72 replies to this topic

[sanford12]

There's some good info in this thread.

[michaelrasbury]

I really appreciate these new updates. However, I feel like there is more color noise in my results after shooting flats. I assume this is just my imagination would have nothing realistically to do with flats?

[moosestang]

I really appreciate these new updates. However, I feel like there is more color noise in my results after shooting flats. I assume this is just my imagination would have nothing realistically to do with flats?

I thought so too, when I used the white tee shirt method.  In fact, it made anything using the LP filter look horrible. 

 

I tried again using the blankwhitescreen.com method with my tablet as the light source, and got better results.  I did have to hold the tablet a bit above the seestar.  Setting it right on the seestar caused the tablet screen to go blank after a few seconds, which I didn't notice until my third or so attempt.

[Tinek]

In my case I've tried with another phone and I got horrible banding. I suspected it's because of pwm dimming causing flickering of the screen - humans don't see it but camera sensor did. Then I've done white printer paper (2 layers) on top of the seestar first and then phone with white screen on top of that - that finally seems to have fixed it for me. Now, that also shows that telescope doesn't actually check if the flats are correct or not and it being accepted doesn't mean it's actually done well. It seems to be only checking if the brightness is within norms when taking flats.

[buramu]

It doesn’t seem possible to remove/disable the user-generated flats, right?

[redbaron12]

I think I'll just sit on the fence for a while and see how this pans out.  I'm happy with what I'm getting now and I DON'T need to fix something that ain't broken.

[buramu]

Meh, it seems there's no way (that I can find) to do a factory restore of the Seestar, so no way at all to remove the flats - and also no way to tell if your home-made flats are any good. 

 

I kind wish I hadn't tried making them now 

[CA Curtis 17]

 A couple of points about Seestar Flats:

 

1.  It appears that the Seestar has been using Flats long before we were given the option to do them ourselves.  If you take a look at the text below the "Flat Shoot" function it says "If the built-in flat-field cannot meet the calibration requirements, you can control Seestar lens at the uniform light source and click the Shoot button, and the system will automatically take and save the flat-field file"   

 

      My bold above.  So I take this to mean that the Seestar App has had a factory flat field included either from the very beginning or after one of the earlier updates.  Would make sense that they developed a generalized flat master and included it in the App without mentioning it.

 

2.  As some have noticed, there is no way to turn off the flat field so it would appear that it will always apply the latest flat frame.  And, it is not clear whether the App reverts back to the factory flat upon reset, but it might very well do so.

 

3.  Given the likelihood that the Seestar now uses our latest flat field all the time one needs to be careful in making sure that the flat field is done correctly.  With all due respect to the Space Koala's, I think it is possible to take a poor flat and not have the Seestar reject it.  My suspicion is that the Seestar fails the flat frame if the light intensity is to high or too low and doesn't actually run an algorithm to determine a quality level for the flat frame.  I have an idea how to test this and will report back if I find anything definitive.  I can think of multiple ways folks new to flat frames could mess it up but still be within the light level window the Seestar wants.

 

4.  There is no reason to repeat flats nightly.  Flat must be re-done when something changes in the optical path which typically means the camera is rotated or replaced with a different camera, a filter is inserted or removed from the optical path, a focal reducer or field flattener is added or removed or a dew shield is removed or added.  The only one which applies to the Seestar is the dew shield.  So if you use a dew shield take the flat with it in place.  If you remove the dew shield take a new flat without the dew shield.

 

I will check with the ZWO tech on the Seestar forum on several of these, but I expect that these are correct as stated.

 

Regards,

Curtis

[roelb]

So their must be flats for:

1. no using the in-built 

2. using the in-built IR filter

???

[buramu]

So their must be flats for:

1. no using the in-built 

2. using the in-built IR filter

???

 

You can hear the filters rotate (the familiar click-click) when the flats are being created.

[buramu]

ZWO support has now confirmed that it is not possible to remove user-made flats. Doing a factory reset of the Seestar will only restore the software, but not the factory flats data (so the user flats will remain active).

[Airstrike]

i did  mine late afternoon just before sunset so the weakest part of a bright day pointed away from the sun to a clear blue sky , placed a piece of A4 over the lens and now have perfect flats 

 

before i used my phone with a white screen app and had loads of weirdness in the subs but with natural light filtered with a sheet of A4 i think you get far better quality personally

Edited by Airstrike, 26 May 2025 - 08:44 AM.

[CA Curtis 17]

I posted a series of questions on the ZWO Seestar Forum over the weekend about the Flat Frame function which came up while I was making a video on this subject.  Below are my questions and the responses in quotation marks.

 

"Please see our responses to each point below:

 

1. Was the Seestar using internal flats created at the factory before the user flat option became available?
Yes, Seestar had a built-in flat field calibration applied at the factory. This internal flat was automatically used in image calibration before we provided the option for users to create their own flats.

 

2. Were the same flat frames installed on every Seestar S50, or were they customized per unit?
The same flat-field data was installed on all Seestar S50 units at the time of production. It was not customized individually for each device.

 

3. If a user performs a factory reset, will the original factory flat be restored?
No, performing a factory reset does not affect the flat-field calibration data. The reset only restores system and application settings.

 

4. Does the flat algorithm use a fixed exposure/gain, or does it adjust based on the light intensity?
The flat capture process automatically calculates the appropriate exposure and gain values based on the average brightness of the light source. It is not fixed and will adapt for optimal results.

 

5. Can a flat capture fail for any reason other than the brightness level being too high or too low?

Yes, a flat may also fail if the light source is not uniform.  "

 

 

 

My comments after ZWO's response.

 

1.  I highly suspected this and it is now confirmed.  So, if you do not see a big difference in images after making your own flats this is likely why.

 

2.  Again, this is what I expected.  

 

3.  I guess Buramu got his info in post #61 from the forum as well.  So new flats simply over write the exiting flat file.  So make sure you do the flat properly.

 

4.  In the video I made I already came to the conclusion that the Seestar had the ability to measure the light level and adjust the exposure, but I wasn't sure whether it adjusted the gain or not.  This was obvious when I measured the time it took to complete the flat frame with 1) a single sheet of paper - 11sec; 2) a stack of 5 sheets of paper - 24sec.  (times vary with the amount of ambient light, of course)  Clearly the Seestar was measuring the light level and adjusting the exposure.  Since I also found that the flat would fail if there was just too little ambient light it is also clear that the exposure range the Seestar uses is limited.  This should not be a surprise and is exactly what we have to do when taking flats on our other astrophotography rigs.  We adjust the exposure and gain so that we get the peak(s) of the curve to be close to the middle of the histogram range.  Seestar obviously does the same.

 

5.  Again, exactly as I expected and only asked to confirm.  Some folks seem to think that if the Flat succeeds everything must be ok, but I wanted to dispel that thinking.  I tell people to make sure that the sheet of paper is flat against the face of the Seestar with no gaps around the edges to let stray light in.  And, if you use a cotton cloth or t-shirt to make sure that there are no wrinkles in the light path.  While this all is obvious to a seasoned astrophotographer, there are lots of rookies with no prior experience and understanding of these methods who have purchased their own Seestars. 

 

The one question I forgot to ask was how many flats does it take to create the master flat.  They should take many more than 5 since the exposure time is short enough to do so, but I am just guessing.

 

Per Airstrike in #62 above, I also prefer to take flats in twilight skies and had questions about whether we could truly trust the tablet white screen approach. 

 

Best Regards,

Curtis

[gus1989]

Total rookie here, and I don't even have the S50 yet.

If you plan on using a dew shield, would you do the flats with it on or off or does it even matter.

 

Thanks

[Airstrike]

Total rookie here, and I don't even have the S50 yet.

If you plan on using a dew shield, would you do the flats with it on or off or does it even matter.

 

Thanks

off , i waited till just before sunset aimed the scope to the zenith ( directly above ) to nice clear blue sky placed a sheet of white A4 paper over the lens and fired the flats off perfectly , and is far better using natural light as phones and pads placed ontop can cause weirdness and it will show in your subs 

[appiantiqua]

If you take a flat you have to do this in the more accurate configuration :so put the dew/light shield on your Seestar before you do the flats

[CA Curtis 17]

off , i waited till just before sunset aimed the scope to the zenith ( directly above ) to nice clear blue sky placed a sheet of white A4 paper over the lens and fired the flats off perfectly , and is far better using natural light as phones and pads placed ontop can cause weirdness and it will show in your subs 

Sorry but this is not correct.  Flats are always done EXACTLY as the light frames (or images) are taken.  If you use a filter, flats are taken with the filter - the Seestar Flat routine automatically takes flats with each of the two internal filters.  And if you use a dew shield the flat must be taken with the dew shield on.

 

Flats are there to correct 3 things:

 

1.  Dust on the internal filters and cover plate on the imaging sensor

 

2.  Photo response non-uniformity, i.e. unequal response of the individual pixels to the photons striking them

 

3.  And, most importantly, the gradient in the photon intensity across the imaging sensor caused by physical restrictions (light baffles or other restrictions including a dew shield) to the incoming photons.

 

Take flats with the dew shield on if that is how you intend to take the light frames at night.

 

Regards,

Curtis

[gus1989]

Thanks for the information. Just trying to collect as much information as possible before I get my telescope. 

[Airstrike]

Sorry but this is not correct.  Flats are always done EXACTLY as the light frames (or images) are taken.  If you use a filter, flats are taken with the filter - the Seestar Flat routine automatically takes flats with each of the two internal filters.  And if you use a dew shield the flat must be taken with the dew shield on.

 

Flats are there to correct 3 things:

 

1.  Dust on the internal filters and cover plate on the imaging sensor

 

2.  Photo response non-uniformity, i.e. unequal response of the individual pixels to the photons striking them

 

3.  And, most importantly, the gradient in the photon intensity across the imaging sensor caused by physical restrictions (light baffles or other restrictions including a dew shield) to the incoming photons.

 

Take flats with the dew shield on if that is how you intend to take the light frames at night.

 

Regards,

Curtis

hmmmm ??  how do you take flats when using a big scope like a reflector ..ect. with a custom foam sleeve that wont support the weight of a light panel if you are supposed to leave the dew shield on ?

 

also i thought the SS takes and adjust the light measurment based on the lighting conditions at the time automatically as is stored in the unit and applys the flats to all sessions you do until you want a fresh batch of flats again , i could be wrong but i dont think it makes any difference with built in filters as the SS is mostly automatic , all a human has to do really is make sure the lighting is even flat and not too dim or harsh

and then the app either excepts or refuses the flat making so you have to adjust again so its correct

i tried with light panel / phone but i got loads of uneven weirdness in my subs so i re-did them again with with flat A4 white paper without any light leaks and now my subs are perfect 

il try your method leaving the dew shield on when i next renew my flats

 

il stand corrected if im wrong but its worked fine for me so far 

Edited by Airstrike, 17 June 2025 - 05:33 PM.

[CA Curtis 17]

hmmmm ??  how do you take flats when using a big scope like a reflector ..ect. with a custom foam sleeve that wont support the weight of a light panel if you are supposed to leave the dew shield on ?

 

also i thought the SS takes and adjust the light measurment based on the lighting conditions at the time automatically as is stored in the unit and applys the flats to all sessions you do until you want a fresh batch of flats again , i could be wrong but i dont think it makes any difference with built in filters as the SS is mostly automatic , all a human has to do really is make sure the lighting is even flat and not too dim or harsh

and then the app either excepts or refuses the flat making so you have to adjust again so its correct

i tried with light panel / phone but i got loads of uneven weirdness in my subs so i re-did them again with with flat A4 white paper without any light leaks and now my subs are perfect 

il try your method leaving the dew shield on when i next renew my flats

 

il stand corrected if im wrong but its worked fine for me so far 

One wouldn't use a light panel in that situation, but t-shirt method instead.  I have used t-shirts on both my 14" and 11" SCT with flexible dew shields without any issue.  Believe what you want, but those new to the hobby and learning about flat fields for the first time deserve to know what the astrophotographers know.

 

Indeed, the Seestar does adjust both the exposure and gain (just like regular astrophotographers do) to center the response of the sensor in the histogram, which we don't see with the Seestar, but do see when we do this ourselves on all other non-Smart scopes.  And, yes, so long as the ambient light is not too bright or too weak, the Seestar can make the adjustment for a successful flat frame.

 

Back to the dew shield.  Keep in mind that depending upon the length of the dew shield you use, there may not be a great deal of difference between the flat with it on and with it off.  Since we cannot see the flats themselves, we have to look at the sub-frame like you mentioned and determine if there are any visible artifacts or not.  If everything looks ok to you with flats taken with the dew shield off then, by all means, continue to do that.  But, the OP asked about the "correct" method for taking flats and, as any experienced astrophotographer will tell you, you take the flats with the exact same physical setup as you do for the light frames.

 

Best Regards,

Curtis

[Airstrike]

One wouldn't use a light panel in that situation, but t-shirt method instead.  I have used t-shirts on both my 14" and 11" SCT with flexible dew shields without any issue.  Believe what you want, but those new to the hobby and learning about flat fields for the first time deserve to know what the astrophotographers know.

 

Indeed, the Seestar does adjust both the exposure and gain (just like regular astrophotographers do) to center the response of the sensor in the histogram, which we don't see with the Seestar, but do see when we do this ourselves on all other non-Smart scopes.  And, yes, so long as the ambient light is not too bright or too weak, the Seestar can make the adjustment for a successful flat frame.

 

Back to the dew shield.  Keep in mind that depending upon the length of the dew shield you use, there may not be a great deal of difference between the flat with it on and with it off.  Since we cannot see the flats themselves, we have to look at the sub-frame like you mentioned and determine if there are any visible artifacts or not.  If everything looks ok to you with flats taken with the dew shield off then, by all means, continue to do that.  But, the OP asked about the "correct" method for taking flats and, as any experienced astrophotographer will tell you, you take the flats with the exact same physical setup as you do for the light frames.

 

Best Regards,

Curtis

 

thats fair enough i get what you are saying , heres a couple of my images using just a sheet of A4 paper for flats doing them just after sunrise , same focal length same focus yada yada , obviously not on my seestar but my main rig , im not a pro by any means but just a happy astro snapper

Attached Thumbnails

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[CA Curtis 17]

Really nice images!

[Airstrike]

Really nice images!

many thanks bud , very kind btw love your rig , looks epic