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Author Topic: Flat analysis  (Read 554 times)

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Offline johnadams

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Flat analysis
« on: 19:50:58, 08 November, 2017 »
Hi

Can anyone tell me if this flat looks normal.

Thanks

John
officina stellare veloce rh200 OTA
William optics 132 flt
Paramount MX
QSI 683 mono
QSI 690 mono
loadstar
astrodon filters
baader lrgb
ZWO Optical ASI120 color
lakeside focus controller
Maxim/Theskyx
pulsar 2.2m dome
warm room

Offline Einari

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Re: Flat analysis
« Reply #1 on: 20:18:13, 08 November, 2017 »
Not quite as you have something blocking (bottom) in light path.
Flat should be symmetrical.
Can you tell about your imaging setup ?
Tapio

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

Offline johnadams

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Re: Flat analysis
« Reply #2 on: 20:25:06, 08 November, 2017 »
Hi

Using a Veloce Rh200 with QSI 683 wsg . All flats from LRGB filters look like this. Average ADU is 30,000 . This is  a master flat from 30 frames stacked with Pixinsight.
officina stellare veloce rh200 OTA
William optics 132 flt
Paramount MX
QSI 683 mono
QSI 690 mono
loadstar
astrodon filters
baader lrgb
ZWO Optical ASI120 color
lakeside focus controller
Maxim/Theskyx
pulsar 2.2m dome
warm room

Offline Eccoskies

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Re: Flat analysis
« Reply #3 on: 20:57:13, 08 November, 2017 »
Are you using an OAG John?

Mark
Mark
53N 1W

Pair of binos and a beer

Offline johnadams

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Re: Flat analysis
« Reply #4 on: 21:03:06, 08 November, 2017 »
Hi

Yes I am but I am sure its not the prism casting a shadow.
officina stellare veloce rh200 OTA
William optics 132 flt
Paramount MX
QSI 683 mono
QSI 690 mono
loadstar
astrodon filters
baader lrgb
ZWO Optical ASI120 color
lakeside focus controller
Maxim/Theskyx
pulsar 2.2m dome
warm room

Offline Eccoskies

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Re: Flat analysis
« Reply #5 on: 21:14:43, 08 November, 2017 »
John,

I have a similar shadow in my flats which is the prism. I do have it as far away from the light path as I can without affecting performance. My problem is the focal reducer causes the shadow from the prism.
Have you got any FR too?

Mark
Mark
53N 1W

Pair of binos and a beer

Offline Einari

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Re: Flat analysis
« Reply #6 on: 05:02:11, 09 November, 2017 »
Veloce Rh200 being f/3 don't need reducer but there is a rear correcting element near focuser. I don't know if that's a problem with oag.
Tapio

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

Offline Nomis Elfactem

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Re: Flat analysis
« Reply #7 on: 10:50:27, 09 November, 2017 »
Have to say it looks like the OAG prism blocking to me.... if you look at the top corners you can clearly see that the chip is bigger than the light path and the vignetting is quite severe.... out of interest, how long was the exposure and what did you use to illuminate the flat-field ?

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 chris.bailey

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Re: Flat analysis
« Reply #8 on: 11:06:05, 09 November, 2017 »
I have to say that with that focal length/sensor combo I would expect the OAG prism shadow to be more of a square intrusion rather than for the full length of one side.

Stretched flats are always dangerous as they tend to magnify what can be very small differences in ADU levels. What does the flat contour plot look like if you run this through the Flat Contour Plot script in PI?

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

Online Roger B

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Re: Flat analysis
« Reply #9 on: 17:49:45, 09 November, 2017 »
Do your light frames have this ?

Roger
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 johnadams

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Re: Flat analysis
« Reply #10 on: 20:58:09, 09 November, 2017 »
Hi

The exposure of the flat is around 8 seconds. Heres a image of the Contour plot but no igea what to look for.
officina stellare veloce rh200 OTA
William optics 132 flt
Paramount MX
QSI 683 mono
QSI 690 mono
loadstar
astrodon filters
baader lrgb
ZWO Optical ASI120 color
lakeside focus controller
Maxim/Theskyx
pulsar 2.2m dome
warm room

Offline chris.bailey

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Re: Flat analysis
« Reply #11 on: 21:20:22, 09 November, 2017 »
That looks OK (fish) to me. The light falloff in the corners is very normal and I suspect the darkness along part of the bottom is then the shadow from the OAG or just the normal readout  from the CCD.
Do the calibrated lights work ok?

Chris

ps I find 30,000 ADU for the 8300 chip to be a little on the hot side and limit mine to under 20,000.
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 johnadams

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Re: Flat analysis
« Reply #12 on: 08:25:28, 10 November, 2017 »
Hi

This is a 5 min sub after calibration . To me the master flat hasn't remove the shadows along the bottom.
officina stellare veloce rh200 OTA
William optics 132 flt
Paramount MX
QSI 683 mono
QSI 690 mono
loadstar
astrodon filters
baader lrgb
ZWO Optical ASI120 color
lakeside focus controller
Maxim/Theskyx
pulsar 2.2m dome
warm room

Offline chris.bailey

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Re: Flat analysis
« Reply #13 on: 10:13:34, 10 November, 2017 »
John

It hasn't done a BAD job of it though! I would be happy with that!

I did a bit of analysis with by Atik 383 a while back after having similar problems with flats not performing 100% and came to the conclusion that the 8300 chip looses a little bit of linearity past about 22,000 ADU. After that I dialled back my flats to have a peak of 20m000 ADU and they worked a lot better. Might be worth a try.

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 johnadams

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Re: Flat analysis
« Reply #14 on: 11:02:28, 10 November, 2017 »
Hi Chris

Thanks for your help. Whats your opinion on this 8 x 2 mins RGB.

Thanks
John
officina stellare veloce rh200 OTA
William optics 132 flt
Paramount MX
QSI 683 mono
QSI 690 mono
loadstar
astrodon filters
baader lrgb
ZWO Optical ASI120 color
lakeside focus controller
Maxim/Theskyx
pulsar 2.2m dome
warm room

 

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