Sun Saturday 27 November 2021

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ffellah
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Sun Saturday 27 November 2021

Post by ffellah »

Hello all: I am experimenting with the new CaH filter and the Evostar 72mm stopped down to 35mm. Yesterday was sunny but very windy, with wind gusts up to 35mph. I had to hold on to the equipment ! I tried the full disk with different cameras. Today we have snow showers, so no imaging.

Franco
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114002 Flea 3 3.2 Mp color.jpg
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121310 GH3 9.1 color c.jpg
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Re: Sun Saturday 27 November 2021

Post by EGRAY_OBSERVATORY »

Thank you Franco for sharing your experiments and of the gear.
Certainly show the capability of imaging through the H-Line and not surprised at the need to stopped-down to half-aperture.

Well done

Terry


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Re: Sun Saturday 27 November 2021

Post by ffellah »

Thank you, Terry. This CaH filter seems easy to use and works with pretty much all my equipment.

Franco


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Re: Sun Saturday 27 November 2021

Post by EGRAY_OBSERVATORY »

Indeed Franco and I could consider getting one too, but the Lunt CaK does enough of the business (when I can use it though)... :?

Cheers
Terry


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Re: Sun Saturday 27 November 2021

Post by eroel »

Franco:
Beautiful FD´s and setup, looks like you experimented a lot and getting what you want.
Best regards.
Eric.


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Re: Sun Saturday 27 November 2021

Post by DeepSolar64 »

Franco,
I seriously considered getting an Evostar 72ED a couple of summers back. I ended up getting the Astro-Tech AT72EDII instead.

What is exactly the purpose of stopping down an already small scope that much? It it to attain the F30 focal length for the Quark to work properly? It seems a barlow or PowerMate could do that without losing aperture and therefore resolving power. BUT I do understand that it being a short wavelength resolution is higher for a given aperture than it would be at a longer wavelength and that short wavelengths are also more prone to atmospheric seeing conditions. I intend to use my AT72EDII in the future for CaK, CaH or K-band imaging and/or visual use with a monitor. Would I have to stop my 72 down for visual use with a monitor?

Your CaH images look really good for just 35mm of aperture!!

James


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Re: Sun Saturday 27 November 2021

Post by ffellah »

Thank you Eric and James. James: stopping down the scope is to reach the focal length to make the Quark work properly and, I believe, is also used to achieve more contrast. I will leave any other explanations to Mark T., who is more of a hardware expert.

Franco
Last edited by ffellah on Sun Dec 05, 2021 4:16 pm, edited 1 time in total.


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Re: Sun Saturday 27 November 2021

Post by Montana »

Terrific images Franco, I feel the GH3 image looks better (more contrast) but this could be processing?

James a Barlow would come after the Quark, therefore the input f ratio would not be changed, you need to change the telescope f ratio. It is the input that is critical for the Quark to work well.

:bow :hamster:

Alexandra


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Re: Sun Saturday 27 November 2021

Post by Ivan »

Franco, great shots in such a strong wind.

Ivan


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Re: Sun Saturday 27 November 2021

Post by ffellah »

Thank you very much, Alexandra and Ivan, for your nice comments.

Franco


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Re: Sun Saturday 27 November 2021

Post by Carbon60 »

Great CaH FDs, Franco; nice and even.

Marty has a nice spreadsheet that enables focal ratio and pixel size to be matched at any given wavelength to achieve the best sampling. It would be worth checking this out with your combinations to calculate the best ‘iris’ diameter for your scope for your cameras in CaH, not forgetting the internal Barlow. This is what I do for every combination I own (scopes, cameras) for Ha, CaK and 540nm and use the information to create a crib sheet of best matched combinations.

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Re: Sun Saturday 27 November 2021

Post by ffellah »

Thank you, Stu, for your feedback and tip. I will ask Marty if he is willing to share the information.

Franco


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Re: Sun Saturday 27 November 2021

Post by rigel123 »

Those look great Franco!


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Re: Sun Saturday 27 November 2021

Post by ffellah »

Thanks a lot Warren

Franco


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Re: Sun Saturday 27 November 2021

Post by arnedanielsen »

Beautiful capture and setup, Franco!

Best regards,
Arne


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Re: Sun Saturday 27 November 2021

Post by ffellah »

Thank you, Arne. I always admire your full disks, perfectly executed.

Franco


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Re: Sun Saturday 27 November 2021

Post by marktownley »

Great disks Franco!

Regards image sampling scale; using the setup as above with your large chipped FLIR with a 2x barlow nose screwed onto the camera will tease more detail out yet, even at 35mm. 35mm in CaK is equivalent to 60mm in Ha. Use the auto histogram function in firecapture and set at 90% will get you more detail in the plage areas.

DeepSolar64 wrote: Mon Nov 29, 2021 2:59 am What is exactly the purpose of stopping down an already small scope that much? It it to attain the F30 focal length for the Quark to work properly? It seems a barlow or PowerMate could do that without losing aperture and therefore resolving power. BUT I do understand that it being a short wavelength resolution is higher for a given aperture than it would be at a longer wavelength and that short wavelengths are also more prone to atmospheric seeing conditions. I intend to use my AT72EDII in the future for CaK, CaH or K-band imaging and/or visual use with a monitor. Would I have to stop my 72 down for visual use with a monitor?
Hi James. Stopping down a refractor has a number of benefit at CaH and CaK wavelengths:

The longer the focal ratio a filter like this sees the more contrast the filter will have. The shorter the f-ratio the wider the bandpass the filter will operate on, wider bandpass = less contrast, so longer focal length is better as the filter then operates closer to it's specified bandpass.

Refractors show spherical aberration this far down in the blue. SA is a radial aberration of a lens, becoming worse the further from the centre towards the periphery. Stopping down uses the centre portion of the lens where there is little SA. SA manifests itself in a softness to the image, the focus does not snap sharp at one point, this also manifests as a loss of contrast.

Would you have to stop down your 72 for visual work? I think for visual it will depend on how bright the image is at the eyepiece. It will be 4x brighter at 72mm than 35mm, this might be significant in your case. Having used the CaH filter myself visually, choice of eyepiece is very important, with different ep coatings transmitting more / less light at 396nm. I found TV plossls the best choice out of my ep collection.

Mark


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Re: Sun Saturday 27 November 2021

Post by DeepSolar64 »

Thanks for the detailed explanation on refractors concerning short wavelength viewing, Mark. I do have a 20mm TV plossl.

Are ED/apochromats any better for short wavelength work than achromats?

James


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Re: Sun Saturday 27 November 2021

Post by ffellah »

Thank you, Mark, for your positive feedback and the detailed explanation of the advantages of stopping down the scope in the Calcium lines. As I am learning more about this filter, it is becoming even more interesting.

Franco


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