JamesF

"There's nothing you can do now that can't be fixed. If you were going to break the mirror you should have done that on day one." To quote John Dobson James

Please do start a thread for the grinding machine. I'd love to see how you get on. James

I used to use IRC a lot for work. Haven't touched it for probably ten years though. James

There are IRC clients for just about everything, but I don't know if they're all free. It might work quite nicely though with multiple channels, one for general chatter and others for more targeted information. There are free IRC server implementations, but I'm only aware of ones that are UNIX/Linux-based. James

A private chat server (IRC-based, perhaps) might do the job. It would need some sort of sign-up validation though. The one advantage radio does have over internet-based services is that you don't tend to get quite so many people joining in who just want to sell you viagra or request your help to transfer millions of dollars from Nigeria. James

Allegedly ethe and ethea are acceptable plurals of ethos, whilst ethoi isn't because it applies the wrong grammatical rules for forming the plural. Personally I'd say it's "one Ethos" and then "too many if you want a quiet life". James

Is it one of those things like being an alcoholic? (In that you never stop actually being an alcoholic, you just become an alcoholic who doesn't drink.) James

I modded my handset so it could take external power from a 9V wall-wart James

For those unfamiliar with this scope, here's more: http://www.wetherellart.co.uk/sculpture_greatwetherellrefractor.html James

I'd love to have seen that scope "in the flesh" as it were. Sadly Tim told me that it has been sold and won't be accomanying him when he moves back to the UK. Still, eyepieces or scopes, you only sell one to make room for another, eh? James

Spend too much time at the optics and you can end up completely parabolised, that's for sure. James

Sees a lot of use, but the views can get badly blurred after long sessions. James

I'm not sure the grass actually stopped growing this winter, it's been that mild. It certainly has been cold this weekend though, particularly today. James

Your persistence is admirable, and looks like it is being rewarded James

What's required is some of this: http://www.lakeland.co.uk/70136/Lakeland-Non-stick-Turkey-Foil James

I did think it looked somewhat precarious when I saw the photos James

Actually, with apologies for wandering off on a tangent a little, a suitcase dob is something I really want to think about. The childrens' swimming club are doing a "club families" trip to Lanzarote (I think -- one of the islands anyhow) in October 2016 and it's tempting to go, but I'd be gutted if I went and didn't take a scope of some kind. As it's all school-age kids in the club it would be really nice to "spread the word", too. So a dob that would go on an aeroplane fairly easily would be an excellent thing to have. Given that I have a year and a half perhaps that should be my first self-made mirror project. In fact, I've just looked at the BA website (as an example) and the the maximum hand luggage size is 56cm x 45cm x 25cm. I wonder if it might be possible to make an 8" "cabin baggage" dob? James

Certainly inspires me to give it a go (and I have a 14" glass blank waiting), but I want to try something smaller first I think. James

Certainly does. It's looking absolutely beautiful there. James

Very much enjoying it too. I'm most impressed so far. James

As has been posted above as I was writing, I'm in agreement. It doesn't seem to make sense that the backfocus should reduce. James

That would give you a larger image and change the point of focus, certainly. James

In a colour camera each pixel corresponds to a particular colour in the image, red, green or blue. For pixels in red positions, for example, there is no green or blue data. It's derived from adjacent pixels of those colours and as such may not be entirely correct. Effectively the resolution is decreased slightly by doing this. Also, in order to make the pixels respond to the colours required you start with a mono sensor and add a filter for the required colour to the front of each pixel. That filter causes some loss of light and reduces the sensitivity of the sensor. With a mono camera you use a filter in the optical train for each of the three colours, so every pixel records data for each of the colours and you get no loss of resolution. Also, the external filters tend to allow more light to reach the camera sensor, so overall the sensor is more sensitive. Of course the (arguably) negative side of using a mono camera is that you have to take three sets of data; one for each of red, green and blue and then combine them afterwards to get a colour image rather than getting all your data in one hit. And in the case of Jupiter you'll be trying to do all that data collection in the two-minute period before any distortion in the image due to the rotation of the planet becomes apparent. And you need to buy the filter wheel and a decent set of filters, which could easily cost more than the camera. But... the result of using a mono camera should be a much better image than is possible from a colour camera of the same sensor size and resolution. James

The 120MC takes a bit of time to get the hang of, but it's capable of good results. This is from the same camera with my 127 Mak: James

Consider: The average user of the video mode of a consumer grade compact or DSLR camera is interested in the overall result. They won't be too fussed about noise or a bit of lost data unless it affects the video as a whole. They're certainly very unlikely to go pixel-peeping individual frames of a video. Manufacturers know this and take advantage of it to allow them to increase the resolution or produce frame rates that would otherwise be impossible with the same kit. When you want to use a camera for planetary imaging however, every pixel of every frame counts. You're after the most accurate record of the light that hit the camera sensor. That's somewhat at odds with the situation above. If two adjacent pixels are different colours, even only very slightly different, you want to know. You don't want some camera firmware deciding that they're close enough that in a 25fps video no-one will notice if they're made the same colour to reduce the required storage space for the frame. James