The present “King of Unusually Inexpensive Refractors” has to be the SV510 for $14.95. I’ve been playing with a couple of SV510s these past few weeks and here’s what I’ve learned:
The optics are sharp, the solar filter is so-so.
While the view through the attached solar filter isn’t bad, the filter and not the optics is the weak link when it comes to resolution. When I removed the attached filter from one SV510 using an X-Acto knife and substituted a Herschel wedge prism the resulting views were very good within the constraints of its 53mm effective aperture diameter.
Viewing objects in the night sky during hazy and windy conditions last night I could observe the four dominant stars in the Trapezium and brighter stars in general show beautifully formed airy disks. The facility with which this scope shows airy disks was a surprise to me. I’m still waiting for a decent night of seeing and transparency to test the limits of this scope, but I’m optimistic for good results.
It’s easy and inexpensive to improve.
I added a red dot finder for $12, thereby more than doubling the cost of the scope, but it’s worth it for the convenience of easily acquiring targets. A free and useful modification is to move the attached dovetail back towards the focuser to improve balance. I used the existing rear most dovetail mount hole and drilled an additional hole closer to the focuser. You can see where I covered the original forward hole with a dot of self adhesive flocking paper. If you do this to your own scope you may have to notch the focuser mounting flange a bit to clear the rear nut; I had to do this to one of my two SV510s but not the other.
Even the flimsy included mount can be significantly improved for a few cents worth of damping grease.
The biggest problem with the mount and tripod is that in addition to being flimsy the mount suffers from a large amount of stiction. Between the one and the other the mount is basically unusable. You can’t in any reasonable fashion do anything to reduce its flimsiness, but by disassembling it and lubricating the rotating contact surfaces with Nye PG-44A damping grease the stiction can be reduced to a degree that the mount actually works, kind of. If you use a lighter grease than Nye PG-44A I don’t know that you’ll have the same results, but it’s basically free to try out.
Thanks Jim, good to know how the optics are w/o the solar film. Am looking forward to the 'decent night' report which could cause my SV510 to become a loaner / give away for night viewing w/ the addition of a better tripod. (fawc - I've not done much for quite a while) Good to know about Nye pg-44a grease too. fwiw - Newgate Simms says Tribosyn PG44A is a less expensive alternative with the same formula.
Also interesting are npbarker's comments - thanks npbarker.
I learn something every time I come here.
Cheers everyone!
Edited by AstroPhotog, 14 April 2025 - 11:53 PM.