Imaging scope advice

[Shiinsuh]

Hi all. After my lack of success with my current two scopes and people contently stating that my Celestron C130 Mak is just not cut out for imaging with my DSLR at its F/15, I am looking to buy a new scope after the holiday season, purely dedicated for imaging DSOs.

I have been drawn to the Skywatcher QUATTRO-8S (steel) f/4 but I am unsure if this is a good scope for what I want to do and also if its the best option as for the same price I could get the bigger aperture but slightly slower Skywatcher EXPLORER-250PDS f/4.7. Dose the f/0.7 make all that much difference? Is the quality of the Quattro's optics better? I also remember reading somewhere that the Quattro dose not need a coma corrector is this true?

There are many questions about comparing the two scopes, id appreciate any input.

If there are any other alternatives out there for around the £400 mark id be happy to look into them and consider them.

Thanks

[swag72]

How about the Skywatcher ED80? This scope is a great DSO scope and is the basis of many peoples rigs. You can also get the reducer that works well.

If you've not already done so have a look http://www.12dstring.me.uk/fovcalc.php to really get your field of view clear in your head.

[MiguelMJr]

I give my vote to the SW ED80. You will love it.

Miguel

[Shiinsuh]

What sort of exposure times / amount of subs is there with the SW ED80 compared to the two scopes I listed are they close to each other or is the ED80 faster / slower? (camera is an unmodified canon 600D)

Also the FOV calculator is a nice tool, however looking at it. if I was to use the reducer for the ED80 I would get very small resolution for most things due to the sensor being so big on the DSLR

[iksose7]

Yup, i think a refractor like the ED80 would be much better for getting started in imaging. Putting it simply it will be easier to use, maintain and give you great results with the DSLR.

Callum

[swag72]

Your exposure times are going to be limited by your mount rather than the scope. For example I do 30 minute exposures with both my 85mm refractor and my 8" RC.

What mount do you have?

[michael.h.f.wilkinson]

A short frac is much more forgiving in terms of guiding errors and polar alignment. It doesn't need collimating either. Especially with a focal reducer, the ease of use of a small frac much greater than that of a Newtonian (which will need a coma-corrector as well).

[themos]

Congratulations Sara, by the way, on making Sky at Night last night!

[Shiinsuh]

Your exposure times are going to be limited by your mount rather than the scope. For example I do 30 minute exposures with both my 85mm refractor and my 8" RC.

What mount do you have?

I have a decent(ish) mount, the Celestron CG-5 GT and I have a guide scope too so its not keeping on the starts that will be the problem, mainly just the camera getting hot.

A short frac is much more forgiving in terms of guiding errors and polar alignment. It doesn't need collimating either. Especially with a focal reducer, the ease of use of a small frac much greater than that of a Newtonian (which will need a coma-corrector as well).

I already knew I would need a coma corrector for a Newtonian. Ease of use isn't really something that concerns me I have the patience to learn and fiddle with things.

As for guiding errors and such, I do have a guide scope so those should not be much of an issue.

I'm looking for a scope with the most bang for your buck. something that will last me while I slowly upgrade other parts as funds come available as this hobby isn't cheap (dedicated guide camera, then better tripod, then CCD) before I would need to look at getting a better scope.

Regards

[swag72]

I think your mount is similar to the EQ5 from Skywatcher?

[michael.h.f.wilkinson]

I would say the Newtonians you are considering are too heavy for the CG-5. Guiding is a problem for longer focal lengths, and even the much heavier EQ6 could have difficulties at 1m focal length and over (guide scope or no).

[Chris]

The Quattro will most certainly need a coma correcter, a good one at that. At f/4 collimation is super critical. Its not too difficult to collimate initially with the correct collimation tools but its keeping it there thats the problem.

Metal tubes at f/4 are hard work as the expansion over the time of imaging will be enough to put collimation out at f/4. I would think twice before having another one! I'd have the carbon fiber version but they are more expensive.

The most important thing for imaging is the mount, and you have a goto CG5 which is quite light duty. I would stick to very light scopes with short focal lengths so you can accurately track for as long as possible. My C8 has a long focal length and I only get 30 seconds unguided on a Belt modded NEQ6, where' as my little short frac will do 3 minutes! 

Something like the skywatcher 130pds or ED80 would be good

[Shiinsuh]

I think your mount is similar to the EQ5 from Skywatcher?

Yeah, the CG-5 is the same basic mechanics / build as the EQ5

I would say the Newtonians you are considering are too heavy for the CG-5. Guiding is a problem for longer focal lengths, and even the much heavier EQ6 could have difficulties at 1m focal length and over (guide scope or no).

I the CG-5 has a weight capacity of around 7kg for imaging (including counter weight) and a maximum weight capacity of 10kg (visual) and the QUATTRO-8S is 10kg. So you are right about it being too heavy.

The Quattro will most certainly need a coma correcter, a good one at that. At f/4 collimation is super critical. Its not too difficult to collimate initially with the correct collimation tools but its keeping it there thats the problem.

Metal tubes at f/4 are hard work as the expansion over the time of imaging will be enough to put collimation out at f/4. I would think twice before having another one! I'd have the carbon fiber version but they are more expensive.

The most important thing for imaging is the mount, and you have a goto CG5 which is quite light duty. I would stick to very light scopes with short focal lengths so you can accurately track for as long as possible. My C8 has a long focal length and I only get 30 seconds unguided on a Belt modded NEQ6, where' as my little short frac will do 3 minutes! 

Something like the skywatcher 130pds or ED80 would be good

Ahh, that's something to keep in mind then, I did not know that collimation would become such an issue. It sounds like it would need collimating each use once it had cooled down?

I already have a SW 130mm Newtonian, but its doesn't have enough back focus, thus iv not been able to try it for imaging otherwise it would give me a better understanding of imaging with Newtonian.

Thanks for the comments / feedback

[swag72]

Personally I wouldn't contemplate anything other than a light scope for the mount that you have. While you may have patience, I think you are in danger of throwing away loads of subs. Folks always say that they do OK with their EQ5's..... but they are quick to change them to an HEQ5 if given a chance

Have you read the book Making Every Photon Count? A good read for imaging. It's really all about the mount. Don't get sucked into bigger is better when you are using an EQ5 variant ....... in my humble opinion.

[michael.h.f.wilkinson]

It is not just the weight of the imaging rig that is key, the torque exerted by longer and wider scopes is an issue too. The aperture of an 8" Newtonian will act as a sail if the wind gets up, and cause all sorts of shaking that a lighter mount cannot easily damp out. Most DSO imagers go for an HEQ5 with small frac as starter set for these reasons

[happy-kat]

The smaller 130p-ds is lighter.

Why not move the primary mirror in your 130p so you can try it?

There are threads on here by members who have done it.

If it is back focus have you tried an extension tube?

[Chris]

The smaller 130p-ds is lighter.

Why not move the primary mirror in your 130p so you can try it?

There are threads on here by members who have done it.

If it is back focus have you tried an extension tube?

This is a good idea. You can use longer bolts and springs for the primary mirror, or place a plywood disc behind the primary mirror and have longer bolts for the mirror clips.

If you don't fancy the DIY then a 130pds imaging newtonian is only 165 quid.

[michael.h.f.wilkinson]

The 130M listed has 900mm focal length, and may be a bit slow and has rather a long focal length for the mount. It might be worth a shot, of course

[Chris]

The 130M listed has 900mm focal length, and may be a bit slow and has rather a long focal length for the mount. It might be worth a shot, of course

This is a good point which 130 do you have? f/ratio?

[Shiinsuh]

Personally I wouldn't contemplate anything other than a light scope for the mount that you have. While you may have patience, I think you are in danger of throwing away loads of subs. Folks always say that they do OK with their EQ5's..... but they are quick to change them to an HEQ5 if given a chance

Have you read the book Making Every Photon Count? A good read for imaging. It's really all about the mount. Don't get sucked into bigger is better when you are using an EQ5 variant ....... in my humble opinion.

I understand that bigger don't always mean better, but larger aperture means more light gathering and thus my original thoughts on what scope to get. I also know that when imaging its all about the mount. it is my intention to get a HEQ5 when I can, but I do need a scope in the meantime.

It is not just the weight of the imaging rig that is key, the torque exerted by longer and wider scopes is an issue too. The aperture of an 8" Newtonian will act as a sail if the wind gets up, and cause all sorts of shaking that a lighter mount cannot easily damp out. Most DSO imagers go for an HEQ5 with small frac as starter set for these reasons

That's a valid point! Something to consider.

The smaller 130p-ds is lighter.

Why not move the primary mirror in your 130p so you can try it?

There are threads on here by members who have done it.

If it is back focus have you tried an extension tube?

The scope I have, the SW 130M I have already moved the mirror in as far as it goes so not much else I can think of doing. I also cut down the focuser too. these mods got me with in a few mm of being in focus but I just cant get any more unfortunately.

An extension tube would not help as I need to get closer the the primary not further away

This is a good point which 130 do you have? f/ratio?

I have the SW explore 130M 900mm f/6.92 (the old blue one not newer black one)

[Chris]

I understand that bigger don't always mean better, but larger aperture means more light gathering and thus my original thoughts on what scope to get. I also know that when imaging its all about the mount. it is my intention to get a HEQ5 when I can, but I do need a scope in the meantime.

That's a valid point! Something to consider.

The scope I have, the SW 130M I have already moved the mirror in as far as it goes so not much else I can think of doing. I also cut down the focuser too. these mods got me with in a few mm of being in focus but I just cant get any more unfortunately.

An extension tube would not help as I need to get closer the the primary not further away

I have the SW explore 130M 900mm f/6.92 (the old blue one not newer black one)

If you have some travel left on the primary mirror clips of the mirror cell you can place a disc behind the primary thus pushing the mirror even further forward. But to be honest its still quite long at 900mm for someone starting out.

I think you would be better off spending the 165 quid on the 130pds 650mm f/5. 

[Shiinsuh]

If you have some travel left on the primary mirror clips of the mirror cell you can place a disc behind the primary thus pushing the mirror even further forward. But to be honest its still quite long at 900mm for someone starting out.

I think you would be better off spending the 165 quid on the 130pds 650mm f/5. 

The 130pds is cheap indeed, but I don't mind paying extra for the 80ED if it would yield better results. The 80ED is also lighter and smaller too which would work out better on the mount it would seem from what people are saying.

[Chris]

The plus points for the ED80 are that its easy for for beginners as you don't tend to need to collimate a frac, so its more plug and play. The down sides are that its more expensive and a bit slower f/7.5 natively or f/6.3 with the reducer flattener. 

The plus sides for the 130pds are its cheap, fast at f/5 natively so more signal per unit of exposure time. The downside is that it will need collimating once and a while, but probably only of you knock it. 

I've imaged with both and they are both very good, you can't go wrong with either

Check out SGL member Uranium235 pics using the 130pds before you decide.

[Shiinsuh]

The plus points for the ED80 are that its easy for for beginners as you don't tend to need to collimate a frac, so its more plug and play. The down sides are that its more expensive and a bit slower f/7.5 natively or f/6.3 with the reducer flattener. 

The plus sides for the 130pds are its cheap, fast at f/5 natively so more signal per unit of exposure time. The downside is that it will need collimating once and a while, but probably only of you knock it. 

I've imaged with both and they are both very good, you can't go wrong with either

Check out SGL member Uranium235 pics using the 130pds before you decide.

Wow some really lovely pictures Uranium235 has with the 130pds (obviously I wouldn't get that sort of lovelyness due to not currently having a modified dSLR or CCD) nevertheless the £150 saved from not getting the ED80 could be spent on getting a cheap astro-modded dSLR or putting towards a CCD.

It would be interesting to hear other people's opinions regarding the SW 130pds opposed to the SW ED80.

thanks for the additional food for thought starfox. 

[swag72]

The ED80 will be as plug and play as you can get - It depends I suppose on how important that is to you. Rob takes stunning pics with his 130 pds, I think he's had to make some modifications to get to this point. 

If you are fine with tinkering, then the 130pds will hold no fear for you