Flats issue with ZWO6200MM - Forums

GDay all.
Im currently using an Askar FRA500. I was using a ZWO 2600MM and Antlia filters prior and never saw what Im seeing at the moment. Went mad and purchased a ZWO6200MM, FW and 50mm Antlia filters. I took a 300s dark frame when I put it all together and no light leaks. Thought Id take a flat and see what the vignetting is like. They look like I took an X-Ray of some ones fingers. So I thought it has to be the panel. I use a plastic bag, opaque perspex then a trace panel to do my flats and had pleasing results previously. I then purchased a Giotto flat frame generator and still have a weird flats.

The scope is a petval and is at correct focus as I took some 5min subs on Carina with each filter and they look ok to this non guru.
Unsure if I installed the filters in reverse... Pattern stands out more on Ha and Sii. The FW has a 54mm opening at the rear and my adapters screw straight in. I checked prior to see If the adapter would snag and scratch the filters before putting the FW on the camera etc.

I have attached a couple of pics. I also have a safe link to one drive if a guru had time to take a look at my lights etc. Maybe its all due to flat panel/s..Or my scope cant handle the a FF camera.

Maybe some one has encountered this before? Appreciate your time. Regardshttps://1drv.ms/f/c/ddfc7008f79a866e/EoZXIKkdT3JJl53GH842zYwBMcIXR_LqV8smhkfc1fb5DQ?e=otX7T0

Oh my…those "pillars" kinda look similar to the single I get when I lower the chip temperature of my asi294mc pro very quickly.
Especially during warm season I tend to do that gradually after 0°, step by step, decreasing by 2° untill I reach my -10°.
Maybe you have similar issue. I suppose it is some kind of water vapor condensation happening.

GDay Vitaly
The attached pics are just flats taken inside with flat panels. One with a trace panel the other with a Giotto.

It is just my assumption that it might be related also to the colling of the camera's chip. If you are coolling it for flats, I do.

Nothing wrong with the flats. As far as I can see they are safe to use (no condensation or ice on the chip). Incidentally, the ASI294MC is a rather different beast and would not be producing anything like that, when condensation occurs.

andrea tasselli:
Nothing wrong with the flats. As far as I can see they are safe to use (no condensation or ice on the chip). Incidentally, the ASI294MC is a rather different beast and would not be producing anything like that, when condensation occurs.

No like that but I always get a huge pillar stretching vertically if I am rushing with cooling.

Those images are stretched, correct?

I have had the similar flats on my Ha and Sii filters (and to a lesser extent on my Red filter) on my 6200mm and my Player one Zeus. Never got a clear explanation why this happens but I am told this is normal.

GDay all
Appreciate the comments. Ta
Yes the bottom pic is an STF stretch from PI. The top pic is just a screen grab from my Ipad showing the same pattern on Ha and Sii filters. The scope is at the same focus from a couple of nights ago when I took some 5min subs of Carina for a test. I did cool the camera as well whilst on the bench. I could try 0 gain. Was not sure of that Lum filter; so hard to tell if I placed it into the FW the correct way. The fits are in the link which look pleasing enough. Just wondering if that pattern though will effect the stacked image as well. Just not sure. The pattern is very dominant in the Ha and Sii.

As always the question is, do they calibrate properly?

Stephen Jones:
GDay all
Appreciate the comments. Ta
Yes the bottom pic is an STF stretch from PI. The top pic is just a screen grab from my Ipad showing the same pattern on Ha and Sii filters. The scope is at the same focus from a couple of nights ago when I took some 5min subs of Carina for a test. I did cool the camera as well whilst on the bench. I could try 0 gain. Was not sure of that Lum filter; so hard to tell if I placed it into the FW the correct way. The fits are in the link which look pleasing enough. Just wondering if that pattern though will effect the stacked image as well. Just not sure. The pattern is very dominant in the Ha and Sii.

My Ha flat is waaaay worse that any of those and calibrates out just fine. You'll be all right, I'd reckon.

I recently upgraded from the 2600MM to the 6200MM as well and noticed the same vertical pillar patterns in my flat frames. I used the exact same flat panel and very similar settings as I did with the 2600MM, so I suspect the artifacts might be inherent to the camera itself. That said, they don't seem to cause any issues during calibration. My calibrated images still look fine even when using these "pillar flats." Still, I wonder if this pattern could be considered a defect.

Or maybe the IMX455 just naturally has worse consistency than the IMX571 and tends to read out those pillars.

Just throwing this out, purely theoretically… How flat is your sensor? Could sensor tilt (most commonly aggravated by FF sensor size) be causing some funky interference patterns? I have a FF 2400MC and my Ha/Oiii and Si/Oiii filter flats show a somewhat similar pattern of alternating but very soft R - GB blotches. I know I have some sensor tilt but have not addressed it.

Hi Stephen,

I got a similar pattern with my IMX533 mono chip when taking flats with Ha and SII. Until now, I did not check in detail where it is coming from. At the moment I skip flats for those filters as I struggle to get good calibration results. I think that the narrowband filter in combination with the small pixels is the issue (intrapixel etaloning?).

Best,
Thorsten

My flats look "blotchy" (not necessarily fingers, though) when taking NB flats of a refractor with excellent coverage. Since there's little fall-off from the center, it shows every imperfection in flatness or unevenness of the filter or scope or camera. But if you look at the actual differences between values (or look unstretched), they are actually very even and calibrate just fine. You would never see these patterns in a DSO subexposure since the stretching covers a much larger range, swamping the subtle patterns.

My flats of my 10" newt look super even with FF, but that's because there's significant light fall-off and that swamps everything else.

Ashraf AbuSara:
I have had the similar flats on my Ha and Sii filters (and to a lesser extent on my Red filter) on my 6200mm and my Player one Zeus. Never got a clear explanation why this happens but I am told this is normal.

I too have a Player One Zeus that I just put together with Chroma filters and have strange patterns in my Ha, Siii, and Red filters.

It looks like there's variability in the QE of the pixels on the IMX455 in the longer wavelengths.

Do you use Asiair power to flat panel and do you try to use Asiair as dimmer (decreasing power)? I have had something like this when doing so because Asiair is a very bad dimmer.

Tommi Liinalampi:
Do you use Asiair power to flat panel and do you try to use Asiair as dimmer (decreasing power)? I have had something like this when doing so because Asiair is a very bad dimmer.

I think that results in horizontal lines due the the rolling shutter interacting with the PWM frequency of the panel.

This is completely normal. It's only an issue if they don't calibrate properly. Source: I went down this crazy path once.

hi, all

I have that same camera (6200mm) and for a year I used the same filters, my FLATS with this camera are between 24k to 26k ADU, that pattern is not normal in any way, have you tried with different light sources, including natural light, that would be my first question, then did you make FLATS using another OTA.

CS
Brian

Appreciate your input fellas. Ta

I will give it some time and see what occurs. Surprised though Im not the only one with a few gremlins in regards to their flats. Ref the tilt; I used astap and it showed 5-7% tilt with subs. Unsure how accurate that can be as an indication. Im not that pedantic. If it was extreme Id be jumping up and down…
I tend to do the flats inside the house. I used my bluetti portable power box to take the flats. It is a beast and did not use the Asiair Plus to power the panel. Good thought as I will use my other box as it could be a power 'thing'.

Brian; I try to get that 24-26 ADU as well. The shop were I purchased them also asked for sky flats. Never tried them but I will give them a whirl for sure.

Hi Stephen, Have you tried using natural light instead of the LED panel?
I'm having a somewhat similar issue with a red filter from a ZWO LRGB set (Yes, I know, not the best but my local dealer, who I know well and trust, advised that the ZWO LRGB are OK). I've been using a $25 LED panel to make flats for about a year and it worked fine until I upgraded from a Nikon camera (no filter) to a 2600mm (needs filters). My L, G, and B flats look normal but my red flat is much brighter on one side (the Lights look normal). It's not due to a light leak (I checked); it doesn't change if I rotate the LED panel; it doesn't change if I take flats with the LED panel outside at twilight; but the bright area does rotate with the filter when the filter is rotated. Flipping the filter over doesn't change this. Finally, I used ambient light from the window on the ceiling of the room I'm shooting test flats in and I and got a normal looking flat image.
The spectrum from a white LED is not smooth, so perhaps there are slight variations in the filter coatings and these interact in an unexpected way with the LED spectrum, but I don't know this for certain. In any case my issue seems to be related to a combination of the LED panel and the filter. It's weird.

If there is any flicker due to the design or the power to the panel, and its intensity is rapidly changing, even slightly, this will be recorded by the rolling shutter of the sensor as a pattern such as these because each row of pixels is read out at slightly different times as the light level varies over time

Are you using very short exposure times for your flat? This will capture the flicker as intensity changes across your image.

Try a daylight flat exposure against clear sky. I put a white microfiber cloth over my telescope objective to take afternoon flats at very short exposures and have never seen these patterns from any of the cameras including some mentioned in this thread.

I have two ASI 6200 MM cameras and neither has exhibited behavior similar to yours. Morning sky flats are working best for us. If they fail, due to clouds or some other obstruction, I use a flat panel with a folded sheet and that works fine also. This is with both an ASIAIR and a NINA flat wizard. I purchased one camera used from a guy that lived in a high humidity climate and condensation formed on the sensor when cooling rapidly. It looked like tiny rain drops in the center of the sensor and not vertical stripes like you are seeing. I fixed that by disassembling the camera and drying out the desiccant discs in the microwave. I am fairly certain that artifacts like you are seeing are corrupting your images, even if it is not obvious on your masters. Also have a 6200 MC which has the same sensor with a Bayer matrix. No problem with it either. I agree with the suggestion that you try sky flats, and if they look okay, you should consider that the problem is with your flat panel. Good luck sorting out the problem.
Dale Bush

If there is any flicker due to the design or the power to the panel, and its intensity is rapidly changing, even slightly, this will be recorded by the rolling shutter of the sensor as a pattern such as these because each row of pixels is read out at slightly different times as the light level varies over time

The PWM of the panel interacting with the rolling shutter would give horizontal lines, not vertical. And they'd all be parallel to each other.