Help me spend my money - ASIxxx cam

[Vox45]

Hi all,

I will be travelling to my home country of Canada and with the exchange rate I can make some good savings on an ZWO ASIxxx camera.

My endgame is:

(1) use an ASIxxx camera with a MAK180 for planetary/lunar imaging

From what I read, the ASI224 is the way to go but there are other models that might be better on planets/lunar with such a long focal... 

(2) replace my Philips webcam with an ASIxx as a guide cam on my SW80ED for DSOs and use my DSLR for imaging

Are there potential pitfalls of using an ASI color cam for guiding ?

Please share your thoughts

[CraigT82]

I think the ASI224 with a 1.5x barlow for f22.5 would put you in the right ball park for planetary.  You'd be sampling at 0.19 arc" PP which is about a third of the dawes limit of the 180mak and would give you a decent image scale.  

Of course if you want bigger pictures you could go with a 2.5x barlow/powermate but you'd be oversampling by quite a bit and the individual exposures may get quite long, slowing down the frame rates considerably, in which case a camera with bigger pixels may be more suitable, maybe the ASI174?  I think it all depends on how big you want your planets to be!

To get the best frame rates out of these cameras you will probably need a laptop with a SSD hard drive and USB3 ports.

I think this new generation of CMOS cameras are so sensitive with low read noise that guiding isn't any problem at all, though I'm just regurgitating what I've read elsewhere... never done any guiding myself!

EDIT: Just to add, my view is that in very good seeing you can get away with small pixels/long FL and over sampling by a lot, as even with the inevitable slower frame rates, you'll still get plenty of  sharp frames to stack and you'll want those smaller pixels to catch the fine detail thats available.

In mediocre seeing it's probably best to stick with the larger pixels as you'll want to keep frame rates high in order to make the most of the fleeting moments of relative clarity.

[D4N]

Well the mono cameras are more sensitive than the colour ones but since you have been using a webcam for guiding it should be a big step up anyway.

[Vox45]

17 hours ago, CraigT82 said:

I think the ASI224 with a 1.5x barlow for f22.5 would put you in the right ball park for planetary.  You'd be sampling at 0.19 arc" PP which is about a third of the dawes limit of the 180mak and would give you a decent image scale.  

Of course if you want bigger pictures you could go with a 2.5x barlow/powermate but you'd be oversampling by quite a bit and the individual exposures may get quite long, slowing down the frame rates considerably, in which case a camera with bigger pixels may be more suitable, maybe the ASI174?  I think it all depends on how big you want your planets to be!

Thanks you for taking the time to answer. I am just a bit confused about the relationship between "Image Array" and "Pixel Size"

These are the specs of both cameras:

ASI224 specs are: Image Array: 1305 x 977 and Pixel Size: 3.75um

ASI174 specs are: Image Array: 1936 x 1216 and Pixel Size: 5.86um

I used the FOV calculator here www.skyatnightmagazine.com/field-view-calculator and was surprised to see that the image was much smaller on the 174... my assumption was that it would look bigger, I was wrong.  I would guess that the smaller the pixel, the better the resolution (smaller details) but what would I gain from a bigger sensor size (Image Array) ?

I never really understood that part. I use a DSLR so never had to think about this

[Owmuchonomy]

A very simple rule I try and adhere too is aim for a f/ratio around 4 to 5 times the pixel size for planetary imaging.  Therefore I use an ASI 174MM with my SCT 9.25 and a 2.0 or 2.5 x powermate (f/20-25).  Same for solar and my Lunt 60 and a 2.5x powermate (f/20 ish).  This is why I chose the ASI 174 MM over the ASI 178 MM because I wouldn't gain anything from the smaller pixels (see Craig's post above).

[CraigT82]

41 minutes ago, Vox45 said:

Thanks you for taking the time to answer. I am just a bit confused about the relationship between "Image Array" and "Pixel Size"

These are the specs of both cameras:

ASI224 specs are: Image Array: 1305 x 977 and Pixel Size: 3.75um

ASI174 specs are: Image Array: 1936 x 1216 and Pixel Size: 5.86um

I used the FOV calculator here www.skyatnightmagazine.com/field-view-calculator and was surprised to see that the image was much smaller on the 174... my assumption was that it would look bigger, I was wrong.  I would guess that the smaller the pixel, the better the resolution (smaller details) but what would I gain from a bigger sensor size (Image Array) ?

I never really understood that part. I use a DSLR so never had to think about this

The 174 has much more pixels than the 224 and each pixel is bigger, so the sensor is physically much larger, this is why the image 'looks' smaller.  It isn't actually smaller of course, there's just more empty space around planet on the sensor.  Image scale is purely a function of focal length so if you're using the same scope/barlow combo with both cameras, the size of the planet on the sensor will be the same.

The larger sensor size would be beneficial for imaging things like the moon and sun, as you'd get more of the surface in the image for a given magnification than you would with the smaller sensor of the 224.  Also it would be easier to capture images of the ISS as it zooms overhead with a larger sensor!

Heres something I knocked up to illustrate the difference in sensor size of the current range

[Vox45]

50 minutes ago, CraigT82 said:

if you're using the same scope/barlow combo with both cameras, the size of the planet on the sensor will be the same.

Ho I see, thanks for that graphic and explanation ! I went back and read your previous post once more with this new understanding, it makes a lot more sens to me now

So would the ASI185 be a better compromise as it has lower read noise than the 174, bigger sensor than the 224 and with the same pixel size ?

I have to admit that the praises are really high for the ASI224 and I never read comments on the ASI185 ... It looks like they use the same Sony IMX Exmor sensor ?

[CraigT82]

43 minutes ago, Vox45 said:

Ho I see, thanks for that graphic and explanation ! I went back and read your previous post once more with this new understanding, it makes a lot more sens to me now

So would the ASI185 be a better compromise as it has lower read noise than the 174, bigger sensor than the 224 and with the same pixel size ?

I have to admit that the praises are really high for the ASI224 and I never read comment on the 185 so ... not sure if that is a good choice.
 

Yes the 185 may actually be a good compromise, especially if you are going to be doing a good amount of lunar work as well as planetary.  I probably wouldn't worry too much about the read noise of these cameras, as there's not much between them and even the noisiest of this new generation are still extremely low noise.  

 

[Vox45]

7 minutes ago, CraigT82 said:

Yes the 185 may actually be a good compromise, especially if you are going to be doing a good amount of lunar work as well as planetary.  I probably wouldn't worry too much about the read noise of these cameras, as there's not much between them and even the noisiest of this new generation are still extremely low noise.  

 

yes and they'll be noisier than the next generation and so on ! it's a never ending pursuit until we reach zero

I've seen pretty amazing images with previous generations of sensors, so you are correct, I should not worry too much about the read noise.

I will go for the ASI185 as I intend to do a lot of lunar imaging and maybe some solar. I understand that I should go for a monochrome in this case but I have to make some compromise price wise.

[Owmuchonomy]

Just to add to Craig's excellent post, the ASI174MM chip size allows me to get a full disk of the Sun with my solar set up, just.  Something to consider.

[Vox45]

On 22/07/2016 at 15:28, Owmuchonomy said:

Just to add to Craig's excellent post, the ASI174MM chip size allows me to get a full disk of the Sun with my solar set up, just.  Something to consider.

Ho the agony of the buyer's remorse !

I took the plunge and got the ASI185. I did consider the 174 as you suggested but I had to make a choice at some point. I figured that having a larger chip than the 224 would give me a bigger fov for lunar and catching more moons of jupiter and saturn and having small pixels would give me a better resolution. That with the low read noise in between the 174 and 224 ...

That being said, quality in seeing and ability to use the gears and post processing plays a big part in the quality of the end result!

I'll post some pictures when I get the chance. It will be a while anyway. Truth is, for now, I just bought a real fancy guide cam

[Owmuchonomy]

Excellent. A bit late in the day but I started this thread

  because like you I just couldn't decide!  I'm sure you will gain great pleasure from your purchase.  Me, well I will be buying a second camera soon!

[Vox45]

16 hours ago, Owmuchonomy said:

Excellent. A bit late in the day but I started this thread

  because like you I just couldn't decide!  I'm sure you will gain great pleasure from your purchase.  Me, well I will be buying a second camera soon!

I read your thread and it was very informative, thanks!

I would have gone with monochrome but the price of filter wheel + filter + more time spent on each target is not worth the only few imaging session I can do as I have no permanent setup.

I'll be saving for a better camera as I intend to go to NB CCD once I can build an obsy... For now, this camera will do. All in good time

[Vox45]

Got my camera while on vacation in Canada I was near the US border so I got it shipped (free shipping in the US) to a friend in Vermont and saved on taxes and custome and with the favorable exchange rate I ended up saving 126€ from the listed price here in France. Good deal !

There is a clear glass over the sensor but I seem to remember that it is not IR cut (The documentation only talks about the ASI120)

I do have a Baader IR filter for my old webcam that could fit on the nosepiece...

[D4N]

Nice one, according to ZWO the 185MC comes with an IR cut window so you shouldn't need a separate filter.

https://astronomy-imaging-camera.com/products/usb-3-0/asi178mc-color/