iantaylor2uk

I have the same telescope but don't use an OAG - have you tried guiding through a simple guidescope attached to the telescope? In my view you don't really need an OAG for a telescope of this focal length.

It would be worth, in my view, trying shorter subs. 3 mins sounds like a long time to me. Try 30-60 seconds if you are using a UV/IR filter only. Each sub may look less impressive, but if you image for the same total time, you will have a lot more subs to stack. I only go to 2 mins if I'm using the L-enhance filter. If your telescope is f/6 and you are using a 0.8x reducer you are effectively at f4.8 which is quite a fast system, so shorter subs should be fine. Shorter subs mean you can also put the gain up on your CMOS camera (with the advantage of lower noise) without filling up the well of the sensor.

I have an Orion Optics CT-8, which is also advertised as a 900 mm focal length (f4.5) but my ASI Air Pro told me the actual focal length was also about 870 mm. However, if you use a coma corrector you will likely see a focal length above 900 mm (my Explore Scientific HR coma corrector will multiply the focal length by 1.06 when used at the correct spacing - so it should come up to about 922 mm).

Good explanation vlaiv - in terms of seeing RMS though, how does the widespread use of multi-star imaging impact this factor - it seems to me you can go to 0.5 secs or 1 secs guide camera exposure, and the fact you are guiding based on 8 or 10 stars must surely reduce the effect of seeing (compared to guiding on a single star).

There are some at the links below - note though that I didn't use a coma corrector or UV/IR filter for these photos, so they have been cropped a bit. I used an APS-C sized sensor (a ZWO 071 Pro camera). You can still see a bit of coma towards the edges. I now have a coma corrector for my reflectors! Also I collimated the reflector before imaging using a laser collimator. M3 & M51: 10, 30 & 60 sec exposures: https://chesterastroblog.wordpress.com/2021/04/11/m3-and-m51/ M101: 60 sec exposures: https://photos.google.com/share/AF1QipOnmkqD1kWZYsvqMm8W8diHwSoXJn47oD7ZgiVB2iS3j6m_KeyJCI-lWtSR6Ss36g?pli=1&key=cnZtb3RGbHE3aWxNSGQ5OS1CN2dva1YyYzVnanpR Hope this helps

I had a 12" Orion Optics (DX300) f/4 scope and personally wouldn't go more than 60 sec exposures with an astro camera. I got some good photos of M51 with just 10 sec exposures, after stacking two or three hundred of them.

Maybe not, but my approach is to go with as short an exposure as possible since it is the total integration time that matters, not the length of the individual subs. Using the excel spreadsheet for sub exposure, the minimum sub time decreases as the gain goes up. With a UV/IR filter I usually image at 30-60 secs, and use 2 mins for the L-enhance filter. I may go to even shorter subs if I'm using the f/4.5 Newtonian.

Did you reduce your exposure time when you upped the gain to 200? I tend to use higher gain on my ASI 071 Pro camera, but tend to only go up to 2 mins when using a narrowband filter (usually the one I use is the L-enhance).

The whole point of relativity is that the speed of light is constant, irrespective of the frame of reference - the frame of reference quite simply doesn't matter. You can argue how accurately we can actually measure the speed of light but the simple concept that it is constant, and independent of the frame of reference, is all you need to derive special relativity.

In my earlier comment I was careful to say that fundamental particles sometimes act as if they are point particles (e.g as in the photoelectric effect) and sometimes as waves (e.g. as in diffraction). We don't really understand what a particle is. They must be some sort of stable state of space-time ultimately.

Tried out my OO CT8 for the first time last night. Used a ZWO 071 Pro MC camera, but did not use a coma corrector or UV/IR filter, just to see what the raw images looked like. Not surprisingly, towards the edge of the image I could see the effects of coma, so will need to use a coma corrector if I want to use the whole of the sensor. Took 100 shots each, at 30 second exposure, of M51 and NGC4565 (with sensor cooled to -5C) to see what it could do. I did collimate the telescope before use, and took calibration frames. The best 80% of frames were stacked in DSS and then processed in Nebulosity 4. The images below are crops, but looks pretty good to me for a first outing, and not bad for just 40 mins or so of integration time for each object. I used an ASI Air Pro on a Losmandy G11 for autoguiding, dithering, etc.

You clearly have no understanding of modern physics. Firstly, particles interact via fields, not through "touch". Electric and magnetic field are everywhere and interact in this way. Secondly, the position of particles is not known precisely due to the uncertainty principle. Particles under certain circumstances act as point particles and under other circumstances as waves. Thirdly, it is experimentally obvious that photons do exist. I don't know where you got your definition of existence from, but photons can be created and destroyed, and time obviously passes for observers of the photons but time stands still for the photons themselves.

Physicists understand plenty about photons. Relativity shows that objects can travel through space and time, but if a particle travels at the speed of light (and only massless particles can) then those particles don't travel through time at all. So time stands still for photons, but they definitely exist.

No it's not cheating

If you are a photon, time does not exist

I have a ZWO 071 Pro camera but am very tempted by a 533. It's plenty big enough for most objects.

Not been that active for a while, mainly due to the weather, but managed a quick session on 19th March, when I looked at M3. Photo below is a stack of 100 30 second images taken with a ZWO 071 Pro camera (gain = 200, sensor cooled to -5C). Stacking was with DSS, and processing was with Nebulosity 4 and Affinity. Telescope used was a Takahashi 102 TSA with 1x flattener and UV/IR filter. Autoguiding/dithering etc. was all done via ASI Air Pro and the mount used was a Losmandy G11.

I had a f/4 Orion Optics DX300 which I sold last year - I think the equivalent nowadays would be the VX300 f/4. The nice thing about the OO scope is that it was quite light (as these things go) at around 14 kg, whereas many other scopes of this size from other manufacturers would be much heavier. I used it with a G11 on a losmandy heavy duty tripod and it was solid and I managed to autoguide it at less than 1" RMS, although the size of the scope meant it was sensitive to the wind (I don't have an observatory). An OO Newtonian should be OK, the problem with Orion Optics is that it is quite a small manufacturer and there is a lot of demand, so you are probably looking at a 6 month or greater wait for a new scope. If you can find one second hand that would be good, but they don't come up that often.

I use Deep Sky Stacker (DSS), which is free, for stacking light, dark, flat and bias frames as it is very fast. I tend to use a combination of Nebulosity 4 (which is also now free) and Affinity for processing the final fits image from DSS. There is a bit of a learning curve with both DSS and Nebulosity, but I think less of a learning curve than with some of the more complex software. Hope this helps

If you're autoguiding, you only need to get polar alignment accurate to less than 5 mins. Once it is less than that I stop.

I think if you want to set up from scratch and get good results in a short amount of time it will cost quite a bit, especially if you want to image at longer focal lengths (>800mm). On the other hand, I believe many people on here though have started small, and built up gradually over many years. Although a good telescope or mount will be expensive, they will also last many years, so if you average the cost over 10 years or more, it doesn't look quite so bad. In addition, there is the option to buy second-hand, on UK astro buy and sell, or ebay. Buying a pair of binoculars and learning the night sky is relatively cheap, before you decide whether to dive in deeper.

Incidentally, when I visited the University of Central Lancashire's Alston Observatory a couple of weeks ago, the 1920's 15" refractor there had a Grubb clockwork equatorial drive (inside the white metal base)

I have a G11, purchased new back in 2009, and it is a great mount. I've been using it with an ASI Air Pro, so don't use Gemini much, but if you have Gemini-2, it's quite a good system once you learn all it can do. I see yours has been modified as you have a belts on the RA and DEC axes. Hope you enjoy using it.

I use fairly cheap CooWoo 5V USB dew straps from Amazon (which have low/medium/high settings) on my guide and main scopes, with one USB plugged into the mount and the other into a USB hub on the back of my ZWO camera. This works quite well for me, but you would need bigger straps if your scope objective diameter is more than 110mm.

I think the rule of thumb is to dither around 10 pixels in the main camera - if you haven't altered the dither settings and you have binned 4x4 your main camera pixels will effectively be 4x larger, so you may not have dithered enough. To be honest it looks pretty good to me at that focal length without any guiding.