ZWO ASI 290MM vs 178MM

[SyedT]

Having looked around a fair bit, I haven't found much in terms of comparison between the ZWO ASI 290MM and 178MM. Their prices are identical, and the main differences seem to be pixel size (2.9 microns vs 2.4 microns), resolution (2.1 MP vs 6.4 MP), max frame rate (170 fps vs 60 fps) and ADC (12 bit vs 14 bit).

I would be using it with an Edge HD 8 for planetary and lunar work during this summer. I have a 2.25x Baader barlow which I can use with the camera. Would appreciate any advice regarding which camera I should go for.

Cheers

[johninderby]

You want to match pixel size to your scope.

This online calculator lets you work out the best match for your scope and has all the ZWO cameras in the calculator.

https://astronomy.tools/calculators/ccd_suitability

I went with the 290 as it was the best match for my scope.

[SyedT]

7 minutes ago, johninderby said:

You want to match pixel size to your scope.

This online calculator lets you work out the best match for your scope and has all the ZWO cameras in the calculator.

https://astronomy.tools/calculators/ccd_suitability

I went with the 290 as it was the best match for my scope.

Thanks for replying John! I've already used the calculator and it seems both will give me a degree of oversampling for "OK" seeing, slightly more with the 178MM (0.13 vs 0.11 arcsec/pixel with barlow, 0.29 vs 0.24 arcsec/pixel without barlow). Not sure where that leaves me really!

Edited April 8, 2020 by SyedT

[johninderby]

Trying other camers in the calculator? 

[SyedT]

7 minutes ago, johninderby said:

Trying other camers in the calculator? 

I've tried all of the ZWO cameras, and they all oversample. I think it's fairly unavoidable due to the FL and pixel sizes being used. 

[johninderby]

Just now, SyedT said:

I've tried all of the ZWO cameras, and they all oversample. I think it's fairly unavoidable due to the FL and pixel sizes being used. 

Hopefully someone will be along with the same scope and tell what camera they are using. 🤔

[Skyline]

Is it not better to be oversampled then under sampled ?

[CraigT82]

Either will be good. Dont get too hung up on the sampling, as long as you're in the right ball park, you can tweak it by varying distance between Barlow and sensor if you really feel the need. 

Personally I'd go with the 290 as it's a superb camera for everything, but the 178 will get you more surface area for lunar work, mosaics etc... 

[Zakalwe]

Id go with the one with the fastest framerate. All things being equal, a faster framrate captures more data in the same time and has a much better chance of "freezing" the seeing.

[newbie alert]

For planetary you're going to get over sampled images due to the focal length/ pixel scale... for 8 inch sct the pixels would have to be 6.6um in size to get it on the cusp of the .67 mentioned..you're not going to get dodgy stars in a solar system image?

So as mentioned, look at frame rate, fov etc that's far more important than getting hung up on sampling

[SyedT]

1 hour ago, Skyline said:

Is it not better to be oversampled then under sampled ?

That was my thinking but wasn't 100% sure. The CCD suitability calculator does say oversampling is OK for planetary/lunar imaging etc

1 hour ago, CraigT82 said:

Either will be good. Dont get too hung up on the sampling, as long as you're in the right ball park, you can tweak it by varying distance between Barlow and sensor if you really feel the need. 

Personally I'd go with the 290 as it's a superb camera for everything, but the 178 will get you more surface area for lunar work, mosaics etc... 

 

1 hour ago, Zakalwe said:

Id go with the one with the fastest framerate. All things being equal, a faster framrate captures more data in the same time and has a much better chance of "freezing" the seeing.

 

53 minutes ago, newbie alert said:

For planetary you're going to get over sampled images due to the focal length/ pixel scale... for 8 inch sct the pixels would have to be 6.6um in size to get it on the cusp of the .67 mentioned..you're not going to get dodgy stars in a solar system image?

So as mentioned, look at frame rate, fov etc that's far more important than getting hung up on sampling

Thanks guys! Bit the bullet and went for a 290MM earlier on, on the basis of frame rate and FOV.

[vlaiv]

Don't use that calculator (that is wrong btw) for planetary critical sampling rate as it is aimed at deep sky imaging.

Don't choose planetary camera based on pixel size. You can always add much cheaper barlow to any camera and if you vary distance from barlow lens to sensor, you will vary magnification / sampling rate to suit your pixel size.

Just use quality barlow like Baader VIP that already has T2 connection and you are set - add a spacer of two to get to wanted distance. You have focal length of that barlow and it is easy to calculate magnification from that (I believe there is Baader pdf that explains that as well).

What you want to compare is max frame rate, QE and read noise. To lesser extent, you want to consider chip size as well if you do large targets like lunar and solar (you'll need less mosaic panels to cover whole target with larger sensor).

290 QE vs 178 QE - 80% vs 81, I would say that is pretty much a tie.

290 read noise vs 178 read noise - 1e vs 1.4e - here 290 is winner.

290 is winner in FPS as well, as it is capable of higher FPS, but 178 is not bad - it can also do over 200fps (that is enough not to loose frames on 5ms exposures - you won't go lower than that on any of the planets except on lunar and solar).

And finally - If you are interested in lunar and solar primarily - 178 has quite a bit larger sensor being 1/1.8" vs 1/3" 290 (or in diagonals  8.93 vs 6.45mm - almost 40% larger diagonal in 178 model - x1.9 by sensor surface ). Sensor size is also important in EEVA applications if that is of interest to you.

There you go - for planetary if lunar and solar are occasional thing and not primary concern - go with 290. If lunar / solar is primary thing and you do a lot of panels - go with 178.

Btw - optimal F/ratio for 178 is about F/10 due to pixel size, so you can just use it directly attached to EdgeHD 8" - since it is F/10 scope.

For 290 - it is about F/12, so you'll need a bit of barlowing.

Finally, just to clarify things - I'm giving you sampling rate recommendations based on theoretical resolving power of the telescope - for details see this thread:

 

[johninderby]

I bought my 290 for lunar / planetary with my 8”:Claasical Cassegrain f/12 which should be a good match. 🙂

[SyedT]

2 hours ago, vlaiv said:

Don't use that calculator (that is wrong btw) for planetary critical sampling rate as it is aimed at deep sky imaging.

Don't choose planetary camera based on pixel size. You can always add much cheaper barlow to any camera and if you vary distance from barlow lens to sensor, you will vary magnification / sampling rate to suit your pixel size.

Just use quality barlow like Baader VIP that already has T2 connection and you are set - add a spacer of two to get to wanted distance. You have focal length of that barlow and it is easy to calculate magnification from that (I believe there is Baader pdf that explains that as well).

What you want to compare is max frame rate, QE and read noise. To lesser extent, you want to consider chip size as well if you do large targets like lunar and solar (you'll need less mosaic panels to cover whole target with larger sensor).

290 QE vs 178 QE - 80% vs 81, I would say that is pretty much a tie.

290 read noise vs 178 read noise - 1e vs 1.4e - here 290 is winner.

290 is winner in FPS as well, as it is capable of higher FPS, but 178 is not bad - it can also do over 200fps (that is enough not to loose frames on 5ms exposures - you won't go lower than that on any of the planets except on lunar and solar).

And finally - If you are interested in lunar and solar primarily - 178 has quite a bit larger sensor being 1/1.8" vs 1/3" 290 (or in diagonals  8.93 vs 6.45mm - almost 40% larger diagonal in 178 model - x1.9 by sensor surface ). Sensor size is also important in EEVA applications if that is of interest to you.

There you go - for planetary if lunar and solar are occasional thing and not primary concern - go with 290. If lunar / solar is primary thing and you do a lot of panels - go with 178.

Btw - optimal F/ratio for 178 is about F/10 due to pixel size, so you can just use it directly attached to EdgeHD 8" - since it is F/10 scope.

For 290 - it is about F/12, so you'll need a bit of barlowing.

Finally, just to clarify things - I'm giving you sampling rate recommendations based on theoretical resolving power of the telescope - for details see this thread:

 

Thanks! I'm hoping to do planetary work mainly, so seems like 290MM was a good choice.

[Zakalwe]

Long focal lengths, go for the biggest pixel size and fastest frame rate that you can get. The ASI 174 is great for Lunar as it has large pixels and a screaming fast FPS. It's also very good for Solar when using a Quark, as the Quark has a built in Barlow. It's a lot more expensive though,.

 

Don't forget to make sure that your USB and disc subsystem is up to muster. You will need a SSD in the PC/laptop and good quality USB3 cables. My ASI174 will drop it's framerate significantly if I use even a 7200PRM hard disc...it absolutely demands SSD. Likewise, USB3 is very sensitive to cable length and quality. I run short cables from the camera to a quality powered USB3 hub on the mount, and then a high quality cable back to the PC. I also don't put any other devices on that line, especially USB2 (yes, USB3 can segregate USB2 traffic without slowing down the USB port, but I find it works better in practice if the camera is on it's own able and hub).

 

[SyedT]

Thanks for the advice all. Quick update, received the 290MM and managed to capture Venus as a test. Quick RGB stack below:

[SyedT]

On 09/04/2020 at 17:56, Zakalwe said:

Long focal lengths, go for the biggest pixel size and fastest frame rate that you can get. The ASI 174 is great for Lunar as it has large pixels and a screaming fast FPS. It's also very good for Solar when using a Quark, as the Quark has a built in Barlow. It's a lot more expensive though,.

 

Don't forget to make sure that your USB and disc subsystem is up to muster. You will need a SSD in the PC/laptop and good quality USB3 cables. My ASI174 will drop it's framerate significantly if I use even a 7200PRM hard disc...it absolutely demands SSD. Likewise, USB3 is very sensitive to cable length and quality. I run short cables from the camera to a quality powered USB3 hub on the mount, and then a high quality cable back to the PC. I also don't put any other devices on that line, especially USB2 (yes, USB3 can segregate USB2 traffic without slowing down the USB port, but I find it works better in practice if the camera is on it's own able and hub).

 

My Mini PC has an M.2 SSD so I'm good with that, the 290MM was capturing very nicely on SharpCap via a USB-3 port on the Mini PC. Looking forward to capturing a lot more!