120mm vs 150mm aperture for White Light High Res?

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MalVeauX
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120mm vs 150mm aperture for White Light High Res?

Post by MalVeauX » Sun May 14, 2017 6:00 pm

Hello,

I mainly image in HA, and I have a smaller aperture white light setup with baader solar film.

I recently picked up an used baader solar continuum filter and I have a 120mm achromat and a 150mm SCT. I'm looking to pick up a new baader solar film filter for the front, full aperture, and will be using a baader UV/IR cutter too. But I'm curious which would be best for high resolution and magnification with this: the 120mm achromat or the 150mm SCT? I know theoretically the 150mm aperture should be higher resolution. But I'm curious how the central obstruction plays into things and whether the 120mm would produce a similar enough scale for it to be very close.

I ask because it would be easier for me to outfit my 120mm refractor to white light because my 120mm refractor is also my HA scope (with my Quark). It would be nice to be able to simply change out the filters and Quark and image between white light and HA without changing scopes so that I don't have to do anything extra on my mount etc. Just makes it simple.

But if the 150mm SCT would be significantly better for this, I would just deal with changing scopes out between imaging and all that. That's the context here at least. If it's close enough to not matter much, I'd rather use my refractor simply due to not changing scopes during images so I can do whitelight and HA from the same setup basically for a nice comparison.

Thoughts?

Very best,

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Re: 120mm vs 150mm aperture for White Light High Res?

Post by marktownley » Sun May 14, 2017 7:33 pm

I think you will get best results from the 120 overall most of the time, seeing is the governor, and contrast is always slightly lower with SCTs... Couple of times a year it will be best with the 150...
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Re: 120mm vs 150mm aperture for White Light High Res?

Post by MalVeauX » Sun May 14, 2017 10:02 pm

Thanks,

That's what I'm thinking. Just wanted to see if anyone would argue for the 150mm SCT instead, having higher potential resolution.

Ultimately I think the simplicity of simply swapping filters on the same scope where I'm able to go from whitelight to HA on one scope already pointed at the sun will be a more common practice than swapping scopes completely on the mount each time.

Very best,

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Re: 120mm vs 150mm aperture for White Light High Res?

Post by GreatAttractor » Tue May 16, 2017 7:04 pm

My 2 cents: after doing WL for a few years (and after watching lots if images on forums and Astrobin) I concluded that the resolution I'm interested in (for sunspot/granulation time-lapses) comes with at least 180 mm/7 " of aperture (like my former Mak 180, http://astrob.in/full/23205/D/). Granulation definition out of ~150 mm is just too low for my wishes (of course I still admire good-seeing material, like the WL pics from Alexandra's TEC140). My personal preference would be a compact ~10" scope (an SCT, TAL250K), but the daytime seeing is indeed problematic. Until I can move permanently to Canaries or South California mountains, I'm not pursuing this.

That said, smaller resolution WL time-lapses can be satisfying too (like these from a Mak 127: http://astrob.in/104814/0/, http://astrob.in/full/105926/0/).
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Stackistry — an open-source cross-platform image stacker
ImPPG — stack post-processing and animation alignment
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SW Mak-Cass 127, ATM Hα scope (D=90 mm, LS50 etalon), Lunt LS50THa, ATM SSM, ATM Newt 300/1500 mm, PGR Chameleon 3 mono (ICX445)


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Re: 120mm vs 150mm aperture for White Light High Res?

Post by MalVeauX » Sun May 28, 2017 4:36 pm

Update:

Rigged the 120mm with the white light stuff. And first light.

Celestron Omni XLT 120 (F8.3)
Full aperture Baader Solar FIlm Filter
Baader Solar Continuum Filter (found a used one for $50)
GSO ED 3x Barlow (to get me to F30 for sampling with pixel size)
ASI174MM

Image

Image

First Light (noted, I can see convection cells and faculae fairly well):

Image

Image

+++++++++++++

I'm now thinking of adding Ca-k to this setup, for a three wavelength imaging platform (656.28nm, 540nm, 393nm)

Very best,

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Re: 120mm vs 150mm aperture for White Light High Res?

Post by Montana » Sun May 28, 2017 6:28 pm

Very nice white light image :hamster: :bow
Alexandra

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Re: 120mm vs 150mm aperture for White Light High Res?

Post by marktownley » Sun May 28, 2017 9:10 pm

Good stuff!
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