102mm f/10 Achro Vs 80mm f/6.3 ED Doublet

[MjrTom]

Hello!

I have the opportunity to pick up a Vixen SP102M 102mm achromatic refractor.

How will it perform in comparision to an 80mm ED doublet refractor.

My understanding is that the 102mm f/10 correction would probably be on par to the ED doublet since the ED doublet is far faster producing a more pronounced light cone making the focusing of the differing wavelengths more tricky. Since the ED element only compensates to a certain point I think the correction between the scopes should be similar.

If I have read correctly once a 4 inch achro refractor reached f/9 or so the correction improves to a point where it is acceptablly focused and there is little to no CA.

Please correct me if this assumption is not correct and very interested to hear your thoughts on this comparision.

My interests are Planetary & Lunar observing plus star clusters, Globulars and Planetary Nebulas

Also anyone fancy guessing the weight of the OTA?

My money is on about 12kg but not sure...

Should be ok on my Alt/Az with a counterweight.

[Damo636]

Hi Mark. I have just bought a 4'' f11 but the Tal100 RS it replaced was an f10scope and i can honestly tell you the CA was very minimal, even on the moon. As to The ota weight both the Tal and my new addition weighed in at around 5kg.

[MjrTom]

Thanks Damo

I was looking for something along the lines of the Tal 100RS or similar when this scope came up for sale.

[John]

The SP102M is a nice refractor but it will show some CA - more than Skywatcher ED80 for example, which is practically CA-free, visually. Bear in mind that you can pick up a used F/9 100ED (Celestron or Skywatcher) for under £300 which, again, is virtuallly CA-free visually.

The TAL100 and the Vixen SP102M are really good examples of achromats - a bit better corrected than the more recent chinese made equivalents, but they still show some CA. You would need something like an F/15 to reduce the CA to near the levels of the ED scopes I've mentioned.

In case you wonder, I've owned all the scopes I've mentioned above.

[MjrTom]

Thanks John

So looking at it I would need to get it at a pretty good price to make it a good choice?

I was also looking at the 100mm ED synta scopes as well by comparision.

Visually is it worth it? It has twice the focal length and another inch in aperture but the down sides are size in addition to your comments

Is the ED80 a more rounded package?

[John]

Given your observing interests I think you would find 80mm (even an ED) ultimately too limiting although I see from your sig that you already have one so you already know what they can (and can't) achieve.

[MjrTom]

Thanks again John.

Yes the ED80 is quite limiting regarding what can be seen for DSO's

However performance on the moon and planets is really good producing a really sharp & contrasty image.

My concerns are that the optical correction (CA in particular) on the Achro might be a big detractor. I dont want a big long scope which is a one trick pony.

Would I be better missing this completely and just sticking to the C8 upgrade path....

[andrew63]

I have recently replaced my 100ED F9 and was looking for something even smaller for a grab and go - was at the point of getting a 80ED but was advised for visual use it would be quite a step down. Ending up getting a 100ED F7 which is almost the same size as the 80ED synta which use 100mm tubes for some reason. See this review which is excellent. I would recommend a 100 of some sort for visual use.

Astro-Tech AT102ED - Review

Good luck with your choice!

andrew

[MjrTom]

Thanks Andrew

[MjrTom]

Just out of interest which would you take to a star party and why?