D700/Tamron 90mm issue.........

Discussion in 'Casual Photo Conversations' started by stuart_pratt, Jul 15, 2020.

  1. This seemed like the best place to post this.

    Maybe I'm being really thick here (why change the habits of a lifetime) but I can't fathom this one out. I have an old manual focus Tamron 90mm f/2.5 adaptall, that I use on a number of film bodies, and also in stop down mode on a D700. Just recently I noticed it didn't stop down to f/32 with the Nikon adapter attached. After a bit of playing and thinking, I came to the conclusion that the stop down 'wheel' (not a pin like on most other old MF lenses) wasn't getting fully depressed, only reaching f/32. However, it went to f/32 when pushed with a finger.

    To check this out, I put the mearest skim of Araldite (a 2 part glue) on the adapter at the point where it meets the stop down wheel, and left it to set, to ensure the adapter pushes the wheel down far enough to engage f/32, and hey presto, problem solved. This may, or may not be associated with the actual problem which is this.

    The D700/90mm combo underexposes by about 1 stop. In stopdown mode the camera should choose an appropriate shutter speed for the manually set aperture to give a correct exposure, so it shouldn't matter what aperture is set, a correct exposure should be had (I've been using the uniform light brown of my decking steps to compare it with other lenses). I've checked it at similar focal length to 2 other modern AF lens that give correct exposures and it is about 1 stop underexposed regardless of the aperture set. I can get round it by setting +1 exposure compensation which presumably gives twice the shutter duration.

    To start with I thought maybe the aperture ring had got out of whack with the actual aperture and, say, when f/8 was set, the actual aperture was f/11. But that doesn't make sense as the camera doesn't care less what number is written on the lens barrel. In stop down mode it exposes correctly (or at least should do) for the size of the 'ole.

    Looking down the lens barrel, wide open at f/2.5 the aperture blades just dissapear into the body of the lens, as I would expect, so I don't think there is a problem with the aperture areas.

    So I tried it on a film camera with a different adaptall 2 adapter (M42) and it's fine.
    I feel like I'm asking a stoopid question that has a VERY obvious answer here, but I'm stumped. Enlighten me someone, please!
  2. In one of my old John Shaw (nature photographer) books he talked about calibrating his film cameras to give the exposure he wanted. He didn't expect his Nikon bodies to be carbon copies of each other, so if one required some compensation one way or another he'd set it and go to work.

    If it's just the D700 that is reading the light from the lens 1 stop off, adjust the compensation and enjoy shooting. I have a friend that had (maybe still has) a Tokina lens that was off by 1 stop on one of his Pentax bodies.

    Eric Sande
    stuart_pratt likes this.
  3. When using manual lenses on DSLR's I often find exposure variations, so I'm in the habit of shooting an evenly lit surface and setting the exposure compensation to centre the histogram.

    What metering pattern are you using? I've got a D700 which overexposes by a whole stop with all lenses, the more so with matrix metering. They do seem to be susceptible to exposure errors.
  4. Applying the Sunny 16 rule leads me to believe some manufacturers are over rating their ISO.
  5. I use matrix 99% of the time. It’s just odd it’s only with this lens, and when the thing is already stopped down, when you would expect there is even less possibility of exposure error?!
  6. Back when I had a Nikon D2x I checked out Sunny f/16 on a clear blue sky (which we have plenty of in the desert) and it was far from "correct". Camera meters are subjective so you figure out how they work and continue on.

    Eric Sande
    Sanford likes this.
  7. I’m sure that’s how I’ll end up using it, it’s just peculiar, you mount this lens and the body says ‘engage -1 stop exposure compensation?’
  8. Here are the histograms

    Tamron 90.jpg
  9. Why are you using stop down metering?
    Old non-AI Adaptall mounts are extremely rare, and most Adaptalls are fully AI compatible - or even AI-s compatible. So you should only need to enter the lens data in the non-CPU lens menu, and use open aperture metering.

    I see from the above EXIF data that the aperture is unknown to the camera on a couple of those exposures. Why is that?

    Plus the metering mode has been altered from matrix to CW between the Nikkor lens and the Tamron. That's going to account for some difference.

    If the Adaptall you're using is an ancient 'rabbit ears' pre-AI version, then it's unsurprising that there's some wear in it that's preventing proper coupling with the lens. (IME there was always a bit of slop in those adapters that made the aperture ring less than 100% accurate.)

    Anyway, to me the easiest option would seem to be to get a new, or newer, AI-s compatible Adaptall mount for use with the D700.
    stuart_pratt likes this.
  10. If camera can't read aperture setting, what kind of metering we are talking about?:)
  11. It’s not actually an adaptall adapter. It came with the lens, just happened to be Nikon fit, and there is no aperture coupling, so you can only use it stopped down. I never noticed the change from matrix to CW (well spotted!) but that would be a function of it not reading the aperture I guess, and is the default position for the camera under those circumstances. I suppose there would be some difference in exposures. I’ll take the advice and get a new adaptall Mount, see if that makes a difference. Thanks for the help.
  12. Well I did just that and the new bona-fide adaptall mount works just fine with correct exposures. Swap it for the old one, and it under exposes by one stop? To resolve this issue, I've consigned the old one to the metal recycling bin!

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