Prime Focus

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Re: Prime Focus

Postby Gfamily2 » Fri Sep 07, 2018 8:55 pm

If using a webcam, the field of view is really very small. However, for planets, what you can do to help find them is to put the scope really out of focus, because that makes the 'disc' much larger, and you can often see it even if the planet itself is out of the field of view.
Guess who discovered this by accident :)
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
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Re: Prime Focus

Postby Graeme1858 » Sat Sep 08, 2018 1:35 pm

Aratus wrote:
Graeme1858 wrote:OK, cheers for that. I probably need to sort the alignment first. I wasn't getting an image at all. I thought my finder red spot was set up accurately but perhaps not!


Using a barlow reduces the field of view quite a bit. Cameras generally tend to reduce the field of view even more, sometimes considerably more A red dot finder may not be accurate enough. To make matters worse, just focussing an SCT can move the image out of view. If you can, focus the telescope on an object easier to find first. (the moon, perhaps). Then increase the ISO to it highest setting, and a 1 second (or more) exposure. Move over to where the red spot, or GOTO says the the planet is, and wander about until you find it. One technique is to use the hand control to gradually 'spiral out' until you see it. Once you have it, reduce the ISO and exposure to give a correctly exposed view.


Yeah, I put the Barlow on to decrease the field of view in an attempt to magnify my image of Saturn but the x3 might have been a bit over the top! I need to get some more practice in when the clouds go!

Spiral out is a great idea. I usually zig zag back an fourth but it's easy to get lost!

Regards

Graeme
_______________________________________
Miranda 10x50 Binoculars
Celestron CGX 9.25 SCT
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Re: Prime Focus

Postby Graeme1858 » Sat Sep 08, 2018 1:37 pm

Gfamily2 wrote:If using a webcam, the field of view is really very small. However, for planets, what you can do to help find them is to put the scope really out of focus, because that makes the 'disc' much larger, and you can often see it even if the planet itself is out of the field of view.
Guess who discovered this by accident :)


Would one of these do the job?

https://www.ebay.co.uk/itm/USB-50MP-HD-Webcam-Web-Cam-Camera-with-MIC-for-Computer-PC-Laptop-Desktop-WN/153146573068?epid=930594269&hash=item23a83f410c:g:c-AAAOSwf2pbesKW

Regards

Graeme
_______________________________________
Miranda 10x50 Binoculars
Celestron CGX 9.25 SCT
Graeme1858
 
Posts: 146
Joined: Tue Jul 24, 2018 2:32 pm
Location: Kent, UK, 51°28’N 0°38’E

Re: Prime Focus

Postby Gfamily2 » Sat Sep 08, 2018 2:49 pm

Graeme1858 wrote:
Gfamily2 wrote:If using a webcam, the field of view is really very small. However, for planets, what you can do to help find them is to put the scope really out of focus, because that makes the 'disc' much larger, and you can often see it even if the planet itself is out of the field of view.
Guess who discovered this by accident :)


Would one of these do the job?

https://www.ebay.co.uk/itm/USB-50MP-HD-Webcam-Web-Cam-Camera-with-MIC-for-Computer-PC-Laptop-Desktop-WN/153146573068?epid=930594269&hash=item23a83f410c:g:c-AAAOSwf2pbesKW

Regards

Graeme

It's hard to tell.
You need to remove the existing lens from the cam and replace it with a 1.25" eyepiece adapter like this Image
Whether you can do that will depend on how the existing lens is attached.
There are some standard lens mounts used on cameras, and this adapter will work with an internal M12 , thread (which is one of them) but I can't guarantee that it'll work with the camera you're suggesting.

But if you're willing to just araldite the adapter to the webcam circuit board, that would probably be fine.
NB The adapters come with or without IR cut off filters, and as removing the lens is likely to remove the camera's internal IR filter, it's probably worth getting one with the filter otherwise the colour balance is likely to be 'out'. In addition, if you were using a refractor, the lack of an IR filter would probably cause Halo-ing around your image as a form of IR Chromatic Aberration.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
(Not a moderator)
Gfamily2
 
Posts: 476
Joined: Thu Jun 25, 2015 10:38 pm

Re: Prime Focus

Postby Aratus » Sun Sep 09, 2018 5:30 pm

Web cams have got far too complex now-a-days! A basic sensor and lens seems very difficult to get hold of even second hand. The Philips ToUcam used to be standard, but I can't find one even second hand in the UK. I expect the cheap camera you found on eBay will work. Hopefully you can unscrew the lens and stick the adapator on to it. If not then as has already been mentioned, you might have to take out the circuit board and make your own housing.

Another possibility is an old second hand Celeston NexImage.
I found this one.
https://www.ebay.co.uk/itm/Celestron-Neximage-Colour-Solar-System-Planetary-Lunar-Solar-Imaging-Camera/253858621253?hash=item3b1b272745:g:9aUAAOSwq2JblAOi
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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