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Edge HD 8in for DSO

astrophotography cassegrain ccd Celestron CMOS imaging equipment SCT dso
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#1 Mmarett

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Posted 16 November 2019 - 05:01 PM

I know similar topics have been posted but this is a bit specific.

 

I currently have:

 

Camera: ZWO 1600mm Pro

ZWO filter wheel and 6nm filters

Sirius EQ-G mount (capacity 30lbs)

 

I with this set up would the Edge HD 8 be a good scope for DSO at its native focal length? I can also look at adding the .7 focal reducer. I calculated the weight of the set-up to be about 60% of the mount capacity. I would like one day photograph at a focal length that allows some smaller DSOs but everything I read says SCT is a bad idea and to stick with a refractor (which I have) 

 

I like the Edge HD because i can upgrade to the hyperstar one day and the upgraded filters too. Seems like this scope would be a good compliment to my current set-up because it gives me a higher focal length scope, the ability to have an f/2 scope one day and may not require a mount upgrade out the gate.

 

What am i missing? Why does everyone knock this scope for DSO?

 

Note: I image from the inner city so the idea of having the hyperstar oneday with high quality mono filters is appealing. 

 

Thanks!



#2 Benni123456

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Posted 16 November 2019 - 05:46 PM

the problem is that the reducer seems to have a bit color issues. and at least mine works better at 136mm than at 105....

Also, when i screw in the reducer, the imaging train will end at a different rotation angle.

The collimation has to take the tilt of the imaging train into account. So when using the reducer, you need a different collimation than with the native edge if your imaging train has a small tilt from a filter wheel or an off axis guider or something.

 

Natively, the edge resolves good. with pinpoint and round stars. 

It is just f10.

 

ideally one would need something at 5.6 or f7 or f4.

 

There is the rasa at f2.2 but this is very good for widefields.

Many objects like a focal length of around 900-1500mm.

 

But screwing on the reducer means color problems. somehow, at a backfocus where the green channel is round, the blue channel isnt.

 

the edge 9 has less vignetting and a larger image circle. Perhaps the edge 9 works better with the reducer....

 

An alternative would be an rc at f8, but these are very collimation intolerant. And they produce large spikes, and some stars have a strange shape because of the large secondary.

 

A takahashi epsilon is an interesting rasa alternative. Colimation tolerant, f2.8 but like a newton or an rc it has spikes

 

There is the mak newton 190 from skywatcher. But one needs to know how to collimate it, it is more difficult than in a newton. 

 

Then there are ordinary newtons with good coma correctors.

 

And refractors. Those with built in flattener correct at best in my opinion.

But a good 150 or 120 triplet with builtin flattener costs much money...



#3 carolinaskies

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Posted 16 November 2019 - 06:08 PM

The SCT always gets knocked at native F/10 regardless whether it's the 8" Edge or not.  

As was mentioned above there are issues with the Celestron focal reducer which has to be specifically designed for each size Edge scope and costs $300 and still apparently isn't perfected.  

On the Sirius EQ-g  you'll be facing getting very good balance and accurate guiding at F/10 or F/7.  Possible, but challenging at FL above 800mm when mount capacity vs OTA package are above 60%.   

My issue with the Edge 8" for imaging is the cost vs return.
You can buy an 8" RASA for 1700
or Edge 8" for 1350 add $300 F/7 reducer(1650)
add $1000 hyperstar... 2650.   


  
 



#4 WadeH237

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Posted 16 November 2019 - 08:09 PM

I have been imaging with an EdgeHD 8, the F/7 reducer, and an ASI1600MM-cool for the last two years or so.

 

I'll start with the question "why does everyone knock this scope".  And the answer is that context matters.  For an experienced imager with a good mount, it's a fine imaging scope.  It is a pretty poor platform for getting started - even with a good mount.  With a mount like the Sirius, it could be a pretty significant challenge.  So it's not so much that everyone knocks this scope, it's more that people who are experienced with it, knock this scope as a platform for getting started in imaging.  It's that last part that sometimes gets lost in translation.

 

If you ignore the learning curve, the combination of EdgeHD 8, the F/7 reducer and an ASI1600 works really well.  I don't have the color problems mentioned above, but my corner stars are not perfect, but also not terrible - it is dependent on focus quality.  With spot-on focus, the corner stars are pretty good.  With corner stars a bit out of focus, or even with poor seeing, or with less than perfect collimation, then you can see that the stars in the corners are not round.  I also think that if I increased the distance between the camera and the reducer by just a bit, then it would completely solve the problem.  But it's just not been a big enough problem for me to play with it to do that.

 

Regarding Hyperstar, don't get distracted by that.  If you want to set out to build an F/2 imaging scope, then Hyperstar is a reasonable way to go and is a solid platform (and the RASA is even better).  But consider what you would actually need to do.  You'd need to buy the Hyperstar, which costs as much as a decent wide field refractor.  You'd also probably want to buy a new camera.  Remember that you cannot use a filter wheel with the 8" Hyperstar.  So your ASI1600MM would either take just monochrome images, or you'd need to buy a filter slider drawer and manually change filters as needed.  Personally, I would only use a one-shot-color camera with Hyperstar.  And finally, F/2 imaging is not all roses and sunshine.  An F/2 scope has a razor thin critical focus zone.  It is quite sensitive to miscollimation or tilt (and sometimes the tilt is inside of the camera).

 

Here are some other observations that I've made:

 

  • If you are going to be doing subs for more than about 3 minutes, then you need to use an OAG.  This is true even with the mirror lock clutches tightened.  My scope has some image shift over time, and OAG has been the only reliable solution.
  • If you are going to be using the ASI1600, with it's 3.8 micron pixels, then you should probably just plan on using the F/7 reducer.  With the reducer, I am getting right around 0.5 arc seconds per pixel.  If I were to image at F/10, then I'd get a smaller field of view, but no better resolution, since I'm already seeing limited.  You would need close to 1 arc second seeing to see a significant resolution enhancement by going with the full F/10 focal length.  If you use a camera with bigger pixels, then imaging at F/10 makes more sense.
  • I said it above, but I'll repeat it here.  You are going to want to make sure that you have fully tamed your mount.  Even at F/7, the focal length is very unforgiving of the mount - especially with the ASI1600 pixels.  I'm using an Astro-Physics mount to carry my scope, so it's not a factor.  If you have lots of experience, and you have your mount totally dialed in, then you might be ok with a Sirius mount.  If you don't already have experience imaging at long focal lengths, then you may be in for a rough ride trying to make a Sirius work.

 

So to sum up, the optics and camera are a pretty decent combination and are capable of some really nice imaging.  The mount is iffy, and is not for someone who's inexperienced or easily frustrated.  My general suggestion is to use something like an 80mm refractor for learning to image on a Sirius class mount.  Personally, I would not want to use anything less than an Atlas (and would prefer even better than that) for this combination.

 

I hope that this helps,

-Wade


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#5 rzgp33

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Posted 17 November 2019 - 01:25 AM

This is going to be a bit "stream of consciousness..." but here goes.

 

I'm just a beginner, I bought the C8 EdgeHD/AVX deal back in July.

 

IMHO Celestron is punking us with that deal.

 

The AVX has a similar capacity to the EQ-G     (GEM level 5)

 

C8/Reducer/OAG/ASI294 = ~8kgs well over the 6kgs that the these mounts can handle for AP.(i,e 50% of payload)

 

It took me forever to find the right adapters,extenders,shims to get the right back focus.

 

So far I've not been able to get this platform to work as a DSO imaging platform. Its great for planetary(without the Reducer etc) obs/imaging

I guide fine for a little while, then it all falls to pieces. Without the reducer(400g) its better, but the greater magnification means I *need* to be better....

 

I'm just making fluffy cotton balls instead of stars.

 

The AVX is not enough mount.   I have requisitioned my brothers CGX and am looking forward to steeling it from him

(don't feel bad he has a mesu.... the CGX was idle in the corner)

 

I ended up buying an evostar72 and flattener. The cheapest "apo" refractor I could find. So far is its great and I can guide fine.....

 

I think the SCT are for focal length i.e planetry obs. For this you need a good goto as well and that's what Celestron does well.

 

Hyperstar gives me a 300mm/f2 scope ... better off buying a nice general photo lens then i can bird with it.

 

My 2c...for DSO

 

Buy an Evostar72 with flattener and use it with the EQ-G

 

or

 

Buy a better mount... something like a Skywatcher EQ6-R pro, and a Evostar72 with flattener ;)

 

With the EQ6-R you could use one of the $300 GSO 750/f5 Newtonians (meade 6" lx85) and get excellent results.

 

Astrophotography is a Money pit....

 

YMMV sigh....

:)

Brian


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#6 luxo II

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Posted 17 November 2019 - 01:42 AM

I'd suggest you trawl Astrobin searching for "ZWO 1600" and see what others are using.

 

My preference would not be an SCT - focal length is too long - a TS Photoline 130 triplet APO, at f/7, possibly with a reducer. OTOH for lunar & planetary the SCT is not long enough... 


Edited by luxo II, 17 November 2019 - 01:44 AM.

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#7 Benni123456

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Posted 17 November 2019 - 03:46 AM

for refractors where you buy an additional flattener i would also have some caution. often these also produce eggs even at the correct distance. 

 

One neeeds to find a correct apo flattener combination that does not produce eggs or pinced optics...


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#8 Mmarett

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Posted 17 November 2019 - 08:42 AM

So much great rationale. Sounds like refractors are the way to go. That said, what is a great refractor for small DSO? I’ve see a few with a 1000 FL, like the skywatcher 150mm. Does anyone have any recommendations? I would like to one day be able to do my own rendition of the eagle nebula and a relatively good look at a recreation of the pillars of creation photo. I realize I won’t be able to ever get the level of detail in the Hubble but I’d like to do have the best scope for the job at least

#9 WadeH237

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Posted 17 November 2019 - 09:53 AM

That said, what is a great refractor for small DSO?

This isn't really the right question.

 

The right question would be "What mount for small DSO?"  Once you have the mount sorted, there are lots of scope possibilities.


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#10 WadeH237

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Posted 17 November 2019 - 10:22 AM

... ~8kgs well over the 6kgs that the these mounts can handle for AP.(i,e 50% of payload)

In my opinion, "the 50% rule" is nothing but an urban legend.

 

I have two AVX mounts and I have had two CG-5 mounts, the predecessor to the AVX.  I've used all of them for visual with a C8 and for some imaging.  They can handle the weight of a C8 like it's not even there.  There is absolutely zero problem with weight.

 

The issue with mounts in this class is accuracy.  Even with a smaller refractor, like we recommend, they are not very accurate.  The deal is, that the image scale that you get with the shorter focal length hides the accuracy issues with the mount.

 

But when you go for smaller objects, the whole objective is to change that image scale to increase the resolution, and that reveals all of the issues.


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#11 PowerM3

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Posted 17 November 2019 - 11:23 AM

In my opinion, "the 50% rule" is nothing but an urban legend.

 

I have two AVX mounts and I have had two CG-5 mounts, the predecessor to the AVX.  I've used all of them for visual with a C8 and for some imaging.  They can handle the weight of a C8 like it's not even there.  There is absolutely zero problem with weight.

 

The issue with mounts in this class is accuracy.  Even with a smaller refractor, like we recommend, they are not very accurate.  The deal is, that the image scale that you get with the shorter focal length hides the accuracy issues with the mount.

 

But when you go for smaller objects, the whole objective is to change that image scale to increase the resolution, and that reveals all of the issues.

I don't know if I agree with the 50% rule being urban legend but I do agree that you can certainly use an AVX for some imaging with the EdgeHD8. I typically use a g11 for most visual and EAA work but last summer I was visiting some family out in Montana during a new moon. They also live under a dark sky so I could not pass up on the opportunity to bring a setup out there to do some EAA. There is no way I'd fit the g11 in the car so I had to settle for the AVX. I was easily able to do 30sec exposures unguided with the c8HD @f/7. I'm sure that with guiding I could do at least 3-5min. I think with an entry level mount its a bit of luck of the draw of how well it tracks out of the box though.

 

Similarly on my g11 I usually run an 12" ACF @ f/10 and can do 1min exposures unguided.  I would say that the mount is at about 70% of rated capacity(although Losmandy does state that their rated capacity is photographic). Again I'm doing EAA so I'm not concerned with uber crisp stars, but mine are round! Attached is an image of NGC 604. Not very impressive until you realize that it is a nebula inside m33 2.5 million light years away! This is a stack of about 3 hours of 60 sec unguided exposures with a 294MC Pro. 

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#12 Bataleon

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Posted 17 November 2019 - 11:47 AM

My C8 is great for OBSERVING DSO, but yeah I can't imagine it would do much for imaging.

Edited by Bataleon, 17 November 2019 - 11:48 AM.


#13 MrRoberts

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Posted 17 November 2019 - 12:20 PM

I have done some nice imaging/video with my C-8/E on an Ioptron CEM25P in the past (it was all I had at that time). With and without FR. But as spoken of here you real quest should be a great mount. I plan on getting the CEM40 for my C-8/E and Esprit 80. And the CEM60 for my new Esprit 120. A great mount can make even a mediocre OTA (SC/APO) perform well.

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#14 Mmarett

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Posted 17 November 2019 - 01:13 PM

Is the SW EQ-6 R not a good mount? Do I really need to get a 70lb payload capacity if I want to run a ~20lb scope and 5lb of accessories? I feel like the 44lb capacity of the EQ-6 was a good value. If you all think i should look at something better please send some recommendations! 

 

Thanks everyone this has already been very helpful 



#15 Bataleon

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Posted 17 November 2019 - 01:17 PM

Is the SW EQ-6 R not a good mount? Do I really need to get a 70lb payload capacity if I want to run a ~20lb scope and 5lb of accessories? I feel like the 44lb capacity of the EQ-6 was a good value. If you all think i should look at something better please send some recommendations!

Thanks everyone this has already been very helpful

I'm not an imager, but I have the same mount and it should be fine for AP with a C8 and accessories. I know several guys at my local club who use our exact same setup for AP.

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#16 WadeH237

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Posted 17 November 2019 - 11:52 PM

Is the SW EQ-6 R not a good mount? Do I really need to get a 70lb payload capacity if I want to run a ~20lb scope and 5lb of accessories? I feel like the 44lb capacity of the EQ-6 was a good value. If you all think i should look at something better please send some recommendations!

As I mentioned above, it's not capacity, it's accuracy.  You certainly do not need a mount with a 70 lb capacity to image with a 20 lb scope!

 

Regarding the EQ6 specifically, I have not used one personally, but I have spent quite a bit of time working with the Orion version - the Atlas - when helping people to get things going.  So I am pretty familiar with them.  I think that they are one of the better mounts for the money, and when you combine all of the variants, it may be the most popular imaging mount out there.  The people that I've worked with have been using refractors, usually 5 or 6 inches, and the mount carries them fine.  And while I've not done it personally, lots of people have used 8" SCTs for imaging on one.  It seems to be a fine combination (but not necessarily a good one for getting started in imaging, due to the focal length of the SCT).



#17 charlesgeiger

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Posted 18 November 2019 - 12:56 AM

I would say that if you plan to do astrophotography and get good images on a consistent basis you really need an astrophysics or paramount class mount.  In the old days I used to hand guide a 12" f/5 Newtonian and nothing less than a Byers mount with 10.625" main gear and 6" dec drive would produce good exposures. Other things to consider is basic mount bearings and orthoganal allignment and polar allignment.   All other mounts of the day either would not handle the weight (vibrations) from wind, etc. plus the periodic error was so bad and not repeatable.  I spent countless hours hand guiding and came up with horrible exposures due to crappy mounts.  The Byers did the trick.  After hundreds of dollars in poor mounts wasted, I spent the money and got the Byers and that is what worked.

True you do not need 30 minutes for one exposure anymore as you can stack, etc.  But you do need a good mount for consistency.  I had a 41/4" f/15 refractor for guiding too.

Anyhow, with a SCT, the images can be fantastic but you would need to guide with an OAG and a great mount (in my opinion).

And truthfully, you need a burning desire to do this and budget the proper amount of money.  The telescope for imaging is one thing, but the quality of the mount is absolutely imperative.

Charlie



#18 Benni123456

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Posted 18 November 2019 - 05:35 AM

As for the mount, i found that my tuned skywatcher  heq5 can do 30 secs on the native edge 800 without guiding.

 

It needs off axis guiding at longer times. 

 

What is more important than the mount is accurate polar alignment.

I do this via the polemaster camera. never align manually. 

 

When you have a h eq5 and align via polemaster and use an off axis guider, the edge 800 could be used for 10 minute exposures. i have not tried longer. I must still create a darklibrary for longer exposures.

 

the problem is then only the f10.... soon you will wish a faster f number...



#19 Benni123456

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Posted 18 November 2019 - 05:40 AM

this is the native edge 800 aligned with pole master and off axis guiding. If you find a guiding problem tell me where it is.

 

Do not spend too much money on the mount. In fact the mount is a thing that wears down. in 10 years the gears of the moumt will need replacement.

 

gallery_273095_11730_31379.jpg


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#20 Stephen Kennedy

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Posted 19 November 2019 - 02:03 AM

There are no small aperture refracters that can be used to image small DSOs.  This is a single 120" unguided image of a favorite small DSO, M57 the Ring Nebula.

 

IMG_2603 (8).JPG

 

It  was taken with a Canon T3  DSLR through a Mikage Newtonian reflector with an aperture of 210 mm,  focal length of 1,623 mm and mass of 23 kg .  The mount was a Pentax MS-5 GEM with capacity of 50 kg , a periodic error of 2 arc seconds and mass of 145kg.  In this cropped image you can see how  small it looks.  With an 80 mm F/6 refractor the nebula looks like a small green circle.

 

A 210 mm F/7 APO refractor would cost nearly $40,000.  Even 210 mm is a minimum aperture for small DSOs.  Even though I have been using this OTA and GEM since 1988, I am seriously looking at an F/8 300mm aperture Ritchey-Cretien reflector for capturing small and distant galaxies such as the ones in the Virgo and Coma clusters.


Edited by Stephen Kennedy, 19 November 2019 - 02:04 AM.


#21 PowerM3

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Posted 19 November 2019 - 12:12 PM

There are no small aperture refracters that can be used to image small DSOs.  This is a single 120" unguided image of a favorite small DSO, M57 the Ring Nebula.

 

attachicon.gif IMG_2603 (8).JPG

 

It  was taken with a Canon T3  DSLR through a Mikage Newtonian reflector with an aperture of 210 mm,  focal length of 1,623 mm and mass of 23 kg .  The mount was a Pentax MS-5 GEM with capacity of 50 kg , a periodic error of 2 arc seconds and mass of 145kg.  In this cropped image you can see how  small it looks.  With an 80 mm F/6 refractor the nebula looks like a small green circle.

 

A 210 mm F/7 APO refractor would cost nearly $40,000.  Even 210 mm is a minimum aperture for small DSOs.  Even though I have been using this OTA and GEM since 1988, I am seriously looking at an F/8 300mm aperture Ritchey-Cretien reflector for capturing small and distant galaxies such as the ones in the Virgo and Coma clusters.

Totally agree as far as the small DSO. A small refractor is great for the larger DSO's but once you are done with the 100 or so objects that a refractor frames well you will be ready for a larger scope. I actually had to go up to a 12" ACT form the c8HD as I wanted a larger image scale for the smaller galaxies and planetary nebula(witch there are probably at least 100,000 in the reach of the 12" with EAA and certainly enough to keep me busy for the rest of my life). Its also why I do EAA at f/10 and not faster as is usually what folks are after(in fact I might try at f/20 when the seeing is really good). 


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#22 Janco

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Posted 19 November 2019 - 01:50 PM

I disagree with most of what is being said here in terms of people just trying to recommend going a short refractor to start off. In fact starting off with a short refractor might just make you lazy in terms of doing things right i.e. polar alignment, proper balancing etc. 

 

If you switch to a decent focal length scope eventually it will be like you are starting all over again and might just get frustrated because of how easy it used to be. 

 

You know your own ability to deal with "challenging" situations. If you are willing to do the necessary effort to get your setup working properly you will succeed. Many many people are imaging with similar setups successfully. I frequently do exposures up to 15 minutes with my SW NEQ6 pro at a focal length of 1645mm and almost never have to discard subs. 

 

The reducer will be a must IMO, not because of focal length but F10 is too slow for narrowband imaging. I know I can't even get decent exposures on some objects from a dark site after 30 minutes even with 200 gain at F10 using the ASI1600MM with NB filters.

 


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#23 Achernar

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Posted 21 November 2019 - 09:26 PM

I would use the reducer simply to keep exposure times within reason. The reducer will not cover a full frame chip, but chips APS sized and smaller are. The field of view is suited to many larger and medium sized DSO's through the reducer, and you can use the telescope at F/10 for small, very bright objects such as the Cat's Eye Nebula.

 

Taras



#24 Astrojedi

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Posted 26 November 2019 - 10:44 AM

EdgeHDs are superb scopes for long FL imaging. The advice of switching to a refractor the way it is presented usually on these forums is not correct.

In imaging you will need a long FL scope for the small stuff and a short FL scope for widefield imaging. It is not an either or. Assuming you have a good mount a long FL scope is just as easy to image with (with some additional considerations).

The reason people find imaging with long focal length scopes hard is because they have poor mounts. But these days there are some good low priced mounts on the market which can easily handle a 8” or 9.25” OTA.
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#25 Benni123456

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Posted 26 November 2019 - 02:17 PM

EdgeHDs are superb scopes for long FL imaging. The advice of switching to a refractor the way it is presented usually on these forums is not correct.

In imaging you will need a long FL scope for the small stuff and a short FL scope for widefield imaging. It is not an either or. Assuming you have a good mount a long FL scope is just as easy to image with (with some additional considerations).

The reason people find imaging with long focal length scopes hard is because they have poor mounts. But these days there are some good low priced mounts on the market which can easily handle a 8” or 9.25” OTA.

It is true that one needs an sct e.g. for small galaxies or planetary nebulas.

 

But still, many dso's can be photographed around 1400mm. And for dso's one wants a speedy system.

 

Many dso's are simply too dark for an f10 scope, although that changes with every cmos generation that is more and more sensitive.

 

I admit that I still have to try using the edge more often natively and with a higher gain number or a more sensitive camera than the asi1600. Maybe f10 is then more usable than at unity gain?

 

 

The problem is not so much that the native edge 800 has a long focal length.

 

It is that it has f10 and not f7 or f5.

 

One now has things like the rasa. But that is a dedicated wide field concept.

 

Ideally, One would like something at 400mm for really wide fields. Such systems exist en masse (Celestron has the rasa now, and one can use affordable flat field refractors)

 

Then I would like something at 1200-1400mm for middle sized dso's at f5-8 (for which celestron only has problematic focal reducers with coma problems)

 

and one would like something with 2000-3000mm for really small planetary nebulas and small galaxies. At best this should also have f<10 but that would become untransportable. For that, Celestron has the edge hd line.

 

I personally use the edge 800 for small things, but for really small planetary nebulas, one needs probably an edge 11 or something... 

 

The problem is that we do not really have something unproblematic at around 1400mm focal length. 

 

The refractors in that area are extremely expensive.

If I use the 190mak newt from skywatcher, I get collimation problems. I would get spikes in the image and I would have to rebuild the scope basically.

An RC will give me the same collimation hell and create even stranger spikes.

 

So I think there would really be a market for a telescope of around 1400mm and f8-f5.6 which does not produce spikes and delivers the performance and problem free handling of the native edge 800.

 

At their native focal length, the models from the edge series are absolutely fine telescopes.




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