SV501P 70mm OTA for a guide scope, what's your opinion?

[chris_g]

Hello All

I'm looking for a lightweight inexpensive refractor that has at least a 400mm focal length to use as a guide scope that weighs less than my ST80. The SVBony 501P 70mm F/5.7 seems to fit the bill. The complete weight including tripod and backpack that it comes with is 4 pounds so I can imagine the tube weight being probably no more than half that since the tripod is made of aluminum, I've posted the question to the manufacturer and will update if they answer. The focuser is a 1.25-inch draw tube and has a 42mm standard thread for a T-adapter, though that is not necessary for my application, it's a nice feature. The objective is 2 elements in 2 groups and multi coated for high transmission. The camera would be an ASI120 or 290. Only issue I see is dew because the tube is made of plastic. The 60mm version would weigh even less but it's F/6.3

Anyone have or used this scope? Thoughts about its use as a guide scope?

https://www.svbony.com/sv501p-/

[JayTee]

I'm sure it will work just fine. I found my guide scope from the local classifieds for 10 bucks so if that works then this scope should have no issues.

The one feature you would like to have is a way to lock the focuser. Locking the focuser is nice because it eliminates image shift by the focusing tube moving within the focuser housing.

[chris_g]

I'm sure it will work just fine. I found my guide scope from the local classifieds for 10 bucks so if that works then this scope should have no issues.

The one feature you would like to have is a way to lock the focuser. Locking the focuser is nice because it eliminates image shift by the focusing tube moving within the focuser housing.

Thanks, I thought as much but liked confirmation, I still feel new at times. It has a twist screw on top of the focuser draw tube, cool. This will be a nice upgrade.

Weight has really become an issue on the EQ6. I sat down tonight and added it all up by the ounce, my ratio is at 77%, didn't think it added up quite that much. I had it out a couple nights back and guiding was not the greatest, chocked it up to average seeing that turned poor. Could see wispy clouds in PHD2 in my clear skies with above average transparency. Hope to try again this weekend. Curios to see how it will perform with that load with all around decent skies.

[Gmetric]

My guide scopes cost about the same as JT's scope. I bought mine from Yahoo auction. Both have 60mm objective lenses with 420mm focal lengths and they are both achromats. I drilled and tapped locking screws in them both. They are working with no issues at all. You don't need to spend mega bucks on a guide scope. Just make sure it's solidly mounted and the image scales between your guide scope and imaging scope are close. My main imaging setup image/guide ratio is 1:077 which works great even with a relatively rough polar alignment. Some recommend no more than 1:4, Personally, I don't go any higher than 1:2. But, it depends on your focal lengths, pixel pitch and physical limitations.

You can use this site to find a suitable setup. https://astronomy.tools/calculators/gui ... uitability Just adjust the values until you find something that gets you within a ratio that's desirable and meets your physical needs.

[chris_g]

My guide scopes cost about the same as JT's scope. I bought mine from Yahoo auction. Both have 60mm objective lenses with 420mm focal lengths and they are both achromats. I drilled and tapped locking screws in them both. They are working with no issues at all. You don't need to spend mega bucks on a guide scope. Just make sure it's solidly mounted and the image scales between your guide scope and imaging scope are close. My main imaging setup image/guide ratio is 1:077 which works great even with a relatively rough polar alignment. Some recommend no more than 1:4, Personally, I don't go any higher than 1:2. But, it depends on your focal lengths, pixel pitch and physical limitations.

You can use this site to find a suitable setup. https://astronomy.tools/calculators/gui ... uitability Just adjust the values until you find something that gets you within a ratio that's desirable and meets your physical needs.

Thank you for the link, that scope's ratio to my C8 is 1.2 at 1280 and 1.318 at 2032. It also opens up my thought process to adding a Barlow to the guide scope later, if that would improve guiding.

Clear Skies,
Chris

[chris_g]

Just got an answer on the weight of the OTA by itself, .45kg, 1 pound! That change alone would change the weight ratio from 77% to 71% And the planned PC upgrade will take the ratio to 53.84 if I remove the Primaluce saddle plate and use Velcro instead to secure the new PC to the rail.

Wow, no reason not to do this when some funds become available for upgrades.

Cler Skies,
Chris

[JayTee]

Adding a Barlow to the guide scope later, if that would improve guiding.

PHD2 can effectively guide at 1/10 of a pixel. Of course if you're mount can't do that then PHD2 is guiding better than your amount can provide. Using a barlow in most cases is unnecessary. You're introducing a new optical surface, actually two of them, and it's another mechanism to move, or get misaligned, or whatever giving you potential headaches.

[chris_g]

Adding a Barlow to the guide scope later, if that would improve guiding.

PHD2 can effectively guide at 1/10 of a pixel. Of course if you're mount can't do that then PHD2 is guiding better than your amount can provide. Using a barlow in most cases is unnecessary. You're introducing a new optical surface, actually two of them, and it's another mechanism to move, or get misaligned, or whatever giving you potential headaches.

Thank you, I have a lot to learn about optics...