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Author Topic: Guide star to dim?  (Read 574 times)

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Offline clive

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Guide star to dim?
« on: 15:34:52, 30 October, 2017 »
If my guide star is to dim will my mount have trouble guideing last night i lost 6 15 minute subs two subs the stars were nice and round  so i dont think my polar alignment is out  last november i checked it it was ok   just done ballance it was to heavy east now its a little heavy east so thats done 

Offline Nomis Elfactem

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Re: Guide star to dim?
« Reply #1 on: 16:31:38, 30 October, 2017 »
When you say you "lost" the subs, what exactly do you mean Clive ?  Did you get images but the stars were trailed of you actually lost the subs i.e. the camera didn't download them ?

Also, what software are you using to guide with ?


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 chris.bailey

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Re: Guide star to dim?
« Reply #2 on: 17:13:15, 30 October, 2017 »

Guiding relies on being able to accurately determine where the centroid of the star is. As the signal decreases this becomes less accurate. It used to be a perceived wisdom to slightly defocus guide scopes to 'smear' the star a little but this is actually bad practice with modern guide setups. The ideal guide star will have plenty of signal but no saturated or near saturated pixels. This give the most accurate calculation of the centroid.

Low signal guide stars tend to oscillate giving oval stars on the imager or worse still the guide star will frequently be lost and regained.

Longish guide exposures will also be helpful to average out some of the shorter period seeing variations.

LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

Offline clive

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Re: Guide star to dim?
« Reply #3 on: 17:39:53, 30 October, 2017 »
hi chris and sim think chris got it right guide star was to dim think phd was set at one second exposures moon was bright sorry for saying i lost some of the subs i did 8 15 minute subs 4  with ha filter 4 s2 filter 2 of the subs were just about round stars the other subs had streaks to the left well i think   and my light polluton filter was loose i was useing sequence generater pro ill use 3 second guide star exposures next time when its clear ill check polar alignment to  cheers   


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