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Old Feb 1, 2004, 11:50 AM   #1
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Default Wich Digital camere adapter EYEPIECE?

I finally got my Mak-Cas (MCS) spotting scope with a 25mm and a 9mm plossi eyepiece.
Now I want to use my Nikon CP 4500 with this scope and with another one with shorter focal lengh.
The scopes are:

- MeadeETX, 90mm aperture, 1250mm focal lengh (f=13.8) Mak-Cas scope
- Syntha (Konus), 90mm aperture, 500mm focal lengh (f=5.6) Mak-Cas scope
-
I would like to know wich of the below DCA eyepiece are the best for digi-birging with the scopes (coupled with my CP4500):

- William Optics DCA-28 (24mm)
- Scopetronix STWA14 (14mm)
- Scopetronix STWA18 (18mm)
- Scopetronics MaxView 40mm + nikon adapter for 28mm

And what about Scopetronix MaxPower Lens for the scopetronix
eyepiece - digital camera adapters wich boost the magnification of
the scopetronics eyepiece (40mm to 25mmm; 18 to 12mm; 14 --> 9mm) ?

I would also like to make some shot to the moon and to try with some DSO deep-sky object like orion nebula and andromeda galaxy.


I could find the WO-DCL28 in Italy for 130euro (aprox 160 us $)
but I could not find any scopetronics eyepiece in Italy shops.
The US prices of these eyepiece are on the internet on-line shops, ranging from 80 to 110 us $.

Thanks in advance for your advice and help.

Francesco
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Old Feb 1, 2004, 5:33 PM   #2
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Some stuff here on using a scope which sounds rather like the second you mention but with the extremely challenging Nikon CP 5700 :
http://www.3ge.com/pix/digiscoping/digiscoping.html

Wonder if the Vixen (& various other names) 8-24mm zoom would be an acceptable choice for that scope; would give nice 20ish to 60ish zoom range.
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Old Feb 2, 2004, 12:32 PM   #3
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The 500mm spotting scope is the one shown at:
http://www.3ge.com/pix/digiscoping/ScopeTronixGear.html

but mine is coloured in orange :?

Thanks, ToToRo
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Old Feb 2, 2004, 5:24 PM   #4
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The William Optics DCL-28 (24mm) is a good match with the Meade ETX-90 and your C4500L. Using a shorter focal length eyepiece with the 1250mm focal length Meade tube would be counter productive.

I'm not familiar with your 500mm focal length scope. Does it also use a 1.25" eyepiece? If so you need to decide which focal lengths are most usable for your purposes, then select an eyepiece which will give you that focal length or range of focal lengths.

Do the calculations as follows:

Divide the focal length of the scope by the mm of the eyepiece. For example:

With the Meade ETX-90 (1250mm focal length) divided by the William Optics 24mm DCL-28 gives a power factor of 52.083x.

So the "native" power of this combination is 52.083x. To then calculate the focal length this would equate to start with the full wide angle of your camera in mm which would be for the CP4500 38mm. Then multiply 38mm times 52.083 to get 1979.154mm if you use your scope/camera combination at full wide angle. Since your camera has 4x zoom, you can either simply multiply 1979.154 by 4 or choose a particular focal length and the formula above to get a precise focal length for the specific camera focal length in 35mm equivalency. At full zoom you would get about 7916mm which is a bit more than useable (you terminate at around 6000mm for light gathering usefulness).

You can see by the formulat that the longer the focal length of the eyepiece, the less overall "power" of the combination. Conversely, the shorter the focal length of the eyepiece, the more power. So assuming you can use the William Optic 24mm (1.25") eyepiece with the 500mm focal length scope, you would have a range of between 20.8x and 83.33x power with your camera. That equates to 790.4mm to 3166mm (35mm equivalency).

For this scope you may want a shorter focal length eyepiece such as the ScopeTronix 18mm (27.7x to 110.8x) or the 14mm eyepiece which yields 35.7x to 154.8x.

However, be advised that "only" if your scope takes a standard 1.25" astro type eyepiece without an adapter can you be certain this will work properly. As an example, my Swarovski ST-80 HD does not work with the "standard" ScopeTronix 18mm eyepiece (it won't focus properly). The Swarovski takes a special Swarovski adapter to use astro type 1.25" eyepieces. However, ScopeTronix does now make an 18mm eyepiece which "will" work with the Swarovski, it's just that the "standard" 18mm eyepiece doesn't.

Best regards,

Lin
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Old Feb 4, 2004, 7:57 AM   #5
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I found this usefull internet calculator for DCA afocal coupling.

http://velatron.com/dca/formulae/english

It seems that the final focal lengh with afocal coupling is much more shorter than the one you have suggest.
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Old Feb 4, 2004, 8:37 AM   #6
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If there is a difference then the forumula used by the "calculator" or your imput data is wrong.

It's really quite straight forward:

The 35mm "equavilency" produces a range of focal lengths in a zoom lens. For example, the zoom range of the CP4500 is 38mm to 155mm.

If your telescope has a "power factor" of 52x with a given eyepiece such as the 24mm DCL-28 (power factor is determined by a formula agreed on by everyone which is simply focal length of tube divided by focal length of eyepiece) then that power factor times the focal length of the attached camera equals the overall focal length.

Any "calculator" which reaches a different number is either incorrect or the data was entered incorrectly.

You can take the above or reject it - your choice - but that's the way it is.

Best regards,

Lin
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