37 replies to this topic

[BillP]

Over my observing life I have had multiple C8s, C6s, and 4" and 5" Maks.  Never liked how long they took to acclimate and with the SCTs, the coma and field curvature (FC) was a significant annoyance.  But, I keep coming back to the design because it is after all quite compact.  In my latest attempt I decided to try a conventional non-Edge C9.25.  I've often read how many feel that it is more than any other SCT size closer to the Edge series in performance.  So not willing to drop  an extra $1000 for an Edge OTA, not to mention the cost for a pricey Edge reducer (when they make one for the 9.25), I decided to yet again try to like an SCT and borrowed a C9.25 from an observing friend.

 

On first use, I moved the C9.25 from a warm 70 degree house to a 35 degree outside yard.  After 2 hours the scope actually reasonably cooled, not the experience I ever had with a C8.  It was not perfectly acclimated, but what thermal activity was left was slight enough to not be a very big deal as the star points were reasonably tight and behaved.  So instead of a full woolly star as I like to say, maybe they were just slightly fluffy.  In any event, definitely better that I had expected.

 

Using a variety of XWs in the scope, the FC of the scope is easy to see.  Coma not so much though.  As example with the 40XW the stars at the field stop are quite bloated, but can be refocused to a nice pinpoint.  So mostly all FC.  Using the Celestron .63x reducer helped a little, but not significantly IMO.  The FC, which IMO is severe in a C8, is at the edge of being tolerable for me in the C9.25.  I also used my 40mm Titan-II ED.  Similar to the XW, it showed a lot of FC in the C9.25 (note that these eyepieces show little in my 81mm through 152mm Apos, and none in the XT10 Dob with Paracorr).  So this made me wonder about all the posts I've read where people say the Edge 9.25 is not really significantly better off-axis than the Edge 9.25.  Either people have a lot of tolerance for FC or the extra $1000 for the Edge model is not getting one much.  Which I am not sure as I have not observed critically through the Edge 9.25.

 

While I had the C9.25, I decided to give it a compare to my 152 Apo.  In previous side-by-side of my 152 Apo against a C8 they seemed more on-par than different.  The C8 did go a very slightly bit deeper on Globs but not significantly so to my eye.  Going back and forth at equalized magnifications between the 152 Apo and the C9.25, brightness of the stars were readily apparent as being much brighter in the C9.25 compared to the 152 Apo.  So things like the Double Cluster looked much brighter in the C9.25.  When examining the Double Cluster more deeply, it was interesting as I could actually see a few of the faintest stars in the cluster just a little easier in the 152 Apo.  I think this is due to the finer star point the refractor was mustering.  The more fluffy star points of the SCT meant that the faintest dimmest one, which typically need a perfect focus setting to see well, were difficult in the C9.25 but were readily apparent in the Apo.  Just talking 2 or 3 really dim ones so not a lot of stars.  It was interesting though, as the combination of the slightly more fluffy stars and having them all appear obviously brighter in the C9.25, made the Double Cluster much more pronounced and dimensional looking in the C9.25 than in the 152 Apo.  So regardless of the more precise and tight star point in the 152 Apo, the Double Cluster still looked more aesthetically pleasing in the significantly brighter and larger aperture C9.25.

 

As I pumped the magnification up to 200x in both scopes, it was interesting to see some of the brighter stars in the Double Cluster show a classic airy disk pattern in the 152 Apo.  The C9.25 however showed none of this at 200x.  Now the star points in the C9.25 were not bad as they were fairly tight, but they still had that fluffy attribute because there were still some very slight thermals going on in the OTA that I could see.  I do have a CatCooler to maybe bring the thermals fully under control in the SCT, but I have yet to conduct that experiment.

 

Staying at 200x I then moved to the Gamma Andromedae double.  Colors were nice in both scopes, but in this case the more precise and tight star points in the 152 Apo made doubles much more pleasing.  Gamma Andromedae  was not bad in the C9.25 actually, but in comparison to the Apo, it could not hold its own on this class of target. 

 

Now my main purpose for borrowing this C9.25 was a desire to move from a 10" Dob to a more compact and user friendly platform.  If I could achieve this, then what I feel is important is if I can keep a relatively good star point off-axis and get something more than around 1 degree TFOV.  The DOb with Paracorr easily does 2 degrees TFOV and stars are pinpoint with Paracorr in the off-axis.  So far with the C9.25, the off-axis loses a lot in comparison to my eye as the FC is quite significant.  Again, not as much as the C8, but still at an annoying level unfortunately.

 

Next up I did some experimenting with the Celestron .63x reducer on the C9.25 to see if I could stretch that TFOV some.  I used the reducer with the Baader BBHS 2" diagonal.  This combo with the 40XW unfortunately vignetted the FOV more than I liked.  The views were just not nice.  So I moved to the 30XW and was much more pleased.  There was some very slight darkening near the field stop, but the field stop stayed sharply defined and stars did not wink out when they approached the field stop so I thought quite acceptable.  The additional TFOV was also quite nice, making observing the Double Cluster very aesthetic with lots of room to spare, and even most of M45 fit in the FOV or at least enough of it to make it an interesting and engaging observation!  So I was very happy.  The off-axis FC also improved a bit with the reducer in place.  The off-axis still showed obvious FC with the reducer, just not as much as before, so more tolerable.  Still though, off-axis stars in M45 or the Double Cluster were obviously bloated from the FC so not entirely happy.

 

So after all this evaluating it was looking like as much as I liked the SCT form factor, I was just not liking the off-axis performance enough to replace my 10" Dob.  I was a little bummed too as the thermal behavior of the C9.25 seemed a lot better than my experiences with the many C8's I've had.  Every evening I took the C9.25 out into the cold weather, after 90 minutes or so it was plenty stable for some good viewing.  And what little thermal activity remained, seemed to destabilize star points much less dramatically than the C8s I had.  So I was very happy with the C9.25's thermal behavior.  It was just a shame that the off-axis had such noticeable FC to my eye in everything from the 40XW to the 10XW. 

 

Before I returned the C9.25 to my friend, I decided to try one last experiment.  I've never read of anyone trying a Paracorr on their SCT, but I decided to give it a shot.  So with the C9.25 configured with a short 2" visual back, the 2" Baader BBHS diagonal, and a 40mm Titan-II ED, I slipped my adjustable top Paracorr I into the diagonal, then the 40mm eyepiece on that.  To my delight I could actually reach focus!  And guess what....star points were perfect all across the FOV.  Wow...this was a nice view and what I was looking for!  Now I did notice with this arrangement that there was some slight dimming near the field stop.  This did not occur without the Paracorr.  But it was slight and not a bother.  Turing to The Double Cluster and M45 it was grand to see this conventional C9.25 performing all across the FOV supposedly like an Edge series would.  Best of all, since I have these components already for my Dob, also means no need to spend the extra $1000 for the Edge too as I was getting pinpoint stars all across the FOV.  Moving to the 30XW there was now no dimming near the field stop and the view was simply killer!

 

Finally, I was wondering could a reducer work with this multitude of added glass components to the train.  From previous experiments I knew I could only come to focus with the reducer and BBHS diagonal if I removed the nose of the diagonal and screwed the diagonal directly onto the reducer.  So I did this, placed the Paracorr in the diagonal, then the 40mm Titan-II ED eyepiece in the Paracorr.  Unfortunately, my hopes were dashed as it was about a half a turn of the focuser knob from being able to focus.  I tried the 30XW and still no joy in this experiment.  Too bad as getting the little extra TFOV is really nice with the reducer and the 30XW.

 

Before I decided to break everything down and go back into the warmth (it was 35 degrees this last night of experimenting), I remembered that the Baader Zeiss 2" Prism diagonal has a shorter light path than any mirror or dielectric 2" diagonal than I tested or used before.  So I figured I would give it a shot and removed the nose of the Zeiss prism so I could screw the diagonal directly onto the reducer, then the Paracorr in the diagonal and 40XW into the Paracorr.  Note that in doing this, the diagonal tightens not straight up but at a 45 degree angle from straight so not so convenient for viewing.  However, all you need to do is to put a small shim on the reducer's threads so the diagonal then tightens in the straight up position (I use an alt-az mount so no need to readjust position - would be more of a pain with a GEM I imagine).

 

Once the Zeiss prism diagonal was in place and the 40XW with Paracorr in it, I was delighted that to see that there was plenty of focus travel left in the C9.25 to reach focus.  And better yet, once again all the star points were perfect all across the FOV.  Wow was this a pretty view!  The vignetting was still there using the 40XW, so I switched back to the 30XW and all was fine in the FOV with almost no dimming and of course enough TFOV to fit the majority of M45 in the FOV.  And yes, perfect star points all across the FOV.  I was a very happy camper on seeing this as it meant that yes, I could get a nice and portable setup compared to my XT10 and could manage maybe close to a 1.3 deg TFOV with reducer and Paracorr with perfect star points [Edit: Measured -- 40XW w/no reducer gets me 1.1deg TFOV; 30XW w/reducer gets me 1.5 deg TFOV).  So looks like I can achieve a more portable setup with very close to the same aperture punch as my XT10 but in a nicely smaller package.  And better yet, no need to shell out another grand for an Edge 9.25...not that I would have anyway.

Edited by BillP, 10 December 2016 - 10:27 PM.

[Michael Covington]

Very useful.  Remember that many eyepieces have appreciable field curvature -- it's hard to tell what is your telescope and what is your eyepiece.  My 20mm Pentax XL had field curvature opposite to that of my conventional C8.  When I got an EdgeHD it no longer matched -- no longer *seemed* flat -- and I ended up selling it and getting a DeLite.

[Peter Besenbruch]

That was the craziest review of an SCT I have ever read. Thank you.

[MortonH]

Was not expecting a Paracorr!!!

 

Thanks for a great read.

[janapier]

That's an interesting report, no doubt. It makes me wonder how much worse the Lunt 152 Apo I tested was compared to the one Bill owns. The one I got from Bresser performed noticeably worse on Jupiter and the moon than my C8. The C8 went considerably deeper as well. 

[Procyon]

Very interesting Bill. Concerning acclimation with your past C8, do you think if it had a similar vent system like an Edge 8, and with added Temp-est fans, it would have helped in the winter? Or just in hotter weather? Or not much at all.

Edited by Procyon, 10 December 2016 - 04:47 AM.

[junomike]

Interesting twist on the PC.  I do have one also but don't feel I need it for my non-EdgeHD SCT's. I DO feel my 8" EdgeHD is the best off-axis however, just not by a large enough margin.

One thing to note is I wouldn't expect the PC to cause and issues (Aperture reduction) as the 15% Barlow effect should move the Focal Point enough as to not

hinder the optimal back-focus.

 

Mike

[BillP]

Very interesting Bill. Concerning acclimation with your past C8, do you think if it had a similar vent system like an Edge 8, and with added Temp-est fans, it would have helped in the winter? Or just in hotter weather? Or not much at all.

 

The Edge with Tempest probably do help some, but I see mixed reports.  But from a passive cooling perspective the C9.25 seems to handle itself thermally much better than any of the C8s I had.  I've had the C9.25 out quite a number of times now in the 30s temps and not once after a 90 minute acclimation have I had thermal plume visible.  In the C8s that plume would stick around forever.  The 2 scopes are engineered differently so they seem to behave differently as well with respect to the thermal acclimation.  The C9.25 I am feeling is pretty good in this respect (passively).

Edited by BillP, 10 December 2016 - 09:26 AM.

[Eddgie]

I am surprised that a C9.25 on the necessary mount would be easier to set up than a 10" dob.    I found the C9.25 to be heavy enough to require an EQ-6 class mount and 30 lbs of counterweights.

 

There are truss Dob OTAs out there that weigh less than the counterweights required for the C 9.25, and that will give far better performance.

 

I move my 12" dob out and set it up quicker and more easily than I could move out my C9.25.

 

Also, A 10" dob will give a bigger true field with a binoviewer too even with a 1.3x OCS.

 

C8 is Compact and easy..  Past that and in my own opinion, you really have to step up the effort necessary to get the scope out the door and this makes just enough difference to make it less likely to get used.

 

I enjoyed reading your experiments though, and your experiences generally match mine.    The C9.25 (and in fact all of the SCTs I have owned except the EdgeHD) are poor off axis performers.  Like you, I found no benefit to the .63 reducer. 

 

The high magnification of Nagler type eyepieces (for a given true field) showed the bloated stars far more than a Panoptic with a similar sized true field did, so I stopped using 82 degree types and went exclusively to Panotics in the SCTs (except the EdgeHD which was nothing sort of marvelous with a 31mm Nagler).

 

The 6" Apo did not give the resolution on Globulars (as you also have seen) but many of the fainter stars were indeed still there if one looked for them.   The pin **** stars of the Apo don't show with the same authority as they do in the 9.25, but careful scrutiny shows that there are more stars there than would be evident at a glance.

 

I did not care for the C9.25 in the end and quickly moved past it to the C11.  It mounts on the same class mount, has much better planetary performance, goes much deeper, and only weighs a few pounds more.

[nevy]

I'm surprised that such a critical viewer as yourself is even considering replacing a dob with an sct especially with slightly less apature. 

I like your thinking with the paracor ,I've thought of it in the past but never got round to it , the C11 just don't get used much since the dobs arrived. 

[Eddgie]

...the C11 just don't get used much since the dobs arrived. 

Yes.  Same problem with the C9.25.

 

It was just enough effort that it made it far less likely to get used than the C8  on a light mount.

 

And a good 10" dob, or a lightweight 12 dob is just a better game for the same amount of setup effort. 

 

My 12" Go2 dob is not light at all, being on the order of 140 lbs, but I can move it on one trip using a hand truck, and it took three trips to move the C9.25.     It took the same number of trips and only a bit more weight to lift to take out the C11.

 

But the 12" dob rolls out from my covered patio in 60 seconds and the hand truck does all of the work.  Now I keep it outside so this in itself is a great boon to easing the setup.  The fact that it sits in a 30" circle means I can keep it stowed in a corner, which was not possible using a scope on a tripod.

 

Ed Ting loved the C9.25 and much of the allure I think is due to what I feel is an urban myth that suggest it is better than the other SCTs.  I found nothing in that premise.    It is just so much bigger and heavier than the C8 that the C11 makes more sense to me. The C9.25 lasted me 6 months.  The C11 lasted about 5 years before being replaced by the C14.  The C14 lasted about 5 years before being replaced by the 12" dob, and the 12" dob has been my favorite of the three for pretty much all uses.

[Procyon]

What to do than, if one wants goto, has to go up and down stairs to the backyard or within the house, and no safe shed in the backyard? I think the Edge 8-9.25's are a great solution for this issue. Good aperture, goto, 35-65 lbs, good fov with right setup. I liked the views through my old 10" dob  better but even with no heavy goto it felt a bit too crazy carrying it up and down.

 

If ones has it on a trolley or quick access to it than the dob is probably is better. Very happy with my Edge 8, it does take a good 1-2 hrs to come into perfect acclimation though, I wonder how much the temp-est fans will help with that, only one way to find out I guess, too bad deepspace products doesn't answer their emails even after one week, I'd have already ordered one, maybe it's time to pick up the phone. Than again if you leave them on too long in the winter, I hear they cause quick frost buildup.

 

But this thread was probably made to show that a paracorr can possibly work great for some people's SCT setups, so   .

Edited by Procyon, 10 December 2016 - 11:19 AM.

[BillP]

I am surprised that a C9.25 on the necessary mount would be easier to set up than a 10" dob.    I found the C9.25 to be heavy enough to require an EQ-6 class mount and 30 lbs of counterweights.

 

OMG the weight difference is enormous and the ergonomics as well are significantly better when the C9.25 is riding on an alt-az (not theory here as I have both instruments).  Remember, I do everything alt-az and am not into tracking mounts and will never humor getting a GEM as do not want to have to have dead weights.  So what I do now is just collapse the tripod legs so they are not spread, lift the entire thing up and sling it over my shoulder and walk out the house with one hand free.  Try that with a Dob   This C9.25 on my alt-az is a way better game all around than the 10" Dob and the views (except for max TFOV) are every bit as good!  Anyway, I'm delighted as I can get a used C9.25 for under $900 easily and with equipment already in hand also get pinpoint stars with reducer and low power wide field without needing the crazy extra expense of the Edge design.  And in addition to all that, have an easier to carry and lighter setup than the 10" Dob and way way easier to transport.  And for dark site excursions, will only need the one alt-az mount and a C9.25 with my 102 or 81 Apo and will be well equipped in minimal space with near zero setup time.  So win-win-win-win

Edited by BillP, 10 December 2016 - 11:43 AM.

[REC]

I read a review a while ago and can't remember his name, but he said the C9.25 was the best SCT he ever used.

 

I have a Meade 8" with ACF optics in them and get sharp stars to the edge. Never though about FD though?

[BillP]

What to do than, if one wants goto, has to go up and down stairs to the backyard or within the house, and no safe shed in the backyard? I think the Edge 8-9.25's are a great solution for this issue. Good aperture, goto, 35-65 lbs, good fov with right setup. I liked the views through my old 10" dob  better but even with no heavy goto it felt a bit too crazy carrying it up and down.  .

 

This is quite true.  Carrying an awkward solid tube Dob assembled down any amount of steps is a recipe for disaster.  With my setup as I have configured it it is no issue because the entire rig rides slung on my shoulder and held balanced that way with one arm while the other arm is free to hold onto hand rails on the steps.  Definitely cannot do that with my Dob safely unless I take it apart (which I do not like to do).  But if you are the type that is fine with multiple trips to do setups then anything of any size is ok really.  So I am just speaking to the observers who are more interested in getting out and observing rather than going through setup chores.  All I do is carry the entire scope out in one trip, then second trip is the eyepiece case and chair together.  Done.

[nevy]

I'm surprised that such a critical viewer as yourself is even considering replacing a dob with an sct especially with slightly less apature. 

I like your thinking with the paracor ,I've thought of it in the past but never got round to it , the C11 just don't get used much since the dobs arrived. 

I should have quoted Billp's post , I was referring to the general optical performance between the reflector vs the sct. 

Considering the small difference between top end minimal glass eyepieces , the difference could be lost between the average dob & sct , unless the reason for changing the dob for a cat is portability.  

[BillP]

Well you have to realize that different tools for different purposes.  I have the 10" Dob not for doubles and planetary, but for deeper capability for DSO.  This is where the design excels.  Similarly the larger SCTs excel here as well, plus they have a much better form factor.  IMO what you pay for with that smaller form factor over a Dob is more difficult thermal behavior which shows up in less precise star points compared to a Dob when not 100% cooled, and of course TFOV. 

 

For my tastes, when at a very dark site I feel a 9" is plenty big enough as I am not going to be looking for galaxies and planetary nebula at the limits of aperture.  I would much rather take advantage at dark sites to see the more details available on the less challenging items -- so enjoy the enhanced views of what I normally can see.  Plus I absolutely hate extensive setups.  It was very funny to me one day watching another set up their big SCT on a GEM and spend all the time time trying to get it precisely polar aligned and when they finally did they had forgotten to put the dew shield on so the corrector was then fully dewed.  For all the time they were doing that, I was of course observing having zero setups to do with a manual alt-az.  So I do not like setup time as for me that is wasted time.  I can do just fine with charts and star hopping so I do not need the handicap of automation.

 

So anyway, I have my Apos for planetary and lunar and doubles.  But even a big 6" Apo is not going to magically go deeper into a Glob or Planetary Nebula like a significantly larger 9.25" can go.  Like I said, the 8" SCTs I did not feel go much deeper than the big Apo so the 8" class was a non-starter, but this 9.25 shows satisfyingly better in comparison.  So I want the larger aperture capability (not chasing largest aperture but "enough" aperture) there for when I do want to go deeper into the more difficult targets, but I want this capability to be easy and ready with least hassle.  Dobs are more of a hassle IMO than an SCT riding on an alt-az.  So why I am pursuing this.  My biggest heartache was the dismal off-axis in the standard SCTs not wanting to shell out the ridiculous extra they want for the few corrector lenses in the Edge.  So now I have that with the Paracorr   Glad I tried it!

[Jon_Doh]

Even if you couldn't use the Paracorr the 9.25 SCT would have a place in your stable because it can be used for viewing nebulae and galaxies while your refractor with its wide field of view is perfect for open clusters and splitting doubles.  With each type of scope you'll have the best of all possible worlds.  

[Cpk133]

Hey op, you owe it to yourself to revisit doubles with the C9.25 when it's fully acclimated and when the seeing is good.  Pump the magnification to about 380X + and I think you'll be surprised at what it will do, and how good it will look.  I was able to split a .47" double this fall on a couple occasions at 587X.  The Airy pattern is more obvious at higher powers when the seeing is good.  

Edited by Cpk133, 10 December 2016 - 03:54 PM.

[wargrafix]

I read a review a while ago and can't remember his name, but he said the C9.25 was the best SCT he ever used.

I have a Meade 8" with ACF optics in them and get sharp stars to the edge. Never though about FD though?

Damien peach

[RGM]

BillP, thanks very much for the info on the Paracorr.  It is surprising that the two of us have ended up in a similar place.  I spend around 75% of my time doing VSO.  For that I have an alt-az goto mount holding a 9.25 and a Tak FS78.  I never really wanted a SCT, but for my purposes I needed a compact large scope.  I had a C8 and was never happy with the quality of the view.  I bought a 9.25 and was quite happy with the improvement.  With the f6.3 reducer/corrector, the star images were still not "refractor like", but close.  

 

It is now winter up here in Canada, and I will not have my scopes out until March.  I am looking forward to trying out my Paracorr in the 9.25.  The 9.25 may become a lot more than just a VS scope.  

[Bill Barlow]

What type of alt az  mount do you use, Bill?  I observe also with only alt az mounts and use a few UA Unistar's on various size tripods.  I like to find my objects by star hopping as well, more fun and rewarding that way.  

 

Bill

[BillP]

Heads I have are Helix Hercules, Orion Versago, Porta II.  Tripods are CG-4, then just two light aluminum ones.  So nothing extravagant.  Btw, just did a measurement tonight and with reducer and 30XW I get a nice 1.5 deg TFOV.

Edited by BillP, 10 December 2016 - 10:31 PM.

[xHarry]

After I get my dob mounted on it's cart and finish the ramp I need to move it outside to the terrace, I expect that I will only use my Evo 8" Edge HD when I'm away from the house or I need access to the western sky or need tracking. The luxury of a good 12.5" (Discovery PDHQ) dob with easy access to half the sky is something I am increasing grateful for. The luxury of an 8" traveling scope is equally wonderful. 

 

Happy Harry

 

PS If I get a chance I'll borrow a paracorr. 

[charlesgeiger]

I do remember someone trying a paracorr for visual along with a couple other reducer/correctors (Starizona possibly) a few years ago with a SCT and had bad luck.  And again the Starizona type being made for photographic only...so this interests me as I have a C14.  But the C14 has a flatter field than the smaller SCT's (I have had a couple C5's) but I have not viewed with the C91/4.  It would be a very expensive experiment...So I would like to hear of others who have tried a paracorr or other type coma corrector in their SCT's.  You find the explore scientific or Baader and other brand coma correctors fairly cheap second hand on astromart. 

 

Again, Bill has had a great experience with the paracorr and the C91/4, and we can bet his observations are accurate.  So anyone else in the game got a paracorr and a C14?  It would be a great experiment for someone to actually use a paracorr in all the different size SCT's.  I would also be interested in Al or David Nagler's feeling about this as they were designed for Newtonians.  If they are consistently improving the view in the older SCT's, Televue might have another group of customers. 

 

Maybe Bill P. could run an evaluation for us...?  Has Bill tried the paracorr in his C8 or M8?

 

Charlie