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08-02-2008, 02:17 AM   #1
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celestron c5 spotter

What have i done
I was a little bored and started searchin for som "cheap" fun.
I ended up with a brand new Celestron C5 spotter with adapters etc, and a Berlebach tripod and a gitzo video head. it's 1250mm f10
mounted on the k20d . I think i need more training to get the most out of this setup but i post an example. Celestron have this Reducer/Corrector that gives f/6.3 and are suposed to give better image quality but im not shure what focal range i end up with. mayby i go for one in the future.

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08-04-2008, 07:46 AM   #2
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QuoteOriginally posted by Phaser Quote
What have i done
I was a little bored and started searchin for som "cheap" fun.
I ended up with a brand new Celestron C5 spotter with adapters etc, and a Berlebach tripod and a gitzo video head. it's 1250mm f10
mounted on the k20d . I think i need more training to get the most out of this setup but i post an example. Celestron have this Reducer/Corrector that gives f/6.3 and are suposed to give better image quality but im not shure what focal range i end up with. mayby i go for one in the future.
The reducer/correctors will multiply the focal length (and hence f-number since lens diameter stays the same) by 0.63.

So a 1250mm f/10 will become a 787.5mm f/6.3.

Pretty nice considering that you effectively have the speed of a Bigma at 1.4x the focal length.
08-04-2008, 08:28 AM   #3
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Entropy, please help me understand.

By adding an adapter and the camera, you are physically adding to the length of the lens - so why would the focal length be shorter?

P.S. If it involves particle physics and advance calculus - never mind, as I won't understand!
08-04-2008, 09:23 AM   #4
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I guess it's because the C5 is a 1250mm "lens" with the adapter and the camera. If you insert a reducer between the adapter and scope................... need i say more?

08-04-2008, 12:56 PM   #5
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QuoteOriginally posted by Phaser Quote
I guess it's because the C5 is a 1250mm "lens" with the adapter and the camera. If you insert a reducer between the adapter and scope................... need i say more?
Is the reducer actually affecting the width of the light passing through it, or is it reducing one thread size to another? If it's not restricting the light, then I still wonder why it reduces the focal length.
08-04-2008, 01:14 PM   #6
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QuoteOriginally posted by Tom S. Quote
Is the reducer actually affecting the width of the light passing through it, or is it reducing one thread size to another? If it's not restricting the light, then I still wonder why it reduces the focal length.
Actually it increases the light angle exiting the scope therefore changing the focal length. We are not talking lens but a scope. "F" ratio is calculated by taking the focal length (1250mm) divided by the front lens(refractors) or mirror diameter for SC(Smith-Cassegrain, Newtonian..). So if the mirror is 5 inch (125mm) divided into focal length 1250mm = F10. Now if I took the light and made it appear to focus at 787 versus 1250mm than we would get F6.3. That is what the reducer does. To calculate the power view in an eyepiece simply divide the focal length of the eyepiece into the focal length of the scope, ie a 25mm eyepiece = 50x in that scope.
08-04-2008, 08:16 PM   #7
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Phaser you have done a very good thing. The C5 is a great really long lens. Your setup is almost a carbon copy of mine. My wood tripod looks bigger and has a different brand head (made by the tripod company - no name on it). Have the same K20D/C5 setup. You do need to put a lens shade on. It really helps such a big piece of glass.
If you search this forum for TIPS USING A BIG MIRROR LENS LIKE C5 you will find a lot of tips for using big mirrors.
Telecompressors are neat. Always thought we would see one for our cameras. It would reduce FF lenses to match APSc sensor and give us more light. Camera companies stole the teleconverter from the telescope
guys.
Nice wildlife shoot. Not easy to follow with 1250 lens. Good job.
thanks
barondla

Check out POINT & SHOOT CONTEST 9 WINNERS IN P&S forum. Enter #10. Any type camera except slr. Any brand. Any subject. Enter now.
08-04-2008, 10:01 PM   #8
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Thank you for the Lens shade tip haven't tought about that. should be obvious though.
I shall do some more reading but now it's time for work.

BTW barondla. do you have any pictures of what you managed?

08-05-2008, 05:29 AM   #9
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In the tips thread there is an eagle shot. No processing because wanted people to show what the lens can do. Looks much better have adjusting color/levels, etc. Have a white egert shot that needs to get posted some day. Also have moon, lunar eclipse shots.
Celestron sells a neat lens shade for about $30. It is a flat piece of plastic that has padded strip on one end. It wraps around C5 and attaches with velcro. It is almost as long as the lens!
Enjoy the new lens.
thanks
barondla

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08-05-2008, 07:30 AM   #10
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QuoteOriginally posted by Tom S. Quote
Entropy, please help me understand.

By adding an adapter and the camera, you are physically adding to the length of the lens - so why would the focal length be shorter?

P.S. If it involves particle physics and advance calculus - never mind, as I won't understand!
The adapter is not just a physical adapter - It has optics in it.

It is effectively the exact opposite of a 1.4x teleconverter.
08-05-2008, 08:39 AM   #11
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QuoteOriginally posted by Entropy Quote
The adapter is not just a physical adapter - It has optics in it.

It is effectively the exact opposite of a 1.4x teleconverter.
Ah ha! That clears it up! Thanks!
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