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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).
So the little circular bubble level is weak.
But how to improve the levelling stage a head of the alignment stage?
A traditional level like this one
Or a simple multi purpose one like this one?
And we do this on the tripod before adding the mount & OTA?
The mount looks gently curved. How do we check that for level or do we trust the ‘fit’?
By Anthony RS
I'm selling these 2 filters since I'm getting a mono astro cam. The filters are barely used and in perfect condition, no scratches, no fingerprints, not even dust. They are both amazing filters, probably the best investment I've made. I've attached some images
taken with these filters, using a 100$ celestron newtonian, a 250$ Canon 500D and the infamous AVX. Also attached are images of the filters showing their perfect condition.
Astronomik CLS-CCD Canon Clip in Filter: https://www.astronomik.com/en/filter-gegen-lichtverschmtzung-filters-against-lightpollution-lpr/cls-ccd-filter/clip-filter-eos-mit-astronomik-cls-ccd.html
Original price including VAT is 155 Euros (around USD 182). I got it for around USD230 including VAT, shipping and custom taxes.
Selling for USD 120.
Astronomik Ha 12nm Canon Clip in Filter: https://www.astronomik.com/en/clip-filter/clip-filter-canon-aps-c/clip-filter-eos-mit-astronomik-h-alpha-ccd-12nm.html
Original price including VAT 194 Euros (around USD 228). Got it for around USD 270 including VAT, shipping and custom taxes.
Selling for USD 180
I am willing to ship them on my own expense using LibanPost (from Lebanon). Shipping might take time; if you would like to use some other shipment method please contact me to discuss the price.
Feel free to buy one or both together.
Let me know if you have any questions.
You can also contact me on <private email address removed>
Hello everyone, I'm wondering if I could get some help, sort of ripping my hair out a little.
I have the EXOS2 PMC-8 and last night I used Sharpcap to Polar align, I set the mount up as usual and adjusted until Sharpcap said excellent Polar alignment.
So my next step was to do a 3 star alignment I was using a program called Explorer Stars to achieve this, so when I asked the mount to slew to the first star it was way off even in the finder scope, is that normal? So I used the controls to get the star in my FOV and centred it, it was the same for the next two stars way off. so I did the same.
I finished the 3 star alignment and when I asked the mount to find an object the object was not centred it was bottom right of the quick photo I took.
I've made sure all the information is correct by setting my Longitude and Latitude and also made sure my time is correct, the mount is balanced and level and pointing North. I think I'm doing something wrong somewhere.
Also may I ask should my counterweight bar be parallel with the mounts front leg? I have two little arrows on the mount that should be pointing at each other when in the home position but when they are the counterweight bar is pointing to the right quite a fair bit.
I'm new to all this only been doing it for a few months so a lot of things are quite confusing.
Thanks in advance Bill.