H-alpha 31 august, 7 inch Intes, reflections and a BF30.

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bart1805
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H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by bart1805 »

The good thing about a slow sun is that it is a good time for experiments! Doublestacking two PST etalons behind the 7 inch Intes went reasonably well, but there still were a lot of reflections. The Circular Polarizer does the job it is supposed to do: not a lot more reflections than when using just one PST etalon. So back to square 1. Single stack and what can I do against the reflections. Tried a lot of combinations but here is what worked best:
Baader D-Erf
Intes M703
1,25 inch Baader 35nm
PST etalon
2 inch Beloptik UV/IR cut on KG3
Lunt B1200, blue glass removed.

The biggest difference was changing the 2 inch Baader 35nm for a 1,25 inch, mounted just before the etalon. Here is the image, 2% out of 5.000 images, exposure time was 2ms. Camera used was the ASI290MM. Autostakkert, IMPPG and PS helped a lot.

Image11_32_28_l3_ap2577_imppg2PS_defzw by bart moors, on Flickr

About the circular polarizer between the two PST etalons:
Mounting it backwards gives a tiny bit amount more transmission. Changing the orientation of the CP seems to have no effect.

And I got the BF30 working: viewtopic.php?f=4&t=25332&hilit=bf30. It really needs the Beloptic UV/IR cut on KG3 and the B+W Redfilter 630(091) 48 mm MRC F-Pro. Tilting the BF is easy and you can clearly see the image go from a blurry mess to really clear. Transmission is really low, had to use an exposure time of about 20ms to get an image I could compare with the image posted above.
CS! Bart.


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by pedro »

This is a fantastic image Bart, glad you got the BF30 working


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by bart1805 »

Thanks Pedro! Yes I am glad it works. But the transmission is really low compared to the Lunt BF1200. So have to think about it if it is worth to experiment more. And how to make good use of it.


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by Astrophil »

Bart, that's a great image and interesting experiment. I look forward to your final determination and results.
Good luck,

Phil


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by xn44 »

Good work, Bart!


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by Carbon60 »

Hi Bart,

I assume the D-ERF is tilted a little bit to reduce the reflections from this surface? Similarly with the Baader 35nm? Actually, can the Baader filter be fitted on the camera nose-piece instead? I add a 656nm/7nm FWHM filter (to boost contrast) on my optical train (250mm RCT), but I place the filter at the camera.

Just a thought.

Stu.


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by bart1805 »

Carbon60 wrote: Sun Sep 01, 2019 11:48 am I assume the D-ERF is tilted a little bit to reduce the reflections from this surface? Similarly with the Baader 35nm? Actually, can the Baader filter be fitted on the camera nose-piece instead? I add a 656nm/7nm FWHM filter (to boost contrast) on my optical train (250mm RCT), but I place the filter at the camera.
Thanks Pepe and Phil!
Stu, I originally used a 2 inch 35nm filter to protect the etalon. Even with the D-Erf it is stil getting quite warm at minus 200mm. So yes, the filter can be mounted on the nosepiece of the camera, but I want to be careful with the etalons.
I suspect that the 2 inch filter reflects more of the light back to the corrector than the 1,25 inch does. The D-Erf is tilted a bit, at the moment the 35nm (and the Beloptik filter) are not tilted, have to put in on the "to do" list.
I suspect the contrast wil be a bit better when I can use the full 7 inch of the Intes. The D-erf is 160 mm, so the linear obstruction is bigger than when I would use a 180 mm.


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by ffellah »

A great image, Bart, well done !

Franco


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by MAURITS »

Very nice capture Bart.


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by marktownley »

Its a great outcome Bart!


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by MapleRidge »

Superb image Bart, and I appreciate the discussion on the ERF/in line Ha filter options too :bow

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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by bart1805 »

Thanks guys! Really curious about the outcome when using a full aperture Erf. Think I have to bite that bullit.


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by yltansg »

Beautiful capture, Bart. The Proms look great on the fine disk details.

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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by christian viladrich »

Hello Bart,
This is a quite good image. Getting rid of these reflections is quite tricky. Keep us posted !
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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by bart1805 »

christian viladrich wrote: Sun Sep 15, 2019 2:12 pm Hello Bart,
This is a quite good image. Getting rid of these reflections is quite tricky. Keep us posted !
Christian
Thanks Christian (and Alfred).
The season is almost over here. Hope to start next season with an Aries 8 inch Triband Erf, to be used with the Intes 703 and the 8 inch f/8 Newton for which I will start making the mirror next month.


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Re: H-alpha 31 august, 7 inch Intes, reflections and a BF30.

Post by eroel »

Bart:
Beautiful result.
Thanks for sharing your experiments.
Best wishes,
Eric.


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