Celestron C8 vs Edge HD 8 for visual ?

[johninderby]

£800 for a c9.25 on ABS.  

          John

[Chris]

1 hour ago, si@nite said:

Not sure I buy into the fact that an Edge sct is any better optically than a standard xlt after reading comparisons on CN, granted the mirror lock is a plus, & for dso work, the field correction also useful end off! For planetary imaging or visual it will bring nothing to the game in my IMO, the corrector in the baffle tube can also be a problem when cooling too! Certainly not worth the price differential!

Try looking at the double cluster with a standard C8 plus ES100 20mm, then doing the same with the C8 Edge. My take on the former was hmmm? a bit mushy, and the later was a wow because the stars were so sharp for an SCT  

[si@nite]

26 minutes ago, Lockie said:

Try looking at the double cluster with a standard C8 plus ES100 20mm, then doing the same with the C8 Edge. My take on the former was hmmm? a bit mushy, and the later was a wow because the stars were so sharp for an SCT  

Im still not convinced by all the hype, you may have had a bad c8 xlt!

[Stu]

I've had a C8 Edge and currently have a C925.

I thought the Edge was a great scope. Although I've not used a C8 so have no basis for comparison, I certainly felt like the additional Optics to flatten the field were worthwhile if using 100 degree eyepieces. I found that stars were sharp to the edge and very satisfying to view.

I believe that a standard C8 will cool quicker than an Edge, because the baffle tube is not blocked by the Edge Optics. You cannot use a CatCooler in an Edge, and the additional vents are really quite small, although you can by a fan kit for them it is expensive.

The C925 is significantly bigger, and although it is a wonderful scope, the C8 is begging to be taken away with you, whilst the 925 you have to think about a lot more and it needs a more significant mount. I used my C8 on an Ercole mount on a Gitzo tripod, and reckon I could also have used the C925 on the same rig. Not sure if the Giro-WR will take the bigger scope though, will try it soon.

I still like the stars more in the Tak, and feel it splits doubles in a much more satisfying way. Chuck a lot of mag at it with the SCT and I'm sure you will get there but with pretty fuzzy stars.

What were you planning on using it for @John? Tak for widefield and SCT for aperture and higher power/res is a nice combination  

[Chris]

15 minutes ago, si@nite said:

Im still not convinced by all the hype, you may have had a bad c8 xlt!

I've owned 4x 8" SCT's over the years by Celestron and Meade, some were better than others, but the Edge was the best and so it should be, it places a corrector at the optimum position! Adding a corrector to the back of a standard SCT is also reasonably effective but it's still a compromise  

 

[Stu]

One more thing. I think that locking the mirror in position before collimation, and using a second focuser on the optical back must lead to collimation being maintained better by eliminating mirror flop. Surely the collimation must change if the primary position shifts?

[Chris]

9 minutes ago, Stu said:

One more thing. I think that locking the mirror in position before collimation, and using a second focuser on the optical must lead to collimation being maintained better by eliminating mirror flop. Surely the collimation must change if the primary position shifts?

This is an interesting question, and I don't really know the quantitive answer. However, I did like how my Edge HD could be made to zoom around the sky on an EQ6 and focus was maintained! This certainly wasn't the case for the big 14" Meade's I used at Uni many years ago! I think maybe SCT 'floppyness' scales with aperture? The Edge mirror locks are a big plus if you ask me  

[John]

56 minutes ago, Stu said:

...What were you planning on using it for @John? Tak for widefield and SCT for aperture and higher power/res is a nice combination  

 

Not entirely sure yet Stu. I want something more portable and "handy" than the 12" dob and the 5.1 triplet frac but with decent "oomph" on a range of DSO targets.

I've also been kicking about the idea of an 8" F/6 OO newt OTA with their best optics inside to fill this spot in my scope fleet.

Lots of interesting feedback in this thread so thanks to all for that

I've owned an older C8 and that seemed to have good optics but I used it mostly for higher power viewing plus I didn't have 100 degree EP's back then.

 

[nightfisher]

On first glance the OO 8" F6 might be a good option, but longer tube, so you lose the "grab an go" size of the C8...........choosing a scope can be such a minefield, i had been tempted by the c8`s smaller brother the XLT omni C5 but read a few less than good reviews

[jetstream]

The Celestron "white paper" explains what they did to reduce mirror flop etc, it is a very informative piece of work. I might wonder if Celestron could "cherry pick" the better mirror sets for the Edge?

[Stu]

23 minutes ago, John said:

Not entirely sure yet Stu. I want something more portable and "handy" than the 12" dob and the 5.1 triplet frac but with decent "oomph" on a range of DSO targets.

I've also been kicking about the idea of an 8" F/6 OO newt OTA with their best optics inside to fill this spot in my scope fleet.

Lots of interesting feedback in this thread so thanks to all for that

I've owned an older C8 and that seemed to have good optics but I used it mostly for higher power viewing plus I didn't have 100 degree EP's back then.

 

Do you actually want to take it away on holiday or to dark sites with you or is it just for when you don't want to get the 12" out at home?

I think if just at home the 8" f6 might well be a good option. Quicker cool down and one piece to take out into the garden.

For me, the ability to have some aperture under a dark sky in a compact OTA made the C8 very attractive. Despite the narrower field of view, I found it excellent when hunting around Sagittarius on targets like M8 and M20 etc.

[John]

24 minutes ago, Stu said:

Do you actually want to take it away on holiday or to dark sites with you or is it just for when you don't want to get the 12" out at home?

I think if just at home the 8" f6 might well be a good option. Quicker cool down and one piece to take out into the garden.

For me, the ability to have some aperture under a dark sky in a compact OTA made the C8 very attractive. Despite the narrower field of view, I found it excellent when hunting around Sagittarius on targets like M8 and M20 etc.

Not holidays but for outreach sessions in places where getting the 12" dob set up would be difficult. I've been using the ED120 which has been great for planets and doubles but creates a challenge if its my turn to show folks some galaxies. Also at home sometimes when I want something between the 5.1" and the 12"

I guess I could just get a cheap Skywatcher 200P F/5 OTA for the outreach stuff

[Chris]

2 minutes ago, John said:

I guess I could just get a cheap Skywatcher 200P F/5 OTA for the outreach stuff

I think this would be a good outreach choice, less to worry about  

[scarp15]

The OOUK 8" F6 on dobsonian mount is very easy to lift and carry outside as one unit. Collimation tends to remain steadfast and cool down is shorter than an 8" SCT. Easy to transport, I have taken mine to Lancashire for family outreach trips. Balance is very stable with 21 Ethos and of course a wider field of view. Mine has the 1/10 PV wave mirrors, I enjoyed my former C8 Celestar but I am very happy with this, which in particular comes into its own when the 14" is too much.

[morimarty]

18 hours ago, Stu said:

I believe that a standard C8 will cool quicker than an Edge, because the baffle tube is not blocked by the Edge Optics. You cannot use a CatCooler in an Edge, and the additional vents are really quite small, although you can by a fan kit for them it is expensive.

The inability to use the catcooler in all the edge sct's as been the bane of many dedicated imagers both planetary and deepsky!

[nightfisher]

@John this must be a tempting scope for you    http://astrobuysell.com/uk/propview.php?view=127537

[John]

On 27/06/2017 at 05:28, nightfisher said:

@John this must be a tempting scope for you    http://astrobuysell.com/uk/propview.php?view=127537

Thanks Jules - it does look nice

I'm on holiday in France ATM so buying power is curtailed for a while ......

[Mark at Beaufort]

@John as you know I do quite a bit of outreach work with my local astro society. Of all the scopes that I have used to take to the dark site my Orion VX8 f4.5 ticks all the boxes. I have an Orange Celestron C8 available plus various fracs + 12" Dob but I still prefer the Orion.

By the way enjoy your French holiday - see you sometime.

[Davesellars]

I think a 2nd hand standard C8 for the purpose stated would be a good choice.   IMHO the focal reducer / corrector is necessary - It does make a significant different to the image across the FOV as well as avoiding really long focal length eyepieces for low power.

The C8 suffers quite a bit from mirror flop - and yes this does affect collimation as I tested this one evening with the scope pointing at various positions checking the collimation at various angles.  Still, it was a good scope for DSOs and lunar and its portability (I used to hike with a couple of miles) means you can be setup quickly at some remote dark site easily.  For planetary also it's a good scope but as collimation needs to be absolutely dead on (which was virtually impossible with the mirror moving) I felt that at high power it was always lacking a bit in sharpness.

I think the C8 is a difficult scope to beat though for performance / portability especially at second hand prices.  You do need a dew shield and dew strip for it though.

[Peter Drew]

Mirror flop?, are we talking early or recent C8's?. No mirror flop on my C8Se.   

[Stu]

54 minutes ago, Peter Drew said:

Mirror flop?, are we talking early or recent C8's?. No mirror flop on my C8Se.   

Even when focusing Peter? I've found with both my C8 Edge and C925 there is image shift when focusing so I have fitted secondary focuser to avoid this and always locked the mirror once positioned correctly.

[Peter Drew]

1 hour ago, Stu said:

Even when focusing Peter? I've found with both my C8 Edge and C925 there is image shift when focusing so I have fitted secondary focuser to avoid this and always locked the mirror once positioned correctly.

No, not even when focusing Stu. Quite surprised really as my experience has been with older ones, I presumed the issue had been resolved. Of the two 16" SCT's, one has a little image shift when focusing with the factory focuser and the other one lots, both have secondary focusers for fine focus.  

[Merlin66]

My experience based on using MANY Meade sct's 8",10", 12" and a few C925 and now the C11 (xtl) is that the focus mechanism on the celestron is much better than the Meade design. The last two Celestrons I used (925 and the C11) had minimal mirror flop. I could use the Feathertouch 10:1 micro focuser on both with no functional issues.

 

[Stu]

1 hour ago, Peter Drew said:

No, not even when focusing Stu. Quite surprised really as my experience has been with older ones, I presumed the issue had been resolved. Of the two 16" SCT's, one has a little image shift when focusing with the factory focuser and the other one lots, both have secondary focusers for fine focus.  

Interesting. It is not extreme by any means but still there to a degree I don't enjoy.

Am I correct in assuming that collimation will shift if the mirror does? It has to surely?

[Peter Drew]

2 minutes ago, Stu said:

Interesting. It is not extreme by any means but still there to a degree I don't enjoy.

Am I correct in assuming that collimation will shift if the mirror does? It has to surely?

Yes it does. Best to move the mirror upwards against gravity before collimating and then always focus from the same direction.