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Jupiter - 30 October 2022


geoflewis

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34 minutes ago, johnturley said:

However, some people suggested that I should be aiming for just 3x the pixel size of the ASI 462

It really helps if one understands underlying physics (at least on the basic level of actual formula used) and looks at the context.

When discussing regular OSC planetary imaging, then I would say that using x3 pixel size is wrong advice - but it does not have to be, depending on what is being recommended.

I'll explain.

Actual formula goes like this:

F/ratio = pixel_size * 2 / wavelength_of_light

Where Wavelength of light and pixel size are in same units of length (micrometers for example).

Using 400nm as shortest wavelength to be recorded - above turns into

F/ratio = pixel_size * 2 / 0.4 = pixel_size * 5

So for general RGB / OSC planetary imaging correct F/ratio = 5 * pixel_size

How can then x3 be right? Well, it depends on context. Maybe advice was given in context of lunar imaging with use of Ha narrowband filter? NB filters (and Ha in particular) are often used by Lunar imagers to tame the seeing. Then using the same formula - we can get different result:

F/ratio = pixel_size * 2 / 0.656

This time we use 0.656um as wavelength because we use Ha filter that is centered at ~656nm.

This reduces to

F/ratio = pixel_size * 3.04878.... = pixel_size * 3

In context of mono + Ha for lunar - yes, F/ratio = pixel_size * 3 is good formula and good recommendation.

I'll give you even weirder one.

If you use ASI462 - and want to do IR imaging at 850nm, then following is correct:

F/ratio = pixel_size * 2 / 0.85 = pixel_size * 2.35

How about that? With 2.9um pixels you actually need only F/6.8 if you want to shoot IR at 850nm and above.

If you said someone that they need not go over F/7 for planetary imaging (example Jupiter at with IR pass filter) - they would say that you are nuts :D

 

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40 minutes ago, vlaiv said:

 

If you use ASI462 - and want to do IR imaging at 850nm, then following is correct:

F/ratio = pixel_size * 2 / 0.85 = pixel_size * 2.35

How about that? With 2.9um pixels you actually need only F/6.8 if you want to shoot IR at 850nm and above.

If you said someone that they need not go over F/7 for planetary imaging (example Jupiter at with IR pass filter) - they would say that you are nuts :D

 

Yes I do reduce my FL when using my 850nm IR filter and 889nm CH4 filter, though not by as much as that. I normally just take the spacer out of the Barlow. Oversampling doesn't bother me really but the 12" aperture isn't really enough to produce a bright enough image for using the CH4 at the same FL as with the other filters.

Id seen a talk by Cristopher Go when he was using the CH4 filter with his 290 mono and he would bin 2x2. but once he got the 462C he stated that it was so much more sensitive in IR that he doesn't need to Bin with it, for ease of use he doesn't adjust his FL as that would mean re focussing and be more time consuming. 

So all of his images are taken at F24 with the C14 at 8.5m FL

His CH4 images are still presented at a smaller scale, but I think thats because his 1.5x drizzle stacks his visible light captures but not the IR ones.

Saying that though I may still try taking the Barlow out altogether for the 850 and CH4 next time as ive not been happy with either of them compared to my IR742 which always seems to do a better job, and there isn't as much detail to capture in CH4 anyway

Lee

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4 hours ago, Magnum said:

So all of his images are taken at F24 with the C14 at 8.5m FL

Hi Lee, I'm not sure about Chris using F24, but maybe he is. This is from his website...

All images were taken using a Celestron  C14  mounted on an Astrophysics AP900GTO mount.  A QHY 290M and a QHYIII462C cameras were used is these images.    RGB is done using a set of Chroma Technology RGB filters on a Starlight Xpress Motorized filter wheel.  Methane band images are done using a Chroma Methane Band filter (889nm  18nm bandpass).  UV images are done using a Astrodon UV filter.   Amplification is done using an Astrophysics Advance Convertible Barlow working at 2.0X.

So his amplification is 2.0x and the nominal FR of the C14 Edge (FL3910mm)  is F11, so I think more like F22, than F24 (depending on where he positioned the main mirror in his initial focusing), unless you have another source of info from him. It's still a lot more than the ~F12 that I've been using.....🤔

I now have the Baader x2.25 barlow with the removable x1.3 lens, to add to my image amplification toolkit, so lots of options to play around with.

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15 minutes ago, geoflewis said:

Hi Lee, I'm not sure about Chris using F24, but maybe he is. This is from his website...

All images were taken using a Celestron  C14  mounted on an Astrophysics AP900GTO mount.  A QHY 290M and a QHYIII462C cameras were used is these images.    RGB is done using a set of Chroma Technology RGB filters on a Starlight Xpress Motorized filter wheel.  Methane band images are done using a Chroma Methane Band filter (889nm  18nm bandpass).  UV images are done using a Astrodon UV filter.   Amplification is done using an Astrophysics Advance Convertible Barlow working at 2.0X.

So his amplification is 2.0x and the nominal FR of the C14 Edge (FL3910mm)  is F11, so I think more like F22, than F24 (depending on where he positioned the main mirror in his initial focusing), unless you have another source of info from him. It's still a lot more than the ~F12 that I've been using.....🤔

I now have the Baader x2.25 barlow with the removable x1.3 lens, to add to my image amplification toolkit, so lots of options to play around with.

Chris told my personally that hes working at f24, this was a few weeks ago.

Barlows never give the exact multiplication factor they claim and the adc spacing to the barlow will add a bit more, im sure hes measured jupiters disc in pixels to get a true value before telling me. as I do that with mine each time i change anything.

i hope you like the baader barlow, at least it wasnt too expensive, i bought it after seeing an amazing saturn taken with one, 

Lee

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1 minute ago, Magnum said:

Chris told my personally that hes working at f24, this was a few weeks ago.

Barlows never give the exact multiplication factor they claim and the adc spacing to the barlow will add a bit more, im sure hes measured jupiters disc in pixels to get a true value before telling me. as I do that with mine each time i change anything.

Lee

Thanks Lee, can't argue with that 👍

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1 hour ago, geoflewis said:

How do you do that please, I've never done it?

Quite simple procedure.

Take your Jupiter image as recorded (no drizzle, no binning, no rescaling) - but it can be stacked and sharpened (and it really should be for measurement precision).

Measure diameter of Jupiter disk on equator (there is actually quite bit of difference as I recently found out between measuring at equator and at an angle) and check current or rather at the date of recording, apparent angular diameter of Jupiter.

Divide the two to get pixel scale - and from that and pixel size - derive actual focal length.

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2 minutes ago, vlaiv said:

Quite simple procedure.

Take your Jupiter image as recorded (no drizzle, no binning, no rescaling) - but it can be stacked and sharpened (and it really should be for measurement precision).

Measure diameter of Jupiter disk on equator (there is actually quite bit of difference as I recently found out between measuring at equator and at an angle) and check current or rather at the date of recording, apparent angular diameter of Jupiter.

Divide the two to get pixel scale - and from that and pixel size - derive actual focal length.

Yes and to measure a simple way is to just crop the image in photoshop until it’s just touching the limbs the go to image size to see how many pixels it is.

though first make sure it’s rotated so the equator is level and wack up the mid level slider to expose the limb darkening enough to see the true edge.

alternatively win jupos can do image measurements precisely.

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4 minutes ago, vlaiv said:

Quite simple procedure.

Take your Jupiter image as recorded (no drizzle, no binning, no rescaling) - but it can be stacked and sharpened (and it really should be for measurement precision).

Measure diameter of Jupiter disk on equator (there is actually quite bit of difference as I recently found out between measuring at equator and at an angle) and check current or rather at the date of recording, apparent angular diameter of Jupiter.

Divide the two to get pixel scale - and from that and pixel size - derive actual focal length.

Thanks Vlaiv, so I'm getting more and more confused and/oruncertain about my sampling with the C14 and ASI462MC camera. I've loaded a recent image into WinJupos which reads the image as 339.8 px and 0.1407"/px (see below image)

image.png.707ea333b9de8ec565d6b57fbdc68c99.png

Dawes' and Rayleigh limit calculators (see below) give the max resolution of my scope (C14 dia = 356mm) at between 0.33" to 0.39", so allowing for min 2px ideal sampling will be half of those so somewhere in the 0.16" to 0.20" range.

image.thumb.png.26bf1477b8b267f46a92c87337a26f69.png

If WinJupos is correct and I'm already sampling at 0.1407"/ px, then aren't I already oversampled?

FWIW I checked one of my images from last year with the ASI290MM + x2 TV PM and WinJupos gave me 0.9" / px.....!!

I'm really confused now, so please can anyone let me know what I am doing wrong with my maths?

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16 minutes ago, geoflewis said:

Thanks Vlaiv, so I'm getting more and more confused and/oruncertain about my sampling with the C14 and ASI462MC camera. I've loaded a recent image into WinJupos which reads the image as 339.8 px and 0.1407"/px (see below image)

image.png.707ea333b9de8ec565d6b57fbdc68c99.png

Dawes' and Rayleigh limit calculators (see below) give the max resolution of my scope (C14 dia = 356mm) at between 0.33" to 0.39", so allowing for min 2px ideal sampling will be half of those so somewhere in the 0.16" to 0.20" range.

image.thumb.png.26bf1477b8b267f46a92c87337a26f69.png

If WinJupos is correct and I'm already sampling at 0.1407"/ px, then aren't I already oversampled?

FWIW I checked one of my images from last year with the ASI290MM + x2 TV PM and WinJupos gave me 0.9" / px.....!!

I'm really confused now, so please can anyone let me know what I am doing wrong with my maths?

My jupiters measure around 500 pixels with my current sampling with the 12” scope, I’ve found that about the ideal. So about 0.1”/pixel, Damian and GO are a bit higher than that around 6-700 pixels or around 0.08-0.09”/pixel but that’s with 14” scope and perfect seeing.

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18 minutes ago, Magnum said:

Yes and to measure a simple way is to just crop the image in photoshop until it’s just touching the limbs the go to image size to see how many pixels it is.

though first make sure it’s rotated so the equator is level and wack up the mid level slider to expose the limb darkening enough to see the true edge.

alternatively win jupos can do image measurements precisely.

Thanks, I just did that and got 345 px, so very similar to the 349 that WinJupos gave me. I did the maths myself based on Jupiter's diameter at 49.2" on that night which confirms the ~0.14"/px (49.2/349). So am I actully then already oversampled without any further amplification....?🤷‍♂️

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6 minutes ago, Magnum said:

My jupiters measure around 500 pixels with my current sampling with the 12” scope, I’ve found that about the ideal. So about 1”/pixel Damian and GO are a bit higher than that around 6-700 pixels or around 0.8-0.9”/pixel but that’s with 14” scope and perfect seeing.

Do you mean 0.08" to 0.09" per px. Jupiter at say 49" / 500px = 0.1" / px not 1" / px - or what am I doing wrong please?

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1 minute ago, geoflewis said:

Do you mean 0.08" to 0.09" per px. Jupiter at say 49" / 500px = 0.1" / px not 1" / px - or what am I doing wrong please?

Yes sorry I typed it wrong I will go back and correct it to avoid confusion in the thread

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42 minutes ago, geoflewis said:

Thanks, I just did that and got 345 px, so very similar to the 349 that WinJupos gave me. I did the maths myself based on Jupiter's diameter at 49.2" on that night which confirms the ~0.14"/px (49.2/349). So am I actully then already oversampled without any further amplification....?🤷‍♂️

In Damian’s talks he classes anything below 0.06” pixel as oversampling, 0.08” - 0.10” as ideal sampling , and 0.14” as under-sampling. 
this is for scopes in the 30-40cm aperture range.

im attaching screen shots from his talk.

this is of course under perfect seeing In barbados, but  I still find 0.1 works best for me.

remember those calculators aren’t taking into account unsung lucky imaging with 10s of thousands of split second exposures.

 

CCF5AB24-179D-43B9-8504-CC119215DE05.png

A8A42BBA-8ED3-4348-86D7-D0CFD2B67EFD.png

C0232D86-45CF-49CE-8C9D-2A1798EE571C.png

Edited by Magnum
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41 minutes ago, Magnum said:

Yes sorry I typed it wrong 

Phew....!! So I've checked my images with the ASI290MM from 2020 and see I was very similar to Go & Peach at 0.07"/px and according to FireCapture FL = 8500mm, equivalent to F23.

image.png.b8292489f65966a0e5c22533239505b3.png

That worked really well, so I'm definitely going to try again with the ASI462 at greater amplification.

Edited by geoflewis
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31 minutes ago, Magnum said:

In Damian’s talks he classes anything below 0.07” pixel as oversampling, 0.08” - 0.10” as ideal sampling , and 0.14” as under-sampling. 
this is for scopes in the 30-40cm aperture range.

im attaching screen shots from his talk to demonstrate.

this is of course under perfect seeing In barbados, but  I still find 0.1 works best for me.

remember those calculators aren’t taking into account unsung lucky imaging with 10s of thousands of split second exposures.

 

CCF5AB24-179D-43B9-8504-CC119215DE05.png

A8A42BBA-8ED3-4348-86D7-D0CFD2B67EFD.png

C0232D86-45CF-49CE-8C9D-2A1798EE571C.png

Thanks, that's great to know.....:thumbright:

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3 minutes ago, geoflewis said:

Phew....!! So I've checked my images with the ASI290MM from 2020 and see I was very similar to Go & Peach at 0.07"/px and according to FireCapture FL = 8500mm, equivalent to F23.

image.png.b8292489f65966a0e5c22533239505b3.png

That worked really well, so I'm definitely going to try again with the ASI462 at greater amplification.

From UK 0.07” will be pushing it, but around 0.09 - 0.10” is doable

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9 minutes ago, Magnum said:

From UK 0.07” will be pushing it, but around 0.09 - 0.10” is doable

Thanks Lee. This whole discussion the last couple of days has been eye-opening for me. I've just fairly blindly followed the px_size x5 rule of thumb, then watched the on-screen image to see what worked. I felt including the x2 PM with an ADC was too much and I think last year I took the PM out when imaging Jupiter which was still very low down. On Anthony Wesley's (Bird's) advice I'd taken the ADC out for Mars in 2020, but I was happy with my results still including the x2 PM. As I discussed with @neil phillips yesterday, I think I was too hasty to give up on the x2 PM with the 462MC sensor, but with the Baader barlow I have some options to increase amplification without going as far as 0.07" / px. It will be good to experiment some more, as Mars moves towards opposition over the coming weeks.

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11 minutes ago, geoflewis said:

Thanks Lee. This whole discussion the last couple of days has been eye-opening for me. I've just fairly blindly followed the px_size x5 rule of thumb, then watched the on-screen image to see what worked. I felt including the x2 PM with an ADC was too much and I think last year I took the PM out when imaging Jupiter which was still very low down. On Anthony Wesley's (Bird's) advice I'd taken the ADC out for Mars in 2020, but I was happy with my results still including the x2 PM. As I discussed with @neil phillips yesterday, I think I was too hasty to give up on the x2 PM with the 462MC sensor, but with the Baader barlow I have some options to increase amplification without going as far as 0.07" / px. It will be good to experiment some more, as Mars moves towards opposition over the coming weeks.

Yes I think if you weren’t using an ADC then you could use the 2x powermate, but the adc will push it a bit too far so the Baader barlow will get you something in between. 
rember though that with barlows extending the spacing increases the magnification, but with power mates it’s the opposite, extending the spacing decreases the magnification. So you could theoretically back of the mag with your power mate by using a bit more spacing.

do you have the ADC before the barlow or between the barlow and the camera? As that makes a big difference too.

Lee

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1 hour ago, geoflewis said:

so I'm getting more and more confused and/oruncertain about my sampling with the C14 and ASI462MC camera. I've loaded a recent image into WinJupos which reads the image as 339.8 px and 0.1407"/px (see below image)

339.8px and 0.1407"/px seems about right. That gives diameter of Jupiter to be 339.8 * 0.1407 = 47.80986" which seems right.

Stellarium is giving apparent diameter at the moment to be 47.27" and this image was probably taken some time ago.

1 hour ago, geoflewis said:

Dawes' and Rayleigh limit calculators (see below) give the max resolution of my scope (C14 dia = 356mm) at between 0.33" to 0.39", so allowing for min 2px ideal sampling will be half of those so somewhere in the 0.16" to 0.20" range.

These two criteria have nothing to do with sampling rate. They give rule of the thumb for visual separation of two equally bright stars.

Sampling rate is determined by maximum frequency of the image in frequency domain by applying Nyquist sampling theorem. There is cutoff frequency due to nature of light (waves and interference). This is "hard" cutoff frequency - meaning it is indeed maximum frequency that the optics of given aperture can produce. There are no higher frequencies.

This limit is given by simple expression:

https://en.wikipedia.org/wiki/Spatial_cutoff_frequency

but actual math behind deriving that expression is a bit more complex (involves Fourier transform of aperture to get Airy disk function and then another Fourier transform of Airy disk function to derive low pass filter resulting from Airy pattern).

Formula that I presented above directly derived from above formula on wiki page:

image.png.3ae60e3187c62312d96bd1427f8f4b85.png

and application of Nyquist sampling theorem (which states that you need to sample at twice max frequency - or that pixel needs to be half of shortest wavelength associated with max frequency).

By the way - when we speak of frequency and wavelength in this context - it is not frequency and wavelength of light / photons - but rather Fourier transform of image represented by 2d function (so FT of that function).

1 hour ago, geoflewis said:

If WinJupos is correct and I'm already sampling at 0.1407"/ px, then aren't I already oversampled?

There is really simple way to check that.

0.1407"/px implies that your setup is at effective:

0.1407 = 2.9 * 206.3 / focal_length => focal_length = 2.9 * 206.3 / 0.1407 = ~4252mm

C14 has 356mm of aperture so effective F/ratio is F/11.96

For 400nm wavelength you want to sample at x5 pixel size, so F/ratio should be 2.9 * 5 = F/14.5

If you go by that criteria, then you are slightly under sampled, but I don't think that you are, as I often say that it is better to use 500nm as baseline and instead use x4 pixel size (from above mentioned formula F/ratio = pixel_size * 2 / 0.5um = pixel_size *4), because of seeing effect on shortest wavelengths and fact that most sharpness (perceived) comes from green part of spectrum - which is 500-550nm.

Going by that criteria 2.9 * 4 = F/11.6 - so you are spot on.

 

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1 hour ago, Magnum said:

this is of course under perfect seeing In barbados, but  I still find 0.1 works best for me.

Seeing should not play a part here.

Optimum sampling for lucky imaging is based solely on aperture size. We ignore seeing influence because we hope to get lucky few subs that are almost unaffected by it.

In fact, seeing effects don't disturb cut off point. They just lower MTF curve and produce result that needs to be sharpened more - but cutoff point remains the same and is only product of aperture size.

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28 minutes ago, Magnum said:

Yes I think if you weren’t using an ADC then you could use the 2x powermate, but the adc will push it a bit too far so the Baader barlow will get you something in between. 
rember though that with barlows extending the spacing increases the magnification, but with power mates it’s the opposite, extending the spacing decreases the magnification. So you could theoretically back of the mag with your power mate by using a bit more spacing.

do you have the ADC before the barlow or between the barlow and the camera? As that makes a big difference too.

Lee

Thanks Lee, yes, I'm aware that the change in magnification for TV PMs is different than how it works for barlows. As the below chart of the TV website, shows there is definitely a reduction with the x2.5 PM the further it is from the sensor, but for the x2 PM the change is very marginal.

image.png.76312520e0af59525ddb391677c1ae14.png

It's one of the main reasons I moved from using the TV Barlows to the x2 PM. I have the ADC between the PM and camera as the ADC is 1.25" diameter, whereas the PM is 2" diameter. I'm also using a FW, so that increases the distance to sensor a bit too.

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28 minutes ago, vlaiv said:

339.8px and 0.1407"/px seems about right. That gives diameter of Jupiter to be 339.8 * 0.1407 = 47.80986" which seems right.

Stellarium is giving apparent diameter at the moment to be 47.27" and this image was probably taken some time ago.

These two criteria have nothing to do with sampling rate. They give rule of the thumb for visual separation of two equally bright stars.

Sampling rate is determined by maximum frequency of the image in frequency domain by applying Nyquist sampling theorem. There is cutoff frequency due to nature of light (waves and interference). This is "hard" cutoff frequency - meaning it is indeed maximum frequency that the optics of given aperture can produce. There are no higher frequencies.

This limit is given by simple expression:

https://en.wikipedia.org/wiki/Spatial_cutoff_frequency

but actual math behind deriving that expression is a bit more complex (involves Fourier transform of aperture to get Airy disk function and then another Fourier transform of Airy disk function to derive low pass filter resulting from Airy pattern).

Formula that I presented above directly derived from above formula on wiki page:

image.png.3ae60e3187c62312d96bd1427f8f4b85.png

and application of Nyquist sampling theorem (which states that you need to sample at twice max frequency - or that pixel needs to be half of shortest wavelength associated with max frequency).

By the way - when we speak of frequency and wavelength in this context - it is not frequency and wavelength of light / photons - but rather Fourier transform of image represented by 2d function (so FT of that function).

There is really simple way to check that.

0.1407"/px implies that your setup is at effective:

0.1407 = 2.9 * 206.3 / focal_length => focal_length = 2.9 * 206.3 / 0.1407 = ~4252mm

C14 has 356mm of aperture so effective F/ratio is F/11.96

For 400nm wavelength you want to sample at x5 pixel size, so F/ratio should be 2.9 * 5 = F/14.5

If you go by that criteria, then you are slightly under sampled, but I don't think that you are, as I often say that it is better to use 500nm as baseline and instead use x4 pixel size (from above mentioned formula F/ratio = pixel_size * 2 / 0.5um = pixel_size *4), because of seeing effect on shortest wavelengths and fact that most sharpness (perceived) comes from green part of spectrum - which is 500-550nm.

Going by that criteria 2.9 * 4 = F/11.6 - so you are spot on.

 

Thanks Vlaiv, this is helpful, even if I don't fully understand all of it. Regarding my Jupiter image, WinJupos measured it at 349.8px, not the 339.8px that you used in your calculation and yes, it was when Jupiter was displaying a disc diameter of 49.2".

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11 hours ago, geoflewis said:

Thanks Lee, yes, I'm aware that the change in magnification for TV PMs is different than how it works for barlows. As the below chart of the TV website, shows there is definitely a reduction with the x2.5 PM the further it is from the sensor, but for the x2 PM the change is very marginal.

image.png.76312520e0af59525ddb391677c1ae14.png

It's one of the main reasons I moved from using the TV Barlows to the x2 PM. I have the ADC between the PM and camera as the ADC is 1.25" diameter, whereas the PM is 2" diameter. I'm also using a FW, so that increases the distance to sensor a bit too.

Oh that's a good chart, yes the 2x does seem to have a negligible change doesn't it.

OK, so I would go straight for trying the new Baader at 1.3x, but I would put the ADC and or  filter wheel in front of the Baader 1.3x . if you keep the ADC in the middle like you have it now the spacing will be too much for the Baader and make it act at something like 2.5x.

Though they do say that ADCs work better at higher FL, there is a point where the optical aberrations introduced by the ADC become more important than the gain from removing the dispersion, but as your scope is already f11 I would think its already above the point and shouldn't be an issue. 

You will need to have a play around with the order while previewing Jupiter to get the image size you want, a quick and rough way to check is to adjust your ROI box in the capture program if the planet just fits in the ROI then you know thats how big it is. You can set any custom sized ROI in sharpcap. I like Jupiter to be around 480 pixels at the moment now that its apparent size has shrunk a bit.

Remember all the maths is fine and important, but doesn't hurt to test it with experiment 🙂 and I like to experiment by finding the best images in the world then replicating what they are doing. Mr Peach has been the best planetary imager in the world for almost 20 years he's working at 0.08"-0.1" so I find it very hard to argue with that.

Saying that I think Marco Lorenzi has now surpassed Damian with his last few images since he upgraded to using a 21" dob on his balcony in Singapore, he's also working at 0.8"/pixel https://www.glitteringlights.com/Images/SolarSystem/Solarsystem/i-gJzz7J8/A

 

Lee

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