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Dielectric Diagonals

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37 replies to this topic

#26 turtle86

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Posted 30 May 2021 - 03:53 PM

One complaint I had with the BBHS diagonal is the coatings. On mine they were not that robust. I tried to clean a spot off and it was a coating flaw and by cleaning it I totally made it worse (ruined the diagonal mirror). A lot of this was my fault and lesson learned but still stings a bit, all because I didn't initially recognize that the coating failed

 

Sorry to hear that but I'm sure a lot of us would've done the same thing. I've been intrigued by the BBHS but at that price point the QC should be better IMHO.  


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#27 Tyson M

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Posted 30 May 2021 - 03:59 PM

Now when I want to clean my Vernonscope I just run it under water and use a bulb blower for the water spot removal and air dry, open ended/uncapped

 

By I digress....



#28 alexvh

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Posted 30 May 2021 - 05:50 PM

The baader bbhs click lock has dialectric coatings too... isn’t this a problem?

#29 Mazerski

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Posted 30 May 2021 - 06:56 PM

chemisted has written a bit about how for viewing globulars with NV you don’t want dielectric coatings.



#30 chemisted

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Posted 30 May 2021 - 07:28 PM

The baader bbhs click lock has dialectric coatings too... isn’t this a problem?

The coatings on the BBHS are transparent out to 2 microns so there is no problem.  They are just there to protect the silver from oxidation, etc. and do not interfere with reflectance.



#31 alexvh

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Posted 30 May 2021 - 09:18 PM

Thanks guys!

#32 GOLGO13

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Posted 25 July 2021 - 11:08 AM

I will try again, but when I compared my 1.25 badder prism to my 2 inch Televue enhanced and an old TeleVue diagonal (both not dielectric) I didn't notice a difference in globular.

Anyone do similar comparisons?

#33 ButterFly

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Posted 25 July 2021 - 10:52 PM

My 45 degee prism is the only diagonal I have that lets me directly connect my filter wheel, rather than using it as a mere filter as shown here.  The 41 Pan is quite shy of focus on all my scopes when the wheel is used as a mere filter, so I need some backfocus for that.  Getting rid of the nosepiece, or eyepiece holder, of that diagonal lets my other eyepieces come to focus, 21 Ethos included, with lots of room to spare.  I can swap using the eyepiece holder of the diagonal.

 

I have mostly been using 67/41 with my 80mm so far.  I haven't felt the need to use much higher powers with a widefield instrument.  I have only used the 67PP with the wheel as a mere filter with my 120mm so far, for convenience and fun.  Pretty much the same as straight through, with the caveat that the prism as well may have anti-reflective coatings tuned to visual like my objectives may.



#34 joelin

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Posted 28 July 2021 - 10:46 AM

Does anyone know if the Baader 32mm T2 prism diagonal (commonly used for binoviewers due to the short light path) is good for NV?

 

there’s an extensive article outlining all baader diagonals here and it’s not clear the spectral response of the T2: https://www.baader-p...s_t_2_and_2.pdf

I wonder if I need to get the BBHS no matter what as that’s the only thing advertised to have the widest spectral response 


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#35 Jeff Morgan

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Posted 28 July 2021 - 02:43 PM

Does anyone know if the Baader 32mm T2 prism diagonal (commonly used for binoviewers due to the short light path) is good for NV?

 

there’s an extensive article outlining all baader diagonals here and it’s not clear the spectral response of the T2: https://www.baader-p...s_t_2_and_2.pdf

I wonder if I need to get the BBHS no matter what as that’s the only thing advertised to have the widest spectral response 

If you are doing anything prime focus, shorter light path is always a virtue.

 

Check the clear aperture on the prism though. 20+ would be the target.


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#36 ButterFly

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Posted 28 July 2021 - 03:06 PM

Does anyone know if the Baader 32mm T2 prism diagonal (commonly used for binoviewers due to the short light path) is good for NV?

 

there’s an extensive article outlining all baader diagonals here and it’s not clear the spectral response of the T2: https://www.baader-p...s_t_2_and_2.pdf

I wonder if I need to get the BBHS no matter what as that’s the only thing advertised to have the widest spectral response 

Send an email.  Baader either knows, or can find out.



#37 joelin

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Posted 28 July 2021 - 05:06 PM

If you are doing anything prime focus, shorter light path is always a virtue.

Check the clear aperture on the prism though. 20+ would be the target.


Would 2” eyepieces and afocal affect the desired clear aperture?

#38 Jeff Morgan

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Posted 28 July 2021 - 10:42 PM

Would 2” eyepieces and afocal affect the desired clear aperture?

 

With afocal the host eyepiece determines the focus position.

 

And for illumination, the field stop of that eyepiece is determinant. A T2 prism with a 46mm field stop eyepiece (like the 55 Plossl) is probably not a happy marriage.

 

OTOH, you don't have a back focus issue with the 55 Plossl, no reason to use a T2 prism here. Quite the opposite, and extension tube is required! 


Edited by Jeff Morgan, 28 July 2021 - 10:44 PM.

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