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Greymouser

C5 Refractor equivalant?

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A little advice please. ?

I am still trying to decide on which small travel scope to get and have narrowed things down a bit. Thing is though I am unsure on how to compare equal with equal, I know the C5 and a 127mm Mak would be very similar, but which small frac would offer similar results? I assume that I would be talking about similar to a 100 ED, which is not really portable enough, never mind more expensive, ( depending on brand of course... ) So what would offer a fair comparison with a C5, which to be honest is the favourite so far, particularly as I already own and enjoy a Celestron SCT. I suspect a frac is unwise anyway as I already own a ST 102.

Thanks in anticipation. ?

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I think a 100mm / 102mm ED doublet would be about the same on the moon and planets. The C5 / 127 mak would do better on deep sky objects though.

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I believe that what you intend to use it for will determine the best choice.

The advantage of the C5 over small frac is effective aperture (which for the C5 is 117.5mm). It also has the advantage as you suggest of short length at 30mm and low weight (3kg). Oh and no chromatic abberation :)

For deep sky (both visual and imaging), disadvatages are long focal length. But assuming you use a focal reducer to compensate this your next limits are restricted FOV (vignetting) and spherical aberration.

For planetary the disadvantage is having the central obstruction which will reduce the relative peak diffraction intensity - effectively reducing contrast

I think its really hard to find a refractor that beats the C5 for all portable needs - if I had unlimited budget I think the Borg 90FL would be a great comparison to make :) Borg 101ed would be my next choice but length of OTA increases to 55mm, but can be broken up into smaller peices for travel

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3 hours ago, festoon said:

I think its really hard to find a refractor that beats the C5 for all portable needs

Yes this is beginning to be my opinion too, especially considering I already have the 9.25, with several extras, including the reducer. I think I like the SCT design. ?

Glad to see my assumption about the 100 ED John, which helps enormously, especially when I factor in the extra cost and weight of the ED.  When you consider the C5 only weighs six pounds, and is only 11 inches in length, I am not sure it can be beaten for my purposes. I think that now I only need to decide which of the versions to get. ? ( Unless I over think it again, not least because the refractors do look so good. ? )

Edited by Greymouser

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Also wanted to add that compared to the c5 the 127 mak will have a longer cool down time, and is a little bit heavier.

The 127 has a longer focal length too and smaller central obstruction, so is much more suited to planetary viewing and double splitting.

Personally I think the sct is a more all round good performer (noting that at the end of the day it is only a 5" aperture) with the advantage of being very portable.

34 minutes ago, Greymouser said:

think that now I only need to decide which of the versions to get. 

Just wondering what you mean by versions? Are you talking about the rare c5 f/6 telephoto?

 

 

 

 

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1 minute ago, festoon said:

Just wondering what you mean by versions? Are you talking about the rare c5 f/6 telephoto?

Easy to answer:

https://www.rothervalleyoptics.co.uk/celestron-astro-fi-5-sct-wifi-telescope.html

https://www.rothervalleyoptics.co.uk/celestron-c5-xlt-sct-telescope.html

https://www.rothervalleyoptics.co.uk/celestron-omni-xlt-127mm-sct-telescope.html

https://www.rothervalleyoptics.co.uk/celestron-nexstar-5-se-telescope.html

I am sure I had come across another version too, but the above is just off the top of head. The Astro Fi version gets a decent review on You Tube. ?

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A C5 plus the ST102 you already have make a great pair that compliment each other nicely.  ST102 for low power wide field, C5 for medium to high mags (within reason for the latter of course).

Ed.

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The versions you link to above, the ota is the same in all cases, the difference being the mount (and a different paint job :))

I personally went for an AZ GTI mount and found it a good combination for portability. Similar wifi capability like the Astro-fi.

image.thumb.jpeg.885bde6f45a86efd99f16cd3f02f7584.jpeg

Again the choice really depends what you want to do. The eq mount would be much more suited to long exposure Astro photography the alt-Az good for visual ergonomics and even planetary imaging

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You can compare a Schmidt only to a Newtonian, never a refractor.  A Maksutov is the only reflective design that has been described as "refractor like". 

The only short 100mm-ish refractor that would possess the apochromaticism of a reflector would be an f/6 triplet-apochromat; for example...

https://www.firstlightoptics.com/esprit-professional-refractors/skywatcher-esprit-ed-100-pro-triplet.html

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27 minutes ago, festoon said:

I personally went for an AZ GTI mount and found it a good combination for portability. Similar wifi capability like the Astro-fi.

Yes, I saw your pic of your set up, it almost decided me, looks good. Just a shame I cannot find the orange version, because after all, I am still at heart a member of Alan Brown's Tangerine Army! ( There is/was a second hand version for sale here, but with a SE mount, so to me with the superior Evolution mount, pointless. ) ?

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