I initially posted this where I should not have - within a post in another discussion. My apologies.
Below is a link to one image each of NGC 6888 (light, dark, flat, dark flat and bias). There are two things that I cannot figure out how they are showing up. First, there is a very large oval/circular artifact on the light frames - 30s subs). It also shows up on longer exposures. It does not show up on any calibration frames.
Second, there is a grid-like pattern on the lights and flats that I am not able to identify either. This pattern is present everywhere except where the above mentioned artifact is.
https://1drv.ms/u/s!AhE2Rt0-5SmlgXK04hZ ... I?e=LVfrX0
I used the flats capture in Sharpcap and it appears to be solid. I have never seen anything that was not removed through calibration with my DSLR so this is a new one for me. I appreciate any insight that can be shared.
Aaron
Strange "artifact" on light images
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BlackWikkett
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Re: Strange "artifact" on light images
Hi alinderbaum
I've looked at the data you provided.
Couple of questions:
1. FLat no t shirt.fit Is this a master flat created with the SharpCap flat tool?
2. DSS Stacked NGC 6888.fits Is this Stacked with all calibration frames included in your one drive link/
3. NGC 688 light frame.fits Is this a single light frame? Captured in SharpCap?
I stretched the flat frame you provided and couldn't find any hint of the weird oblong oval you have in the stacked image.
You can see some dust and an offset vignetting which could be image train or caused by the light source you used to illuminate your flat. There's no hint of the oblong pattern in the stacked image.
As an aside, you'll most like get bad results using one application to create calibration frames then use a different app to combine and stack. Best to use the same application to combine single exposures to create the calibration frames.
Look forward to your response
-Chris
I've looked at the data you provided.
Couple of questions:
1. FLat no t shirt.fit Is this a master flat created with the SharpCap flat tool?
2. DSS Stacked NGC 6888.fits Is this Stacked with all calibration frames included in your one drive link/
3. NGC 688 light frame.fits Is this a single light frame? Captured in SharpCap?
I stretched the flat frame you provided and couldn't find any hint of the weird oblong oval you have in the stacked image.
- Flat no t shirt-rs.png (132.39 KiB) Viewed 5187 times
As an aside, you'll most like get bad results using one application to create calibration frames then use a different app to combine and stack. Best to use the same application to combine single exposures to create the calibration frames.
Look forward to your response
-Chris
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BlackWikkett
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Re: Strange "artifact" on light images
Hi alinderbaum
Quick addendum, as I was closing the imaging software used to check the images you provided I noticed all the calibration frames were shot in APT and dated before the image shot in SC. Could you detail the calibration and light frame capture process?
-Chris
Quick addendum, as I was closing the imaging software used to check the images you provided I noticed all the calibration frames were shot in APT and dated before the image shot in SC. Could you detail the calibration and light frame capture process?
-Chris
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alinderbaum
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Re: Strange "artifact" on light images
Chris,
Thank you for your reply. My standard practice for capturing flats has been to do it right after I capture my lights and darks. I did this in this case, however, the flats threw me for a loop as they had the bayered pattern I have never seen or am aware of. I did the flats both manually and also using the flats aid and both had the pattern. Because I am more familiar with APT and it seems to work much more intuitively, I wanted to practice capturing the flats to see if I had made an error or if the pattern was due to something I had not yet learned about. I then proceeded to capture flats with the same camera position and temperature as the all the other frames from the night of imaging...I found the pattern still visible. I have since learned that this pattern is due to using a OSC astro camera in place of the DSLR I have been using. The flats taken with and without the tee shirt were virtually identical in outcome, just using slightly different exposure times. I could have taken a bit more time in attaching a couple of files but in reality the way Sharpcap saves the images is quite unintuitive and confusing compared to what I am used to with APT, so I attached a flat frame that was virtually identical to the one I took with Sharpcap. After working on this for 6-8 hours, I just used a single frame in my OneDrive link. All of the images in the OneDrive link were used to stack and get the stacked image. The stacked image, if I recall correctly, is from 5 lights, a master dark and master bias, 5 flats and 5 dark flats.
In regards to capturing lights, I set up a capture sequence in Sharpcap and utilized this. On every image I saw the circle/oval (as shown in attached document below this paragraph) and made the assumption it was vignetting or something that would be calibrated out and proceeded, with my dew shield on. I have not had a dew issue in the past and did not give it a second thought.
I am shocked you are unable see the huge oval/circle in the center of the light frame and the stacked frame. I have been told today by the fella at the store where I purchased the camera it is likely either a) dew on the camera lens or scope or b) frost on the camera lens. The latter is unlikely, I am told, due to the Altair 269 being constructed the way it is and having a heated lens. I am not aware of the best way to determine if it is on the camera or scope.
Thank you for your reply. My standard practice for capturing flats has been to do it right after I capture my lights and darks. I did this in this case, however, the flats threw me for a loop as they had the bayered pattern I have never seen or am aware of. I did the flats both manually and also using the flats aid and both had the pattern. Because I am more familiar with APT and it seems to work much more intuitively, I wanted to practice capturing the flats to see if I had made an error or if the pattern was due to something I had not yet learned about. I then proceeded to capture flats with the same camera position and temperature as the all the other frames from the night of imaging...I found the pattern still visible. I have since learned that this pattern is due to using a OSC astro camera in place of the DSLR I have been using. The flats taken with and without the tee shirt were virtually identical in outcome, just using slightly different exposure times. I could have taken a bit more time in attaching a couple of files but in reality the way Sharpcap saves the images is quite unintuitive and confusing compared to what I am used to with APT, so I attached a flat frame that was virtually identical to the one I took with Sharpcap. After working on this for 6-8 hours, I just used a single frame in my OneDrive link. All of the images in the OneDrive link were used to stack and get the stacked image. The stacked image, if I recall correctly, is from 5 lights, a master dark and master bias, 5 flats and 5 dark flats.
In regards to capturing lights, I set up a capture sequence in Sharpcap and utilized this. On every image I saw the circle/oval (as shown in attached document below this paragraph) and made the assumption it was vignetting or something that would be calibrated out and proceeded, with my dew shield on. I have not had a dew issue in the past and did not give it a second thought.
I am shocked you are unable see the huge oval/circle in the center of the light frame and the stacked frame. I have been told today by the fella at the store where I purchased the camera it is likely either a) dew on the camera lens or scope or b) frost on the camera lens. The latter is unlikely, I am told, due to the Altair 269 being constructed the way it is and having a heated lens. I am not aware of the best way to determine if it is on the camera or scope.
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alinderbaum
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Re: Strange "artifact" on light images
Chris,
I may have read your message wrong and thought you could not see the oval in the light frame. After rereading I noticed you said flat frame. You are correct, it is not in the flat frame or any other frame other than the light and the stacked.
Aaron
I may have read your message wrong and thought you could not see the oval in the light frame. After rereading I noticed you said flat frame. You are correct, it is not in the flat frame or any other frame other than the light and the stacked.
Aaron
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BlackWikkett
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Re: Strange "artifact" on light images
Hi alinderbaum
Yes I saw the weird oblong pattern on your light frame. Sound like you figured out where this apparition came from? In any event you're going to use DSS to stack you images I would suggest you capture all calibration, and light images in the same application as single frames then stack them in DSS. I've tried using calibration frames and light frames from different apps to create a final image. Let me save you a headache and warn you away from it.
-Chris
Yes I saw the weird oblong pattern on your light frame. Sound like you figured out where this apparition came from? In any event you're going to use DSS to stack you images I would suggest you capture all calibration, and light images in the same application as single frames then stack them in DSS. I've tried using calibration frames and light frames from different apps to create a final image. Let me save you a headache and warn you away from it.
-Chris
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alinderbaum
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Re: Strange "artifact" on light images
Agreed, Chris. I will only use one source.
I am still trying to figure out where the apparition is coming from. I have been told it is likely NOT dew because there is no impact on focus in the impacted area. This would also hold true for frost, I would think, if the focus is good on the stars in the impacted area. Sounds like good logic to me, but not certain. I cannot get a reply from Altair as of yet.
On my second night of imaging, it was significantly reduced (maybe a third of the size) but still there. I hope it is just dew as I can deal with that!
Aaron
I am still trying to figure out where the apparition is coming from. I have been told it is likely NOT dew because there is no impact on focus in the impacted area. This would also hold true for frost, I would think, if the focus is good on the stars in the impacted area. Sounds like good logic to me, but not certain. I cannot get a reply from Altair as of yet.
On my second night of imaging, it was significantly reduced (maybe a third of the size) but still there. I hope it is just dew as I can deal with that!
Aaron
Re: Strange "artifact" on light images
Here is my experience with dew:
https://astrotuna.com/youve-got-a-dew-m ... t-problem/
That is a single frame of M27. The stars look in relatively good focus within the dewy region so I am suspicious of anyone telling you otherwise.
Brian
https://astrotuna.com/youve-got-a-dew-m ... t-problem/
That is a single frame of M27. The stars look in relatively good focus within the dewy region so I am suspicious of anyone telling you otherwise.
Brian
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alinderbaum
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Re: Strange "artifact" on light images
Brian,
Thanks so much for this! The pattern looks almost identical to what I am seeing. I will study this article. IF you have any insight as to how to isolate the location of the dew, please share. I do not think it is the camera as it has a heater to address this. I have a Celestron 150 Newtonian scope. I am assuming this would likely be on the primary mirror.
AAron
Thanks so much for this! The pattern looks almost identical to what I am seeing. I will study this article. IF you have any insight as to how to isolate the location of the dew, please share. I do not think it is the camera as it has a heater to address this. I have a Celestron 150 Newtonian scope. I am assuming this would likely be on the primary mirror.
AAron
Re: Strange "artifact" on light images
Aaron,
The dew in my blog post was on the protective window of my sensor's CCD. My CCD is cooled but is 10 years old with no built-in anti-dew mechanism. Prior to owning a cooled CCD I used uncooled CMOS cameras. I can't remember ever having a problem with dew on the sensor window of an uncooled camera but there was one occasion where dew completely covered my objective lens on a very humid summer night. And there was one occasion when an ice crystal the size of a nickel formed on my objective on a frigid, damp night. I've not had a problem ever since I've been using homemade dew-heater strips on the objective and the nose of my camera. (One note on that: I made sure that the heater string is midway between the CCD sensor and the filter in the filter wheel just in case dew is forming on the filter. Since using these strips I have had zero problems.)
Brian
The dew in my blog post was on the protective window of my sensor's CCD. My CCD is cooled but is 10 years old with no built-in anti-dew mechanism. Prior to owning a cooled CCD I used uncooled CMOS cameras. I can't remember ever having a problem with dew on the sensor window of an uncooled camera but there was one occasion where dew completely covered my objective lens on a very humid summer night. And there was one occasion when an ice crystal the size of a nickel formed on my objective on a frigid, damp night. I've not had a problem ever since I've been using homemade dew-heater strips on the objective and the nose of my camera. (One note on that: I made sure that the heater string is midway between the CCD sensor and the filter in the filter wheel just in case dew is forming on the filter. Since using these strips I have had zero problems.)
Brian