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Choosing a Ha filter

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#1 Galaxyhunter

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Posted 12 November 2019 - 08:44 PM

I started looking at Ha filters.  There a lot of "nm" to choose from.  I have an ST10.  The filter wheel sits in front of the guide chip.  Is there a range of "nm" filters I should stay away from?



#2 Der_Pit

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Posted 13 November 2019 - 08:39 AM

Unless the guide chip is utterly sensitive, stay away from filters below 5nm.  Even 5 might be difficult.  If you have a good mount you can go for longer guide exposures, but I'd try to borrow a filter first for a test...


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#3 ezwheels

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Posted 13 November 2019 - 11:04 AM

I don't know what an ST10 is, but can you move the OAG to the telescope side of the FW? I would guess an ASI290mm-mini could probably shoot through a 5nm filter. I have both but I keep the OAG prism in front of the filter wheel, so I have not tried it. The 290 is super super sensitive.



#4 WebFoot

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Posted 13 November 2019 - 12:26 PM

Guiding through a NB filter can be very challenging, absent (i) a very good mount, and/or (ii) a very short focal length.



#5 Galaxyhunter

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Posted 13 November 2019 - 01:06 PM

I don't know what an ST10 is, but can you move the OAG to the telescope side of the FW? I would guess an ASI290mm-mini could probably shoot through a 5nm filter. I have both but I keep the OAG prism in front of the filter wheel, so I have not tried it. The 290 is super super sensitive.

ST10 is an SBIG selfguiding  camera,  the OAG is fixed.



#6 Galaxyhunter

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Posted 13 November 2019 - 01:12 PM

Guiding through a NB filter can be very challenging, absent (i) a very good mount, and/or (ii) a very short focal length.

I'm using an 18" f4.45.  I have been able with some success guide on a 14th mag star.  My comfort zone for guiding is a 12th mag. I have seen Ha in the 12nm range.  I wonder if something like that would work?



#7 WebFoot

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Posted 13 November 2019 - 01:24 PM

I'm using an 18" f4.45.  I have been able with some success guide on a 14th mag star.  My comfort zone for guiding is a 12th mag. I have seen Ha in the 12nm range.  I wonder if something like that would work?

What mount do you have?  2000mm focal length isn't particularly long (nor, of course, is it short), but the small pixels of the ST-10 (a very fine camera, BTW; I've used one extensively, and loved it, other than the small--by today's standards--imaging chip) add a level of challenge.  If your mount can do, say, 5-minute unguided images, having a guide exposure of 5 seconds shouldn't be a problem.  But if your mount needs all the help it can get, you could have a challenge even guiding through a 7nm filter.  I know of no 12nm Ha filter, and I wonder (i) about the quality of such a filter, and (ii) about how useful it would be.



#8 Galaxyhunter

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Posted 13 November 2019 - 07:05 PM

What mount do you have?  2000mm focal length isn't particularly long (nor, of course, is it short), but the small pixels of the ST-10 (a very fine camera, BTW; I've used one extensively, and loved it, other than the small--by today's standards--imaging chip) add a level of challenge.  If your mount can do, say, 5-minute unguided images, having a guide exposure of 5 seconds shouldn't be a problem.  But if your mount needs all the help it can get, you could have a challenge even guiding through a 7nm filter.  I know of no 12nm Ha filter, and I wonder (i) about the quality of such a filter, and (ii) about how useful it would be.

MY mount is an ATM.   

No chance of a 5 minute unguided image.    I use an AO8 unit.  I can run it at 10 hz per second on a 12th mag star w/o any problem. If I have to use a 14th mag, I need to slow it down to 5hz.



#9 WebFoot

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Posted 13 November 2019 - 07:33 PM

MY mount is an ATM.  

No chance of a 5 minute unguided image.    I use an AO8 unit.  I can run it at 10 hz per second on a 12th mag star w/o any problem. If I have to use a 14th mag, I need to slow it down to 5hz.

Good luck guiding with a mag 14 star through an Ha filter!  Heck, you'd be very fortunate to get 1hz out of a mag 10 star through an Ha filter.

 

Enjoy!



#10 ezwheels

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Posted 13 November 2019 - 09:25 PM

Really, if there is room in the optical train and you can send guide pulses from PHD via a separate OAG in front of the wheel, you would be a much happier camper. I really do not understand the design of having an OAG behind the FW. 5nm is sort of my wide band range and my next filters will be 3nm. Probably not a chance of guiding through a 3nm Sii filter with 3-5s exposures unless I am guiding on Vega or Alnitak. 



#11 Galaxyhunter

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Posted 13 November 2019 - 10:16 PM

Good luck guiding with a mag 14 star through an Ha filter!  Heck, you'd be very fortunate to get 1hz out of a mag 10 star through an Ha filter.

 

Enjoy!

I had no intention of trying to do a 14th mag.frown.gif  I can wait for my new camera,  I thought I might just "Test the Water" before  hand.


Edited by Galaxyhunter, 13 November 2019 - 10:26 PM.


#12 Galaxyhunter

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Posted 13 November 2019 - 10:24 PM

Really, if there is room in the optical train and you can send guide pulses from PHD via a separate OAG in front of the wheel, you would be a much happier camper. I really do not understand the design of having an OAG behind the FW. 5nm is sort of my wide band range and my next filters will be 3nm. Probably not a chance of guiding through a 3nm Sii filter with 3-5s exposures unless I am guiding on Vega or Alnitak. 

This camera design is probably 20 years old.  The current cameras do have the guider in front of the filters.  One of those are on my retirement list. bounce.gif

I fiddled with PHD before I got my ST2000.  I will never waste another second on PHD.



#13 ezwheels

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Posted 13 November 2019 - 10:50 PM

Huh, I guess we had bad ideas 20 years ago as well. If you switch filters, then wouldn't you have to adjust guide exposures for that was well? Good luck with whatever you find that works.

 

Clear skies



#14 the Elf

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Posted 14 November 2019 - 03:59 AM

You can probably put an OAG in front of the filter wheel and use this for guiding and ignore the chip behind the filter. Guiding thru Ha is two problems in one: the stars are brighter in the image und guiding is worse due to bad SNR. If you are serious about imaging you will probably not complain about the $$$ for an OAG and a guide camera. Even a low priced one in front of the filter will guide better than a very sensitive one behind.



#15 Galaxyhunter

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Posted 14 November 2019 - 12:22 PM

Huh, I guess we had bad ideas 20 years ago as well. If you switch filters, then wouldn't you have to adjust guide exposures for that was well? Good luck with whatever you find that works.

 

Clear skies

20 years ago,  there wasn't much in the way of cameras.  Back then, selfguiding camera was ahead of the times. Now a days, they move the guide chip in front of the filters. Lesson learned. 



#16 ezwheels

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Posted 14 November 2019 - 06:01 PM

I definitely wasn't criticizing you, I was only talking about the camera config. I hope you get it all worked out, because NB imaging is very much worth the time and effort if you can.



#17 Galaxyhunter

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Posted 14 November 2019 - 06:33 PM

I definitely wasn't criticizing you, I was only talking about the camera config. I hope you get it all worked out, because NB imaging is very much worth the time and effort if you can.

Don't worry about it, I didn't take it that way. I have been imaging on & off for 25 years, all monochrome.  About time for new camera  equipment & try something different for retirement.




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