SyedT

Hi all, Chasing after large mosaics, I decided to take the plunge and have got a full-frame sensor (Altair Astro 61MFX). I already have a Tak FSQ106-ED and its matched 0.6x reducer which brings the scope down to an insane f3. I was previously using a QHY268M with this combination, and corner stars were not perfect, but not that bad either. Binning was causing a headache with star shapes and colour combination, however, I definitely wasn't expecting perfect stars with the new combination, but despite accurate backfocus (56.2 mm) there's significant star distortion all around the image, which makes me think this is related to field curvature (despite Tak advertising a 44 mm corrected imaging circle at f3). I removed the reducer and hey presto, the distortion is gone apart from one corner (which is definitely tilt as Tak focusers leave a lot to be desired). I've uploaded some images on Google Drive, would appreciate any advice: https://drive.google.com/drive/folders/1K2318n9blCVL9acrAl0ybandzZ-HgB_f?usp=drive_link If this reducer doesn't work, I may end up trying the 0.73x reducer or just using the FSQ at its native f5 speed. Cheers!

Well done Jon, especially on your perseverance. I've thought about throwing my kit in the bin many times, but only just end up buying more!

Thank you! The more I visit Wales, the more I want to live there.

Wales is my favourite place to visit, and for good reason. I recently stayed at a cottage which was at the end of a winding single-track road near the top of a mountain. Getting there was not the easiest thing, but boy was the view worth it! Unfortunately the moon was full and clouds were plentiful, but I managed to get enough subs in between clouds to get something usable out of it. I can only imagine how this image would look if it was a new moon and the skies were clear. Experiences like these make me want to move to the countryside for sure. Equipment: Astromodified Canon 6D Mark I Canon 24-70 mm f2.8 @ 24 mm f2.8, ISO 3200 Optolong L-Pro EOS Clip Filter

Is it doing it in both axes? My M-Uno stopped slewing in RA and it turned out that the belt had disintegrated! If it's both axes then very unlikely, but just something to keep in mind I suppose.

Thanks for starting the thread! For those with 64-bit Windows and NVIDIA GPUs, this webpage takes you through using the GPU for Starnet when using Pixinsight, which massively accelerates the process: https://darkskies.space/pixinsight-starnet-cuda/ Starnet V2 is a huge improvement on V1, both from a star removal and speed perspective. In PI, V1 took 1 min 55 seconds and V2 took just 55 seconds via the GPU-accelerated process described above. It's much better at identifying and removing larger stars and also leaves fewer and less obvious removal artefacts. Original: V1: V2:

Thank you, I'll go for the ZWO filter in that case! Will report back with results. Cheers Olly, saving this to my workflow!

Thank you, this is really helpful! I'll have a look at the threads on the reducer today and put an order in. Would the filter I suggested be OK? Or are there any other filters you've heard good things about?

Thanks Olly. Do you have any tips for processing bright stars? I find the main issue is that while the core of the star gets reduced OK, the actual outer halo just displays "softening", with not much of an effect on the halo itself. So would you say that the filter needs to be right next to the sensor? My issue there is that my backfocus is very tight so I'm using a direct connection from the camera to the filter wheel i.e. there are screws which go through the filter wheel directly into the body of the camera. The rest of my connections are threaded with no nosepiece interface. My current imaging train is: QHY268M --> QHYCFW3 --> M54-M54 male-male adapter --> Rotator --> M54 male-male adapter --> 4 mm M54 extension ring --> 0.6x reducer (which slots and then screws into the 0.6x reducer extension ring). If the 0.6x reducer has female threads at the telescope end, could I attach the UV/IR cut filter to these threads? Or would that be too far away from the sensor? I'm thinking of going for the Astronomik L3 filter: https://www.astronomik.com/en/uv-und-ir-block-filter/luminance-filter-l-1-l-2-l-3.html

Thank you for the reply, that explains it. Much appreciated! Do you think adding a separate UV/IR cut filter will help?

Hi guys, Looking for some collective wisdom from SGL regarding star bloat. I've recently acquired a lovely FSQ-106ED and the matched 0.6x reducer. I've noticed that the brightest stars are significantly bloated in the blue channel, the smaller stars seem to be OK so I think focus is fine. Images attached below (unedited RGB, R, G, B respectively). I've done some reading and it seems that it's unavoidable even in some of the best scopes e.g. TEC 140. What I'm interested in are suggestions that a separate UV/IR cut filter can be installed in front of the imaging train to reduce bloat e.g. Astronomik L3. If anyone has tried that or there are any other suggestions to tackle this, would be much appreciated! Equipment: QHY268M, Chroma RGB filters, Takahashi FSQ-106ED, Takahashi Focal reducer QE 0.6x Acquisition: Gain 0 Offset 20. 50 x 120s exposures per channel. Cheers

Ordered a Tak adapter expecting it to take months considering it's not an item which is purchased very often, received it in about 3 weeks. I also wanted to say that whenever I've had to return items, FLO have been very responsive and the returns have always been no-fuss. Thank you FLO!

Cheers guys. My thoughts were about spacing too, but the issue I had was that with the 0.7x reducer, the recommended spacing is reduced to 105 mm (vs 133 mm without it). The only thing I can think of is that this is inaccurate as it may be based on the advertised focal length of 2032 mm, whereas the actual focal length in the white paper is 2125 mm. This would also fit in with the extra focal length that I seem to need according to the back calculation (if it really is as simple as that). I'll try out extra spacing at the next session and see how it turns out.

Hi guys, After finally getting some clear skies, I've managed to get collimation as good as it will be for now. The issue now is that I'm either having tilt or spacing issues. I have an Edge HD 8 with 0.7x reducer, camera is the QHY268M (APS-C chip). I have an external Primaluce Lab Esatto 2" microfocuser to reduce the effects of mirror flop by using the mirror locks. Stars are reasonably round in the centre, but getting significant distortion at the edges (see below). The vignetting is easily sorted with flats so that's not an issue. Initially I thought it may be a spacing issue as the stars seem to radiate outwards i.e. I need more spacing. Not convinced though as the pattern doesn't appear to be consistent all the way around (could be tilt mixed in here causing differing distortion?), and more importantly my spacing is already beyond the optimal (106 mm is the recommended spacing including 1 mm for to compensate for filter thickness, and I'm currently at approx. 108-110 mm). The other option is tilt. I've run ASTAP's tool for checking tilt which seems to indicate very minimal tilt if any. All connections are screw-on or threaded except for the focuser which is held on by 3 grub screws (they're pretty solid and the adapter allows for a self-centering mechanism so it sits in the same position regardless of how you've put it on). The mirror locks are engaged at all times except when I've needed to adjust collimation. I tried the method of back-calculating focal length and comparing the theoretical operating focal length and seeing whether I actually do need more spacing regardless of the manufacturer's recommendation. My current calculated focal length based on the image scale for 2x2 binning is (7.52 * 206.3) / 1.06237 = 1460 mm. The theoretical operating focal length according to the white paper https://s3.amazonaws.com/celestron-site-support-files/support_files/edgehd_whitepaper_final.pdf should be 2125 * 0.7 = 1488 mm. This according to a rule of thumb I found somewhere would equate to an extra spacing of 28/3 = ~9 mm. Looking at this, do I need more spacing? Or is it really not as simple as that considering the mirror moves during focusing, and I have an external focuser? Would appreciate any help! A picture of the rig for motivational purposes

Steve, if it ain't broke don't try to fix it! If you find that your narrowband images look reasonable then I'd leave the LP filter alone, unless you notice a significant degradation in your LRGB subs. I've not routinely heard of anyone having particularly better results with the filter in place, and it could potentially cause some issues with internal reflections; if you're not having this then I wouldn't adjust the setup. That said, it's hard to know what the difference will be unless you try it! I suppose I'm using the term lucky imaging liberally, hence the commas. It usually refers to taking hundreds to thousands of very short exposures and stacking a small selection of these to overcome the effects of atmospheric blurring. Light pollution is constant, but atmospheric disturbances and the position of the target in the sky can have an additive effect. In order to "beat" these disturbances, a greater number of shorter exposures can be taken, and a selection of these stacked. Compared to a smaller number of longer exposures, I've found that my background skyglow in the integrated image can be a lot better. It has the added benefit of allowing guiding to be more forgiving. I end up discarding way fewer subs at the end of an imaging session.