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Bigfoot 9907

StarShoot G3 Color

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Dear all,

Would anyone know what the pixel size is for a Orion Starshoot G3.The specs says 8.6 micron by 8.3 micron pixels. However, I am trying in to work out the field of view, and yet the Field of View Calculator only has room for one number for the pixel size. The image size is 752 X 582 pixels.

Cheers

Surinder

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What’s the focal length of the OTA? You need to know FL to determine FOV. Here’s a screen shot of an Excel spreadsheet I was working intently on a while back – but with everything else going on – it’s been on the back burner for months.

It’s designed strictly for the Messier objects - to find out if they’ll fit in a given sensor’s FOV. There are formulas that can tell you a sensor’s FOV based on its physical dimensions – but the entire surface of a sensor doesn’t capture photons. Sensors have tiny - and I do mean tiny - "gutters" which "drain" the electrons that "overflow" when the photosites get "full". So my spreadsheet uses the pixel (photosite) array and the photosite dimensions to return a true FOV. I don’t think Stellarium even has that feature. You could do it if you knew the sensor’s active surface but you need to know the right formula which isn’t built-in to Stellaium but it is built-in to mine :)

I also have a G3 so you’ll notice (if you can make it out) the data at the top is for the G3 based on a FL of 480 which is the FL of my 80mm ES refractor...

Just post the FL of your OTA and I’ll respond with the G3’s true FOV for that scope. I can even tell you the FOV when adding barlows and focal reducers :)

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Edited by Scorpius
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The spec sheet says the pixels are 8.6um wide by 8.3um deep so at 752x582 that would give you a sensor size of 6.47mm x 4.83mm.

At 1000mm focal length the resolution is 206.3 arcseconds per mm, giving you a field of view of about 22.2 arcminutes by 16.6 arcminutes, assuming I've done my maths correctly.

James

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Hi Scorpius,

I have a SW 200P, so the FL is 1000mm (f5).

Many Thanks for your help   :icon_salut:

No problem, glad to help out! So here’s 4 images giving you a complete read out for the G3 in conjunction with an OTA having a FL of 1000 mm. You should be able to save and zoom the first image since it will probably be too small to read. A green square in the far left column indicates that Messier object will fit in the frame based on the current parameters. If you’ll notice, the drop down for framing allowance is set to 10% which is part of the formula that “lights up” the green squares but the True FOV table is unaffected by that setting and still provides the sensor’s total FOV  – which includes the framing allowance.

As I said, it’s been a while since I’ve worked on this but it’s accurate to my knowledge. It would be great to hear back if you - or anyone - discover any inconsistences  – or even if you don’t... :)

Regards,

Scorpius

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The spec sheet says the pixels are 8.6um wide by 8.3um deep so at 752x582 that would give you a sensor size of 6.47mm x 4.83mm.

At 1000mm focal length the resolution is 206.3 arcseconds per mm, giving you a field of view of about 22.2 arcminutes by 16.6 arcminutes, assuming I've done my maths correctly.

James

Your sums are dead-on and your post made me realize I needed to add another decimal place to the "active surface of sensor" cells - Thanks! :)

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Many Thanks Scorpius

You're welcome Bigfoot 9907. I plan to upload the spreadsheet in a separate post so anyone who wants to try it will have access and can make suggestions for future improvements. It will work for any sensor as long as you know FL of OTA, pixel array & photosite dimensions in microns. Stay tuned... :)

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Dear all,

Would anyone know what the pixel size is for a Orion Starshoot G3.The specs says 8.6 micron by 8.3 micron pixels. However, I am trying in to work out the field of view, and yet the Field of View Calculator only has room for one number for the pixel size. The image size is 752 X 582 pixels.

Cheers

Surinder

Your best bet is to download Ron Wodaski's CCD calculator plus the catalogue of the images of the popular DSOs. Load the particular's of your scope and camera and then choose a target and it will show you how much of the target will fit in the FOV. It is very accurate and easy to use. Your sensor is on the small size and with the FL of your scope you will find that a lot of the DSOs will just not fit on your sensor.

A.G

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First, I goofed by initially posting this in the wrong thread but have got it in the right spot now...  :)


 


Bigfoot – Just a word of advice. There’s a lot of folks who will keep telling you the G3’s sensor is too small to be useful for much of anything and my response to that assertion is – DON’T FALL FOR IT! Where the G3 really comes in to its own is imaging medium to small objects at longish FL’s. If you look at that spreadsheet image I posted, the apparent angular size of most Messier objects is simply not that big. For example – at your OTA’s FL of 1000 mm – and accounting for a 10% framing allowance – 68 of the 110 Messier objects will fit in the G3’s FOV! Will you ever be able to capture M31, 42 or 45 in a single frame? – of course not – but there’s a lot of other objects up there that you can. The caveat is that guiding is pretty much a necessity at these longish FL’s but I’ve had no issues getting 300-600 sec. subs at 1280 mm with my 8” SCT and f/6.3 focal reducer. Also, just because they’ll fit in the frame doesn’t mean you can image them because they’re so dim that the exposures would need to be so long the mount would have to track accurately for more than entry level equipment could typically manage.


 


I think you & me – and others – on SGL are pretty much in the same boat. We’re new and didn’t have boat loads of cash to invest in high end cameras since there was a lot of other gear we needed to purchase at roughly the same time. However, I don’t see why we should sit around and agonize over the fact our cameras don’t have sensors the size of Texas when the camera we do have is perfectly capable of capturing acceptable images of many popular targets.


 


For example, M57 – which is next on my list - is a very popular target but it’s only 3.8 arc minutes in apparent diameter which will easily fit in the G3’s FOV at a FL of 1000 mm. If you look at the columns labeled object size in pixels – that is telling you (based on your current configuration) that M57 will occupy 129 x 134 of the 752 x 582 pixels on the G3’s sensor. So it won’t be huge in the frame but it will still be a lot bigger than an image captured with the Canon EOS 60D having a pixel array of 5184 x 3456 with pixels that are 4.3 microns square. For the Canon at 1000 mm FL – M57 would only occupy 66,563 of the sensor’s nearly 18 million pixels. And the sampling rate for the Canon would be 0.89 which would not do you much good under normal sky conditions. On the other hand the G3’s sampling at 1000 mm is about 1.7 arc seconds which is a lot closer to what normal sky conditions can support.


 


Check the images I posted on this thread for an example of what the G3 can do. http://stargazerslou...3-colour/page-3 Do I think they’re magazine quality images? – absolutely not – but they’re a good illustration of the point I’m trying to make regarding the G3’s ability to get “up close and personal” on the right size objects at the right FL. My suggestion - if you’re guiding - would be to focus on targets like M27, 51, 57 and others of similar size and magnitude. Then please post your images which may help others understand the G3 is a solid entry level camera when used at the correct FL’s. Also, keep in mind it does a pretty good job on faster scopes as well however, the object won’t occupy as much of the frame - but that’s the case with any sensor as the FOV increases.


 


Now I’ll sit back and prepare for the onslaught from folks with fast scopes and huge sensors who think the only good astro-images are the ones which include huge chunks of sky in a single frame…   :grin:


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