SingAstro

Hi people,

Just got myself the C70 for mainly for terrestrial use. Understand it can also be used for astronomy. Read from forums that replacing the stock eyepiece can improve viewing dramatically. Not sure if upgrading the eyepiece is worth it. Hope someone can give me some insight in this.

A good eyepiece can fulfil the potential of any scope but that potential varies from scope to scope. Views with a good eyepiece will definitely be better than the views from an average eyepiece, etc.

However, a crappy scope will not become an excellent one with a good eyepiece.

The main flaw of that built-in 7-21mm zoom eyepiece with C70, the AFOV is only 30-43 degrees.

Thanks guys for the insight.
I tried it out last night and the FOV is not that good. Moreover, at high magnification, it blurs.
What then would be a good recommendation for an eyepiece?

Can try this one , SGD $16 shipped
http://www.aliexpress.com/item/Standard ... eb201560_7

from
http://www.cloudynights.com/topic/50314 ... -aspheric/

for high magnification, I don't think the scope is capable of much further than 70x , due to the 45degree angle prism that flips the image from upside down to right side up

Thanks, will check it out.

Hi Hardwarezone, I checked the Aliexpress website and saw that there are many other eyepieces.
Your recommendation is for a 23mm eyepiece. Would it be practical then for me to get a 10mm one so that there is higher magnification?

For basic optics the rule of thumb for magnification is 2xAperture in mm. Hence the magnification used should not exceed 2 x 70 = 140.
Your scope FL is 750mm, which yields x75 with a 10mm eyepiece. So its still doable but 10mm has lesser eye relief and for an aperture of 70mm under Singapore skies, pushing x75 may be ok for moon/bright planets but not DSO..

Yes Jerison , you can get the 10mm one in the same series but don't get the 3-in-1 set as the 4mm not suitable.
Aliexpress have lots of traps there like junk grade plastic stuff and bad monoculars & binoculars , so do note .... don't anyhow buy , also cross check if any item is available on ebay.com.sg for paypal protection.

The 2x per mm general guide is for refractors ... mirror less reflectivity, central obstruction, less surface smoothness on low-mid tier auto-polished products ... all these lower the maximum achievable magnification compared to a "perfect" refractor of equal size.
The human eye reach it's limit at 1.3x per mm , higher magnification makes it easier to catch tiny details but does not bring out what the scope isn't capable of resolving. (quote Jon Issacs from CN forum)
Again the 45 degree "amici" prism is well documented to reduce image clarity and brightness.
With the scope focused to infinity , indoor pointed 1 feet from a wall and shine a laser or strong flashlight 6 inches away into the eyepiece , the scope will project a circle or donut onto the wall for you to measure the exact operating diameter. I would not be surprised if you get the result a few mm less than stated example 70mm 90mm 127mm. This is due to either the primary mirror on Synta maksutov or limited by undersized prism.
The same test can be done on binoculars , with the worst offender the common 15x70 binoculars losing 10% aperture.

For plossl eyepieces, the eye relief is approximately 2/3 of the stated focal length.
That brings the plossls under 15mm focal length to uncomfortable threshold even for non-spectacle users.
Eyepieces of other design you need to refer to the spec listed by seller.
This 62degree plastic aspheric cheapo series is marketed as long-eye relief , the eye relief spec is not listed but it should be fine. It is NOT a plossl design.

Thanks guys, you fellas are experts.. very cheem for me but I sort of gotten a rough idea.

Anyway, I intend to use the scope at nature reserves, not looking up to the skies.

On a final note, what I want is better clearer views and better AFOV. Would then a 20mm Plossl eyepiece be good in this case?