used to have an 1100D mirror camera and the unnecessary clacking of the mirror was annoying (no mirror lock). I can keep the ASI 178 MM and pick up a second hand M100 this month, it is porbably a better option.

I gave the 1100D to my granddaughter and it got burglarized the next month. The insurance money upgraded her to a 1300D and a new lens!

[nfotis]

On 13/09/2021 at 19:15, vlaiv said:

One of the things that you need to be careful with comparing two different sensor sizes is that you need to pair them with different scopes in order to fully understand benefits.

Best way to do it would be to match FOVs with similar type scope just larger FL and aperture (If you are matching them by using 130PDS - then look at 150PDS and 200PDS as OTAs to match with).

Once you have similar FOVs - then bin as necessary and then compare sensitivity - taking into account aperture size and also any bayer filters.

I think that 462 is quite unique as it is designed to be very sensitive in IR part of spectrum:

That puts sensitivity in blue somewhere around 0.5 or so (since peak at 800nm is likely to be around 80% absolute QE so each reading from above relative chart should be multiplied by 0.8 - peak in blue is 0.67 * 0.8 = 0.536).

It is good choice for planetary imaging (especially IR and Methane bands), and there have been models like that previously - although not as sensitive. I have one like that ASI185 that I use for guiding:

It also acts almost as monochromatic sensor for wavelengths above 800nm - but no where near as sensitive as ASI462

 

Note that there's also the IMX464 sensor (exactly double the area of the IMX462, and double the megapixels, four instead of two), with the same technology.

At least Player One offers this sensor:

https://player-one-astronomy.com/product/neptune-c-ii-usb3-0-color-camera-imx464/

 

N.F.

 

[Andrew_B]

On 13/09/2021 at 21:56, vlaiv said:

Again, I can't really tell if you do.

Pixel wise, ASI485mc and ASI178mm are very similar - 3840x2160 vs 3096x2080 - you are really only getting about 800px in width and 80px in height.

If you want larger sensor just for the FOV - then with above trick you can extend FOV of ASI178 to larger size and still have 3096x2080px (mind you - you could do some hybrid approach when doing mosaics - if you put 3x3 panel mosaic for example - you'll end up with roughly 9000 x 6000 px - you could bin that x3 as described above or maybe even x4 and end up with 2250 x 1500px image in the end - gaining a bit more SNR in the process - not many people have displays to show 2250x1500 without resizing).

If you want ASI485 for "speed", well, we need to do calculations - 2.9µm pixel size with 1/4 getting red, 1/2 getting green and 1/4 getting blue vs 2.4µm some sort of LRGB imaging with full pixel usage - for example you could do LRG. You really don't need to do full LRGB to get proper color - since we are using luminance that collects all three color bands at the same time thus increasing SNR for given imaging time and since luminance is more important visually then chrominance and since we need only 3 components to get color - you could do something like 3/4 of lum and split 1/4 of time between Red and Green.

Which one would be faster in that case, Color camera or mono + filters? It is very hard to tell if we don't do the math (and even then we would need exact color matrices in order to calculate things properly - that is if you want true color rendition).

If you want ASI485 for "novelty factor" - time to get new gear, then maybe consider getting cooled version of some camera instead?

There are cheaper and better alternatives as well. How about APS-C sized mirrorless camera? If you mod that by removing IR cut filter - you'll get very good 6000x4000 large sensor camera that is essentially the same for DSO (it won't be as good for planetary).

We touched up on that subject in another thread (might be interesting read):

 

 

I second the suggestion of a modded mirrorless camera. You can pick them up secondhand for very little money compared to what a dedicated astro camera would cost. I got a full spectrum converted 24MP Fuji for just £180 and the performance is very respectable even when shooting narrowband.

[BrendanC]

Interesting thread! Just to chime in regarding mosaic software, Affinity Photo has an excellent mosaic feature. 

[Ags]

There is an open source mosaic util called Hugin I will give a try.

Edited September 15, 2021 by Ags