2307 replies to this topic

[AstroPhotog]

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.

[RichA]

Forgive me if this has been addressed elsewhere, but I didn't find it in a search of this or related threads: I just did an effective aperture flashlight test of the 60mm 501p and found it's effective aperture to be 37mm. 

 

I picked up the 501p as a knock around scope for my four year-old, but of course I started tinkering and experimenting with replacing the focuser with a one of the cheap (but metal) units available on ebay. I used an acryclic tube as an adapter, pressure fit everything and tested on the moon last night. Compared to views with the stock focuser, things looked *bad*. Haze, terrible contrast, and very soft images, esp on the outer third of the FOV. I made some adjustments to ensure all the elements are properly lined up. I'm sure it wasn't perfect, but I do lots of hand tool woodworking and I have both the tools and the experience for the fine work of making things square, plumb and flat. Star tests looked pretty well collimated. So I think I got things close. 

 

Reading here I suspected the stock focuser is clipping light and acting as an aperture mask, improving the scope's optical quality vs with the new focuser, which has a wider, shorter drawtube. Tonight I ran the test again, with the same results. That's when I looked in the stock focuser drawtube and discovered the fairly large baffle inside, about a third of the way from the objective-end of the drawtube. The flashlight test confirmed 37mm effective aperture with the stock focuser. 

 

I'm no expert on these matters, and mostly know what I've absorbed here over the past couple years, but it appears to me that the 501p is perhaps a 37mm f10.8. What do others here think of this assessment?

 

If that's the case, it's still a fun little scope to experiment with that produces pleasing and surprisingly sharp views of the moon, bright double stars, the Jovian system and a few other objects (and on a basic photo tripod it's great for a 4 year-old). I've got an SV510 on order because I couldn't resist more opportunities to tinker for $20. 

 

Screen_Shot_2025-04-08_at_8.19.52_PM_3_optimized_200.png

Let us know if you find anything that that focuser will thread into.  I've got two, one cobbled onto an 80mm f5 scope and one I haven't used.  But a flat, square plate on the bottom would have made it much more usable for a "test bed" OTA.

[RichA]

More than once, in his reviews of inexpensive refractors, Ed Ting has noted that ironically these types of products are better suited for experienced customers who can, (possibly at more extra expense than they are worth) work around their failings. 
When I have bought these refractors it was always with the understanding that the only useable part is the basic OTA. The included accessories, well, very often I agree with RichA’s assessment, ‘landfill fodder’. 

Worst accessories I've ever seen came with a weird, toy-like "semi-apo" from Japan I got.  The scope/lens is not great.  The correction is like a strange achromat, but the lens is a cemented doublet which was either ground, or glued off-axis.  But, the accessories were pure trash.  0.96 plastic eyepieces of the lowest quality imaginable.  They make the inexpensive metal Huygens supplied with 1960's 60mm refractors seem like Claves.

[Polyphemos]

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!

I’ve entered my area’s “breezy” period, which lasts ten months give or take, so a decent night’s viewing is going to take a while.  Here’s my observing situation:

 

 

It gets worse as the season warms up and into the summer and fall so a more rigorous evaluation of the scope is going to take a while, but I do continue to play with the scope and have some further thoughts.

 

First off, while the optics are decent they’re made to a very low price point and so, you know, there’s that. Polish, figure, alignment, and coatings are good enough, but unlikely to wow anyone who’s looked through pricier scopes aimed higher in the market. That doesn’t mean they’re bad, and even the low end of the market optics can be remarkable when considering their cost, I’m just not sure the SV510 scope will be one of those remarkable examples.

 

Next, I measured the clear objective diameter to be 52.5mm, which closely agrees with my flashlight measurement of the effective aperture. Keep in mind that I’ve knocked out the baffle in the draw tube than would otherwise reduce the effective aperture. Let me know if you’d like me to explain how I did that without damaging the delicate plastic focuser.

 

52.5mm isn’t a lot for urban skies and old man eyes, and it would be much better if it were the 60mm claimed in the ad copy, but it’s not. It’s possible the optics really are terrific but limited by the less than advertised aperture. I’ve thought some of the views dim but that could be the coatings, aperture, my skies, my eyes, or a combination of them all.

 

On the plus side of the ledger, 52.5mm over the claimed 400mm focal length gives a focal ratio of 7.6 and achromatic aberration ratio of 3.7, so chromatic aberration is quite subdued. Then there’s the nice airy disks I’ve observed, so the doublet was assembled and aligned well and the lens cell isn’t pinching anything. As to the overall quality, let’s just say the jury is still out and scheduled for a long recess.

 

I continue to enjoy using and evaluating the scope, and it’s a perfectly suitable instrument for someone wondering if astronomy is for them, or anyone who enjoys playing with telescopes to see how they perform and what they can show. Like you, I’ll give mine away and with a better mount and tripod some youngster is sure to have a good time with it. I will not have any concern it will diminish anyone’s enthusiasm for astronomy.

[RichA]

98 percent humidity is time for planets and double stars.

[Polyphemos]

98 percent humidity is time for planets and double stars.

What is a 62 mph wind gusting to 70 time for? 

[jrussell]

Geez, and I thought it's been ridiculously windy here lately.

[AstroPhotog]

Thanks for taking the time to do a write-up Jim. Yeah, for the price I didn't expect anything to brag about, but it sounds good enough to get someone started in viewing the night sky. (Certainly better than my first scope. :-) And if my sample ain't too good then I'll put Baader 5.0 solar film on it and go from there.

 

Those wind speeds sound too much for a kite.

 

Edit: Oh, feel free to explain removing the tube baffle. Someone may use it even if I don't.

Edited by AstroPhotog, 15 April 2025 - 09:33 PM.