Marmo720

Thanks Carole. Interestingly, I had a look at my old M27 flats and each was around 1/100 sec and they worked much better (minus the strong dust donut). I also didn't have advanced bias/flats selected so couldn't change exposure length for flats until now so will play around and see what I can get tonight. Will share once I am done with tonight session. In the meantime, I wish everyone happy holidays and enjoy this time with family and friends.

Thank you for the analysis. Yes I noticed the bunnies dancing too. My camera to telescope is pretty firm but I only have 1 second wait between flat exposure so will change to be longer and see if that fixes the issue. My flat panel is inside the original box with circle cut to allow the dew covers inside and block outside light. It rests on the dew cap when I take the flats so I don't touch any part of the imaging chain. The two flat-flat calibration, is the first one the flat panels (the good one) and the second set is the iPad? If so, I will stop using the iPad and stick with the lightbox. Carole showed me how to do the flats manually so I can change the exposure time etc so will try 1sec instead of the current default APT plan. Thanks again.

Ok good. We have clear skies tonight so will try a few sets of 50 flats and see what they look like when combined with relevant lights. Thanks

Is it still under exposed? Even with the iPad and lightbox at maximum brightness and with just 1 white paper, I could only get the combined histogram at about 50%. I will try to do the flats manually and aim for 75% peak. At least if the new histogram are less under exposed then we are heading in right direction...

Will do later tonight when I get home. Thanks, Mo

Thanks @RolandKol. Yes the camera was originally removed for storage and attached it now for testing and tonight. Probably out of focus too. I had both ipad and lightbox at max brightness so interesting there is under exposure. Can you see any gradient for the light box due to led on one side or is it even?

I had a quick go in between rain showers to take some flats with the lightbox and iPad using white papers. I aimed for about 75% on the histogram and used ISO800. Each flat was taken 5 times so you will see 5x5 flat attempts. Hopefully this is useful in diagnosing a potential solution. Clear ish skies tonight so will try with lights too https://we.tl/t-0s7e1vQpx3?src=dnl

That is fair point and would explain why I could see the same issue on different target several hours later. Interested to see if Roland had luck with some of the subs and why that might be.

That is interesting and I really hope it was just a cloud and I can salvage/learn from this. But I think I also had the same issue with M42 which was much later in the evening. I will check once I get home from work in a few hours. @vlaiv If almost 50% have a cloud then it is possible you chose single sub with a cloud? Also, this might be a combination issue where single subs show the issue with my under exposed flats while full stacked image shows the impact of the clouds more?

Thanks @RolandKol. Interesting that the master flat looks fine but the stacked image has one side looking so bad. I would think the issue might have been due to lightbox having LED on one side but why doesn't that show in the master flat? Is it possible the issue is with my lights instead of the flats? I think I will do the flats that @vlaiv recommended with both the lightbox and the iPad methods just to rule that out as a potential issue. @carastro - a little bit frustrating to stay up all night imaging and to find out that it can't be used due to flats issue. But I am learning loads and looking forward to solving this and hopefully producing some good images. The last good images I took were the Witches Broom and M27 and both had stubborn dust bunnies which we finally resolved. So I am sure this will be too and excited for when it finally is all working

Thank you - helpful advise and appreciate the support. I will do the flats/bias and share so we can work through them. Based on the last part then, is it ideal then for the histogram for lights and flats to be in similar position? Or at least not too far apart to result in over/under correction without the use of large number of flats? I guess going further, I am imaging from bortle 8 location so at some point I would need to maximise my sub duration/iso settings so will be interesting to know where the light histograms should be? Around 80% to maximise SNR without clipping? I have guiding so I could technically do 5 min subs but without LP filter, I am easily pushing the histogram too far to the right even at ISO800 and sub lengths of 3mins. For reference, the images I attached have the histogram for the lights at about 50-60% while the flats are around 30% although I am not so sure on the flats reading as they took 10-30 seconds to capture. Both taken at ISO800 and lights duration is 60 seconds.

Thanks for the advise. I will try this. Just to check: - The idea is to stack flat1 and flat2 in DSS where flat1 is input as a light sub and flat2 is used as a flat sub? So the DSS process will subtract the two and result in uniform sub? Of course using Bias as well as suggested. - How do I view the histograms you shared? I have been using the histogram in APT and you said the split between the peaks is correct but the location of the entire histogram should be to the right about 3/4? I have noticed this is the case if I take brighter flats so just want to check that increasing the brightness of the lightbox so that the histogram in APT is about 3/4 of the way from the left is going to be correct? Or have I misunderstood? I read a few places the histogram in APT should be 1/3 from the left so just checking. Many thanks again.

Thank you so much for taking the time to provide feedback. Flats are probably underexposed due to me setting the lightbox on lowest setting and using 6 white papers. Each flat took significantly longer than I thought it would take but as the histogram looked correct, I assumed it was fine. In the past, I used an iPad at about 75% brightness and a t-shirt. So I guess change the brightness of the lightbox to being mid-high might be better and will try that next. I will also try with the iPad just in case as that used to work fine in the past. I didn't realise a single flat fielding would show the impact so much so I could spend the next clear night just checking my sub/lights/darks/bias using single files before wasting another evening of lights that I can't make use of. There wasn't any change between lights/flats besides moving the scope to better position for the flats. Don't think there was any focus shift as I followed up the M31 Flats with M42 lights and they also have the same issue. My setup train is currently Altair Wave 80 ED APO -> Altair 1.0x field flattener -> Canon astromod 600D. My mount is the is the Skywatcher HEQ5 Pro and I am using the ASI 224 MC for guiding. Software is APT for capture, PHD2 for guiding and Stellarium for target selection. I don't currently have any dew heaters and my original thought was maybe dew had covered centre part of the scope lens but I would think that would be obvious from lights and flats? Is this something could explain my images? Forecast is clear skies after midnight on Christmas Eve so maybe I will get a gift from Santa and I can have clear images too Thanks, Mo

Haha now I understand why you were asking about my gear setup. Confused me considering you pretty much helped me choose and setup my entire gear Thank you so much for spending some of your time trying to get this resolved and I appreciate the help. Absolutely confused at the moment and hoping it is an easy fix. @RolandKol thank you for the help too. I did think the flats took a lot longer this time than before and the lightbox is set to lowest with 6 sheets of white paper. I have in the past used ipad at much higher brightness and a t-shirt, and the flats would be much quicker but the histogram was about 2/3 towards the right side instead of where it is now.

Hi all, Below are links to my files from last week. Not having luck with stacking and cleaning the image so hope the community wisdom will help spot what I might be doing wrong and how to improve it. My camera is astromod Canon 600D, I have a field flattener on that and using an Altair Wave 80. I am using APT for capture, PHD2 for guidance with ASI 224 and I am applying dithering. Finally, I use DSS for stacking and a quick check on GIMP or Photoshop shows bright white halo in the middle and darker outsides. Many thanks in advance for any help. Lights: https://we.tl/t-9O4TS659iR?src=dnl Flats @ ISO100: https://we.tl/t-7UAh1fkHKr?src=dnl Flats @ ISO800: https://we.tl/t-GtRCNFfw5X?src=dnl Darks: https://we.tl/t-WTV5rQXlVg?src=dnl Bias: https://we.tl/t-8RNquuP4ZE?src=dnl

I am glad to hear your eyes are OK now. I spent the entire night out capturing last night in the freezing cold. Went to bed at 3am and woke up at 6am for work. So very tired at the moment but hopefully worth it. I captured 90x60sec subs of M31 at ISO800. Took new bias and darks too. I also took 53x60sec subs at ISO800 of the Rosette Nebula before the clouds stormed in. For Flats, I reduced the panel brightness to its dimmest and took: - 10x ISO 100 with panel in normal position. - 10x ISO 100 with panel in inverted position. - Same as above 2 but with ISO 200. - 20x ISO 400 and ISO 800 in the normal panel position. I inverted the panel to check for any gradient from the LED lights being on one side. Visually, I couldn't see any at all and the flats looked the same regardless of panel orientation. Hopefully you guys can spot any gradient once I upload the masters for each setup. I did a quick stack on the first set of IS100x10 Flats with my M31 this morning before rushing to work and I could still see the brighter centre and darker outsides after stacking. I will do stacks with all the different flats to see if any work and/or if you guys can spot where my issues are. Thanks, Mo

Didn't know - I hope you recover fast and well. Are you planning to image tonight if your eyes are better?

Thanks both. I will upload the master flats for different ISO as well as the lights/darks/bias after the session tonight. Hopefully can also tell me if there is gradient from the lightbox or if that is OK. Can't believe your filters haven't arrived yet Roland. Any hope of them arriving this side of Christmas before all the holiday posts?

The flats alone look fine to me in that I can see the slight vignetting and and dust bunnies that would be subtracted from the lights. Unfortunately, once I have stacked them in DSS with the lights, the final image looks bright at the centre and darker on the outsides. To the point where there is a massive bright halo around my target. In saying that, I sent the final tiff to @carastro and @RolandKol, and both produced fantastic looking images after some processing so maybe that is where my issue is? I just don't remember seeing such a huge halo back in the summer when I was using ISO100 for flats and found I could process easier. Hopefully skies stay clear tonight and I can produce a bunch of different flats to see what works.

Thanks. Not sure why I am getting bright centre and dark edges then as I currently take flats at same settings as lights. Maybe using too many flats? I currently use 50 flats while I see most people using closer to half that. I would think DSS should be able to take care of too many flats if that was the case? Forecast is clear tonight so will try as many different things as possible. Now that I have a working light box, I can just take a bunch of flats at each ISO and see what works.

Amazing images and really love that M42 as it is one of my favourite targets. I have to say - your dedication to the hobby against backdrop of such light polluted city and being out in the street etc is amazing. I am looking forward to seeing more of your images!

Really nice image! It was one of my first targets and seeing those colours just floating in space is lovely

Thanks - not much more than mine and says even light. Will get it if the current one shows light gradient in my imaging. The bright centre/dark outer + dust bunnies is what I saw after using the new light box to produce Flats so that is good news at least compared to iPad method I was using before which resulted in illumination on one side. I just need to get the correct Flat setting in APT to remove those effects. I hope!

Thanks. I don't remember the shutter speed but will check. However, I did the flats again last night using the lightbox instead of the iPad method and I didn't have the issue with the one side illumination which suggests to me that it might have been ipad slipping slightly or similar instead of camera issue/settings. However, using the lightbox last night resulted in bright centre and darker outer image so hoping the change the ISO down to 100 will help fix that.

Thanks for all the replies - apologies on my slow response as we had clear skies last night and I spent my time freezing trying to get the flats to work. @Davey-T - that is the exact same setup I did last night. I placed 6 sheets of white paper and set the light to the lowest level. Looking at the flats, I don't see any gradient caused by the LED being to one side so looks like it works for me even without rotating. @fireballxl5 - I thought it would also be evenly lit as well until I received it hence the post here. At a cost of £12, I was willing to try it with some white papers to diffuse the light. Seems to be working OK from last night test but will update once I have another clear night to test more. Not seen any that are evenly lit and assume might cost a bit. I did notice the light in the box looked "blue" but maybe that is due to everything else being in night vision. The histogram on APT looked fine as far as the colours go. @carastro - I forgot to add my setup to my signature, which would be helpful! I am using astromod Canon 600D with Altair Starwave 80 ED. No filter wheel etc. My current Lights setup is 60sec at 800 ISO. For Flats, I was using ISO 800 too which I now believe is the cause of my issues. My combined histogram for the Flats is pretty much dead centre or slightly to the right. I think it is meant to be about 1/3 from the left from reading online and discussion with you. I was using ISO100 during the summer for Flats, which resulted in better flats but had a few stubborn dust bunnies that I was able to clear a few weeks ago. For some reason, I forgot to change the ISO down from 800 so hopefully that will resolve some of my headaches with Flats. @Laurin Dave - Is your tracing pad also lit from one side? No issues with that using a few papers to diffuse the light? The gradient to me seems less obvious when the dimness is set to the lowest but considering whether I need to rotate or not as per @Stub Mandrel suggestion? Many thanks all for the advise as always.