Which refractor would you choose and why?

[Iandmr]

Please be patient with me as I have never looked through a telescope and everything I have written is only supported by what I think I understand after reading a lot of information online. My understanding could be incorrect, the information I have read may be inaccurate or both!! Guidance is very welcome.

I have just bought a Rowan modified HEQ5-Pro mount and I would now like to buy a 3-4 inch refractor to go with it in a few weeks time. I hope that  a 3-4 inch refractor would allow me to do some casual observing from time to time with friends and family but really I am more interested in dipping my toe into astrophotography and then developing that hobby over the months and years ahead. I wondered if anybody had an opinion on the telescopes I am considering at different prices. A cheaper scope would allow me to buy a better camera to start with although I would expect, if I enjoy good success with the challenges posed by imaging, to be able to upgrade a cheap camera before the end of the year. Here is my shortlist which I have arrived at with the stipulation that the scope must be about 5-6Kg or under (for imaging on the HEQ5-Pro which has a limit of about 8-10Kg for astrophotography) and contain FPL53 glass to help with CA.

William Optics Zenithstar 81 with the 0.8x field flattener/reducer. The aperture is 81mm and the focal length is 559mm allowing hopefully decent solar system observation with up to 160x magnification. WO has a decent reputation and the scope has been well regarded for quite some time. This is the cheapest option and it would allow me to spend about £400-£500 on a starter astro camera for planetary work and a good range of DSO. I would be able to buy a few decent Vixen SLV eyepieces and a Tele Vue barlow to get me going so this would be a decent starter setup but with the cheapest scope.

Starfield 102 ED with the 0.8x field flattener/reducer: The aperture is 102mm and the focal length is 714mm offering slightly better (and more flexible) observation because of the larger aperture. I have sometimes read that apertures less than this do not give satisfactory viewing but opinions vary. This scope is just a little bigger and heavier than the ZS81 but negligibly so I suspect in practice. The extra cost really means a little extra aperture I think as I expect the optics and build quality to be the same as the ZS81 but I could be wrong. The budget for an astro camera may be similar to the budget for the ZS81 but I would need to rethink the eyepieces and/or barlow to do that. Matching a camera to the Starfield may be a little harder as the focal length is longer and I believe that some cameras paired with the Starfield/reducer may result in oversampling (according to online calculators anyway). This may be not an issue in practice of course!

William Optics GT-81 IV with the 0.8x field flattener/reducer. The only triplet and so presumably the best optically and certainly the most expensive. This scope has been around for a long time and seems to be consistently well regarded. It has the shortest focal length at 478mm and is commensurately the 'fastest' scope at f/4.72 with the reducer. It would seem that this is the best suited to astrophotography with less time needed for exposures although I feel the other two would be very capable. I would really only be able to start with something like an ASI224mc astro camera (which seems odd given the cost of the mount and scope) allowing me to literally learn astrophotography technique but on a very limited range of targets. Astrobin does have some examples of good work with the ASI224mc so it may not be a truly terrible option if it means a better scope. I would be able to at least get going though and would seek to upgrade the camera as soon as funds allow; at least I would have a mount and scope that would not need to be upgraded for some time. I would only be able to buy one eyepiece and barlow to begin with but that would change over time.

I have already budgeted for a WO dielectric diagonal and a dew heater and I am aware that some software such as PixInsight can be expensive but there is a lot of very well regarded free software available which is brilliant! The other potential extras much further down the line certainly can add up such as an electronic focuser, electronic polar alignment, a guide scope and camera and well, it is a long list!

So, I have three well regarded scopes at different price points.

Am I misunderstanding or underestimating anything?

Which of the three options would you take and why?  

[Elp]

It's actually refreshing to see that you've actually spent some time looking into equipment as many don't, and the choices you've narrowed down show this. You can't really go wrong with either.

Something you have to consider, are you primarily going to image or view? I ask because if your hearts set on seeing solar system objects a longer focal length helps, but this will affect your ability to frame a lot of emission targets well though the longer FL helps with galaxies as most galaxies are tiny.

Another thing to note is have you tried a telescope simulator like Telescopius website to frame a few targets as this will have a huge weighting on which one you decide to go with, you will however need to narrow down your camera in order to complete this process. The 224 is a decent planetary camera but that's all it's really useful for other than autoguiding. Some people have managed DSO imaging with it but the sensor is so small that it's difficult as it also amp glows quite bad during long exposure likely also due to the small sensor making the effect worse. A better astro choice would be a 385/485/585 sensor, or if you have a camera body at hand use that. I've used the 485 for planetary and long exposure DSO perfectly fine.

The triplet scope will be the best corrected for imaging, especially if star sizes are likely to be an issue for you, if not a doublet will be fine (well one of the ones you've narrowed down anyway).

I have a Z61 and Starfield 102 so know their qualities, both are excellent scopes. If I had to choose again from the beginning I'd likely still do the same, get the Z61 first. Short FL imaging is more forgiving than long FL, your guiding doesn't have to be as good but for both you'd really need autoguiding and a computer controller to manage it all. The WO Redcat is also a good starter scope but I believe you can't use it visually so I'd still go for the Z61. I've seen Jupiter and Saturn with it, though they were tiny you could still see some banding detail because the optics are sharp, anything I've done with the scope it has excelled with, visual/imaging, planetary, lunar, solar (both white light and HA), DSO.

All three scopes you've looked at would be good, but do check framing. I find my SF 102 is a bit of an odd FL, it'd be fine on some galaxies but not long enough for a lot of them, and it's too long to fit a lot of emission nebulae so I'd have to mosaic which adds to the project imaging time, so I don't use it too often for imaging.

Another suggestion would be if you already have a camera body and lens at hand try using that. You'll be surprised how much you can image with them. In fact one of the best pieces of AP equipment out there is not a telescope it's the Samyang 135mm F2 manual lens.

 

[Cosmic Geoff]

I'd just comment that while any of the telescopes mentioned may be fine for deep space astrophotography they are on the small side for visual use on planets.  An 8" Newtonian (not a big expense on top of what you are spending already) or an 8" SCT would give better views.

I also second Elp's comments about the ASI224MC.  I have used one for deep-space imaging (EVAA style) but only because I already owned it.  A DSLR camera body (if you have one) would be more suitable.

[Iandmr]

13 minutes ago, Elp said:

It's actually refreshing to see that you've actually spent some time looking into equipment as many don't, and the choices you've narrowed down show this. You can't really go wrong with either.

Something you have to consider, are you primarily going to image or view? I ask because if your hearts set on seeing solar system objects a longer focal length helps, but this will affect your ability to frame a lot of emission targets well though the longer FL helps with galaxies as most galaxies are tiny.

Another thing to note is have you tried a telescope simulator like Telescopius website to frame a few targets as this will have a huge weighting on which one you decide to go with, you will however need to narrow down your camera in order to complete this process. The 224 is a decent planetary camera but that's all it's really useful for other than autoguiding. Some people have managed DSO imaging with it but the sensor is so small that it's difficult as it also amp glows quite bad during long exposure likely also due to the small sensor making the effect worse. A better astro choice would be a 385/485/585 sensor, or if you have a camera body at hand use that. I've used the 485 for planetary and long exposure DSO perfectly fine

 

Thank you for you kind introductory comments. I have tried to read as much as I can. 

You make an excellent point regarding framing and I have used Telescopius and Astonomy.tools with different combinations of telescope, camera and target to see what the outcome is. In truth I think I have tried the same combinations several times as I have played with the tools so much I forget what I have tried before! I will definitely use both tools more once I think I have made a decision on the scope. Thank you for pointing out the astro cams. I have tried the 585 a few times in the tools and done some further research on that model as it seemed promising. I notice ZWO have released a cooled version that is more expensive. The amp glow with the 224 is noteworthy too.

Again, many thanks for your help.

 

[Iandmr]

15 minutes ago, Cosmic Geoff said:

I'd just comment that while any of the telescopes mentioned may be fine for deep space astrophotography they are on the small side for visual use on planets.  An 8" Newtonian (not a big expense on top of what you are spending already) or an 8" SCT would give better views.

I also second Elp's comments about the ASI224MC.  I have used one for deep-space imaging (EVAA style) but only because I already owned it.  A DSLR camera body (if you have one) would be more suitable.

Thanks for confirming that all three scopes would be fine for imaging. That's helpful and reassuring.

I will primarily want to image and hope the hobby will provide lifelong learning. It would be great to drag out others on a nice night with good seeing to look at the moon though or anything else that is accessible but that would be a tangential benefit rather than the deciding factor. A dob or SCT, for example, would definitely provide a much better visual experience for less money I think and maybe a long time into the future I might add one but all things considered a 3-4 inch refractor seems a better entry point for me into astrophotography.

I don't own a camera although my wife has an old lumix that I think was quite expensive at the time. I'm not sure if that would be useful?

[Bivanus]

Welcome ! All the above advices are spot on. Personal favourite from the three OTA's listed would be the WO Zenithstar 81, it is in my opinion the best bang for buck AND let's you some monetary leeway in either getting a better camera&accesories and/or an aditional OTA for visual ( again , purely personal preference - I would choose a MAK over the SCT since I'm guessing you'll go 5-6" rather than the 9.25" and upwards from where the SCT rules)

However , since you tell that AP would be the main interest , the ZWO ASI585MC would be very good for both planetary and beginer AP and / or EAA. If I was to choose , I would rather choose to buy the ZWO ADC too rather that going for the cooled PRO model . Being in a similar position of not being able to get too many nights in arow , I've slowly but surelly come to understand why the ADC can do the difference.  

Regardles what you chose , remember the old saying: the best telescope is the one you actually use 😊

[Iandmr]

That's great advice and so helpful. I have a feeling that the ZS81 provides the best value and your comments support that so it's a good start! You also point out that the extra resources left by going for the ZS81 allow better options for the camera etc I mentioned above that I had had spent some time looking at the 585mc so it is nice to find experienced members referring to it as a decent option in the price range.

Nice call on the additional scope for visual. I'd certainly want to give a MAK some thought. It would be nice to just have one of everything!!

[Giles_B]

I think the "just one of everything" option is unfortunately  never quite achievable - I speak from experience having started with a 10" dob and tried and failed to adapt it to other uses. I haven't got the experience at astrophotography to choose between the refractors you've researched - they all look decent - and a 585MC will be a good camera to start out your journey with, but in the long term expect to end up with a few telescopes that are suited to different jobs.

This can be a bit overwhelming when you start out, but just take things slowly and don't expect to get everything in one fell swoop. Think of it like getting a really good toolkit (or a library if you're more cerebrally inclined) - you can't get the lot all at once, because you only know what gaps you need to fill through experience. But what you've planned will get you off to a great start!

[bosun21]

To me it boils down to how much visual do you want to do in relation to imaging? If you intend to set up often to allow the family to observe with you then I would definitely go for the Starfield 102. If however you intend to be imaging the majority of the time and are serious about the hobby then go for the triplet. Camera wise I would be looking at something like the 585MC. Good luck with whichever you decide.

[Iandmr]

Thank you for your input above Giles_B and bosun21.

There is some good guidance overall so far here that points towards the 585MC as a good astro camera to start with. That is helpful to know and it appears to work well with the shortlist of scopes. As the observational use with the scope would be very occasional it seems as though it might not be that sensible to consider the Starfield 102 over the ZS81 as the extra investment seems to be more beneficial for more frequent visual use. There appears to be a consensus that the ZS81 would be a decent first scope for astrophotography alongside the HEQ5-Pro and 585MC although the GT81 would be better. It is, of course, very hard to weigh up whether the improvement moving to a triplet is worth the extra cost and especially when this would be my first step into the hobby. And the savings can be used for other things when the time is right. Does anybody have experience of using both the original ZS81 and the GT81 IV?

[Elp]

For your usage scenario I don't think there's any reason other than budget to consider the Z81 over the GT81.

Just a note on the 585, it's a 16:9 wide-screen aspect ratio so you might find the height lacking, I certainly did when I had the 485 but then again I am used to slightly larger sensors, you can always mosaic if you need to.

Ref larger aperture, they collect light quicker due to more area, with the associated longer focal length you will also resolve slightly more detail.

[AstroMuni]

1 hour ago, Iandmr said:

It is, of course, very hard to weigh up whether the improvement moving to a triplet is worth the extra cost and especially when this would be my first step into the hobby

You have done a lot of research and you should be able to enjoy with either of those scopes. Just out of interest was there a reason you ruled out reflectors?

[Mr Spock]

If you are doing visual then you'll want the 102mm. Going from 80mm to 100mm is quite a big step in terms of planetary observing.

[Iandmr]

3 hours ago, Elp said:

For your usage scenario I don't think there's any reason other than budget to consider the Z81 over the GT81.

Just a note on the 585, it's a 16:9 wide-screen aspect ratio so you might find the height lacking, I certainly did when I had the 485 but then again I am used to slightly larger sensors, you can always mosaic if you need to.

Ref larger aperture, they collect light quicker due to more area, with the associated longer focal length you will also resolve slightly more detail.

Unfortunately I need to think about the budget as there is so much to get going forward and a more expensive scope means a less expensive (bargain basement 😂) camera. I would always pick the GT81 over the Z81 otherwise I suppose it boils down to whether the extra investment in the scope is sensible. Thanks for the information about the 585MC I have looked at the field of view in astronomy.tools with a range of scopes.

[Elp]

The Z81 will be fine otherwise, take a look at images on Astrobin, or look at my Flickr profile for images ive done with the Z61 for an idea, the Z81 will be better resolved.

[Iandmr]

1 hour ago, AstroMuni said:

You have done a lot of research and you should be able to enjoy with either of those scopes. Just out of interest was there a reason you ruled out reflectors?

I like the fact that a refractor is more beginner friendly as there is a little less to worry about (collimating and temperature change for example) and a refractor is easier to get out and store, albeit there are some good examples of easy to handle reflectors of course I believe. I think a refractor might have the edge for DSO astrophotography as they are a little easier to guide, although again I expect that can depend on the scope.

[Elp]

Just now, Iandmr said:

refractor might have the edge for DSO astrophotography

A reflector will be much faster due to the larger aperture, but yes, the box dimension size can be an issue.

[Iandmr]

Hi Michael, and thank you for your input on the Starfield 102 there is something about that scope! I understand it has many advocates and punches above its price when it comes to performance. I certainly haven’t ruled it out!

[Iandmr]

Thanks again Elp and will check out the photos 😀

[Earl]

if your looking at imaging, consider what is the best match for the camera you are going to use... yes this can be a circular issue however its best to think about it at the same time to make sure nothing causes potential issues further down the line.

[Iandmr]

Thanks again Elp and will check out the photos 😀

[Iandmr]

Earl, thanks for the heads up. I am going to get some more advice on the camera although I think the spec on the 585MC is a decent match for all the scopes I have listed. I thought a while ago, when my research started, that the Astro camera would be somewhat simple to decide upon. I thought it would be more about price. Like many things in the hobby, it is much more complicated (and interesting) than that.

[Iandmr]

8 minutes ago, Elp said:

The Z81 will be fine otherwise, take a look at images on Astrobin, or look at my Flickr profile for images ive done with the Z61 for an idea, the Z81 will be better resolved.

Just had a look and there are some fantastic images. If I can ever get even close I’d be delighted. I notice that you have a lovely image of Jupiter taken with the Z61. I wouldn’t have expected it to look so good with the Z61. Thanks for the viewing invite.

[Elp]

1 hour ago, Iandmr said:

lovely image of Jupiter

Thanks, it was an early test (I don't spend that much time on planetary but might return to it when they pop up again later this year). Visually it's even better, though quite tiny in the Z61.

[900SL]

100mm aperture / 700mm fl is longish to start imaging with, but a nice place to be for visual.

If you are more likely to be imaging, then The GT81 would be a good scope, I have the GT71, a nicely corrected triplet, FPL53. The Stella Mira 90mm f6 would also be a good scope for imaging, pretty fast with a 0.8 reducer. Doublets typically can show some CA when imaging, but are lighter, and cool down faster. 

You will need a guide scope and guide camera if imaging, at these focal lengths and with a HEQ5 mount

 

Edited May 7 by 900SL