inFINNity Deck

Hi Brendan, If I look at the graph, I think that imaging should have ended at least half an hour earlier and perhaps started slightly later. In addition I would have added more subs for this object to reach at least 20, but preferably 40 subs per filter. You are used to DSLR, but remember that those shoot RGB at the same time but at a lower resolution (the Bayer pattern only has two green, one red and one blue photosite per four). So shooting in LRGB with a mono camera means considerable more imaging time than when shooting in colour to achieve the same result. The main issue here is the total integration time: IMHO one night simply is not enough to achieve a decent result, certainly not on this faint object. There is only an hour and a half of luminance in that image. On the other hand your OTA is f/5, whereas mine is f/7, so you may expect better results in a shorter period than I do (maybe @vlaivcan comment on this, I am not sure about how to calculate the difference between your 130mm aperture f/5 Newton and my 150mm diameter f/7 APO). My advice is to try adding more time to this object and see how results improve. Nicolàs

I have analysed the subs using my FITSalize and produced the following SQM-graph based on what ASTAP managed to calculate using the H18 star-database: Obviously ASTAP has some trouble determining correct SQM-values when the blue and red filters are in use. ASTAP has been tested against an Unihedron SQM-meter by the developer and earlier tests by myself and the developer have shown that with luminance and green filter the SQM-values are pretty correct, while blue and red generally score too high. The thing that worries me is the differences in the blue filter SQM-values. Ignoring the fact that their values are way too high, they should be closer together and form a smooth line, similar to the other lines. Imaging started quite early in luminance, which can be deducted from the slope during the first hour. Still at 19magn/"^2 it should be dark enough. The red session suffers from the same issue: dawn is measured during all of this session. The jump from green to red indicates that the red-filter SQM-values are too high and that the last red-sub was shot with an SQM-value of about 17magn/"^2. Interesting is the jump around 23:00, where luminance SQM-value drops slightly. This could be an indication of local light pollution (garden illumination?). Nicolàs

Normally not as the scope will not be focused to the light panel. That foam cap I use to dampen the light has structure and inconsistencies as well, but they do not appear to affect the flats. Are you taking flat-darks as well (so darks to correct the flats) and is the camera cooled while taking the flats? I normally take flats, darks, and biases at night to ensure there is no ambient light affecting the subs. Nicolàs

I had to do quite a search for the original thread in which I discussed this matter with the owner of a ZWO ASI1600 Cool, Jac Brosens (jbrosens), on a Dutch forum, but here it is (if you open it in Chrome it will be automatically translated). It appears that there have been different firmware versions causing different effect. The graph I showed before was taken with jbrosen's camera and had the tipping point between rolling and global shutter at 1 second. According to ZWO (see post 55 in that thread), the tipping point should be at 2 seconds for the ASI1600 and at 1 second for all other cameras. At the same time they told me that the Pro has no tipping point (whereas they first wrote that it was at 2 seconds), so there is some contradiction in their explanation, which is further discussed in post 56. Post 55 shows that the Pro that I have has no tipping point. In post 57 the effect is shown by jbrosens in his own flats using the same approach as Vlad just did, but now clearly showing the effect. I was sent the original fits which I processed using my own software and resulted in the graph I posted earlier. The original FITS-files are still in my possession and can be downloaded from my server. Nicolàs

I always use a white foam cap on the Esprit 150ED. A friend of mine has darkened the flat-panel by applying car window tinting foil to it. I would be interested receiving a few flats from that camera taken with exposures of 0.95s, 1.05s, 4.95s and 5.05s to see if that gradients shows. The graph I posted earlier was actual data of a non-Pro ASI1600MM. If possible I would like to receive these from both Brendan and Vlad. Nicolàs

Here they are, all three models ASI1600MM Cool, only the one with PRO on the housing does not suffer from this issue if I am right. By the way, my version of NGC4236 shown above has an integration time of 11 hours, 7 hours of which was luminance and still I think I need to at least double that. Nicolàs

Hi Hughsie, great images! I especially like the first one. What equipment did you use? I see that you have both a Lunt and a Quark and multiple cameras. Nicolàs

Here is the same galaxy taken by myself using a ZWO ASI1600MM Pro Cool and SkyWatcher Esprit 150ED (it light lacks a lot of light): https://www.dehilster.info/astronomy/deep-sky-objects/NGC4236_211029.jpg Nicolàs

Hi Brendan, the patterns around the brightest stars are the result of microlens diffraction, see https://www.cloudynights.com/topic/635937-microlens-diffraction-effect-explained/ There is not much you can do about that, apart from trying to reduce the amount of stretch and saturation around those stars. The ZWO ASI1600MM Cool comes in a normal and pro version. The normal one does not like flats taken with exposure times below 1s (USB2) or 5s (USB2). Those produce a sloped ADU level when compared to longer exposures: So these gradients can simply be solved by taking care that the flats-exposures are longer than 1s (USB3) or 5s (USB2). HTH, Nicolàs

Found another advantage of the ADC today: centring the so-called Sweet-Spot. H-alpha viewers such as the Lunt have an internal etalon, two glass plates that are very close to each other and therefore act as a filter. The light passing through an etalon is reflected between the two glass panes and by varying the distance from the light path, it is possible to amplify or extinguish certain frequencies. There are two ways to vary that distance: by forcing air between them (pressure tuner) or by tilting the etalon (tilt tuner). Regardless of the type, the etalon has the property that it has an area, approximately one degree in diameter, within which the damping/amplification is more or less uniform, the so-called sweet spot. Now the Sun is about half a degree in diameter, so it fits perfectly within that area. Since the damping/amplification within the area is just not quite the same, it is best to centre the Sun as well as possible around the sweet spot. Failing to do so will result in a solar-image that is not equally bright everywhere, something that can be clearly seen in the photo above (top right it is too dark, bottom centre too light). Today spent a few hours puzzling to get the Sun centred around the sweet spot. To do so, I first mounted the QHY163 without ADC and without Barlow behind the Lunt and shifted the sun over the image by slewing the scope until the sweet spot was centred in the Sun. Whether it is properly centred can be seen when the image is slightly overexposed. If the image of the Sun is not in the sweet spot, there is an overexposed area on the Sun's surface that is not centred within it's limb. It is then a matter of slewing the telescope until the overexposed area is neatly visible in the centre of the Sun. In my combination (Lunt and QHY163), the sweet spot turned out to be approximately at (2680, 1580) pixels. The camera chip has a resolution of 4656 x 3522 pixels and a size of 17.7mm x 13.4mm. Based on this, we can calculate that the sweet spot was projected approximately (1.34, 0.69) millimetres from the centre of the chip. Now, as this is just a small offset, I was wondering if the ADC could correct for it. So I mounted the 2x PowerMate and ADC and again checked the sweet spot again by slewing the scope and looking at the image. The sweet spot now turned out to be that far from the centre of the chip that the Sun didn't quite fit any more. Then played with the ADC (first only moved the levers, then turned the entire ADC a quarter of a turn and played with the levers again), until the Sun was neatly centred on the chip again. Since the telescope was still pointed at the Sun in the same way during this operation, the sweet spot was now also neatly centred (and without Newton rings :-)). Then at 15:48UTC attached image was taken (it was not the first of this afternoon ;-)). The seeing was not optimal with a mere 4″, but the important thing in this image is that the Sun is nicely and evenly exposed. Nicolas

Hi Pete, The idea is not mine, but I found it in the post on Solar Chat Forum that I mentioned above directly below my first image: https://solarchatforum.com/viewtopic.php?t=21128 Nicolàs

Can't wait to the final results! Here the sky is fully overcast... Nicolàs

Hi Steve, is this a cooled version of the ASI1778MC? If so, it could well be that we are looking at ice-crystals due to too rapid cooling. Nicolàs

This post and the one further below discusses solutions to problems I encountered when I recently added a QHY163 mono camera to the 80mm f/7 Lunt LS80THA in our observatory. Using an ADC I managed to get rid of Newton-rings and centre the Sun in the Lunt's sweet-spot. In addition I managed to get rid of the chessboard-pattern caused by the Panasonic chip that is used in the QHYCCD QHY163 (and ZWO ASI1600) and remove the vertical banding caused by the Unsharp-Mask routine. How it all began: A check with Stellarium learned that the combination of a Lunt LS80THA solar scope and QHY163 camera could theoretically produce full-disc images of the Sun when used in combination with a 2x Barlow. So day before yesterday I mounted a barlow (TeleVue 2x PowerMate) and the QHY163 camera behind the scope and took an image of the Sun (seeing was rather poor, about 8"): Needless to say that the Newton rings were rather disappointing. I never experienced them when using a ZWO ASI174MM, so it must be due to the camera. I had read about them before and knew this could be solved by applying a tilt-adapter. This, however, was not at hand and before ordering one I first checked if Newton-rings could be solved at all with this camera. The answer I found, although not immediately concerning this camera type, on SolarChat forum: instead of using a tilt-adapter one could also use a dispersion-filter (optical wedge) to eliminate Newton rings. The good point of that is that I do own two of them, which together form an ADC. And we do not need even need to take the ADC apart, but simply apply the whole ADC to the imaging train: In above image the levers of the ADC are at perpendicular orientation to each other. In that way the two wedges have a perpendicular orientation to each other, resulting in enough optical tilt to get rid of the Newton rings. In below image the above shown solar-image (i.e. without ADC) is shown at the left. At the centre another solar-image is shown with ADC and with levers in a zero degree orientation, while at the right a solar-image is shown with the levers at a perpendicular mutual orientation. Clearly the Newton-rings have vanished completely in the right-hand image. Adding the ADC has another advantage as is shown by the left two images: with ADC the solar disc is shown 2.5% larger than without. Of course there is also a downside to the used of the ADC: exposure time dropped by 33% from 0.73ms to 0.97ms, but that still is acceptable. Yesterday seeing was around 4", so I gave it another try with significant better result. This time I noticed that the camera results in a chessboard-pattern, ouch! I had seen this pattern in a milder form when using a ZWO ASI1600MM Pro Cool (same Panasonic MN34230 chip). Another Internet-search resulted in a post by Qiu Hongyun, founder and CEO of QHYCCD, in which he explained that it was "... due to the channel difference between R,G,G,B channel" even though this is a mono-camera. Simply because the Panasonic chip was originally designed for a RGGB-Bayer-pattern, the parameters for the four photosites of the chip vary. Qiu Hongyun did not specify whether it was due to variations in gain or offset, but stated that they could be solved by either using a flat-frame or dark-frame. Problem is that with the current capturing software this requires to take full-frame images, which is rather undesirable as it significantly affects frame-rate. Solution was given directly below that post: applying a 1.5px pre-blur in AutoStakkert! (can be found under experimental features) to the original data during processing. Indeed this greatly reduces the chessboard-pattern without significantly affecting detail as can be seen when comparing two images (left without pre-blur, the pattern can be seen in the solar surface, centre with pre-blur and significant less pattern): Both the left and centre images also show vertical banding (noticeable in the prominence). This is caused by the Unsharp-Mask algorithm in PaintShop-Pro that I use. To get rid of that I first resized the whole image by 200%, then applied Unsharp-Mask, followed by a 50% resize. The result is shown at the right in above set of images. So with that solved as well, I could finally produce full-disc image of the Sun using the QHY163 mono (image taken on 9 May 2022 @ 08:27UTC): With a diameter of about 2840px this has a significantly higher resolution than the 900px diameter I managed with the ZWO ASI174. Now the waiting is for sunny weather with better seeing. Above image still has an issue with the sweet-spot, as a result of which the illumination is uneven. This can be solved with the ADC as explained in the second part of this post below. Hope this post is of use and inspiration to others! Nicolàs

Hi Ags, I do not know the Solar Scout, but I recognise the differences when imaging with my Lunt LS80THA. I always try to tune my Lunt to have an even illuminated solar disc as contrast can be improved by using a non-linear stretch in IMPPG. If I look at your images, then 0-setting is spot-on, while the others result in uneven illumination, marked in red in below copy of your images: In processing I can easily deal with the left image, but cannot get rid of the dark section of the middle one or the banana-shaped dark section in the right-hand image. So I would go for setting 0. Nicolàs

Great animation Alex! Which scope and camera did you use? Nicolàs

Especially to those among us that do unguided imaging a new and free software-tool I recently created may be of interest: FITSalize. When doing unguided imaging stability of the set-up is of the essence. Question is how one can properly assess the stability of a tripod or an observatory and distinguish flexure in the imaging train from deformation of the basis of the set-up. From the images themselves it is impossible to assess whether elongated stars are the result of tracking errors or due to stability issues. FITSalize is a command-line tool that runs under JAVA and uses ASTAP to plate-solve the images taken and to determine their SQM values. It is built to analyse FITS-files from a stationary scope (i.e. a scope firmly attached to the pier or base of the mount and pointing in a fixed direction) and to convert the images to accurate alt/azi coordinates. Being taken with a stationary scope the alt/azi coordinates should remain unaltered during the imaging period. Any deviation may indicate issues with the stability of the set-up. As these plate-solves result in J2000 RA/DEC coordinates they cannot be directly used to analyse stability. FITSalize corrects for precession to produce mean JNOW RA/DEC coordinates from the J2000 RA/DEC, then corrects for the effect of nutation in longitude and obliquity of the ecliptic and for the effect of annual aberration to find the apparent JNOW RA/DEC. These are then converted to alt/azi and stored (with all intermediate results) in a .csv-file. The algorithms in FITSalize are based on J. Meeus, Astronomical Algorithms, (Richmond (VA), 2005) and have been compared to results from the SOFA-library (many thanks to Massimiliano Chersich for testing this, he also initiated this type of measurements last year at the 10Micron forum) and with the algorithms in Han Kleijn's ASTAP and Stellarium (only Stellarium does not apply annual aberration to the calculations). Using your favourite spreadsheet (examples are provided) graphs can be produced to visualise the stability: Above example shows the stability of InFINNity Deck (my observatory) over a period of approximately six hours. Deformation in altitude was less than 4 arc-seconds, in azimuth less than 2 arc-seconds. In addition to deformation measurements FITSalize can also be used to plot SQM-values against alt/azi. For this regular FITS that were acquired to image a target are analysed: In this example light pollution affects the SQM-values in the north-east of the observatory. From those same FITS the focuser gradient and intercept can be calculated: For more info and download of the software see the FITSalize-page on my web-site. Nicolàs

Nice images indeed. Here in the Netherlands seeing was around 6-7" according to my Solar Scintillation Seeing Monitor today, so not much details to be seen... 😞 Nicolàs

An alternative is using Stellarium for that. There it also is possible to define scopes, cameras and reducers/barlows. It directly shows you a nice red window over the heavens (here is SkyWatcher Esprit 80ED @ native focal length with ZWO ASI1600MM Pro Cool): It also provides information like pixel scale and actual FOV. Here is a way too short exposed image using that same scope/camera combination: Appears to be spot-on. 🙂 Nicolàs

I do agree with most that has been said in the last few posts, but the OP was asking for the pros and cons of mono vs colour. The point I tried to make is that you need to understand the basics so that you can avoid 'serious' mistakes in the acquisition of new equipment. As @Elp wrote "...if it were easy anyone would be doing it." This hobby is for sure a steep learning curve for all of us. Using the wrong combination may result in unnecessary frustration (not to mention having spent money on the wrong horse). I fully agree with @ollypenrice that we are indeed for a great deal processing limited (I found out myself very recently, still am reprocessing most of my images now). The next one would be seeing limited, closely followed by (un)guiding limited and then diffraction limited. Sadly enough only a few of us will be in a situation where the latter is an issue... Somewhere in that order of limitations we should add 'money limited'... 😉 Nicolàs

Hi Olly, normally we will not see the difference due to seeing, which for most of us is well beyond the resolution of our set-ups. I image at 0.73"/px, but seeing conditions here in the Netherlands are usually about 2-3", so 3-4 pixels. So theoretically my statement is perfectly fine (I would say double the resolution though, not four times, but that depends if you look at it in number of pixels or distance between pixels), but seeing usually is the limiting factor in our long-exposure deep-sky captures. If our images would not be affected by seeing, I am pretty sure we would see the difference between mono or interpolated colour data. Nicolàs

There is another difference between mono and colour not mentioned here so far: the resolution. A mono camera with 3.86 micron pixels (ZWO ASI1600MM Pro Cool) has a pixel every 3.86 microns, but a colour camera with that same pixel size (ZWO ASI1600MC Pro Cool) has a red and blue pixel every 7.72 pixels and a green pixel every 5.46 micron. In other words: if you look at the real resolving power of the camera (presuming both are used with the same OTA), the mono camera wins (in a 16 megapixel colour camera, 12 red and blue megapixels and 8 green megapixels are the result of interpolation not of actual sampling). It all depends on the OTA you want to use with the camera, whether or not you will actually loose detail (it depends on whether the combination is under- or oversampling). The optimum f-number can be calculated simply by multiplying the pixel-size with 3 for a mono-camera and by 6 for a colour one, so the MM camera needs about f/11.5, the colour f/23. Using the colour camera on a f/10 SCT will thus cause undersampling (which equals shorter exposure times), while the mono-camera is more or less on par. If we want to compare image quality between a mono and colour camera, we should take a mono-camera with twice the pixel size of the colour-camera. We will then immediately realise that at this same actual resolution the mono camera will collect 4 times as much light in the same period and thus is it possible to reduce exposure times by a factor 4 by using a mono-camera (at this same resolution). For more info see my article on determining the f-number (it is in Dutch, but Chrome should properly translate it): https://www.starry-night.nl/vergroting-onder-de-loep-hoe-bepalen-we-het-optimale-f-getal/ Nicolàs

That is why I changed to an EdgeHD in the first place. Sadly enough they fail to overcome the issue, at least in my C11... Nicolàs

hmmm, being an optical surface I would hesitate polishing it as that may affect the parallelism of the two surfaces. Better to dissolve it in an acid as recommended by Lunt (in response by Lunt to my inquiry): Being from the Netherlands, where CLR is not available, I used cleaning vinegar in increasingly long immersions until it was clean. Nicolàs

Just to make things clearer: mirror-shift and mirror-flop are two different things. The former is the effect of the native focuser pushing against the primary mirror and by that causing it to tilt. Mirror-shift is defined by Celestron as being less that 30" and hardly affects collimation. Mirror-flop is caused by poor mounting of the primary mirror in combination with gravity. Mirror-flop can have a significant effect on collimation. I had a C11 XLT carbon and still have a C11 XLT EdgeHD, both of which show severe mirror-flop. The EdgeHD has been returned to Celestron in order to get the mirror-flop fixed, but it came back as poor as it was before, so apparently this is how a C11 should behave. Celestron does not specify how much mirror-flop a SCT may have, so I have no way to check if transporting my C11 back may have caused the issue. More info about mirror-flop, and Celestron's response to questions about it, in this thread on a Dutch forum (opening it in Chrome should provide a reasonable translation). I only use the C11 for solar and planetary imaging. The way I deal with mirror-flop now in planetary imaging, is to collimate the C11 prior to imaging on a nearby star and to repeat that collimation after the meridian flip. Nicolàs