EdgeHD issue with reflections - Forums

Hello everyone,
I am having a problem with my EdgeHD that I am trying to figure out. I wonder if you have some theories or if you've been through this before. Here is my imaging train:
ASI533MC Pro -> EFW (astronomik L3 uv/ir) -> zwo 11mm, zwo oag (prism far from sensor) -> celestron adapter -> celestron 0.7x reducer for the EHD 8

Spacing is correct, I am getting good stars around the field, even with the ASI1600MM Pro.

Below shows the issue (left with flats, right without)

This is another image without calibration, I think I can see another line as well, tried to highlight it, but I am not sure about this 100%:

I started imaging M51 after this target, during the same night, it's not very obvious that the issue is here:

Once the new moon is out of the way, I will dismantle my imaging train and try without the OAG and without the reducer. But for now, I seek the wisdom of astrobin community for thoughts. I wonder if the reducer is the issue, as it is also creating the aberration you see in stars, which makes me wonder how celestron can screw this up, your scope, your specific reducer to it, come on celestron! but that's for another topic....

~~I don’t see any images in your post~~.

Ara

EDIT: Nevermind, they appeared upon refresh.

My current assessment, having looked at your pictures closely, is your flats are undercorrecting.

Are you performing your calibration steps manually in PI or are you using the latest WBPP script? Are you including bias frames in your calibration? Before dismantling your current imaging train, I would look at your calibration process closely.

Ara

My current assessment, having looked at your pictures closely, is your flats are undercorrecting.

Are you performing your calibration steps manually in PI or are you using the latest WBPP script? Are you including bias frames in your calibration? Before dismantling your current imaging train, I would look at your calibration process closely.

Ara

I am using wbpp and flat darks instead of bias. I have tried multiple flat adus (18K and 30K), I also tried to manually change the flat intensity using pixel math, tried -0.2, -0.1, 0.05, 0.1 and 0.2. Nothing removed it. It is not in my flat files as well:

also when it comes to dust motes and vignetting, it seems my flats are doing well? Also I've used the same flats for the M51 image.

Could it be miniscule height differences in the sensor itself (from sensor attachment to the camera in factory). Have you tried with the same imaging train and a different camera?

I've seen the same problem with the asi1600, same imaging drain, I just swap between the asi1600 and asi533.

My current assessment, having looked at your pictures closely, is your flats are undercorrecting.

Are you performing your calibration steps manually in PI or are you using the latest WBPP script? Are you including bias frames in your calibration? Before dismantling your current imaging train, I would look at your calibration process closely.

Ara

your reply made me rethink a few things. I debayered the master flat and split the RGB channelsC Could this be the issue that Green is more exposed than others? If so, I need to figure out a way to take flats with the 3 channels aligned...

I've been getting the same type of artifacts and trying to figure out the cause for months via process of elimination … YMMV, but in my case (with newt) the latest self diagnosis is the cause of my artifact rings like yours, is internal reflections due to off-axis rays. If I integrate without flats I do not get these rings.

I would try different methods of flats acquisition and varying distances of your flat panel in relation to your OTA. Also the positioning of your filter, (in the filter wheel verus at the end of your reducer. ) Also try with a different filter and filterless.

FWIW, my best results so far have been with skyflats at dawn without any diffusion, just directly at the pre-dawn sky. SMH because I have a Spike a Flat!
I'll next try the spike a flat at a very reduced brightness level and at varying distances to the front of the OTA.

Good luck!

Internal reflection from the Schmidt corrector plate seems to me the most reasonable explanation, since the ghosting looks like an image of the inlet pupil. I'll second Jayastrobin; the best flat are sky flats, just after sunset or before dawn, if you can keep awake that long

Michel

I Have the same setup but on a C11" EdgeHD using an OAG both with and without the reducer and I have used many cameras including the 533 with no issues. I make dark flats (not bias) and I have used the sky as well as a light panel and they all work just fine and I have used PI WBPP as well as APP. So, none of these should be the cause of your issue. Your flats look fine which makes this more perplexing. Unless you are getting some other external light source causing this reflection, I cannot think of what could be causing this other than the filter. If you have not done so, try it without the filter and see what happens.

I had some reflection issues with my C11 Edge when I first set it up in 2013. It turned out that there was a reflective element in the imaging train somewhere (camera adapter, extension tube, etc.) that was at fault. Upon the advice of someone else, I painted the inside of it with flat, black Rustoleum paint, and the reflection disappeared, just like that. It may be a longshot, but you can look at the inside of any adapters or tubes in your train with a flashlight, and see if anything is obviously reflecting visible light. There should be nothing with shiny/reflective walls between the camera and the optics.

I have the same problem with my 8" EdgeHD. I have not pinned it down, but I took some photos down the imaging train with different things connected and pointing toward a window during the day. The item that shows the most reflections is 0.7x reducer, and they are mostly internal (so I would have to take this apart to paint pieces of it).

I have heard that you can take some black paper and roll it up and insert it at different parts of your imaging train that you suspect could be contributing to the reflections and see if it has any effect. Since you know a specific coordinate in the sky that produces your reflections, just keep using this location for debug.

Does this show up with all of your filters?

My post about my issue:
https://www.cloudynights.com/topic/760137-help-debugging-reflection-on-image/

I was using an ASI294MC Pro, 2" Optolong UV/IR Cut filter, 0.7x reducer, some spacers, T2 rotator and ZWO 2" filter drawer. I bought a Baader UV/IR cut to see if the filter is the issue but have not had a chance to try it yet.

That kind of circular artifact is a dead give away that you have internal stray reflections in your system. Remember that stray light is additive to the signal and flats only correct for multiplicative errors such as vignetting, PRNU, and cos^4 radiometric fall off. Stray light is a killer for image calibration. The first thing to do is to remove your camera package, point your scope at a bright source (like out a window in the daytime) and look backwards through the optical system. Study it carefully for any stray reflections coming from edges or the inside of any connectors. Then you'll have to eliminate those strays either with black paint or black flock paper. Since you are looking for very low light signals, it does not take much in the way of stray light to totally screw things up so you have to be very careful to get everything as non-reflective as possible. You'll know when you are successful because your images will calibrate properly.

John

thank you all for your replies, I've reconfigured my imaging train with different lum filter closer to the sensor and without the efw. I've also replaced the celestron t adapter, so now it is 533mc, 11mm, 21mm (new), oag, extenders replacing the t adapter (new). So far, the issue is still there, only when imaging in the area of ngc2146. Since I don't see this on my M51 image, I am thinking maybe it is some bright stars in the oag field that's causing this?

few quick answers to the above:
1- the issue is way worst with flats, and I don't see this ring in my flats
2- if it ends up being the reducer, it will make this whole setup useless, given the native F ratio
3- I've added a dew shield, covered the area around the telescope to bounce off terrestrial light straying into the tube
4- I tried to test without the reducer, but with my seeing and very small sensor, I gave up
5- i still need to try without the oag. But then again, this puts me in the same shoes as without the reducer, end up with a useless setup

6- if the stray light is bouncing off the extensions, I've replaced everything except the oag and reducer. I find it highly unlikely another piece is creating the exact same reflection

The search continues...

@Bruce Donzanti , which oag are you using?

I use to use the Starlight Xpress filter wheel with the built-in OAG but I now use the Celestron OAG and it works very well. It has the largest prism I am aware of and combining it with a large sensor guide camera like the ASI174mm gives you a large field of potential guide stars.

I know you want to test the reducer but just to reiterate, the reducer works fine and should not cause your problem unless for some reason it is damaged by not attaching correctly. Your optical image train sounds fine unless, like what John was referring to, you have some spacing issue causing stray light to enter. I also use a dew shield like what you just added and that is a good add-on.

Michael,

You are correct, this is due not to stray light but due to bright stars off-frame. They are still in the FOV of your telescope. You can try to re-frame near that pointing position and see if the problem is still there or not as a workaround.

To confirm that it is not terrestrial light, just take images of the same target but at different times in the night. If the reflections are in the same position then it is a bright star (at least I believe this would prove it if you are less convinced).

It may be worth buying a $3 can of flat black paint and brushing up the inside of your less expensive components and trying again?

If you visited my CN link and looked at my views down the tube with the reducer you'll notice some very bright reflections.

Most people that notice this issue just re-frame the shot or just cross that target off their list altogether sadly.

Hoping you find your solution. I'm still hunting down mine as well.

I wonder if it would work to have your setup pointing at the offending target ready to shoot, but instead take your imager off and use a 2nd camera to peer down the imaging train with longer exposure to see if you can pickup on the offending part of the optical train. Time to take drastic measures…

I doubt that the OPs problem is due to light from off axis. Here is what scattering from a bright off-axis star looks like. The circular pattern shown in the OP's original image is almost certainly due to internal reflections that occur from the brightest star within the field. It doesn't appear in the M51 image because that field is relatively dark and lacks any bright stars.

John

Looks like a calibration issue to me. My first thought is your flats are too hot. Exposure time for L, R, G and B needs to be carefully set so each is optimal for your camera.

Can you publish your stacked L, R, G and B flat files so we can take a look?

I've followed the suggestions here and took the camera off during the day and pointed the scope out of the window, I've taken some images using my phone. This is with the 533mc/11mm/lum filter removed, so you're looking down the 21mm + oag + t-adapter + reducer + edgehd.

Photos: https://drive.google.com/drive/folders/133iI6m_E1AMGieZhECEyHZw9f2NuKXLy?usp=sharing

What caught my eye is the below, this reflection is on the iphone sensor:

Again this is not visible with my naked eye, the iphone camera is picking it up. And it exactly matches the reflection I see in my lights:

What do you guys think? Is that the seconday?

i removed the reducer and replaced it with the second part of the t adapter, I can still see the reflection, although smaller and harder to find:

Ok, there you go! Do you see all that light around the exit pupil? That's your problem. Here's what it should look like when you look backwards through the system: https://www.astrobin.com/xfedon/I/?nc=user. Images E - H show the problems that I had. When it's right, you should see ONLY the exit pupil as in revision 'I" of my page. It should look like a circle of bright light surrounded by inky blackness. That little stray reflection that you see off the glass surface is due to a poor coating. That's not good and it's a symptom but that's not causing the majority of the problem. That is just scattering from the surface showing the out of focus bundle of rays headed to the focal plane.

The easies way to fix the problem in your scope will probably be with black flock paper.

John

John Hayes:
Ok, there you go! Do you see all that light around the exit pupil? That's your problem. Here's what it should look like when you look backwards through the system: https://www.astrobin.com/xfedon/I/?nc=user. Images E - H show the problems that I had. When it's right, you should see ONLY the exit pupil as in revision 'I" of my page. It should look like a circle of bright light surrounded by inky blackness. That little stray reflection that you see off the glass surface is due to a poor coating. That's not good and it's a symptom but that's not causing the majority of the problem. That is just scattering from the surface showing the out of focus bundle of rays headed to the focal plane.

The easies way to fix the problem in your scope will probably be with black flock paper.

John

Hi John,
Thank you first for taking the time and sharing your experience. Just to make sure I got you right, the reflection is due to poor coating on the glass by Celestron? I didn't get the part of it being a symptom and not the cause of the problem?

Also what you're suggesting is that I flock the whole tube? or just the imaging train?

Michael,
To be clear, here's a diagram. Yes, I am suggesting that you have to flock the insides of pretty much everything that you can see when you look backwards through the scope. That's almost certainly where the stray light is coming from. I don't have time to hunt down the images right now but years ago, I had a similar problem in a C14 with a connector tube. The inside of the tube produced a significant stray with colors from diffraction introduced by the turning marks. A little black flocking paper quickly solved the problem. From the look of it, you may need to cover more area so you'll have to figure out how to get in there. Getting good calibration results requires serious attention to detail so get everything as black as you can. If you get it all black and that doesn't solve the problem then we'll need to talk again, but I think that your odds of a simple fix working are pretty high.

Finally, it looks like your images may have been taken with a flash and that's no good. When you are looking for stray light, you cannot use a flash. We are looking for the light from the optical system--not the flash. So it's a little hard for me to say with certainty what is stray light and what is light from the flash in your images. Either way, cleaning up the areas that I've indicated in the illustration should go a long way toward fixing your problem.

John

John Hayes:
Michael,
To be clear, here's a diagram. Yes, I am suggesting that you have to flock the insides of pretty much everything that you can see when you look backwards through the scope. That's almost certainly where the stray light is coming from. I don't have time to hunt down the images right now but years ago, I had a similar problem in a C14 with a connector tube. The inside of the tube produced a significant stray with colors from diffraction introduced by the turning marks. A little black flocking paper quickly solved the problem. From the look of it, you may need to cover more area so you'll have to figure out how to get in there. Getting good calibration results requires serious attention to detail so get everything as black as you can. If you get it all black and that doesn't solve the problem then we'll need to talk again, but I think that your odds of a simple fix working are pretty high.

Finally, it looks like your images may have been taken with a flash and that's no good. When you are looking for stray light, you cannot use a flash!! We are looking for the light from the optical system--not the flash. So it's a little hard for me to say with certainty what is stray light and what is light from the flash in your images. Either way, cleaning up the areas that I've indicated in the illustration should go a long way toward fixing your problem.

John

John, thanks again for taking the time, that's an awesome amount of information, in this post and the image thread you've shared. It must be a very bad case of stray light if you thought I used flash. I am sure I didn't use flash while taking the photos.

I also just looked down the tube and noticed it's not baffled, nor even black, more greyish. Now I have to make the decision of either going down the road of blackening everything, or selling it and get another telescope.

Thanks again a well to everyone who contributed with answers, what a nice community

Clear Skies everyone!

I don't think you can buy another edge scope and expect different results to be honest. It's just the way they are manufactured. It is mostly a non-issue unless a star's light hits it just right. Personally, if you are ok attacking this in two phases rather than one, I would flock the imaging train first. The reflection might begin in your OTA but it is likely to be bouncing around in the imaging train. That may be easier to flock or blacken. Your OTA will definitely benefit from flocking, but is it worth taking apart on your own? Anyway, that's more of a question for myself…makes me nervous to think about putting it all back together the same way it was before it was apart.