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Astronomic ProPlanet 642 IR Pass Filter for Lunar Imaging - Does it make a difference?


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I recently bought the Astronomik ProPlanet 642 IR pass filter to accompany my ZWO ASI 462mc camera which is very sensitive in the infrared, so in theory an IR pass filter should make a great match for it.

It is said that these filters can increase contrast and sharpness, the reason being that the 200nm bandpass between 642nm and 840nm is effected less by a turbulent atmosphere compared to the wavelengths below 642nm, and above 840nm the image can become a little soft with the longer IR wavelengths.

So in a nutshell I wanted to see if this filter was a useful tool for Lunar imaging and maybe planetary down the line. 

Below I perform a controlled test of the 642 IR pass filter for lunar imaging using the ZWO ASI462mc camera, Sky-Watcher 200p telescope, and a 2.5x Revelation Barlow lens giving 2500mm focal length.

 

 

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I am not sure that keeping the shutter speed and gain similar is the correct way to compare the two views.

We want to expose "correctly" for each filter (it's not worth it to use the same exposure for an IR pass and IR cut filter - the histogram is quite different)

A comparison with a traditional 850nm IR pass filter would be quite interesting, IMHO.

N.F.

 

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5 hours ago, nfotis said:

I am not sure that keeping the shutter speed and gain similar is the correct way to compare the two views.

We want to expose "correctly" for each filter (it's not worth it to use the same exposure for an IR pass and IR cut filter - the histogram is quite different)

A comparison with a traditional 850nm IR pass filter would be quite interesting, IMHO.

N.F.

 

Hi, shutter speed was increased but gain was kept the same. I was keeping an eye on the histogram in the bottom right hand corner of SharpCap and both pre and post filter histograms sat in the same place. 

I would like to test the 850nm IR pass, but I read that it's for 10" plus aperture telescopes, so maybe one day if I ever get something like a C11 :)

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I don't understand why an 850nm IR pass filter has to work with larger scopes (I was using one with my Skymax 127, I didn't see any bad effects, but then I am a newbie in planetary imaging)

Wonder if there's an IR pass filter which starts at 650 or 700nm, it could use a larger part of the sensitive response of the IMX462 sensor, judging from the diagrams I see.

 

N.F.

 

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11 hours ago, Lockie said:

I would like to test the 850nm IR pass

I've got a ZWO 850nm I can send to you if you want to test it. 

I used it pretty successfully on Venus with my 8.75" fullerscope at f/20. Obviously the smaller the scope it the dimmer the image but there is no solid cut off aperture so when you hear it recommended only for scopes over 10" that is claptrap! 

1 hour ago, nfotis said:

Wonder if there's an IR pass filter which starts at 650 or 700nm

The 642nm bandpass outlined above? Also Baader 685nm longpass

Edited by CraigT82
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On 26/04/2021 at 04:00, neil phillips said:

Thats interesting Chris. what i dont understand is, Chris go said with the 462c chip anything below IR 850 nm would start to show bayer pattern noise. But i can not see a trace of it here. 

I was thinking about this... I think this would be the case if tracking were pixel perfect but your normal lunar capture is drifting and wobbling around the sensor and so the differences in pixel brightness below 850nm would average out over many pixels?

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12 hours ago, Lockie said:

Hi, shutter speed was increased but gain was kept the same. I was keeping an eye on the histogram in the bottom right hand corner of SharpCap and both pre and post filter histograms sat in the same place. 

I would like to test the 850nm IR pass, but I read that it's for 10" plus aperture telescopes, so maybe one day if I ever get something like a C11 :)

Not with this camera Chris, here is a lunar image taken with a SW Capricorn  70mm F 12.8 Frac. Gain wasnt even a problem. or a hopelessly slow exposure. Its very sensitive in 850nm enough to use a 70mm lens. 

capricorn.70 finished.png gamma (1).png

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45 minutes ago, CraigT82 said:

I was thinking about this... I think this would be the case if tracking were pixel perfect but your normal lunar capture is drifting and wobbling around the sensor and so the differences in pixel brightness below 850nm would average out over many pixels?

Hadnt thought about that, possibly Craig

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1 hour ago, CraigT82 said:

The 642nm bandpass outlined above? Also Baader 685nm longpass

 

The Astronomik filter cuts above 850nm, that's not desirable for the IMX462 sensor (I attach this sensor's response)

The 807nm looks more suitable to my eyes:

https://www.astronomik.com/en/infrarot-passfilter-infrared-pass-filters/proplanet-807-filter.html

Look at the ZWO diagram:

ASI462-QE-curve.png

 

N.F.

 

 

 

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Its all mute in my opinion IR850 is too heavy handed on fine detail. (on lunar) thats my conclusion. Lower IR wavelengths will produce a better result. I can tell this from the comparison shooting in colour. Can you get good results yes. ideal ? not really. Great for venus. Too heavy handed for lunar. Which is why i was interested in this test. Heres another small scope 114 newtonian 2x barlow IR850 80% so 20% downsized

Taken before it was dark on the 19th April so light affecting the quality somewhat

 

 

 

April 19th IR850.tif SGL.tif 80 PNG.png b.png c.Dpng.png

Edited by neil phillips
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3 hours ago, nfotis said:

 

The Astronomik filter cuts above 850nm, that's not desirable for the IMX462 sensor (I attach this sensor's response)

The 807nm looks more suitable to my eyes:

https://www.astronomik.com/en/infrarot-passfilter-infrared-pass-filters/proplanet-807-filter.html

Look at the ZWO diagram:

ASI462-QE-curve.png

 

N.F.

 

 

 

Seems to peak about 825nm doesnt it

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8 minutes ago, neil phillips said:

Seems to peak about 825nm doesnt it

 

You don't want only a narrow signal (I think), but to collect more signal all over the range beyond the 750-800nm, as I can understand.

We are not shooting narrow band here.

 

N.F.

 

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On 26/04/2021 at 04:00, neil phillips said:

Thats interesting Chris. what i dont understand is, Chris go said with the 462c chip anything below IR 850 nm would start to show bayer pattern noise. But i can not see a trace of it here. 

It could be dithered out like someone mentioned, and I can test that at some point by stacking a very short run of 100 frames which would literally take a second or so, as apposed to thousands of frames which takes close to a minute.

if a 1 second run which wouldn't allow time for tracking errors to kick in shows the Bayer pattern, I guess we can be pretty sure the above images were dithered by tracking errors from much longer runs. 

I hope that makes sense? 

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16 hours ago, nfotis said:

I don't understand why an 850nm IR pass filter has to work with larger scopes (I was using one with my Skymax 127, I didn't see any bad effects, but then I am a newbie in planetary imaging)

Wonder if there's an IR pass filter which starts at 650 or 700nm, it could use a larger part of the sensitive response of the IMX462 sensor, judging from the diagrams I see.

 

N.F.

 

That's good to hear :) I think it's just recommended for larger scopes because it probably blocks a lot of light and the extra aperture off sets this. You can of course use any filter that fits with any scope or camera etc just results may vary. I should have probably worded it " 10" plus telescopes for best results" my bad :)

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15 hours ago, CraigT82 said:

've got a ZWO 850nm I can send to you if you want to test it. 

I used it pretty successfully on Venus with my 8.75" fullerscope at f/20. Obviously the smaller the scope it the dimmer the image but there is no solid cut off aperture so when you hear it recommended only for scopes over 10" that is claptrap! 

Very kind of you Craig but I'll probably buy it at some point, though I want to try the 742 next. I Appreciate the offer though :)

I think it may have been my bad wording, maybe it read 'gives best results with 10" plus scopes' ? I'll have to track down the text and check.  

Found it "If the seeing is not so bad or if the telescope is smaller than 10" (250mm) we recommend the use of the Astronomik ProPlanet IR 742."

 

Edited by Lockie
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14 hours ago, neil phillips said:

Not with this camera Chris, here is a lunar image taken with a SW Capricorn  70mm F 12.8 Frac. Gain wasnt even a problem. or a hopelessly slow exposure. Its very sensitive in 850nm enough to use a 70mm lens. 

capricorn.70 finished.png gamma (1).png

That's a fine image from the Capricorn 70mm achro :) Yeah perhaps it was bad wording on my part regarding larger aperture and the 850nm filter, although I also read that longer IR wavelengths can soften image detail so maybe the 742 would be the better compromise? 

Edited by Lockie
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Here's an example of a stacked lunar image I did with my Skymax 127 (at f/12) and my ASI462 using the ZWO 850nm IR pass filter.

I had exposure time at1.8ms and gain at 227, shot an AVI RAW8 video at 4000 frames and 135 FPS on my old Thinkpad laptop. Stacked the 15% of the best frames in the first quarter of images with Autostakkert!3, and used its own sharpening (didn't bother with Registax), then colour corrected the image and saved as a JPEG.

 

00_11_36_l4_ap96_conv_corrected.jpg

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17 minutes ago, Lockie said:

That's a fine image from the Capricorn 70mm achro :)Yeah I think I might have got slightly the wrong end of the stick regarding larger aperture and the 850nm filter, although I also read that longer IR wavelengths soften image detail so maybe the 742 would be the better compromise? 

The thing is that the longer the wavelength the worse your scope's resolving power is.  Radius of airy disc = 1.22λ/D.

So at 850nm your scope is only resolving fine details twice as large as if you were using a blue filter (at 425nm ish). This is why people say it softens the detail... it doesn't so much soften the detail as not capture it at all! 

 

 

 

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42 minutes ago, Lockie said:

That's good to hear :) I think it's just recommended for larger scopes because it probably blocks a lot of light and the extra aperture off sets this. You can of course use any filter that fits with any scope or camera etc just results may vary. I should have probably worded it " 10" plus telescopes for best results" my bad :)

But in this case you can get good results with smaller scopes than perhaps with previous cameras

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3 minutes ago, neil phillips said:

But in this case you can get good results with smaller scopes than perhaps with previous cameras

Yes that's a good point, the 10" scope recommendation was probably written a while back when cameras weren't so sensitive. 

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