Autoguiding kit

[cadman342001]

Will this be ok for my rig ? Price is in US $ so works out just under $400 AUD

https://www.cyclopsoptics.com/camera/qhy5l-ii-m-with-miniguidescope/?setCurrencyId=1

HEQ5, OTA is SharpStar 65mm EDQ f6.5 (FL 420mm), modded Canon T2i dslr.

Running BackYard EOS, will be running PHD2 for guiding.

Andy

[hamiland]

Looks nice, Personally I like to run ~50mm Aperture in my guide scope as it means that you may not need to increase your guide cam exposure or move the guide scope to pick up a suitable star in its FOV.

Have a look at Bintel, they have the ZWO ASI120MM (Same sensor I believe, so it's only if you object to the form factor) and either an orion 50mm or ZWO 60mm guide scope fairly close to your budget. Once you take the shipping into consideration you may end up with a bit more aperture for the same money. As well as supporting a local supplier.

Anders

[cadman342001]

Thanks Anders

why is the mono version more expensive than the colour version ? 249 vs 219. The descriptions of the specs seem to be the same.

[hamiland]

It most likely comes down to sensor demand and volume of production, there is a much more limited market for a mono sensor versus a colour sensor. These sensors are most likely being used in all manner of consumer goods as well as being a great sensor when used for our purposes.

I'm assuming you are aware of the advantages for guiding of a mono over a colour sensor in respect to sensitivity?

[cadman342001]

Nope !:shrug::lol:

I assumed that mono would be cheaper than colour, but then when I discovered that the mono one was more expensive presumed that maybe the mono was more sensitive but then on reading the blurb it seemed to say that both were the same.

So mono is better ?

[cadman342001]

Given that I might want to use the 127L OTA for planetary imaging, would the colour not be the better option ?

[hamiland]

Ok, so the underlying sensor is the same, however on the colour there is a colour filter array which means there is a colour filter in front of each pixel (Bayer matrix) with the result of 4 pixels used to map the colour (2 greens to best replicate our eye's higher sensitivity to green). So effectively each pixel (when pointed at a white target) only receives that part of the spectrum. So while the underlying sensor has the same sensitivity, the colour camera's pixels are effectively only sensitive to one colour. This results in (and there are some software tricks involved to improve this) a lower resolution and a lower per pixel sensitivity to white light (for guiding most stars are "white" or close enough for this purpose). Check out the link below as they explain it better than I can: https://photographingspace.com/colour-vs-mono-camera/

For planetary colour may be better, for guiding mono is preferred, you may want to calculate your pixel scale to make sure your pixel size is in the ideal range for your scope so you are not over or undersampling. I would recommend 2 cameras one for each purpose if the budget allows. I know there are some Skyris cameras, with Sony CCDs on sale at bintel at the moment.

[cadman342001]

Thanks again. Those Skyris cameras are seriously reduced ! and USB 3.0 (not sure if that matters but it's gotta be a good thing right) Any idea how to calculate my pixel scale ?

[hamiland]

For Pixel sale, you can use https://astronomy.tools/calculators/ccd_suitability give that a try and see how you go.

USB 3 is not a bad thing, it means that for bright objects (solar system) you can increase your frame rate, however you can also use them as USB 2 devices by using a cable without the extra pins or attaching them to an older PC/Mac so it give you a bit of extra flexibility.

[axle01]

I have just finished setting up this exact kit on a Sony A7s on a 55FL F3.6 Astrograph, not used it as yet though.

Alan

[cadman342001]

My laptop has 1 x USB 3.0 and 3 x USB 2.0 ports so I'm good there.

So I ordered the 618M for $149 reduced from $499 with free shipping (too good an opportunity to miss at the sale price) and will add a 60mm / 240mm FL guide scope once funds allow.


The calculation for pixel ratio I believe is =

pixel size / FL x 206.3

and you want the ratio to be greater than 0.25 or less than 4x greater depending on how you do the equation

Looking at my own configuration (Canon 550D DSLR pixels of 4.3mu, 65EDQ 420mm, 618M 5.6mu, potential 60mm guide scope 240 mm) I get

Long ways -

Imaging: ([4.3mu x 2 (bayer)] / 420mm) x 206.3 = 4.22

Guiding: (5.6 / say 240mm) x 206.3 = 4.81

Ratio - 4.81/4.22 = 1.14


Other ways - (pc/ft)/(pg/fg)

pg = pixel size guide camera
fg = focal length guide scope
ft = focal length of main OTA
pc = pixel size imaging camera x 2 for bayer sensor

pg = 5.6
fg = 240
ft = 420
pc = 2*4.3


So, current rig = 0.87 which is > 0.25 so all good ?

This means I think that for every 1 pixel movement of the guide scope, the main OTA moves by 0.87 pixels.

Andy

[cadman342001]

I'm assuming I still do the 2x pixel size for the bayer sensor even though I have a fully astro modded dslr?