Chris Parfett:
Alan Brunelle:
Another issue I found with this lens is the stock dew/light shield sucks. I never trusted it and quickly made an extended shield
Hey Alan, what did you make your extended shield from?
Edit: I see it in your description. I missed that. Did you leave the OEM shield on and attach it to that?
Chris, no problem. My description is not detailed. It really it could be made from just about anything. I found a fairly stiff thin foam sheet material at an art supply store. I liked how it could be easily wrapped around the stock shield, roughly following the flair of the stock shield. But it is a bit tighter than the stock one. Using the stock shield as the structural base of the extension adds stability and an easy means to still remove the shield. The foam is also naturally very non-reflective, but the whole inside is still coated with a flat black "chalkboard" paint. The square plastic artboard mask is used to keep the foam shield from becoming not round and rests on my oversized losmandy plate. This also helps isolate the front of the optics from the heat of my computer. The placement of my computer and power pack might have been better designed!
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Thanks Alan. So far I have painted the inside of the ZWO adapter a flat black as well as found an extremely small spacewhere the filter drawer connects that i will also cover ( I don't know if it is big enough to matter. I had to have the flashlight right up against it at its brightest level to see it) and attempt to make a slightly longer dew shield. The long range looks extremely poor, but if I can get a little time in with no moon interference this is where I'm going to start to try and figure this out.
Chris.
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Best of luck Chris.
I should add, that I know that I have some light leaks in my connections between the back of the lens and my camera. I see that when I take darks or flats during the day and do not wrap that area with a black sock! I do not think it really causes me problems during an imaging session in the dark. However, even still, I have taken to wrapping the area with some cloth electical tape, just in case. It is non-obtrusive and the adhesive is rather weak and allows for easy removal.
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To get this lens to correct properly I need 75 flat frames at .250s per exposure using a white LED tv screen with a tshirt, 2 layers, over the lens.
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Thanks Wes,
I have been using 50 flats/dark flats, and have ran them at about the same exposure time as you as well as ~ 2.6 seconds with different light sources. 2 layers of a white T-shirt were used as well.
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I had same issue with different lens but I was shooting M101 directly into light pollution. I knew I am going to deal with Lens Vignetting. I tried GraxPert with Lowest Setting through PI and it helped with Vignetter removal ( I did not take FLATS).
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OSC Neon Palette:
I used the following settings: everything in default, except High Threshold set to 0.40, Scale set to 2.20, Smoothness set to 0.12 with automatic convergence, and Structure Protection disabled for this issue and data.
I just tried these settings except I kept automatic convergence checked for my M101 data and it seems to have worked using Gradient Correction Tool. Thanks  |
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Chris Parfett:
Thanks Alan. So far I have painted the inside of the ZWO adapter a flat black as well as found an extremely small spacewhere the filter drawer connects that i will also cover ( I don't know if it is big enough to matter. I had to have the flashlight right up against it at its brightest level to see it) and attempt to make a slightly longer dew shield. The long range looks extremely poor, but if I can get a little time in with no moon interference this is where I'm going to start to try and figure this out.
Chris.
@Chris Parfett now I’m curious! Did your painting and extended dew shield work to solve your issue?
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Michelle Rousset:
Did your painting and extended dew shield work to solve your issue?
Negative. I had a 30 minute window just recently and both of those plus covering up the filter drawer area for possible light leakage did not help. Next step is to run wide open to see what that looks like.
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Chris Parfett:
Michelle Rousset:
Did your painting and extended dew shield work to solve your issue?
Negative. I had a 30 minute window just recently and both of those plus covering up the filter drawer area for possible light leakage did not help. Next step is to run wide open to see what that looks like.
* So bizarre. I hope you can find the cause. Good luck!
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Chris Parfett:
The F-stop remained the same for flats, and I re-took some sky-flats even to try something different than the flat master flats. So I'm still scratching my head on it if it is flats not doing their job or something else.
Chris Parfett:
@Alan Brunelle @andrea tasselli
After some further investigation the ZWO lens adapter does have an exposed aluminum flange that does face the camera sensor. Could this possible be the problem that is maybe causing an internal refection?
Is there any chance you could aim the camera you used to get this photo, more directly into the image train and scope here? Ideally, if you can get the optical axis of the camera you are using to take the photo, right on the optical axis of the scope (i know it won't be perfect, but as close as possible)... If you can do that, you would get a better feel for what your imaging camera will "see". Anything that you see from that vantage point that reflects could be the culprit.
Oh, I guess another thing before you get that photo. You would ideally want the light illuminating the inside of your scope and image train to be coming from the front, and the back should be shaded. That way, any reflections would be more representative of the kinds of reflections your imaging camera might in fact "see" when attached.
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Chris Parfett:
Thanks Wes,
I have been using 50 flats/dark flats, and have ran them at about the same exposure time as you as well as ~ 2.6 seconds with different light sources. 2 layers of a white T-shirt were used as well.
you do 2.6 second flats? Thats too long, Im doing .250s exposures, a fraction of a second. Im using the same setup as yours, you dont want too long of a flat because it over illuminates the interior of the lens.
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Jon Rista:
Is there any chance you could aim the camera you used to get this photo, more directly into the image train and scope here? Ideally, if you can get the optical axis of the camera you are using to take the photo, right on the optical axis of the scope (i know it won't be perfect, but as close as possible)... If you can do that, you would get a better feel for what your imaging camera will "see". Anything that you see from that vantage point that reflects could be the culprit.
Oh, I guess another thing before you get that photo. You would ideally want the light illuminating the inside of your scope and image train to be coming from the front, and the back should be shaded. That way, any reflections would be more representative of the kinds of reflections your imaging camera might in fact "see" when attached.
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Wes Schwarz:
you do 2.6 second flats? Thats too long, Im doing .250s exposures, a fraction of a second. Im using the same setup as yours, you dont want too long of a flat because it over illuminates the interior of the lens.
I also did do sky flats at .210 to try something different and that was the same outcome.
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Chris Parfett:
Jon Rista:
Is there any chance you could aim the camera you used to get this photo, more directly into the image train and scope here? Ideally, if you can get the optical axis of the camera you are using to take the photo, right on the optical axis of the scope (i know it won't be perfect, but as close as possible)... If you can do that, you would get a better feel for what your imaging camera will "see". Anything that you see from that vantage point that reflects could be the culprit.
Oh, I guess another thing before you get that photo. You would ideally want the light illuminating the inside of your scope and image train to be coming from the front, and the back should be shaded. That way, any reflections would be more representative of the kinds of reflections your imaging camera might in fact "see" when attached.
Alright. I think there are two potential surfaces that might indeed be reflecting that could cause the issue. The flange at the back there, in particular, might benefit from some diffuse blackening (more than one way to do that). There might be another surface farther in, that if you can do the same to that, it might help. That assumes the issue is indeed a reflection issue.
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Jon Rista:
Alright. I think there are two potential surfaces that might indeed be reflecting that could cause the issue. The flange at the back there, in particular, might benefit from some diffuse blackening (more than one way to do that). There might be another surface farther in, that if you can do the same to that, it might help. That assumes the issue is indeed a reflection issue.
That's very unlikely, since it shielded by the camera flange and it is well blackened. The most likely source of reflections (back-reflections, as it were) is the Nikon flange on the adapter, which is all shiny chrome.
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andrea tasselli:
Jon Rista:
Alright. I think there are two potential surfaces that might indeed be reflecting that could cause the issue. The flange at the back there, in particular, might benefit from some diffuse blackening (more than one way to do that). There might be another surface farther in, that if you can do the same to that, it might help. That assumes the issue is indeed a reflection issue.
That's very unlikely, since it shielded by the camera flange and it is well blackened. The most likely source of reflections (back-reflections, as it were) is the Nikon flange on the adapter, which is all shiny chrome.
If there is another flange that may block the light, then I'm inclined to agree. Something shiny chrome is more likely to reflect. FWIW, anodized elements, even though they may appear black, are also often key culprits of reflections in the image train. That was my main problem back when I was trying to use an RC. I had a bunch of black anodized spacers that were not microbaffled, and they caused significant problems.
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That particular flange is in fact internally threaded or "microbaffled". If you already have a anti-reflection paint handy then it may well worth the effort to cover all likely areas within the filter drawer holder.
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andrea tasselli:
That particular flange is in fact internally threaded or "microbaffled". If you already have a anti-reflection paint handy then it may well worth the effort to cover all likely areas within the filter drawer holder.
The Nikon lens flange that the ZWO filter drawer attaches to is definitely exposed aluminum as shown in the picture. I could try and apply some flat black paint to it. I curious as to why more people using this lens are not having the same issue if that is what is causing the issue?
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Filters, possibly. Or the lack thereof. Have you tried the suggested test of maximum aperture and, I shall add, Just the lens and the camera?
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andrea tasselli:
Filters, possibly. Or the lack thereof. Have you tried the suggested test of maximum aperture and, I shall add, Just the lens and the camera?
It looks like there maybe a couple hours tonight to finally test it wide open. When you say just the camera and lens do you mean no filters? If so I have only ran this setup without any filters as of yet. The odd part about it is when I was imaging in the fall when the lens was new this problem did not exist as far as I can tell. Nothing changed in the image train, and the F stop was also not changed. I will try and attach some starless images when I first was testing the lens in a bit.
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I mean just the camera and the lens, with no filter holder. Just in case. Best of all, just lens and a DSLR, so no intervening adapters.
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andrea tasselli:
I mean just the camera and the lens, with no filter holder. Just in case. Best of all, just lens and a DSLR, so no intervening adapters.
Ok. I will see what tonight brings.
Here are some fall images with the same setup. I can't really see it, but maybe it's there....
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Strong reductions in noise do then to blunt the appearance of such artifacts so it might be hard to tell. It is easier to compare flats. The before and after would provide an interesting comparison.
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Chris Parfett:
Wes Schwarz:
you do 2.6 second flats? Thats too long, Im doing .250s exposures, a fraction of a second. Im using the same setup as yours, you dont want too long of a flat because it over illuminates the interior of the lens.
I also did do sky flats at .210 to try something different and that was the same outcome.
Chris, I have the exact same set up as you. I use a 2600 MC with no filters. I use a ZWO magnetic EF filter drawer to attach to my lens. I have blackened the bayonet on my lens. I have went through the ringer trying to get flats to work on this lens way back when I bought it in 2015. In fact, the reason that I purchased Pixinsight was because it corrected my flats on the first try after messing with other programs, that would not work. Specifically for this lens.
are you using Pixinsight? I have pasted in a table from their website, which suggests the proper way to integrate flats. Are you manually creating a master flat?
I will say that based on your last response, I have never been able to get Sky flats to work properly- with this lens. The only way I have ever had 100% success no fail with flat frames in this lens is to take very short exposures with a white shirt stretched over the lens Hood with the camera flush against a white TV screen as I mentioned earlier. I use .250 second exposures. You need about 75 to average out the refresh rate of the screen.
using a flashlight is never going to work Sky flats I doubt will work properly. In my opinion, there is only one way to really make it work and that is with either an EL panel or a LCD screen illuminated white and diffused by a tshirt. If you are using gain 100 and shooting F2 .8 there is no way your flat exposures should be more than half of a second.
Also, make sure you are using large structure rejection when you integrate your flats. Edit: I should say try experimenting with this if you use tv flats, it can make a big improvement.
The table is on line 39
https://pixinsight.com/doc/tools/ImageIntegration/ImageIntegration.html
Also, have you tried using a master bias instead of flat darks? That is the only other thing I can think of that I have done differently. Im not realizing I dont have any examples on astrobin of me using this combo, they are on my flickr page.
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