Vignetting of Nikon 10x Plan Achromat

Geopressure · Post by **Geopressure** » Wed Jul 26, 2017 3:19 pm

Hello all. I am rather new to this hobby, and find that my Nikon 10x CFI infinite objective experiences significant vignetting when used with a Canon 28-135mm zoom as a tube lens. This is on a Canon T5i camera. The zoom is set at 135mm and focused at infinity at f 5.6. I can address the issue using extender tubes however it seems that the sharpness suffers a bit.

Is this the expected result with a short zoom lens? I seem to have read that a 100mm prime lens would not have this issue and should be sharp at 5x...I'm a bit confused here.

Thanks to everyone for this excellent forum!

DavidG1980 · Post by **DavidG1980** » Wed Jul 26, 2017 5:03 pm

Hi there,
I've read, like you, that the Nikon is usable throughout 5-10X using a 100mm to 200mm tube lens.
Mine, like yours' vignettes heavily when used with a tube lens of less than 135 mm. It seems that the new version of this objective has a smaller field of view.

rjlittlefield · Post by **rjlittlefield** » Wed Jul 26, 2017 5:07 pm

Welcome aboard.

Yes, what you're observing is a typical result with a short zoom lens. The problem is that the entrance pupil (the apparent position of the aperture) is too small and/or too far back, so that light rays headed for the edges of the sensor get blocked by the lens iris.

I regularly use infinite objectives with my Canon EF 100mm f/2.8L macro IS USM lens, without experiencing significant vignetting. Compared to your lens, the 100/2.8 lens has a larger entrance pupil, probably farther forward, so the edge rays do not get blocked.

And indeed, the combination of a 10X CFI infinite objective with that 100 mm rear lens makes a very sharp 5X combo. See http://www.photomacrography.net/forum/v ... hp?t=15876 and http://www.photomacrography.net/forum/v ... hp?t=15922 for some comparisons. You might also be interested in http://www.photomacrography.net/forum/v ... hp?t=16348 , which shows what such a combo can do with a real subject. (That last thread uses a different model of objective, but it's still a Nikon CFI.)

I hope this helps!

--Rik

Geopressure · Post by **Geopressure** » Wed Jul 26, 2017 7:06 pm

Rik,

Thanks for your clear explanation. Is it safe to assume that a Canon 100mm f2 telephoto would be likely to get good results? I would prefer to use a Canon 135mm prime however they are quite a bit more expensive.

I have been using a Tamron 70-300mm zoom (set at 200mm) with my 4x Nikon objective and getting good results.

rjlittlefield · Post by **rjlittlefield** » Wed Jul 26, 2017 7:40 pm

100mm f/2 sounds very promising. But "safe to assume" would be too strong. In this matter of coupling one lens with another, it seems that nothing is certain until it's been demonstrated -- and even then I worry that a particularly good result was somehow due to quirks of the individual lenses.

--Rik

ChrisR · Post by **ChrisR** » Thu Jul 27, 2017 12:40 am

Geopressure wrote: I would prefer to use a Canon 135mm prime however they are quite a bit more expensive..

Nice lenses, but perhaps an order of magnitude more expensive than you need.
The "tube" lens is working at quite a small aperture, and its quality is nowhere near as important as that of the ojective. Many members use old 135mm and other lenses reporting good results. There are old Zeiss, better Vivitar, and many such as Olympus which are fine. You can get cheap adapters for most makes including M42, to Canon. I have a Nikkor 135mm f/3.5 which is fine.
With 100mm you're more likely to see some dimming or optical degradation in the corners.

A Raynox DCR-250 (125mm) works well, though you need a bunch of hollow rings/adapters.

Geopressure · Post by **Geopressure** » Thu Jul 27, 2017 6:54 am

Many thanks, I will explore some of these lower cost options!