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Goodby to Band-Shift Blues!

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#1 chemisted

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Posted 10 January 2022 - 07:58 PM

Gavster's recent post on band-shift has induced me to try something that has been percolating in the back of my mind since I received my Baader High Speed 6.5nm H-alpha filter.  This evening I used an afocal setup that had my 45mm Plossl with this filter attached to the end and inserted into a 50mm Nikon lens set to f/2.0.  This yields the equivalent of a 30mm optic operating at f/1.2.  Luckily the sky was very clear, transparent and calm although there is a first quarter moon shining too.  The news is that all nebulae were bright from the middle to the edge of the FOV!  I moved the Heart and Soul complex from one side to the other with no dimming.  Same for the California.  In fact I had a very nice view of it at one extreme and the Tadpole/Flaming Star complex at the other.  But, of course, the 'star' of the show was Orion.  A magnificent Barnard's Loop and Angel Fish display was joined by the Rosette - all in the same FOV.

 

That's the scoop.  I would write some more but I would rather go back outside and drink in some more of these views.  If you are wondering I do not have the 3nm High Speed filter to try with this lens configuration.  The 6.5 is clearly a winner.


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#2 Deadlake

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Posted 11 January 2022 - 03:14 AM

I have an H-Alpha Antilia 3 nm and Baader 6.5 nm f2 inbound. I’ll take a look once clouds and supply chain problems align.


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#3 Mort H

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Posted 11 January 2022 - 12:10 PM

+1 on Ed's favorable view of the f/2 6.5nm filter, I've had mine since September and when located as Ed's using it, it's often been my favorite.  I've used it down to f/1.4 but more so with my 200mm f/2.

 

I have the f/2 3.5nm also and it's good too.  I've appreaciated having both for my sky conditions, but if I could only keep one I've have to say it would be the 6.5nm.

 

Since November I've relocated my filter on the afocal camera lens setup to between the EP and NV device, therefore deviating from Ed's approach.  I like it there because I enjoy using a filter wheel a lot.  (Note:  My EP has sufficient eye relief to avoid vignetting.)  Because there is no light cone at that location (any given point in the FOV is made only from parallel light rays not from a cone), I don't use the f/2 filters there, I use the non-f/2 ones.  This filter location has the slight advantage of giving the absolute maximum H-alpha brightness in the center of the FOV, can't do any better than that.  To the negative side, the edge of the FOV is made from light rays all hitting the filter at a steep 20 degree angle (half of 40 degrees), so the band shift is in full effect there with the 3.5nm filter!  Since it's really only at the outer edge of the FOV, it doesn't bug me and I really like the high-contrast views anywhere in the center of the FOV with the 3.5nm.  I also think it's kind of cool to see the band shift.  So anyway the compromise is worth it to me (though the same compromise might bug a different astronomer or imager...I don't do imaging).

 

Ed I think if you got the f/2 3.5nm you wouldn't be disappointed (at least I wasn't), but I wouldn't trade in the 6.5nm for it!


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#4 John Vogt

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Posted 14 January 2022 - 09:07 AM

Hi Ed,

 

Is your Baader filter 2" or 1.25"? If 2" what kind of adapter are you using to mate the eyepiece/filter

to the lens?

 

Thanks!

John



#5 chemisted

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Posted 14 January 2022 - 09:45 AM

I have the 1.25" filter. It has worked well in all the applications I have tried thus far so I don't think I will get the 2" ever.

#6 bobo99

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Posted 27 January 2022 - 08:30 AM

I have an H-Alpha Antilia 3 nm and Baader 6.5 nm f2 inbound. I’ll take a look once clouds and supply chain problems align.

Any updates on this comparison ?



#7 Deadlake

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Posted 27 January 2022 - 10:51 AM

Any updates on this comparison ?


Not with the cloud cover…..
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