Mandy D

I recently bought a Vixen refractor. It is my first refractor, so naturally I was concerned about chromatic aberration, especially as the plan was to image with it. Of course, I was expecting the usual 3 weeks of dense cloud cover that come with any astronomical purchase, so was pleasantly surprised when the clouds parted in the early evening. Once I was set up and had the scope pointed at the Moon, focusing with the single speed rack and pinion focuser was a cinch and I was rewarded with a crystal clear view of craters and rilles along the terminator and began imaging with the D800 at ISO 100 and 1/60s. Viewing the first images, I could see that there was almost no colouration. Bumping up the exposure time introduced the expected chromatic aberration, but at 1/60 the image was already perfectly exposed, so I shot a sequence of images at that. I stacked the best 25% of the 110 images and then processed in GIMP, applying just a tiny bit of sharpening. There is nothing I don't love about this scope and can't wait to try it on the Sun. I think the next purchase has to be a Herschel wedge, but for now I have a Seymour solar filter that fits.

Yes, there is a simple solution. Get a USB hub with as many ports as you need. Make sure it is a good quality powered one. Mine has 7 ports and came from PC World.

@PeterStudz That's pretty amazing. I've photographed Uranus several times with my 200P and captured Neptune just once, but nothing like the quality of images you got. I find them both to be difficult targets. Well done! Now I know what the 200P can do, I must try again.

This is something all photographers are familiar with. f/5 is the ratio of the lens (telescope) focal length to the aperture of the lens. Doubling the focal length will cause the image produced to be twice the diameter or four times the area, hence dimmer by a factor of four. Given the greater focal length of an 8 inch telescope at f/5 compared with a 5 inch, you can see it will produce a larger image with light that has been gathered by a larger mirror, but will retain the same brightness level. The field of view of the 8 inch will be narrower than the 5 inch at the same focal ratio. A 200P at f/5 will be 1000 mm FL, compared with just 635 mm FL for the 5 inch.

Here is a brief animation (5 frames) that show the plane appearing from the clouds and where you can see it's exhaust trail as it crosses dark cloud. I have indicated the plane's position in the zeroth frame as it appears in the following first frame as it is quite difficult to spot. 🙂

Last night was very cloudy and I was not expecting to see the sunset, but I set up the RC6 and D800 just in case, as we had already driven to the spot I wanted to image from. Eventually a narrow slit formed in the clouds just below the Sun. I started capturing video and about 4 minutes in I saw a plane descend from black clouds and pass just above the Sun.

OK, so if there no losses directly to the atmosphere along the beam path, that means all the energy is being collected by the receiving station. What happens to that energy then? Do we simply transport it back to space? In which case the efficiency is worse than "a bit pants". Energy is energy. Once it is here it is effectively heating the planet and atmosphere or it is escaping back into space. Which is it? I'm not sure we are ever going to see shadows from such collection stations as they would be so positioned to avoid this problem, otherwise, what is the point? We may as well let the energy just hit the Earth directly from the Sun.

Here is a link to the service. I'm not sure if 4 x 5 (quarter plate) counts as large enough or if that is a standard production item for them. It's worth asking, I guess. https://www.ilfordphoto.com/annual-ulf-sheet-film-ordering-window-for-2022/ It looks like the 2023 ordering window is not yet open. I think they run in October.

Shadows? Global cooling? You are beaming energy (heat) down to Earth that was not destined for our planet, so that is going to increase energy and heat the planet. If these panels are producing shadows on the Earth, we are wasting our time, are we not? Or am I missing something obvious, here? I totally agree that global cooling is the last thing we want or need. Unfortunately, the world is stuck with the idea that warming is entirely a bad thing. Is another ice age what we want? Clive Best has a chart on his website somewhere that lists the levels between Snowball Earth and Fireball Earth. We are just one step up from Snowball Earth at present.

Ilford still make and sell film. They also provide a special service once a year where they make what you want in large format sheet form, etc.

Bonding anything onto the outside of the tube over a large enough area to make a laminate is going to effectively stiffen it. The stiffness comes from the outside surfaces, so as long as it is stiff in tension it should work. You could try plastics or thin wood veneer, or roll some thin aluminium to the same radius.

Or a Lunar Apocalypse, where the Sun eclipses the Moon?

Thank you! That is so nice of you to say so.

Today was a clearer day, sharper image. I've processed this one in false colour.

I finally managed to get some imaging of the Sun done today.

That's pretty much what I bought as my first telescope. I've never looked back. I started with the Moon, as it is very easy to find and you can also readily check alignment of the finderscope with the main scope. Be prepared to be blinded by the Moon with such a large scope! It will be insanely bright at low magnifications! If you have the Skywatcher 250PX, it has a dust cover with a 50 mm aperture in it that is covered by a cap which you can use to reduce the brightness. I've had mine since 2016 and never had to collimate it, yet, even after it was lifted up and dropped by a customs official at Dover! He wanted to check for people hiding inside the box. Don't get distracted by the need to collimate, just yet, even though it is a really simple process because it is nerve-wracking the first time you do it. As long as the image is sharp and the stars are round it will be OK, certainly for visual, at least until you start to get more discerning and picky. The next thing I would point it at is a bright planet. Venus is nicely placed right no, so go for it. You should pick out the phase fairly easily. Mars is also convenient in the evening sky right now, but getting smaller, so don't leave it too long. I'd wait for Jupiter and Saturn to get a bit further from the Sun and higher in the sky before trying them. Right now, they are morning objects, so you have to be up before dawn. Another easy favorite of mine is M42, the nebula in Orion. Very easy to find and well worth a look, but this is the wrong time of year. Autumn / winter is best for Orion. Try your hand at splitting some doubles. There is a very easy one in Ursa Major, that is also easy to find. I'll not tell you which, because it is much more fun to find it yourself. With this being on a Dobsonian mount, it will be very easy to point it directly upwards, which is pretty much where Ursa Major (Big Dipper, Plough) is right now. EDIT: I just noticed someone mentioned the Lunar 100 list, which might be of interest to you. Here is a helpful link: https://skyandtelescope.org/observing/the-lunar-100/

Engine power measured in kelvin-watts? Is that because it is a thermal engine? 🤣

Hi Claire, that all sounds very impressive. I can't wait to see some of your images. Welcome back to the forum.

Why would it not be a durable solution? Solar PV installations have lives in excess of ten years. For sizing, take Vlad's advice. You always size for winter insolation. I guess you can cope with the days when you get no Sun, as you probably won't be observing on those nights, either, plus you are likely to get some on other days when not observing.

You'll like this can of paint from Canada, then! Check the various ways the quantity is listed. None have sensible values.

Yes, I recall this! Personally, I think we should move over to base 8 (octal). It would make life so much easier, all numbers would convert properly and easily to binary. I used to enter octal code into a Honeywell 516 mainframe at college and it was so easy to check against the binary. It would also make the 8 times table, which is the most complained about one, much simpler!

The metric unit for fuel consumption used by car manufacturers is actually litres per 100 km! So, even crazier than you'd think! In SI, it would be metres per kg, m kg-1 😂

@Captain Scarlet I, too, bought an Evoguide 50ED with the idea of using it as a finderscope, but never considered the possibility of using it with a diagonal, the I read that it was impossible without butchering the tube, so I've never really thought about it. I now have a Skytee 2 mount and use it in the top saddle with a straight through eyepiece, but you've got me thinking now and I'll have to keep a note of the parts to do this if I ever feel the need to. This scope does make a nice finder, though. Here is a photo of my setup with the 50ED riding on the Skytee.

1/4" BSW will screw into or onto 1/4" UNC. BSW has 55° thread angle and is radiused, whereas UNC has 60° thread angle and comes to a sharp point. All BSW and UNC threads have the same threads per inch (TPI) excpet for 1/2". Obviously, using mismatched thread forms together will result in a weaker connection. It is up to you to decide if it is worth it.

@Herbert West It certainly is beautiful. I love the colours that you have brought out in it, especially the purple. You don't see enough deep puple in nebula photos. I prefer the first image with the stars, it makes it look as though the nebula is floating through them. You also have some lovely detail in the first mono image, nice and clear. Excellent job.