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Image Mercury with Red Bandpass or NIR Longpass Filter?

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#1 Quaternion

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Posted 12 May 2021 - 08:19 PM

I saw Mercury for the first time in my life tonight, and I actually have a clear view from my driveway ! Furthermore, the Clear and Dark Sky website predicts that I will have a chance to image it in Good seeing on Friday.  I plan on imaging it at f/15 with a 2.3um mono sensor,  but I’m not sure which filter to use? Is it best to go for max  SNR/Min frame rate for lucky imaging or maximum resolution?

 

Thanks for any advice you can give me.

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Edited by Quaternion, 12 May 2021 - 08:31 PM.


#2 StarAlert

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Posted 12 May 2021 - 09:33 PM

I saw Mercury for the first time in my life tonight, and I actually have a clear view from my driveway ! Furthermore, the Clear and Dark Sky website predicts that I will have a chance to image it in Good seeing on Friday.  I plan on imaging it at f/15 with a 2.3um mono sensor,  but I’m not sure which filter to use? Is it best to go for max  SNR/Min frame rate for lucky imaging or maximum resolution?

 

Thanks for any advice you can give me.

Are you sure that’s Mercury and not Venus? It seems awfully bright. 


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#3 John Boudreau

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Posted 13 May 2021 - 02:06 AM

I saw Mercury for the first time in my life tonight, and I actually have a clear view from my driveway ! Furthermore, the Clear and Dark Sky website predicts that I will have a chance to image it in Good seeing on Friday.  I plan on imaging it at f/15 with a 2.3um mono sensor,  but I’m not sure which filter to use? Is it best to go for max  SNR/Min frame rate for lucky imaging or maximum resolution?

 

Thanks for any advice you can give me.

Generally, I've found longpass filters a better choice than bandpass filters. In good seeing, I prefer the Baader 610 LP and in fair seeing the 685LP. The Astronomik 742 results in a stable enough image in somewhat rougher seeing. The deeper LP filters like the Astronomik 807LP work too, but any additional steadiness they offer is usually offset by the necessarily longer exposures and the lower resolution of the longer wavelengths. I expect that the best bandpass filter may be the Astronomik 642, which is a 642-842 bandpass filter--- I bought one a few years ago, but haven't made any Mercury attempts since I received it. I have used R bandpass filters in the past like the Astrodon R (both e and i versions), but the Baader 610 gives similar resolution with more light to work with thus lower gain setting.

 

My avatar was shot with an Astronomik 742 in late 2008. In the years that followed I basically abandoned the consistency of the 742 and relied on the 685 and 610LP filters which in moments of good seeing can result in noticeably better resolution as my goals had shifted from just getting a good image to taking a chance to get the best possible resolution. Experience with your conditions and quite simply your current filter choices are the best guide here. In the end, the typical seeing you'll encounter will probably mean any choice is a bit of a gamble. It's also a good idea to take as many videos as you can, with perhaps a minor focus tweak after every 2 or 3 videos. Focusing in these conditions can be tough, and I relied on at least 10 videos with a bit of what would best be described as bracket focusing to increase my chances of nailing focus. Best results were with the Sun up and behind trees, with Mercury at least 30 degrees high. You don't want the scope in direct sunlight in order to reduce thermal issues.

 

Good luck!


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#4 Quaternion

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Posted 13 May 2021 - 11:45 AM

Are you sure that’s Mercury and not Venus? It seems awfully bright. 

Good question, but yes.  It was even orange/red to the eye, and Capella and Betelguese were there as references.  Venus is white and WAY brighter..



#5 Quaternion

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Posted 13 May 2021 - 11:51 AM

Generally, I've found longpass filters a better choice than bandpass filters. In good seeing, I prefer the Baader 610 LP and in fair seeing the 685LP. The Astronomik 742 results in a stable enough image in somewhat rougher seeing. The deeper LP filters like the Astronomik 807LP work too, but any additional steadiness they offer is usually offset by the necessarily longer exposures and the lower resolution of the longer wavelengths. I expect that the best bandpass filter may be the Astronomik 642, which is a 642-842 bandpass filter--- I bought one a few years ago, but haven't made any Mercury attempts since I received it. I have used R bandpass filters in the past like the Astrodon R (both e and i versions), but the Baader 610 gives similar resolution with more light to work with thus lower gain setting.

 

My avatar was shot with an Astronomik 742 in late 2008. In the years that followed I basically abandoned the consistency of the 742 and relied on the 685 and 610LP filters which in moments of good seeing can result in noticeably better resolution as my goals had shifted from just getting a good image to taking a chance to get the best possible resolution. Experience with your conditions and quite simply your current filter choices are the best guide here. In the end, the typical seeing you'll encounter will probably mean any choice is a bit of a gamble. It's also a good idea to take as many videos as you can, with perhaps a minor focus tweak after every 2 or 3 videos. Focusing in these conditions can be tough, and I relied on at least 10 videos with a bit of what would best be described as bracket focusing to increase my chances of nailing focus. Best results were with the Sun up and behind trees, with Mercury at least 30 degrees high. You don't want the scope in direct sunlight in order to reduce thermal issues.

 

Good luck!

John,  Thank you for all this great detailed advice.  I'm honored to have "Mr. Mercury" reply himself smile.gif .  I will go with the 610 LP, and try the focus brackets as well. Unfortunately, I haven't imaged planets for over a year so I am very rusty, and more than likely I will have some scope/software/setup issue that will torpedo my efforts.  However, I will give it my best. 


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#6 Quaternion

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Posted 17 May 2021 - 11:54 AM

Well, John you were right.  I needed to image Mercury at 30 deg, not the 16deg I managed after I finally found it.  I have to somehow figure out a way to locate Mercury reliably with a Dob BEFORE it is visible to the naked eye. I have an XT10i with the object locator/magnetic encoders, but  I need to reference it to two stars which also are not visible. I wonder if I could roughly calibrate "openloop", and go to the Az/El where two bright star's "should be", then just get in the ball park and scan around for Mercury. I have a BIG FOV with the ASI294MM prior to windowing to a max FPS ROI, so maybe this would work...what do you think? I won't even bother posting my blurry Mercury, which only confirmed what Galileo figured out a while ago, that the inner planets have phases lol.gif


Edited by Quaternion, 17 May 2021 - 11:55 AM.


#7 John Boudreau

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Posted 17 May 2021 - 05:05 PM

Well, John you were right.  I needed to image Mercury at 30 deg, not the 16deg I managed after I finally found it.  I have to somehow figure out a way to locate Mercury reliably with a Dob BEFORE it is visible to the naked eye. I have an XT10i with the object locator/magnetic encoders, but  I need to reference it to two stars which also are not visible. I wonder if I could roughly calibrate "openloop", and go to the Az/El where two bright star's "should be", then just get in the ball park and scan around for Mercury. I have a BIG FOV with the ASI294MM prior to windowing to a max FPS ROI, so maybe this would work...what do you think? I won't even bother posting my blurry Mercury, which only confirmed what Galileo figured out a while ago, that the inner planets have phases lol.gif

There can certainly be a 'learning curve' to finding Mercury in daylight without goto. I was using setting circles for years with a non-goto G11 when I imaged Mercury with a C11. A good FOV helps, but what's also important is picking an eyepiece that has at least a reasonably good focus accommodation across the FOV--- it's best if coma and astigmatism is reasonably under control. A red or orange filter also helps gain contrast between Mercury and a bright sky. Sometimes I'd tap the scope every few seconds just enough to cause a vibration--- the eye usually does better on hard to see star-like points if they are in motion. The eyepiece should also be at least 'in-the-ballpark' as far a being parfocal with the camera if possible. While I've daylight collimated a scope while viewing via a camera and laptop monitor, I've never tried to find Mercury that way but I'm sure it can be done.


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#8 Quaternion

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Posted 18 May 2021 - 06:11 AM

Thanks John.  I'll try your "tapped" orange filtered eyepiece trick to see if I can't locate Mercury. 




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