Eyepiece adapter for Nikon?

[ThomasLondon]

Hi,

After considering a 72 or 80mm refractor for travel for some time I realised that I am always carrying this incredible 72mm 2.8 telescope with absolutely perfect field correction over a full-frame sensor with me - others call it a Nikon 2.8 70-200 ED FL.  Absolutely smooth focuser already built in.

So the only challenge seems to be how to get it connected to an eyepiece. Nikon has a flange distance of about 43mm - that may be difficult with a diagonal, but does not seem impossible. Any advice for a suitable adapter? The Kenko thing does not work, as it does not allow exchanging eye pieces.

Regards

Thomas

[rl]

With due respect to Nikon (some of whose kit I also own) your lens may prove to be a slight disappointment as a scope even if you can find a short enough diagonal to make it work at all. I don't know this particular lens but I expect it's built to produce excellent colour correction and minimal distortion over a 44mm circle compromising absolute resolution on the process; the design tradeoffs with camera lenses usually give the best resolution when stopped down to about f/4 to  f/8. Your lens has the additional design constraint of being a zoom..getting that right will mean the resolution probably is at its best over a limited range of focal lengths.

Run fully open at f/2.8 the resolution probably won't get anywhere the Rayleigh limit since the camera pixel size will always be larger than the theoretical spot size wide open, and you will need excellent eyepieces to cope with so wide a cone angle without some horrible off-axis aberrations. Even TV only test to f/4.

The usual advice using camera lenses for astro use is to stop them down 1 stop to improve the resolution ans star shapes in the corners. 

Astro telescopes are built to optimize resolution first, and trade off flatness of field

Baader do a fairly comprehensive range of adapters; I don't know if they do a Nikon female to T-thread. They do a helical T-thread to 1.25" focuser which would open up the possibility of straight-through viewing. For low power-wide-field use you might be on to a winner capitalizing on the flat field assuming the eyepiece has an equally flat field.

Regards, RL

[ThomasLondon]

Well, this is a lens which is considered extremely sharp even wide open, and you can achieve a lot even with a modern zoom if you have enough optical elements (Nikon uses 6 ED and one fluorite element - the lens costs about 3 times as much as a triplet APO of that size).

I guess if nobody tried it yet, it's high time someone does... after that we know more. I guess I will give the Geoptik adapter a try.

Best

Thomas