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By Cosmic Geoff
With reluctance I am looking to sell my 200mm aperture f5 Helios Newtonian OTA. (Helios is a brand that became incorporated into Skywatcher - this closely resembles Skywatcher OTAs)
The Helios is offered with single speed rack & pinion focuser, tube rings, 22 to 1.25" adaptor, dovetail bar and grab handle for £90 o.n.o. In good condition except that the dovetail bar appears to be discoloured by exposure to sunlight.
I have not used the telescope for many months and with a persistent problem in my right arm my enthusiasm for moving heavy kit around has diminished.
Buyer to collect from North Bucks.
Offered as option with the OTA: EQ5 mount with RA drive + 6 volt sealed lead-acid battery +charger + standard and extra long Dec slow motion manual shafts. £150. Condition - used but working.
If I sell the OTA I will be looking to dispose of its accessories:
9x50 Skywatcher straight finder - in excellent condition except that the small plastic dust cap is missing.
Cheshire collimator, boxed, as new.
Helical fine focuser, range 10mm, ID 1.25", screws into 2"adapter.
3x Datysun Barlow, as new, boxed.
Widefield eyepiece, 22mm f.l., 30mm body (note not 1.25") with built in focus, works well with this telescope.
Plastic collimation cap (no cost).
This bundle would cost around £114 new - offered if bought with scope at £75 o.n.o.
Like many I think Telrads are great scope sites. And want to use mine with different scopes. But I don't want to stick a base to a nice looking OTA.
All base types seem to be curved so sticking to a flat surface such as an accessory plate is not possible.
The only option seems to be using two holes in its base, if they line up with those on a plate. Are there any ideas out there, or aftermarket Telrad bases apart from the company ones?
Decided to put cooling fans on my newtonians a 200pds and a 130pds ,used a 120mm on the 200 and a 80mm on the 130pds ,i used, Be Quite silent Wings2 fans they use rifle bearings and are so quite German made, i did the 200 first and was impressed with this make so ordered the same make for the 130 pds it comes with a lead with four wires but only needed neg ang pos so snipped other two out , made a disc from plastic and cut out around collimation screws on primary then used velcro to attach to OTA fitted a 2.1mm dc socket on to the disc then bought a usb lead to 2.1mm barrel though i may fit another 2.1mm socket on my power box and use 12v either way it works ,i used a dimmer on the 200pds but it doesnt need it and wouldn't use it again but its fitted now so will leave in place.
So, I have gone and got myself a Skywatcher Star Discovery 150p, which has so far proved to be a very good little scope and I've had some very good results.
I have now got the bug for imaging and have gone out and got myself a second hand Nikon D5100 and verious other equipment needed to do this, only to now find I can't get Prime Focus!!!!!!!! So the only way I can image is using a barlow x2 which obviously changes the F ratio from F5.5 to F11 slowing everything x2 this isn't to bad for planetary imaging but for DSO images not so good!!!
After searching through lots of videos on to do this all I can find is......
I can either butcher the standard rack and pinion focuser that's fitted on it by cutting it down and rethreading it or by moving the primary up by 20-25mm, which seems a shame to do a brand new scope still under warranty!
The only other option I have come up with is changing the focuser to a Skywatcher Low Profile Dual Speed Focuser For Newtonian Reflectors.
Could anyone out there shed any light on this before I spend another £130 on the new focuser.
A couple of months ago I bought a 16" Meade ACF F8 OTA from a dealer in Europe to be used in my observatory. I'm now concerned that this OTA has a severe optical issue, as stars won't come completely to focus, I've tried time and repeatedly and the lower FHWM I've been able to measure in Maxim DL is 8.0.
I've also tried to use it visually at magnitude 90x and I could not get sharp stars at all. This week I used a newly acquired artificial star and a ronchi ocular to do some tests an to check for collimation. Using the Atik Infinity camera, I've detected what seems to be a rough edge with its own diffraction pattern. This asymmetry is present both in focus and out focus on opposite edges respectively.
All testing has been done with the scope acclimated to the outside temperature, no diagonals nor other optical elements are present.
Also, the ronchi test shows potential spherical aberration and some zone aberrations, although we lack the experience to make a definitive diagnostic.
I'm attaching some pictures below in the hopes that someone could tell me what's going on:
Some pictures of the aberration infocus and outfocus.
A picture using Maxim DL of a star at the "sharpest" point of focus, notice the tails of the star on the right hand side.
A picture of M13 showing the sharpest point of focus.
As always your input is much appreciated.