JamesF

Nothing is impossible....

...It's just that we haven't figured out how to do it yet!

I'm quite prepared to accept that some things are so incredibly unlikely as to be effectively impossible. Me winning a gold medal in the ladies gymnastics at the next Olympics, for instance

There does seem to be an increasingly prevalent attitude along the lines of "I don't want to/can't see how to/can't be bothered to do it, therefore it can't be done, therefore it is impossible" however. But perhaps that's not entirely surprising when we live in a society where companies spend huge amounts of money on advertising to persuade people that they are unable to do something simply so that same company can then sell them a solution they don't actually need.

James

Maximum risk £200 replacement value :- http://www.ebay.co.u...984.m1439.l2649

That seems like a very reasonable price.

James

I absolutely agree Cath. Too many people confuse "I can't see how that's possible" with "It is not possible". I blame it on a lack of imagination

James

I have seen reports about it not being possible to dissolve CFAs with acetone, so I don't imagine IPA will work as a solvent. Mind you, I've also seen people claiming that it just isn't possible to do at all

James

I'm not sure what you can do in that case. I'm not aware of a motor conversion for the Mak focuser. You'd probably have to fit an external focuser and fit a motor to that.

James

Hanging weight from the tripod or putting it in the tray can help with the stability of the mount. I don't tend to use the eyepiece tray on my EQ3-2, so I often put a couple of decent size stones in it.

As regards the motorised focuser, see the links in my first posting in this thread.

James

So the ultimate focuser mod is to replace the knob with a ship's wheel?

James

Not to mention cheaper

I found there was very little wobble when using the clothes peg, even when imaging at focal lengths you'd never dream of using for visual with that scope so hopefully that will be fine.

James

I'd have thought one of those shouldn't be too hard to make up. I think the plastic lid or clothes peg would work better though, as they significantly increase the radius of the "control surface", making fine adjustment much easier.

If, for example, you effectively increase the radius of the knob by five times by adding a lid or peg then that requires five times the movement at the edge to move the focusing system by the same amount, or, looking at it another way, the same amount of movement generates only one fifth of the focuser movement when applied on the larger control surface than the standard knob.

James

Looks like you linked back to this thread there. I assume you intended it go to somewhere else?

James

Here you go. Perhaps this will be helpful:

http://stargazerslounge.com/topic/77168-peanut-butter-lid-fine-focus-knob-for-sct/

James

There are a number of approaches you can take, including at least a couple that happened to have turned up in other threads in the last day or two, oddly enough.

A common mod for the Mak focuser is to get a plastic lid from a jar (Nutella and peanut butter are apparently favourites) and cut a hole out of the centre to match the focuser knob. The lid can then be fitted over the top of the knob to allow better control of the focuser.

An even lower tech version of the same thing is to use a spring clothes peg clipped onto the focuser knob. The plus side of this is that it's then a single finger "push" to move the focuser either way, but the negative side is that you need to get the focus close before adding the peg because it will foul the visual back. I used to do this, partly because I don't eat Nutella and I can't stand peanut butter It worked ok.

Another option is to motorise the focuser. I modded the standard Skywatcher motor focuser to work:

http://stargazerslounge.com/topic/135260-127-mak-motor-drive-focuser/

(or http://www.tanstaafl.co.uk/2012/02/skywatcher-127-mak-focuser-motor-drive-conversion/ if you want a few more images). I'm very happy with this solution. It can be a bit slow when large amounts of travel are required, in which case I slip the drive belt off and spin the gear by hand. If you're interested in imaging then a motorised focuser is a joy to have.

Perhaps the most expensive option is to buy a converter to fit to the back of the baffle tube to take it up to an SCT thread and then buy an external crayford or rack and pinion focuser with an SCT fitting. You can then use the standard focuser control to get close and the external focuser for fine control. Because of the way Maks (and SCTs) work, using the external focuser alone may not work in all cases. The potential down-side of this approach is that it can make framing more awkward for imaging because the focal length of the Mak increases the further away from the back of the OTA the focus point is. That means, for example, that whilst I can just fit a solar or lunar image onto the sensor of my 450D if I put the camera directly on the visual back, the image is too large if I move the camera further away as would probably be the case if I had an external focuser. If you've no intention of imaging then this isn't likely to be an issue, nor is it for imaging objects with much smaller angular dimensions.

James

Would it be that hard to take the code for one of the existing libraries and modify it for the DS2413?

James

I know. And the majority of the work to create a brokering system has already been done. It's just a question of finding time to hang it all together.

James

Given the time, I would like to set up some sort of brokering system on a central computer with all this sort of data being passed through it such that other applications can say "I'm interested in data of type X" and when a data item of that type arrives it gets passed to that application as well as being stored in a database. The aim eventually being to add bits of automation software that can do different things based on the data that various sensors are collecting or the actions that other applications are taking.

James

Middle of a field I can manage. Erecting something 10m high might have the neighbours making complaints though Being on the top of a hill I start to get nervous about lightning strikes, too. There are a few trees around here that show the signs of coming off second best after a lightning strike.

Having thought about this a bit more though I have some niggling memory which I can't quite drag out into the open that there is some sort of correction factor you can apply for height above ground. I might have to leave it a few days to see if it comes back to me.

James

How do you calibrate the anemometer, Gina?

James

I've had an eye on the Arduino 1-wire support, too. It looks quite interesting.

James

A cardboard tube or a piece of drain pipe should work ok for testing I'd have thought, but make sure you fix the camera to something just in case it falls. Diagonals vary in the length of the optical path, but with a 1.25" diagonal I'd expect it to be somewhere around 70 to 75mm. It's longer than you'd think. I'd probably start with something at about 50mm long and see if it will reach focus. If it does then I'd be tempted to repeatedly shorten it by 5mm and see if you can still reach focus. That way you should find something close to the minimum possible extension length, which is really the most desirable.

Using afocal imaging would almost certainly solve the problem, but can be tricky to get the camera, eyepiece and diagonal perfectly aligned with the optical axis. That means you can end up with part of the image out of focus. Getting everything to work at prime focus would definitely be a better solution if you can do it.

James

It's more complicated in the sense that with a 'frac or newt the primary is fixed and that fixes the position of the focal plane and with a Mak it isn't. So, to get an eyepiece or camera in focus with a 'frac or newt you move the eyepiece or camera back and forth until it reaches the focal plane. With a Mak you have the eyepiece or camera in a fixed position and you move the primary mirror back and forth, changing the position of the focal plane until it reaches the camera or eyepiece. But because the effective focal length of optical systems with multiple elements is dependent upon the distance between them and by moving the primary mirror you're changing the distance between the corrector and primary and between the primary and secondary, the focal length of the entire system will also change slightly.

If you've run the focuser all the way in both directions and can't find focus with the same arrangement as mine then perhaps the focal point can't be moved that close to the end of the telescope with the 90 Mak. Unless someone else with the same scope can suggest what sort of extension will work, I'd go for something that approximates the optical length of a diagonal, perhaps with a few short extensions for fine tuning. For example, I'd be tempted to get the entire set of the extensions you linked to. (It's probably also sensible to bear in mind that whilst I can achieve focus as in the image above, someone else with the same scope says they can't, so there may be differences in the same model of scope over time.)

There is probably a range of distances from the back of the scope in which you can get the camera to reach focus. What happens with my 127 though is that the further the camera is from the scope the larger the image and it doesn't take much for the Sun or Moon to become larger than the camera sensor, so you probably want to keep the extension as short as you can.

James

It's more complicated than that with a Mak. Effectively you move the image plane to be where you need it (ie on the camera sensor) rather than moving the camera sensor to meet the fixed image plane as you would with a 'frac or newt.

I don't know about the 90, but I took this picture today to show someone else how I connect up my 450D and 127 Mak. The EOS<->T ring converter goes straight on the visual back. Does that help at all?

James

Looking up at what people stick out from their windows and balconies I can tell you that there are a lot of seriously heavy pottery looking far more dangerous to me...

You may have a very valid point there

James

Pity anyone who is underneath if a counterweight accidentally slips off the end of the counterweight arm

Very ingenious solution though and particularly impressive given the difficulty of construction.

James

Is there any kind of "programme of events" for Saturday? Some of it might well be interesting to the children, but I think a talk about helium, whilst interesting for a while, might prove a bit of a challenge for them.

James

Will there be postings here about forthcoming events? It would be great to have reminders about what's going on as I can be a bit, well, let's say polite people call me absent-minded

(And as I read the first posting, just for one fleeting moment, I thought the "Space Cadet" section was going to be for people who are a bit, y'know, "out there"

James