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Old 08-12-2005, 03:42 PM
captain3081
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Canon 350D Prime Focus

Can't find this explained on the forum. Can anybody help me out?

I understand that GS 10" Dob. 1250mm FL with 10mm EP = 125x mag.

If I attach a Canon EOS 350D at prime focus, what is the mag? (Without any barlows etc).

How does this work? (How do you calculate this)

Also, where would I buy a t-ring for the canon 350D in Sydney? What is a good price?

Finally, is the adapter from Andrews any good? I bought a 2x barlow but couldn't focus on anything, could only see the secondary mirror. Is this a problem with my scope.

Sorry for asking so many questions in one thread.
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  #2  
Old 08-12-2005, 04:00 PM
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avandonk
avandonk

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FOV(deg)=57.3(widthofsensor/Focal Length) for a canon 350D 24x15mm

So we get 1.1deg x 0.68deg

Bert
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Old 08-12-2005, 04:25 PM
captain3081
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thanks bert, but I don't know how to convert that to magnification.
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Old 08-12-2005, 04:42 PM
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[1ponders] (Paul)
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Hi captain.

I don't know too many imagers that work with magnification in mind. Normally its FOV that's more importants. (Sorry if you know all this already) But for a quick and dirty, rough and ready opproximation without the maths involved:- 35mm cameras equate to about a 50mm lense, so if you have 1500mm of tube FL then the mag will be 30 times. Now the bit converting it to size is the bit I get confused with. I think the magnification increase 1.6 to 50 times for canon chip in the same scope.

help out please knowledgeable brothers and sisters.

Last edited by [1ponders]; 08-12-2005 at 05:10 PM.
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Old 08-12-2005, 05:06 PM
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captain, good to see you back, i thought it was around a fl=50mm therefore 1250 / 50 = 25x

i think???
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Old 08-12-2005, 05:10 PM
captain3081
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Thanks Paul. I don't even know what FOV is all about (I think it means field of view).
I am less than an amateur. I just want to be able to take a photo of what I see through the lens, to keep a history of my viewing.

I know how much detail I can see of Jupiter with my 9mm EP, so I would like to compare this the canon at prime focus. (ie will it be more than a tiny blob.)

Not sure what you mean about the increase of 1.6 to 50x mag. Are you talking about DSLRs being smaller sensor compared to 35mm?
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Old 08-12-2005, 05:13 PM
captain3081
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Thanks Dave

I've always been here, lurking in the shadows. I don't get the scope out very often, but I enjoy reading the forum every couple of days. I seem to be just taking a lot in. I don't really have much to contribute.
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Old 08-12-2005, 05:25 PM
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Quote:
Originally Posted by captain3081
Thanks Paul. I don't even know what FOV is all about (I think it means field of view).
yep field of view.

Quote:
I just want to be able to take a photo of what I see through the lens, to keep a history of my viewing.
I think you might have included 99% of astroimagers


Quote:
I know how much detail I can see of Jupiter with my 9mm EP, so I would like to compare this the canon at prime focus. (ie will it be more than a tiny blob.)
It will only be small, but on a good night with the right exposure it can still look good.

Quote:
Not sure what you mean about the increase of 1.6 to 50x mag. Are you talking about DSLRs being smaller sensor compared to 35mm?

As I understand it, the canon chip will give an equivalent magnification boost of 1.6X to your imaging system compared to 35mm film.
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Old 08-12-2005, 06:37 PM
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my take on this is that you can try and take a picture of what you see through your eyepiece. this is called afocal. a nice steady hand is required.

prime focus with a toucam (webcam) is equivalent to a 6mm ep and prime focus is roughly 30x.

so for a canon, go afocal thru an eyepiece to get a decent size for planets and for beautiful wide views of clusters and nebula, go prime focus (tracking a must).

hows bubs?
Quote:
Originally Posted by captain3081
Thanks Paul. I don't even know what FOV is all about (I think it means field of view).
I am less than an amateur. I just want to be able to take a photo of what I see through the lens, to keep a history of my viewing.

I know how much detail I can see of Jupiter with my 9mm EP, so I would like to compare this the canon at prime focus. (ie will it be more than a tiny blob.)

Not sure what you mean about the increase of 1.6 to 50x mag. Are you talking about DSLRs being smaller sensor compared to 35mm?
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Old 11-01-2006, 05:09 PM
captain3081
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I was very excited about my first attempt.

26mm GS 2" with the kit lens.

Using prime focus, is there any chance of snapping saturn, or is it useless without guiding?
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Old 11-01-2006, 05:52 PM
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Hi Captain, you could try prime focus but it will be very small with little detail. AFocal as DP says below would be the way to go for you. There was a thread recently by jjjnettie (i think) showing some snaps using this method.

Nice moon!

cheers,
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Old 11-01-2006, 06:47 PM
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Quote:
Originally Posted by captain3081
I was very excited about my first attempt.

26mm GS 2" with the kit lens.

Using prime focus, is there any chance of snapping saturn, or is it useless without guiding?
excited right back at you!

that is very sharp focus, well done!!!

as for saturn, give it a go, are you set up for prime focus with the 350d??

i estimate you will get 25x, which will mean quite a small saturn, but at least you can get a fair few shots off before it leaves the field of view.

can you set the camera to keep taking images, ie movie mode???

otherwise, you will have to try and take a shot through the 9mm eyepiece like you did with the 26mm and the moon.

it takes a bit of practise, but make sure the guide scope is lined up properly and then see it you can work out where saturn travels across the cross hairs. that way you can lign up saturn to come across the field of view in say 10 seconds, grab the camera, put it to the eyepiece and try and get a focus.

do this a few times and then once focus is achieved, takes as many pics as you can before it is out of your field of view.

best of luck

hows bubs???
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