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Need help choosing Guide Camera


Newforestgimp
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Hi All,

Feel like I’m chasing my tail trying to decide which guide camera to upgrade to.

Scenario: I have an RC8” 1600 fl imaging scope with ASI071mc pro I want to guide, I’m currently using a 120mm that will move to mobile rig, I have both OAG and guide scope attached so I can easily switch between guide methods. Ideally I’d like to use the OAG but struggling with the 120mm and although not ideal for guiding id like a colour camera for planetary use.

looking at various brands versions of the following…

224, 290, 174, 178, 327

Preferably I just want to buy once and buy right or if I went the mono guide route is there a “cheap” colour planetary I should consider instead of the above cameras ?

Regards

Andy H

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2 minutes ago, bottletopburly said:

I use a qhy 290mm but is usb3 doesn’t work plugging into zwo533mc camera USB ports as they’re usb2, so may be worth going for a usb 2 camera to utilise the camera ports and save on trailing wire .

That’s a consideration I hadn’t made regarding the cables, good point.

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I think USB 3.0 camera can work on USB 2.0 hub - it will only use USB 2.0 speeds for data transfer.

That is how I use ASI1600 and ASI185. First has USB hub, and second is USB 3.0 camera, but can be used on USB 2.0 port.

@Newforestgimp

Why is ASI120mm not working for you in OAG role?

I'd consider ASI385mc that is not on your list. It is as good planetary imaging camera as ASI224 (can be thought of as "bigger brother" to ASI224 as it has same spec but more pixels), it is big enough to be used with OAG (in fact I have vignetting on my 8" RC and OAG on similar sized chip of ASI185mc).

Which ever camera you choose, when using OAG, you'll need to bin it as it will be working at 1600mm of FL - and you don't need that much guide resolution. I bin mine x2 for resulting ~1"/px guide resolution.

 

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Hi @vlaiv

The 120 works, I will move this to another portable set up where it seems more suited partnered with a wide field refractor. Which leaves me requiring another guide cam so I might as well get one that’s a better match for the big rig and OAG & as a bonus if I could use it for planetary once in a while that would be cool too.

my head starts to hurt when I consider appropriate pixel size and how to get best possible guide accuracy.

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5 minutes ago, Newforestgimp said:

my head starts to hurt when I consider appropriate pixel size and how to get best possible guide accuracy.

That really depends on your mount, but I'd say that good rule is that you need at least 1/3 precision of what your mount is capable of.

To cover all cases - you need guide precision of less than say 0.1" as it is unlikely you'll be guiding at 0.3" RMS unless you have mesu or other high end mount.

In order to go from that number to pixel scale - you simply multiply with 16 (it is said that centroid is precise down to 1/16th - 1/20th of a single pixel - so we take upper estimate of that).

You need 1.6"/px or less.

With 1600mm of FL - that is not going to be a problem. With 3.75µm pixels - you can bin x3 and still be lower than that number. With smaller pixels - you can bin even more. In fact - for that OAG, I'd recommend going with 3.75µm pixel size and not smaller (like 2.4µm of 178 or 2.9µm of 290).

That is also nice pixel size for planetary role as it requires F/15 as optimum F/ratio and that is something that is easy to get with "regular" scopes - like x3 barlow for F/5 or x2.5 barlow for F/6 or x2 barlow for scopes in F/7-F/10 range (adjusted for distance so you end up with F/15).

With some maks - you are already at F/15 (like Mak150 and 180 and some Bresser offerings).

Luckily two best planetary color cameras - ASI224 and ASI385 have that pixel size.

 

 

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I went for the 224mc as my first dedicated astro cam as I already had a DSLR so the 224 would be used for guiding duties. Turns out it's also been useful for planetary and solar (not it's best application due to being colour). If needed it's a light option for using as a OSC option on a multitude of targets. My profile pic was taken with a 224.

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13 minutes ago, Newforestgimp said:

Any thoughts on the ASI462mc for guiding ? I see it is the successor to the 290 which is also highly thought of ?

I would consider that for ONAG or maybe IR pass guiding.

With 800nm pass filter - you'll get essentially mono sensor very sensitive in IR. IR part of spectrum is the least sensitive to seeing - which is good thing for guiding.

Otherwise - it is not as sensitive as other cameras. It has very high QE at 800nm - but only 0.9 and 0.85 of that value. Even if it has close to 90% QE (very unlikely with color filters) - that would put regular QE below 80% in regular part of spectrum.

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7 minutes ago, Newforestgimp said:

Looks like it’s a toss up between the 224 and the 385 beyond the 385 it starts getting too pricey for me.

does the 385 justify the extra £100 ? Will my guiding accuracy improve with it over the 224 ? Using a GEM45 mount

Only difference is in sensor size. That is it.

It really depends if extra sensor size will be worth to you or not.

That sensor is about as larger as my ASI185 and here is what guiding with OAG and 8" RC and that sensor looks like:

image.png.9455f6b17573ee3317f756dddcd20c38.png

Vignetting is already starting to show in corners of that sensor. If it was any larger - it would be waste of space really as far as guiding goes.

It's up to you to weigh if extra sensor surface will be beneficial to you. For planetary, it might be only useful for lunar and solar - all other planets fit nicely in FOV of 224.

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7 minutes ago, vlaiv said:

Only difference is in sensor size. That is it.

It really depends if extra sensor size will be worth to you or not.

That sensor is about as larger as my ASI185 and here is what guiding with OAG and 8" RC and that sensor looks like:

image.png.9455f6b17573ee3317f756dddcd20c38.png

Vignetting is already starting to show in corners of that sensor. If it was any larger - it would be waste of space really as far as guiding goes.

It's up to you to weigh if extra sensor surface will be beneficial to you. For planetary, it might be only useful for lunar and solar - all other planets fit nicely in FOV of 224.

That’s really interesting and far different view from my current 120mm where I’m lucky to get one crescent moon 🌙 shaped star 

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15 minutes ago, Newforestgimp said:

That’s really interesting and far different view from my current 120mm where I’m lucky to get one crescent moon 🌙 shaped star 

You should position pick off prism as close to main imaging sensor as you can.

If you put it too far out - you'll get very aberrated stars

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