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How big is the EdgeHD difference?

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#1 swag72

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Posted 14 July 2014 - 05:34 AM

I am currently imaging with a standard C9.25 and have got some results out of it that I am pleased with. I am using it at it's native focal length as well. I am now considering a C8 EdgeHD as a replacement, as this would mean I could dual mount as the C9.25 is too heavy to do this.

Having searched the net and this forum, I haven't found any reviews of the difference between imaging with EdgeHD and non EdgeHD optics. My question to you guys is whether I would see a big difference between the standard and EdgeHD optics? I know that there would be a difference going from a 9.25" and 8", but apart from that?

#2 Patrick

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Posted 14 July 2014 - 07:05 AM

Not sure where you've been looking but there has been a great deal of discussion about imaging with both the standard and Edge SCT'S.

Essentially you will get smaller, tighter stars, and a much flatter field with the Edge scopes. The Edge scopes are designed with imaging in mind. I went with the 8" model for imaging purposes mainly. With. 0.7x focal reducer the 8" yields 1400mm focal length which is a nice f/l for many objects.

Patrick

#3 swag72

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Posted 14 July 2014 - 07:09 AM

Thanks Patrick - What I couldn't find was a comparison between EdgeHD and non EdgeHD optics specifically with imaging in mind.

#4 Footbag

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Posted 14 July 2014 - 07:25 AM

For Deep Sky it's worth it. Round stars right to the corners of the field .

For planetary, the difference won't be dramatic.
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#5 swag72

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Posted 14 July 2014 - 07:48 AM

Will it give any overall increase in sharpness? I am only involved in DSO imaging.

#6 Footbag

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Posted 14 July 2014 - 08:14 AM

At the edge of the field it will. It's not just the stars that are rounder at the edges, any target will also be sharper.

At the center of the field, there really won't be a difference.

#7 gdd

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Posted 14 July 2014 - 08:15 AM

The EdgeHD gives you get smaller tighter stars out to the edge compared to the standard SCT according to Patrick, is that different than an increase in sharpness?

Gale

#8 astroricardo

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Posted 14 July 2014 - 08:55 AM

At native focal length and from a typical suburban location (3-4 arcsecs) your images will only get so sharp. Unfortunately with our long focal lengths we are even more at the mercy of the atmosphere.

#9 mark379

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Posted 14 July 2014 - 10:41 AM

The Edge will make a difference in A/P,though it will be the least difference compared to the 9.25, since the 9 has the flattest field of the standard SCT's already. I compared the 8 and 9.25 visually with 82 degree ep's and they were close. ;)
But for A/P it may be worth it to go for the edge.
You can ready my thread here:

http://www.cloudynig...6569052/page...

#10 JMW

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Posted 14 July 2014 - 11:06 AM

Add Tempest fans for active cooling while observing or imaging. The EdgeHD vents are easily upgraded to active fans. I found this the biggest difference between my old C9.25 and my new to me C11 EdgeHD. The fans help the scope keep up with dropping temperatures throughout the night.

My C11 EdgeHD is a good performer for imaging. Someday I hope to buy a C14 EdgeHD for my home observatory. I will keep the C11 EdgeHD for travel to darker skies.

#11 dr.who

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Posted 14 July 2014 - 11:45 AM

The Tempest fans are a must for this or any other Edge scope. So if you go that route for sure get them. A question to ask is what you are trying to image in the DSO realm?

If it's wide field then you may want to think about another type of scope like an APO refractor. If it's smaller DSO's then the Edge 8" with the focal reducer and Tempest fans is a very good option because it does give tighter/smaller stars to the edge of the field over a standard SCT.

#12 swag72

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Posted 14 July 2014 - 12:08 PM

I have a short focal length refractor for the larger DSO's. This scope is all about the smaller DSO's and the ability to dual mount. I'm not looking at using a focal reducer with this either otherwise why do I want 2m in focal length to then reduce it down?!

Thanks for the comments so far.

@Mark - I saw the review that you posted, but did note that it was all visual - So wasn't sure that it entirely relevant.

I know that people will think that I must be mad to think about f10 imaging, but I've managed OK so far. You can see my latest examples at www.swagastro.weebly.com

#13 ur7x

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Posted 14 July 2014 - 12:58 PM

There are a lot of "ifs" to completely answer your question.

If you have "great" skies
If you have a pricey top of the line wide field of view eyepiece
If you are looking a very wide objects at the edge of the field of view.
If both scopes are colminated within a bazilianth of an inch

Then you might see a difference.

My next door neighbor has an Edge 9.25, and I have the base Starlight XLT version.

I have looked through both on the same night at the same objects with the same "mid ranged" 2" eyepieces.

I simply could not see a difference.
I've done AP through both too... minimal if any difference.

There is no argument that the EDGE scopes hold their value better and there is a certain swagger to owning the best that there is, but unless you are the type who flips his gear every few years I would not spend the extra on the EDGE.

My advice, attend a star party and try to get two of these scopes set up side by side and take a look for yourself, some can see a difference, white paper testing shows there is a difference, maybe you can see a difference, I could not.

Oh and IMO, people who think you are mad to image and F10 have likely never tried imaging at F10. Like you, I have managed to produce very satisfying results at a full F10 with my 9.25, though your images blow anything that I have yet to achieve out of the water... Nice work!

#14 WesC

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Posted 14 July 2014 - 01:26 PM

As you probably know, sharpness is a complex issue. There are several components, some that are in your control and some that aren't... Out of control and the biggest is related to seeing and the focal length you're working at. Long focal lengths really enhance the effects of seeing, no way around it.

More in your control, and also very relevant, are collimation, tube currents and focus stability. Nail those and, on nights of excellent seeing, the optics should be good enough to give you tight stars.

The differences in the Edge scopes are going to be at the outside edges of the field, which for imaging is going to be a very good thing.

Overall sharpness though, should be similar between the two... same mirrors, same coatings... the only difference are the extra elements in the baffle tube flattening the field and removing coma.

#15 dpippel

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Posted 14 July 2014 - 02:11 PM

And while we're on the subject of tube currents, as Dr.Who mentions above one of the other advantages of the Edge tube design are the passive cooling vents that can be retrofitted with TEMP-est fans. There are options for non-Edge SCTs that work well too, but IMO the big plus of the active TEMP-est solution is that it allows you to cool the scope continuously WHILE you're observing. The mirror locks for AP are a consideration as well. Neither of these features are available on Celestron's standard SCT OTAs.

#16 dpippel

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Posted 14 July 2014 - 02:16 PM

My next door neighbor has an Edge 9.25, and I have the base Starlight XLT version.

I have looked through both on the same night at the same objects with the same "mid ranged" 2" eyepieces.

I simply could not see a difference.

I've done AP through both too... minimal if any difference.


The C9.25 and C9.25 Edge will exhibit the least amount of difference since the standard C9.25 already has the flattest field of the four big Celestron SCT models (8"/9.25"/11"/14").

#17 swag72

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Posted 14 July 2014 - 03:36 PM

A continued thanks folks - I think I am probably coming round to the idea of changing the C9.25 for a C8 EdgeHD. The ability to dual mount and just swap the camera over is so very tempting. Looks like as long as I accept the 300mm loss of focal length, then things are at least going to be similar and in some areas even better!

#18 dr.who

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Posted 14 July 2014 - 05:19 PM

I have a short focal length refractor for the larger DSO's. This scope is all about the smaller DSO's and the ability to dual mount. I'm not looking at using a focal reducer with this either otherwise why do I want 2m in focal length to then reduce it down?!


I stated it because I never assume someone knows what I may consider obvious. I didn't mean any offense. As to why you might want to reduce it... It will depending on your refractor's focal length. you may be doubling your FL. For example my TV gives me a FL of 540mm. My Edge 800 gives me 1400mm at f/7 with reducer. Over double what the TV does. This means I can get very deep into a small region of large objects and very good scale on smaller objects.

You also asked how it would do on an AVX. What I stated was my personal experience with the scope and mount. Workable at f/7, challenging at f/10 in my experience. At f/10 guiding will be a must due to exposure length per sub. 45-90 seems to be the range of seconds people are reporting here per sub unguided with outliers that are 30 seconds at the low end to 5 minutes at the high end.

I know that people will think that I must be mad to think about f10 imaging, but I've managed OK so far. You can see my latest examples at www.swagastro.weebly.com


FWIW I don't. Heck there's a guy in my club who images at f/10 with a Edge 1100 on a CGEM. He gets decent results but works hard to get them :) . It's something I have in my plans but will do it on my CGEM with the Edge not my AVX.

#19 dr.who

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Posted 14 July 2014 - 05:23 PM

Addendum: my apologies. It somehow got stuck in my little bean head that you wanted to do this on an AVX! After rereading your post I didn't see that. Please disregard what I said about the AVX and a reducer.

#20 Patrick

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Posted 14 July 2014 - 11:31 PM

What I couldn't find was a comparison between EdgeHD and non EdgeHD optics specifically with imaging in mind.




Take a look at the CELESTRON WHITE PAPER on the Edge HD scopes. In particular note the spot diagrams on page 5, figure 2. The diagram shows a direct comparison between the standard SCT and the EdgeHD.

As you can see from the title and the document itself, Celestron was creating a new astrograph for imaging. Granted, we're still talking about a long focal length instrument, but quite frequently a long focal length is what's needed to capture small objects.

Patrick

#21 AngryHandyman

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Posted 15 July 2014 - 12:59 AM

I've nothing to contribute to your question, but I love your images! Thanks for sharing!

#22 swag72

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Posted 15 July 2014 - 01:53 AM

@Dr Who - Hey no offence taken, you didn't know whether I had other kit!!! I don't think I'd reduce it down though, 2m is an interesting length for me!!

@Patrick - Link downloaded I'll read that in a bit - Thanks!

@Jeremy - Cheers!

#23 dr.who

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Posted 15 July 2014 - 04:16 PM

Cheers mate. Good hunting.

#24 cray2mpx

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Posted 16 July 2014 - 11:48 AM

Just got my Edge HD 8". Celestron appears to produce some very decent SCT optics these days (see attchment).

Clear skies,

Cray

Attached Files



#25 sydney

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Posted 16 July 2014 - 05:47 PM

That's very impressive. I just bought a C14 Edge from a fellow CNer to update my older Meade 12. I expected the views to be brighter but was really surprised by how sharp they are. Much more pleasant and involving to look through especially with widefield eyepieces. And much less extraneous fuzz around bright objects.






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