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4" ED vs. 5" achro vs. 8" SCT

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#26 N3p

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Posted 25 June 2019 - 08:22 PM

After this thread, I am convinced of something, if I ever get a SCT, it's going to be an Edge.



#27 rustynpp

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Posted 25 June 2019 - 08:32 PM

Thanks to everyone for your input and advice. I just submitted payment for an EdgeHD 8 from another CN member! I went with the Edge because I plan to use 100* EPs, which would expose a lot of the field curvature present in a non-Edge C8. I'd also like to pick up the 0.7x reducer at some point, and I love that it works with 2" accessories - 1.8 degree FOV with the 31T5!

 

My 4" ED is a great scope and deserves to get supplanted by another high-quality scope. I think the Edge 8 and C80ED combo should fit my needs for the time being.

 

Thanks again!


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#28 PowerM3

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Posted 26 June 2019 - 05:18 PM

There is no contest, really. The SCT is far and away the best option. SCT's have got a bad rap primarily by those who refuse to collimate them. In particular, Edge HD scopes are the best SCT's made, and I've been using SCT's since 1978. They hold collimation extremely well, and I guarantee they will beat both your ED scopes on double stars and planetary views unless your seeing is awful.

 

For me, the choice would be between 3" ED + 8" SCT or 4" ED + 8" SCT (yes, bring the 4" home and sell the 3" --why isn't the 4" better?)

 

The 5" achro is not even worth discussing as an alternative. Inferior in every way to either the SCT or the ED, it's only redeeming feature is that it "looks like a real scope."

 

Let me address a bit the "convenience" factor, as I think you've got it the other way around. The SCT is the more convenient scope by far. Unless you are a contortionist, you would hate the observing positions that a long 5" achro would put you in (and a short 5" achro will  have so much color that it would be unusable with more than 50x power). Collimation has to be done maybe once a year, cooldown just requires taking the scope out before dark (or, if you get an Edge, using the Temp-Est fans--but I've never seen a need) and dew management means putting a dew shield on (you could add a dew heater if you really need to observe through a very humid night, the combination keeps my Edge able to photograph through the night even when everything else in the morning seems like it's been dunked into a lake).

I have personaly owned all these scopes and compared most side-by-side. I 100% agree with this. Unless you really love very low power observing form a dark sky site an acromat is really not the way to go.



#29 Brent Campbell

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Posted 26 June 2019 - 05:55 PM

I read on this forum somewhere that happiness cannot be obtained until you realize that an sct is not a wide field instrument.  I have a new 4 inch apo (haven’t had the opportunity to use it yet) but I primarily use my sct as a planetary instrument with an occasional DSo.   

 

I agree with Jon.  For far less money (about $600) you can buy a NEW dob that would blow the doors off the sct for DsOs.  And if you really mean cost is no object then consider a night vision rig.  Either of these options would out perform the sct for dsos.

 

Ill qualify my answer by saying that I believe that I have an exceptional sct and it doesn’t change that opinion.



#30 rustynpp

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Posted 26 June 2019 - 07:38 PM

Treat any comments that suggest that the EdgeHD is going to be better than a standard C8 with skepticism.   Here is a test of an EdgeHD 11" with a Strehl of .825.  That is right at the edge of the diffraction limit.

 

http://fidgor.ru/Obs...2/test_367.html

I'm curious to learn about this website - they seem to do a lot of testing to facilitate sales of used scopes, as well as look into complaints. I would imagine both those things would cause a bias in the direction of poor samples.

 

That's not to say this says anything about the Edge's quality as compared with a non-Edge SCT. I just wonder about the ability to say anything at all about these scopes on the basis of this site, given the small sample sizes and potential bias.




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