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Jupiter and Io, 3 Feb - Disappointment


gnomus
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I'm using a C8 Edge HD scope along with a ZWO ASI120MM-S camera.  I've had a few tries at imaging Jupiter with the ZWO 'straight into' the Edge (ie = no barlow - f/10).  I've been reasonably happy with the results.  On 3 Feb, I thought I'd try introducing my 2.5x Televue into the imaging train.  That train runs as follows: scope - visual back - filter wheel - Televue 2.5x - extension tube (I can't get focus without it) - ZWO.

I tried to be careful regarding focus: I slewed to nearby Pollux and used a Bahtinov, locking down focus after I was happy with it.  

Regarding exposure: at 50% gain, I would have needed an exposure of ~50ms.  Therefore, I pushed the gain to 70 to get exposures just below 20ms.  I am capturing 4000 frames and keeping 2000 of them.  AS!2 tells me that the quality is quite good (the graph certainly looks better than my lunar images).  

Firecapture shows that my 'Histogram Max' level never goes above 180.  Yet the centre of the planet looks burned out to me (maybe due to overprocessing).  

I've processed the resulting videos in a number of ways: using a combination of PIPP, AS!2, Registax, Astra, WinJUPOS, and PixInsight.  I am struggling to get anything that I am happy with.  The image is soft and lacking detail.  I have pushed the various 'sharpening' tools (wavelets, Lucy Richardson) as far as I can.  If I do any more I get terrible artifacts.  I cannot get any real detail on the planet surface.  

Re-reading the above it comes across as somewhat "whiny".  I don't mean to come across like that.  In many ways, I am astounded that I can go out into my backyard and produce the image I have got.  But I keep seeing what others are achieving, and I'd like to do a bit better.

Does this look like a focus issue, or is there something else that I am doing wrong?  Any advice would be much appreciated.

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First I will say I know nothing.

So take this as options nothing else.

Use less then 2000 frames, try the best 1000, basically stack only the best ones only and I would stack the best 25% or even 20%. Using 50% seems high.

Get less frames, 4000 frames at 30fps is 133 seconds and I have read that as Jupiter rotates fast going over 90 seconds can lead to the images moving apart too much so detail moves and the image loses sharpness.

After that not a clue. :grin: :grin: :grin:

Edited by ronin
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Are you refocusing after each filter change ? Also having the extension after the Barlow increases magnification so possibly too much for the seeing ?

No, I'm not re-focussing after each filter change.

I had understood that I was under a certain time-pressure to shoot the video due to Jupiter's fast rotation.  Slewing to a star, finding it on the screen, focussing and getting back to Jupiter would take a few minutes I would imagine.  If that is what I need to do though .....

As to imaging train, would people suggest: extension - barlow - wheel - camera? 

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Hi, this is a good effort, keep going would be my first advice :-)

As for your questions the problems can be done due to several issues:

1. focusing, when you focus there are few options, starting out I used to focus with a bahtinov mask (google it) - it's a longer procedure but it's worth it for beginners after doing it for few times you'll know what to expect when focusing directly on the plannet. As for focusing per filter it is usually not needed unless you have an electronic focuser doing it for you (pre-defined for each filter)

2. collimation - this is a must, check you collimation before you begin a night's shooting

3. seeing - this has a lot of influance on the result nothing to do here but go out as much as possible trying to get the best sky possible.

4. on more thing it seems that the image is a bit over exposed I would reduce the exposure a bit to capture finer details in the cloud belts.

5. Go for long AVIs (3 min each channel) and derotate the frames using WinJupos, if you want even better result derotate the AVIs (or SERs).

and again most important go out and anjoy this it will improve the more you try :-)

Dror

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Dror makes some very good points regarding collimation etc. To me this looks like a focus issue. I never use a b-mask because the focus at this focal length can shift depending on temperature changes, seeing conditions or filter changing. I tend to tweak focus every ten mins on jupiter. Near by jovian moons are a good focus point and if seeing is reasonable fine detail on Jupiter will appear as you tweak focus. If collimation is out or seeing poor then you will struggle to see this presuming your scope has cooled for a couple of hours.

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1) Cooling time; at least 2 hours from a warm house

2) seeing; recently its been a heap of Rubbish over the UK. Use http://earth.nullschool.net/#current/wind/isobaric/250hPa/orthographic=11.05,18.71,286

3) Focus - doesnt look great but could be bad seeing. As above says, focus on moons, ideally with electric focuser. The latter makes a HUGE difference (well, it did to me).

4) f/ratio - with the extension tube where you have it, you may be at too large an image scale. Aim for ~0.2"/pixel for now.

5) capture at 40-50 fps ideally. fast enough to freeze seeing, slow enough to get good SNR.

6) collimation - no idea! this doesnt look like bad collimation, as that usually introduces some kind of asymmetry, but its SO important to get this bang on. could be.....

7) reficusing between filters isnt critical for now. i make only a tiny adjustment for B.

Hope that helps. N

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Thanks everyone for these hints. It is possible that the scope had not completely cooled by the time this was shot. I assume that the focus will shift as the scope cools down. I agree about exposure. These were shot so that the histogram appeared to go some two thirds to three quarters of the way along the scale.

I think my collimation is OK, but I will pay more attention to it.

Not sure how to calculate this optimum f-ratio business. If I use the televue, I need to use the extension tube, or else the telescope won't focus. Even with the two inch extension it is only a couple turns away from fully inward travel before I get focus.

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If its a 2.5x powermate you are using then an extension tube will not effect the focal length like it would using a barlow. As for getting it to focus...this may sound like stating the obvious but have you tried pulling the powermate out of the focuser about say 1cm. This is what I have to do with my powermates to have enough focus travel though I am using a newtonian scope.

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If its a 2.5x powermate you are using then an extension tube will not effect the focal length like it would using a barlow. As for getting it to focus...this may sound like stating the obvious but have you tried pulling the powermate out of the focuser about say 1cm. This is what I have to do with my powermates to have enough focus travel though I am using a newtonian scope.

I'm not sure I follow exactly.  I thought that I was using the 2.5x to increase the focal length by that amount.  Is that not correct?  

Yes it is a 2.5 Powermate.  I was a bit surprised when it wouldn't focus (it did with the star diagonal in, of course).  I did try various combinations of 'bits' not being quite pushed fully home, but could not get focus.   As I say - even with the 2" extension, I am only a few clockwise twists away from running out.

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Yes it does increase focal length by 2.5x but unlike a barlow adding an extension tube to the powermate will not increase the focal length so you don't need to worry about over doing the image size that way.  So you have the extension in first then the powermate?

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Ive tried both ways but usualy put the filter wheel first mainly because I get better stability & less flexure that way, with a powermate it will slightly increase your overall fl too! Because powermates are parfocal (retaining the same focus point) the other way around would have the opposite effect, but either way should not affect your imaging!

Edited by si@nite
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Ive tried both ways but usualy put the filter wheel first mainly because I get better stability & less flexure that way, with a powermate it will slightly increase your overall fl too! Because powermates are parfocal (retaining the same focus point) the other way around would have the opposite effect, but either way should not affect your imaging!

Now that I am thinking more about this, I wonder if putting the wheel before the Televue would lead to the Televue 'amplifying' any defects/aberrations in the filters themselves.  What do folks think?

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