Anyone else had these artefacts with L-pro? - Forums

Topic starter

Jul 29, 2021 · Edited: Jul 29, 2021

Hi all, I've been having issues shooting with a DSLR, lens and L-pro clip-in filter. I wonder if anyone else had similar experience and managed to cure it on the hardware level.

The issue is the strange color vignetting as seen on the picture below:

The image is slightly stretched stack of subs available in the zipped folder here:
https://drive.google.com/drive/folders/1w323IZtZq3C1gTitEBftfTYWtr4w3pi4?usp=sharing

The particular setup is stock Canon 60d, Optolong L-pro clip-in and 135mm f3.5 vintage lens (Jupiter 37a). Bortle zone 8-9.

APP reduces these artefacts more or less, but as always, hardware solution would be preferable to post processing.

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Björn Arnold

Jul 29, 2021

When I saw the image, another thread on AB crossed my mind, where somebody likely had issues with light getting into the camera through the finder opening. I'm just not finding the thread in the forum right now. Maybe an artifact from the same issue?

igor.cheb

Topic starter

Jul 29, 2021

Björn Arnold:
When I saw the image, another thread on AB crossed my mind, where somebody likely had issues with light getting into the camera through the finder opening. I'm just not finding the thread in the forum right now. Maybe an artifact from the same issue?

Thank you Bjorn, but no, the finder is closed with a rubber blocker Canon provides with their cameras.

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astroyyc

IOTD Staff

Jul 29, 2021

Are you correcting with flat frames? My L-Pro flats always show colour gradients that are exacerbated in the vignetting regions

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igor.cheb

Topic starter

Jul 29, 2021 · Edited: Jul 29, 2021

Are you correcting with flat frames? My L-Pro flats always show colour gradients that are exacerbated in the vignetting regions

I sure do. Any chance I could take a look at your raw lights and flats with L-pro and a lens?

Here's the stretched flat, colours are there as well:

Michael Broyles

Jul 30, 2021

I'm wondering why this flat has been Debayered. Are you processing RAW image files or Jpeg files to built you master flat?

igor.cheb

Topic starter

Jul 30, 2021

Michael Broyles:
I'm wondering why this flat has been Debayered. Are you processing RAW image files or Jpeg files to built you master flat?

Raw images. This is just a screenshot I took after stretching it in Affinity photo for the demonstration purposes.

Christian Schulbert

Jul 30, 2021

I have also some strange colored areas on my lights with the ASI1600MC and the L-Pro. My flats are, as yours, quite colorful, and the colors calbrate out quite complete. It is even worse with the L-eXtreme - this is a known issue with the ASI1600MC and the 294MC.

CS,
Chris

Björn Arnold

Jul 30, 2021

I'm wondering if this issue is something related to what I had recently with my Atik mono camera and Optolong narrowband filters:
when I tried to capture flat frames, I had the effect of weird looking flats. Here's a photo how the flat looked, in FITSliberator:

After some internet research it confirmed what I had guessed: the camera sensor, actually the golden contacts which connect the sensor to the electronics, reflected light back to the filter which in turn reflected the light back into the photosensitive area.

Since you are reporting the issue being more prominent the lesser light the filter transmits, i.e. going from broadband light pollution filters down to narrowband light pollution filters, I'm getting the impression that what you are seeing is reflection.

I'd propose following test, if you have access to a set of SHO narrowband filters: shoot flats with an Ha filter and with the OIII filter. If the incoming light causes the color gradient, it should be there with the Ha filter and gone with the OIII filter. If it's there with the OIII filter, I would say that you have a secondary light source leaking into the sensor.

CS!
Björn

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Claudio Tenreiro

Jul 30, 2021

I have been struggling a lot with these dual NB filters, and flats have not been able to remove the artefacts.

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Roger Nichol

Jul 30, 2021

After calibrating and integrating the OP's stack, it is apparent that there is just insufficient light getting to the sensor to get the wanted signal out of the noise. Even after stacking 97 images there is next to nothing, so the amount of stretch that has to be applied is extreme. Using PixInsight's Normalise Scale Gradient process, the strange colours were no longer apparent, but the nebula is only just discernible. The issue is that the camera is unmodified and the exposure duration is far too short to capture this in narrowband.

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igor.cheb

Topic starter

Jul 30, 2021 · Edited: Jul 30, 2021

Roger Nichol:
After calibrating and integrating the OP's stack, it is apparent that there is just insufficient light getting to the sensor to get the wanted signal out of the noise. Even after stacking 97 images there is next to nothing, so the amount of stretch that has to be applied is extreme. Using PixInsight's Normalise Scale Gradient process, the strange colours were no longer apparent, but the nebula is only just discernible. The issue is that the camera is unmodified and the exposure duration is far too short to capture this in narrowband.

Getting that modification done tmrw, so maybe it'll help. But I am suspicious of that explanation a bit. There has to be a reason for that vignetting, a material cause. Lights don't contain these artefacts, they show a gradual fall off of signal towards the corners, as expected. It's only in the stacked image that the artefacts appear. It must mean that calibration by flats don't work in this case. Why? Flats seem to match lights quite well in terms of illumination... I wish I knew how to reason further.

andrea tasselli

Frequent contributor

Jul 30, 2021

I suspect not proper flats are the likely culprit. I own same filter but not clip-on but I never witness anything like that.

igor.cheb

Topic starter

Jul 30, 2021

andrea tasselli:
I suspect not proper flats are the likely culprit. I own same filter but not clip-on but I never witness anything like that.

Do you ever shoot in in Bortle 8-9?

Dale Penkala

Jul 30, 2021 · Edited: Jul 30, 2021

andrea tasselli:
I suspect not proper flats are the likely culprit. I own same filter but not clip-on but I never witness anything like that.

I tend to agree with this. I have had this very similar issue with a few images as well using this filter (2”) with my filter drawer. I reshot my flats and 95% of it was gone. In my case my flat panel wasn’t illuminating my frame well enough so I added paper under it so that I could effectively illuminate the frame by brighting the panel light. My flat panel needs to be up quite bright to eliminate that particular artifact. At least thats been my experience anyway.
Like its been mentioned APP did correct most of it but to eliminate it from the get go is best.

Dale

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igor.cheb

Topic starter

Jul 30, 2021

Dale Penkala:
andrea tasselli:
I suspect not proper flats are the likely culprit. I own same filter but not clip-on but I never witness anything like that.

I tend to agree with this. I have had this very similar issue with a few images as well using this filter (2”) with my filter drawer. I reshot my flats and 95% of it was gone. In my case my flat panel wasn’t illuminating my frame well enough so I added paper under it so that I could effectively illuminate the frame by brighting the panel light. My flat panel needs to be up quite bright to eliminate that particular artifact. At least thats been my experience anyway.
Like its been mentioned APP did correct most of it but to eliminate it from the get go is best.

Dale

Anything obvious I should check for? I take my flats by placing my phone with a white screen on medium brightness on top of the lens with a white paper in between. The screen covers the lens completely. Camera is set to Av mode so that the histogram is slightly to the right of center.

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igor.cheb

Topic starter

Jul 30, 2021

Ok, here's the weird part.
If I take a single light and then divide it by a master flat in Affinity photo (new layer, divide) prepared in APP, I get this over correction (disregard the weird colours for now):

But if instead I divide the same light by a single flat, I get a much better result:

Does this mean that there is something wrong in master flat preparation?

Dale Penkala

Jul 30, 2021

Dale Penkala:
andrea tasselli:
I suspect not proper flats are the likely culprit. I own same filter but not clip-on but I never witness anything like that.

I tend to agree with this. I have had this very similar issue with a few images as well using this filter (2”) with my filter drawer. I reshot my flats and 95% of it was gone. In my case my flat panel wasn’t illuminating my frame well enough so I added paper under it so that I could effectively illuminate the frame by brighting the panel light. My flat panel needs to be up quite bright to eliminate that particular artifact. At least thats been my experience anyway.
Like its been mentioned APP did correct most of it but to eliminate it from the get go is best.

Dale

Anything obvious I should check for? I take my flats by placing my phone with a white screen on medium brightness on top of the lens with a white paper in between. The screen covers the lens completely. Camera is set to Av mode so that the histogram is slightly to the right of center.

I like to have my white/luminance channel of the histogram in the 50-60% range trying to keep the other channels with in the 30-80% if possible. It sounds like your in the same ballpark as what I’m doing using SharpCap.

I don’t use a phone so thats a different for me. I’m using my panel on top of a 10” f5 ota and use 3 white t-shirts stretched out smoothly and I set my camera for a 1 second exposure and I make sure that my flat panel is well brightly illuminated with out an variation in brightness. Once I do that I then add white paper between the light panel and the t-shirts until my histogram is where I want it to be.

There are numerous threads on taking flats with SC but its been my experience to shoot the flats with all the same parameters you set for your darks but make your flats exposure time in the 1-3 second range. This will vary based on your camera. My ZWO 294 I shoot 3 seconds, and my 071 I shoot 1 second and have had excellent luck with my images calibrating out.

Some may disagree with my process above Igor and there is a lot of different variations to taking flats but with my work flow I have found this process to work the best for me and my setup.

If nothing else maybe my process will give you something to try differently to help you out.

Best of luck and keep us posted!

Dale

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Dale Penkala

Jul 30, 2021

Ok, here's the weird part.
If I take a single light and then divide it by a master flat in Affinity photo (new layer, divide) prepared in APP, I get this over correction (disregard the weird colours for now):

But if instead I divide the same light by a single flat, I get a much better result:

Does this mean that there is something wrong in master flat preparation?

Good question Igor, I don’t use Affinity so I can’t comment on that but the one from APP is like you said much better. From there I’d take and do a calibration of the background or better yet do the “remove light pollution” which does that and neutralizes the background and see how it comes out. Once I get what I like in APP I save it then post process in Gimp.

Dale

andrea tasselli

Frequent contributor

Jul 30, 2021

Do you ever shoot in in Bortle 8-9?

I shoot with full moon. I suspect that's worse.

andrea tasselli

Frequent contributor

Jul 30, 2021

Dale Penkala:
andrea tasselli:
I suspect not proper flats are the likely culprit. I own same filter but not clip-on but I never witness anything like that.

I tend to agree with this. I have had this very similar issue with a few images as well using this filter (2”) with my filter drawer. I reshot my flats and 95% of it was gone. In my case my flat panel wasn’t illuminating my frame well enough so I added paper under it so that I could effectively illuminate the frame by brighting the panel light. My flat panel needs to be up quite bright to eliminate that particular artifact. At least thats been my experience anyway.
Like its been mentioned APP did correct most of it but to eliminate it from the get go is best.

Dale

Anything obvious I should check for? I take my flats by placing my phone with a white screen on medium brightness on top of the lens with a white paper in between. The screen covers the lens completely. Camera is set to Av mode so that the histogram is slightly to the right of center.

Don't use your phone, for goodness' sake. I'd stretch things and use a good EL panel that has well calibrated white light (some of the cheap ones aren't white at all) or use the sky itself, at dusk or when it is clouded. Maybe with a diffuser panel interposed if the focal length is on the short side.

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Benny Colyn

Jul 31, 2021

Ok, here's the weird part.
If I take a single light and then divide it by a master flat in Affinity photo (new layer, divide) prepared in APP, I get this over correction (disregard the weird colours for now):
<snip>

But if instead I divide the same light by a single flat, I get a much better result:
<snip>

Does this mean that there is something wrong in master flat preparation?

Blink your flats, you likely have one or more that are bad.

igor.cheb

Topic starter

Jul 31, 2021

Benny Colyn:
Ok, here's the weird part.
If I take a single light and then divide it by a master flat in Affinity photo (new layer, divide) prepared in APP, I get this over correction (disregard the weird colours for now):
<snip>

But if instead I divide the same light by a single flat, I get a much better result:
<snip>

Does this mean that there is something wrong in master flat preparation?

Blink your flats, you likely have one or more that are bad.

That's what I thought as well, but then I took those same frames and went though the whole integration process in APP with just one light and one flat and it still gave me this:

Very annoying this.
Apparently division in photoshop (affinity) is not the same as calibration in this astro software. I wonder what the difference is.

Benny Colyn

Jul 31, 2021

The difference is a flat is calibrated (meaning there's a darkflat or a bias subtraction) before it is applied (division)

A problem with bias/darkflat can easily cause such issues.

igor.cheb

Topic starter

Aug 31, 2021

So it turned out to LP disguising as flats issue after all. Managed to escape to bortle 4-5 with the same gear, last night was good seeing. Here's a stack of 40 mins before any further processing. Some gradient is still there, but nothing circular like in the original post.