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Question on seeing vs results

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#1 APshooter

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Posted 23 November 2022 - 10:32 PM

Long time DSO imager/part time planetary imager living in the Midwest.  Seeing here generally is listed as bad to poor to average from Clear Dark Sky.  Overhead jetstream currently is 70 knots.  I see some people making amazing images of Mars in winds twice what I'm experiencing overhead.  I'm getting average results after stacking on 'good' nights (average seeing is the best we usually get) and often so bad it's not worth processing (no sign of the Cassini division or only 3 belts on Jupiter).  So my question is how are folks getting such great results in conditions I would guess are not worth setting up for?  Are folks imaging with high gain and very short exposures?  If I recall from memory my Mars images were about 9ms.  I cropped in very tightly in Firecapture and used guiding when capturing 3 minute sessions.  I do not use Winjupos at this time.


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#2 Ittaku

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Posted 23 November 2022 - 11:07 PM

The resolution of any planetary image is one of seeing, focus, aperture, or collimation limited. Ultra high frame rates have only very limited ability to see through seeing, marginally increasing the amount of good frames. By far the most common reason DSO imagers switching to planetary imaging get poor results is their collimation is absolutely fine for DSO resolutions, but not planetary. Unless you've done a star test to get fine collimation with an airy disc, your collimation is unlikely to be of a satisfactory standard to image at the resolution limits of your aperture. Many an imager has gotten surprisingly good results in apparently average seeing simply by fine tuning their collimation. That would be my first guess.


Edited by Ittaku, 23 November 2022 - 11:10 PM.

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#3 dcaponeii

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Posted 24 November 2022 - 08:28 AM

Ditto!! Collimation first and NOT donuts which is fine for DSO imaging. You need to be doing IN FOCUS star tests. Try out Metaguide and use an IR Pass filter for the collimation.
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#4 RedLionNJ

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Posted 24 November 2022 - 09:16 AM

Can't disagree with the collimation comments, above.

 

Another couple aspects Con mentions are worth a few more words:

 

Focus:  you're trying to record details at the limit of your equipment. As close to perfect focus as possible is essential. The fine focus for planetary details can change pretty quickly at times. Always try to get a 'best focus' right before a capture. Best focus is when the contrast is at maximum. Judge it by eye, for long periods.

 

Seeing: there may be a short period of slightly-better seeing mixed in among hours and hours of poor seeing. You need to be prepared to take advantage of that better seeing when it does occur.  There have been nights I've been out there for several hours, only to come indoors with a single usable video. More often two or maybe three.  Seeing will vary throughout the night in most locations. And also in different directions and at different elevations (low is obviously usually going to be worse).   CSC is not a good predictor of seeing. It doesn't take into account direction or elevation and it's based on data up to only 6,000 feet. Many of the prediction services use the same data sources, so they're no better (although some claim to be).  Learn your own environment. That jet stream is not always your enemy; it's possible to get a laminar flow if it's been steadily positioned for a couple days and you're right under the middle of it.  Likewise, if you get a warm day in winter, that can lead to surprisingly steady seeing, as can a cool day in summer. You really need the experience of learning your own environment to get the most out of your local seeing - anywhere.  Sometimes dusk is a great time, sometimes dawn. Sometimes it's going to be 3am, which tends to lead to those occasions being missed!

 

I was out with Mars two nights ago. I got THREE usable videos. Jupiter was mushy mess and I had missed my window for Saturn,

 

Last night, I went out right after sunset and was shocked to get some really nice Saturn video, despite it being low in the south. The seeing wasn't consistently good - the whole planet & its rings would shimmer in and out of focus, but I could probably have kept capturing for quite some time, but I also wanted to see what things were like over in Jupiter's direction. Jupiter was awful - even at a higher elevation. I just couldn't find a precise focus with any degree of certainty.

 

Remember, we do planetary imaging at tolerances of 10 or more times tighter than typical DSO imaging.  We don't care so much about a FWHM of 2 arcsec, we care about maximizing moments where we can resolve down to 0.10 arcsec/pixel.  And we have to be ready to capture them when they occur.

 

Happy Imaging!

 

Grant


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#5 Borodog

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Posted 24 November 2022 - 11:31 AM

What equipment are you using?

#6 APshooter

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Posted 24 November 2022 - 12:06 PM

First off, thanks to all who responded and Happy Thanksgiving!  This has been a nut that's been hard to crack and I'll see if I can't improve my collimation first.  I've done a prior star test of course and watched the laptop screen while doing so.  I wasn't sure if I was close enough in collimation because as I increased magnification the star turned to mush after a certain point.

 

 

You need to be doing IN FOCUS star tests. Try out Metaguide and use an IR Pass filter for the collimation.

I will certainly try this, thanks!

 

 

What equipment are you using?

MYT mount, C-9.25 with Bob's knobs.  2.5x Barlow, Moonlight focuser with dual control ports.  ZWO 462 camera, IR filter, ZWO ADC.  Scope is set out 2 hrs prior to cool, but sometimes I'm rushed and set it out at 70 degrees when the outside might be 65. 

 

Would some sort of digital collimation device work better than a star test?  Something not dependent on seeing conditions? 

 

I also have an AP130 as well but have seldom tried to image the planets with it.


Edited by APshooter, 24 November 2022 - 02:06 PM.


#7 dcaponeii

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Posted 24 November 2022 - 05:57 PM

Nothing out there is going to beat a star test and don’t fall for masks either as they are no more accurate than donuts.
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#8 Tulloch

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Posted 24 November 2022 - 06:30 PM

I have found that collimating with a red filter in place makes it much easier to see the rings.
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#9 Ittaku

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Posted 24 November 2022 - 07:13 PM

Would some sort of digital collimation device work better than a star test?

Digital collimation yes, but with a star test - using metaguide with an in-focus star to guide fine collimation.

 

 

  Something not dependent on seeing conditions? 
 

You have an IR sensitive camera, if you collimate with an IR pass filter, it is less affected by seeing.
 


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#10 Lacaille

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Posted 24 November 2022 - 08:11 PM

Hi APShooter,

All very good advice above to which I would add:

That is a very powerful Barlow for that setup. My guess is that, with native f10 x2.5 x something more for the length of the imaging train you are well in excess of f25. With your camera as a general rule aim for 2.9x5 = f 15. Without the Barlow you may be close to this, but there is a cheapish turret Barlow from Baader that gives about 1.3X with just the lens element. In the meantime try imaging without the Barlow unless the seeing looks very good- your gain x fps combo will be much improved.

Secondly, you are using Firecapture. I use a function called “Screen Adjust” (look for a button just above the video screen) which allows you to adjust gamma and brightness to enhance contrast, reduce glow, and aid focus, without affecting your capture settings. You may find this helps to focus.

Mark
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#11 RedLionNJ

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Posted 25 November 2022 - 07:09 AM

First off, thanks to all who responded and Happy Thanksgiving!  This has been a nut that's been hard to crack and I'll see if I can't improve my collimation first.  I've done a prior star test of course and watched the laptop screen while doing so.  I wasn't sure if I was close enough in collimation because as I increased magnification the star turned to mush after a certain point.

 

 

Would some sort of digital collimation device work better than a star test?  Something not dependent on seeing conditions? 

 

I'm not aware of any digital collimation device which actually works - what did you have in mind?  If you've never done it before on your OTA, it might be worth borrowing a Hotech SCT collimator to make sure your optical axis is coincident with the mechanical axis and if not, correcting it (just once).

 

If the seeing is too poor to make collimation possible, it's likely not going to be great for imaging, either!



#12 dcaponeii

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Posted 25 November 2022 - 10:32 AM

Digital collimation yes, but with a star test - using metaguide with an in-focus star to guide fine collimation.

 

 

You have an IR sensitive camera, if you collimate with an IR pass filter, it is less affected by seeing.
 

Except any  OSC camera works with IR Pass filter for collimation.  I've use my 290MC, 485MC and the 678MC without any issues.  As Andrew said above even a red filter will get you there too.
 



#13 dcaponeii

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Posted 25 November 2022 - 10:34 AM

Hi APShooter,

All very good advice above to which I would add:

That is a very powerful Barlow for that setup. My guess is that, with native f10 x2.5 x something more for the length of the imaging train you are well in excess of f25. With your camera as a general rule aim for 2.9x5 = f 15. Without the Barlow you may be close to this, but there is a cheapish turret Barlow from Baader that gives about 1.3X with just the lens element. In the meantime try imaging without the Barlow unless the seeing looks very good- your gain x fps combo will be much improved.

Secondly, you are using Firecapture. I use a function called “Screen Adjust” (look for a button just above the video screen) which allows you to adjust gamma and brightness to enhance contrast, reduce glow, and aid focus, without affecting your capture settings. You may find this helps to focus.

Mark

That same (or similar) similar 2x Barlow with the removable lens element is available from Orion as their Orion 2x "shorty" Barlow.  Thread the Barlow in front of the camera and you get just about 1.5x.
 



#14 APshooter

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Posted 25 November 2022 - 05:11 PM

 

That is a very powerful Barlow for that setup. My guess is that, with native f10 x2.5 x something more for the length of the imaging train you are well in excess of f25. With your camera as a general rule aim for 2.9x5 = f 15. Without the Barlow you may be close to this, but there is a cheapish turret Barlow from Baader that gives about 1.3X with just the lens element. In the meantime try imaging without the Barlow unless the seeing looks very good- your gain x fps combo will be much improved.

I went back and looked at what I'm actually using right now...and it's the Vernonscope 1.5x Magic Dakin Barlow, not the 2.5x televue I had used before.  Right now it's connected thusly:  1.5x barlow>ZWO ADC>IR Filter>ZWO 463MC.  Is this order correct, or should the Barlow be directly in front of the camera with the IR filter in front of the barlow?



#15 Tulloch

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Posted 25 November 2022 - 05:27 PM

I went back and looked at what I'm actually using right now...and it's the Vernonscope 1.5x Magic Dakin Barlow, not the 2.5x televue I had used before.  Right now it's connected thusly:  1.5x barlow>ZWO ADC>IR Filter>ZWO 463MC.  Is this order correct, or should the Barlow be directly in front of the camera with the IR filter in front of the barlow?

That configuration looks fine to me. I screw in my IR filter into my powermate at the front, but I can't see that making a difference. My setup is:  IR-cut > 2.5x PM > ZWO ADC > ZWO224MC. 

 

There are a number of reasons why I have the IR-cut at the front, but since I collimate with a red filter in place, having the filter easily accessible is a bonus.

 

Andrew


Edited by Tulloch, 25 November 2022 - 05:28 PM.


#16 APshooter

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Posted 25 November 2022 - 06:19 PM

I got an image in metaguide after installing Direct X.  I got a star on the screen after doing a rough focus.  The red dot was dancing around in all directions, sometimes favoring left and lower left.  However, I found it difficult to go up the ladder and tweak the knobs blindly, then go down and look at the compy screen.  How soes everyone else do it?  It's quite cold and I may call it a night...try again some other night.


Edited by APshooter, 25 November 2022 - 07:10 PM.



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