Mandy D

Looks like a world population graph

Thank you! I've just had a look at the spec, which is pretty awesome. I look forward to seeing images from this one. Should be good with it's full frame flat-field.

Ooh, pretty! But, what is it? I know, I know: It's a telescope ... A bit more detail for those of us drooling who have no idea beyond it being a telescope, please. 😊

The Variac seems properly specified and should work well for this application.

The specification seems messed up. A power rating of 100 W with a 230 V secondary rated at 24 A? I get 5520 VA for that, then add on the other secondary ... That is 100 VA, which must be the 100 W they specify. The weight is given as 1000 kg, which is clearly incorrect, yet 1000 g would be nowhere near heavy enough for the ratings as calculated above. Have you seen a photograph of this thing in which the size is clearly discernible? I'd be cautious about parting with the money for this.

Yes, that is exactly what we are looking at - low voltage, high current. The high current will ohmically heat the aluminium to close to melting point and because it is in a vacuum, the aluminium will boil off it's surface to produce the vapour we need and then deposit itself on everything (literally, everything!) in the chamber. Have a look at the photo. Note, I have secured the ends of the winding to the adjacent turns with cable ties. The blue wire is 6mm². Apply the rated voltage to the primary (presumably 230 V) and measure the voltage across the new secondary. Divide this by the number of times the wire passes through the centre of the core (6 in my photo) and that will give you a turns per volt figure that you can use to determine your required secondary turns. Obviously, the voltage will fall a bit under load, but the Variac allows you to adjust it, so don't worry too much about that. You can safely increase the primary voltage by about 10% or so above rated. 6mm² should be OK for up to about 60A or so for the short period you need to run this. You will need short, heavy cables to the aluminium wire in the chamber to minimise volt drop.

I'm not sure you want to go with either approach with aluminium dust, other than as a fun experiment, but I would seriously try to get a suitable transformer rather than using mains. Two possible approaches I would consider for vapourising aluminium: The first one is similar to the way we did it in the semiconductor lab, but you won't have access to a thick tungsten wire coil, so you might consider experimenting with a short length of heater coil from an old fan heater. This is usually a nichrome wire and if you put a length of aluminium MIG welding wire or similar down the centre of it and slowly(!) increase the current using a low voltage transformer supplied by a Variac it may work. I'm not sure whether you will get any impurities in the aluminium vapour - most likely you will - but it may work OK. The second method is to heat the aluminium directly using an electric current. If you slowly increase the current, using the above method, and keep the temperature of the wire below melting point it will vapourise aluminium from the surface of the metal and eventually, before the wire burns right through, coat everything in the chamber with a thin layer of aluminium. This method should result in lower impurities. The biggest problem, for the second method, is getting a suitable power supply and what I would do is buy or salvage a suitable size toroidal transformer, say 200 VA or so and wrap a few turns of thick insulated wire through the core, over the existing secondary and feed it from a variac. I'm not sure how much power you will need or what voltage, but a bit of experimentation should resolve this issue. Ordinary PVC insulated flex will do, as long as you don't let it get too hot. For the fan heater coil, you should be able to run this from a variable d.c. power supply, but you will need one that can supply up to about 4 amps or so. Obviously, these are only ideas and you will have to consider all aspects of safety, yourself.

Totally agree! I use a professional photography studio for my prints. Vistaprint are great for business cards, letter heads and leaflets but photo printing deserves better.

Good luck, if you try it! I was vac depositing gold onto semiconductors. We put pure gold wire inside the coils of a heavy tungsten wire filament and the prepared semiconductors on the bottom plate, then put a glass bell jar over it and used vaseline for the seal. First stage vaccing was done with a two stage Edwards mechanical vacuum pump. Second stage was a diffusion pump, which took a very long time to get down to the hard vacuum necessary so we left it overnight. In the morning I passed a current of about 30 amps through the filament and vapourised the gold, which covered absolutely everything in the chamber. Then air was allowed back in and we could lift the bell jar and remove our items. It's not the simplest process to get right, but it works well. Admittedly, I've no experience with telescope mirrors, but one of my physics lecturers did a lot of them using the same process. I hope this helps if you decide to give it a try. You will certainly have fun. I know I did.

I wonder if it is worth giving the semiconductor physics or engineering departments in the universities of your country a call to see if they would put it through their vacuum deposition chambers. I recall when I was in the semiconductor lab at Sheffield that we had quite a large chamber which would take a modest mirror. Perhaps one of the grad students would be happy to do it for you at a local uni.

Interesting to read this topic. I bought a Daystar Solarscout in 2018 and could never to get it to tune. I thought it might be me, so I asked the well-known supplier a few weeks after buying it and was referred to Daystar as the only assistance on offer. Not knowing enough about this and lacking a visible Sun to keep testing on, then followed by Covid lockdowns, I gave up trying to get it to work and lacked the confidence to contact Daystar. I did post in here about my problems, but it did not deliver a solution. I rather suspected something was amiss with my scope, especially as the Sun orbited in the FOV as I tried to focus. I was convinced that I had in-focus images, but no matter the heater setting, I could see no detail on the disc, beyond the occasional sunspot. I re-focussed at every heater setting and waited for the LED to turn green each time, but no joy. I don't even bother connecting the battery any more and just use it as a (very expensive) simple filtered refractor for solar viewing. Very disappointed! But, at least now I have some idea that I am not alone and probably not totally incompetent either. Thank you for that much.

Is it atypical or is it, as Nik271 says earlier in this discussion, that gas giants near their star are easier to spot? A huge planet orbiting a modest star in a few days will produce large, easily trackable perturbations of short period, whereas a gas giant orbiting at the distance of Jupiter will cause relatively small perturbations over a very long time.

Oh, OK. Does that mean Raspbian can now allocate more than 4 GB to a 64 bit application? So, if that is the case, I guess Astroberry is still stuck in 32 bit land.

There really must be! DA would not miss an opportunity like that!

Third Rock From the Sun!

My Vixen dovetail for the top of my iOptron RC6 landed this morning, purchased from a member of this site. It is red and shiny.

The Pi 4 with 8GB of RAM will limit you to 4 GB per application, maximum. I think it has something to do with Raspbian being a 32 bit OS, but Astroberry is not limiting you and you could probably run two instances of it with 8 GB of RAM, though I'm not sure why you would want to. If you do go with a Pi, make sure it is properly cooled with large heatsinks and possibly a fan. Mine get very hot, especially when working hard.

This was one of the first test images from my new iOptron RC6. It's far from great, but I only had it on a photo tripod and that was with a Nikon D800 hanging off the back end, so very wobbly. I can't wait to get it on the AZ-EQ5GT and see how it performs after a proper cool down.

I was surprised how tough these scopes are. It may be that being in the original packaging helped a great deal. I'd quite happily have opened the box if only he'd asked. I've just been talking to my GF and she is keen on making the trip, next year. So we might see you there. Thanks for bringing this to our attention.

Thanks for that. It is something I have yet to try. Cool down time might be the issue here as it seems to have a grainy appearance rather more than blurry out of focus. See photo.

I've thought about it many times, but now I have an iOptron RC6 with dual speed focusser which I struggle to focus, I'm not so sure when the 200P (and 250PX) seem to focus so much more easily for me. I must be doing something wrong.

North Dordogne, here, but residing in UK with my 250PX over there.

Buyer to collect.

Looks amazing! This is in Lanuéjols, Gard from their website? Great skies down in that part of France. We once drove down from Nontron to Marseille to take a flight to Rome in the winter and went through the mountains where we had some amazingly dark skies, but unfortunately we did not have time to stop for more than 10 minutes to enjoy them. We keep saying that we really must go back , so perhaps this event next year might be just the thing. I bought my Skywatcher 250PX from a supplier in England whilst we were in France and had it delivered to a UK address. The next time we took the Land Rover down to the house, we took the telescope with us and it has been based out there ever since. We made the crossing by ferry and a nasty customs official asked me to open the back of the Land Rover for inspection, then lifted the back end of the box containing the telescope and deliberately dropped it from about 30 cm before asking what was in the box. I was so angry with him and told him how stupid his actions were. "Uh, sorry!" was all the apology I got. Luckily, no damage done and even the collimation survived.

Is that why BMWs don't have indicators?