Camera purchase - ZWOASI585mc - or alternative?

[Jimbo64]

Hi guys,

I'm very keen to join the ranks of EAA specialists on here, but am struggling with my one main purchase, buying the right camera.  To give perspective, I have a 8" f6 Skywatcher flex tube Dobsonian 200p with wifi goto.  I live on the outskirts of Glasgow (Bortle 7) and am struggling to enjoy visual observing because of high light polution, EAA sounds like an ideal way for me to get more enjoyment and to be able to 'see' DSOs. 

I had initially thought of buying a planetary camera (ASI224mc?) to get me started, I am keen on solar system targets, but also want to be able to capture galaxies and nebulae, so concluded that if a bought the 224 I'd likely want at least one more camera - and that felt likely to lead to that 'N+1' syndrome of always having something else to buy.  

In trying to find one camera that could suit well enough for all my EAA needs I read loads (but probably not everything, so apologies if this is all very well discussed) on here (and CloudyNights), tried to research the complexities of camera tech as best as I could and had settled on the ASI585mc, using astronomy tools had me believing this would work great on a whole host of targets and SharpCap looks and feels like it gives exactly the sort of experience I'd enjoy. FoV is tight though, but adding a 0.5 reducer seemed the answer to fitting larger objects in my FoV and getting me firmly in the green zone for just about anything I'd like to see.  But the good people at FLO have been really helpful in advising me that this won't be as ideal as I had hoped, with my f6 dob I might struggle with reaching focus (but could slide the flexitube in a bit to sort this) and that the reducer wasn't the answer as it would give me big problems with vignetting and coma.  I'd also need to think of adding a 3x Barlow to get a decent scale of planetary image, but small DSOs look likely to be crisp and nicely framed with the camera. A combined coma corrector/ flattener might solve most of my problems, but at nearly £700 that is not at all appealing.

Am I being too ambitious in thinking that there is one camera out there that would suit me, if so I'd appreciate any advice on this, but I fear that I've just not got my head around all of the various factors in buying a camera to make an informed choice, but I do want to try EAA and making a purchase is the next essential step.  The 585 still feels like a good choice, but I'd hate to make a silly error in going for that if there are better options to suit my set up, so I'd appreciate any views on this topic.

Jim

[Mike JW]

Hi Jim,

Sadly so no one camera will do it all, just as no one telescope will do it all. You will have noted as you have looked through the EEVA reports thread that excellent EEVA can be done with a 8" Newtonian.

Quite frankly don't go for planetary EEVA - an 8" scope gives decent visual views of the key planets - namely Jupiter and Saturn. Venus only has subtle detail and Mars is really best viewed when it is at its closest to Earth.  EEVA offers little if any gain for planetary viewing if wishing to be "live".

Best focal ratio is as you realise, the faster the better but don't get hung up about it. (When I was using my C9.25 for EEVA I was using it at F6 ).

Colour cameras are less sensitive than mono and why go for colour anyway - the colour is as we know not real, other than perhaps for stars. Colour is excellent for picking out planetary nebulae.

I use the ultrastar guide camera by Starlight Express (not cheap but large pixels and a decent size chip). If you go for a pixel camera then they are less sensitive than bigger pixel cameras. The key factor for me buying the ultrastar was that it is eyepiece size and thus I would not have any reaching focus issues as it slides into the focuser on my Newtonian (Dob). Martin and Bill use the lodestar v2 starlight cameras (cheaper, smaller chip and larger pixels) and get excellent results using their 8" Dobs (they are faster Newtonians than yours).

Martin has written the software called Jocular which is specifically for EEVA and is very intuitive and easy to use. It gives excellent results with the minimum of fuss. You will see many examples of the results in the thread.

I started with a cheap CMOS camera (eyepiece diameter) on a small scope at first to test the waters and then graduated to the current camera once I felt confident about abandoning visual observing.

Others will have different views to mine - all part of the pleasure of the hobby/journey.

Mike

 

[Martin Meredith]

Hi Jim

It sounds like you've already gone quite deep into the subject, so much of what I'm saying is probably not new to you, but even so this is the approach I would take...

To start to narrow down the choices, I suggest you define a lower and upper bound on the field of view you need.

Too small a FOV and you end up having problems getting the object on the sensor in the first place, then finding enough stars to stack or platesolve. My 800mm focal length scope paired with an ASI 290 provides a FOV which I think is borderline too small, at around 0.4 x 0.23 degrees; my Lodestar is around 0.34 x 0.44. Your 1200mm scope would be proportionally smaller for these sensors, which would make them tricky to use. 

At the other end, you really need to consider the kind of DSOs you want to view. This will define the maximum field of view to aim for. You mention planets, galaxies and nebulae, which represent a huge range from the very small to potentially very large, with galaxies in the middle. If you want to do all of these with your current scope you're going to need a large sensor or reducer (as you mention).

Its a fact that almost all the interesting DSOs/groups of DSOs out there will fit easily in a 0.3 x 0.4 degree field. Apart from nebulae and some clusters, there are only a handful of galaxies that can't be observed using this FOV. This is probably the hardest thing to get 'right' because when starting out there is a tendency to plan for all interesting objects (perhaps with a bias towards the Messiers, some of which are large), but if you really get into EAA you'll most likely end up drilling into the NGC/IC/Hickson/Arp catalogues, pretty much none of which need a large FOV. 

The majority of observing reports posted here have FOVs in this general ballpark, and you can see the variety and number of different objects that have been captured. As Mike says, no scope or sensor can do it all, and my preference is to dispense with the larger objects! Its also worth spending some time looking at the entries for the monthly EAA challenges on CN because you'll see the same objects (both showpiece types and less frequently observed stuff) captured with many different scope/sensor combos, so will judge for yourself what kind of FOV is likely to appeal to you.

An alternative plan is to use the same camera but with a different scope (e.g. a small refractor with a focal length of around 300-500mm) to capture the larger objects. 

On the monochrome versus colour question, most galaxies don't benefit from colour at the timescales of EEA observing (a few such as M82 do), but in my opinion all open and globular clusters, and planetary nebulae, do benefit from colour. Mike mentioned my Jocular software, but its worth pointing out that it doesn't really support OSC cameras in any meaningful sense, so Sharpcap or ASIlive would be better options.

Again, just a few opinions. It would be good to balance this with some input from nebula aficionados!

Martin

 

[Jimbo64]

Hi again, These replies are really helpful, and are swaying me back to thinking that the 585 might be the one to go for.  Planetary EAA sounds likely best avoided, as are the big beasts (like Andromeda and the Orion Nebula) and my playing around with FoV gives good looking scale to most of my key targets, the smaller DSOs like those attached, presumably these sit nicely within the 0.3 x 0.4 degree size Martiun mentioned. It feels like the 585 could be a good middle ground to launch me into EAA with its resolution and pixel size and apparent better performance than the likes of the asi224mc, but again I'd appreciate any alternative suggestions - I'm not wedded to ZWO, but they seem the most popular that I've come across and good value, but it does seem that every time I'm about to make a purchase something costing another £100 on top of where I just was starts looking attractive! I'm sure this sounds familiar?

[M40]

Hello Jimbo64, quite a challenge. I can't offer anything near the experience of others and I can't beat your FOV selection, so all I can add are my thoughts. You live in a bortle 7 area, so the more sensitive the camera the better, which would be a mono camera. Also, I realised that one telescope is not ideal for both DSO and solar system, so if your plan is to use the one telescope get the best camera you can for solar system and a second for DSO. Initially choose your target and get the best you can for that target. For DSO, I think I would struggle to choose between the 174MM and the 178MM.

All the best.

[Jimbo64]

In part driven by the FLO ASI August sale I bit the bullet and ordered the 585 - I appreciate that mono would have given me more sensitivity, but that felt a step too far for my first dabble in camera buying.  Wish me luck, but don't expect any images just yet - the camera is out of stock!  The advice on here about deciding on what was a considered purchase being based on prioritising my targets was really helpful.  Thanks guys, especially those who have commented here.

[StargazerUK]

@Jimbo64 did you get the 585 in the end, if so how did it work out for you. I am in a similar predicament as you were. My scope is not as big as yours (only 6" newt). I too was looking for the perfect camera to do planetary and dso. I now realise that such a camera does not exist so I am torn between getting a planetary camera (asi224mc) and just doing to planetary and lunar eeva to learn the basics then upgrade the camera when I want to do dso, or just bite the bullet and go all in for a dso camera now.

[Mike JW]

Go for DSO - so many adventures to be had. Planetary is limited for opportunities.