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Author Topic: Long Flats  (Read 1238 times)

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Offline Roger B

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Long Flats
« on: 12:32:16, 20 January, 2017 »
I have a Huion tracing panel for my flats.   Although this is a very good flat panel I have noticed in the past that after a while my pre-set exposures started to give off a higher ADU of 25k.     This become apparent when I noticed that every time I turned it on the brightness would go up a tad.    I assumed it was meant to turn on at the same level all the time,  well it does sort off but the change was very slight I didn't really notice.

any way to combat this I though the only way I can get the panel to light the same over and over was to just keep it at it's minimum brightness.

Today I run off the flats wizard in SGP and my longest flat is 109.13 seconds  ADU 25k.     Can these be too long or is it ok taking flats for this length of exposure...    This flat is a 1x1 7Nm Ha with the QSI & 583. 

On the triplet & 694 the SII is 99.98 & Ha 68.15..   

Thinking this could be the only way of my pre set exposures having the same ADU all the time

Rog
Scopes - TS65q, W/O 110 Triplet
Mount - EQ6 PRO via  Eqmod,  Rowan belt modded
Cameras - SX694, QSI583WSG,Lodestar Guidecam, GP-Cam, QHY5II.
TS 9mm OAG
Quantum 7x1.25 EFW, Baader LRGB,Ha,OIII,SII Filters 
Quark chromo

SGPro, Pixinsight.

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Offline Einari

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Re: Long Flats
« Reply #1 on: 12:40:54, 20 January, 2017 »
Weird - as I have same panel and my longest Ha flats have been about 15 secs. Now I don't remember did I make it dimmer.
Have 80mm triplet and same camera.
Tapio

Celestron C8, C9.25" & Hyperstar, iOptron CEM60-EC, TS 80 triplet,  Coronado PST, SXV-694,  ASI120MM/ASI174MC Cool

Offline Roger B

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Re: Long Flats
« Reply #2 on: 12:47:19, 20 January, 2017 »
On mine you keep your finger on the touch on/off button   repress for dimmer.    Plus it doesn't sit on top of the scope,  it's mounted to the obs wall & custom parked to that position.   

(If that makes a difference )

Rog
Scopes - TS65q, W/O 110 Triplet
Mount - EQ6 PRO via  Eqmod,  Rowan belt modded
Cameras - SX694, QSI583WSG,Lodestar Guidecam, GP-Cam, QHY5II.
TS 9mm OAG
Quantum 7x1.25 EFW, Baader LRGB,Ha,OIII,SII Filters 
Quark chromo

SGPro, Pixinsight.

************AND NO TIME TO USE IT************

Offline ChrisLX200

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Re: Long Flats
« Reply #3 on: 13:33:54, 20 January, 2017 »
I keep mine at it's lowest setting - and still need to add a couple sheets of paper in front. Like you, my longest flats tend to be around the 100 second mark.

ChrisH
Chris Heapy - current: 10-Micron GM2000HPS-II U/P, G11/Gemini, TV NP127is, Altair 8" RC, TV Genesis SDF, TV Pronto, SW Equinox 80ED, 10" LX200, 12" f/5.4 Newt, Vixen 90mm.
Atik 490EX, Atik EFW, Baader LRGB filters, Astrodon 3nM NB filters, Lodestar, QHY5L-II all-sky, Canon 70D and 350D
Whirley Obs., MPC Code Z89

Offline Roger B

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Re: Long Flats
« Reply #4 on: 13:52:58, 20 January, 2017 »
Good enough for me, If someone else is taking long flats.

Cheers Chris

Rog
Scopes - TS65q, W/O 110 Triplet
Mount - EQ6 PRO via  Eqmod,  Rowan belt modded
Cameras - SX694, QSI583WSG,Lodestar Guidecam, GP-Cam, QHY5II.
TS 9mm OAG
Quantum 7x1.25 EFW, Baader LRGB,Ha,OIII,SII Filters 
Quark chromo

SGPro, Pixinsight.

************AND NO TIME TO USE IT************

Offline chris.bailey

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Re: Long Flats
« Reply #5 on: 14:13:40, 20 January, 2017 »
My longest flats (3.5nmHa) are about 15 seconds. With LRGB I have to add a couple of sheets of paper even on the lowest setting.

With long flats, you do start to accumulate dark signal so you "should" calibrate the flats with corresponding darks. The 694 has pretty low dark current so you should be ok as the dark will approximate to a bias. The 583 would be a different prospect and would benefit from matched dark subtraction based on my experiences with the 383L

Chris
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 Roger B

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Re: Long Flats
« Reply #6 on: 14:17:33, 20 January, 2017 »
I'll keep that in mind Chris

Rog
Scopes - TS65q, W/O 110 Triplet
Mount - EQ6 PRO via  Eqmod,  Rowan belt modded
Cameras - SX694, QSI583WSG,Lodestar Guidecam, GP-Cam, QHY5II.
TS 9mm OAG
Quantum 7x1.25 EFW, Baader LRGB,Ha,OIII,SII Filters 
Quark chromo

SGPro, Pixinsight.

************AND NO TIME TO USE IT************

Offline Uplooker

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Re: Long Flats
« Reply #7 on: 18:39:05, 20 January, 2017 »
My longest flats (3.5nmHa) are about 15 seconds. With LRGB I have to add a couple of sheets of paper even on the lowest setting.

With long flats, you do start to accumulate dark signal so you "should" calibrate the flats with corresponding darks. The 694 has pretty low dark current so you should be ok as the dark will approximate to a bias. The 583 would be a different prospect and would benefit from matched dark subtraction based on my experiences with the 383L

Chris
Hi Chris,
Would you mind elaborating on the point you make about calibrating the "long" flats with darks?
Do you mean as well as taking darks to calibrate your lights you would then take darks the same length as the "long" flats. How you go about processing these / combining them with the light frames.
Caveat - I am not using Pixinsight


Sent from my iPhone using Tapatalk
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 chris.bailey

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Re: Long Flats
« Reply #8 on: 18:52:00, 20 January, 2017 »
Ian

I think in DSS they are referred to as FlatDarks and yes they are darks taken of the same duration as the flats. For short flats (a few seconds), a dark approximates to a bias as the dark component is small. With the modern Sony sensors I don't bother with darks for exposures up to 10 minutes and its questionable even at 20. With Kodak sensors you "need" darks for anything over about 30 seconds. If you need to take darks to calibrate your flats then all the usual good practice of matching temperature comes into play.

Chris
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

 

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