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Author Topic: Achieving good focus when imaging the sun  (Read 1300 times)

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Offline Uplooker

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Achieving good focus when imaging the sun
« on: 15:24:17, 01 April, 2014 »
Hi All,
Further to a post in another thread about achieving good focus when solar imaging, here is a pdf file that talks you through the use of the histogram. While this is not a panacea it is certainly another weapon in your arsenal when it comes to getting good / better focus. I have found it to be very useful.
It can be a bit tricky to get right as the way the document describes the process and the accompanying pictures seem to show that there is a large change in the “dip” when you move either side of focus – I have certainly not found this to be the case, the changes can be quite subtle.

This is not my work, I honestly cannot remember where I downloaded it from, but I am making it available here so that others may benefit.

Thanks should go to TonyUK for getting the file to size (below 500Kb) that allows me to upload it.

Ian
Ian

Scopes: SW 150P Newt, ST80, Celestron C8 XLT, TAL 100RS / PST Stage 2 Mod & BF10, SW 300PDS (soon to be on a Dob Mount)
Cameras: SPC900, QHY5, Canon 450D, DMK31AU03.AS
Mounts: NEQ6 powered by EQMod, EQ3-2

Offline Nomis Elfactem

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Re: Achieving good focus when imaging the sun
« Reply #1 on: 15:53:35, 01 April, 2014 »
Cheers Ian / Tony !

It's worth noting that this method will only work when imaging the full / near full disk as no such dip exists when imaging at longer focal lengths where the sun fills the full frame  ;)

S.
Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline Starlight

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Re: Achieving good focus when imaging the sun
« Reply #2 on: 22:37:03, 01 April, 2014 »
Ian et al
The original web site can be found here

http://www.hapb.net/Solar/histogram/histogram.html

Simon
sorry to contradict you but .....
If you include the edge of the sun when focusing at longer focal lengths (PST & 2xbarlow in my case) you can get the classic whale shape) as below

Don

ps as an aside I always take screen dumps of my settings so that I can see what works best
Celestron C9.25-S (XLT), HEQ5 Pro Synscan, Meade LXD75 6" F5 Newt, Meade DSI Colour, Panasonic DMC-FZ5, Starchaser 80 Guide Scope, QHY8, 28-70 Zoom Lens, 300mm Zoom Lens, 400mm Telephoto lens, DBK21 & DMK21, 8" F4 Newt, Sony DSC-HX50, Itorex semi-fish eye lens adapter, Coronado PST, ASI 120MM-S,

Offline Nomis Elfactem

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Re: Achieving good focus when imaging the sun
« Reply #3 on: 23:14:16, 01 April, 2014 »
Very good point Don - no need to apologise;  I stand corrected !

(btw I'm sure you already know - your example image histogram is slightly over exposed.... the histogram should ideally only come up two thirds of the way to the white point)  ;) :thumbup:

Taxi  :embarrass:
Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

Offline Starlight

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Re: Achieving good focus when imaging the sun
« Reply #4 on: 23:26:11, 01 April, 2014 »
Simon

Quote
I'm sure you already know

 :embarrass: ??

15 all !!

Don
Celestron C9.25-S (XLT), HEQ5 Pro Synscan, Meade LXD75 6" F5 Newt, Meade DSI Colour, Panasonic DMC-FZ5, Starchaser 80 Guide Scope, QHY8, 28-70 Zoom Lens, 300mm Zoom Lens, 400mm Telephoto lens, DBK21 & DMK21, 8" F4 Newt, Sony DSC-HX50, Itorex semi-fish eye lens adapter, Coronado PST, ASI 120MM-S,

Offline Nomis Elfactem

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Re: Achieving good focus when imaging the sun
« Reply #5 on: 23:42:02, 01 April, 2014 »
 :laugh:   :thumbup: :urock: :-*
Simon

Scopes: Astro-Tech AT-111EDT Triplet, TS65ED Quad, Orion ST80, Modded PST-90 Solar Scope, PST Cak (on loan)
Cameras: SXVF H694, Atik 16ic, Canon EOS 600d, DMK41, DMK21, QHY 5L-II (mono & colour)
Accessories: SX USB Filter Wheel, SX OAG, Baader LRGB Ha SI OII Filters, SharpSky Focuser
Mount: EQ6 (EQMOD), SW Star Adventurer, plus a lot (and I mean a lot) of other bits and pieces

 

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