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AF - Kenko 1.4x Pro 300 DGX TC with Nikkor 70-300 VR

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yukongold

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I just purchased on e-bay the above TC with the expectation of using it with my variable aperture zoom lens. I mounted it on a d7100 with the above lens. And then I found out auto focus was hit and miss! For whatever reason I was not expecting this. It works very well with my 300 f4 of course but I was expecting the option to use it with a zoom - with AF. MF is of course a workable option but less convenient. Was I wrong in my original assumption? Should I be happy with the MF on a zoom?

Thanx for your guidance in advance....
 
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My eyes have been opened! Thanx to all for the education. Some time ago I read somewhere (not this forum....) that this combination worked great together so I thought I would give it a try. Obviously I misunderstood or was mis-led. At any rate will not use/try except in rare / ideal circumstances. Can say that it is not a waste however as I will use with my 300mm f4 AF-S on my D7100.

I will still use the 70-300 with my D80, and the 300 + TC (either Kenko 1.4x DGX or Nikkor 2x II) with my D7100 - especially on my expectant African safari next summer....!!!

Again - much thanx to all...
yukongold said:
yukongold wrote:

I just purchased on e-bay the above TC with the expectation of using it with my variable aperture zoom lens. I mounted it on a d7100 with the above lens. And then I found out auto focus was hit and miss! For whatever reason I was not expecting this. It works very well with my 300 f4 of course but I was expecting the option to use it with a zoom - with AF. MF is of course a workable option but less convenient. Was I wrong in my original assumption? Should I be happy with the MF on a zoom?
Click to expand...
Your expectation disregards the physics. The PD AF sensor needs at least an f-value of 5.6 to more or less reliably "see".

The 1.4x TC turns that value into f8 (1 stop difference), turning the AF sensor half blind. That is why you get such hit and miss results. Alternatively, use live view with contrast AF focussing.

It works fine with the 300mm f4, because the TC turns the combination in f5.6. The PD AF sensor can still see fine.
yukongold said:
Thanx for your guidance in advance....
Click to expand...
 
Thanx for the response - However the 7100 center AF point works at f8 and is the point I use (and therefore ok with the 5.6 and 1.4xTC - theoretically....)
 
Tried that combo once, won't try it again. Yes, it works well on a 300mm f4 AFS.

The 70~300 is too slow. The max aperure with a t.c. is too restrictive, AF is poor, and IQ isn't too good either. It works, but not well enough. I'd rather crop than use that combo.
 
yukongold said:
yukongold wrote:

Thanx for the response - However the 7100 center AF point works at f8 and is the point I use (and therefore ok with the 5.6 and 1.4xTC - theoretically....)
Click to expand...
I thought the D600 was the only Nikon body that Nikon claims will AF properly @ f8 ?

Either way I wouldn't use the 70~300 with a t.c.

--
www.andrewsandersphotography.co.uk
 
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I've used this combination (well, a Tamron 70-300, not Nikon, but close enough) on a D7000 (!) and it works OK if you shoot in bright light. It won't work well in dim conditions with a D7000; can't speak to a D7100 at all.

What sort of lighting are you shooting in? Perhaps your expectations are just too high?

Cheers
 
slimandy said:
slimandy wrote:
slimandy said:
yukongold wrote:

Thanx for the response - However the 7100 center AF point works at f8 and is the point I use (and therefore ok with the 5.6 and 1.4xTC - theoretically....)
Click to expand...
I thought the D600 was the only Nikon body that Nikon claims will AF properly @ f8 ?

Either way I wouldn't use the 70~300 with a t.c.
Click to expand...
 
I was shooting in pretty bright conditions - images attached (one w/o, one with tc)





3b8390fd16584473816bffe6318b670c.jpg




b3e785d9f99841ab8749b1032c32e8f2.jpg
 
yukongold said:
yukongold wrote:

Thanx for the response - However the 7100 center AF point works at f8 and is the point I use (and therefore ok with the 5.6 and 1.4xTC - theoretically....)
Click to expand...
Did you choose single AF mode explicitly? My older DG (not DGX) teleconverter doesn't set it for me; I don't know if the newer model does.

On page 297, The U.S. D7100 manual states that at f/8, "the camera may be unable to focus on dark or low contrast subjects." Looking at your test shot, it seems that the center sensor is pointing at the overhang on the front garage area, which is both dark and low contrast.

--

I miss the days when I used to be nostalgic.
 
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yukongold said:
yukongold wrote:

I was shooting in pretty bright conditions - images attached (one w/o, one with tc)

3b8390fd16584473816bffe6318b670c.jpg


b3e785d9f99841ab8749b1032c32e8f2.jpg
Click to expand...
From the two examples shown it looks like cropping the original shot w/o the TC will give better results. Of course I can't tell for sure but try cropping to see which look better.

--
Snapshott
 
The exposure is very different to draw any conclusion. The first picture has much more contrast than the 2nd photo. They should also be compared at 100% cropped.
 
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Nikon is very clear that this lens will not AF with a tele-extender. In fact, you cannot even mount it on the one Nikon makes. I have known people who do use a Kenko with it, but except in very good light with high contrast subjects, they all resort to MF.
 
Every nikon AF point on every body can AF down to f8 :)

The downside is the AF performance can be very "miss" in low contrast light, low light, and focus tracking is no faster than walking pace :(

This may be why Nikon are economical with the truth saying no AF in older cameras using slower than f5.6.

F8 performance on the newer officially f8 bodies is better, but still far from what I regard as good with my 200-400 with a 2x.

In good contrast, decent light levels and a first class target AF is reasonable with your body, but in other shooting situations I too find it can be more miss than hit :(

If you get the 80-400 AF-s I think you will be extremely pleased at 400mm. Unfortunately many cannot afford the entry price.
 
I have tried the 70-300 with 1.4 kenko and I got better results by cropping. It is arguable that this will be the case with any 1.4 TC and any lens with current digital technology.

I sold mine and now crop even though I have much better telephoto lens than the 70-300.

PS I think the 70-300 is a great lens for the price.
 
romfordbluenose said:
romfordbluenose wrote:

I have tried the 70-300 with 1.4 kenko and I got better results by cropping. It is arguable that this will be the case with any 1.4 TC and any lens with current digital technology.
Click to expand...
I agree a 70-300 at 300mm has relatively low fine detail recording ability before adding a converter.

However cropping the OP's D7100 by the equivalent of a 1.4x converter reduces MP from 24 to 12.

The loss with a good converter on a suitable lens is far less than halving the MP available in the image file.
 
Leonard Shepherd said:
Leonard Shepherd wrote:
Leonard Shepherd said:
romfordbluenose wrote:

I have tried the 70-300 with 1.4 kenko and I got better results by cropping. It is arguable that this will be the case with any 1.4 TC and any lens with current digital technology.
Click to expand...
I agree a 70-300 at 300mm has relatively low fine detail recording ability before adding a converter.

However cropping the OP's D7100 by the equivalent of a 1.4x converter reduces MP from 24 to 12.

The loss with a good converter on a suitable lens is far less than halving the MP available in the image file.
Click to expand...
 
Brandon birder said:
Brandon birder wrote:

Leonard,

I have seen this written many times but what is the theory behind it. I find on all my lenses that an image cropped by half is usually better than one with 1.4tc.

Surely a tc means that you have to double the iso or halve the shutter speed, both of which can cause sharpening degradation. In addition there is contrast reduction with a TC.

As many people are at pains to write a 12 mpx image (half 24 mlx of D7100) still produces a great print at A3 size.

Looking forward to your thoughts.
Click to expand...
That's an interesting exposition. Having 12 mpx available after you've cropped changes things. And since the TC isn't going to improve the image quality, I can believe you're right.
 
yukongold said:
yukongold wrote:

Thanx for your guidance in advance....
Click to expand...
In the wisdom of a classic pinball game, at some point it's necessary to "quit talkin' and start chalkin'." So here's a test I just conducted, and I'll explain why it doesn't mean jack below:

D800, 70-300mm VR wide open, Kenko 1.4 DG Teleconverter

D800, 70-300mm VR wide open, Kenko 1.4 DG Teleconverter

D800, 70-300mm VR wide open, no teleconverter.

D800, 70-300mm VR wide open, no teleconverter.

I shot both pictures from exactly the same spot using a 3-series tripod and large ball head. VR was off, and I used a remote release. I did not use MUp mode. I then did my best to crop the same area of interest out of the center. (As always, NEF's available on request).



At least to my eye, this time the crop "won." With slightly different parameters, it wouldn't surprise me if the TC "won." I could do some MTF-based hand waving here, but in non-mathematical terms, unless your lens and teleconverter are good optically enough to take advantage of the extra sensor "real estate," the unavoidable optical losses in the teleconverter will dominate the advantages of that "real estate."



So why doesn't it mean jack? Simply because the 70-300mm is not designed for use from a tripod, and the vast majority of shots taken through this lens are handheld. Handheld, with VR on, any inherent optical advantage to using or not using a TC is going to get lost in other random factors. Personally, I don't use a TC with this lens. But if you feel a better view of your subject is worth the extra stop of light and AF flakiness, give it a try.

--

I miss the days when I used to be nostalgic.
 
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My eyes have been opened! Thanx to all for the education. Some time ago I read somewhere (not this forum....) that this combination worked great together so I thought I would give it a try. Obviously I misunderstood or was mis-led. At any rate will not use/try except in rare / ideal circumstances. Can say that it is not a waste however as I will use with my 300mm f4 AF-S on my D7100.

I will still use the 70-300 with my D80, and the 300 + TC (either Kenko 1.4x DGX or Nikkor 2x II) with my D7100 - especially on my expectant African safari next summer....!!!

Again - much thanx to all...
 
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