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C5 V. C102: Any Advantage?

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#26 Jon Isaacs

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Posted 13 April 2014 - 06:19 AM

If the difference is staggering you've got one lousy C6.

Pete


If the difference is staggering, I would agree. If the difference is merely noticeable/apparent, then it should be no surprise.. I owned a 120mm F/8.3 for a couple of years, it was not free of CA but it did provide nice views and would give an 8 inch a run for it's money.

Jon

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#27 John Kocijanski

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Posted 13 April 2014 - 06:58 AM

I have a C102 and had the opportunity to view through a C5 a few times. The C5 had a slight edge on brightness but the C102 gave nice contrast. I like to use mine on double stars. It is a great scope for the money.

#28 n1toga

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Posted 13 April 2014 - 09:25 AM

I see now I should have been more specific. By stating the sw120 is good I was only trying to be humorous....should add a gramelin next time :p.

This is the first long tube decent apeture refractor for me. The 'staggering' quote was only to show my surprise about the sharpness of the view. I simply was not prepared for what a refractor view looks like. The targets being specifically the moon, jupiter and mars. Yes there is undoubtly colour presnt but luckily not too distracting for me.

The C6 also gives me very sharp views and definetely puts up a brighter image especially on the fainter stuff. Of course there is no false colour present and mars presented a beautiful image as though it was painted on a canvas. Very warm and comforting is to best described it. The Moon is a blindingly bright mass of detail.

The sw 120 just presents a sharper disc with the same details being more etched on....again this is what blew my relitavely inexperienced socks off. More so on the Moon than anythin else.

Forgive me for my overzealous praise of my newly aquired scope.

Rahul

#29 Eric63

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Posted 13 April 2014 - 09:46 AM

One thing we keep forgetting is the tolerance of the observer. What is a huge difference for one may be subtle for another. I was at a star party last year and got a chance to compare a few ED scopes to my 127Mak. Was there a difference? Yes. Was it worth $1000? No. But a less expensive achro would be a complementary scope (decent views and no cooldown in the winter).

Eric

#30 n1toga

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Posted 13 April 2014 - 09:52 AM

Karl,

What mount is the C102 on?

Rahul

#31 Sarkikos

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Posted 14 April 2014 - 11:55 AM

Given its large CO, Is there any advantage of a C5 over a C102, other than the much shorter tube? I have the C102 and like it a lot. I am curious about the C5. The CA of C102 does bother me a bit. OTOH, there is no CO on the C102.


I own both and have experience with both.

Advantage C5:

- No CA.

- Shorter, lighter, easier to manuveur. I can mount the C5 on my 501HDV on photo tripod. I can carry that setup - in one hand - down my stairs, out the door, down the porch steps, and 500' to a favorite nearby site. I have to mount my C102 on either my CG4 or AT Voyager alt-az. Heavier, more awkward, much harder to carry up and down stairs, not really a setup I'd want to carry very far on one arm, or even two. Ouch!

- Did I mention no CA? In comparable aperture and under the same seeing conditions, I'd take CO over CA for planet/lunar viewing.

Advantage C102:

- Quicker cool-down. Maybe better for cold winter nights. Use the C5 during temperate weather.

Mike

#32 KarlL

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Posted 14 April 2014 - 04:03 PM

Rahul -

I have the C102 on a VersaGo II. I also mount a C90 on it. Both work very well with it.

Regards,

Karl

#33 A6Q6

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Posted 15 August 2014 - 11:41 AM

Hi Karl, If your looking for a great grab and go in a small light weight package, look no further then the C5 and It seems the chances of getting one with good optics is pretty good today, I took a chance on this classic orange tube C5 when I saw it at a pawn shop. It has great optics. The C5 is as easy to move around as the eq 60mm refractor next to it.

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Edited by A6Q6, 15 August 2014 - 11:54 AM.


#34 rmollise

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Posted 15 August 2014 - 12:48 PM

Yeah, it's called "the color purple." You can apply as many filters as you want, but chromatic aberration steals sharpness as well as throwing up color. Once the damage is done, it's done. ;)


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#35 jrbarnett

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Posted 15 August 2014 - 11:51 PM

"...,color free,..."

 

Only "sort of".  Don't SCTs have spherochromatism, and relatively poor polychromatic Strelhs (and therefore contrast) as a result?  If so, perhaps free from secondary spectrum would be more true.

 

- Jim



#36 jrbarnett

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Posted 15 August 2014 - 11:53 PM

Yeah, it's called "the color purple." You can apply as many filters as you want, but chromatic aberration steals sharpness as well as throwing up color. Once the damage is done, it's done. ;)

True, but not as much contrast destruction as spherochromatism.  The f/9.8 achromat has little spherochromatism.  SCTs have considerably more I believe.

 

- Jim


Edited by jrbarnett, 15 August 2014 - 11:53 PM.


#37 Starhawk

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Posted 16 August 2014 - 12:18 AM

One big difference is the C5 is a heck of a lot more portable.  The C102 is seriously clumsy in comparison.

 

As for my own C5, the planetary images are hands down better than the C102.  I have one, and can't say I'm a fan of the CA.  Sure, you can put in filters...and presto, the Pleiades is made up of yellow stars.

 

I can't imagine getting rid of my C5- just too much performance in a coffee can sized package.

 

-Rich


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#38 charlesgeiger

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Posted 16 August 2014 - 01:21 AM

I spent a night many years ago (mid 1970's) inspecting the image of an f/15 Meade 4" refractor (very much like a Unitron) and an orange tube C5.  I found at similar magnifications (about 100X) in each scope, set up side by side, the C5 always had a brighter image.  I remember specifically studying M27 in each.  The center of the field of view in the C5 was good with coma hampering the outer extremities of the field.  I believe I was using Kellner oculars at that time.  The limiting magnitude in the center was very close with mabye a nod to the C5.  The flatness of field and contrast in the refractor was superb.  Every star in the refractor out to the edge was excellent and pinpoint.  I was impressed with each telescope at the time and I personally owned a 12.5" reflector with a 41/8" f/15 Jaegers piggybacked.  The Meade had more contrast than my Jaegers which I attributed to much better baffling in the Meade. 

Since that time, I have owned 2 C5's.  The first was an orange tube.  I bought it second hand and it was essentially in perfect condition.  However, it had much field curvature and coma and I used several different oculars.  Unfortunately, it was stolen from my house.  Thinking hard, I decided to replace it.  I bought a new black tube around 1985.  Even though of that time period, it really turned out to be excellent and I still have it.  I have compared it to a 5" Mak and it was too close to call.

 

So if you want the best star pinpoints, stick with the refractor.  Again, at f/15 and at 4" diameter the color correction is going to be very good and nothing is going to beat it.  If you want a little more aperture, a good C5 is hard to beat.  Recent achromats of 100 to 120 mm diameter and f/6 to f/8 to me are disappointing with too much CA.  I have now an 80mm Lunt ED and find it very good and a great compliment to my C14.  Of course, an ED doublet in 100 to 120mm is great at f/6 and greater with a bit of field curvature at low power especially with my ancient eyes.

 

If I had a good 100mm ED doublet, I would probably want at least an 8" SCT to compete.  But again these are different scopes for different purposes.  Again, as noted elsewhere, it is great to have a smaller ED...80mm or so...for wide fields and excellent contrast and also a larger Mak, SCT or Reflector to go deep.

 

I guess I have gone far off topic!

 

Chas.



#39 KarlL

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Posted 16 August 2014 - 09:02 AM

I was very surprised to see this thread active again.

 

Since then, I have settled on using solely my C90 due to health and convenience issues. Despite its severe limitations, it does everything I need.

 

In fact, I'm trying to sell my Orion XT8 and C102 (this is not an ad).

 

Regards,

 

Karl


Edited by KarlL, 16 August 2014 - 09:51 AM.

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#40 rmollise

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Posted 16 August 2014 - 09:25 AM

 

Yeah, it's called "the color purple." You can apply as many filters as you want, but chromatic aberration steals sharpness as well as throwing up color. Once the damage is done, it's done. ;)

True, but not as much contrast destruction as spherochromatism.  The f/9.8 achromat has little spherochromatism.  SCTs have considerably more I believe.

 

- Jim

 

Which shows up as purple fringing. Which I certainly don't notice in the SCTs. ;)

 

Bottom line? If you want to look at bright stuff, don't get an achromat. :lol:

 

That said, I have very much enjoyed using my wife's fast 4-inch Explore Scientific achromat. ;)



#41 Sarkikos

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Posted 16 August 2014 - 10:43 AM

I know what my eye sees. I see no CA through my C5. I see obvious CA through my C102.  The difference in the image of Jupiter in these two telescopes is obvious and striking.  I'll let the optical mavens discuss spherochromatism versus chromatic aberration. :shrug:

 

Mike


Edited by Sarkikos, 16 August 2014 - 10:48 AM.


#42 Sarkikos

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Posted 16 August 2014 - 10:47 AM

I was very surprised to see this thread active again.

 

Since then, I have settled on using solely my C90 due to health and convenience issues. Despite its severe limitations, it does everything I need.

 

In fact, I'm trying to sell my Orion XT8 and C102 (this is not an ad).

 

Regards,

 

Karl

I'm contemplating selling my Z8 and C102. The C90 is staying.

 

Mike



#43 KarlL

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Posted 16 August 2014 - 11:20 AM

Sarkikos -

 

Absolutely. if one accepts the real limitations of its aperture, and there are, it is a very capable little instrument. I use mine mainly for white light solar. it does a surprisingly good job on the planets. A much better finder is an absolute must.

 

Regards,

 

Karl



#44 Sarkikos

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Posted 16 August 2014 - 11:55 AM

Karl,

 

Which scope are you talking about? The C90, right?   :thinking:

 

Mike


Edited by Sarkikos, 16 August 2014 - 11:55 AM.


#45 KarlL

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Posted 16 August 2014 - 01:30 PM

Yes. The XT8 and C102 are just too much for me and no longer get used.



#46 KarlL

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Posted 16 August 2014 - 01:30 PM

Yes. The XT8 and C102 are just too much for me and no longer get used.



#47 KJL

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Posted 18 August 2014 - 09:06 AM

I own a C6 and have recently acquired the skywatcher 120mm f8.3 achro. The difference is sharpness! It is staggering... Detail is about the same between the two but it is just more obvious in the refractor. More easy to see is how I would put it. Yes there is colour in the achro but my orion V block cures that just fine and sharpens the view even more.

Rahul

 

If the difference is staggering you've got one lousy C6.

Pete

I'm inclined to agree with Pete that Rahul's C6 may need some TLC (collimation, perhaps?). I have a 123mm f/6 triplet with the APO lens cell made my LZOS, and had a C6 XLT alongside it for several months. The refractor's views are beyond reproach, as you can imagine, but the C6 also had excellent optics. Technically, the low-contrast resolution of the 123mm refractor was greater than the SCT, and you could see this when all had cooled down, but the difference was nowhere near as marked as you might expect given the massive 10x price difference. In fact, and I've reported this before, during a nasty 40F degree cooldown race last winter the C6 XLT produced better images faster than the 123mm LZOS: to my eyes, the slight cooldown-induced CA in the triplet was more distracting than the heat-plumy view of Jupiter through the C6. Of course, when everything had finally cooled down the refractor came into its own and outpaced the SCT, but again I think the majority of people would not make the same financial choice as I did (I gave the C6 to my parents).

 

Having said all that, I will agree with most everyone here that a C5 would only provide advantages on compactness. You've got to really need the portability to make the switch IMHO. Your 102mm achro may in fact produce superior views, and definitely will achieve those views faster if you have any degree of cooldown to deal with.

 

EDIT: Holy St Tardis, I missed the entire second page of this thread and also the fact that it was resurrected from awhile ago. I see my comments are irrelevant now ... KarlL has already made his choice to revert to the C90. Incidentally, I loved that scope when I had it -- it was my first telescope, in fact -- and today with my greater experience I have to admit that selling it was a rash decision. It was a tough scope to start on the hobby in a white zone, but now that I have mounts with encoders and DSC I could better appreciate what I could see in that scope.


Edited by KJL, 18 August 2014 - 09:14 AM.


#48 Patrick

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Posted 18 August 2014 - 11:21 AM

Given its large CO, Is there any advantage of a C5 over a C102, other than the much shorter tube? I have the C102 and like it a lot. I am curious about the C5. The CA of C102 does bother me a bit. OTOH, there is no CO on the C102.

Am I missing something?

Regards,

Karl

 

The 127mm C5 with an approx 35% obstruction has the contrast transfer of about an 87mm refractor. However, it will not have any false color which is more pronounced in the C102 achromatic refractor.  On the other hand, the C102 is a fairly long focal length refractor (1000mm f/10) so false color is more controlled than if it were a shorty scope.  Bottom line, I'd say you're not missing much.  I suspect you'd have to go to at least a 6" SCT to do as well as the C102.

 

Patrick



#49 rmollise

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Posted 18 August 2014 - 05:05 PM

For color to be very well controlled in a 4-inch, it needs to be at least an f/15. Not, as I said earlier, that one can't be fun...but an f/10 4-inch achromat isn't a high power planetary and lunar scope, that's for sure. ;)


Edited by rmollise, 18 August 2014 - 05:05 PM.

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#50 Ed Holland

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Posted 19 August 2014 - 02:37 PM

If everything else is perfect, Rod, I agree 100%. However, in the real world (and certainly my bits of it) truly high power planetary observing is quite the luxury, thanks to imperfect seeing. My example of the Celestron 102mm (97mm actually, f/10.3 ;)) has provided rather pleasing planetary views (Mars, Saturn) earlier this year, where 150x or so was the maximum tolerable magnification on most nights. Yes there is CA in comparison to the 118mm Mak, but images were lovely and crisp and it's a cracking grab and go instrument in my humble opinion.

 

Swings and roundabouts... :)

 

Cheers

 

Ed








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