High end telephoto (afs nikkor 2.8/300) or 80mm triplet refractor?

Struggling to find a side by side comparison of a premium 2.8/300 telephoto vs small refractor of similar weight.

My daylight photo gear could accommodate a nikkor 2.8/300 vr lens. But I rarely shoot fast moving targets, I was wondering if I'd be better served by a William Optics GT-81?

If you’re after a lens that provides an alternative to a refractor with a focal length of 500mm or so, I can recommend the Nikon Z 180-600 lens. It’s a very fine lens for wildlife and bird photography but, remarkably, also works ok as a 600/95mm telescope. It is sharpest at 400mm but is good even at 600mm.

Here’s a starfield test taken at 600mm, stopped down from f/6.3 to f/8. It’s a single, uncropped, 30s frame taken with a Z50 (and yes, you can see that the sensor needs to be cleaned).


Pollux

Since the lens is only about 2kg and 32cm long it makes a good travel refractor for astrophotography. The big disadvantage is that it can only be used on Nikon Z cameras.

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Andy

Indeed a great lens Andy, but it would also serve a dedicated astro camera and the Z flange is way too short to be able to add astro filters.

The flange distance is the lesser problem when considering using a Nikon Z lens on a astro camera (it might just about be feasible using an astro camera with a very short backfocus distance). The greater (and insoluble) problem is that you can’t focus the lens, even in manual mode, unless it’s mounted on a Nikon Z camera.

My approach is to use the 180-600 on a Nikon camera for some broadband targets such as large galaxies or galaxy clusters and have a completely separate system for nebula photography, i.e. an 135mm Askar fma135 scope on an astro camera, with a filter drawer in the optical train.

(And I heartily recommend autoguiding when you get up to this focal length)

I have a guide scope that I often mount to a camera L bracket when I shoot astro with camera lenses on my Z cameras. It’s very convenient. However if I happen to change the rotation of the camera for object framing reasons I will then need to recalibrate the guide camera, because it also rotated. This has blindsided me at least once at the beginning of a session when the guiding determinedly sailed off into the unknown, far worse than not guiding at all.

But since telescopes often have a mounting point for a guide scope and also some means to rotate the camera, re-framing doesn’t incur a time penalty related to the guiding.

Anyway, just one more factor to consider.

Properly astro-rigging a large telephoto is indeed not straightforward but doable!

just Tony said:

(And I heartily recommend autoguiding when you get up to this focal length)

I have a guide scope that I often mount to a camera L bracket when I shoot astro with camera lenses on my Z cameras. It’s very convenient. However if I happen to change the rotation of the camera for object framing reasons I will then need to recalibrate the guide camera, because it also rotated. This has blindsided me at least once at the beginning of a session when the guiding determinedly sailed off into the unknown, far worse than not guiding at all.

But since telescopes often have a mounting point for a guide scope and also some means to rotate the camera, re-framing doesn’t incur a time penalty related to the guiding.

Anyway, just one more factor to consider.

--
Wag more; bark less.

Click to expand...

Tomx72 said:

Properly astro-rigging a large telephoto is indeed not straightforward but doable!

Click to expand...

What you said.

On the plus side, a rotation at the provided collar for framing doesn’t mess up the balance.

--
Wag more; bark less.

Tomx72 said:

Struggling to find a side by side comparison of a premium 2.8/300 telephoto vs small refractor of similar weight.

My daylight photo gear could accommodate a nikkor 2.8/300 vr lens. But I rarely shoot fast moving targets, I was wondering if I'd be better served by a William Optics GT-81?

Click to expand...

Both options have their pros and cons...

If you want to use a dedicated astrocamera, especially a mono with filter wheel, the real telescope will be in advantage for focusing. In addition to possible distance problems the newer camera lenses are very often working with focus by wire, so no focus without electric power to the lens mount...

On the other side there are no or only very few telescopes with large apertures in 2.8... And to use the tele lens also for nature and wildlife pictures is also very appealing, because you don´t want to buy it double...

With lenses from standard systems you can get different adapters, but when I tried to use an awesome Mamiya 6/500APO from RB67 medium format, there was exact one adapter available and this one was not perfect. To adapt an Askar FRA500 is no problem at all...

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Reinhard
Olympus E-M5II, E-M1II, OM-1, Olympus lenses from 7 to 300mm
Panasonic S1R, S5, Sigma L-mount lenses (14-24, 24-70, 50, 85, 135, 150-600)