C9.25 - Mushy or Sharp?

[Flame Nebula]

21 minutes ago, paulastro said:

Yes, you're right about the collimation issue.  Strange for SCs since they are about the easiest type of telescope to collimate in my view.  As you can imagine, with Peter Drew present, the SC I mentioned at Kelling all those years ago would have been spot on! 😊

Also, my own and only experience of looking through an sct was when at an astronomy evening in Alice Springs 25 years ago, through what I think was a C11. I remember thinking that the view of Saturn was spectacular, like looking at a photo in a book! Now, THAT, is what I'm looking for. 😊 I bet that scope was fully cooled and collimated, given we were all paying for the evening! But seeing in the outback can't be compared to typical UK seeing, of course. 

Edited March 17 by Flame Nebula

[Elp]

Remember your eyes were likely better that long ago too.

[Flame Nebula]

9 minutes ago, Elp said:

Remember your eyes were likely better that long ago too.

True, but if it was half as good now, I'd be very happy. That's how good it was. 🙂

[mikeDnight]

2 hours ago, Flame Nebula said:

Hi Paul, 

Indeed, as noted in my original post, there does seem to be a larger percentage of people on the CN site(which may or may not mean predominantly American based users) who reported sharp C9.25. But, then I see evidence from one user at least, who said their newt had no issues with the seeing on the same night the C9.25 gave mushy views. Logic seems to vanish then. Clearly, this could be one of those nightmare situations, where multiple factors are at play. So, a mushy view could be due to the OTA and/or seeing and/or collimation and/or thermals. 😬😬

 

A Newtonian will reach thermal stability significantly faster than a SCT, which is far more sensitive to internal heat because of the amplifying secondary mirror. But then a Mak Cass with a much thicker meniscus corrector would likely work at optimum before a SCT, so we come back to the schmidt plate being a problem.

 At the end of the day it comes down to personal preference, so for me I'd want a scope that performs as quickly as possible. I don't want to wait 2 to 3 hours before a scope gives its best. I'm impatient and as soon as the sky clears and I put an eyepiece in the focuser I want great views. If I were an imager I may feel differently, but as a purely visual UK observer, they are not for me. No other scope design gets such mixed bag of opinions.

[Mr Spock]

2 hours ago, paulastro said:

using magnifications between x400 and x600. This would be almost impossible in the UK.

Not so. I regularly use my 12" on the moon with a 3.3mm eyepiece. That's x461 - and it is very sharp. With the C9.25 I used an 8mm eyepiece for x294 on the moon maybe half a dozen times in ten years of owning it.

It didn't have poor optics. The star test was perfect. With SCTs poor MTF is the problem, which is much worse on low contrast objects such as Jupiter's belts. This is why you hear many people say they prefer refractor views. It's also why SCTs are good at imaging as MTF can be corrected for in processing, assuming the optics are good quality.

[paulastro]

19 minutes ago, Mr Spock said:

Not so. I regularly use my 12" on the moon with a 3.3mm eyepiece. That's x461 - and it is very sharp. With the C9.25 I used an 8mm eyepiece for x294 on the moon maybe half a dozen times in ten years of owning it.

It didn't have poor optics. The star test was perfect. With SCTs poor MTF is the problem, which is much worse on low contrast objects such as Jupiter's belts. This is why you hear many people say they prefer refractor views. It's also why SCTs are good at imaging as MTF can be corrected for in processing, assuming the optics are good quality.

This was using an 8 inch SC at up to x600, not a 12 inch Newt at up to x461.

.

Edited March 17 by paulastro

[Mr Spock]

You said:
 

26 minutes ago, Mr Spock said:

This would be almost impossible in the UK.

Implying it's the UK not the scope!

[Flame Nebula]

54 minutes ago, Mr Spock said:

Not so. I regularly use my 12" on the moon with a 3.3mm eyepiece. That's x461 - and it is very sharp. With the C9.25 I used an 8mm eyepiece for x294 on the moon maybe half a dozen times in ten years of owning it.

It didn't have poor optics. The star test was perfect. With SCTs poor MTF is the problem, which is much worse on low contrast objects such as Jupiter's belts. This is why you hear many people say they prefer refractor views. It's also why SCTs are good at imaging as MTF can be corrected for in processing, assuming the optics are good quality.

Thanks Mr Spock. 

I think your last sentence is the key thing here. 

[JTEC]

I’ve owned the 9.25 and the 11 and was pleased with both.  I’m a fussy observer and have a TEC140 to compare them with.  While the character of views through the apo was (and is) uniquely attractive - there’s no disputing that high quality apos render sweet views - both the SCTs resolved and showed finer detail on, for example, the Moon - not surprising, given their substantial aperture advantage.  Both SCTS were good scopes optically and mechanically and this was confirmed for the 9.25 by an expert independent bench test. I’ve had, from memory, 9 Newtonians over the years, from 6 to 14”, including examples with optics by Hinds, Hysom and Grubb Parsons, and would not say that, aperture for aperture, the optically very good Newts generically outperformed the SCTs.  There are so many contributory factors, some intrinsic to the design, some to do with the way different sorts of scopes need to be managed in order to perform at their best.  And, of course, there’s sky quality to contend with, which doesn’t affect SCTs more or less than any other sort of scope.  I liked both of my SCTs. Perhaps I got lucky. Both were rewarding scopes that gave good images and provided decent aperture in a compact package that wasn’t unduly demanding to mount.  The AZEQ6 was a good match, incidentally, as was the AZ100.

[Flame Nebula]

4 minutes ago, JTEC said:

I’ve owned the 9.25 and the 11 and was pleased with both.  I’m a fussy observer and have a TEC140 to compare them with.  While the character of views through the apo was (and is) uniquely attractive - there’s no disputing that high quality apos render sweet views - both the SCTs resolved and showed finer detail on, for example, the Moon - not surprising, given their substantial aperture advantage.  Both SCTS were good scopes optically and mechanically and this was confirmed for the 9.25 by an expert independent bench test. I’ve had, from memory, 9 Newtonians over the years, from 6 to 14”, including examples with optics by Hinds, Hysom and Grubb Parsons, and would not say that, aperture for aperture, the optically very good Newts generically outperformed the SCTs.  There are so many contributory factors, some intrinsic to the design, some to do with the way different sorts of scopes need to be managed in order to perform at their best.  And, of course, there’s sky quality to contend with, which doesn’t affect SCTs more or less than any other sort of scope.  I liked both of my SCTs. Perhaps I got lucky. Both were rewarding scopes that gave good images and provided decent aperture in a compact package that wasn’t unduly demanding to mount.  The AZEQ6 was a good match, incidentally, as was the AZ100.

Thanks JTEC, 

An encouraging post, for the C9.25. Did you find the visual observations were satisfactory then? How did Jupiter appear, as that seems to present contrast issues for some users of sct. Do you mind me asking about the expert independent bench test? Is this a service still offered in the UK? And what was your reason for doing it? 

[JTEC]

@Flame Nebula  Hi, yes, I was satisfied with the views visually.  Both scopes were good with the binoviewer, which, fwiw, is my preferred way of viewing Moon and planets.  The views, of Jupiter and Mars, for example, were not ‘mushy’ and showed good clarity, colour rendition and detail.  The MTF curves I’ve seen would suggest that the SCT might have slight advantage over equivalent unobstructed aperture with high frequency detail but be slightly disadvantaged in the mid range, which, other things being equal, might make it a better choice for some sorts of target than others. The 140 apo image is subjectively nicer to look at and probably samples the available UK seeing almost all the time.  When I decided to ‘rationalise’ my kit recently, it was the SCT that went - the apo wasn’t going anywhere.  
I’ll PM you about the bench test, because a third party is involved - suffice to say, it was done for me by someone whose name most users of the forum would recognise as highly expert and who is a friend.  As far as I know, there is no option available to test SCTs before purchase.  I had it tested purely out of interest.  Please bear in mind that while the SCTs I owned turned out to be good - I’ve heard that quality is more consistent these days - there might still be some ‘less thans’ out there.  My feeling is that if you have doubts, it would be better to look elsewhere and many helpful suggestions have been made 🙂.

Edited March 17 by JTEC

[Elp]

Also possibly go to an astro society meet or star party and make your own decision based on what's available there.

[Flame Nebula]

1 hour ago, JTEC said:

@Flame Nebula  Hi, yes, I was satisfied with the views visually.  Both scopes were good with the binoviewer, which, fwiw, is my preferred way of viewing Moon and planets.  The views, of Jupiter and Mars, for example, were not ‘mushy’ and showed good clarity, colour rendition and detail.  The MTF curves I’ve seen would suggest that the SCT might have slight advantage over equivalent unobstructed aperture with high frequency detail but be slightly disadvantaged in the mid range, which, other things being equal, might make it a better choice for some sorts of target than others. The 140 apo image is subjectively nicer to look at and probably samples the available UK seeing almost all the time.  When I decided to ‘rationalise’ my kit recently, it was the SCT that went - the apo wasn’t going anywhere.  
I’ll PM you about the bench test, because a third party is involved - suffice to say, it was done for me by someone whose name most users of the forum would recognise as highly expert and who is a friend.  As far as I know, there is no option available to test SCTs before purchase.  I had it tested purely out of interest.  Please bear in mind that while the SCTs I owned turned out to be good - I’ve heard that quality is more consistent these days - there might still be some ‘less thans’ out there.  My feeling is that if you have doubts, it would be better to look elsewhere and many helpful suggestions have been made 🙂.

Thanks JTEC

Helpful advice. There is one scope I've seen images of Saturn on a par with a C11 and C9.25, on astrobin. That's a 12" skywatcher Explorer 12" F5 on a Neq6. It's 25kg, and may prove harder to handle as a lone person setting up on an AZEQ6. Alternatively, there is the orion optics vx12L, at only 16 kg, it's Al tube being much lighter. With that comes potential for 1/10 wave mirror, but £600 more than the Explorer and Orion Optics less regarded customer service? I think everyone on this forum would make positive comments about a 12" newt. Plenty to mull over, for sure! 

Edited March 17 by Flame Nebula

[Elp]

If you're going to go around 12 inch newt you might as well dobsonian mount it unless you already have a mount that can handle it, and it better be in a observatory as any slight wind will cause the whole setup to vibrate, larger scopes larger issue.

[Flame Nebula]

1 hour ago, Elp said:

If you're going to go around 12 inch newt you might as well dobsonian mount it unless you already have a mount that can handle it, and it better be in a observatory as any slight wind will cause the whole setup to vibrate, larger scopes larger issue.

Thanks Elp, 

I am about to post on this very topic. 🙂

[Mr Spock]

12" is good 👍 Here's my StellaLyra...

[garryblueboy]

I have owned 3 and let them all go for me they didn’t live up to the planet killer every one boasts about as heavy as C11 nearly I have had up to a C14 which is a beast but now happy to settle with my C8HDEdge .

 

[Flame Nebula]

54 minutes ago, garryblueboy said:

I have owned 3 and let them all go for me they didn’t live up to the planet killer every one boasts about as heavy as C11 nearly I have had up to a C14 which is a beast but now happy to settle with my C8HDEdge .

 

Hi, 

How does the C8edge compare to the other non edge in your opinion? 

[garryblueboy]

I prefer the whole field of view to be in focus and stars pin point which the non HD do not basically in centre not much difference but going outwards the HD has more  sharpness to it plus for Astro photography it already has a flat field but my imaging days are over I’m now about visual .