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New Camera – EAA with ZWO ASI224 with NexStar 8SE

EAA dso equipment ccd observing
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#51 wenjha

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Posted 15 September 2015 - 12:55 AM

that's very nice images!

cannot wait to see you try a cooled ASI224



#52 Astrojedi

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Posted 15 September 2015 - 09:35 AM

Thanks Sam.



#53 charotarguy

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Posted 16 September 2015 - 08:55 AM

Beautiful images, I have a stupid question, can this be done on a tracked dob or this needs to have an equatorial mount?



#54 charotarguy

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Posted 16 September 2015 - 08:55 AM

that's very nice images!

cannot wait to see you try a cooled ASI224

When is the cooled ASI224 coming out?



#55 Astrojedi

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Posted 16 September 2015 - 09:33 AM

Beautiful images, I have a stupid question, can this be done on a tracked dob or this needs to have an equatorial mount?

 

Thanks and no such thing as a stupid question. Yes, you should be able to do this with a tracked Dob. I think this will work even better with larger apertures as the exposures can be shorter.

 

You don't need an EQ mount although for fainter objects longer exposures will produce better results. All the images in this thread were taken with an Alt Az mount.  


Edited by Astrojedi, 16 September 2015 - 09:36 AM.


#56 RafaelP

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Posted 16 September 2015 - 10:01 AM

I love your galaxies! What light pollution filter have you been using?

~Rafael



#57 Astrojedi

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Posted 16 September 2015 - 11:45 AM

I love your galaxies! What light pollution filter have you been using?

~Rafael

 

Rafael,

 

I am using the Orion skyglow astrophotography filter. It is a broadband filter with very high transmission characteristics across the spectrum which is what you need for galaxies. The IDAS filter also has a very similar profile.

 

If you use a LP filter you will of course have to increase your exposure time and/or gain settings to compensate.

 

If you have an EQ mount and can take ~30s+ exposures I would highly recommend a high band pass filter like the Lumicon H Alpha which also lets in IR (for galaxies & emission nebula). From a severely light polluted location such as yours you can get some pretty great results

 

Hiten


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#58 mclewis1

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Posted 16 September 2015 - 12:24 PM

I think this will work even better with larger apertures as the exposures can be shorter.

Let's see if we can put this myth to bed ... again. This is a visual concept, it doesn't apply to imaging extended objects, (but it does apply to point sources of light).

 

With a CCD camera larger apertures will not make the image of an extended object brighter. The f ratio determines how bright an object will be.

 

The larger aperture will give you more ... fainter stars and more resolution, and if the f ratio is kept the same a larger image (from the longer focal length).

 

So yes, all things being equal an extended object in a 2" f2 setup will be the same brightness as in a 10" f2 setup, you will however see much more of the object in the image from the 10" since it will be much bigger on the same chip (more details, and more ability to enlarge it). And since the object will be bigger on the chip you will also have better signal to noise ratios making image processing techniques more effective. This means you can certainly create a better brighter image with a larger aperture scope (and maybe that's the real point) ... but with the raw images the actual brightness of the extended object will be determined by the f ratio and not the aperture.



#59 A. Viegas

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Posted 16 September 2015 - 12:28 PM

Can someone post a screen grab from the ASI 224 of a bright dso like the ring or M27 but a single exposure. No processing. No after image tweaking. Just what does it look like raw at whatever exposure length you need to show it. Also this would be useful with a fainter target like NGc7331 or another lower brightness object.

Thanks
Al

#60 Astrojedi

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Posted 16 September 2015 - 01:00 PM

 

I think this will work even better with larger apertures as the exposures can be shorter.

Let's see if we can put this myth to bed ... again. This is a visual concept, it doesn't apply to imaging extended objects, (but it does apply to point sources of light).

 

With a CCD camera larger apertures will not make the image of an extended object brighter. The f ratio determines how bright an object will be.

 

The larger aperture will give you more ... fainter stars and more resolution, and if the f ratio is kept the same a larger image (from the longer focal length).

 

So yes, all things being equal an extended object in a 2" f2 setup will be the same brightness as in a 10" f2 setup, you will however see much more of the object in the image from the 10" since it will be much bigger on the same chip (more details, and more ability to enlarge it). And since the object will be bigger on the chip you will also have better signal to noise ratios making image processing techniques more effective. This means you can certainly create a better brighter image with a larger aperture scope (and maybe that's the real point) ... but with the raw images the actual brightness of the extended object will be determined by the f ratio and not the aperture.

 

 

I fully understand the relationship (and the physics and math) between f ratio, exposure time and resolution.

 

I think you missed the point I was trying to make... Better results for me mean more resolution...

 

Very simply put at the same f ratio a larger aperture will gather more light vs. a smaller scope which means more arc second resolution... period... which is what we are after... otherwise I would be using video cameras (which are pretty good but don't satisfy my need for resolution)...

 

This means that I can image an object with a slightly slower focal ratio on a 16" dob and still get enough signal to overcome read noise and capture enough dynamic range for stacking. Yes if I am not stacking and using traditional long exposure imaging the image will be less 'bright'.

 

Honestly imaging at f/3.3 on a C8 is a compromise I make for speed. I would really like to see even more detail in live view but not having a permanent observatory means I have to make compromises...


Edited by Astrojedi, 16 September 2015 - 04:47 PM.

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#61 Astrojedi

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Posted 16 September 2015 - 01:20 PM

Can someone post a screen grab from the ASI 224 of a bright dso like the ring or M27 but a single exposure. No processing. No after image tweaking. Just what does it look like raw at whatever exposure length you need to show it. Also this would be useful with a fainter target like NGc7331 or another lower brightness object.

Thanks
Al

 

Al,

See attached. This was taken with my C8 at f3.3 using the Orion skyglow AP filter (I will look for one taken without the filter but cannot find it right now). It is a 12s exposure at a gain setting of 350.

 

The image is completely raw, straight out of the camera with no stretch applied and before debayering. Will likely have some hot pixels.

 

Hiten

Attached Thumbnails

  • dso_220541_0013.jpg


#62 Astrojedi

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Posted 16 September 2015 - 01:40 PM

Here is a 15s exposure at 300 gain for the M51 without the LP filter... again completely raw out of the camera no processing or stretch (except resize) and before debayering...

 

Note I have had to resize both these images to get them under the 500kb limit.

 

dso_203338_0018.jpg


Edited by Astrojedi, 16 September 2015 - 01:40 PM.

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#63 geyes30

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Posted 16 September 2015 - 01:57 PM

Wonderful images! Quick question about your thought process in picking this camera. Why did you choose it over the asi178mc or 185mc? Larger sensors might have permitted more pixels for large objects, no?

#64 Astrojedi

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Posted 16 September 2015 - 02:20 PM

Wonderful images! Quick question about your thought process in picking this camera. Why did you choose it over the asi178mc or 185mc? Larger sensors might have permitted more pixels for large objects, no?

 

Short answer is the low read noise of the sensor and higher resolution vs. other EAA options...

 

The long answer is that the low read noise combined with the high QE means I can get more dynamic range with much shorter exposures.

 

This has a couple benefits: one is that I can use a relatively lower quality Alt Az mount for casual observing and when traveling. Of course a quicker setup and tear down is another side benefit of an Alt Az setup.

 

The second is that I see images much quicker and at a higher resolution (without sacrificing speed). This is more of a personal preference as some folks will be perfectly ok with longer exposures for cameras with comparable resolution.

 

Yes, I would love to get a larger sensor but all other sensors have a slightly higher read noise. A larger sensor will also require me to change my setup as I likely will get more vignetting, coma etc. with my C8 and the focal reducer I use as the imaging circle is very small.


Edited by Astrojedi, 16 September 2015 - 02:26 PM.

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#65 geyes30

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Posted 16 September 2015 - 03:43 PM

Thanks. FYI, as I understand it (from ZWO website), 224 and 185 are essentially the same cameras but with different chip sizes. There may be subtle but important differences that may not be reflected in the simple description on the website.



#66 Astrojedi

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Posted 16 September 2015 - 03:56 PM

Thanks. FYI, as I understand it (from ZWO website), 224 and 185 are essentially the same cameras but with different chip sizes. There may be subtle but important differences that may not be reflected in the simple description on the website.

 

Yes, you are correct in that you can think of 185 as the larger version of 224 but the 185 has 2x the read noise at 3.3e (as per ZWO's website). As a result you may lose some dynamic range with such short exposures (as the ones I am using in this thread) but should still work well enough with15s-30s exposures.



#67 A. Viegas

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Posted 16 September 2015 - 08:01 PM

Thank you Hiten

This question on the 185 is interesting. I wonder has anyone seen any DSO images with the 185 or is the chip too noisy to be effective as a larger chip alternative to the 224

Hiten what would you speculate the benefit will be with the cooled 224 vs the uncooled in terms of ability to further reduce noise and pull out more detail? Ultimately I wonder if the extra $200-300 will be worth it or not? From my experience with the mallincam Xtreme the non cooled jr pro has just so many hot pixels during the summer that the cooling is worth the added cost. I am wondering that with already so low read noise what will the cooled version bring that the uncooled is already doing?

Al

#68 Astrojedi

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Posted 16 September 2015 - 10:40 PM

Thank you Hiten

This question on the 185 is interesting. I wonder has anyone seen any DSO images with the 185 or is the chip too noisy to be effective as a larger chip alternative to the 224

Hiten what would you speculate the benefit will be with the cooled 224 vs the uncooled in terms of ability to further reduce noise and pull out more detail? Ultimately I wonder if the extra $200-300 will be worth it or not? From my experience with the mallincam Xtreme the non cooled jr pro has just so many hot pixels during the summer that the cooling is worth the added cost. I am wondering that with already so low read noise what will the cooled version bring that the uncooled is already doing?

Al

 

Al,

I have not tried the 185 but specs are very promising. I think the results will be very comparable to the 224 but each sub may need a few more seconds of exposure.

 

Regarding cooling I will give you my perspective and a slightly lengthy answer. I don't want to be presumptuous as to how others may use the camera hence will focus on how I have been using the camera.

 

Firstly, I think the 224 is a very good fit for EAA. The low read noise and high sensitivity are critical for short exposures. And the camera delivers higher resolution in rich color with an RGB matrix and just 3.75 micron pixels in a 1/3 sensor format which works perfectly with my Meade 3.3 reducer… all for ~$350 (to put this in context, my Lodestar X2C requires slightly longer exposures to deliver the same dynamic range even with a less obstructive CYMG matrix and 8.2-8.4 micron pixels).

 

The 224 also has a shallow well (just 9k), which I have found you can saturate relatively quickly with  short exposures… but due to the low read noise you still get good dynamic range… almost like it was made for short exposures and stacking.

 

But here is the thing… given the above and how I use it in an EAA context I will almost always need to take darks anyways to address the amp glow (due to the high gain setting) which cooling does not address. Also my sub exposures rarely exceed 30s – 45s even on my EQ mount. Hence I am not sure if for my purposes cooling makes much difference.

 

Having said that I feel the CMOS sensor is noisier than my X2C. Whereas my X2C shows maybe a few hot pixels the ASI224 shows quite a few (see attached a dark frame 10s at 350 gain 90degF). So if you are using the camera at a lower gain setting for longer exposures then cooling should definitely help. Also if in the evenings your location has 70deg+ temps then also cooling will definitely help.

 

Hope this helps.

 

Hiten

Attached Thumbnails

  • Dark 10s Gain 350.jpg

Edited by Astrojedi, 17 September 2015 - 09:56 AM.

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#69 Astrojedi

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Posted 23 September 2015 - 12:08 PM

The Moon last night made viewing any object with low surface brightness next to impossible... so went back to a couple of brighter DSOs

 

Same setup as before - ASI224, with C8@f3.5 on an Alt Az mount (using a LP filter).

 

M27: 25x10s

 

M27 25x10s.jpg

 

Some subtle detail is lost in the the JPG compression... but looked amazing on the monitor... I just stared at the detail for a while... 

 

The moon was less than 15 deg away from the M27 when I viewed it with a waxing gibbous of 62%... so a pretty good result..


Edited by Astrojedi, 23 September 2015 - 12:43 PM.

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#70 RafaelP

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Posted 23 September 2015 - 01:43 PM

Lovely Dumbbell!



#71 Astrojedi

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Posted 23 September 2015 - 08:34 PM

Lovely Dumbbell!

 

Thanks



#72 Dom543

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Posted 23 September 2015 - 09:09 PM

Hiten,

 

I asked this on the gallery thread but it is better to use this thread for questions and discussion.

 

What software are you using to process the images captured with the ASI camera? Does has its own software or are you using Astrotoaster? Or some other software?

 

My second question was if the 25 frames really needed, if you see a noticeable improvement between stack 20 and stack 25. With my Lodestar I don't see any improvement after the third or fifth frame. You may have already answered this on this thread. If the ASI is, indeed, noisier than the Lodestar, than a larger stack may be beneficial to smooth out all that noise.

 

Thank you,

--Dom



#73 Astrojedi

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Posted 23 September 2015 - 09:21 PM

 

Nice capture Hiten!

    What software are you using to process images captured with the ASI cameras? Do they have their own software or are you using AstroToaster or an other generic package? Also is stacking 25 frames really needed? Do you see noticeable improvement between stack 20 and stack 25? I am asking this because my experience with software based EAA cameras (Lodestar) is that a stack of 3-5 is the max to yield noticable improvement.

    Thank you,

    --Dom

 

Dom,

I am using FireCap and AstroToaster. ZWO does not make any EAA software for this camera (unfortunately).

 

In my view stacking serves 2 main purposes:

 

The primary one (for me at least) is the ability to overcome the limitations of my mount and collect more photons.

 

The secondary benefit of stacking is the elimination of random noise and other artifacts via averaging. This benefit usually diminishes after a few subs.

 

Note that while I used 25 frames, these are only 10s exposure (about 1/3 the exposure time you typically use with your Lodestar). Ultimately you cannot cheat Physics and what matters is total exposure time and total photons collected.

 

So ignoring factors such as read noise I would need 15x10s frames to capture the same amount of photons as you captured in 5x30s frames. But in reality read noise matters hence we may need a few more subs.

 

In about 15-20 10s frames the M27 had started to look very good. But since I am viewing the object and playing around with the settings I just let it run for a few more subs in the background.

 

My goal in this thread and with this exercise to understand the art of the possible with a typical Alt Az mount and a low read noise camera like ASI224. Otherwise 4 to 5 30 seconds subs would be more than sufficient with a camera like the ASI224.

Hiten


Edited by Astrojedi, 23 September 2015 - 09:22 PM.


#74 Astrojedi

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Posted 23 September 2015 - 09:22 PM

Hiten,

 

I asked this on the gallery thread but it is better to use this thread for questions and discussion.

 

What software are you using to process the images captured with the ASI camera? Does has its own software or are you using Astrotoaster? Or some other software?

 

My second question was if the 25 frames really needed, if you see a noticeable improvement between stack 20 and stack 25. With my Lodestar I don't see any improvement after the third or fifth frame. You may have already answered this on this thread. If the ASI is, indeed, noisier than the Lodestar, than a larger stack may be beneficial to smooth out all that noise.

 

Thank you,

--Dom

 

Had the exact same thought hence answered you here..



#75 MartinMeredith

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Posted 25 September 2015 - 09:49 AM

Hiten, I really like the results you're getting with that camera. I'm of the opinion that low read noise (and high QE!) is the future of EAA as it opens up some nice low-budget approaches that don't have to sacrifice image quality (yes, I'm talking stacking lots of short subs…).

 

Just to give my take on the "how many subs" question. One often hears imagers say beyond 30 is a case of diminishing returns, and EAA types suggest not much improvement after 3 or 4. My own view is that photons should be collected for as long as you want to observe an object (which might run into 10s of minutes), and not to do so is a waste. My experience is that quality continues to improve during that time (as physics says it should), and the apparent absence of improvement is, I believe, largely a matter of visual psychophysics -- the just noticeable difference between a stack of N and a stack of N+1 gets smaller. Anyway, here are some not-very-scientific captures of short subs of NGC 7331 from the other night, where I saved the image approximately on each doubling of sub count, and the improvement I think is present and worthwhile. I had to reduce the image a bit due to size limitations.

 

NGC7331a.png

 

Keep up the great work

 

Martin


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