c8edge,asi178,hyperion 2.25 x barlow on jupiter,not too happy

[iwols]

hi just been trying to image jupiter tonight with the above equipment but not very happy with the result any guidance appreciated screen shot of typical frame of avi thanks

 

[Davey-T]

I've got worse in the past, what frame rate were you getting.

Dave

[symmetal]

Did you focus on a nearby star or one of the moons with a bahtinov mask or similar beforehand? Also try to get as fast an exposure you can get away with, 5mS or so, along with loads of frames to try and beat the 'seeing' but at its current position from the UK it should be called 'very very very lucky imaging' ?

Alan

[Sunshine]

Looks out of focus to me, as mentioned above, I use a moon for focus point since I don't have a mask.

[michael.h.f.wilkinson]

An ASI178MM has a 2.4 micron pixel size. This works best at around F/11-15. You are working at F/22.5, so about twice that focal ratio. You cannot get that focused well, because you are oversampling the image. An ASI174MM would be more comfortable at that focal ratio.

[newbie alert]

I have a 8 inch sct and a camera with similar pixel size..and have never managed to get a decent shot of Jupiter, now that it's only 20 odd degrees that's going to be alot harder as fighting the atmospheics too..id drop the Barlow and use the roi to get the frame rate up

[beka]

Hi iwols,

To me it seems that the focus is off, unless the seeing is really really bad. I don't think oversampling should be a factor, you will just have redundant pixels. Do you have a better view through an eyepiece?

Best

[michael.h.f.wilkinson]

27 minutes ago, beka said:

Hi iwols,

To me it seems that the focus is off, unless the seeing is really really bad. I don't think oversampling should be a factor, you will just have redundant pixels. Do you have a better view through an eyepiece?

Best

Oversampling by a factor of two means that the sharpest image you can get is clearly blurred (like using the promised 340x magnification in little 70mm department store refractors). It is therefore much harder to hit the optimal point of focus. You also reduce the signal per pixel by a factor of 4, halving your signal-to-noise ratio, which further compounds problems. You can fight this by upping the exposure time (by a factor of four!!), but that means atmospheric blur is much more of a problem. Given the low position of Jupiter in the sky, this is not a good plan.

I tried to get Jupiter with my C8 and the ASI178MM at prime focus, with a R&P focuser, flip-mirror and filter wheel in the optical train, which means I was working around F/11-F/12, or almost optimal sampling. Seeing was so bad I gave up. Adding a Barlow would have made matters WAY worse,

[Grotemobile]

22 minutes ago, michael.h.f.wilkinson said:

Oversampling by a factor of two means that the sharpest image you can get is clearly blurred (like using the promised 340x magnification in little 70mm department store refractors). It is therefore much harder to hit the optimal point of focus. You also reduce the signal per pixel by a factor of 4, halving your signal-to-noise ratio, which further compounds problems. You can fight this by upping the exposure time (by a factor of four!!), but that means atmospheric blur is much more of a problem. Given the low position of Jupiter in the sky, this is not a good plan.

I tried to get Jupiter with my C8 and the ASI178MM at prime focus, with a R&P focuser, flip-mirror and filter wheel in the optical train, which means I was working around F/11-F/12, or almost optimal sampling. Seeing was so bad I gave up. Adding a Barlow would have made matters WAY worse,

Same problem here. Hardly any detail on Jupiter. Saturn was even worse. This was @ prime focus with the C8HD.   

[iwols]

14 hours ago, Davey-T said:

I've got worse in the past, what frame rate were you getting.

Dave

hi dave think it was about 13fps

[iwols]

5 hours ago, beka said:

Hi iwols,

To me it seems that the focus is off, unless the seeing is really really bad. I don't think oversampling should be a factor, you will just have redundant pixels. Do you have a better view through an eyepiece?

Best

slightly but its not brill

[iwols]

so jupiter at the minute is a no no then?

[michael.h.f.wilkinson]

2 minutes ago, iwols said:

so jupiter at the minute is a no no then?

Difficult, but I will keep trying

[iwols]

thanks as long as its not my equipment?

[newbie alert]

6 hours ago, iwols said:

thanks as long as its not my equipment?

More likely conditions, jet stream out of the way..light winds,transparent skies..is it too much to ask!!..but I feel you will get better results without the barlow

I did read here that you was on 13 fps? If you use roi that frame rate will inrease

[beka]

20 hours ago, michael.h.f.wilkinson said:

Oversampling by a factor of two means that the sharpest image you can get is clearly blurred (like using the promised 340x magnification in little 70mm department store refractors). It is therefore much harder to hit the optimal point of focus. You also reduce the signal per pixel by a factor of 4, halving your signal-to-noise ratio, which further compounds problems. You can fight this by upping the exposure time (by a factor of four!!), but that means atmospheric blur is much more of a problem. Given the low position of Jupiter in the sky, this is not a good plan.

I tried to get Jupiter with my C8 and the ASI178MM at prime focus, with a R&P focuser, flip-mirror and filter wheel in the optical train, which means I was working around F/11-F/12, or almost optimal sampling. Seeing was so bad I gave up. Adding a Barlow would have made matters WAY worse,

Hi michael.h.f.wilkinson ,

If I am not mistaken I think you are talking about undersampling. With oversampling you have you have an excess of pixels. For example if your telescope has a 2 arcsec resolution and you end up with 5 pixels per arcsec with your imaging train then you are oversampling but you will not lose detail, though it is not ideal for dim objects. 

Cheers

[Demonperformer]

15 hours ago, iwols said:

so jupiter at the minute is a no no then?

This game is always a case of do the best you can on any specific occasion ... or quit! Conditions are not perfect for planets from northern latitudes atm, but at least the images you take now will mean you are 'learning' when you would not get wonderful images anyway and you will be much better equipped to get good images when they are better placed. Enjoy the journey. 

[michael.h.f.wilkinson]

20 minutes ago, beka said:

Hi michael.h.f.wilkinson ,

If I am not mistaken I think you are talking about undersampling. With oversampling you have you have an excess of pixels. For example if your telescope has a 2 arcsec resolution and you end up with 5 pixels per arcsec with your imaging train then you are oversampling but you will not lose detail, though it is not ideal for dim objects. 

Cheers

Oversampling is a case of sampling the image at a higher spatial frequency than the Nyquist frequency, which is the minimum sampling frequency required by the Shannon criterion. At F/22.5 using diffraction-limited optics, the Nyquist frequency is about one sample per 5 micron. Sampling at 2.4 micron per pixel is therefore oversampling. The PSF of the optics will be clearly resolved, therefore, and the image will appear blurry because of that. This makes achieving optimal focus difficult. You can reconstruct the complete signal, but S/N will be down, unless you increase exposure time

[iwols]

so are we saying the 178 is not suitable with the c8 edge thanks

[beka]

4 hours ago, iwols said:

so are we saying the 178 is not suitable with the c8 edge thanks

I think you should be able to use it but the barlow may not be necessary.

[beka]

6 hours ago, michael.h.f.wilkinson said:

Oversampling is a case of sampling the image at a higher spatial frequency than the Nyquist frequency, which is the minimum sampling frequency required by the Shannon criterion. At F/22.5 using diffraction-limited optics, the Nyquist frequency is about one sample per 5 micron. Sampling at 2.4 micron per pixel is therefore oversampling. The PSF of the optics will be clearly resolved, therefore, and the image will appear blurry because of that. This makes achieving optimal focus difficult. You can reconstruct the complete signal, but S/N will be down, unless you increase exposure time

I kind of get the oversampling, I agree that the 178 with the c8 will oversample probably even without the barlow. But say that iwols had perfect seeing and focus, regardless of the oversampling shouldn't he get the details on Jupiter the scope is capable of?

[Cornelius Varley]

4 hours ago, iwols said:

so are we saying the 178 is not suitable with the c8 edge thanks

It should be suitable. Older cameras (webcams etc) with 5.6micron pixels worked best at around f20. With cameras with smaller pixels the focal ratio required can be achieved without  barlow.

Image scale

"Matching Large Optics

The effects of seeing, the random star motion caused by atmospheric turbulence, increases the practical spot size for larger instruments. In this case, the seeing disk in arc-seconds and the focal length are the important parameters. You can calculate the size of a pixel in arc-seconds using the following formula:

pixel size (arc seconds) = 206 * pixel size (microns) / focal length (mm)

(The result can be quickly estimated by rounding off the constant in the equation to 200. For example, suppose a camera that has a pixel size of 9 microns is attached to a telescope with a focal length of 2000 mm. The pixel size is 9 * 200 / 2000 = 0.9 arc seconds.)

Seeing can vary quite dramatically from night to night, and even during a single night. At a typical low-altitude observing site, the seeing disk typically varies from 2.5 arc-seconds to 4 arc-seconds. You may see the occasional night that is even better, or much worse! A premium site may have seeing as good as 1 arc-second and sometimes even better.

Under reasonably good conditions (2.0 to 2.5 arc-seconds), you need a resolution of 0.6 to 0.8 arc-seconds to adequately sample the images.

At a prime location with excellent seeing, you may need a resolution of 0.5 arc-seconds or better. Higher resolution is also helpful if you plan to use deconvolution to sharpen your images. Imaging at this level requires excellent optical quality and a very stable mounting or a high-speed tip/tilt "AO" guider.

You should also consider how much sky area you wish to cover. If you have a small sensor, you may wish to reduce resolution to as much as 2 arc-seconds per pixel. Acceptable imaging is possible at 4 arc-seconds per pixel, but you will be sacrificing resolution. Beyond this point, your stars begin looking like little squares.

 

Planetary Imaging

The short exposures used during planetary imaging can ”freeze” the seeing and allow full-resolution imaging even with very large instruments (assuming good optics). For planetary imaging with short exposures, start with an image scale of 0.25 arc seconds per pixel; use trial-and-error to determine the best image scale for your equipment, conditions, and the planet being imaged."

[michael.h.f.wilkinson]

1 hour ago, beka said:

I kind of get the oversampling, I agree that the 178 with the c8 will oversample probably even without the barlow. But say that iwols had perfect seeing and focus, regardless of the oversampling shouldn't he get the details on Jupiter the scope is capable of?

The ASI178MM works fine at prime focus of a C8, as shown below. As I explained before: you can reconstruct the signal perfectly from an oversampled image, in the absence of seeing issues, and when perfect focus is achieved. However, oversampling aggravates seeing issues, and makes achieving perfect focus much harder

 

[iwols]

just a quick go at the moon tonight during daylight

[iwols]

slightly better?