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Favorite Light Pollution Filter for EAA?

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#101 alphatripleplus

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Posted 15 May 2016 - 03:39 PM

Jim,

 

Just to say I haven't forgotten this thread.  I have ordered a Lumicon #29 Dark Red filter (I think nominally 600nm Longpass) and an Astronomik Proplant 642 BP which passes between 642nm and 842nm.  I plan to use these with my ASI 224 MC for EAA with galaxies.  The #29 Dark Red should detect more alignment stars, while the 642 BP with 200nm width of band pass should yield less star bloat or chromatic aberration with my achromat Celestron 102 SLT, and when the moon is out in force. I have been struggling to decide which one to buy and eventually decided to buy both, to give me options for different objects and viewing conditions.

 

I think the H-Alpha filters have too narrow band pass and will require exposure times that are too long for my Alt-Az mount.

 

Cheers,

Joseph

 

 

Joseph,

 

I will be very interested to see how much contrast improvement you get on galaxies using these two filters relative to no filter. I've read all of Jim's excellent articles and tests on filters, so it will be very interesting to learn of your results. In particular, I would be interested to see if the #29 needs roughly 6 times as long as a no-filter exposure to start to wash-out the sky background with the ASI224. I think Jim did his tests on M33 using a Mallincam Xtreme in part 4 of his series on Managing IR in video astronomy. Please let us know how it works out for you!

 

Errol



#102 StarCurious

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Posted 15 May 2016 - 04:41 PM

Errol,

 

I will post findings here when I receive the two filters and I have clear skies to test. This exercise was put off for over a month as I was trying to achieve a faster F/ ratio, knowing that adding filters mean increasing exposure time.  What I didn't know was that the increase could be as long as six times. I think that means longer than 10 minutes total exposure, which means vignetting due to field rotation.  Fortunately, at F/2.4 the FOV for my set up is 1.12 x 0.84 degree and I should still have enough FOV after cropping the perimeter.  I will still be limited by how long the SLT can track.

 

Joseph


Edited by StarCurious, 15 May 2016 - 05:53 PM.

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#103 StarCurious

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Posted 15 May 2016 - 07:01 PM

 


 

I would be interested to see if the #29 needs roughly 6 times as long as a no-filter exposure to start to wash-out the sky background with the ASI224. I think Jim did his tests on M33 using a Mallincam Xtreme in part 4 of his series on Managing IR in video astronomy.

 

Errol,

 

This might be the article you mentioned:

 

http://karmalimbo.co...onomy_Part3.pdf

 

#29 took 4 times longer, and IR pass 680nm took 8 times, for M31.

 

The last paragraph in this article:

 

http://karmalimbo.co...onomy_Part4.pdf

 

is particularly relevant to my plan to test 642-842nm band pass:

 

I quote (emphasis mine):

 

6. The relationship between %LT and INT time is not simply 1/%LT as I thought. The impact of progressively narrower filters on INT time increases exponentially. I would expect to get a similar relationship to what I measured in this test if my target was something other than a galaxy.


Edited by StarCurious, 15 May 2016 - 07:10 PM.


#104 alphatripleplus

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Posted 15 May 2016 - 11:49 PM

 

 


 

I would be interested to see if the #29 needs roughly 6 times as long as a no-filter exposure to start to wash-out the sky background with the ASI224. I think Jim did his tests on M33 using a Mallincam Xtreme in part 4 of his series on Managing IR in video astronomy.

 

Errol,

 

This might be the article you mentioned:

 

http://karmalimbo.co...onomy_Part3.pdf

 

#29 took 4 times longer, and IR pass 680nm took 8 times, for M31.

 

The last paragraph in this article:

 

http://karmalimbo.co...onomy_Part4.pdf

 

is particularly relevant to my plan to test 642-842nm band pass:

 

I quote (emphasis mine):

 

6. The relationship between %LT and INT time is not simply 1/%LT as I thought. The impact of progressively narrower filters on INT time increases exponentially. I would expect to get a similar relationship to what I measured in this test if my target was something other than a galaxy.

 

 

 

Joseph,

 

As I mentioned, I was actually referring to Part 4 of Jim's series

 

http://karmalimbo.co...onomy_Part4.pdf

 

On page 4 of Part 4, he has a 55sec exposure of M33 washing out the sky background with a #29 filter, compared with a 9sec exposure washing out with no filter (on page 2). Hence the 6 times ratio. However, you also point that in Part 3 of the series, the ratio for M31 is more like 4 times for the #29 vs no filter. Either way, the mount is going to have to track for several times longer to register stars for stacking when using the #29 filter or an IR pass compared to no filter.

 

 

Unfortunately, I'm not going to be doing much EAA in the next few days/weeks as it looks like the electronics of my old mount finally died this evening. :( So I'll be interested to hear about your experiences with the filters.

 

Errol



#105 jimthompson

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Posted 16 May 2016 - 01:57 PM

Hi All,

 

I will also be very interested to see what the impact on exposure time is using the IR pass filters.  The testing I did that is reflected in the various test reports were all performed using a Mallincam Xtreme with ICX418AKL sensor.  Since that time the cameras that have become popular for video astronomy all use updated EXview HAD or their CMOS equivalents which are considerably more sensitive to IR than the classic 418.  For example recently I have played with cameras using the ICX829, IMX185 and IMX302 sensors and they all worked quite well with a 650nm high pass filter.  I don't know what the relative increase in exposure is with and without IR pass filter when observing a galaxy.  I do know that very roughly the exposure time is the same when observing the Moon between using an IR pass filter and using a UV/IR cut filter.

 

Best Regards,

 

Jim T.


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#106 alphatripleplus

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Posted 16 May 2016 - 07:54 PM

Hi Jim,

 

I really enjoyed reading all your articles on filters and reducers - great stuff. If Joseph's findings on galaxies are encouraging, I'll take a shot with some of the filters suggested in your papers.

 

Errol



#107 StarCurious

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Posted 25 May 2016 - 06:57 PM

Hi Jim,

 

I finally received the Astronomik Proplanet 642 BP (band pass from 642 to 842nm).  I also have the ZWO UV/IR Cut Filter and the Lumicon #29 Dark Red Filter.  I am waiting for skies to clear to test these, in combination as appropriate, at F/2.3 with Sharpcap 2.9 beta

 

1) M51 and/or M101, with 642 BP.  I have previously test #29 Dark Red with M51.

2) M82/M81 with ZWO UV/IR Cut

3) NGC 6995 Eastern Veil Nebula and/or IC 5070 Pelican nebula with 642 BP + ZWO UV/IR Cut i.e. 642-700nm pass i.e. made up "extra wide band" H-Alpha

 

Can you please suggest better targets than these?

 

Thanks,

Joseph


Edited by StarCurious, 25 May 2016 - 07:01 PM.


#108 Censustaker

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Posted 25 May 2016 - 07:36 PM

I recently obtained one of these:  https://astronomy-im...nm-pass-filter/

 

at 850nm its probably a bit extreme, but it'll be interesting to give it a go, and at $22 it was worth a go


Edited by Censustaker, 25 May 2016 - 07:36 PM.

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#109 StarCurious

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Posted 25 May 2016 - 07:49 PM

Censustaker,

Can you please test your 842nm long pass with galaxies such as M51 or M101 while the nesrly full moon is up?

Thanks,
Joseph

#110 Censustaker

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Posted 25 May 2016 - 07:52 PM

If it's clear tonight I try and give it a go. 



#111 Censustaker

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Posted 25 May 2016 - 11:33 PM

Sorry - outta luck - cloudy :(

#112 jimthompson

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Posted 26 May 2016 - 09:07 AM

Hi Jim,

 

I finally received the Astronomik Proplanet 642 BP (band pass from 642 to 842nm).  I also have the ZWO UV/IR Cut Filter and the Lumicon #29 Dark Red Filter.  I am waiting for skies to clear to test these, in combination as appropriate, at F/2.3 with Sharpcap 2.9 beta

 

1) M51 and/or M101, with 642 BP.  I have previously test #29 Dark Red with M51.

2) M82/M81 with ZWO UV/IR Cut

3) NGC 6995 Eastern Veil Nebula and/or IC 5070 Pelican nebula with 642 BP + ZWO UV/IR Cut i.e. 642-700nm pass i.e. made up "extra wide band" H-Alpha

 

Can you please suggest better targets than these?

 

Thanks,

Joseph

Hi Joseph,

 

M51 makes a good galaxy  target to use for testing.  It is high in the sky right now and it is of reasonable size to try and see some structure in the arms and core.  It is also reasonably bright which also makes it a good target to use for testing.  M101 I find is very dim and is a challenging target, perhaps a good target after you have used your new filters for a while on other targets.  There are numerous smaller but good galaxy targets between Ursa Major and Leo.  I like to try face on spirals M106, M63 and M109; edge on spirals ngc4244 and ngc4565; as well as the irregular galaxies ngc4631 Whale & Pup, ngc4656 Hockey Stick, and ngc4490.

 

For nebulae, if you are willing to stay up late, the summer objects are up after 1am.  M27 Dumbbell Nebula is a good one as it has a lot of structure visible in it.  A little later you will be able to catch M16 Eagle and M17 Swan further down into the south-east.  If you have a good clear horizon to the south you can go for M8 and M20 which are both lovely with lots of detail.  Both M8 and M17 are very bright, at least in their central area, so they make good targets for testing.  In the northern sky the good nebulae are poorly placed low on the horizon right now.

 

Have fun!

 

Jim T.


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#113 Censustaker

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Posted 26 May 2016 - 10:32 AM

M51 can be tricky for live stacking depending on your FoV + focal ratio + sky conditions , there aren't too many alignment stars near by in my experience

#114 StarCurious

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Posted 01 June 2016 - 07:59 PM

I tested the ZWO UV/IR Cut and the Astronomik 642 BP last night...

 

 

 

M27 642BP_Stack_76.Untouched.Cropped.png

Attached Thumbnails

  • M51 642BP_Stack_53.Cropped.png


#115 StarCurious

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Posted 01 June 2016 - 08:00 PM

One more ...

 

M82 IR CUT_Stack_76.cropped.png

 

All 3 were captured at F/2.3. Each exposure was 4 seconds long. Please click the image to see the file name with information on object, filter used, number of captures stacked.


Edited by StarCurious, 01 June 2016 - 08:19 PM.


#116 jimthompson

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Posted 02 June 2016 - 10:42 AM

Hi StarCurious,

 

I am guessing you were using your ASI224 camera and 102SLT refractor?  Maybe it is just me but your images look out of focus.  Do you use a focusing mask?  If not I highly recommend that you do.  I also don't understand why your images using the 642 BP filter are not monochromatic red since the filter is only passing the red part of the spectrum.

 

Regards,

 

Jim T.



#117 StarCurious

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Posted 02 June 2016 - 04:55 PM

Hi Jim,

 

I did use the ASI224 MC and 102 SLT. I too am stumped as to why there's not much red with the 642BP.  I did not take darks.

 

Before testing the filters (quickly), I spent a lot of time calibrating centre for Starsense. I ended up getting the test star Arcturus at times just beyond the 0.31 degree diameter i.e. 0.17 degree from centre - 0.42 x 0.31 degree was the FOV for native F/6.4 with no focal reduction.

 

I had trouble achieving focus that night, even with Bahtinov mask.  Sharpcap focus scores could not settle down.  This could be due to too much moisture in the air - at 2:30am. All the images had too much green. There was no hint of red, except M27. When I cropped them for posting here, I made colour adjustments to 2 of them. I also tried 642 BP with NGC 6995 and IC 5070. The stars were bloated, though it was amazing to see so many stars at 4 second exposure stacking successfully at F/2.3.  M13 with 642 BP resulted in a contiguous blob of light - a focus or over exposure issue (see attached cropped to reduce file size but with no other adjustment).

 

I will have to test again when seeing conditions are better, and when I have more time.  However, I have to get my Starsense calibration nailed first to make life easier.  I will test a Barlow lens with ASI 224 MC to get an even narrower FOV and then calibrate, in the hope that this will improve GOTO accuracy for lower F/ ratios.

 

Thanks,

Joseph

 

Attached Thumbnails

  • M13 642BP_Stack_39x4s.Cropped.png


#118 jimthompson

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Posted 02 June 2016 - 08:33 PM

Yikes! Your image looks like something is not correct.  I wonder, are you using SharpCap?  If so, you should start with everything at a default setting, your camera gain at half way, and adjust your exposure until you get an image.  See my attached screen capture which was taken with my ASI 185MC from inside my basement but with a Baader IR Pass filter on (680nm high pass).  Note the settings for Camera Gamma and Display Gamma are at defaults in my screen capture, as well as the Red Balance and Blue Balance.

 

Your latest image and the other one with the star field to me look like your gamma is adjusted way too dark.  See my second attached screen capture that has both Camera Gamma and Display Gamma adjusted to be dark.  Note the strange appearance of false colours...very similar to your images.  I wonder if this is what you are seeing?  You should keep your Gamma at default for deep sky, or if you want higher sensitivity adjust the Camera Gamma to be brighter...I use around 75.  Do not use the Display Gamma, at least not until you are comfortable using the camera at default settings.  You only need to adjust the Gamma darker when you are viewing/imaging solar system objects and want more contrast in your image.

 

I hope I am being helpful.

 

Regards,

 

Jim T.

Attached Thumbnails

  • everything at default_resize.jpg
  • too much gamma_resize.jpg


#119 StarCurious

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Posted 03 June 2016 - 04:51 PM

Hi Jim,

 

Thanks for taking the time to help. I did have a focus problem.  I use Sharpcap beta 2.9 and generally I leave the Gain at 350, Image Controls: Gamma 75, Brightness 120 and leave the Display Gamma at default of 1.

 

Last night I went out again, managed to get Starsense centre calibration done with a cheap Orion Shorty Barlow lens (only) attached to the filter thread of the T adapter nose piece.  I forgot to take and send a picture to Astrometry.net to obtain the FOV and therefore the F/ ratio - I was only trying to get centre calibration done. I did test the Barlow/Camera combination during the day and noticed the FOV of view was about half without the Barlow.

 

I then replaced the Barlow lens with an Antares 0.5x focal reducer.  I achieved focus with a Bahtinov mask.  Previously I noticed that adding a Lumicon #29 Dark Red filter required outward movement of the focuser to retain focus.  Because of this experience, I did the same with the Bahtinov mask after adding the 642 BP filter to the front. I achieved focus with a Bahtinov mask with a pixel error of less than +/- 1. I could infer the seeing was good.

 

Here's the results, all at F/3.7, Gain 350, Cropped to decrease file size, no darks, otherwise untouched:

 

M51 12Sx20, Digital Gain 2

M51. F3.7.642BP DG2 12S_Stack_20.Cropped.png

 

M51 12Sx50, Digital Gain 2

M51.F3.7. 642BP DG2 12S_Stack_50.Cropped.png


Edited by StarCurious, 03 June 2016 - 04:58 PM.


#120 StarCurious

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Posted 03 June 2016 - 04:54 PM

M101 12Sx50, Digital Gain 2

M101.F3.7. 642BP DG2 12S_Stack_50.Cropped.png

 

M63 6Sx100, Digital Gain 4

M63.F3.7. 642BP DG4 6S_Stack_100.Cropped.png


 



#121 StarCurious

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Posted 03 June 2016 - 04:55 PM

M106 12Sx50, Digital Gain 4

M106.F3.7. 642BP DG4 12S_Stack_20.Cropped.png



#122 StarCurious

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Posted 03 June 2016 - 05:02 PM

I then tried edge on Needle Galaxy NGC 4424, but I was unable to get (enough alignment stars for) Sharpcap to Live Stack.

 

Thanks,

Joseph



#123 jimthompson

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Posted 03 June 2016 - 10:14 PM

Hi Joseph,

 

Hmmm, those captures don't look very good.  Are you able to get a sharp focus just using the same setup (scope+focal reducer+filter+camera) during the day time?

 

Regards,

 

Jim T.



#124 StarCurious

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Posted 03 June 2016 - 11:57 PM

Hi Jim,

I don't understand. Do you think my problem is still focusing? Can you please explain steps for the test during day time?

Thanks,
Joseph

#125 jimthompson

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Posted 04 June 2016 - 12:17 AM

I am not sure Joseph.  It looks like focusing but it may be something else.  During the day time manually aim your telescope with camera and filter at a target like a tree or building reasonably far away, a few hundred feet anyway.  Then set your gain to minimum and adjust your exposure time to get an image.  You should be able to achieve a good focus just by eye.  If you can get a nice sharp focus looking at a terrestrial target during the day, it will eliminate any funny business with the camera and filter.  By the way, is there a thumbscrew on your focuser that allows you to lock it after you are focused?  Maybe your focuser is moving after your focus is set using the mask?

 

Regards,

 

Jim T.




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