Issue with L-Extreme Filter

Right, so if you never got good results with the filter then your conclusion that the iPad is not the issue may not be correct.Don't forget that the L-Extreme filter is an interference filter and an uncalibrated light source like an iPad shining from close by may introduce side effects that otherwise may not be seen (or may be seen but at a very low and non-intrusive level).

What do you mean with "the new flat method"? I understand that you must be very frustrated by now but please try to be more verbose because the more info we have, the better we can try to help you.

I'll have a look at the new darkflats today so hopefully I can see if those or the flats are the main issue. I do agree with Wouter regarding the iPad. A flat panel (or natural light), specifically made for taking flats, is designed to emit a broad spectrum across all wavelengths. If there are differences across the spectrum, you may have a different illumination in 1 over the other wavelength. This would cause issues for a nice flat as well, but I'm suspecting an issue with the darkflats as well, because the effect you show is so big. I'll investigate further today.

Thank you both. Some of my flats were also taken with natural light with a Tshirt over the end of the scope. I use both methods depending on what is available to me at the time. 

@wvreeven sorry I didnt tag you in my reply, but I used a tshirt with natural light too and didnt get any good results. 

@alpaca Sorry to hear that. This *may* indicate an issue with the filter because when I take flats like I described I get good results. But perhaps you may want to try even other methods (be creative!) to see if you can fix it. And wait until @vincent-mod is done analising your new data.

Ok, having a look now and the new darkflats do look better indeed, I see a normal signal there, as well as for the master-dark. The annoying thing with flats is, that you need to tackle issues step by step to find the issue.

I did perform another "experiment", by using your master darkflat as bias for the lights and not using the masterdark. This actually produced a better result! Soooo, the plot thickens? Could you take actual bias frames with your camera, so just like dark-flats but with exposure times of 0.5 seconds each. Take about 40 and use that as bias for the lights. What do you see? Not sure why that would produce a more normal result, it seems that the bias signal provides a better correction of the background in the lights, which makes APP have a better estimate of the background and how to correct it.

I think I may have solved it last night! Ok... so. Normally when I make my master flat file in Sharpcap, I have a target "brightness" on the histogram. Sharpcap does "live stacking" and calibration so it will literally apply the flat and dark to a fresh frame coming in and stack them live. So I set that up so I could see what it looks like (I normally do not do the calibration because if I screwed up the flat, then the data is ruined). To my surprise, the master flat that I made actually made the images look a little better than no calibration. The flat pattern also matched the pattern on the image, but the flat was not very bright. So I then got the idea to crank up the brightness on the master flat. I did a longer exposure than normal but ensured that I did not clip on the histogram and... SUCCESS!

I think my flats were just too dim for this data. I am sure I am doing something wrong, but as of now I got a pretty amazing result from MANHATTAN using 40 minutes of data on the heart.

Unprocessed APP output below!

Awesome! Well done on solving your issue! Yes, with the L-Enhance filter I actually take 10 sec flats 🙂

The L-eXtreme was doing 2.5 second flats last night with my iPad on full brightness. 

I guess I was just screwing up! I was worried my camera was breaking.... but when I looked at the darks, I saw no pattern so was perplexed to say the least. I will be shooting this target for a while and will post a link to the finished product!

Ah interesting. I did check your flat for clipping, but it seems to be exposed properly actually (it wasn't clipping on the left side). Anyway, it's solved and that's what matters. Congratulations! 🙂

Posted by: @vincent-mod

Thanks @wvreeven that's indeed likely the issue. Flats need to be corrected with a bias signal. For new cmos sensors and some other ones, this does indeed not work well. But taking bias frames at at least 0.1-1 seconds seems to work everywhere. Flat darks are therefore a good substitute. The flats need this calibration for APP to get a grip on the vignetting signal etc.

Vincent I have to hop in with a fast question and most likely one with an obvious answer. I have a ZWO2600mc pro used with the L-Extreme and get this message now when doing flats to create a MF. Is it telling me the master bias and master darkflat are needed to properly process? I never got this message with my 183mc Pro and I always skipped darkflats and sometimes bias.

Flats always need a bias signal yes, so either a bias or darkflats. This so APP is able to properly "see" the background and vignetting signal.

Posted by: @vincent-mod

Flats always need a bias signal yes, so either a bias or darkflats. This so APP is able to properly "see" the background and vignetting signal.

Thanks Vincent. I figured it was scolding me for a reason. I like that the program is wiser than I am. 

Haha well, questions are always good to ask anyway. 🙂