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Suggestions on getting better at imaging Jupiter

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#26 RedLionNJ

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Posted 27 August 2021 - 11:55 AM

Thanks for the calculation! I do suspect that the flip mirror added to focal length. I would respectfully disagree with @ dcaponeii; the length of the image train does in fact change focal length with SCT. I know this because when I do DSO imaging, plate solving reports different focal length depending on whether I use a short T adapter or a long T adapter. I will tinker the image train to reduce that focal length.

Correct. You're always focusing at infinity, but you're deliberately changing where the focal plane lays relative to the rear cell.

 

The further back from the rear cell you need your focus to be, the further forward (I think) you need to make the primary relative to the overall OTA. And since the secondary is fixed, that separation will be different, so the overall focal length will also be different.


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#27 Borodog

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Posted 27 August 2021 - 01:46 PM

Thanks for the calculation! I do suspect that the flip mirror added to focal length. I would respectfully disagree with @ dcaponeii; the length of the image train does in fact change focal length with SCT. I know this because when I do DSO imaging, plate solving reports different focal length depending on whether I use a short T adapter or a long T adapter. I will tinker the image train to reduce that focal length.

You are correct. SCTs do not have a fixed focal length. Changing the location of the camera sensor means changing the ratios of the internal lengths when you focus by moving the primary mirror, which in turn means changing the entire focal length. In fact my orange tube C90 works the same way; not by moving the primary, but by moving the secondary. I can easily get focal lengths from 800 to 1000 mm (or more) by changing the length of the imaging train on the rear cell.



#28 MarMax

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Posted 27 August 2021 - 06:42 PM

Another consideration with focusing an SCT is the concept of "optimum" focus. I've had no success in generating any discussion on the topic. For my C11 there must be a factory sweet spot or "optimum" focus position for the primary mirror. For lack of any solid confirmation of this I'm assuming it's the mid-point of the available primary mirror travel. This is also where a 2" factory visual back, diagonal and eyepiece comes into focus.

 

SCTs are a very forgiving design and seem to accommodate quite a range of focus. But IMO, if you can, why not design your kit to be at or close the the "optimum" position of the primary mirror. That's what I shoot for anyway.

 

The C11 is 37 focuser turns lock to lock with about 18 turns from either full forward or full rearward to be in the "optimum" position, which also happens to be where the scope is at f/10.


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#29 HarveyDeckAstro

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Posted 28 August 2021 - 07:09 AM

Intuitively it makes sense that the scope works best at its design point. Don’t know if there is any proof :-)

#30 RedLionNJ

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Posted 28 August 2021 - 09:53 AM

Intuitively it makes sense that the scope works best at its design point. Don’t know if there is any proof :-)

Over the years, this has come up on this forum multiple times.  Each of the "popular" SCTs from Celestron & Meade have their own optimum backfocus distance for their optics.  I can't point to some of the threads right now, but several people have documented these on CN over the years.


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#31 dcaponeii

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Posted 28 August 2021 - 10:02 AM

I agree that the focal length does change but I don't think it's the major factor going on with the insertion of a flip mirror.  10% (ish) changes are not a factor in planetary imaging as they might be in serious DSO astrophotography.  As long as your sitting in that 5x - 7x pixel size f/number you going to have to examine other factors.  Seeing and collmation come roaring to the top of the heap in my opinion.


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#32 rehling

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Posted 28 August 2021 - 01:29 PM

This is fundamentally echoing what others have said, but the incredible (and uncontrollable) importance of seeing might mean that someone can, as I did, be discouraged by instances of negative progress. After I took a comparatively good image of Jupiter once, and then had poorer ones after that, I felt frustrated and blamed myself. It was later that I realized that the reverse progress was not really my fault.

 

However, more than just seeing was involved. There were also cases where I didn't allow my telescope to reach thermal equilibrium. Moreover, I shoot from a rooftop, and the use of any laundry appliances in my building, or people walking around, can really mess things up. Finally, the year-by-year worsening of Jupiter's declination from my US location made it hard each year to match the results from the year before. That is at an end for now.


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#33 CrazyPanda

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Posted 28 August 2021 - 01:34 PM

This is fundamentally echoing what others have said, but the incredible (and uncontrollable) importance of seeing might mean that someone can, as I did, be discouraged by instances of negative progress. After I took a comparatively good image of Jupiter once, and then had poorer ones after that, I felt frustrated and blamed myself. It was later that I realized that the reverse progress was not really my fault.

 

However, more than just seeing was involved. There were also cases where I didn't allow my telescope to reach thermal equilibrium. Moreover, I shoot from a rooftop, and the use of any laundry appliances in my building, or people walking around, can really mess things up. Finally, the year-by-year worsening of Jupiter's declination from my US location made it hard each year to match the results from the year before. That is at an end for now.

This echos my experience as well. Had relatively good luck starting out, and made rapid progress, then "regressed" because of seeing conditions and because Jupiter was getting really low in the sky. Started out at 42 degrees, and then steadily marched towards 25 degrees. Took me a couple good images in between many bad ones to realize that 90% of the issue was just atmospheric conditions.


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#34 Stargezzer

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Posted 28 August 2021 - 02:14 PM

Harvey how high (altitude) above the horizon was Jupiter when you ran your session? If the target is too low you should consider an ADC.



#35 Kokatha man

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Posted 28 August 2021 - 07:59 PM

Another consideration with focusing an SCT is the concept of "optimum" focus. I've had no success in generating any discussion on the topic. For my C11 there must be a factory sweet spot or "optimum" focus position for the primary mirror. For lack of any solid confirmation of this I'm assuming it's the mid-point of the available primary mirror travel. This is also where a 2" factory visual back, diagonal and eyepiece comes into focus.

 

SCTs are a very forgiving design and seem to accommodate quite a range of focus. But IMO, if you can, why not design your kit to be at or close the the "optimum" position of the primary mirror. That's what I shoot for anyway.

 

The C11 is 37 focuser turns lock to lock with about 18 turns from either full forward or full rearward to be in the "optimum" position, which also happens to be where the scope is at f/10.

They are are readily available on the net for Celestrons: https://www.celestro...-celestron-scts  but apart from altering the f/l there are no real issues with varying that distance to ep or sensor. ;)


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#36 HarveyDeckAstro

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Posted 29 August 2021 - 01:33 PM

Harvey how high (altitude) above the horizon was Jupiter when you ran your session? If the target is too low you should consider an ADC.


It was about 32 degrees. Indeed I can see strong color separation in the moons. I have ordered ZWO ADC, and hopefully it would help to sharpen the image.

I re-examined my raw videos I shot for a wider view to include the moons. Io and Ganymede were quite close. From frame to frame the two sometimes were clearly separated and sometimes completely smeared out. The smearing was in most frames, so the seeing was pretty bad. Hopefully I will get a better seeing next time.

I often hear people would stop imaging planets when the seeing is bad. Love to hear how one decides that. Would be quite useful to avoid fruitless imaging sessions.

Harvey

#37 rehling

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Posted 29 August 2021 - 03:13 PM

I use this site to check the predicted seeing:

 

http://www.cleardark...LAXCAkey.html?1

 

Depending upon your local climate, this may be very accurate or not very accurate.

 

I don't think I'm imagining this – I can walk outside and almost always tell if the seeing will be good or not without even looking up. If there is absolutely no wind at all (rare) or if there is an absolutely consistent light breeze, my seeing will be good. If there is a breeze, even a small one, that fluctuates in direction, my seeing will be bad. If it feels like the breeze turns on and off, the seeing will be bad.

 

How much stars twinkle would presumably be a visual indication of the same.

 

Less helpful but more reliable – when I see the planet through the eyepiece, it is obvious if the seeing will be good or bad, and then I still have gone to a little trouble but not the full trouble of imaging. (And I leave my gear outside, often for weeks at a time, so that's not much trouble.)

 

Obviously, a lot of this will depend on your climate and local geography. Some aspects of one person's local climate may be unimaginable for another's.



#38 HarveyDeckAstro

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Posted 29 August 2021 - 04:02 PM

Thanks! Judging seeing certainly comes with experience. I guess for inexperienced like myself should just use bad seeing days as practice, as a previous post says.

#39 RedLionNJ

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Posted 29 August 2021 - 04:02 PM

I use this site to check the predicted seeing:

 

http://www.cleardark...LAXCAkey.html?1

 

Depending upon your local climate, this may be very accurate or not very accurate.

 

I don't think I'm imagining this – I can walk outside and almost always tell if the seeing will be good or not without even looking up. If there is absolutely no wind at all (rare) or if there is an absolutely consistent light breeze, my seeing will be good. If there is a breeze, even a small one, that fluctuates in direction, my seeing will be bad. If it feels like the breeze turns on and off, the seeing will be bad.

THIS.

 

ClearDarkSky is a fair indicator for low-level (under a mile elevation) seeing over the majority of the country.  It's not real accurate for high plains, inland mountainous areas or low-laying coastal areas (except for the FL area).

 

For most of the country, you also have to take the jet stream into account. Seeing is best when it's far, far away.

 

For me personally, I know seeing has a chance of being better when there is a light, steady wind off the general south-east (from the ocean). There is no high ground between the shore and my location, just a very, very gentle incline up to the massive elevation of 50 or so feet (sic).  It helps when the difference between daytime and night-time temperatures is not excessive. Generally this leads to spring or fall having a better chance of being optimal, but occasionally (like today) we get a cooler day where the temperature is going to remain stable into the night.

 

You have to learn your own local conditions and determine what factors play most into your personal seeing, then watch for them and make use of them.


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#40 Kiwi Paul

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Posted 29 August 2021 - 04:18 PM

Absolutely. You need to get to know your own area and what the situation is when seeing is good. That way, as you say, you can look for those general conditions in the weather element forecasts (wind, cloud etc).
Paul
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#41 rehling

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Posted 29 August 2021 - 05:53 PM

I realized that because of the topic title, I was thinking specifically of Jupiter. For Jupiter, Mars, and Saturn, the optimal observations will always be somewhat near midnight. But for other objects, time of day could vary quite a bit, and for Venus, for example, the time right before sunrise is often great for me, because the temperature will almost always have been stable for hours. The time around sunset is much worse, as the heat of the day is convecting up from rooftops and pavement into the cooling evening. Some of my favorite imaging sessions ever have been those of Venus or the Moon right before sunrise, and I sometimes time them almost to the minute to end when the Sun rises.


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#42 Kiwi Paul

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Posted 29 August 2021 - 09:09 PM

Yes, once the sun rises and heating starts to take place it stirs the air near the surface and density differences in parcels of rising air will lower or destroy the seeing.
Paul

#43 matt_astro_tx

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Posted 30 August 2021 - 06:05 AM

I check both the Clear Dark Sky web site and Meteoblue's Seeing Forecasts daily.

 

Here's a link for you with Short Hills, NJ as the location:  https://www.meteoblu...america_5104630


Edited by matt_astro_tx, 30 August 2021 - 06:06 AM.


#44 Kiwi Paul

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Posted 30 August 2021 - 09:41 AM

I like to keep an eye on Meteoblue (MB)’too. Use it as a general guide and watch for trends in the data besides the actual values. I have posted some thoughts on using MB previously. The clouds fields are a convenient tool for looking for windows. Remember that targets may still be visible in the sky for cloud RH values of say around 50% or less. The arc sec value has something to do with the wavefront (I need to research that more). Values for Index 1 of 4 or more along with values of Index 2 of 3 or more indicate potentially favourable conditions but values less than these are a more reliable indicator of poor seeing. Watch the Jet Stream speed and the thermal gradient value on the RHS. This is related to inversions in the atmospheric profile where temperature gradients are stronger. But overall, look for the weather patterns you know are favourable for you and then look at these MB numbers. Also, eyeballing the actually sky (twinkling etc) helps with the final decision of setting up or not.
Cheers Paul
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#45 Lopper

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Posted 30 August 2021 - 10:28 AM

Stale, stagnant air that feels smothering and conditions that bring fog often mean the seeing will be good. If your afternoon sky has cumulonimbus clouds then you've probably got significant atmospheric updrafts that will likely mean the seeing will be poor at night.

 

There's also that pesky relationship between the quality of the seeing and the rarity of the celestial event that you hope to capture.


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#46 RedLionNJ

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Posted 30 August 2021 - 11:11 AM

I check both the Clear Dark Sky web site and Meteoblue's Seeing Forecasts daily.

 

Here's a link for you with Short Hills, NJ as the location:  https://www.meteoblu...america_5104630

One of the (several) limitations of these forecasts is that they are for the immediate vicinity of the location. Actually quite fine for close-to-overhead imaging. But right now, Jupiter and Saturn are low in the SE/S/SW. So you also need the forecasts for locations in these directions, sometimes 25 or more miles out, to also be very good.  This may not be that big an issue in parts of the country which are largely unpopulated and generally flat, but get into areas like Short Hills and you're going to be very hard-pressed to find a night where the seeing forecast is not only good there, but also for 25+ miles to the south. Conditions in such areas are so complex, they're essentially impossible to model.  So the best way often remains "get out there and take a look".

 

Last night was a great example for me:  awesome seeing forecast (CSC 5/5) for my location and generally all the way to the Jersey shore (CSC has very few data points in between, alas). CSC also reported cloudless. Windy.com showed very light, almost nonexistent winds from the east. In theory, superlative conditions.

 

The clouds cleared on-schedule around 10:30pm. Went out, set up under a pretty transparent sky, let things cool down, test images looked promising, but not great. Still looking through far too much atmosphere. Then around 11:30pm, transparency took a nose-dive. Low-elevation haze (almost indistinguishable from cloud) materialized, strengthening in opacity as time went on.  By 1am, you couldn't see anything at all in the sky.  By 1:30, I packed up and went indoors. 

This morning I read those horrific conditions were due to condensation on smoke particles in the cooler night air.  Lovely.  One more thing to perhaps factor into whether it's worth staying sober, setting up, etc.



#47 HarveyDeckAstro

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Posted 30 August 2021 - 07:32 PM

I check both the Clear Dark Sky web site and Meteoblue's Seeing Forecasts daily.

Here's a link for you with Short Hills, NJ as the location: https://www.meteoblu...america_5104630

Thanks Matt! This is very helpful! Thanks everyone the guidance!

Edited by HarveyDeckAstro, 30 August 2021 - 07:49 PM.


#48 HarveyDeckAstro

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Posted 10 September 2021 - 10:37 AM

Update

 

Happy to report that I got a better image of Jupiter! And also got the Great Red Spot for the first time!

 

I followed the suggestions in this and other threads. Most importantly, I did -

 

(1) Focused on Jupiter itself, and no BN mask! Really spent time to see the details on Jupiter to come out as I focused. I am sure the focus was not ideal still, but it was better than I did anytime before.

 

(2) Ordered and used ADC. Color separation was reduced, and I could see more details. This also helped with focusing as well.

 

(3) Cut down the exposure time to 10 ms. I tried to cut down to 5 ms, but my frame rate was stuck at around 90 fps using ASICap. To go to the next level I really need to switch to FireCapture. Hope it will work on Mac...

 

(4) Captured 6 x 2 min videos, used 44 AP points in AS3, lightly sharpened in PS6, and de-rotated to combine them, enhanced with DeNoise AI and PhotoShop. Before I was using way too many AP point in AS3! Also learning not to be over aggressive in sharpening when the image does not support further sharpening.

 

Currently my focal length is way too long. ADC and 2X Barlow made the image scale too large for my sensor. If I get rid of the flip mirror this can all be better controlled. But the flipper mirror is useful for getting planets on the tiny sensor. Besides, it was fun to visual observe Jupiter. This is something I need to figure out.

 

Perhaps seeing was better too? The moons were dancing quite a bit, but not greatly. I moved my scope to a central Pennsylvania location, where I need to go for work. It has a better sky than NJ. Downside is that I don't have the scope all the time.

 

A lot to do, but I am happy with the progress. Thanks for all the suggestions, and please give further suggestions!

 

Harvey

 

 

 

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#49 matt_astro_tx

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Posted 10 September 2021 - 11:18 AM

Wow what an improvement!  Congrats


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#50 Borodog

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Posted 10 September 2021 - 11:56 AM

Congrats on the process.


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