iantaylor2uk

Enjoying the scope greatly - although it's been pretty cloudy in the UK since I bought it. Had some good views of Jupiter at around 200x but it was quite low in the sky and seeing wasn't great, but could still make out some detail on Jupiter and a wider field lower magnification view with all the moons was very impressive. Also have had a look at the moon too and that was very sharp and I could go to high magnifications easily. Not yet done much in the way of DSOs or globular clusters, although I imagine I'll have a look at the Orion Nebula through it once it starts coming into view at a reasonable time. Have not managed to do any imaging yet as I've had to order an extension tube so my OSC camera can come to focus. (there was an 1.25" extension tube with the scope but I need a 2" one for my camera) which should be arriving today. It's been working fine visually using a diagonal. At the end of the month the clocks will change so it will be darker much earlier in the UK, and I'm hoping to use it a lot more then. Thanks for asking.

I have a fairly new gaming PC (AMD Ryzen 5 5600X 6-core processor + 16 GB ram, with an Nvidia GeForce RTX 3060 graphics card), and it does meet the requirements for Windows 11, but I'll leave it for a few months in case there any teething problems for early adopters.

I've been getting good results with a cooled OSC (a ZWO 071) and the L-enhance filter, and with limited time to spend (and image) don't see a need to move to mono, so agree an OSC would be a good choice for an upgrade.

It's pretty easy to put a larger SSD into a laptop - you can simply clone the old disk (using freely available software and copy it to the new one). A good 480 GB SSD only costs around £50 and a 1 TB SSD around £80 or so - I personally tend to use Samsung SSDs. You can also put an SSD into an old laptop which had a conventional hard drive, and these laptops may be available to buy much more cheaply.

I have to thank the previous owner for the handle! I think it is a door or cupboard handle, but it's a really good idea if you have the William Optics tube rings, and get a handle which is the right size.

I took the plunge and purchased the Takahashi 102 from @dweller25 that was recently advertised on sale here. It is in immaculate condition. Below are a couple of photos of the telescope on my G11 mount. It looks like it's going to be clear tonight so will try it out on Jupiter, and may even try to get some images - I've not done any planetary imaging since about 2005! Ignore the garden hose in the background. Also, I need to apologize to the Takahashi afficionados on here, as I have a WO diagonal fitted to the scope.

I bought some new Kenko waterproof 10x32 binoculars about 2 years ago in a sale at a camera shop in the UK and they are fantastic quality. If you can find any of these still around I would highly recommend them.

It’s the root mean square, so if you square the RA value and add it to the square of the DEC value, and then take the square root, that should be the final guide error.

I think it is working out what is the right comparison which is difficult. If you wanted to keep the focal length the same (so the field of view is the same) then you should be comparing an 8" f/5 with a 4" f/10. On the other hand if you keep the f ratio the same then the field of view is altered. There is also the other fact that larger telescopes tend to have lower f ratios - many refractors in the 80mm to 120mm range are f/6 to f/8 whereas many large (Newtonian) reflectors (250mm +) will be f/4 or f/5, so they are not only better at gathering light but also faster too.

I think the link below is quite useful: https://cosmicpursuits.com/943/telescopes-explained/

I agree that the focal length of the telescope, the human eye, or the eyepiece, are all fixed values. However it is the focal length of the "whole system" that is important. If we go back to the example of a camera sensor, it is accepted that field of view is inversely proportional to the focal length of the telescope. As I said before, if you use a 2x Barlow lens to get higher magnification, the effective focal length of the system is twice as long, the field of view is half what it was, and since the aperture of the telescope is the same, the f ratio "of the system" has effectively doubled. If it was f/6 it has now become f/12. When you use an eyepiece, for visual observing, the same logic holds. If you start off with a 20mm eyepiece, and then move to a 10mm eyepiece, with the higher magnification eyepiece, the field of view has effectively halved (compared to the 20mm eyepiece) and so the effective focal length of the system has also doubled, and since the aperture of the telescope has not changed, the f ratio has also doubled. Just to be clear what I am saying here. If you have a telescope with twice the aperture of another telescope, but they have the same f ratio, then 4x as many photons will enter your eye, at each point on your retina. This is why objects are brighter with larger telescopes. If you are doing visual observing, and changing eyepieces to change magnification, then you are effectively changing the f ratio "the system" and at higher magnifications, the f ratio will be higher, so acting as a slower lens, which is why objects appear dimmer.

Let's go back to astro cameras. They have a fixed sensor area, and when you attach them to a telescope you get a field of view (which determines the magnification) which only depends on the focal length of the telescope (which is fixed). If you want to change the magnification you use a reducer or a Barlow. If you use a 0.8x reducer on an f/6 telescope it becomes f/4.8. if you use a 2x Barlow it becomes f/12. Although the focal length of the telescope is fixed, the f ratio of the system has changed. What I am saying is that if you are a visual observer, changing eyepieces has a similar effect to that for cameras and a higher magnification eyepiece will give a larger f ratio for the system.

I think you need to distinguish between the light gathering properties of the telescope - which is determined by the scope size, and the focal length, which effectively is the rate at which photons arrive. If you "zoom in" to a planet or galaxy, for example with a zoom lens, the focal length will be increased, and the f ratio will be higher. So even though the light gathering capacity of a scope may be larger, if the f ratio is increased (for example when you zoom in) then of course it will appear dimmer (it is well known in photography that low f ratios are "fast" and high f ratios are "slow" - so with a fast lens you can go to shorter exposures). When you increase magnfication of course things will get darker since the f ratio is higher. I don't buy your argument between point-like sources and extended objects. For example, take a galaxy, this can be considered as a large number of point-like objects, and so my argument would still apply - at each point in the galaxy there will be more photons hitting the back of the eye.

Your example is where the object you are viewing is very bright already and extended over many receiving cells in the retina. However, my understanding is that telescopes of larger aperture allow you to see fainter objects and I think if you consider pointlike objects such as stars, my explanation would allow you to understand why the larger aperture allow you to see fainter objects.

I've probably come in late to this conversation, but I feel an essential element is missing. If the aperture is twice as large, the light gathered will be 4x as great - this is accepted as fact. However, I think the discussion about the magnification and field of view is a red herring. The fact is that the retina at the back of the eye is the "receiver" and it's area is unchanged whatever the field of view. If 4 times as many photons are gathered by the telescope, then surely 4 times as many photons will enter the eye. Let's consider a faint star that is not visible in the smaller scope but is in the bigger scope. Surely the explanation for larger telescopes being able to see fainter objects is that there are not enough photons received by the eye for the smaller telescope to trigger a response, whereas in the example I gave, where there would be 4x as many photons (in the larger telescope) and that is then enough to trigger a response. Then if we consider a galaxy, treat it as many individual stars - the only logical conclusion (for the example I give) is that there 4 times as many photons at each point in the galaxy - that is why it appears brighter - the fact that it is bigger (due to a greater magnification and smaller field of view in the eyepiece) is surely irrelevant.

I've used Nebulosity 4 for quite some time, which I paid for five or six years ago, but I believe it is going open source soon, so will then be free. I find it quite straightforward to use - there is a Digital Development button I usually use first, then levels and curves, and repeat if necessary, and there is an option for auto colour balance. There is also a synthetic flat option if you didn't take any flat frames. I've tried more complex software and there is quite a steep learning curve, and I get results I'm happy with using Nebulosity.

As I understand it the ASI Air Pro is using a cut down version of PHD2, so I would be surprised if there is a difference between the figures reported by the app and the figures reported by PHD2 in standalone mode on a PC - where are the reports that there is a significant difference? (the numbers I have been getting on my Losmandy on the ASI Air Pro look comparable to what I was getting when I ran PHD2 on a laptop before I got the ASI Air Pro)

Yes - I agree with you that these recommendations are a minimum and you can go longer if you wish - the whole point however is that there is not a lot to be gained by going longer (apart from having less subs). Shorter subs means that if you have to lose any (due to satellites or bad guiding) there is less of an overhead. I think you misunderstand though the effects of light polluted and dark skies - if you are in a light polluted area the spreadsheet (and Dr Glover's presentation) would guide you to shorter subs, whereas if you are fortunate enough to be in dark skies, you can use much longer subs. There are plenty of people around who use short subs (and thousands of frames) - I saw a good M57 where the subs were only 1 sec each: https://www.astrobin.com/345864/?image_list_page=2&end_date=2020-05-02&nc=AnonymousUser&page=3 I used to have a 12" f/4 Newtonian, and I got a good image of M51 using just 10 second exposures (I live on the outskirts of Chester where it is a Bortle 6 sky) - the photo below is a stack of just 180 subs (only 30 mins integration time) - I didn't use a coma corrector so some of the stars at the edges won't look too good: https://photos.app.goo.gl/eDNKesm8ZSNoLCPX9

If your background light pollution is high, you should be using shorter subs. I have a 7 year old i3 dual core desktop and I can still stack 400 subs in deep sky stacker in 30-45 mins or so.

I should have added, as it isn’t obvious, but if you aren’t using a filter, or just using a uv/ir filter choose green from the filter list.

I downloaded the spreadsheet from the link below: https://www.cloudynights.com/topic/753380-gain-and-sub-exposure-calculator-spreadsheet-for-zwo-cameras/

The L-enhance filter only lets through H alpha, H beta and OIII wavelengths so greatly improves the signal to noise ratio of emission nebula (and is also great at reducing light pollution) but the overall signal is lower so you have to go to longer subs. There is a spreadsheet for ZWO cameras where you can put in details of your telescope (aperture and focal length), sky brightness level, and it tells you min exposure times, also for different filters - you need around 3x longer subs for the L-enhance filter compared to no filter.

I generally use unity gain on my ZWO 071MC Pro camera (which is 90 on my camera) and usually image NGC 7000 at 1 min subs if just using a uv/ir filter but I go up to 3 mins if I’m using an L-enhance filter. I also usually just cool the sensor to 0 or -5 C.

Here's a photo of my set up from my back garden from the 19th/20th Sept when I was imaging the Heart Nebula (note that the photo was taken with a Sony RX100IV compact camera which is great at low light photos).

Sounds about right, usually the worms should be made of a softer material than the gear wheel that turns it (as you want any wear from running in to be on the worm, which is easier to replace). A lot of people use superlube with PTFE for regreasing.