inFINNity Deck

In order to check the collimation of the objective one can place a Cheshire in the focuser, cover the objective with its lens-cap, illuminate the Cheshire and examine the reflected image of the Cheshire. If properly collimated a series of concentric reflections can be seen. If not, the reflections will not be concentric. Nicolàs

I agree with @ollypenrice that this is not a tracking issue. I have taken Tony's second image (the NINA screendump), cut out the image and extended it upwards. I found this point from which radial lines seem to coincide with all star elongations. The stars near the centre of the upper edge are almost round, no significant elongation there, but those near the bottom are terribly elongated. To me this is an indication that the issue must be sought in the imaging train, just as Olly wrote: something is not perpendicular in it. Nicolàs

I discovered mine was overdue after some two years and a half. I remember reading about this issue when I had the scope for about a year and at that time it showed no degrading. The replacement was done end of September 2020 (installed the scope in May 2018). Incidentally I checked the new filter three days ago and it still looks fine. Replacing the filter is fairly simple and is shown in this video. The retaining ring was fixated with a small drop of silicon. So I first removed that and could then already rotate the ring without tools. It has to remain fairly loose, so a simple pair of compasses should do the trick. Nicolàs

I had the same issue with my B1200 and that was solved as indicated above by others. Perfect service by Lunt and Bresser! I cleaned the old filter using descaling agent and keep it as a spare. Although the descaling worked fine, I still can see some unevenness in the area where it was affected most. Nicolàs

Hi Astroblagger, have a look at this video: Instead of cotton I use odour- and colourless Kleenex as recommended by Baader. Nicolàs

I use colourless nail polish for the spider threads, it comes in small quantities and with a nice small brush. May also work for horse-hair and even thin copper wires. Normally the thicker wires (e.g. horse-hair, copper wire) are not glued but attached with small cylinder-head screws. Nicolàs

In the old days cross-hairs were either made of spider's cobweb or horse-hair. The former is a bit tricky to install, while they may be a bit too thin for astronomical purposes, the latter is fairly easy to install and should be thick enough. I have restored several geodetic instruments using both types of material, here are three examples: http://www.dehilster.info/geodetic_instruments/1919_keuffel_esser_transit.php http://www.dehilster.info/geodetic_instruments/tavistock_theodolite.php http://www.dehilster.info/geodetic_instruments/graphometer.php Nicolàs

Hi Andy, Try step-by-step elimination (so apply each of below steps and take new images before applying the next step): - turn around the filter wheel - remove the filter wheel - remove flattener (if present) - use a different camera (if available) ZWO has masks for the 36mm unmounted filters, but those remove other artefacts that those seen here. I have described them on a Dutch forum (opening in Chrome should translate it): https://www.starry-night.nl/forums/topic/maskers-voor-zwo-efw/ The old style ZWO H-alpha and S-ii filters (produced before June 2018) produced concentric halos, which I described here: https://www.starry-night.nl/forums/topic/halos-en-zwo-filters/ HTH Nicolàs

Quality as always, congratulations Nigella! Nicolàs

Please note that the bigger the aperture, the more the seeing will affect the minimal observable details. So it also depends on the climate you are in whether more aperture is key above certain limits. Nicolàs

that looks very clean, no issues there then. Nicolàs

I can see them both and wonder what your flats look like. Did you make and apply any? If you made them, could you post the master flat here? Nicolàs PS: nice image!

You could take a strip of aluminium of a convenient width, drill two holes in it and bolt it to the two rings. Then take some tie-wraps and fixate anything you like to that aluminium strip. Nicolàs

Some scope rings allow mounting a dovetail on top of the scope. That second dovetail will be a nice platform for a PC, dew-controller, USB-hub, etc. So it merely depends on the type of rings you have. Can you post an image of your rig? Nicolàs

I do exactly the same (laser for secondary, Cheshire for primary), works like a charm. Nicolàs

Mind you that the larger mounts also have a minimum payload, even though it is never specified. I once wanted to do some tests with only a single scope on my GM3000HPS, but found out that the 15kg SkyWatcher Esprit 150ED was not heavy enough to get my mount balanced, it required at least 5kg of additional weight to be able to use a counterweight on the counterweight shaft. The shaft alone was just too light to balance the scope and the counterweights I have are 20kg each... (as far as I am aware there are no lighter ones for the GM3000). Nicolàs

This of course depends on the mount that is used. So far I have not been guiding (10Micron GM3000HPS), although I have to admit that I will try guiding for the first time coming months to see if that is beneficial to star size. My subs are usually between 30s and 420s, here is one consisting of 60 x 420s subs (7 hours data) in H-alpha, O-iii and S-ii: https://www.dehilster.info/astronomy/deep-sky-objects/NGC7380_211028.jpg Nicolàs

Hi Paul, most important points have already been mentioned above, and I agree that the mount is key, so do not economise on that. Regarding the various APOs: I started out imaging using a SkyWatcher Esprit 150ED. A few months ago I added a SkyWatcher Esprit 80ED to the set-up as I noticed that the 150ED is a fine scope, but with very limited FOV (Field Of View). Here is the difference: M13 using SW 150ED and ZWO ASI1600MM Pro Cool: https://www.dehilster.info/astronomy/deep-sky-objects/M13-colour.jpg M13 using SW 80ED and ZWO ASI1600MM Pro Cool: https://www.dehilster.info/astronomy/deep-sky-objects/M13_210823.jpg When I started looking for a smaller scope I used Stellarium to make my decision. In Stellarium it is possible to define a camera and all the scopes you possibly want. Then Stellarium will show what will fit the sensor, so you get an idea of what you can/cannot achieve with the combination. At the time I made myself the following comparison-grid with the 150ED at the upper left as reference, the red rectangle represents the imaging chip of the ZWO ASI1600MM: HTH Nicolàs

Hi Malcolm, any luck with the weather lately (and with chasing the root cause of the artefacts)? Nicolàs

Hmmm, clicking that link redirects to FB, here is the proper link: https://webb.nasa.gov/content/webbLaunch/whereIsWebb.html Nicolàs

Even if the filters are not parfocal, this can be done without the need of a full refocus. Packages like SGP and NINA have the option of filter offsets. Those offsets need to be determined once and then entered, after which the software applies them for the filter changes. Although I image in traditional sequences (i.e. colour by colour) I use the offsets to shorten the focus-runs by always focusing in luminance and applying the offset for the filter that is used for the current set of subs. Above package do allow repeating LRGB-NB sequences. I do not bother too much about non-finished sequences due to clouds as most of my sequences do not fit a single night anyway (they tend to be 20-45 hours). So I check in the morning what was properly recorded and adjust the sequence for next night to get the balance right again. Nicolàs

Add to that: "for short darkflat exposures (i.e. <= 5s)", as indicated in the OP's article. Nicolàs

For me that would indeed be of interest. As I explained before my flats range from 1s to 67s, depending on the filter used. So I hope this experiment is repeated for longer exposures like 30s as @clouzot suggests, but also for 45s, 60s and 90s. As my mount is in Italy since the first week of November for maintenance and not expected back until after Christmas, my observatory is completely stripped down, so I have no easy way to produce some results myself (and last night we had crisp clear skies... :-(). Looking forward to further tests! Nicolàs

I am still following this interesting thread and agree with @vlaiv that running this simple test provides more insight than telling each other they are right or wrong based on gut feeling only. So if using a constant suffices, then the suggested test should indicate so. Nicolàs

Hi David, where reasoning stops, sealants start... 😉 Most important in avoiding the ingress of water is simple: avoid it getting there in the first place! If the concrete slab has yet to be pored, try to make it in a way that water will not want to go to the inside of your observatory. There are multiple solutions for this, but in basic principle they are all quite alike, the next image shows four variants of it (dimensions are exaggerated): So the red and blue lines are the surface of the concrete slab. The basic principle is that the surface outside the footprint of the observatory is sloped by at least 5mm per meter. In above figure profile A represents the most basic version of that profile. Ingress is even further prevented by having a raised floor inside the observatory as in profile B. Profile C has the raised floor all the way to the outside of the wall, which helps to keep torrential rains out, but is not as good against ingress as profile B. Profile D is even better as it combines all three defences: the outside slope, a raised edge along the outside of the wall and a further raised floor inside the observatory. Once again, the dimensions are exaggerated: the slope 5mm per meter minimum, the raised edges 10mm should normally suffice, but the higher the better. Nicolàs PS: of course the pier should have a separate concrete foundation that is not in contact with the slab.