Autoguiding camera questions

[George Gearless]

I'm currently windowshopping for guide cameras. It'll be a while until I can actualy buy one, because I just spent the next many months budget on a Mak180 and some dewstraps. But I guess my eventual purchase will be all the more informed, if I start researching it now. Somewhere down the road to poverty, I'll propably also be buying an actual AP camera for the picture taking. But to start it all off, I'd go for just the guide camera and use my DSLR for the picture taking.

So I figured FLO's website was a good place to start. Fairly quickly I realized that I might not have fully grasped even the basics. And so I turn to the SGL forum to pester its members with ignorant questions and 'what-ifs' 😉.

1. You have guide cameras, regular cameras, and cameras that can do both. So, can a dualpurpose camera both guide AND take pictures at the same time? Or can it just do either operation, depending on whether you place it in the guidscope or main scope?

2. It seems to me that there is a very wide pricerange for a camera which sole purpose is to send adjustments to the mount. So, what can a €600 guidecamera do that a €100 guidecamera can't? I mean, where would the difference be noticed, were I able to run them side by side?

3. Because of weight issues, I plan to use an off axis guider. I realize that if I use this option, I will be limiting myself in choice of guidestar. Especially if I use it on my Mak180. But apart from that, are there any pro's and con's that you think I should be aware of?

4. I don't have a lap top per say. I have a tablet with detachable keyboard. The USB's do not supply enough power to operate an external HD. So I've solved this by using an externaly powered USB-Hub. The question is if the programs that I need for operating the guidescope are more CPU demanding than my tablet can provide? Is there a minimum requirement (system, CPU, RAM, etc.) that I can check?

 

I'm sure I'll come up with more questions before my actual purchase. But I think this is enough to be getting along with.

 

 

 

[PeterCPC]

1. Camera will either be imaging or guiding - not both.

2. Ideally for guiding a mono camera would be best but you might want to get a colour camera so that you could also use it for planetary imaging without guiding.

3. The issue of finding a guide star will be the main issue.

4. Some people use tablets but I would always use a laptop myself for the power.

Peter

[ollypenrice]

The guide camera sensitivity will always be important when using an OAG. Having one which is USB powered saves a cable and power supply as well.

This may not be the time to say so but a Mak 180 is a strange choice for deep sky imaging because of the long focal length and slow F ratio.

Olly

[johninderby]

Love my 180 mak but just use it for planetary and lunar.

[George Gearless]

13 minutes ago, ollypenrice said:

The guide camera sensitivity will always be important when using an OAG. Having one which is USB powered saves a cable and power supply as well.

This may not be the time to say so but a Mak 180 is a strange choice for deep sky imaging because of the long focal length and slow F ratio.

Olly

For DS targets I'll be using my Evostar 80. I merely mentioned my Mak180 with regards to understanding the limitations of an OAG.

[George Gearless]

34 minutes ago, PeterCPC said:

1. Camera will either be imaging or guiding - not both.

2. Ideally for guiding a mono camera would be best but you might want to get a colour camera so that you could also use it for planetary imaging without guiding.

3. The issue of finding a guide star will be the main issue.

4. Some people use tablets but I would always use a laptop myself for the power.

Peter

1. Ugh...I figured. I couldn't quite wrap my head around how the camera would do both at the same time. Not unsurprising, since it can't. 

2. I do want to keep my options open. So thanks for that little tip. It would however need to be quite the bit superior to that of my DSLR to justify the extra cost of a colour one.

3. Indeed. I was just wondering how big a problem this is. If at all. I suppose the problem varies according to what scope you are using it with.

4. Power wise I should be ok with the USB-hub. The question was/is if there is a minimum requirement system wise and CPU wise. But if I understand you correctly it is just more convencient to work with a 'real' laptop.

[PeterCPC]

2. A DSLR is not really suitable for planetary imaging - you want a high frame rate camera like an ASI224 or similar. If you use a DSLR you will find that the planet(s) are quite small even with a Barlow etc.

Peter

[SteveBz]

15 minutes ago, George Gearless said:

1. Ugh...I figured. I couldn't quite wrap my head around how the camera would do both at the same time. Not unsurprising, since it can't. 

2. I do want to keep my options open. So thanks for that little tip. It would however need to be quite the bit superior to that of my DSLR to justify the extra cost of a colour one.

3. Indeed. I was just wondering how big a problem this is. If at all. I suppose the problem varies according to what scope you are using it with.

4. Power wise I should be ok with the USB-hub. The question was/is if there is a minimum requirement system wise and CPU wise. But if I understand you correctly it is just more convencient to work with a 'real' laptop.

The colour cameras, for reasons I don't understand, are usually cheaper than the monochrome, eg zwo 120mc-s vs 120mm-s. But the monochrome is several times more sensitive (about 3 or 4 times) because for every red pixel the colour cam throws away a blue and 2 greens etc. Whereas for the monohrome they are all um, monochrome.

Good luck

Regards

Steve.

 

[George Gearless]

6 minutes ago, PeterCPC said:

2. A DSLR is not really suitable for planetary imaging - you want a high frame rate camera like an ASI224 or similar. If you use a DSLR you will find that the planet(s) are quite small even with a Barlow etc.

Peter

Hmm. Hadn't considered that. Once again, thanks.

[Adam J]

1 hour ago, PeterCPC said:

1. Camera will either be imaging or guiding - not both.

Cant agree with that statement. The best amature image of M82 I have ever seen was taken with a ASI290mm.

Or do you just mean that it a single camera cant do both jobs at the same time?

Adam

[George Gearless]

2 minutes ago, Adam J said:

Cant agree with that statement. The best amature image of M82 I have ever seen was taken with a ASI290mm.

Or do you just mean that it a single camera cant do both jobs at the same time?

Adam

I think he means, as did I, at the same time.

[JamesF]

I'd personally agree with Peter that a DSLR isn't the most desirable choice for planetary imaging.  When DSLRs with video modes originally became common they had relatively slow frame rates and also delivered a lossy compressed datastream whereas I'd prefer my data to be delivered as close as possible in form to that which left the sensor.  It may be that things have changed since then.  I've not kept up with these things as my 450D doesn't do video and I haven't felt the need to change it.

That said, I have seen some planetary images created using DSLRs that were better than I would have expected.

James

[JamesF]

Just now, George Gearless said:

I think he means, as did I, at the same time.

That was my interpretation too.  There are actually some cameras that achieve both by having two sensors in the same unit, one operating as an OAG.  Whenever I see them my brain automatically brings up the expression "ruinously expensive" however :D

James

[Adam J]

1 minute ago, JamesF said:

I'd personally agree with Peter that a DSLR isn't the most desirable choice for planetary imaging.  When DSLRs with video modes originally became common they had relatively slow frame rates and also delivered a lossy compressed datastream whereas I'd prefer my data to be delivered as close as possible in form to that which left the sensor.  It may be that things have changed since then.  I've not kept up with these things as my 450D doesn't do video and I haven't felt the need to change it.

That said, I have seen some planetary images created using DSLRs that were better than I would have expected.

James

One of the best DSLR for planetery is the 550D as it has a 60fps crop video mode. 

[PeterCPC]

As an illustration of what I was saying above re field of view:

Peter

[JamesF]

It's not really the field of view that's relevant for planetary imaging though.  All that empty space can be thrown away.  It's the pixel size (assuming you can get enough light on the pixels to get a decent SNR).  A planetary image from two sensors with the same pixel size (using the same optical train) will be the same size on-screen regardless of the actual size of the sensor.  The 224MC has 3.75um pixels and the 550D is just over 4um I think, so in terms of resolution the 224MC does a little better, but it's quite possible some DSLRs with a video mode have similar size pixels these days.  As I said, I don't really pay much attention to these things at the moment.

[Actually, a quick check on a random camera suggests that the 750D has pretty much the same pixel size as the 224MC.]

James

[PeterCPC]

Where a DSLR really comes in useful is when you want more widefield shots to show the moons:

 

Peter

[George Gearless]

57 minutes ago, JamesF said:

It's not really the field of view that's relevant for planetary imaging though.  All that empty space can be thrown away.  It's the pixel size (assuming you can get enough light on the pixels to get a decent SNR).  A planetary image from two sensors with the same pixel size (using the same optical train) will be the same size on-screen regardless of the actual size of the sensor.  The 224MC has 3.75um pixels and the 550D is just over 4um I think, so in terms of resolution the 224MC does a little better, but it's quite possible some DSLRs with a video mode have similar size pixels these days.  As I said, I don't really pay much attention to these things at the moment.

[Actually, a quick check on a random camera suggests that the 750D has pretty much the same pixel size as the 224MC.]

James

I just looked up the pixel size for my EOS 7D Mark 1. It's 4,1 µm. I realy have no idea if the difference between 3,75 µm and 4,1 µm is a lot or not. Numerically they look close, but in the AP universe that may be worlds apart.

The 7D has either 50 FPS or 60 FPS at HD resolution. I visited a few websites where there seems to be much discussion about this precise topic. Some say that only the Mark2 is capable of 60. Others say that it doesn't matter. In any case, 50 Fps seems to be a safe bet. The 224MC has 30 FPS at maximum resolution. But ofcourse, the FPS increases dramatically as the resolution decreases. 

It's difficult for a novice like myself to find out what these numbers translate into. But I do think that my EOS 7D deserves at least a few good runs before I rush out and buy myself even poorer on a new one.

 

[George Gearless]

9 minutes ago, PeterCPC said:

Where a DSLR really comes in useful is when you want more widefield shots to show the moons:

 

Peter

Along with making love to Kate Beckinsale, aquire superpowers and talking to Elvis, it is a dream of mine to take a picture such as this.

Can you share some details on how you took this photo? I mean, equipment wise?

[JamesF]

1 hour ago, George Gearless said:

I just looked up the pixel size for my EOS 7D Mark 1. It's 4,1 µm. I realy have no idea if the difference between 3,75 µm and 4,1 µm is a lot or not. Numerically they look close, but in the AP universe that may be worlds apart.

The 7D has either 50 FPS or 60 FPS at HD resolution. I visited a few websites where there seems to be much discussion about this precise topic. Some say that only the Mark2 is capable of 60. Others say that it doesn't matter. In any case, 50 Fps seems to be a safe bet. The 224MC has 30 FPS at maximum resolution. But ofcourse, the FPS increases dramatically as the resolution decreases. 

It's difficult for a novice like myself to find out what these numbers translate into. But I do think that my EOS 7D deserves at least a few good runs before I rush out and buy myself even poorer on a new one.

If you're of a mind to experiment I'd certainly give the 7D a go and see how you get on.  I'd not be in too much of a hurry to buy a camera for planetary imaging right now anyhow given that they're hardly well-positioned for imaging from higher latitudes such as Denmark at the moment.

Frame rate (or exposure time), pixel size, gain and focal ratio are all part of a balancing act that's about getting the best signal you can from the target and probably the most helpful thing you can do to learn about that is practice.  Even now when good results might be hard to obtain, time spent getting your head around how things work is worthwhile.  Smaller pixels used not to be particularly favoured for planetary imaging, but as cameras have become more sensitive the game has evolved and one thing changes another.  Not that long ago people were talking about planetary imaging with focal ratios approaching f/40, whereas modern dedicated cameras make f/15 or even lower much more feasible, which changes how one might choose to set up the optical train and so on.

James

[George Gearless]

@JamesF 

Oh, I'll definitely experiment the lens-cap off the 7D. On as many targets and as often as I can. As I said in my initial post, it'll be a while before my budget allows yet another purchase of equipment anyway. I'm just off to an early start 'researching' what, when and where to improve my kit. Regardless of the shortcomings of the 7D, I am sure it will grant me many hours of delightful experimentation, frustration, elation and above all, experience. 

 Yeah, the planets are not presenting themselves favorably right now at my location. I'm keeping my fingers crossed for a clear evening or two when next the moon passes over my house at a decent hour.

FPS, pixel size, gain, etc. are concepts I've only just started delving into. There is so much to learn before I can confidently place an order at FLO for a camera. I've still got many niggles to work out with regards to a laptop, power supply, cords and what not. As I am writing this, a dual purpose colour camera (guide for DS and camera for planets) seems to be the most versatile option. But it is far too early to call. I may go a completely different way come October/November when I'll be ready to make a commitment to whatever I decide.

Thanks for your input.

[Helen]

If you go for an asi colour cam like the 224 you might want to consider getting an asi air instead of messing about with a laptop 😉 

https://www.firstlightoptics.com/zwo-accessories/zwo-asiair.html It is really neat and the functionality is increasing almost weekly!

Helen

[PeterCPC]

15 hours ago, George Gearless said:

Along with making love to Kate Beckinsale, aquire superpowers and talking to Elvis, it is a dream of mine to take a picture such as this.

Can you share some details on how you took this photo? I mean, equipment wise?

It was taken with my C9.25 with a 2.5 Televue powermate and a Canon 550d. I took a video exposed for Jupiter and one exposed for the moons and combined them. If you expose for the planet only you will not see the moons. If you expose for the moons the planet will be blown out.

Peter

[Stub Mandrel]

1 hour ago, PeterCPC said:

It was taken with my C9.25 with a 2.5 Televue powermate and a Canon 550d. I took a video exposed for Jupiter and one exposed for the moons and combined them. If you expose for the planet only you will not see the moons. If you expose for the moons the planet will be blown out.

Peter

I find that this is only an issue for widefield shots where the moons are essentially 'point sources'.

When the focal length is enough for them to be 'extended objects' (i.e. small discs) they expose the same as Jupiter itself - after all they are equally illuminated and at the same distance.

In these pics you can see the moon is actually slightly brighter than Jupiter.

[George Gearless]

17 hours ago, Helen said:

If you go for an asi colour cam like the 224 you might want to consider getting an asi air instead of messing about with a laptop 😉 

https://www.firstlightoptics.com/zwo-accessories/zwo-asiair.html It is really neat and the functionality is increasing almost weekly!

Helen

I've on occasion seen this advertised and browsed over it, without really knowing what I was looking at. It does seem to be a very cheap way to solve my laptop issue (I only have a tablet with a detachable keyboard).

Good tip. Thanks, Helen.