Trouble with Flats

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Baskevo
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Trouble with Flats

#1

Post by Baskevo »


Hey everyone,

So I set up APT last night and used the flats plan, which auto-selects the exposure time. But even before last night, I have been having trouble with my flats looking fine in my DSLR (between 1/2 and 3/4 of the way to the right on the histogram, and they look white), and showing up dark in pixinsight (histogram is below 1/3 in Pixinsight).

I took some flats last night with APT, and the histogram was about half way. This is what I'm seeing in Pixinsight of my flats shot with my Canon DSLR t7i:

Unstretched, 800 ISO:
Screen Shot 2019-10-01 at 5.10.54 PM.png
Same image, stretched:
Screen Shot 2019-10-01 at 5.11.19 PM.png
Here's what it looks in photoshop:
Screen Shot 2019-10-01 at 5.14.17 PM.png
Here's what I'm guessing... my exposure time is too short, so I need to turn down the brightness on my iPad to get a higher exposure time. Is that right?
Do I have to take flats right after I image, or could I take them right now and stack it with my images last night? I still have my camera hooked up to my telescope from last night...

Thanks!
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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fatboy1271
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Re: Trouble with Flats

#2

Post by fatboy1271 »


Good luck... My "Are My Flats Failing Me>" post is 3 or 4 pages long. I'm using NINA now and it seems to be functioning well with its Flat Wizard, but I'm still at a loss as to what I'm really looking at :|

fat
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
EPs: Stock Celestron 9mm and 24mm / Celestron Omni 32mm (I love this one!) / Celestron X-Cel LX 3x Barlow (I think 2X would have been smarter...)
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Re: Trouble with Flats

#3

Post by Baskevo »


thanks, Fat.

Yeah I was reading your post, that's where I got the idea that maybe my exposures were too short (they were at 1/6th of a second). but I wonder why it was coming up in pixinsight darker than in photoshop, my DSLR, and APT... that would explain why my flats haven't been working, but I'm curious why it's like that.
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Trouble with Flats

#4

Post by fatboy1271 »


I'm right there with ya!!!
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
EPs: Stock Celestron 9mm and 24mm / Celestron Omni 32mm (I love this one!) / Celestron X-Cel LX 3x Barlow (I think 2X would have been smarter...)
Support Staff (Loved Ones!): CeCe, Ro, and Geno
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Re: Trouble with Flats

#5

Post by Baskevo »


Haha I guess I'll give NINA a try. Thanks fat!
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Trouble with Flats

#6

Post by fatboy1271 »


I love it, minus when it randomly shuts down my Canon. Thankfully it doesn't do that during Sequences though. It's free and their support on Discord is awesome! Live chatting "in the field" rules 🤘
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
EPs: Stock Celestron 9mm and 24mm / Celestron Omni 32mm (I love this one!) / Celestron X-Cel LX 3x Barlow (I think 2X would have been smarter...)
Support Staff (Loved Ones!): CeCe, Ro, and Geno
Let's Go Pens!!!
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Re: Trouble with Flats

#7

Post by Baskevo »


Oh nice! Live chatting would be a huge bonus. I will give it a try! I was blown away by APT the other night... So much easier than a intervalometer! lol
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Trouble with Flats

#8

Post by fatboy1271 »


Haha. Glad you had success with APT. For whatever reason I just didn't get it...
OTAs: Explore Scientific ED80 Essential Edition / The Little Guy (Celestron 90SLT)
Mount: Celestron Advanced VX
Gear: Canon 70D / Hutech LPS-D1-48 / ES 2" Field Flattener / QHY PoleMaster / Celestron GPS / ZWO ASI120MC / Orion 50mm Guide Scope / ZWO EAF
Software: CPWI / PHD2 / N.I.N.A / Stellarium/StellariumScope/Remote Control / PI / RegiStax 6 / AutoStakkert!2 / PIPP | Retired? BackyardEOS Premium
EPs: Stock Celestron 9mm and 24mm / Celestron Omni 32mm (I love this one!) / Celestron X-Cel LX 3x Barlow (I think 2X would have been smarter...)
Support Staff (Loved Ones!): CeCe, Ro, and Geno
Let's Go Pens!!!
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Re: Trouble with Flats

#9

Post by Baskevo »


Jeez, man, flats are a pain in the ***...
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Trouble with Flats

#10

Post by yobbo89 »


Baskevo wrote: Wed Oct 02, 2019 12:17 am Do I have to take flats right after I image, or could I take them right now and stack it with my images last night? I still have my camera hooked up to my telescope from last night...

Thanks!
yes you should be taking flats every night you image per every filter especially if you are using a mono setup or an lp filter,this keeps you at the focus point of your light frames and the crucial one is getting the evil dust bunnies (motes) out of the lights in stacking which can move around from time to time in the imaging train over the course of different imaging sessions.

If you have a rather clean imaging train and not so such much noticeable dust motes ,then taking flats on different nights will be ok given that you are focused well and if vignetting is just your main concern.
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

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Re: Trouble with Flats

#11

Post by Baskevo »


yobbo89 wrote: Mon Oct 07, 2019 5:48 am
yes you should be taking flats every night you image per every filter especially if you are using a mono setup or an lp filter,this keeps you at the focus point of your light frames and the crucial one is getting the evil dust bunnies (motes) out of the lights in stacking which can move around from time to time in the imaging train over the course of different imaging sessions.

If you have a rather clean imaging train and not so such much noticeable dust motes ,then taking flats on different nights will be ok given that you are focused well and if vignetting is just your main concern.
Thanks for responding Yobbo. That's good to know. Unfortunately, I had figured this out the hard way, and now have to deal with some angry dust bunnies present in 2 great nights of imaging :(
I have quite a few dust motes in my imaging train... but I'm still trying to figure out how to get good flats. When I try to do it in AV mode, my flats look bright enough on my DSLR and in photoshop, but are too dark in pixinsight, which is probably why they weren't working... I tried decreasing the brightness on the iPad app that I'm using, but it was still too dark in PI.
If I do it at a 2.5" manual exposure, with my histogram in the middle, and even off to the right, I'm still seeing dust motes in my stacked images. I have a new set of lights and flats from last night's session, taken with a white, semi-transparent trash bag and my iPad. Hopefully those work... They look fine in PI, just very blue (I'm assuming from my LP filter).

I have 2 questions tho:
1) If I am using a light pollution filter, and I only used a light pollution filter, I only need to take flats with the light pollution filter on, correct?
2) If I image 2 seperate targets at the exact same ISO and exposure, do I have to take 2 sets of calibration frames for both sets of light frames? or can I just take one set of 30 darks, 30 bias, and 30 flats, and use that one 1 set on both stacks?
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Trouble with Flats

#12

Post by yobbo89 »


Baskevo wrote: Mon Oct 07, 2019 7:37 am
yobbo89 wrote: Mon Oct 07, 2019 5:48 am


I have 2 questions tho:
1) If I am using a light pollution filter, and I only used a light pollution filter, I only need to take flats with the light pollution filter on, correct?
2) If I image 2 seperate targets at the exact same ISO and exposure, do I have to take 2 sets of calibration frames for both sets of light frames? or can I just take one set of 30 darks, 30 bias, and 30 flats, and use that one 1 set on both stacks?
(q 1)
yep,take the flats with everything in that camera imaging train as the lights you took,even make sure you keep the camera in the same orientation in the scope.

(q 2) 1 set used for both is fine, i typically use a set for 1 year then re do the calibration frames as the camera chip ages,my flat frames are regularly updated,only when dust motes a present, my vignetting stays the same which is very little.

since you are using a dslr and can't adjust the temperature then you might need to take darks every night as temperature introduces dark current and the variance of temperature from night to night may change and having the darks not match the lights will cause a lot of trouble .

you should be recording the temperature on each session then doing your darks and making a library per temperature recording , if the camera is at that temperature again at a given night then you can go find for say the darks at 20 deg in your library and use them again.

edit:i don't quoting a quote works to well on the forums?,maybe i did something wrong.
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

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Re: Trouble with Flats

#13

Post by Baskevo »


yobbo89 wrote: Mon Oct 07, 2019 8:24 am
(q 1)
yep,take the flats with everything in that camera imaging train as the lights you took,even make sure you keep the camera in the same orientation in the scope.

(q 2) 1 set used for both is fine, i typically use a set for 1 year then re do the calibration frames as the camera chip ages,my flat frames are regularly updated,only when dust motes a present, my vignetting stays the same which is very little.

since you are using a dslr and can't adjust the temperature then you might need to take darks every night as temperature introduces dark current and the variance of temperature from night to night may change and having the darks not match the lights will cause a lot of trouble .

you should be recording the temperature on each session then doing your darks and making a library per temperature recording , if the camera is at that temperature again at a given night then you can go find for say the darks at 20 deg in your library and use them again.

edit:i don't quoting a quote works to well on the forums?,maybe i did something wrong.
Awesome thank you for answering that for me Yobbo!

I will start recording the temperature on my darks and begin building up my dark library :) I don't mind taking calibration frames every night, I basically just take my flats and bias as I'm tearing down and putting stuff away, then I place my telescope with my camera on my desk in my room, turn on the air conditioner to match the temp. outside, and let it run while I'm sleeping.

Now I just have to get my darks down!

How do you get calibration frames at a dark site? I have heard of people taking darks on the way home, but how would they do flats at a place where a bright light would be intrusive? Would you just take it when you get home and be careful not to change the position of the camera/focus?
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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Re: Trouble with Flats

#14

Post by yobbo89 »


I would use a dark black hood over the light box if you're out on site
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

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Re: Trouble with Flats

#15

Post by Baskevo »


Great idea lol Thanks again Yobbo! I appreciate it. Clear skies to you!
-James W.

Telescope: Explore Scientific 80mm FCD100 Triplet APO Refractor
Mount: EQ6-R Pro
Cameras: ZWO ASI1600mm Pro (Cooled) | Canon DSLR EOS T7i
Auto-guiding: ZWO ASI120mm-Mini + Astromania 50mm Guidescope

Filters: ZWO 31mm Ha/Oiii/Sii 7nm + LRGB | Orion 2" Skyglow Filter
Accessories: Explore Scientific 2" Field Flattener, ZWO EFW 8 Position
Software: APT, SharpCap Pro, PHD2, CPWI | PixInsight, DeepSkyStacker, Photoshop

Flickr: https://www.flickr.com/gp/186194203@N06/18B629
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