ED80 for imaging - why?

[PorkyB]

If you read this forum a lot you notice certain trends that represent a body of opinion.  Lots of people like Dobs, lots of people think (wrongly in my experience) that you can't image with a 200P/EQ5.

Lots of people think that the Skywatcher ED80 is a great imaging scope.  Why?  It's small and it's seriously slow.  At f/7.5 you need 135 seconds to take an exposure that would take 60 seconds on an f/5 scope.  Even with the Focal Reducer / Field Flattener fitted it's still f/6.375 which means you need 98 seconds instead of 60.

Add to this the cost.  An ED80 is £450, or £619 with the FRFF.  A 130PDS is £165, or £262 with the coma corrector.

So if you can have a 130PDS which is faster than an ED80, has a very significantly larger aperture than an ED80, and leaves you with £357 change to put towards your mount, why would you buy an ED80?

Now I know someone will say "collimation".  Collimation of a Newtonian takes about two minutes in the field.  Or it would, but despite checking it every time I take it out, my 130PDS hasn't needed adjusting since the first time I used it.

[Naemeth]

In part at least it's probably down to people recommending one over the other, other people picking up that advice and handing it down. Not pointing any fingers mind you .

It would be interesting to see some comparison images, if someone has them .

[nmoushon]

There are a couple reasons people prefer and recommend the ED80 over a Newt to image with.

1.) Most ED80s aren't native f/7.5. Yes some obviously are. Like mine for instance is a native f/6.25 with a reducer is brought down to f/4.75. Now thats pretty fast for a doublet and even beats most Newts that are at F/5. But most refractor can be reduced down to around F/5.

2.) Another reason is because its a more dedicated wide field scope than any Newt could ever be. Well beside Taks Epsilons but thats just a crazy scope that deserves its own class in my opinion lol. My ED80 is brought down from a native 500mm FL to 380mm FL. There are only a couple other scopes that can get wider than that and by then most people just use a lens attached the camera.

3.) Now the bigger reason the the shorter FL is important is that it will allow for longer exposures without the need for guiding. My scope at its native 500mm would barely allow me to take 70sec exposure unguided on my HEQ5 but reduced to 380mm I was able to get 120sec unguided consitantly. Thats a HUGE jump when it comes to unguided imaging. Especially when your starting out.

4.) Yes the price is more. Its just the design that makes it this way and Newts will always be cheaper than fracs.

5.) The ED80 as a much smaller surface area than the 130PDS. Why is this important? Because the 130PDS will act like a sail in even the smallest of winds and will produce error that even guiding can not fix and thus will trash your subs. This can happen with an ED80 but much much less likely. It is also lighter which puts less strain on the mount allowing for longer subs. This might not seem a lot if you only have the scope on the mount but once you add a guiding set up to it and a CCD/filter wheel that can push the mount to or past it point which can cap your mounts ability to track accurately enough to take long exposures. Even with guiding you could limit yourself to 10min instead of 15min becuase of the weight.

6.) I think you know this but not sure since you brought it up. The only thing aperture adds to imaging is that it allows you to have a longer focal length but keep the f/ratio down. Aperture size does not have any other effect on imaging than that. It will not collect more light for the image or make imaging faster. If you had a 10" @f/5 and a 5" @5/f they would collect the same amount of light for imaging. The scales would be different because of the FL but the amount of data would be the same.

7.) You say collimation is easy, which it can be, but some people like going as little fuss as possible. Especially if you have to tear down every night. Which is where a frac just becomes a lot easier. Plus if something does go wrong a frac is a lot easier to deal with and try to figure out what wrong. Theres just less fuss.

Now thats why the ED80 is very popular. There's nothing wrong with imaging with the 130PDS. Theres several people on here that producer wonderful images with them. Its just the above that is why so many people suggest them to new comers.  I'm sure others will add their 2 cents.

[Earl]

For me, Diffraction spikes are not to my taste, im no fan of collimation even if it took 30 seconds and did it itself .

Saying that if neither of the above are an issue then the focuser supporting a coma corrector, filterwheel, oag and camera will need to be replaced, but then so does the one on the ED80.

[Ibbo!]

the 80 is not as demanding on the mount.

Steve

[swag72]

I agree with diffraction spikes - I really don't like them - Would turn me off a newt every time.

Rob (Uranium) has modded his 130PDS for imaging - He has it working really well. But for me, I want an out of the box solution and a modding project and / or a reflector isn't out of the box plug and play. Fracs are as simple as they get, and I like simplicity.

[LouisJB]

it's a good question. One I've wondered about.

Especially if you're using a DSLR and maybe already have a 300mm F5 or similar high IQ lens in the kit bag, by the time an ED80 is reduced to give you some F5 or similar speed you're not going to be a million miles away from the camera lens in terms of focal lengths.

I think if I didn't already have a zoom camera lens the small ED80 refractor would be nice, but if you have then getting something with a longer focal length - say not the 130PDS but the 150 or 200 PDS at 750mm or 1000mm F5 is starting to give you something that doesn't overlap with the purpose of the ED80 (or camera lens) for a fraction of the cost. Also visually on DSOs you're going to be able to see something due to aperture whereas with the smaller 80mm refractor objective lens, I expect all but the brightest objects are too dim to see.

within the limits of a mount though, the small refractor (and similar camera lens) do have appeal since they place much less load on the mount.

Again, it  appears there is no perfect scope for all purposes.

[MikeWilson]

If I could, I'd change the title to "ED80 for DSO imaging - why?", because the newts mention are superior for imaging the solar system (moon, planets, solar and comets) imaging and assist the eyeball with getting plenty of light for the given focal length too

[Astrosurf]

As has been said, there's no good all-round scope! That's why have a two, plus my 200mm lens (max) on the Astrotrac (or I will when I get it sorted!). I got my 200P with the HEQ5 Pro first (lucky to come into some money!) and even though I had problems with breezes blowing the scope, I found it excellent.

Then I wanted wider field so bought the frac. Now I have everything I want. Most nebulae are very large so small fracs are best. I use my newt for solar system and smaller DSOs such as planetary nebulae, and galaxies etc.

Alexxx

[Pete Presland]

i would quite like switch to using my celestron 80ED instead of my 200PDS. but using it the other week i had horrible vignetting and poor star shapes away from the center of the field of view.

on the plus side the amount of room i suddenly had in the obsy was superb!

having done a little research about flatteners it seems that to use a flattener you have to ensure that the camera sensor has to be a quite accurate distance from the flattner. also not all flatteners are suitable for all refractors, you have to match the flattener to the F ratio.

[LouisJB]

also it should be mentioned about true colour, star colour, I think you only get this from a triplet not a doublet?

In any case people who want to use a wide-field ED80 or similar will be imaging big wield-field objects like large nebula.

The sort of DSS I tend to think of more generally are the small galaxies, they wold be tiny at a short focal length. So people switch from newt to small refractor and vice-versa depending what you want to image... I can't imaging say the ring-nebula looking that great on an ED80, whereas for a cheap 1000mm newt you might start to see something useful.

Always happy to be corrected. I'm considering the 200P (equivalent) on an HEQ5 in-spite the fact I know it will be hard work because there is no cheaper way to get that focal length for small DSOs like galaxies. I had originally expected the 8" GSO RC but by the time it's been reduced to speed it up and flatten the image it's lost some of it's focal length advantage (and it's comparatively very expensive). 

Probably everyone needs:

A good small refractor or comparable camera zoom lens for wide-field

A powerful aperture Newt for DSOs

A compound of some sort for planetary

Which is why it appears most people who are into this hobby have at least one of each type and probably more to boot...

[Helite]

Well I got the 80ED to go on my EQ5 just to reduce the size/load on the mount. I was using my 200p and decided to give guiding a go but once the ST-80 and dovetail, synguider, and DSLR were on it I found it a bit cumbersome and prone to catching the wind, so decided to reduce the size of the equipment.

I don't think I have ever read anyone say you CANT image with a 200p/EQ5 combo, just that it is not the best combination.

Whatever your weapon of choice it always comes down to a personal opinion and preference of what suits your situation best. 

[Luke]

I've used a DSLR with an F5 8 inch Newt, a few different refractors, and a couple of SCTs.

The most used scope was the ED80. Many times I couldn't use the SCT because there was too much wind, and the Newt was a bit of a wind sail as well. I've had my ED80 out in gusts of up to 40mph. The ED80 is around the 500mm focal length where accurate guiding is not too tricky and there are plenty of interesting DSOs to image.

Collimation may not be too big an issue when you are used to it but it already takes me ages to set up and pack away an ED80, so I appreciate that not being needed. I don't mind collimating my dob for DSO observing, because it's a far less hassle setup for observing. And some newbies already have a lot to learn, so not having to collimate might be a bonus.

An ED80 is lighter and easier to handle and setup and balance.

I can definitely see why it is recommended for beginners, it is what I would start with (and carry on using).

That's not to say other scopes are not good options too. And I've met a few people now who have made some amazing images with gear that they were told was not suitable for imaging at all! So I hope when folks see "oh that's a very slow scope, not suitable for imaging" or their mount is not a HEQ5 etc, that it doesn't put them off.

In terms of speed, I have lower expectations than some of the people on here and I'd be happy enough with F7.5 (my ED80 is actually F6.25, but my 120 is F7.5). I used to think the F6.25 Equinox 80 was a better imaging option than the Evo ED80, but now I think it's a close call, as the latter has the optically matched reducer...

[lensman57]

If you read this forum a lot you notice certain trends that represent a body of opinion.  Lots of people like Dobs, lots of people think (wrongly in my experience) that you can't image with a 200P/EQ5.

Lots of people think that the Skywatcher ED80 is a great imaging scope.  Why?  It's small and it's seriously slow.  At f/7.5 you need 135 seconds to take an exposure that would take 60 seconds on an f/5 scope.  Even with the Focal Reducer / Field Flattener fitted it's still f/6.375 which means you need 98 seconds instead of 60.

Add to this the cost.  An ED80 is £450, or £619 with the FRFF.  A 130PDS is £165, or £262 with the coma corrector.

So if you can have a 130PDS which is faster than an ED80, has a very significantly larger aperture than an ED80, and leaves you with £357 change to put towards your mount, why would you buy an ED80?

Now I know someone will say "collimation".  Collimation of a Newtonian takes about two minutes in the field.  Or it would, but despite checking it every time I take it out, my 130PDS hasn't needed adjusting since the first time I used it.

Refractors are almost plug and play, they are almost mainteneance free unless they are abused. They do not have contrast reducing resolution robbing secondary mirror . They do not usually need collimation, long cool down time or suffer flexure of the tube due to the weight of the optics or misalignment of the mirror cell as it flexes due to temperature change. They do not need the mirror recoating after 2 or 3 years that would normally cost nearly the same price as the scope. They are atleast,  for fast F ratio short variety, quite compact compared to a NEWT. The budget line of NEWT available, although good value, do not have the same optical quality as the well corrected ED or APOs. Speak to any supplier that is unbiased and they will tell you that you can push a well corrected APO or ED well beyond the same aperture NEWT. In  AP the size of the aperture is not relevant, it is the FL and therefore the effective F ratio that detrmine the exposure and the FOV. As for the SW or any other ED, now that I have aquired a few, with regret these will not be my recommendation. I would rather save` a bit more and go for a proper APO TRIPLET, these ED scopes as good a value as they are , are more like lame ducks . Better than a similar  Achro but way behind a proper APO. So yes something like a 130 or even 150 PDS will represent excellent value first scope, but soon after the itching for quality starts to bug you.

Regards,

A.G

[LouisJB]

I don't quite understand the issue of resolution, even with the smallest and cheapest 130 if you take the secondary away from the primary you still get a bigger objective lens, by quite a bit by area. That's what determines resolution? I'm no expert in refractors so please correct me if I'm wrong. I know there are other factors in play, but I suppose it comes down the comparing like for like, e.g. say 150PDS at ~£220 is going to deliver quite a lot for that price, there aren't a lot of alternatives at that cost. Also it's possible to get newts with objective lenses (minus secondaries) for relatively minor cost that either have no refractor counterpart of where they do, the cost difference will be massive. the 130PDS and 150PDS both deliver something an ED80 can not, native fast F5 while retaining their native longer focal lengths, so again it depends what you want to image. APO triplets are that bit more expensive again, it's not really a like for like comparison. I'd consider the best APOs something like the best camera lenses, fully corrected for best image quality, for that, neither comes cheap.

Ultimately for imaging there are so many factors, the mount, guiding, camera and processing that out of a fixed budget you should get the best in each area you can but it all has to work well together. No point sticking a big 8" newt on an eq5 for imaging, if you had an eq5 you'd most likely be better served with something smaller like the ed80, 130 newt or a camera with good zoom. Then again the cost of a 150PDS vs an ED80, I think would pay the difference to upgrade EQ5 to HEQ5 or even NEQ6. So many options, I guess that keeps it an interesting field. All the more when people try and experiment with unusual combinations and with skill and patience get amazing results and push the envelope of what people consider possible. If we were all using the same tube, mount, camera and processing techniques, that would make it much less interesting as a hobby.

I'm still learning and weighing up the pros and cons, so I say these things for discussion, please do correct me where I'm wrong then I'll learn something along the way.

[brantuk]

Hi Porky - I knew when I read your question it was going to spark a big response. I've nothing to add other than general agreement with most of the points above which are mostly, good technical, sensible reasons,  and sound advice.

But it was fun watching you get gently beaten up in the nicest possible way - very entertaining lol

(I don't remember if it was mentioned but the 130's do hold collimation very well and is rarely an issue in the field)

[Uranium235]

I'll jump in on this one a bit later, I have both scopes - and can clue you up on the merits/cons of each system for imaging

[Chris]

I've owned both the 130pds and ED80 and they are both excellent choices for imaging. On a budget simply nothing beats the 130pds I think its astonishing for the money and there are very little down sides to it for the beginner. For example it is the easiest Newt I've ever collimated and I only had to do it once (5 minutes job done). It is seriously fast, I mean seriously! even on very short subs of 60-120 seconds I got amazing signal which would have needed guiding to achieve with a native ED80. The diffraction spikes don't bother me and dare I say it I even like them on some pics. Anyway they give the star colour of a triplet apo which is enough said if you ask me! The weight of the 130pds is comparable to the ED80 also. I have doubts about the previously comment regarding having to recoat the mirror every 3 years, maybe decades ago before modern coatings were introduced but I would expect a mirror coating to last a good 10 years now days. I will go one step further and mention that my father in law has had is 8" Newt for 30 years and I don't think he has ever recoated his primary mirror! It quite possible needs it of course, but despite this it gives cracking views visually. Now onto the ED80, if you're an absolute newcomer to imaging then this might be the way to go, even though collimation is very easy on the 130pds it is still one extra thing that needs doing, and even though you need to do it once in a blue Moon its another thing for a newby to worry about. It will also be less of a wind sale for non sheltered setups (not that the 130pds is much of a wind sale compared to the 200p or larger). The slower optics will make focus slightly easier, and of course there are no diffraction spikes which really seem to bother a lot of people. Ermm, thats all I can think of really, they both ward off dew very well perhaps due to their small aperture, both great choices. I will say that if you want to start out non guided then you will get much more signal on your images with the the 130pds, but if you want to start out guiding then the ED80 will help keep the setup super compact.

I do regret selling my Newt and I will be getting another one soon, perhaps at 1000mm fL such as the 200pds to compliment my 2000mm fL C8 and my 432mm fL Meg72.

Chris   

[JB80]

Especially if you're using a DSLR and maybe already have a 300mm F5 or similar high IQ lens in the kit bag, by the time an ED80 is reduced to give you some F5 or similar speed you're not going to be a million miles away from the camera lens in terms of focal lengths.

See this is why I am considering a smaller Apo or Ach than the 80. My 300mm camera lens while it is OK it is not great and full of artifacts yet I can get a similar focal length with probably better optics using a small telescope and at either the same cost or substantially less then forking out for a decent/excellent camera lens.

Problem is it has to be smaller than the ED 80 and much lighter but still have good optics.

[wxsatuser]

Looks like I need a 130pds.

[LeeWilky]

Whoever says you cant image on a 200p EQ5 might want to check out this blog http://astrocasto.blogspot.co.uk/search?updated-min=2013-01-01T00:00:00-08:00&updated-max=2014-01-01T00:00:00-08:00&max-results=38

[Chris]

Whoever says you cant image on a 200p EQ5 might want to check out this blog http://astrocasto.blogspot.co.uk/search?updated-min=2013-01-01T00:00:00-08:00&updated-max=2014-01-01T00:00:00-08:00&max-results=38

Thats our Marks site aka Quatermass, he's done wonders with his Eq5 200p setup, but then again he's a master at processing and needs to correct significant star trialing in his images in post processing. I'm sure he'll agree that there are easier ways to image than the eq5 200p. My eq5 was useless for imaging I don't know how mark does it, he's a bit of a legend! You had any luck with yours? I was lucky to get 30 second subs with mine

[kirkster501]

"ED80 for imaging - why?"

Lightweight, good colour rendition for the price, easy to mount, cost effective, robust.

Downsides?  Quite slow (F7.5 without the reducer).  Reducer to speed it up costs another £170.  Blue channel can sometimes need a refocus.

[LeeWilky]

Thats our Marks site aka Quatermass, he's done wonders with his Eq5 200p setup, but then again he's a master at processing and needs to correct significant star trialing in his images in post processing. I'm sure he'll agree that there are easier ways to image than the eq5 200p. My eq5 was useless for imaging I don't know how mark does it, he's a bit of a legend! You had any luck with yours? I was lucky to get 30 second subs with mine

Yep its his fault i just spent over £1000 on the scope, camera and accesories after finding his blog lol!

Not had any luck yet because since ive had the scope we havnt had a single clear night here in the Wirral.  It cleared up a bit last night and as soon as i got everything out and set up it clouded over again and i havnt seen the sky since.

Such is life lol

[davew]

From what I've learned over the years I think the bottom line could well be statistical. The chances are, all things being equal, that a small refractor will give a greater chance of success straight from the box than a Newt. If scopes were handed out to a broad range of people who had never used a scope before I'm sure the majority would be up and running at the end of the night with the refractor and fearful of even looking at the collimation screws of the Newt.

Another factor is effort and time. Some are stuck with a few minutes here and there because feeding their children takes precedence over a nice picture. Other are, sometimes, a touch lazy and want the scope to do all the work with little input. A small scope wins more often than not.

Why someone would recommend an ED80 if they've never even owned or tried both scopes is however a mystery. I've tried both and found that for me the Newt was much harder.

But.... Enter the 130 P-DS. I can't speak for the effort Uranium has put into imaging with this scope but I feel I can speak about the quality. For the money ( Leaving out second hand ) I can't remember seeing such quality. The main downside I can see is that he already has some experience of imaging and what he does would take a complete newbie a few weeks to get close to. It would, I'm sure, make a superior visual scope than an ED80 so it wins in the dual use stakes. ( I hope there aren't too many experts who are going to try and persuade me that 80mm beats 130mm ! I already have an 80mm and know well what it does )

The 130 has piqued my interest. Now all I have to do is decide whether I want to put Uranium's effort in or not. For goodness sake, £ 262 for a Newt and corrector !!

Dave.