C8, C9.25, or sw ED120

[festoon]

I am hoping for some advice about my next OTA purchase.

I currently own an old C8 OTA and an ed80. Thinking about OTA would be a good option for me. I have no idea how good the optics are on my C8 and found collimation difficult to perform.

Like many users here I don't want to upgrade to something which is very heavy to carry round and set up. Also I live in a quite badly light polluted area. Mainly I enjoy visual observing of planets but I do enjoy a look at easy to see DSO objects such as the Orion Nebula. I would do more DSO observing but the light pollution makes this very difficult. I also do like to, if I have the time do some planetary imaging...but my main passion is visual observing.

Price wise I would like to spend in the £1000 region so was thinking either a ed120 which has very good reviews of high contrast planetary performance and give me a nice increase in FOV for DSO's or a c9.25 which would increase my aperture for better resolution and may help with the light pollution.

I have a eq6 mount so weight should not be an issue for me.

If I had the money and big garden observatory I'd go for a 150mm refractor....but for now have to keep it real ?

So in summary should I stick to my C8 and try to get it as good as possible, should I upgrade to a c9.25 or possibly an ed120 refractor. Open to other suggestions too ?

 

[Chris]

45 minutes ago, festoon said:

I have no idea how good the optics are on my C8 and found collimation difficult to perform.

45 minutes ago, festoon said:

 

 

Have you used your C8 much? Which do you prefer using out of your C8 and ED80?

[Peter Drew]

My vote would be for the ED120 as being the best compliment to your ED80 and C8. The ED80 would cover wide field visual and grab and go, the ED120 would offer good double star, lunar and planetary potential and the C8 for planetary imaging.    

[laudropb]

I would recommend the ED 120 too. I have had one since just before Christmas, but not had a lot of chances to use it because of the poor skies. When I have been lucky enough to get it out I have been very impressed with its performance. I had some lovely views of Venus last night and tonight I had a very impressive session on some old favourites.

 

[festoon]

8 hours ago, Chris Lock said:

Have you used your C8 much? Which do you prefer using out of your C8 and ED80?

I have used my C8 quite a lot and have owned it for about 3 years now (I have had my ED80 for about 2.5 years). Its usually 50/50 split between using the C8 and the ED80. The C8 is heavier but gives brighter views of planets and DSO objects. Because of the narrower field of view objects can be difficult to find especially if sometimes my finder has been slightly misaligned (I'm using a telrad and some velcro strips - so this can happen as the telrad can move and its not possible to see DSO objects with the naked eye). But the ED80 is really quick and easy to set up and gives great wide field views. However for instance if I use a filter for nebula there is hardly any light left! The same is true for planets, even the views are softer in colour and show nice details in the ED80 the view is very dim above x150 magnification.

I guess I prefer the ED80 but long for brighter views!

[festoon]

Thank you Peter and Laudropb. I had not thought of it that way about having a good set to compliment each other. And its good to know you back the reputation of the ED120!

What is tempting right now about the C9.25 is the very low sale price that FLO have on at the moment and I guess aperture fever

[festoon]

One question I do have...is how do you know if you have a telescope which has good QC optics or not. I guess most of you guys on here go on experience. But is there someone who can test this? I've always bought my scopes secondhand, and feel I'm taking a risk. For instance the ED80 I have has been superb, but when I bought it, it had about a small area of fungus between the doublet. I was still happy to buy it because at the time I could never of afforded an ED doublet new or secondhand with pristine optics. And I accepted that it had an issue but this issue would probably not affect visually the performance of the scope. But is there someone who can quantify what affect it does have?

The same for my C8....I have no idea if its a 'goodun' from celestron. Its old, bought second hand, but I'd really like to know someday if I should keep it or not!

[Chris]

24 minutes ago, festoon said:

I have used my C8 quite a lot and have owned it for about 3 years now (I have had my ED80 for about 2.5 years). Its usually 50/50 split between using the C8 and the ED80. The C8 is heavier but gives brighter views of planets and DSO objects. Because of the narrower field of view objects can be difficult to find especially if sometimes my finder has been slightly misaligned (I'm using a telrad and some velcro strips - so this can happen as the telrad can move and its not possible to see DSO objects with the naked eye). But the ED80 is really quick and easy to set up and gives great wide field views. However for instance if I use a filter for nebula there is hardly any light left! The same is true for planets, even the views are softer in colour and show nice details in the ED80 the view is very dim above x150 magnification.

I guess I prefer the ED80 but long for brighter views!

As you can probably tell, I was trying to dig out a preference between your existing scopes as your choices are between a larger version of each. I've owned a number of both myself and understand they both have their different strengths  

Your last sentence is quite telling, go for the ED120  

[PeterCPC]

I love my ED120 and can thoroughly recommend one. I also love my C9.25.

Peter

[festoon]

Thank you Peter for the advice, its good to know that you rate both OTAs I know its a difficult hypothetical question, but if you had to choose one which would it be ?

[PeterCPC]

For general purpose it would be the ED120.

Peter

[YKSE]

I agree that 120ED is a good compliment to your scopes.

Don't know when you C8 was made, what I've read, as long as it's not during the 1986 Halley comet period, it should be a decent performer. Good collimation for a SCT is vital for its performance. I can warmly recommend Ed's guide for anyone who's unsure about collimating SCT.

http://www.astromart.com/articles/article.asp?article_id=548

As to the dim images on nebula in 80ED, it's much more depend on eyepiece you use than the aperture, same as C8. e.g. using a 20mm EP in C8 on a nebula, the image will be dimmer than the same EP in 80ED. The brightness of entended DSO (nebulas e.g.) depends solely on  exit pupil, not aperture.

[Mr Spock]

I use a C9.25 on an EQ6 and it's a perfect combination. The C9.25 excells on planets and can reach faint fuzzies despite me being in the LP zone of the mighty Sheffield.

If you've had collimation problems with the C8 in the past, I would suggest adding a set of Bob's Knobs to the C9.25. I have on mine and collimation is easy
Easy to fit too. Just take out the fastar assembly and fit them in comfort. You have to collimate anyway and fiddling with the screws while it's still in place is tricky at best.

[festoon]

6 minutes ago, YKSE said:

I agree that 120ED is a good compliment to your scopes.

Don't know when you C8 was made, what I've read, as long as it's not during the 1986 Halley comet period, it should be a decent performer. Good collimation for a SCT is vital for its performance. I can warmly recommend Ed's guide for anyone who's unsure about collimating SCT.

http://www.astromart.com/articles/article.asp?article_id=548

As to the dim images on nebula in 80ED, it's much more depend on eyepiece you use than the aperture, same as C8. e.g. using a 20mm EP in C8 on a nebula, the image will be dimmer than the same EP in 80ED. The brightness of entended DSO (nebulas e.g.) depends solely on  exit pupil, not aperture.

Thank you YKSE My C8 was bought third hand and the owner before me had had it for 5 years. He thought it was probably 15 years old in 2014, so based on that I'd say it was made in the late 1990's. Possibly a bit after the period you quote in your post as a 1986 period.

And I appreicte the point you make about brightness depending on exit pupil (essentially aperture/magnification which equals eyepiece fe/focal ratio of OTA).  However for a given magnification the surface brightness is higher for the larger aperture. So as you say you can achieve the same surface brightness in the ED80 but at a signifcantly lower magnification, or if you run both scopes at say x150 the image is dimmer in the ED80.

[festoon]

19 minutes ago, Mr Spock said:

I use a C9.25 on an EQ6 and it's a perfect combination. The C9.25 excells on planets and can reach faint fuzzies despite me being in the LP zone of the mighty Sheffield.

If you've had collimation problems with the C8 in the past, I would suggest adding a set of Bob's Knobs to the C9.25. I have on mine and collimation is easy
Easy to fit too. Just take out the fastar assembly and fit them in comfort. You have to collimate anyway and fiddling with the screws while it's still in place is tricky at best.

I agree...I used to live in Sheffield (crookes area) and the sky was very difficult to use a telescope for anything but planets even though we had a great view across the city.

I do have bobs knobs on the C8 but my issue with collimation is finding a steady star and keeping it in the FOV whilst adjusting the collimation. Maybe its just my lack of experience, but I have never found the process easy!

[Mr Spock]

Just now, festoon said:

I do have bobs knobs on the C8 but my issue with collimation is finding a steady star and keeping it in the FOV whilst adjusting the collimation. Maybe its just my lack of experience, but I have never found the process easy!

Tiny tweaks - less than 1/16th at a time. Patience is a virtue where collimation is concerned!

[festoon]

3 minutes ago, Mr Spock said:

Tiny tweaks - less than 1/16th at a time. Patience is a virtue where collimation is concerned!

Probably says a lot about me Thanks for the advice Michael!

Sometimes this runs thin, when I've left my scope out for 45 mins to cool down, its cold...possibly late and partly cloudy, and all I want to do is look at something that I've planned to I work as a physicist and lots of my job is automation...sometimes I wonder why this process has not been automated on OTAs! But that a thread for another day! But you make a very valid point about the need for patience and I think I can get more out of my C8!

[YKSE]

18 minutes ago, festoon said:

And I appreicte the point you make about brightness depending on exit pupil (essentially aperture/magnification which equals eyepiece fe/focal ratio of OTA).  However for a given magnification the surface brightness is higher for the larger aperture. So as you say you can achieve the same surface brightness in the ED80 but at a signifcantly lower magnification, or if you run both scopes at say x150 the image is dimmer in the ED80.

That's correct, the image's smaller in small scope with the same exit pupil, that's why the saying: smaller scopes for large DSO, larger scopes for small DSO.

Light pollution is the No. 1 enemy in seeing faint DSO, going up in aperture is an very ineffective way, better to put money in petro, driving to a dark site, where you can see e.g. North American Nebula in its whole glory with 80ED, while maybe only a tiny bright part in light-pulluted backyard with C8.

 

[RT65CB-SWL]

If you are generally happy with the performance of your C8, then why not let Steve at http://sctelescopes.com/  have look at it. As it is old, than possibly just a routine checkup; (think of it as a health check at your doctors surgery or MoT for telescopes ); is maybe all that is needed. I was in 'two-minds' about parting company with my 'modded' ETX 105 about two years ago and upgrading. I let him have look at it and was surprised at the end result. I decided to keep it in the end.

[festoon]

9 minutes ago, Philip R said:

If you are generally happy with the performance of your C8, then why not let Steve at http://sctelescopes.com/  have look at it. As it is old, than possibly just a routine checkup; (think of it as a health check at your doctors surgery or MoT for telescopes ); is maybe all that is needed. I was in 'two-minds' about parting company with my 'modded' ETX 105 about two years ago and upgrading. I let him have look at it and was surprised at the end result. I decided to keep it in the end.

Hi Philip, are you able to please say how much this service of your ETX105 cost? Did they test the optics in terms of PV or modulation transfer function -MTF for you?

[RT65CB-SWL]

Yes he did test the optics and he noticed the collimation was slightly out. Sorry! not sure what PV or modulation transfer function is. Though that was not what I saw him for originally. I cannot remember what it cost me now. I think it was <£100.00GBP inc. VAT.

[Stu]

1 hour ago, festoon said:

I do have bobs knobs on the C8 but my issue with collimation is finding a steady star and keeping it in the FOV whilst adjusting the collimation. Maybe its just my lack of experience, but I have never found the process easy!

Have you tried using Polaris? It stays pretty much stationary so is easier to use. Not a bad elevation either in terms of achieving a collimation which works across the range.

[festoon]

57 minutes ago, Stu said:

Have you tried using Polaris? It stays pretty much stationary so is easier to use. Not a bad elevation either in terms of achieving a collimation which works across the range.

Hi Stu,

No i've never used Polaris before. Usually Vega, Sirius, or Capella depending on the season. Its a good point about polaris and its lack of movement Thank you

I dont have a guiding system set up, or a reticule eyepiece, so what I find difficult apart from the stars natural movement is getting it centred, adjusting the collimation screws bringing it back to centre or even back in FOV and iterating the process.

[ecuador]

I had settled in an ED80 + a C8 for my main scopes, until I came across an inexpensive second hand C9.25 XLT and I did an upgrade from C8 -> C9.25 for less than £300 difference, not expecting a huge difference... And yet there was! I am not sure why, maybe it has to do with the fact that the C9.25 is easier to collimate (the C8 seemed to require much more precision to give the best image) and holds collimation well, maybe the claims about the different design with a slower main mirror that gives a sharper image hold water, maybe my C8 which was older was not a great specimen, but the planetary views are obviously better and you get more perks, like the baffle tube being wider so you actually can get a WIDER FoV than the C8 with the appropriate eyepiece (see here) - or less vignetting with the f/6.3 reducer if you are imaging. So, if you ever have the chance of doing a low-cost upgrade to a C9.25, I suggest you take it.

That said, I am more of an imaging person. For a person who is more into observing, apart from planets where the C9.25 has the edge, the views of an APO are stunning and the 120 ED would be a great addition to your arsenal.  So, I guess my suggestion would be probably go for the 120ED if you are more into observing, but keep an eye open for C9.25 deals to do that as well if you ever get the chance  

Now, back to collimation. Forget about doing it by hand, especially if your C8 is like mine and needs more precision than seeing would allow and doesn't hold it in general - yes I also had bob's knobs. Just use metaguide with your QHY camera. Not only will metaguide stack live so it will "beat" seeing conditions, but if your mount is a tracking mount, then it can also follow the star as you are doing adjustments and it tries to leave the FoV. But a C9.25 in my experience will be even easier (still with metaguide of course).

[Stu]

The C925 has a slightly slower primary I believe, f2.3 seems to ring a bell. That's why is is supposedly the pick of the bunch because all the others have an f2 primary.

I picked up a very cheap C925 and have been pleased with it so far. I am going to do some cooling mods on it to see have far I can improve the performance.