pipnina

This is a quote from the seller. Do the measurements seem similar to other scopes, do these numbers help indicate if it's possible to easily switch focuser or not really? Cheers

If it's only happening at the edges, then it seems likely to me that edge-of-field illumination is partially going past the edge of the iris aperture blades, which would make the aperture it's looking through no longer well-rounded and induce spikes in the image. I'm not familiar with this lens though, what do star shapes look like when stopped down, say to f5.5 or f8?

Note I say theoretical, I'm sure I can find a way to make diet-induced diabetes, workplace hazards, or something else cut that short haha.

I've given a lot of thought to fast "camera" style scope myself. Though for now I am falling back to your own classical advice point. Which as I recall boiled down to: "Refactors are easy, and this hobby is hard. Make it easier by using a refractor", and I am thus ditching my f4 newtonian which was a source of stress and weight training in favour of a 130 f6.6 apo, to be reduced to at least f4.9. I hope the ease of use and weight reduction is worth it in the face of the slower f speed, but time will tell! I'd love a RASA, but sadly I'm using a mono cam right now and love my narrowband imaging, so being unable to use an electronic filter wheel hurts! Here in old blighty we still have very poor cloudy weather so betting on having 3 nights to create an SHO image with a RASA using filter drawers sounds risky! Maybe the solution is just to buy 3 RASAs haha. I think my bank would have some concerns though. Can't wait to see your result on VDB123! You are one of the best imagers here and have made several pieces I don't think I will ever be able to top in the theoretical 50 years I have left on this sphere!

More likely a problem with the design. USB hubs, dedicated or integrated, are almost never built to meet the actual needs of the USB standard, or are incomplete. Sometimes the software even shuts down devices that don't communicate for a while which can cause a host of issues for astronomy. Much like the typical USB hub built into a PC monitor, the USB hub in a camera is to be avoided if at all possible...

My RisingCam 571 hub couldn't handle ANYTHING. Even the autofocuser and filter wheel would randomly disconnect from it. I wouldn't trust a camera hub with diddly squat. Maybe a dew heater?

Doesn't look quick and dirty to me at all! Nice colour, very sharp, and very clean looking to me! You've tamed the RC telescope very well. My favourite galaxy too.

Sadly I am working under an aim to reduce weight if possible. My current 200mm f4 newt is about 8.5kg with tube rings, while this refractor is only 6.5 with rings AND guidescope! That also looks like it'd be bigger than the whole 130mm scope! Thanks for the link though! Ah, I hadn't considered looking at hotech! I'll give them a looksies now. Thanks!

I'm possibly going to be getting a 130 f6.6 APO triplet soon, but it comes with a 2" focuser. So far, the highest quality corrector I have found seems to need at least a 2.5" focuser (Here) or even a 3.5" (Here). I have an APS-C sensor at current so these would allow me to bring the scope down to a more reasonable f4.95 while also being extremely sharp out to full frame distance, with barely any vignetting across a full frame sensor, let alone my APS-C one. But this also makes me wonder if there are stronger reducing correctors I could use, that would allow me to take the scope even faster for my camera? The other thing was to do with replacement focusers in general. It seems rack & pinion is very popular, and having googled it, it seems many actually have a strong distain for crayfords, even the mighty diamondtrack not free from criticism from many! Yet R&P would suffer backlash and leave me at risk of having to set backlash compensation settings precisely on my EAF? Are there any particularly good 3" focusers that would fit on the back of such a telescope without mechanical issues? I come from the land of mirrors as it stands so I am not well read up on refractors, but I have finally had enough of cheap newtonians and the many problems they have that I am unable to solve! Any help and suggestions welcome : D

Ah fair point. I found some brass worm gear sets on ebay for pretty cheap. But they are only 1:60 ratio so they'd probably need to be "doubled up" in some way as big mounts have several hundred to 1 gear ratios. https://www.ebay.co.uk/itm/203162743596 I guess 3D-printed large gear attached to the worm and a smaller 3D-printed gear on the motor, with a belt between them would be pretty cheap in component parts to boost the ratio up to 200:1 or so? Belts are pretty cheap from the rowan set so maybe it could work? https://www.firstlightoptics.com/rowan-astronomy-mounts/rowan-astronomy-sky-watcher-heq5-pro-spare-belt.html To be honest your idea makes a lot of sense.

I couldn't find a spare part listing for the main worm-driven gear, but the motor-to-worm gear train replacement parts are about €35 and a worm gear replacement is €45 for EQ5 tier mounts! They are made of brass and low volume however so not surprising that they are expensive.

I often avoid star blow-out by using the curves tool. Drag the upper end down and brighter parts of the image get more manageable, drag the lower section up to compensate. I find it sort of "compresses" the dynamic range and lets you stretch a bit more. Maybe there's a more sophisticated way to do it but I haven't worked it out yet!

Good lord, not a small tag then! FLO wasn't listing a price so I was still hopeful it wouldn't be too unreasonable haha.

It's kinda freaky that I was looking at cameras capable of seeing further into the IR than our normal CMOS/CCDs (that almost vanish by 1000nm even on the most sensitive), going from google search to search, only finding cameras intended for military or industrial use. And today I look at FLO and see... ZWO have released a SWIR camera which is sensitive from 400 to 1700nm! This means we could use our ground based scopes to observe the Paschen hydrogen lines (2 of 3 anyway), both iron emission lines (1.2 microns ish and 1.64 microns ish) and in general we can add to our planetary observations (jupiter for example, as well as see through some nebulae and create more variety in our colour pallets! It is a tiny sensor mind you, only 3.6x2.4mm, but maybe some focal reducers can help us out? What do you guys think? https://www.firstlightoptics.com/zwo-cameras/zwo-asi-990mm-pro-swir-short-wave-infrared-dso-cooled-camera.html

Now that I've added a little baffle to my focuser, and a big dew shield on the front of my scope, my flats are calibrating a lot cleaner than before and my backgrounds have much less "mottling". This is the first RGB image I've done to completion since buying this new scope that has come out to my standards! But I think it has come out very nicely indeed! 6hrs total 20x300s R, G, and B It also shows how far my astrophotography has come, as this was my result last time I tried M33 on my old scope and unmodded DSLR: No comparison! I also made a quick n dirty north america RGB while I was testing the new telescope modification, so here's that while I'm here: Now things sure aren't perfect yet, I think my flats still *slightly* over-correct. But I think to improve things even further I need to take the primry mirror cell off and fully flock the inside of the tube, which is a lot more work! For now at least, I am happy : )

Some advice I can offer here is to stretch the histogram on R, G and B separately. This allows you to balance the background to grey and then any other automatic tools you use have a much easier time. I know pixinsight can't correct the background colour very well until I have balanced it a little with the histogram mixer myself.

My personal choice would be the skywatcher 130p heritage that Philip has linked to. In my mind refractors are great, but are worse than reflectors at these low price points. Chromatic aberration and star bloat are going to be more noticeable. Also consider that an 80mm refractor might be a lot better than the human eye, but the 130p is a massive step up again from that, and with the right eyepieces can be a deep sky and planetary telescope while also being portable and easy to use! For visual use I wouldn't stress too much about telescope collimation. The secondary mirror is usually good enough out of the box for visual, and the primary is easy to adjust on skywatcher scopes with a low cost Cheshire eyepiece. Just shine your phone torch down the cheshires mirrored hole and look down to see the cheshires eye shadow and the primary mirror mark, which need to line up. It takes me about a minute or so on my 10" dobsonian although these days I cheat by using a laser! I hope you find the right scope for you, happy hunting : )

Not entirely sure I follow the dynamic range explanation as I'm still struggling to understand how a dynamic range in electrons (FW / RN) can be expressed properly when converted to ADU, since 14 doublings of brightness can't fit in 12 doublings of 2 as a base unit. Unless the electron read noise at that high a DR is merely expressed as less than one ADU on average? Not sure if that is the right conclusion to draw. Displays actually use a neat trick to get around this. When a 6-bit per pixel (BPP) screen is asked to display a brightness of 129/256, it can't send a signal of 129 to the pixel, but it can send 64/128 and 65/128 which are equally far apart from that value of 129/256. So it will choose either the higher one or lower one and flip between them every frame if looking at a static image, and the neighbouring pixels that have the same brightness are also all randomly chosen to be above/below the unsettable value of 129/256. This dithering of the values simulates an 8-bit colour depth to our eyes. Posterization can be seen on true 8-bit panels as well, most often in video games or CGI or gradients from graphics programs. This is because there is no natural dithering in the form of noise that we'd get from a photograph for example. So we see gradients as big solid steps up. In video games it's most visible in smoke effects in dark scenes I find. I also made a picture to demonstrate posterization when displaying a solid gradient in an 8-bit colour space, while showing a software-dithered gradient below it. It's best viewed on a high monitor brightness and has to be viewed at 100% zoom (not lower, but I think higher is fine) to not break the illusion of a better colour depth. Opening this image in a new browser tab or a photo viewer and then looking at 100% of higher shows how lacking even true colour 8-bit displays are in some situations. Dithering is a necessary process in computer graphics to get a clean looking gradient. Sadly only HDR content and pro artist monitors use 10 or 12 BPP displays.

I think DR only helps us astronomers by reducing star blow-out and helping us avoid HDR techniques on high contrast targets such as M42, or imaging planets with their moons at the same exposure time. I think it is worth saying however that, a good sensor is mostly linear (some more than others... but the IMX 571 for example is 99%+ linear as per some sharpcap screenshots I've seen.). This means one stop of dynamic range represents something close to a doubling of ADU. Which means for a 12 bit camera you genuinely cannot represent more than 12 stops of dynamic range, as each binary bit you add only allows us to double the maximum ADU value. Considering that our astrocams add offset which pushes the noise floor to above 0, this means we lose several stops already as you can wipe out 3 stops in the ADU range of 0 to 8 (1-2, 2-4, 4-8 are all 1 stop apart). Leaving only 9 stops between 8 and 4096 ADU. Thus going from 12 to 16 bit ADC not only means you can avoid posterization but actually means you improve dynamic range too. Maybe there's a flaw in this somewhere but it's how I've currently rationalised it all in my head...

Tolerable for long enough to set up the equipment for the night when imaging, or long enough to see your chosen targets for the night... But after an hour I retreat back home / indoors for hot chocolate... Not to mention my visual 10" dob being metallic makes it sting to touch in the depths of winter. But the eyepiece locking screws are too fiddly for thick gloved hands!

Are we talking about distortion from an 0.5x reducer in terms of barrel and pincussion, or in terms of abberations like spherical, coma, astigmatism, unflattening the field etc? Barrel and pincussion can be corrected very easily in pixinsight. The others, not so much.

I've been thinking about this a little myself. Is it possible to use an IMX585 based camera with a 0.5x telecompressor in place of say an IMX571 to bridge the FOV gap somewhat, as cooling the cameras isn't so important these days and the IMX571 has a MASSIVE increase in cost to consider. £350 Vs £900 for OSC, and the ASI IMX571 costs almost £2000!

This sounds very similar to a super frustrating issue I dealt with recently when computerizing my setup. it turned out that the USB hub in my RisingCam IMX571 was rubbish and was the source of my guidecam/filter wheel/autofocuser disconnections. I bought a proper USB3 hub which fixed the USB2 peripherals. They now all connect flawlessly. HOWEVER. My USB3 RisingCam does NOT work through the USB3 hub! Turns out it can only make a USB2 connection through it and crashes the driver when trying to transmit data. That has to stay plugged into my laptop... I also had an issue with my guidecam where dust or something got into the USB port, I got very frustrated with it not working correctly for an hour before trying the classic nintendo "blow on the cartridge" solution on the USB port.

I did pinch the tube on one support, one of the supports bent a little at the tube wall end after I eventually did them all up far enough. Hopefully those aren't the issue but I was surprised I had issues to begin with, since one of the spider screws wasn't fully finger tight when I bought it and it was secure then.