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Darren Knight

C9.25 for galaxies?

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Hi guys,

A month ago I purchased a C9.25. At the moment the only extra fitted to it, is a skywatcher Crayford focuser. I would like to use it to image galaxies but unsure if this is the right way to go. I have a Atik 4900 and filter wheel that's currently fitted to my refractor.

I was thinking about moving the camera and wheel onto the SCT, but wanted to know what else I should add / purchase.

The SCT doesn't have any rings, so should I purchase some rings and use my guide scope or buy an OAG?

Should I consider a focual reducer?

Should I consider a lakeside focuser?

Will all of the above work together?

Sorry, a lot of if buts and maybes but I'm just planning for the future.

Many thanks in advance.

Darren Knight

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Been there and wow, what an experience... !! :huh:

The ideal way of imaging with a C9.25 is with an Off Axis Guider, but having tried this, it is fraught with difficulties. I now use a side by side saddle arrangement if I want to use the C9.25 for piccies.

With a focal reducer, I can't see what can be gained over a standard refractor. If I'm having a go at a galaxy, I use it at the native focal length and try to get the guiding as good as I can.

Which ever method you choose, good luck.

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Hi ET,

Thanks for the reply, but was was your experience, good or bad? And what problems did you encounter using an OAG?

Many thanks

Darren

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The 9.25 isn't an uncommon scope, but how often do you see people posting galaxy-type images having used one? Lots of biases there, but just an observation.

I want to have a go at guiding sometime with my C11, for a laugh, but i know if will be harder and i will have different issues to contend with (mirror flop etc), and that my results are never going to be like the ones taken though a compact and fast refractor. If i wanted to be serious about deep space imaging, i would get a fast scope and not try and do it the hard way with my f/10.

Good luck and i look forward to seeing what you do and achieve.

Jd

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The 9.25 has too long a focal length for galaxies - the image size formed is proportional to the focal length meaning the collected light is spread over a bigger area, so it is dimmer. Additionally the long focal length means the tracking has to be accurate - any error in the tracking accuracy is multiplied by the longer focal length.

Isn't the 9.25 on an Alt/Az base/mount?

If so that is not applicable to galaxies and long exposure's. Field rotation of the object will occur and images blur and/or will not stack.

Before you go buy anything I would look at what the equipment is that imagers use for their images, as that is really the proven equipment for the job.

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Here's my thoughts - Bear with me!! Interesting, but I can see that with my experience of the C9.25 I am going to go against the grain.

I am a self confessed refractor girl ........... hang on ........... WAS!!! I've used refractors for 3 years and in January got a C9.25 specifically for galaxy and PN work. I LOVE it :grin:

Admittedly I've only managed 1 image since January - Yes our weather has been awful too. The resulting M51 image was taken with a reducer, so imaging at f6.3 there or thereabouts. It was fine. I have resorted to an OAG for this scope and having never used one before it was a learning curve, but nothing too difficult. Make sure that you have a good sensitive camera though, such as a Lodestar, there's not many stars about through an OAG!!

Next I decided that I may as well take off the reducer, what's the point at imaging at 1370 when I have 2350mm of loveliness!! Of course, I am taking a hit on the speed. F10 is slow and people say that it can't or shouldn't be done!! Sadly I do not have an image yet at f10, just a half completed one! My thoughts on f10? It's fine!! But I am taking 30 minute subs at 2x bin in narrowband. If I was doing RGB I'd be looking probably at about 5 minute subs.

So this brings me onto THE most important part of it all - The mount. You don't say what mount you have. I had an HEQ5 before and I know that there is no way it would have dealt with this focal length. You NEED a good mount with this. Tim Jardine, who I think is THE person to look at for f10 imaging did well with an EQ6. For me, one of the 6's would be an absolute minimum.

Hope that helps. I hope to prove that it can be done - Watch this space when the weather clears, if it ever does!! If you are interested in my half image so far at f10 (M97) you can see it on my website.

My caveat to all of this is the mount. You must have a good solid mount and it must be accurate at guiding and up to the job.

Edited by swag72
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I hope i didn't give the impression it "can't be done" or "shouldn't be done" - i love going against the grain and trying things people are adamant won't work, that's part of the fun in life.

I just think if you want an easier life, quicker data acquisition, no mirror flop, etc, then i would look for a faster scope. Swag72 is very convincing in her arguments, and it sounds exciting work, but, we still don't have a complete galaxy image in nearly four months.... ;)

Jd

(I can't really pass judgement as i have only a handful of any images since january too!)

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The 9.25 has too long a focal length for galaxies - the image size formed is proportional to the focal length meaning the collected light is spread over a bigger area, so it is dimmer. Additionally the long focal length means the tracking has to be accurate - any error in the tracking accuracy is multiplied by the longer focal length.

Isn't the 9.25 on an Alt/Az base/mount?

If so that is not applicable to galaxies and long exposure's. Field rotation of the object will occur and images blur and/or will not stack.

Before you go buy anything I would look at what the equipment is that imagers use for their images, as that is really the proven equipment for the job.

I think you are mixing up lots of things here.  First, the C9.25 can be bought in many configurations. You have the CPC series and yes they are dual fork Alt-Az standard without wedge. Then you have the Advanced VX, CGEM and CGE combo's, which are all EQ Mounts.

Or you can just buy the OTA?

The standard focal length of the C9.25 SCT is 2350mm and with a 0,63 Focal Reducer this is reduced to 1481mm focal length. Perfect for galaxy and small planetary nebula imaging.

Believe it or not, the C9.25 SCT is among the most popular long focal length imaging scopes. That it's very affordable and doesn't break the bank, has something to do with that as well. ;)

Just make sure you got a good Mount. A NEQ6 Pro or CGEM is the absolute minimum, if you want to use it for long exposure imaging.

( It's one of the reasons I bit the bullet and went for the NEQ6 Pro myself, to future proof myself and be able to put C9.25 (or similar) on it down the road. Both for planetary and long focal length imaging. )

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I say go for it, use a reducer that flattens to start with as it means you will get workable data while you sort out balance, polar alignment, guiding and PEC

I use a small 127mak with a reducer f6.7 and can get subs of between 5 and 10 min with a finder guider.

Why? Because it is hard and frustrating and immensely rewarding when it works plus my budget is limited.

Not sure on your mount, but you will need a Gem.

+1 on the EQ6 or celestron equivalent.

Good luck and rem to post your pics.

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I don't disagree that refractors and imaging at 329mm is FAR easier. If you want data that is quicker to obtain, then don't work at f10!!

Rest assured that a galaxy image WILL be forthcoming and it WILL show that this type of imaging is doable, of that I am certain. What it may also show is that it is NOT possible to take a couple of hours worth of data and produce an image. I think that it will show that you need to throw a lot of time at it and perhaps this is time that people are not willing or able to spend.

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Can someone post a link to the M51, i can't find it.

Jd

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Flippin' heck!!!!

That is very tidy :)

I'm ordering a focal reducer :)

Well done. Smashing result.

Jd

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Well... A very interesting thread indeed! I asked the question at the beginning of the year: what scope shall I get to image galaxies. The overwhelming response was a Celestron 8" EdgeHD. So, I got one. It's running on my HEQ5-Pro mount. The great thing is... It all works! I have no (well, little) trouble with 1200s subs and could go longer I'm sure. I tried with a finder guider, but that was a complete waste of time, so bought the Celestron OAG. The guide camera is a QHY5-II and so far, I have found a guide star relatively easily. It's not nearly as simple as the finder guider / 80ED setup, but that's no surprise. The important thing is, it works. The issue is the weather! Very few chances to use everything...

So, it is possible and I'm sure that the C9.25 would work fine, but definitely get the OAG. It's not easy and I only have one passable DSO image and many poor seeing Jupiter attempts to show for it all so far. The learning curve has been steep and bumpy. However, I now feel that I'm in a position to start working properly and gather some good data to make some decent images.

Oh, I currently use a DSLR, so things are even trickier, but we don't do it because it's easy!

One other thought - apparently the correct distance to the chip is essential, so make sure that is taken into consideration - I have the reducer, but can't use it as I can't get the right spacing with it until I purchase an adapter that is not yet available in this country... Will be soon!

Anyway, good luck and I look forward to hearing how this progresses. I am also interested in what the alternative scope recommended is. I went for the SCT as I didn't want diffraction spikes...

Sorry to waffle on!

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Well... A very interesting thread indeed! I asked the question at the beginning of the year: what scope shall I get to image galaxies. The overwhelming response was a Celestron 8" EdgeHD. So, I got one. It's running on my HEQ5-Pro mount. The great thing is... It all works! I have no (well, little) trouble with 1200s subs and could go longer I'm sure. I tried with a finder guider, but that was a complete waste of time, so bought the Celestron OAG. The guide camera is a QHY5-II and so far, I have found a guide star relatively easily. It's not nearly as simple as the finder guider / 80ED setup, but that's no surprise. The important thing is, it works. The issue is the weather! Very few chances to use everything...

So, it is possible and I'm sure that the C9.25 would work fine, but definitely get the OAG. It's not easy and I only have one passable DSO image and many poor seeing Jupiter attempts to show for it all so far. The learning curve has been steep and bumpy. However, I now feel that I'm in a position to start working properly and gather some good data to make some decent images.

Oh, I currently use a DSLR, so things are even trickier, but we don't do it because it's easy!

One other thought - apparently the correct distance to the chip is essential, so make sure that is taken into consideration - I have the reducer, but can't use it as I can't get the right spacing with it until I purchase an adapter that is not yet available in this country... Will be soon!

Anyway, good luck and I look forward to hearing how this progresses. I am also interested in what the alternative scope recommended is. I went for the SCT as I didn't want diffraction spikes...

Sorry to waffle on!

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Gav,

I use a T-Ring and Antares 2inch adapter attached to a Celestron 0.63 focal reducer and field flattener.

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have you thought about hyperstar ? yes expensive, but advantages are mega quick imaging times, no real need for guiding as subs can be less that 1 minute. so when you add up the cost of hyperstar to the cost of all the other bits you need to guide and run a sct scope for imaging then the cost look alittle better.

i`ve used my 8" sct for imaging, a reducer i find is a worth while purchase, a canon 1100d on the back of the reducer and guided with a st80 and a atik titan on a dual mount bar, works well for me.

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Hi Darren,

The C9.25 has an ideal focal length for galaxies. It certainly isn't too long and is pretty similar to the FL Yves and I used for our galaxy images over the last couple of years. We worked at 2.4 metres. This kind of thing;

http://ollypenrice.smugmug.com/Other/Best-of-Les-Granges/i-p5JCSFT/0/O/M64%20LRGB%205Hrs%20WEB%20CROP.jpg

What is difficult is guiding at these focal lengths. (Well really it's the small number of arcseconds per pixel which make it difficult but calling it the focal length is a shorthand.) If you have the mount then go for it. When I say this I mean that the mount has to be very accurate under guiding. An OAG is by far the best method because you guide at the focal length of the image and will get no flexure due to mirror movement, which is always likely in a reflector.

The issue of reducer or no reducer is vexed. If your galaxy will fit on the chip at F10 (and many of them will) then what do you gain with a reducer? You get no more photons from the galaxy when you put the reducer in, you just pour them onto fewer pixels. A better way to work would probably be to bin your pixels 2x2 at F10. You have to be careful when saying 'F6.3 is faster than F10.' On a small target which you can cover at F10 it isn't. This is called 'the F ratio myth' and causes quarrelsome exchanges on forums! 

Cheers,

Olly

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This is a fascinating thread.

How much does the added aperture of say an 8" sct offset the fact the optics are much slower (f/10) compared to say the smaller aperture of an 80mm f/6 refractor?

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This is a fascinating thread.

How much does the added aperture of say an 8" sct offset the fact the optics are much slower (f/10) compared to say the smaller aperture of an 80mm f/6 refractor?

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Oh no! That's the terrible question! I wouldn't ask it in that form. It's better to ask what telescope is best for what object and that comes down, firstly, to focal length. Pick a focal length that will frame the object nicely. Now that you've done that, pick the fastest focal ratio you can at that focal length. (This simply means pick the biggest aperture, of course.) In reality amateurs can expect to put up with slower and slower F ratios as their focal lengths go up because they just can't afford, or afford to mount, apertures vast enough to give fast F ratios at long focal lengths. 

At some point in all of this you have to decide that your focal length will have to stop 'here' because you simply can't afford the aperture needed to give a bearble F ratio.

The trouble with sticking doggedly to the virtues of fast F ratio comes when, instead of adding more aperture to get the speed, you start reducing the focal length. Is this worthwhile? In my opinion it depends on whether or not you are going to be filling the chip with empty background sky or with more object or objects of interest. If all you are going to do is make a small object smaller I can't see the point. If you are going to pull in more object then yes, you will get a good image faster.

Olly

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Well... A very interesting thread indeed! I asked the question at the beginning of the year: what scope shall I get to image galaxies. The overwhelming response was a Celestron 8" EdgeHD. So, I got one. It's running on my HEQ5-Pro mount. The great thing is... It all works! I have no (well, little) trouble with 1200s subs and could go longer I'm sure. I tried with a finder guider, but that was a complete waste of time, so bought the Celestron OAG. The guide camera is a QHY5-II and so far, I have found a guide star relatively easily. It's not nearly as simple as the finder guider / 80ED setup, but that's no surprise. The important thing is, it works. The issue is the weather! Very few chances to use everything...

So, it is possible and I'm sure that the C9.25 would work fine, but definitely get the OAG. It's not easy and I only have one passable DSO image and many poor seeing Jupiter attempts to show for it all so far. The learning curve has been steep and bumpy. However, I now feel that I'm in a position to start working properly and gather some good data to make some decent images.

Oh, I currently use a DSLR, so things are even trickier, but we don't do it because it's easy!

One other thought - apparently the correct distance to the chip is essential, so make sure that is taken into consideration - I have the reducer, but can't use it as I can't get the right spacing with it until I purchase an adapter that is not yet available in this country... Will be soon!

Anyway, good luck and I look forward to hearing how this progresses. I am also interested in what the alternative scope recommended is. I went for the SCT as I didn't want diffraction spikes...

Great post, thank you. I'm pleased to hear that the QHY5-II works well. I've just replaced my QHY5 with the 5L-II as I couldn't get a guidestar in my OAG (with a C11 and Antares focal reducer).

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I have only just got to grips with my C11 and guiding and a new modded 600D and the image i'm posting is not anything to write home about more this is a starting point things can only get better, the Scope is a C11, guided by a Lodestar in a Finder Scope, DSLR Modded Canon 600D setting were ISO 1600, 8 X 180 second.

M3 

m3-600D-120-600a.jpg

Edited by Tinker1947

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It's interesting, that as I read this thread, I've been playing with my 314 on the back of my C9.25 with a view to imaging some of the spring galaxies.

Perhaps we should have a thread on 'Images I've taken that really shouldn't have worked'......

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Gav,

I use a T-Ring and Antares 2inch adapter attached to a Celestron 0.63 focal reducer and field flattener.

It's the OAG that creates the problem - it takes up too much space. I can use the flattener with the t-adapter and all is fine, but it all goes too long when using the OAG. Good thing is, I don't really need the flattener... It's working at full focal length and I'm in good and close with round stars. There are plenty of other problems to overcome (accurate focus, clouds and correct sub length to maintain colour being the current list toppers) but it works and when the adapter arrives I can use the flattener too and move to targets that need that set up.

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Hi Guys,

thank you for all your views and opinions. I've been trying to read them all via my phone but I will take a closer look from my PC. I will Just to give you a little more insight as to who I am and my set up.

I purchased my 1st scope in October 2012 and started to take my 1st images with a DSLR around 12 months ago. The reason I'll telling you this is just to clarify I'm still very much a novice and don't always fully

understand what dovetails with what and what equipment is best suited for different objects. A few people have questioned my mount, so I will list my equipment just to clarify.

DSO set up.

1. Permanent pier.

2. Avalon Linear fast reverse mount.

3. Skywatcher ED 80 refractor.

4. Atik 4900 mono camera.

5. Atik electric filter wheel.

6. Skywatcher travel star guide scope.

7. Lode star guide camera.

8. Windows 8 laptop.

Planetary set up (as from last month)

a. C9.25 (the non Edge version)

b. Skywatcher Crayford focuser.

c. Skyris 618 colour camera.

Possible DSO set up with the SCT.

1. Permanent pier.

2. Avalon Linear fast reverse mount.

3. C9.25 (the non Edge version)

4. Skywatcher Crayford focuser.

5. Atik 4900 mono camera.

6. Atik electric filter wheel.

7. OAG???????

8. Lode star guide camera.

9. Focal reducer?????

10. Windows 8 laptop.

As I've said, I do need to read all of the views and opinions a little more closely, but thank you again and if any of the additional info above can help, please feel free to keep them coming.

Regards,

Darren

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