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order in rotation of imaging filters in filter wheel

astrophotography beginner
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#1 manusfisch

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Posted 11 February 2018 - 10:01 PM

I am getting ready to load a filter wheel with LRGB filters.   I intend to put an H Alpha narrowband filter and an OIII narrowband filter in the mix and an LPR.  I am still in"science fair project mode" and am looking to practice and get comfortable with this new process

 

My question is simple

 

Do I put the filter in sequence on the wheel with an LRGB sequence followed by the narrowband filters in same color sequence  Hb, OIII, Ha, SII

 

Or do I group them as to general wavelength. 

 

I know there has got to be a sequence,  i would like to start with simple star clusters and then nebulae in widefield to keep it simpler.  however there has got to be some standard or preferred methods for sequencing these filters next to each other for efficiency.  



#2 ZL4PLM

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Posted 11 February 2018 - 10:03 PM

I put mine in an order I can remember 

 

LRGB SHO 

 

I have SGP set up with the names and slots so L = Luminance

 

So I don't have to think about it :)

 

Cheers

 

Simon 



#3 baron555

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Posted 11 February 2018 - 10:07 PM

LRGB HOS



#4 Ken Sturrock

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Posted 11 February 2018 - 10:09 PM

It's not important. As long as you can remember the order.

 

Traditionally, filters were usually RGB, then RGBL after L became a thing. Now LRGB is common. I'd say Baron's suggestion: LRGBHOS is most typical for the 7 usual filters. It's what I use too.



#5 manusfisch

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Posted 11 February 2018 - 10:18 PM

LRGBHOS sounds like a plan.  I have 8 slots now I can get busy.  



#6 ZL4PLM

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Posted 11 February 2018 - 10:19 PM

good to remember which slots empty so you can do direct thru as well :)



#7 manusfisch

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Posted 11 February 2018 - 10:38 PM

good to remember which slots empty so you can do direct thru as well smile.gif

should the empty slot have a clear focus filter???



#8 Alex McConahay

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Posted 11 February 2018 - 10:51 PM

>>>> should the empty slot have a clear focus filter???

 

Your Lum filter should be doing this job. 

 

If you have enough slots, a "dark" has some uses, and is pretty much a necessity if you do not have a shutter. 

 

As for the order--it really does not matter. When taking LRGB, one does not necessarily image in the order of L, then R, then G, then B anyway. Catch your Reds early in the evening (when the object is low), your blues and luminances when higher, and Luminances especially when highest. So........there is not exact link between order of use and preferred order in the wheel. Besides, no filter takes more than a few seconds to turn all the way around between filters, and you do not change filters all that often. So little time is wasted waiting for a filter wheel to position itself. 

 

Alex 



#9 ZL4PLM

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Posted 12 February 2018 - 12:42 AM

>>>> should the empty slot have a clear focus filter???

 

Your Lum filter should be doing this job. 

 

If you have enough slots, a "dark" has some uses, and is pretty much a necessity if you do not have a shutter. 

 

As for the order--it really does not matter. When taking LRGB, one does not necessarily image in the order of L, then R, then G, then B anyway. Catch your Reds early in the evening (when the object is low), your blues and luminances when higher, and Luminances especially when highest. So........there is not exact link between order of use and preferred order in the wheel. Besides, no filter takes more than a few seconds to turn all the way around between filters, and you do not change filters all that often. So little time is wasted waiting for a filter wheel to position itself. 

 

Alex 

what he said :)



#10 freestar8n

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Posted 12 February 2018 - 02:22 AM

If you are using filter offsets and if you want quickest time between exposures - there is a small benefit putting the filters in order of increasing or decreasing focus offset - depending on which way backlash goes for your focuser.

 

So if L has an offset of 0 and B is 10 and G is 20 and R is 30 you might do LBGR so you can quickly change filter and focus in order - and then when you get to R you wrap around back to L and unwind backlash.

 

This is a minor optimization but it's something to consider - especially if your focuser has a lot of backlash like mine.

 

If your filter wheel can go both directions there is less of a win in terms of the filter position - but you would still want to go in a consistent direction of focus offsets.

 

If you don't have filter offsets I would go by something easy to remember - like the suggestions above.  I would always have L or C as 1.

 

Frank



#11 jdupton

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Posted 12 February 2018 - 10:52 AM

manusfisch,

 

   In addition to what others have suggested, you might consider putting the L filter in the first (default) slot. Many (most? / all?) filter wheels will initialize themselves to a default position when they power up. Having the filter with the highest overall transmission in that slot can solve a lot of head-scratching in the dark when you are in a hurry and can easily make mistakes.

 

   Confession Time: My own stumbling on this was with my filter wheel. I have two interchangeable filter carousels that I can use. One has an LRGBHaOiiiHb set of filters while the other has my Sloan set of UGRIZ filters. When using the LRGB set, i got lucky and had the L first. I never had problems. When using the Sloan set, I shouldn't admit to the number of times I wasted many minutes of set up time and couldn't find a bright enough star to focus on when getting ready for an imaging session. I always forgot about the G (UV band) filter being in the first / default position. Not may bright stars show up well in the UV bandpass region. I reordered the Sloan carousel to be GRIZU so that I wouldn't (repeatedly) make that mistake again.

 

   Anyway, always starting off with a high transmission filter like L in the first position can save some confusion. Other than that, as others have mentioned, put them in any order you can remember easily or any order that makes sense to you. (BTW, I like Frank's suggestion to order them by offsets. Once they are ordered and labeled for what they are in your software, names really don't matter.)

 

 

John


Edited by jdupton, 12 February 2018 - 11:09 AM.


#12 Pauls72

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Posted 12 February 2018 - 11:06 AM

ASCOM Simulator and my QHY ASCOM drivers let you put the name in for each position.

 

FilterWheel.jpg



#13 manusfisch

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Posted 12 February 2018 - 07:32 PM

"Confession Time: My own stumbling on this was with my filter wheel. I have two interchangeable filter carousels that I can use. One has an LRGBHaOiiiHb set of filters while the other has my Sloan set of UGRIZ filters. When using the LRGB set, i got lucky and had the L first. I never had problems. When using the Sloan set, I shouldn't admit to the number of times I wasted many minutes of set up time and couldn't find a bright enough star to focus"

Confession is good for the soul and an amazing teacher.  These are all great points and will lead to a better understanding of how to get a decent image.  Thanks for all the comments and suggestions. ,  from a pilgim.     Clear Skies, Tom



#14 Lead_Weight

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Posted 13 February 2018 - 10:41 AM

The software I tend to use works through the filters in the order they're installed. So if I have L R G B HA OIII SII as my order, and I'm shooting LRGB, it does them in order top to bottom. But it just occurred to me that If I start imaging about 40° above the horizon, I should probably start with RGB, and do L last as the scope gets up near the meridian (depending on imaging session length) since the seeing will be best near the meridian. I could alternatively shoot L R G B, L R G B, L R G B in succession, but I think the room for error with the filter wheel moving every frame increases. So I like to do all of one color at a time.

 

How does everyone else shoot? One color at a time, or do you rotate a new filter every frame?


Edited by Lead_Weight, 13 February 2018 - 10:42 AM.


#15 bobzeq25

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Posted 13 February 2018 - 11:47 AM

The software I tend to use works through the filters in the order they're installed. So if I have L R G B HA OIII SII as my order, and I'm shooting LRGB, it does them in order top to bottom. But it just occurred to me that If I start imaging about 40° above the horizon, I should probably start with RGB, and do L last as the scope gets up near the meridian (depending on imaging session length) since the seeing will be best near the meridian. I could alternatively shoot L R G B, L R G B, L R G B in succession, but I think the room for error with the filter wheel moving every frame increases. So I like to do all of one color at a time.

 

How does everyone else shoot? One color at a time, or do you rotate a new filter every frame?

A few people rotate every frame, so that they get an image even if clouds roll in.  You'd better have filters that focus exactly the same if you want to do that.

 

More imagers consider atmospheric refraction, shoot all the reds when the target is lower, green and blue nearer the max altitude the target gets to.  L is less critical.

 

I think the most important thing for order is that you can remember it easily, without assistance.  There's a lot to be said for having L in the default position.


Edited by bobzeq25, 13 February 2018 - 11:49 AM.


#16 Alex McConahay

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Posted 13 February 2018 - 12:07 PM

>>>>>> The software I tend to use works through the filters in the order they're installed.

 

What software is that?

 

Alex



#17 Lead_Weight

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Posted 13 February 2018 - 04:34 PM

>>>>>> The software I tend to use works through the filters in the order they're installed.

 

What software is that?

 

Alex

AstroImager for the Mac. I can omit filters, or run a sequence, but it’s always in order 1-8. If there’s a way to reorder them, I’m not aware of it. I’m in the process of getting EKOS running though, so that might change with the new software.




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