Thought I might post this for people deciding between a 1600mm and 294mm so they could see how microlensing issue resent in the 1600mm affects a final lrgb image. I haven't really noticed it in narrowband however. This is from an Esprit 100 F5.5 refractor so there should be no diffraction spikes but the bright stars to the lower right are showing diffraction effects.
David, of course Orion (M42) is notoriously difficult to process correctly, easily fixed in Photoshop using a layer mask. I believe the 294 has significantly more issues than the 1600, such as the AMP glow and poor sensor cooling scene as, leading to dependance on gymnastics with Flats. The 294 backlit architecture does not lend itself to even substrate cooling, producing gradients when used in traditional long sub imaging. The 294 is fine for high frame rate video, and EAA use. By comparison the 1600 does not require Flats at all, I never found them necessary.
That’s not microlensing on the 1600. It’s much more obvious than that...it’s a square grid pattern. If you point it at Alnitak or another similarly bright star it’ll become very obvious after you’ve integrated a few subs.
I also have an Esprit 100 and 1600 and the only image I’ve felt the microlensing effect has ruined an image is around the Horsehead nebula, with above mentioned Star featuring heavily :LOL:
You’re most likely seeing something actually causing diffraction, like the leaf of a tree or something else funky.
I've grabbed a cropped sub from the blue filter it shows the grid a bit better, it's definitely not an obstruction, the star probably isn't bright enough to really show it. I can also agree that the 294mc is not without its issues but with the 1600 sensor being discontinued it will soon be the only new option. Is there a way of using something like a layer mask to fix microlensing? I've had some success with the clone tool but I admit my photoshop/gimp experience is fairly limited.
Ok now I'm confused, Is in not the reflections of the microlens array being reflected back due to the lack of AR coating on the sensor cover glass? Or are you saying the sensor itself is being reflected back from my filters and/or AR Cover glass on the front of the camera. As far as I know my Astrodon filters are AR coated both sides? Also If it was the filter, corrector or something else would the reflections not be further from the star? Each circle is no more than 65px apart.
I guess I just assumed because it looks exactly like what I'd expect with all those circles.
Ok now I'm confused, Is in not the reflections of the microlens array being reflected back due to the lack of AR coating on the sensor cover glass? Or are you saying the sensor itself is being reflected back from my filters and/or AR Cover glass on the front of the camera. As far as I know my Astrodon filters are AR coated both sides? Also If it was the filter, corrector or something else would the reflections not be further from the star? Each circle is no more than 65px apart.
I guess I just assumed because it looks exactly like what I'd expect with all those circles.
The grid pattern in your blue channel image is the microlens grid pattern, the larger and more obvious circular pattern is something else.
I might have a go when Orion gets high enough over the neighbours, as I've never noticed the grid pattern on those stars you're seeing it on (and I do go looking for it!)
Ahh I see, yeah I was only talking about the grid. Not sure about the circular one. Now that I look at it I see it wasn't very clear. The circular one is a mystery to me to to be honest, this is the only image I've encountered it. Maybe the grid is not quite overlapping and making a circle
Been doing a little research and learned some pretty cool things. First of all when I examined the channels separately a found the grid was larger and more spread out in the red channel while it was small and tight in the blue. I thought to myself if that corresponds to the wavelength of light, maybe I can use it to calculate the thickness of the cmos cover glass?
Turns out the person who runs Geoastro has done most of the work for me. Unfortunately they did not provide their spreadsheet so I had make a copy for myself to make the calculations a little easier. I will provide a link for anyone who would like to play around with it themselves. Using it I calculated an average distance of 1.3mm, which sounds about right to me. It also appears I was correct in my assumption that an uneven overlap results in a round artifact in the final image.
If you push any system on a bright star you'll get ghosts. Here's my CN-212 with just mirrors in the imaging train but for the camera CCD glass.
That's alpha crux.
David, I like the analysis - it appeals to me being a spectroscopist.
I have also had to look at the sensor cover plate as a source of resonance banding in the spectrum. The effect we see is very similar to that produced by an F-P etalon filter.
I experienced this effect while testing a high resolution spectroheliograph.
The reason for mentioning all this related testing, is to remind you that the sensor cover plates were all measured to be around 0.3 to 0.5mm think.
None were in the range you seem to calculate.
I need to double check my data files, but from memory the cover plate in the ASI 1600 is 0.5mm thick.
Thanks for the input Ken. I really don't claim to be an optical expert it's quite possible I'm wrong I wasn't able to find the data on the spec sheet so I just googled cmos cover glass thickness and got a result of about 1mm. I think I might just blame the data, its not a single wavelength so my results say ~=1.3mm +-1mm
The “geoastro” ghosts were generated between the sensor and a remote (20mm) filter element.
I think this could be a different process from the narrow band etalon effects we see in Spectra.
David, are your three images above R G and B channels (in that order) ?
I think they are GBR, I think if you hover your mouse over them it should tell you which is which. I Probably should have paid more attention while uploading.
Dunk and Marc - it seems there is a difference of opinion over what microlensing actually is.
I always thought it was precisely what we see above - a reflection of the microlens array from the back of the sensor window on particularly bright stars (Alnitak being notorious). Also, Marc - I can't see anything particularly wrong with the image you posted - where is the microlensing you refer to in that image?
Sorry for being a dunce - maybe I've misunderstood this all along?