24 replies to this topic

[Spaceorion]

Hello everyone,

After a long pause (9 years), my commitments allow me to get back into the hobby of astrophotography!

 

I've got a Skywatcher Equinox 120ED (900 FL), AM5 ZWO mount and will be using a DSLR Canon EOS500D to start off with.  If all goes well, I'll be changing to a dedicated CCD cooled camera.

 

My main issue right now has to do with selection of a suitable guide scope and guide camera. I've done a lot of research on the topic, seen a lot of videos from popular youtubers, but there seems to be a lot of contradicting information that's only making things more confusing for me.

 

My understanding is that there is a general rule of thumb that the guidescope should have a focal length (FL) 1/3 of the primary imaging scope. In my case, this is 300mm since the imaging scope has a FL of 900mm.

 

I've also read that today's advanced guide cameras change these rules, allowing us to use guidescopes with shorter focal lengths, but this is after taking into consideration all your equipment according to Astronomy tool's guidescope suitability calculator (https://astronomy.to...ope_suitability), where the  imaging/guiding ratio should be kept to as close to 1:3.

 

My question is what would be the best guidescope/guide camera for my current setup?

 

I'd also like to take into account that I'm likely to switch from DSLR to CCD (colour) imaging later on. Possible recommendations I've seen from youtube videos include the ASI 120mm and ASI 220mm, but I'm not sure what would be the most ideal guidescope.

 

If you have a similar setup, I'd really love to hear about your experience and recommendations as I don't want to end up wasting money on something that either won't work for me or is an overkill.

 

To help further, I'm considering of setting a budget of around $750AUD and do not mind purchasing second-hand equipment.

 

Thank you very much and I look forward to your replies!

Chris.

[jlinsobe]

The 120/220 mm are monochrome guiding cameras.

I’d say get the 220mm or 290mm.  The format is optional, whether mini or standard.  I prefer standard.

 

My biggest refractor is a 103Z by William optics and I use the 50mm f/4 guidescope and the flat 6aiii (0.8).  It works fine.

My camera is a 294mc pro.  Not the latest but it’s quite alright.

Edited by jlinsobe, 06 May 2024 - 10:27 PM.

[PIEJr]

Hi Chriss!

Welcome back to the Black Hole of AP.

 

I running an AT 130mm EDT. I jumped up from a ED80mm T CF.

Not long ago I decided to upgrade my guide scope to a 60mm to go with my ASI 290 MM guide camera (Mini)

I chose the 290 for it's higher resolution. (over the 120MM)

So, while my 240 FL in the guide system is a tad below 1/3 of my 910mm main telescope, everything is working very well together.

I think the 60mm guide scope gives a better balance with the larger 900 FL refractors.

If I could have found a 70mm guide scope, I'd have had that.

[jml79]

The old rules don't really apply as much any more. I guided for almost 2 years using a 30mm guide scope and an SV105 web camera and it will guide my rig as low as 0.6 arc seconds reliably. So you likely don't need as much as you think. But if I wasn't going to use the OAG's that I use now and wanted bulletproof guiding I would likely go with a 290MM and a 50mm or 60mm guide scope like the SV106/60mm. It should be far under your budget and offer great guiding. I find the 2.9um pixel size a very nice balance between sensitivity and resolution. If you were using a smaller scope (102mm or so) with a reducer I would recommend the same camera and the smaller SV165 30mm guide scope. If you were jumping right into an astro camera I would recommend the 120MM or 220MM and an OAG. I currently run an ancient (and not very sensitive or good) Orion SSAG and an OAG on one scope and a Ceres-M (120MM equivalent) with an OAG on the other scope and love them. But on my EAA mount, I still use my 30mm mini scope with either the ultra cheap SV105C or my SV705C (IMX585) which are both colour cameras with 2.9um pixels and they work great.

Edited by jml79, 06 May 2024 - 11:46 PM.

[Mark Lovik]

I have used an FMA180 and ASI178mm combination.  This works well guiding all sizes of scopes - and it has flexible, lightweight, and stable options for mounting on a scope.  It also does well for widefield imaging.

[Juno18]

I just moved to an ASI220mm mini from an Orion SSAG and the difference is like night and day. The 220 is MUCH more sensitive than the SSAG. I only occasionally saw multiple guide stars in PHD2 with the SSAG and see 8+1 consistently with the 220mm mini and that is still the case after moving to an oag.

I also use a ASI120mm mini/30mm ZWO mini guide scope on my 275mm Sharpstar refractor and it works well in a wide field setup.

 

If you plan to go with an oag in the future, the 220mm mini is a great choice, and a good match for the ZWO OAG.

[Oort Cloud]

I've been doing this for a while, so if you ask me, the best guidacope is an off-axis guider.

It is a bit more complex, so not the best solution for everyone, but once you get it working, it's fantastic. No concerns with guiding vs imaging scale, and no concerns with flexure, regardless of what style of OTA you mount it to.

When you want to switch OTA, just unscrew the entire image train, including the OAG, and move it to your other OTA. Easy peasy.

[Spaceorion]

Firstly, I'd like to thank everyone who has taken the time and effort to reply. It's truly amazing to see so many passionate people willing to share their experiences and knowledge!

 

After reading everyone's response, it seems like a 60mm guidescope (svbony that most recommended), alongside with an ASI220mm or an ASI290MM is the best solution for me right now.

 

To touch on the OAG recommendations from Oort Cloud, Juno18 and jml79, I must admit that I was considering OAG to start off with, but after a lot of research, I understood that it got more complicated because I'm starting with a DSLR camera, and if I was to change to a dedicated CCD, I would then likely need to change the OAG as well and this would prove to be an expensive exercise. I therefore decided to stick with the more simple and cheaper approach of getting a 60mm Guidescope and camera. 

 

The other issue I was puzzled about with OAG, was the image circle in relation to the Telescope and current DSLR (EOS 500D), but also any future CCD camera I might upgrade to. I understand that these also need to be well balanced and taken into consideration.  At that time, I felt I was being pulled in by the Black Hole of AP PIEJr mentioned

 

If I was to move to an OAG, I definitely wanted to have a slot-in filter tray, so I can insert filters to enhance my photos, and then it got even more complicated.

 

If I can come up with an OAG setup that will work with my current DSLR and a possible future dedicated CCD (colour only! No RGB wheel etc!), then I might consider changing to AOG

 

Thanks again for your input guys and help - truly appreciate it!

 

Chris,.

[Oort Cloud]

Hey Chris, I'm sure I can speak for all of us when I say we're happy to help.

The OAG can be a bit much if you try it too early. I often forget what it was like when all this stuff wasn't second nature.

Still, even a guidescope can give problems, like flexure, so if something doesn't seem like it's adding up, be sure to come by CN and let us know what's happening. We'll be here to help whenever you need us.

[idclimber]

Like Oort I have moved on to an OAG, but it really is only needed with the longer focal lengths, especially my 12" SCT. 900mm is on the edge of needing one. 

 

The AM5 also has unique needs for guiding that are worth mentioning as you may need to go as low 0.5" guiding intervals for the best tracking. As such I would look for a larger guide scope like a 60mm version or an OAG with a larger prism. For a guide camera I would skip the ASI120mm and use either the 220mm or the 174mm. The latter is my choice to pair with a larger prism OAG. The former for a guide scope or a small prism OAG at a more reasonable price. 

[Oort Cloud]

Like Oort I have moved on to an OAG, but it really is only needed with the longer focal lengths, especially my 12" SCT. 900mm is on the edge of needing one.

The AM5 also has unique needs for guiding that are worth mentioning as you may need to go as low 0.5" guiding intervals for the best tracking. As such I would look for a larger guide scope like a 60mm version or an OAG with a larger prism. For a guide camera I would skip the ASI120mm and use either the 220mm or the 174mm. The latter is my choice to pair with a larger prism OAG. The former for a guide scope or a small prism OAG at a more reasonable price.

I've thrown the 174 into a 30mm guidescope before. It's awesome no matter what you do with it.

[idclimber]

I've thrown the 174 into a 30mm guidescope before. It's awesome no matter what you do with it.

No doubt either will work. The 220mm has 4um pixels, the 174mm has 5.8um. The larger pixels of course increase pixel scale. This is largely irrelevant for an OAG but with a guide scope where the ratio matters the 220 is both cheaper and keeps the ratio more appropriate. This is especially true for the OP where he is already at 900mm with the main scope.

[Spaceorion]

Oort Cloud and idclimber, ok, so you've got me motivated to examine the OAG as well!  

 

One very important question here -  is there a specific OAG that would be suitable for DSLR cameras (EOS500D) and dedicated CCD cameras or will I need to change it when I switch from DSLR to a CCD camera?

 

Thanks guys.

[idclimber]

Oort Cloud and idclimber, ok, so you've got me motivated to examine the OAG as well!

 

One very important question here -  is there a specific OAG that would be suitable for DSLR cameras (EOS500D) and dedicated CCD cameras or will I need to change it when I switch from DSLR to a CCD camera?

 

Thanks guys.

A DSLR is a difficult pairing with an OAG. They consume too much backspace for most systems. 

[Spaceorion]

idclimber, agreed. I recall reading something similar elsewhere, which is why I thought it's best to move to a guidescope solution first.

 

BUT, if I was to consider a CCD colour camera, what would you guys recommend for a starter like myself?

[idclimber]

idclimber, agreed. I recall reading something similar elsewhere, which is why I thought it's best to move to a guidescope solution first.

 

BUT, if I was to consider a CCD colour camera, what would you guys recommend for a starter like myself?

There are two and only two good choices. A camera based on the IMX533 sensor or the IMX571. This is the ASI533, 2600 if you like ZWO. 

 

I think a guide scope will work fine and I would look for one at 60mm aperture. I would consider the 174mm if you are thinking longer term plans and an OAG, otherwise the 220 is a good choice and a fair bit cheaper. 

[Spaceorion]

There are two and only two good choices. A camera based on the IMX533 sensor or the IMX571. This is the ASI533, 2600 if you like ZWO. 

 

I think a guide scope will work fine and I would look for one at 60mm aperture. I would consider the 174mm if you are thinking longer term plans and an OAG, otherwise the 220 is a good choice and a fair bit cheaper. 

Thanks for the input idclimber!   Regardless which way I select to go (guide scope or OAG), I saw a video stating that the 178mm was the best camera for guiding as it provides a 6Mp resolution - would you agree or do you prefer the 174mm instead?  Also, would you select the mini or normal (larger) version that supports usb3?

 

Many thanks,

[idclimber]

I believe 178 is a now discontinued camera, at least for the ZWO version. Always use a mini if you intend to use it for an OAG. The pancake cameras sometimes won't reach focus because they can not be inserted as far as the mini. 

 

For a guide scope many cameras will work including OSC. However at 900mm and a mount that likes shorter guide intervals, you are already asking a lot from the newer 220. 

[Oort Cloud]

All good advice from Dave. I apologize, when I first mentioned OAGs; I failed to realize you were shooting with a DSLR.

 

I definitely wouldn't buy one until you're ready to buy an astrocamera, and which one I'd recommend would depend on what camera you planned on getting, as the fittings are a bit different on some of them.  I've had good results with both of ZWO's offerings, but the regular one wasn't really enjoyable to use until I put a helical focuser on it (which comes with the larger OAG-L).  As it stands now, the only one I can recommend is the OAG-L, because the regular one really needs the helical focuser and if you add the two together, it's almost the price of the OAG-L, which has a much larger prism.  The OAG-L has no threads on the camera side, so it would need to bolt to either a ZWO electronic filter wheel, or a ZWO filter drawer.  If you're using a color camera, the drawer makes the most sense as you'd ideally want a Luminance (UV&IR cut) filter, and a dual-narrowband filter.  And an extra filter holder if the drawer only comes with one, so you can keep whatever filter you aren't using, mounted.  With mono, you'd want a filter wheel, and ideally a set of filters containing: Luminance, Red, Blue, Green, Sulphur II, Hydrogen-a, & Oxygen III.  You can of course start with L, R, G, & B, which are far less expensive than S, H, & O.  When you do buy the narrowband ones (SHO), you can also start with just H, since that's what most of the universe is made of.  Sorry to get so wordy with my reply, but one of the things with this hobby is there are a lot of factors that affect each other.  Planning goes a LONG way, especially where spending is concerned.  Take your time, do your research, and keep asking questions! 

[dna.oneill]

Welcome back to AP Chris!
 

Not sure if you will be using a focal reducer/field flattener in your imaging train, if so that will reduce your FL and should make it reasonable to pair a 60mm f4 guidescope with an ASI120 mono camera. I think this would work even without the focal reducer. I’ve successfully used that combo with a 1200mm focal length setup - and it’s inexpensive!
 

[Spaceorion]

More great advice from you guys - thank you!

 

dna.oneill, thank you for the welcoming! I've decided not to purchase a focal reducer/field flattener for now, mainly because of the costs.It also seems I'm a bit limited to my options with the Equinox 120ED as there are only 2 models suitable for it (Skywatcher and some other brand I can't recall).

 

Nevertheless, Oort Cloud, you're right about the OAG - the Large version is the only one that makes sense, but as you and Dave so rightfully mentioned, it makes sense to move to an OAG once I'm ready to commit to the investment.

 

I think its best that I approach things slowly here.  I'm going to start with the DSLR solution with a guidescope and if I progress, then move to the OAG solution

 

I'm looking between two different scopes, the Svbony SV106 60mm (widely available) and the Astromania 70mm Guide Scope (doesn't seem to be easily available in AU).

 

Any other recommendations?

 

@Dave, I'm going to see if I can source a asi178mm as it seems like a better solution for now. Let me know what you think.

 

Thanks,

[jml79]

With a DSLR, especially the type you have, an OAG would not usually be possible. So a guidescope is best.

 

There are two and only two good choices. A camera based on the IMX533 sensor or the IMX571. This is the ASI533, 2600 if you like ZWO. 

 

I think a guide scope will work fine and I would look for one at 60mm aperture. I would consider the 174mm if you are thinking longer term plans and an OAG, otherwise the 220 is a good choice and a fair bit cheaper. 

I respect your inputs a lot Dave but I do wish you would add the IMX585 to the list of decent cameras. It isn't as amazing as the 3.76um series but it is the next best and a great value. I actually love it uncooled for the crazy price of $305 and have begun recommending it over a used DSLR as the low budget option.

 

The pancake cameras sometimes won't reach focus because they can not be inserted as far as the mini.

Mini's are preferable with an OAG but a pancake can usually reach focus by removing the focuser and using a 10mm or so spacer ring. It makes focusing more difficult and the Mini plus Focuser combo is preffered but it can be done. My SSAG and IMX585 both work on the standard small ZWO OAG this way, although the prism is a bit small for the IMX585.

[Spaceorion]

I believe 178 is a now discontinued camera, at least for the ZWO version. Always use a mini if you intend to use it for an OAG. The pancake cameras sometimes won't reach focus because they can not be inserted as far as the mini. 

 

For a guide scope many cameras will work including OSC. However at 900mm and a mount that likes shorter guide intervals, you are already asking a lot from the newer 220. 

Dave, can you kindly elaborate on the preferred shorter guide intervals of the AM5? Where is this information found and how does this affect the guide camera selection (e.g between a asi220mm and asi174mm that you recommended) ?

[idclimber]

Dave, can you kindly elaborate on the preferred shorter guide intervals of the AM5? Where is this information found and how does this affect the guide camera selection (e.g between a asi220mm and asi174mm that you recommended) ?

The AM5 owners thread and reading about optimization of that mount and other strain wave mounts. They are great mounts but have more periodic error than more traditional equatorial mounts. It all boils down to how steep the periodic error curve is and how long the mount can go before it needs a correction.

 

A premium mount with extremely low PE can go many seconds before any correction is needed. The corrected error of my MX+ is under 1". The AP 1600 ATE I have replacing it even less.  As such I can eliminate guiding at moderate focal lengths and If I do guide the mount only needs an occasional bump. This allows longer guide exposures if needed. 

 

A mount like the CEM40 or EQ6 have a PE curve closer to 10". This is still low enough that one or even two second intervals are enough to keep the tracking well under the image scale of most systems or at least under the seeing. 

 

The PE on the AM5 is higher around 20 to 30". I have seen some reports above that. How good your specific mount is unknown. I am not sure how valid the test reports are they send with them. What matters is the guiding results. If you find that 1 second intervals is not keeping up you may like others need to reduce the interval so corrections are made more frequently. 

 

Shorter guide exposures mean less stars. The best way to combat that is with the newer sensor that are known to work with this mount. Both the 220 alone and the duo which has the same sensor prove that sensor works. The 174mm has an equal reputation and even more so with a large prism OAG and large scopes like my 12" SCT. 

Edited by idclimber, 08 May 2024 - 12:40 AM.

[Spaceorion]

Dave,

 

Much appreciate your lengthy response and very useful information provided. Once I start testing the mount, I'll be able to provide a report.

 

Based upon your information, but also the technical specs of these cameras, it seems like the ZWO ASI174MM Mini (Sony IMX174) is the ideal candidate as a guiding camera for my mount.

 

From your experience, would it make much of a difference if I manage to source a 2nd-hand camera that uses the Sony IMX174 chipset?