What's the consensus on planetary cameras these days?

[The Lazy Astronomer]

Looking at adding a new planetary camera to my repertoire to allow my 290mm to be dedicated to guiding duties for my DSO imaging.

I'm looking for a OSC, and I'm aware there's been a whole host of new planetary cameras recently released, so, what's the general consensus on the top ones these days? 

[happy-kat]

Have you seen the thread on the 585 it looks interesting from a flexible angle

https://stargazerslounge.com/topic/397896-zwoplayer-one-imx-585-sensor-image-showcase

Edited December 2, 2022 by happy-kat

[vlaiv]

Consensus is that they are good at what they do

 

[Mandy D]

7 minutes ago, vlaiv said:

Consensus is that they are good at what they do

 

Great answer! Made me smile.

[The Lazy Astronomer]

It seems like we're in a HGTTG situation here - perhaps I need to start a thread on the right question to ask first 😁

I'll try again: what are people's thoughts on which is the best planetary cam to buy these days? I think the 462mc was generally regarded as a good option previously, but are there any new thoughts on that given the new cameras that have been released in the past few months? 

Find a way out of that, @vlaiv 🤣

[ONIKKINEN]

If we follow the ideal sampling formula for broadband captures of: f_ratio= pixelsize in microns x 4 (for 500nm light). Most or all of the modern sensors will do the trick excellently or just plain well. Some will do the trick without a barlow.

What f/ratio of scope do you have? All of the new ones are top tier if matched with a suitable scope, and almost all of them can be matched.

Only outlier is the 678MC with its tiny 2micron pixels, which means an ideal scope is f/8-f/10 (preferably closer to f/8).

[vlaiv]

8 hours ago, The Lazy Astronomer said:

It seems like we're in a HGTTG situation here - perhaps I need to start a thread on the right question to ask first 😁

I'll try again: what are people's thoughts on which is the best planetary cam to buy these days? I think the 462mc was generally regarded as a good option previously, but are there any new thoughts on that given the new cameras that have been released in the past few months? 

Find a way out of that, @vlaiv 🤣

No, seriously, they are all good in most important aspects for planetary. Here, have a look (I'll use ASI examples as they are easy to find, but other brands should have same/similar specs):

Read noise:

224 - 0.8e

585 - 0.8e

678 - 0.6e

662 - 0.8e

Peak QE:

224: 75-80%

585: 91%

678: 83%

662: 91%

All provide very fast readout times.

It is just the matter of selecting pixel size (although - you will use barlow to get wanted F/ratio anyway, so maybe only advantage is if you can have setup without a barlow, but good barlow will be virtually invisible in optical path as far as quality goes), and selecting sensor size that will suit you - larger for lunar and solar, otherwise, size does not matter much for pure planetary (but might for other uses like EEA and such).

 

[PeterC65]

8 hours ago, ONIKKINEN said:

If we follow the ideal sampling formula for broadband captures of: f_ratio= pixelsize in microns x 4 (for 500nm light) ...

I'm struggling to square this formula with the one used by the Astronomy Tools website, Resolution (ArcSeconds per Pixel) = Pixel Size / Telescope Focal Length x 206.265, where we should be aiming for a figure of 0.67-2"/pixel for average seeing conditions.

My main camera scope is a 72mm / 432mm refractor which with my IMX585 camera (2.9um pixel size) gives 1.38"/pixel, so ideal sampling for average seeing. But it is F6 so the formula given by @ONIKKINEN suggests it is far from ideal and I should instead be using my Mak!

Working this backwards, I would need the refractor to have an aperture of only 37mm to satisfy both formulae, so should I be stopping it down?

Neither the Mak nor stopping down the refractor makes any sense.

 

[ONIKKINEN]

1 hour ago, PeterC65 said:

I'm struggling to square this formula with the one used by the Astronomy Tools website, Resolution (ArcSeconds per Pixel) = Pixel Size / Telescope Focal Length x 206.265, where we should be aiming for a figure of 0.67-2"/pixel for average seeing conditions.

My main camera scope is a 72mm / 432mm refractor which with my IMX585 camera (2.9um pixel size) gives 1.38"/pixel, so ideal sampling for average seeing. But it is F6 so the formula given by @ONIKKINEN suggests it is far from ideal and I should instead be using my Mak!

Working this backwards, I would need the refractor to have an aperture of only 37mm to satisfy both formulae, so should I be stopping it down?

Neither the Mak nor stopping down the refractor makes any sense.

 

That tool is hardly usable, best not to give it much thought. If you must use the tool, aim for the lowest resolution it suggests as the higher estimates are pure fantasy and not really possible to achieve for most imagers.

But the critical sampling thing i mentioned is only applicable in lucky imaging applications, so planetary, lunar, solar where we use exposures fast enough to freeze the seeing and hope that some of the frames are sharp.

And maybe dont stop down the scope, while its true you could manipulate your f/ratio like that, its going the wrong way with it. Use of a barlow is what will get you to the ideal ratio. With your mak you will not need a barlow with that camera by the way, when doing lucky imaging that is (or with DSO definitely).

[johnturley]

3 hours ago, PeterC65 said:

I'm struggling to square this formula with the one used by the Astronomy Tools website, Resolution (ArcSeconds per Pixel) = Pixel Size / Telescope Focal Length x 206.265, where we should be aiming for a figure of 0.67-2"/pixel for average seeing conditions.

My main camera scope is a 72mm / 432mm refractor which with my IMX585 camera (2.9um pixel size) gives 1.38"/pixel, so ideal sampling for average seeing. But it is F6 so the formula given by @ONIKKINEN suggests it is far from ideal and I should instead be using my Mak!

Working this backwards, I would need the refractor to have an aperture of only 37mm to satisfy both formulae, so should I be stopping it down?

Neither the Mak nor stopping down the refractor makes any sense.

 

The formula given in Astronomy Tools is absolute rubbish, at least as far as Planetary Imaging is concerned, it suggests that with my Esprit 150 and ZWO ASI 462 under O.K. Seeing Conditions, I should be using a Focal Reducer rather than a Barlow.

geoflewis I gather regularly successfully uses f22 (2x Barlow), or even f26 with his C14 and ASI 462.

John 

Edited December 3, 2022 by johnturley

[PeterC65]

@ONIKKINEN, @johnturley, I've seen the formula I mentioned used widely, not just on the Astronomy Tools website (which is often recommended on here by the way). The formula is based on Nyquist and the explanation of its use makes complete sense when looking at stars.

Where does the F number formula come from? Any formula that considers sampling must be based on the size of the projected object compared with the sensor pixel size and the scope aperture (and therefore its F number) cannot be involved in such a calculation since the scope aperture has no effect on object size.

Is it the case that the F number formula is measuring some other (independent) factor that is worthy of consideration under certain circumstances (such as when imaging planets)?

@vlaiv, can you offer an opinion (since you seem to understand the maths better than most)?

 

[vlaiv]

45 minutes ago, PeterC65 said:

@vlaiv, can you offer an opinion (since you seem to understand the maths better than most)?

Sure.

These two attempt to tackle two very different things.

Astronomy.tools formula attempts (but fails) to address sampling rate of long exposure astro photography.

One that @ONIKKINEN gave is related to critical sampling of planetary imaging.

Two differ by how they threat atmospheric and mount influence. With planetary imaging all we are concerned is to capture all the detail that aperture can provide. We don't care about mount tracking / guiding performance nor do we care about atmospheric seeing effects. These are dealt with in different way (by using very short exposures to "freeze" the seeing instead of letting atmosphere create additional level of blur due to its motion - kind of motion blur on top of distortion, as well as selecting the least affected frames - often only few best percent out of tens of thousands of frames and also by means of stacking - that differs from long exposure stacking in how it is performed).

With planetary - it is size of aperture that dictates level of detail, and since arc seconds per pixel depends on pixel size and focal length - it turns out that for certain pixel size there is optimum F/ratio (combination of aperture size and focal length) that will let you capture all the detail.

This is based on Nyquist criteria and also on cut off frequency due to limited aperture size.

Exact formula for that is:

F_ratio = pixel size * 2 / wavelength_of_light

(where pixel size and wavelength of light are in same units of length - either micrometers or nanometers, and 2 is from Nyquist).

If you put in 500nm as being relevant wavelength for visual (400-700nm) - you get F/ratio = pixel_size * 2 / 0.5um = pixel_size * 4

There ya go - as far as planetary is concerned.

Back to long exposure imaging. I'll briefly go over what is involved, and why Astronomy.tools calculation is wrong.

In long exposure imaging there are several factors that contribute to total FWHM of the stars in the image - that is seeing FWHM, guiding RMS (mount performance) and Airy disk diameter (or telescope spot diagram RMS if telescope is not diffraction limited - surprisingly enough most astrographs are not as they trade field flatness and corrected imaging circle over central field sharpness).

Sampling rate is related to FWHM by factor of 1.6 - so sampling rate should be FWHM/1.6

If you are able to achieve 3.2" FWHM stars in your subs - correct sampling rate is 2"/px

You can measure your subs for average FWHM to see if you are sampling properly, or you can try to estimate it (but that is more involved) from seeing FWHM, guiding RMS and airy disk size (or spot diagram RMS).

First you need to "convert" all to same thing and there is relationship of FWHM and RMS that goes like FWHM = 2.355 * RMS

(everything should be in arc seconds)

so your final FWHM = sqrt( seeing_FWHM^2 + guiding_FWHM^2 + airy_disk_or_spot_diagram_FWHM^2)

 This shows how all contribute in non trivial way.

Factor of x1.6 is also related to Nyquist - but FWHM does not directly relate to frequency so it must be calculated from Fourier transform of gaussian approximation .... (complex stuff).

[PeterC65]

Thanks @vlaiv, that makes more sense.

So the two formulae apply to different situations, the F number formula for very short exposures and the FL formula for longer exposures.

I take your point that the required resolution (arcseconds per pixel) depends on more than just the seeing conditions, also on the mount guiding and the performance of the scope, but it sounds like the formula used by Astronomy Tools is correct and useful when considering longer exposures, just that taking account of only seeing conditions is not the whole story.

My takeaway from this is that when imaging planets I should be using the Mak, or the refractor with a Barlow. From trial and error, I actually use the refractor with a x2.25 Barlow giving me F13.5, close to what the F number formula is saying (2.9um x 4 = F11.6).

 

[nfotis]

11 hours ago, PeterC65 said:

Thanks @vlaiv, that makes more sense.

So the two formulae apply to different situations, the F number formula for very short exposures and the FL formula for longer exposures.

I take your point that the required resolution (arcseconds per pixel) depends on more than just the seeing conditions, also on the mount guiding and the performance of the scope, but it sounds like the formula used by Astronomy Tools is correct and useful when considering longer exposures, just that taking account of only seeing conditions is not the whole story.

My takeaway from this is that when imaging planets I should be using the Mak, or the refractor with a Barlow. From trial and error, I actually use the refractor with a x2.25 Barlow giving me F13.5, close to what the F number formula is saying (2.9um x 4 = F11.6).

 

 

In short, planetary imaging (or "lucky imaging") is quite different from DSO imaging.

A rule of thumb for planetary imaging says you want f-ratio 4x to 5x the pixel pitch. So, with a 3nm pixel, you want f/12 to f/15 or so, with a 4nm pixel you want f/16 to f/20.

Hope this helps,

N.F.

[nfotis]

On 03/12/2022 at 02:01, The Lazy Astronomer said:

It seems like we're in a HGTTG situation here - perhaps I need to start a thread on the right question to ask first 😁

I'll try again: what are people's thoughts on which is the best planetary cam to buy these days? I think the 462mc was generally regarded as a good option previously, but are there any new thoughts on that given the new cameras that have been released in the past few months? 

Find a way out of that, @vlaiv 🤣

 

If you want to shoot Moon mosaics, you may want a larger sensor like the 662 or the 585.

The 462mc is still fine if you want to go after Jupiter and Saturn etc, but I have seen amazing results with the 533 too.

What scope and Barlow combination do you have in mind for this task?

Cheers,

N.F.

[johnturley]

9 hours ago, nfotis said:

 

In short, planetary imaging (or "lucky imaging") is quite different from DSO imaging.

A rule of thumb for planetary imaging says you want f-ratio 4x to 5x the pixel pitch. So, with a 3nm pixel, you want f/12 to f/15 or so, with a 4nm pixel you want f/16 to f/20.

Hope this helps,

N.F.

It also depends on the effective focal length of your system, to get decent sized planetary images ideally you need to aim for an effective focal length of not less than around 3-4,000 mm (achieved with a Barlow if necessary), which is one reason quite a few planetary imagers favoured Celestron C14's as they give this sort of focal length without the need for further amplification with a Barlow.  Having said that as mentioned previously, I understand geoflewis still likes to use a 2x Barlow with his C14 and ZWO ASI 462 (pixel size 2.9 um) giving an effective focal length of nearly 8,000 mm at f22.

I regularly do planetary imaging with my Esprit 150 (as 90% of the time it gives sharper images than my 14 in Newtonian), using a 2.5 x Powermate, which gives an effective focal length of 2,650 mm @ f17.5. With my ASI 462 camera (pixel size 2.9 um), the formula also suggests that I would get better results with the cheaper ASI 224, which has a larger pixel size of 3.75 um, not sure whether this would be the case.

John 

Edited December 4, 2022 by johnturley

[geoflewis]

1 hour ago, johnturley said:

It also depends on the effective focal length of your system, to get decent sized planetary images ideally you need to aim for an effective focal length of not less than around 3-4,000 mm (achieved with a Barlow if necessary), which is one reason quite a few planetary imagers favoured Celestron C14's as they give this sort of focal length without the need for further amplification with a Barlow.  Having said that I understand geoflewis still likes to use a 2x Barlow with his C14 giving an effective focal length of nearly 8,000 mm at f22.

John 

There’s been a long discussion on optimum FL for planetary imaging on another SGL thread. The maths does indicate that x4-x5 pixel size is the optimal FR (focal ratio), which was my rule of thumb with older cameras with larger pixels, BUT even with the small pixels of modern cameras, many of the worlds leading planetary imagers still operate at longer FL, so at FR much more than x5 px size. For my recent session with Mars on 2 Dec, I started without any barlow, so with just the amplification from using the ADC, taking my C14’s native F11 to F13 (FL=4500mm). However, with the good seeing that night I popped the Baader barlow lens in, giving me F21 (FL=7650mm) and the resulting image on screen was much easier to focus and final image superior. At F21 with camera pixel size =2.9mn (ASI462MC), that’s a FR more than x7….!! Seeing is everything for planetary imaging and there’s no way that I could operate at x7 in poor seeing, so 2 Dec was the first time this year that it’s worked for me, but when the seeing is good I’d say you can push the amplification despite what the maths shows.

Edited December 4, 2022 by geoflewis
Added camera model ASI462MC

[BGazing]

On 02/12/2022 at 14:23, The Lazy Astronomer said:

Looking at adding a new planetary camera to my repertoire to allow my 290mm to be dedicated to guiding duties for my DSO imaging.

I'm looking for a OSC, and I'm aware there's been a whole host of new planetary cameras recently released, so, what's the general consensus on the top ones these days? 

Long story short, they are great. I've only started shooting in August and I am absolutely floored with how easy it is to produce something useful or even nice...and I am a complete novice. They are fast, have low readout noise and, as indicated, it is just a matter of pairing it with your f ratio. I have a 678 with my SCT, so no barlow.

[The Lazy Astronomer]

Thanks for the input everyone! My current planetary scope is a lowly 6" SCT. Hopefully will be able to get something larger for next year, so will take a look at camera options to find something to fit both.

On a related note: is an ADC considered a necessity, or a nice-to-have?

[nfotis]

1 hour ago, The Lazy Astronomer said:

Thanks for the input everyone! My current planetary scope is a lowly 6" SCT. Hopefully will be able to get something larger for next year, so will take a look at camera options to find something to fit both.

On a related note: is an ADC considered a necessity, or a nice-to-have?

 

If your planetary targets are low on the horizon, I would think that's very necessary (especially if you use optical glass elements in your chain - I think that a mirror-only scope like the Classical Cassegrain doesn't suffer from color fringing)

What mount do you have?

If you have an EQ6-R class mount, you can mount up to a C11 for planetary imaging/visual (heck, I even used a C9.25 on my HEQ5). My favourite is the Skymax 180, but that's especially suited for planetary and double stars - it's rather specialized.

Cheers,

N.F.

 

 

[geoflewis]

5 minutes ago, nfotis said:

I think that a mirror-only scope like the Classical Cassegrain doesn't suffer from color fringing)

It makes no difference if lens or mirror as it’s not the optics that cause the colour fringing, it’s the atmosphere, hence the ADC’s name - atmospheric dispersion corrector.

[The Lazy Astronomer]

3 hours ago, nfotis said:

What mount do you have?

I've got the flimsy Nexstar mount the C6 came with, and the eq6r does DSO duties. I'm reluctant to be swapping scopes on the eq6r constantly (plus I'd then have to pick between DSO and planetary on a clear night). I wonder how much weight the little nexstar mount would take... 🤔

[nfotis]

On 05/12/2022 at 21:02, The Lazy Astronomer said:

I've got the flimsy Nexstar mount the C6 came with, and the eq6r does DSO duties. I'm reluctant to be swapping scopes on the eq6r constantly (plus I'd then have to pick between DSO and planetary on a clear night). I wonder how much weight the little nexstar mount would take... 🤔

 

According to Celestron, the mount can handle up to approximately 5.5 kg or 12 lbs:

https://www.celestron.com/products/nexstar-6se-computerized-telescope#specifications

Note that you will have to include a Barlow and the camera at least into the mass budget.

For visual and planetary imaging, you can load the mount almost to the maximum stated limit, since you don't need accurate guiding (heck, I don't even guide on my HEQ5 when doing this). Obviously, the EQ6-R is a much better platform for this, but if you don't want to mess with it, you can try your C6 and a barlow on the Nexstar mount, if there's enough room for a straight connection  - else, you have to use a prism.

N.F.