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Hi, I have changed the focuser on my newtonian but its too short.
I realise that I can just add an extension tube to it but I’m not sure if that is the best solution.
I also seem to have have a stray light problem (I’m getting a hazy image on a 5mm eyepiece).
A third problem is that I find it quite cumbersome that the focuser has to stick out so far (155mm+eyepiece).
I wonder if I might solve the stay light problem by extending the main telescope tube instead of the focuser and therefore getting the eyepiece closer to the secondary. And also maintain more precision in the focuser by not extending it.
As it stands the focuser would have to come out 265mm from the centre of the secondary mirror in order to focus. The secondary is 50mm wide. From primary to secondary is 950mm approx.. The primary is 200mm Thanks for reading. Any advice will be much appreciated.
Originally brought for my C11 HD Edge, which its made for, but if used with filter wheel, OAG, and 0.7 focal reducer the spacing is to far out, hence the reluctant sale of this A+ Condition, unused (other than to see if it worked) focuser. The price includes special delivery. Bank transfer, paypal is ok, or cash/collect...ect... The price is £200. This would be great for planetary imaging, imaging without using an OAG, bringing the travel closer. Thanks for looking.
By Mark 2020
Help please. Last night I purchased an old celestron c8 sct, 2000mm fl, f10 on a fork mount. The mount has no power cable so is pretty useless, but i brought it to defork the ota for planetary imaging and hopefully some small faint dso's. It was a reasonable price. Ive got a heq5 pro mount that i will be mounting it onto. The guy said it needs collimation. I know i need to mount it on a vixen dovetail but the bolt holes dont line up anywhere. Its as if someone has rotated the corrector plate housing around 120 degrees. Would it make a huge difference if i removed the housing screws and put it back so that the bolts line up, keeping the mirror and plate in the same spot on the housing bracket, or would i have to try put everything back separately in different positions and collimate everything from scratch. The picture at the minute doesn't quite get crisp so whatever has been done needs rectifying. Can this even be done by us regular folk? Any thoughts or ideas, instructions? I feel the plate could do with a clean and the primary mirror itself. I just want it as optimum as possible. And can a hyperstar be fitted to these older versions? Im literally starting from scratch with an sct setup. Also what type of camera would suit a scope with this focal length for faint dso's, i have a gp290c for the planetary side of imaging. Sorry for the bombardment of questions.
The focuser on my SkyWatcher 150i is a basic rack-and-pinion, unsurprising for the price point, but sometimes a bit of a pain to control finely enough. I’m not looking to spend any serious money upgrading it, but I did want to see what I could tweak.
The first thing I did was to slacken off (slightly) the screws holding the plate against the spindle, as the operation was very tight when new – that helped a bit (and I think that without doing this first, the “friction fit” approach described below wouldn’t have worked). I will eventually get around to taking it all off as per AstroBaby's tune-up.
Improving the fine control without a major change means doing something with the focusing knobs – they’re quite small, so the effective “gearing ratio” when you operate them is on the harsh side. Some folk have described fitting larger diameter replacements, either bought or made, and even using ones with a planetary-style mechanism to achieve a reduction in the ratio. I didn’t fancy this, as I couldn’t see how the existing knobs were attached to the spindle without trying to prise them apart (possibly terminally). The other option is to increase the effective diameter of the existing knobs, for which purpose a clothes peg is apparently quite popular, but I’ve also come across descriptions of chop sticks inserted into holes drilled at intervals into the circumference, and punctured lids from peanut butter jars.
I wanted something that was cheap, relatively tidy and non-destructive. The answer seemed to be some sort of thick sleeve that I could fit over the knob. It would need to be a tight fit so as not to slip in use, to be not so large as to foul against either the focuser tube or the main OTA, and to be thick enough that it didn’t flex sideways when grasped. I thought I might find some larger rubber washers that would do the job, but none were thick enough to be rigid in use. However, a bit of searching found these spacers that are apparently used in vehicle shock absorbers.
My calipers said the diameter of the focuser knobs was around 29.5mm, and the nearest spacers that were available had an internal hole 30mm and outside diameter 60mm. I ordered one that was 10mm thick, not quite as deep as the knobs, but which allowed a bit more space on the inside edge for free operation. I’d hoped the internal hole might be a but undersized when it arrived but it was spot on, so I wound five or six turns of masking tape around the knob first. To avoid taking the tape off when fitting the spacer, I positioned one side first and stretched it across the face as I pushed. When it’s flush with the knob’s outer face, it’s just clear of the focuser body and OTA. There might be enough room to stick some kind of friction surface around the outside to improve the grip, but I don’t think it’s going to be necessary.
I decided to do only the one knob, so I now have a very Noddy “dual speed” affair. Because the clearances around the fitted spacer are quite tight, it’s worth checking the positioning of the spindle in the focuser body first – mine was fractionally off centre, so there was more room one side than the other (assuming you have no preference).
Originally brought for my C11 HD Edge, But when used with filter wheel, OAG, and 0.7 focal reducer the spacing is to far out, hence the reluctant sale of this A+ Condition, unused (other than to see if it worked), focuser. Asking price is £240 which includes special delivery. Bank transfer, paypal or cash/collect ect......