Different exposure on different lens but same camera settings

I'm still not completely convinced that this has nothing to do with jpeg processing.....

 

- Sorry Ed, I'm not about to repeat the experiment wasting time, money and natural resources by shooting film!

When you focus to 0.6m with the 50mm lens you lose 1/4 stop of light due to extension.

When you focus to 0.6m with the 50mm lens you lose 1/4 stop of light due to extension.

 

- Apparently a lot more in real life.

I kinda assumed (dangerous i know!) that the pics were OOC JPEGs and not RAW conversions?

I kinda assumed (dangerous i know!) that the pics were OOC JPEGs and not RAW conversions?

 

- Mine were OOC JPEGs, but the histograms confirmed the shift in exposure was real.

 

I also repeated the process several times, and in reverse order, just to make sure it wasn't a one-off fluke. The above 3 samples were typical.

 

Did the same using a Sony MILC fitted with a 50mm Jupiter 8 preset aperture lens. So no way the aperture could physically vary between exposures. The Jupiter 8 only focusses down to 1 metre, and yet there was a very noticeable drop in exposure going from infinity to 1 metre focus. F/4 and 1/125th used again BTW.

 

Theoretically, from infinity to 1 metre, the drop in exposure ought to be less than 1/6th stop. So how come it's easily seen?

In addition i see in Joe's examples a clear difference in colour rendering, wich may add to an impression of difference in exposure ….

I've often noticed that 1/3 stop difference in Exp. Comp. 'seems' much more obvious on a modern DSLR than 1/3 EV on 100 ASA B/W film or even 64 ASA E6 slide.

I've not been following this too closely, but... with an electronic lens that sets the aperture from the camera rather than with the aperture ring, the camera should be reporting a different aperture according to the focus distance (and corresponding change to effective aperture as the sensor-to-lens distance extends). Hence, unless the lens is designed otherwise, you should see the maximum aperture drop on a macro lens the closer you get; I'm reasonably sure I've seen this and didn't imagine the behaviour. I believe Nikon have done this for a while: the aperture reported in the viewfinder as that used to determine exposure (corresponding to T-stops) rather than the at-infinity f-stop which IIRC Canon reports.

 

In other words, unless you've run out of aperture, focus distance shouldn't be modifying exposure on any vaguely recent Nikon lens. Obviously if you set the aperture by the aperture ring, it can't adjust the aperture dynamically with focus distance (or at least, it doesn't - I suppose someone could make one that moved the aperture ring as you turned the focus ring). I'm now second-guessing myself because I have a nagging feeling there was a special manual 50mm or similar that actually did do something weird like this, but I can't find a reference to it, so maybe I'm hallucinating.

focus distance shouldn't be modifying exposure on any vaguely recent Nikon lens.

 

- I'm not sure if that's true for any but specific macro - or micro - lenses. It seems to be a function of the lens chip, and not implemented in 'normal' zooms or primes. Otherwise the indicated aperture would be wobbling all over the place as focus was shifted.

 

Besides, nobody wants to be reminded that their f/1.8 lens is 'only' f/2(.025) at minimum focus. Nikon would rapidly get tired of dealing with the complaints, I'm sure.

You're right, Joe - so much for one more thing I thought I knew. I just tried a 50mm f/1.8 AF-S on my D810, pointing it at a wall lit by artificial light, spot metering, and then manually racked the focus back and forth. The camera resolutely thinks the lens is set at f/1.8 (in manual exposure), but the exposure reading (or auto ISO, in my case) varies significantly, with close focus being quite a lot darker.

 

Putting on my Sigma 150mm f/2.8 macro, the aperture readout in my viewfinder (in manual mode) won't actually read f/2.8 at maximum in my (smallish) study - the far wall is already reading a maximum of f/3, and that drops below f/4 by the time I get anywhere near minimum focus distance.

 

I wouldn't have minded either approach really, but I'm a little surprised that they're not consistent. For macro, DoF depends on the physical aperture, doesn't it? So changing is actually counterproductive if you're trying to calculate depth of field at a given focus distance.

 

I guess AF lenses that weren't AF-D would never have been able to change the reported aperture, so Nikon would have had to explain why their AF-D versions of lenses were "slower". I guess it makes sense for the lens to control it - with focus breathing and relatively constant-aperture (I believe) macros like the 70-180, you can't just use the thin lens equation with the focus distance.

Edited October 12, 2018 by Andrew Garrard

this isnt a new problem, on eg a RB67 is a table to calculate the compensation for close focussing

Yes, I understand it's a thing for large format, too. It's something that always made me a bit nervous about large format shooting without having an in-camera meter (which exist but are rare for large format).

So changing is actually counterproductive if you're trying to calculate depth of field at a given focus distance.

 

- Depends on the DoF formula used. A decent algorithm will automatically take the lens extension into consideration; after calculating the physical aperture diameter. But of course this only works with 'old fashioned' unit focussing.

 

Personally, I'm done with relying on spreadsheets that work out DoF to the nearest micron. It's all hooey that totally depends on the degree of viewing magnification, and basically comes down to a very (very) rough guide.

 

FWIW. The only TTL meter for large format that I know of is the Sinar-six meter. Having used one, it has a huge design flaw, and is about as useful as a chocolate fireguard.

Edited October 12, 2018 by rodeo_joe|1

- Depends on the DoF formula used. A decent algorithm will automatically take the lens extension into consideration; after calculating the physical aperture diameter. But of course this only works with 'old fashioned' unit focussing.

 

Personally, I'm done with relying on spreadsheets that work out DoF to the nearest micron. It's all hooey that totally depends on the degree of viewing magnification, and basically comes down to a very (very) rough guide.

 

FWIW. The only TTL meter for large format that I know of is the Sinar-six meter. Having used one, it has a huge design flaw, and is about as useful as a chocolate fireguard.

 

I never had a large format camera but I have the Minolta booster II when attached to a Minolta meter can make measurement on the ground glass. Don't know how well it works though.

when attached to a Minolta meter can make measurement on the ground glass. Don't know how well it works though.

 

- Ah, there's the rub. 'Measurement on the ground glass.' All sorts of flies in the ointment there. Firstly there's diffusion and loss of light through the focussing screen, which needs calibrating out. Secondly, there's light entering the camera from every other area of the ground-glass, which may well swamp the light from the lens itself. I don't know about you, but my dark-cloth certainly isn't big and opaque enough to keep every scrap of extraneous light off the viewing screen. And then how do you read the meter in pitch darkness?

 

Nope. A good ole incident meter remains my weapon of choice. I do have a spotmeter, but really don't know where to stick it.

Suggestions please?

It would appear the consensus is leaning toward the zoom internal focus design not changing exposure with distance nearly as much as the unit-focusing primes. I'd considered that, but initially thought all the extra glass in the zoom might neutralize the effect. Rodeo_Joe's test proves otherwise- very useful info!

I'm now second-guessing myself because I have a nagging feeling there was a special manual 50mm or similar that actually did do something weird like this, but I can't find a reference to it, so maybe I'm hallucinating.

 

You're not hallucinating: you're thinking of the once legendary, but now mostly forgotten, first 1963-1968 version of the 55mm f/3.5 Micro-Nikkor Auto lens. When it was introduced, the Nikon F only had externally coupled (non-TTL) selenium meter options. Trying to build on the F reputation for innovation, Nikon's clever solution to the problem of exposure drift at closer macro focus distances was having the lens itself figure the exposure compensation needed based on distance, and adjust its own aperture for constant EV.

 

The lens was an instant legend, for both optical quality and the auto-compensating feature, but it does have limitations. Your shooting aperture needs to be f/8 max to give the mechanism two stops leeway to open up as distance gets closer. The feature cannot be disabled, so when using cameras with TTL metering you end up with the reverse problem: the meter reads at full aperture but the lens over-rides exposure as the shutter is fired. The workaround was stopped-down metering, which is more painful on Nikons than other brand cameras, so the lens fell out of favor a couple years after the "Photomic" meter prisms arrived.

 

The lens remains a minor cult item today because it was the only Micro-Nikkor completely optimized for macro work. Its non-compensating replacements had a tweaked optical formula making them better at infinity, but reducing performance slightly at macro. The auto-compensating-aperture glitch is more manageable on digital Nikons where you can quickly chimp to change settings, and if used on Sony or Canon bodies without mechanical coupling you're always metering in stop-down mode anyway.

 

For those interested in trying one, look for serial numbers below 28xxxx and be sure the name ring does not read "Micro-Nikkor-P Auto" - it should read "Micro-Nikkor Auto" without the P. The performance difference isn't huge, but some pros like Bjorn Rorslett vastly prefer the older lens for true macro work. Just as some Hasselblad shooters prefer the older slower 120mm S-Planar f/5.6 over the newer Makro-Planar f/4 (the older lens is optimized for macro, the newer sacrifices some of that for better infinity).

Edited October 12, 2018 by orsetto

Your shooting aperture needs to be f/8 max to give the mechanism two stops leeway to open up as distance gets closer.

 

- Two stops?

The ones I've played with only focussed to 1:2, I'm pretty sure, and needed the M ring to get to 1:1.

 

Once the extension ring was fitted there was obviously a disconnection between the marked aperture and effective aperture; although I think the focussing scale carried aperture correction markings. That's IIRC.

 

Not the only lens to employ focus-corrected aperture BTW. Zeiss Jena employed such a mechanism on some of their Pentacon lenses.

Edited October 12, 2018 by rodeo_joe|1

- Two stops? The ones I've played with only focussed to 1:2, I'm pretty sure, and needed the M ring to get to 1:1.

 

Right, the whole concept falls apart once you add the M extension ring for 1:2 thru 1:1. Coupling the ring as well would have been far too complicated in that era, even for Nikon: the M ring deliberately omits the meter coupling fork to remind you to use the engraved scales for additional manual exposure compensation. My two examples compensate over a range of approx. 1.4 stops according to my D700, so I use f/8 as a practical maximum on film bodies. The lens will blow past f/5.6 and edge toward f/4 territory as it reaches 1:2 closest focus (without the extension tube). One could probably get away with a f/5.6 starting point, but the full compensation range seems to require approx f/7.0 (impossible to set with Nikon's firm full-stop aperture ring detents). There may also be some age and wear related lens to lens variations in the compensating aperture mechanics.

Edited October 12, 2018 by orsetto

Thanks, orsetto - that sounds cool, and I'm now slightly more educated about another obscure corner of the F system.

 

I wish I could claim I'd been thinking of something that interesting. Sadly I was actually only thinking of the 45mm GN, which I believe adjusts its aperture with focal length, but doesn't communicate the result to the camera. I'm guessing, though - I've never seen one.

The 45mm GN Nikkor does have a similar compensating aperture feature. But unlike the 55mm Micro-Nikkor, the feature wasn't intended for normal available-light photography. The compensation gimmick in the 45mm was for flash exposure only, and was disabled with a switch most of the time. Back in the era of flash bulbs and fully manual electronic flash, the GN Nikkor offered a semblance of flash auto-exposure. The GN stood for Guide Number, a standardized power rating assigned to most flash devices. If you switch the GN Nikkor to flash mode, and set the Guide Number of your flash on the lens, it will then adjust aperture as the focus ring is turned (maintaining consistent exposure, in essence a mechanical version of auto-flash).

 

A nifty feature, but limited to just this one lens, which at the time nobody was particularly fond of. 45mm was considered an odd focal length, SLRs were big so a pancake lens seemed pointless, and the f/2.8 Tessar derivation was rather slow and mediocre compared to the 50mm f/2. Once cheap auto-flash units from Vivitar and Sunpak flooded the market in the 1970s, demand for the GN Nikkor fell off a cliff (every NYC camera emporium was literally giving them away in their used depts). The introduction of DSLRs resurrected the GN Nikkor from its grave, and now they're inexplicably popular and pricey. It can't be the obsolete flash feature, so I assume it must be the pancake size and/or Tessar optics that attracts buyers. Perhaps people associate it with the crazy-expensive collectible 45mm Nikkor-P update Nikon offered with the FM3a (arguably the same lens, without the GN flash feature but with electronic contacts for compatibility with newer Nikon bodies).

Edited October 13, 2018 by orsetto

my dark-cloth certainly isn't big and opaque enough to keep every scrap of extraneous light off the viewing screen

take a black t-shirt

The earliest versions (IIRC F Type) of the 45mm GN are also used by people to image in UV. The simple optical formula with only 4 elements and a lack of multi-coating make it serviceable enough. LV focusing on a modern DSLR makes the UV focus shift irrelevant.

For what it's worth, the "pancakeness" is what attracted me to the E series 50mm, and I gather the GN version is similar. The 50mm AF-D and AF-S both have deeply-recessed front elements, providing a kind of integrated "hood" (even though the AF-S version actually comes with a hood). Given that I tend to put one of these on the camera when I want something relatively easy to carry around, and that a DSLR will just fit in a coat pocket if the lens isn't much thicker than the depth of the grip, the unnecessary sticky-outiness of the autofocus lenses annoys me. For some reason Pentax is unusual in working this out, and I envy their pancake AF lens selection.

 

Still, could be worse - the older version 90mm Tamron macro that I own has a similar (but worse) recessed front element. Whatever benefit it gave to construction and handling, it mostly has a catastrophic effect on working distance when macro shooting. Sometimes an extra inch matters, as my wife tells me.

Well, the search function in photo.net works.

I recently had a brief thread about my D850 underexposing. I sent it back to Nikon for adjustment, which took about a week. I updated that it was working fine-had a great trip to Zion National Park after Christmas.

Anyway, I bought another copy of the manual focus 50-135 f3.5 Nikkor lens since my old copy was suspect. I found the new copy was underexposing as well.

Here's the connection to this thread. I followed convention (I think) that I entered the low end of the zoom range for the "non-CPU lens data" setting, 50 mm in this case. I just did some quick testing, and entering 50-70-85-100-135 in the setting increases the exposure. By about 85-100 the exposure is correct on this manual focus lens.

Why would an entered focal length number alter the function of the exposure meter? I don't recall seeing this on other manual focus zooms I have owned. Obviously the meter function is very complicated, with many variables.

It's getting dark here, but I will test this further tomorrow.

Why would an entered focal length number alter the function of the exposure meter?

 

- Errr, because Nikon's TTL metering is a complete fudge?

 

It can easily be shown that using lenses with an aperture greater than f/1.8 makes absolutely no difference to the screen brightness, nor to the apparent depth-of-field shown. It therefore follows that there's some kind of optical aperture restriction in the viewing system - this is the same for all Nikon SLRs, and every other brand of SLR that I've been able to test.

 

Neither is the viewfinder response to changes in aperture linear at apertures smaller than f/1.8. The lens aperture needs to be smaller than f/5.6 before viewfinder brightness doubles or halves with each one stop aperture change.

 

Now, since Nikon's metering sensors are in the prism-housing, and above the focussing screen, the metering system must also be non-linear. Hence the need to 'tell' the camera the aperture of any non-CPU lens fitted. If you report the maximum aperture wrongly, then the exposure is off - try it!

 

This wouldn't be the case, or even be necessary, unless the metering system applied a 'fudge factor' to the exposure dependent on aperture.

 

How this relates to focal length, I'm not sure. Except that the viewfinder aperture-restriction may well depend on the exit pupil diameter of the lens, and its distance from the viewfinder screen. Zoom lenses is strange beasts!

 

Incidentally, I've always set a mid-range focal length value for any non-CPU zoom I've used - which isn't many I'll admit.

Edited January 12, 2019 by rodeo_joe|1