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Old Feb 2, 2003, 8:18 PM   #1
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Default meade 70 ,90, 125

I have a nikon 5700 with the digi-t adapter. This camera is best used in well lighted situations.
I have a etx-70 that is ok, but it takes a lot of light to use it with the 5700.
I am considering upgrading to the the 90 or the 125. I understand that these both gather much more light than the 70. Is this enough of a factor to make them more desirable for digiscoping and/or astrophotography?
Is the etx 125 suitable for digiscoping as well as for astrophotography?
I don't understand the relationship of "f" ( the 125 is f15) to photo taking ability.
I would also consider adding a nikon 990 or 995 to my bag.
Is the 990/995 better to use with high magnification such as a 90 or 125.
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Old Feb 2, 2003, 11:47 PM   #2
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A couple of points - first, the 125 "can" be a decent scope for digiscoping, but a lot depends on whether you are using it for terrestrial or celestial purposes.

The "F" stop gives you some indication of how much light you will have available at the fixed focal length of the tube. Actually, the Meade ETX-90 might make a better terrestrial lens because it's rated at F13.8 at 1250mm focal length, while the 125 has a bit less light available, but at considerably longer focal length. A lot would depend on the focal length of the eyepiece. Obviously, the 125 gathers more light than the 90, but for terrestrial purposes, this may or may not be a factor depending on the circumstances under which you use the scope as a lens - and primarily whether you are using it in an "afocal" (fixed lens camera) manner or with a removable lens SLR or dSLR.

When used with a removable lens camera, a "T" adapter couples the camera sans lens to the telescope and the scope becomes a fixed focal length lens at a fixed F stop. The lower the "F" number, the more light is available. The only variable is the crop factor on a dSLR such as 1.6 on a Canon D60/D30 or 1.5 on a Nikon D1, D1h, D1x, 1.3 on a Canon 1D, or Kodak DCS-760 and 1.0, or zero crop factor on a full frame sensor Canon 1Ds.

When used in an "afocal" manner with a CP4500, 990, etc., the "F" rating of the lens is dramatically affected by the zoom of the camera. The higher the zoom, the less light.

My suggestion would be to also look at other alternatives such as the Celestron C5 with a large mirror and shorter focal length where more light is available. Great shots can be made with a Meade 125, but in practical use a Meade ETX-90 may be just as good to about 6000mm. Beyond this, there is insufficient light available to a fully zoomed CP series Nikon to make terrestrial digiscoping practical.

More light with a shorter focal length tube can often produce stunning results on birds, etc., where the truly good working range or "sweet spot" is between 3000 and 4000mm. When you get to the extreme ends of the range, it's necessary to have excellent light available to get reasonable results. Even though I routinely shoot at 5989mm with my ETX-90, I "must" have excellent sunny weather to get really good images. With a C5, it's possible to get the same quality images under less ideal conditions.

Truthfully, though a camera like the 5700 "can" be used, I would not recommend it. Better, in my opinion, to buy a good used 990 or 995 (or even a 4500) where the more limited zoom produces better digiscoping results. Super long zooms like the C2100UZ Olympus, Nikon 5700, or Canon Pro 90 are not as good for digiscoping as the more moderate zoom cameras like the CP990/4500, etc., It just takes too much in the way of an eyepiece - that is a long focal length eyepiece - (40mm or greater) to reduce the focal length to useable range. Can you do it? Yes. Should you do it? Probably not...

Best regards,
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