Technical aspects of the AFS 300mm f/4 E PF lens

[Øivind Tøien]

....
 And a PN11 in a bag btw...

That caught my interest. I have been looking at my PN-11 (which already has a custom chip) to evaluate the possibility of feed through of the signals for E-lenses. It looks like cables could be fed through without disassembly and without blocking the light path, however I am not sure the contacts in the front could be fitted without disassembly and dremel work. It is also a question of finding a front contact block with adequate amount of connections for the E-lenses.

[Erik Lund]

It's a lot less hassle to use a TC... I have done it with an TC20E to try this out, just rip out the glass, works perfectly 

However, many/most/all modern lenses especially with floating elements doesn't do well with extension...

[Øivind Tøien]

It's a lot less hassle to use a TC... I have done it with an TC20E to try this out, just rip out the glass, works perfectly 

However, many/most/all modern lenses especially with floating elements doesn't do well with extension...

Thanks, the 300PF did pretty well wide open on the PN-11 when I tested it even in combination with TC-14E, but only if set at the close focus limit. This was on a DX body and I have not really checked corners much though. Getting a used TC-20E to "slaughter" is pretty expensive just to get an extension tube (almost as much as I once paid for PN11+105/4 although I do see some lucky purchases in the past on ebay). One would loose the tripod mount that can be useful for shorter lenses like the 105/4. But of course if one has to get a scrap body to scavenge for the contacts, that would also add to the cost. How long is the extension of TC-20E?

[Erik Lund]

Øivind I know the price of a used TC  ... do you know the hourly price for work of a machine shop 
I used a discarded TC20-E mark I or II
 
Aligning those contacts inside the PN11 would take a lot of tinkering and also soldering, with the TC you also get the correct electronics.

I remember a guy that did modify a PN11 like you suggest btw.

I will have a look how the 300 PF does on my TC20E extension tube

[Øivind Tøien]

....with the TC you also get the correct electronics.
...

Still considering the TC-20E, some further searching indicates one can get it for a little more than $100 with some good luck. I wonder about aperture readout though - it would report -2 stops to the camera. This seems too be much compensation for the amount of extension it will provide.

[Bjørn Rørslett]

That's because it - erroneously in this application - thinks 2 stops of light are "lost" due to the TC optics. Ordinary light metering will address and correct this by indirect means believing the incoming light has become almost 2 stops brighter, though. 'Almost' as there will be some change in effective aperture the size of which depending on the master lens in use.

[Øivind Tøien]

Yes, it is of course mostly an exif issue, unless exit pupil data get messed up. With 105/4, the compensation would be correct at 1:1.
Edit: No it will not because the 105/4 is not an AFS lens and responds  like my AF 300/4 that reports the aperture set on the lens.

I have noticed with TC-14E that there is a tendency for underexposure and perhaps more so with 300/4 PF than AF 300/4. I wonder if that could be due to the lower contrast, or possibly due to different degree of light falloff towards edges wide open in the two models, more so with the 300PF. If the body somehow receives data that compensates for this and there is less falloff with a TC, this would influence total metering.

[Erik Lund]

The metering on the D3 and D3X is spot on using the 'glass less' TC20E with any Nikkor/chipped lens.

It's more the issue with image quality form CRC or IF lenses..

[Bjørn Rørslett]

From the exposure standpoint a change in the [relative] entrance pupil will be decisive *given* the incoming rightness is constant. If an 1.4X TC is added, the focal length increases while the absolute entrance pupil is fixed, thus you "lose" 1 stop of light.

Nikon usually implement their aperture readout so the effective f-number is shown when a lens focuses closer. Behind the screen so to speak the actual diaphragm (determining the aperture) opens up to compensate for the decline in f-number caused by change in magnification of detail. This arrangement has the obvious advantage that the user don't need to bother about what the effective aperture really is. If an incident light meter shows "f/5.6" that is what the lens should read and be set to as well, even though the nominal value changes to say f/4 in order to end up as effective f/5.6.  The caveat here of course is the lens cannot open up the additional stop(s) when it is already at the maximum aperture, so here Nikkor lenses alter the readout instead to reflect the current change.

A quick test indicated that I got the same exposure (say f/5.6 at 1/30 sec) with or without the TC-14E.2 attached to the 300PF. This is of course what one would expect as exposure per se is not determined by the lens only by the actual light level of the scene. If I set the 300PF to f/4 without the TC and then added the 14E, one stop underexposure would result unless corrected by having twice as long exposure duration. Again by the book as it were.

[Øivind Tøien]

I just performed the same test on a uniform target (white wall):
"Correct" exposure according to meter on D5100:
Without TC-14E : 1/30s f/4
With      TC-14E : 1/30s f/5.6
Same results with spot-metering, except for 1/15s on both instead of 1/30 sec.

"Correct" exposure according to meter on D200:
Without TC-14E : 1/20s f/4
With      TC-14E : 1/8s f/5.6

"Correct" exposure according to meter on D40x:
Without TC-14E : 1/15s f/4
With      TC-14E : 1/10s f/5.6

So I am not imagining things. The meter on different bodies may differ in response - D5100 was my initial reference. It is suspicious though that there is exactly on stop error on D5100. Perhaps the angle at which the metering system looks at the screen comes into play. All bodies have Katzye all matte screens. Only D200 has the Optibright treatment. Perhaps a further investigation of how lenses with different max aperture meters on D5100 should be performed...

[Bjørn Rørslett]

Then the problem here is the camera not lens or TC. As I stated before, the Df handled the situation correctly and as long as the aperture was set to f/5.6 or smaller, identical exposures occurred as indeed should be expected.

[Øivind Tøien]

Yes, agree. I need to explore what further quirks the metering of the D5100 may have. Also a Ph.D. student in our lab has a 5100 with the original screen I can compare to. Perhaps you could check your red IR body (was it D5300?) The D200 and D40x results are as expected as exposure can easily flip by 1/3 stop.

[Bjørn Rørslett]

A good idea. Despite IR not being "light" in the usual sense, the camera's circuits don't know or care about such nitpicking details. Just need to track down an IR light source with constant illumination over a sufficiently wide field.

[Øivind Tøien]

No exposure needed to check the intentions of the light meter, which will be happy with a regular light source. None of my above tests included any exposure; it was just a light meter test.

Edit: I tested my AF 300/4 ED (non-AFS) on the D5100, and with that lens the meter responds in the same way as D200 and D40x did with the 300PF except that the camera will of course not report the correct aperture with the TC. So no metering problem with the AF 300/4 on D5100.  Could there  be a firmware bug in D5100 with respect to how it handles TC-14E with an E lens?  Bjørn, if you are able to reproduce this discrepancy with your D5300 it would be interesting to compare TC-14E/TC14E II to TC-14E III.

The manual exposures I did in this last comparison were as expected from the shutter speed/aperture so there is no indication that there is any problem with the aperture control of 300PF. At f/5.6 the same shutter speed will give identically exposed frames with the two bare lenses, at f/4 there is more light falloff to the edges with the 300PF, while the center seems close to the same. However as indicated by the tests above the meter on the D5100 reports to exposure by 2/3 stop faster shutter speed with the 300PF than with the AF 300 on a uniformly lit white wall (no TCs).

[Erik Lund]

I would not trust the metering readout of the camera, I would definitely make the exposure and look at it as well...

Only reports I have heard about the 300mm PF is that it is actually brighter T stop than f/4