Lunar and planetary images with ZWO ASI 224

[IDM]

Hi,

I am very new to imaging and just trying to learn some very basic steps. In the first instance I am looking to take decent photos of the moon and then move to other planets.

My setup is a TAL100RS refractor which has a  100mm diameter and 1000mm focal length (this scope works well with eyepieces at 6mm (166x)) the telescope is being used with a Zwo ASI2 44MC camera.

When I use the camera straight into the scope I can get quire decent images that I have successfully stacked. However, the magnification is a little low. So I thought I would try a 2x barlow. When I  do this the magnification is very high and all the images I get look like the same effect as pushing the telescope to a too higher magnification, in that the images are blurry and nowhere near as detailed as I can achieve with an eye piece. Do I need a 1.5x barlow or am I doing everything wrong?

 

As I say I am just learning my way round capturing images and so would be grateful for any advice.

 

Many thanks,

Ian

[rnobleeddy]

Probably worth a little more info on how you've captured and processed data - the usual approach for lunar imaging is to record a short video and use software such as registax or autostakkert to pick out the sharpest frames, and then stack them, in order to get the best image.

[IDM]

Hi,

 

I have been capturing 30 second videos and processing through Autostakkert. From the analysis I normally take the best 50% and stack these. The image is then taken through Registrax. However, it is clear to me from the very beginning that the results are not going to be good enough.

Indeed when I look at the laptop screen at the time of capture, the image looks just like when you push a telescope beyond its maximum magnification. I have tried being really careful with focus etc but I am not impressed with any of the images taken. I have had some success without the Barlow, though sharp as these photos are, they are nowhere near as magnified as when I just use the 6mm eyepiece. This was why i was wondering about how or when to use a Barlow or other knowledge I need to get a descent photos.

Thanks,

Ian

 

[Gogleddgazer]

This is a really helpful thread for those of us just about to dip our toes into the AP pool. Thanks to all those with knowledge and experience for sharing that so fully with us noobs

J

[CraigT82]

Are you sure it's a 2x barlow? Does it work OK with eyepieces? 

[Cosmic Geoff]

I note that you are using a f10 refractor. Some experts advise using a f/ratio of up to f20 (including Barlow) for planetary imaging.  However I have tried planetary imaging a lot with a f10 SCT and found that while images at f10 were often successful, images with a Barlow were often worse than at f10 and I could rarely figure out why.  I suspect that the seeing at my site does not support imaging at long focal ratios.

 

[IDM]

1 hour ago, CraigT82 said:

Are you sure it's a 2x barlow? Does it work OK with eyepieces?

Hi, Yes is seems to work ok with my 24mm eye piece, though the exact magnification I am unsure of. It is a cheap barlow, I would be happy to upgrade but am not confident based on the results I am currently getting that it would be worth while.

[IDM]

39 minutes ago, Cosmic Geoff said:

I note that you are using a f10 refractor. Some experts advise using a f/ratio of up to f20 (including Barlow) for planetary imaging.  However I have tried planetary imaging a lot with a f10 SCT and found that while images at f10 were often successful, images with a Barlow were often worse than at f10 and I could rarely figure out why.

Oh dear, that is concerning! Are there any definitive or good 'starter-guides' to getting the right equipment together in the right combination? I was contemplating upgrading my scope at come point but recently concluded that there was a lot I needed to learn before spending considerably more.

 

Many thanks,

Ian

[IDM]

This is a stacked image from a 30 second video, I have done little or nothing to enhance beyond the stacking. It gives you an idea of the magnification with the 2x barlow. Does it seem a reasonable magnification and if so what can I do to improve my photos?

 

Many thanks,

Ian

2021-04-19-1920_5-Moon_lapl3_ap1587_conv.tif

[vlaiv]

8 minutes ago, IDM said:

Does it seem a reasonable magnification and if so what can I do to improve my photos?

With imaging - there is no such thing as magnification. There is something else - called pixel scale.

In fact, since aperture of telescope is limiting factor - for planetary imaging there is suitable F/ratio that depends on pixel size. Around F/15 is good focal ratio for 3.75µm pixel size - like ASI224 has.

You did go a bit higher with F/20 - but not by much. For beginning that is quite OK. Barlow magnification changes when you change distance from barlow element to sensor. If you can try to just use barlow element (if it is 1.25" thread type) with your own extensions to dial in F/15 (barlow to be x1.5 amplification).

Besides that - there are couple of things that you can do to improve overall image quality:

1. use higher gain settings

2. shoot in 16bit mode (8bit mode requires somewhat careful handling)

3. shoot calibration frames - darks and flats if you can. Darks are quite easy - just cover the scope and shoot with same settings (same exposure length). For flats - you ideally need flat panel or something like that, but many people have success with sky flats as well (T-shirt over scope while it is still daylight outside - but no sun, just before dawn or after sun sets)

4. Use very short exposure time. One of important things with lucky imaging is to shoot very short exposures to freeze the seeing. Don't look at histogram at all. Max that you should go for is 5-6ms, but Moon often allows for 3-4ms exposures. Just be careful not to saturate (this can usually happen on low pixel scales - like when not using barlow)

5. Wait until the Moon is highest in the sky. Sometimes it is good to shoot the moon while it is still daylight. Seeing can be excellent just after sunset, but make sure that Moon is high in the sky.

Your image looks like:

- you did not use UV/IR cut filter with your ASI224

- you shot while moon was relatively low down

- maybe you used longer exposure than is good for lucky imaging

There is also pattern visible after wavelet sharpening - what bayer order did you give to AutoStakkert? it should be RGGB for ASI224 if I'm not mistaken.:

[blameTECHIE]

3 minutes ago, vlaiv said:

With imaging - there is no such thing as magnification. There is something else - called pixel scale.

In fact, since aperture of telescope is limiting factor - for planetary imaging there is suitable F/ratio that depends on pixel size. Around F/15 is good focal ratio for 3.75µm pixel size - like ASI224 has.

You did go a bit higher with F/20 - but not by much. For beginning that is quite OK. Barlow magnification changes when you change distance from barlow element to sensor. If you can try to just use barlow element (if it is 1.25" thread type) with your own extensions to dial in F/15 (barlow to be x1.5 amplification).

Besides that - there are couple of things that you can do to improve overall image quality:

1. use higher gain settings

2. shoot in 16bit mode (8bit mode requires somewhat careful handling)

3. shoot calibration frames - darks and flats if you can. Darks are quite easy - just cover the scope and shoot with same settings (same exposure length). For flats - you ideally need flat panel or something like that, but many people have success with sky flats as well (T-shirt over scope while it is still daylight outside - but no sun, just before dawn or after sun sets)

4. Use very short exposure time. One of important things with lucky imaging is to shoot very short exposures to freeze the seeing. Don't look at histogram at all. Max that you should go for is 5-6ms, but Moon often allows for 3-4ms exposures. Just be careful not to saturate (this can usually happen on low pixel scales - like when not using barlow)

5. Wait until the Moon is highest in the sky. Sometimes it is good to shoot the moon while it is still daylight. Seeing can be excellent just after sunset, but make sure that Moon is high in the sky.

Your image looks like:

- you did not use UV/IR cut filter with your ASI224

- you shot while moon was relatively low down

- maybe you used longer exposure than is good for lucky imaging

There is also pattern visible after wavelet sharpening - what bayer order did you give to AutoStakkert? it should be RGGB for ASI224 if I'm not mistaken.:

well I'm learning loads here for my ASI224MC, currently mounted on a SW ED80DS.  Looks like I need to be investing on a 1.5x 2" barlow for my Celestron 9.25 XLT then - that should give me F/15 which should, if I've read @vlaiv message correctly, puts me in the sweet spot for the sensor.

[IDM]

5 minutes ago, vlaiv said:

Your image looks like:

- you did not use UV/IR cut filter with your ASI224

- you shot while moon was relatively low down

- maybe you used longer exposure than is good for lucky imaging

Thank you so much for the fantastic feedback, really helpful!!

With the questions you raised, I do have an IR blocking filter on the ASI224MC, I did try without and it looked worse! The moon wasn't terribly high, so maybe this contributed to the problems. Your exposure comments are really interesting as I had mistakenly thought that I should keep the gain low to prevent noise and then compensate with the exposure time. I will have to try the other way round!

Your other comments are also really helpful I will need time to digest them, but thanks.

Ian

[vlaiv]

13 minutes ago, IDM said:

Your exposure comments are really interesting as I had mistakenly thought that I should keep the gain low to prevent noise and then compensate with the exposure time. I will have to try the other way round!

While SNR per exposure is of course very important - in lucky imaging it is more important to freeze the seeing. If we use longer exposure length than seeing allows - we just add motion blur to distortion created by atmosphere and blur increases.

Lunar is particularly good for this approach as one has rather long time window to shoot the movie.

When doing planetary AP - one must be aware that planets rotate and there is limited amount of time in which video can be taken without need for special processing like "derotation". For Jupiter it is something like 4-5minutes or less with larger scopes (it also depends on scale of the image - sampling at higher rates means smaller detail and shorter time needed for rotation blur to start showing)

With lunar - we can take very large number of frames. This restores lost SNR as stacking improves SNR. For this reason, per frame SNR does not need to be very high and long exposure is not needed. There should be just enough SNR so that stacking software can stack properly and identify features instead of thinking it is noise.

What is more important - is low read noise. Only difference between thousand millisecond subs stacked and single one second sub as far as SNR is concerned is read noise. If we had camera with 0 read noise - there would be no difference in SNR between the two - and we could do very short subs indeed.

Interesting thing with CMOS sensors is that read noise goes down as gain goes up (that is because read noise comes in "two chunks" - one pre gain and one post gain. One that comes post gain - can get smaller in relation to signal once signal is boosted by gain):

This is actually good for you - using higher gain will not make things noisier - it will actually make them less noisy after stacking.

If you for example use 20ms exposure and stack 200 frames - that is total of 4s. When you lower your exposure to say 5ms - just keep in mind that you need to stack 800 frames to have same total integration time. Camera FPS actually makes this possible. If you use 20ms - max FPS you'll achieve will be 50fps, but if you switch to 5ms exposure - you'll be able to do 200fps (and that is why FPS is important - so you don't loose frames when doing short exposures).

In any case - using say 10% of best frames - will end up with same total integration time - regardless of exposure length in most cases - if you can maintain given FPS. If not - then good thing you are doing Lunar - just shoot for longer

 

[Cosmic Geoff]

I append an actual camera settings file for a ASI224MC shooting the moon through a f10 8" SCT.  Note that the gain is about 358 and I have reduced the area to 800x600 to speed up the frame rate.

[ZWO ASI224MC]
Debayer Preview=On
Pan=332
Tilt=248
Output Format=SER file (*.ser)
Binning=1
Capture Area=640x480
Colour Space=RAW8
Temperature=15.2
Hardware Binning=Off
High Speed Mode=Off
Turbo USB=80(Auto)
Flip=None
Frame Rate Limit=Maximum
Gain=358
Exposure=0.008653
Timestamp Frames=Off
White Bal (B)=95
White Bal (R)=52
Brightness=0
Auto Exp Max Gain=300
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1
TimeStamp=2020-10-26T21:35:17.0822658Z
SharpCapVersion=3.1.5049.0
 

[IDM]

On 25/04/2021 at 17:57, Cosmic Geoff said:

I append an actual camera settings file for a ASI224MC shooting the moon through a f10 8" SCT.  Note that the gain is about 358 and I have reduced the area to 800x600 to speed up the frame rate.

Sorry for the delay in responding to this, but can I ask a very basic question! When I reduce the area what I see is smaller area of the moon, which is effectively blown up to the same size as when using a larger area. The affect being like increasing the magnification, however, the image quality is reduced. I had imagined that reducing the imaging area was primarily useful when looking at planets where the majority of the observable image was outside the planet in view and therefore a waste of the detector. Is my understanding correct or not? Also if you do as Cosmic Geoff suggests, how do you get a better more crisp image? Again I apologise for the basic nature of my questions.

Many thanks,

Ian

[powerlord]

reducing the imaging area just means it only captures from that bit of the sensor. so setting 800x600 means that 800x600 pixels of the total will be used - wherever you have picked. defaults to middle usually. So - if the moon took up the whole FOV at 'full sensor' 1304X976 then capturing only 800x600 is like a window into that. the purpose is really to increase fps. If all things were equal, and you got 100fps at 1304x976, and you got 100fps at 800x600 crop they'd be little point in shooting 800x600 as all the data is in the full sensor frames. But that's not the case - 800x600, less data to read off sensor, less data to save to disk, so fps goes up. the downside, is you only get a window into the sensor.

it's not like, say with a DSLR, where you might choose 720p to get 60fps, or 1080p and you only get 30fps, but in both cases you get the same fov. there, the camera is reading off the native sensor resolution (much higher than 1080p and binning it down to 1080p or 720p - its not saving any effort reading from sensor, but you do save on file sizes).

[AstroMuni]

On 25/04/2021 at 13:26, IDM said:

TAL100RS refractor which has a  100mm diameter and 1000mm focal length (this scope works well with eyepieces at 6mm (166x)) the telescope is being used with a Zwo ASI2 44MC camera.

I find a similar problem with my 130mm, 650mm focal length scope using a barlow and the ASI224mc. The focus is not very crisp and I was told that one of the reasons could be the high IR sensitivity of the camera and using an IR cut filter should help. Also having a better focusser to get fine focus helps.

Edited May 21, 2021 by AstroMuni

[Cosmic Geoff]

I was aware of the high infrared sensitivity of the ASI224MC when I bought it, and accordingly bought ZWO IR-cut and IR-pass filters at the same time. I always use the camera with one or the other filter attached.  As I proved when trying the camera out in my kitchen, if you don't use the IR-cut filter, the colours come out looking wrong.

To repeat, the camera is intended to be used with an IR-cut filter, and if you don't use one your colours will come out wrong.

I should think that with an achromat, any IR that passes through it will be focused in a slightly different place than the visible light, so using an IR-cut filter should be beneficial.

[rnobleeddy]

Alternatively, these cameras (with high IR sensitivity) can be pretty effective with a IR pass filter, effectively becoming mono IR cameras above 800nm. 

That works well for lunar imaging because those wavelengths suffer less from seeing, and so in theory, you can get sharper images.

[IDM]

Hi,

Funny the IR issue has been raised. Just last week I watched a you tube video on lunar photography that suggested that best results would be  obtained using an IR pass filter and I have just received an Astronomik 742 IR pass filter to try.

 

I am also working on an electronic focuser using an Arduino Nano board, step motor and myFP2M software. So far for about £9.00 i have the motor working with the software. I just need to work out how to attach it to the Tal scope. all good fun. 

Thanks again for the thoughts and feedback, there is so much to learn.

 

Ian

 

 

[Neil H]

You could always mount the motor and use a belt on the focused knob