Mandy D

No longer relevant.

@Samop I think I see the problem, here. Without the eypiece there is no magnification of the image formed by the primary mirror. Look into your focuser tube with no eyepiece and the telescope pointed at the Moon and you will see an extremely bright, but very small image of the Moon. I recommend wearing sunglasses if you try this. I did it accidentally, just this morning! To figure out what size this image is at the focal plane, we can simply place a camera there and calculate, from the camera's resolution and sensor size, the actual size of the image in mm. @Mr Spock has kindly provided a suitable image for me to do this with, but unfortunately, he has scaled the image. If I resize it using GIMP to the number of pixels across his sensor (5568) then count the pixels across the height of the Moon, knowing the length of the sensor (23.4 mm) I can calculate the height of the Moon in mm on his sensor. I make it about 3580 pixels, so 23.4 x 3580/5568 = 15 mm. I think his Barlow is actually giving a bit more than 2x magnification, but with Barlows there is some adjustment possible, so we can ignore that. Now, if we project Mr Spock's image onto the sensor of my D800, it will cover a smaller proportion of the space available, as being a full-frame camera as opposed to the D500 being a crop sensor camera, so the image will appear smaller when we print the full image at the same size. Now, if you use a mobile phone with a very small sensor (after carefully removing it's lens to keep things equal), the opposite happens and the image will spill over the edges. So, the number of pixels we grab for a given focal length (assuming the image fits on the sensor) depends only on the focal length and pixel size, not the sensor dimensions. As it turns out, my D800 has larger pixels than the D500, so I get a lower resolution image at the same focal length. So, now we know what size the image is that is formed by the primary mirror of the telescope, we can consider it as a photograph placed at the focal plane of the telescope, so we now look at it with a magnifying glass, which we call an eyepiece, to make it look bigger and dimmer. Hence, your magnification comes from the eyepiece. A longer focal length of telescope will produce a larger image to start with, so less magnification is required from the eyepiece to get the same view. Finally, let's look at the actual magnification of the Moon by the telescope, rather than angular magnification. It is the latter that we are after when using a telescope visually as that will determine how big the image is on your retina. But, what is the ratio of the image formed by the telescope at prime focus (or after Barlow amplification in this case) and it is simply image size / Moon size. So, the Moon is about 3475 km, or 3 475 000 000 mm in diameter and our image is 15 mm, which gives a 'magnification' of about 4.3 x 10-9.

@Nikolai De Silva Vlaid is right. But, also, I suspect that is Jupiter and it's moons you are trying to image, in which case you will need high ISO and long(ish) exposure for the moons. Not so much so for Jupiter itself. Remote shutter release is pretty much essential, but self-timer will also work. For Jupiter's moons you might be down at 1/30 (as Vlad says, 30ms) with ISO as high as 6400. For the planet, drop the ISO to 100-400 and shorten the exposure to see surface detail. Also, make sure your camera/phone is solidly mounted to the focuser or eyepiece.

We had a scattering of snow overnight, but at 06:00 the sky was pretty much clear around the Moon, so I got the 200P out. It was a lot better than yesterday, although the seeing was changing rapidly back and forth, but I managed to get good focus with the 2x focal extender and grabbed enough images to make a good stack. All images are full resolution if you click on them and zoom in.

The Moon in daylight at 07:30 today. Skywatcher, 200P, Nikon D800, Explore Scientific 2x focal extender Click and zoom in for full resolution image.

@MalcolmP Although Jupiter is nowhere near massive enough to ignite hydrogen, the planet does produce it's own heat in it's core, due, I think, to gravitational effects.

Yes, Jupiter so dominates the planetary side of the Solar System, that it's barycentre with the Sun is outside of the Sun's body. It is the only one to do that. So, do we have to declassify Jupiter as a planet, as it is not technically orbiting the Sun, rather the pair orbit a common point? 😁

@badhex Sorry, for getting off track. Yes, it is the fact that L4, L5 are stable Lagange points that allows planetry mass bodies to exist there. L1, L2, L3 are like trying to balance a pencil on it's point.

@badhex it is well known that L4 and L5 are stable, whereas the other three are not. JWST is at the Sun-Earth L2 point beyond the Moon's orbit and has to orbit that point to avoid falling into the Sun's's gravitational well. This is known as a halo orbit.

That gas tap is real old school and identical to the ones we had in my school back in the 1970s and they were old then. I'm pretty sure Michael Faraday used ours ... 😁 The bench tops look simiar, too.

@CumbrianRed You should expect to be paying about £200 for a 200P and it should come with two eyepieces and the 1.25" and 2" extensions for the focuser at that price. Nobody keeps those eypieces when they sell these things as they are low end, although acceptable, especially the 25 mm, the 10 mm not so much. As @Ricochet has said the mirrors are excellent. If you are going to store the telescope assembled with the tube upright on the base, the 150P, 200P and 250PX all take up exactly the same floor space of 520 mm diameter. The only real difference in terms of handling is the weight of the OTA (tube) - 150P: 5.3 kg; 200P: 8 .5 kg; 250PX: 12.7 kg. The bases all weigh about 11.5 kg each. So, if you can manage the base, you can probably manage any of the OTAs. I struggle more carrying the base than I do carrying the 250PX OTA, because of it's awkward shape. Another bonus with these telescopes is that they will all focus with most DSLRs, so you can do basic astro-photography (Moon, bright planets, etc) without buying expensive astro-cameras. I completely agree that you want to make sure the finderscope is included, as it is really not a bad piece of kit and is useful to have. I almost never use mine, though. Unless you are going to get serious about astro imaging, the Dobsonian mount is very practical and extremely easy to use; much more so than an equatorial mount which will require polar aligning each time you set up. As Ricochet says, check that everything works smoothly and is in good condition. However, dust on the mirrors is not something to worry about and even small scratches will not degrade the performance noticeably. I have a big (3 - 4 mm) black blob on my primary mirror and it makes no difference to performance. Don't worry too much if you cannot see anything through the eyepiece when you check it, as the mirrors could be hugely out of alignment, but that is very easy to correct. My 200P was bought secondhand and was so far out of collimation (alignment) that I could see nothing through it. 5 minutes with a Cheshire collimator (cheap) and it was working very well, although not perfect.

I believe I was told my physics teacher in school that an 8 inch telescope was required for visual observation of it at the time. I now have a 12 inch and it is still not big enough, today. At least you have imaged it, whereas for me it remains on my list, having imaged all the planets in our solar system.

@badhex well, it's made for an interesting discussion. Yes, it has to meet all three criteria to be classified as a planet, but as you said, we were only discussing trojans at L4, L5. I'm perfectly happy for Pluto to be 'demoted' on this basis, but perhaps a little sad. I suppose the other thing up for debate, now, will be the satellites of the gas giants with Jupiter being expected to have 500 - 1000 or more. What happens when we get to that point? I'm fully expecting the 'planet' definition will be applied to bodies orbiting such large masses. I honestly cannot see anything that makes more sense. We really cannot go on adding pebbles to the collections of moons. There was similar debate around asteroids after the first few were found, so this is all following a rather predictable pattern.

@badhex I would say it is pretty clear that anything trapped at L4 and L5 are not obstructing the planet's orbit as they orbit the star with the planet. Hence, the planet's orbit is 'clear'. i.e. it cannot crash into bodies at those points as they have the same average angular velocity as the planet. Hence, I believe the modern definition of a planet is correct or, at least, acceptable.

And right across North America, too.

I'm not sure what size thread we are looking at in your photo, but if it is supposed to go into a ball head, I suspect it will be 3/8" UNC. Your camera and tripod will usually be 1/4" UNC. I think there are two options: 1. Take the bolt out of the adapter and use a 1/4" bolt to secure it to the base of your ball head. 2. Buy a new ball head with a 3/8" thread. It will probably be sturdier than one with a 1/4" thread. 3. (secret option, not for the faint-hearted!) Drill and tap the base of you ball head to fit the adapater thread.

Oh, yes, of course it is. 2.45 GHz is 12 cm, as used in microwave ovens!

Very interesting. So, it is basically a very high sensitivity infra-red sensor.

@Nikolai De Silva I just had a look outside and then photographed the same effect. I noticed that you have Jupiter on the wrong side of the Moon. Did you use mirror view on a mobile phone? My picture is here: https://stargazerslounge.com/topic/416373-moon-halo/

After reading @Nikolai De Silva's topic A Strange Ring Around the Moon, I went outside to take a look and it really was quite incredible, so I decided to photograph it. Not having much success from home due to lighting and unattractive foreground elements, I decided to wander up to the local church and see if I could get it's spire into frame with the Moon and halo in the background. Next to the Moon is Jupiter and above the spire we have a star. Nikon D800, 14 mm f/2.8 prime lens, tripod and remote shutter release. f/2.8, 12.1 sec, ISO-400 The exposure time is a bit bizarre and I have no idea how that happened as the camera was set to 13 seconds. Editing in GIMP. I think the processing could be improved a bit, especially in the deep shadow at the base of the Spire.

It looks like you've also captured Jupiter there, so potentially 5 moons in total!

I saw the same thing last night whenI was setting up. It is as others have described above. I've seen it many times, right from being a small child and it never gets old or less beautiful. You got a nicepic of it there! Enjoy it.

Awesome!

@900SL I think this might be the one at the Yangtse River show in China. @FLO posted about it a couple of days ago.

Assuming 10 feet per floor, that is 300 ft vertically downwards and 300√2 = 425 ft at 45° would not be an unreasonable starting point. I think a bit more than 10x might just be required. A 300 mm lens on an APS-C sensor is not going to give much of an image size.