TMax 100 with a Tamron Adaptall 28-50 lens

I’d had a roll of 35mm TMax 100 loaded in a Mamiya ZM camera for months without shooting it, so I decided it was time to use it up last month and took it on two trips, one to Kirkley Hall in Northumberland and one to Tanfield Railway, where I also shot some pinholes.

Click on the images for a larger view

I previously blogged about the Mamiya ZM and explained that the meter wasn’t working. Since then the camera developed another fault, with the dial that adjusts the exposure compensation and ISO coming loose. I purchased a second body, which works fine and threw the first one out. I have a Mamiya ZE 50mm lens, which works but has a loose focus movement, so for these trips I took instead a Tamron-Adaptall 28-50mm zoom.

I have a few of these Adaptall lenses and I really like the flexibility of being able to use the same lens on several different camera bodies. I have adapters for Canon FD (but no longer have a Canon FD body); Nikon, Pentax K, M42, Minolta, Olympus.

The 28-50 lens cost me about £25 and although I had used it before a couple of times, I forgot which frames it had been used for. This time I used it for the whole film so I could be definite it had been used for all those frames.

From this test, I was quite happy that the lens was in full working order; there was nothing obviously wrong in the technical quality of the images. I’m not in a position to make detailed comparison of resolution and contrast with other lenses, but there are other sites that can give you such detail.

One interesting feature of this lens is that there are two sets of aperture markings (marked in orange and blue below), to indicate the actual aperture for 50mm, and for 28mm. It’s obvious when you think about it that, since the diameter of the aperture is expressed as the focal length divided by the f number, then the same diameter cannot produce the same f number at two different focal lengths.

For example if the focal length is 50mm and the desired f number is f8 (or f/8 to be more correct) then the diameter of the lens opening will need to be 50/8 = 6.25mm.

At 28mm the lens opening at f/8 should be 28/8 = 3.5mm.

However, older mechanical lenses such as this don’t have an infinite number of diameter options which can be chosen according to the focal length in use at the time. If the diameter to which the lens closes down is optimised for 50mm, then the same diameter when chosen at 28mm will under-expose by a stop or more. Hence, the markings placed on the lens by Tamron will lead you to place the aperture-selection collar at a different position to match the long and short ends of the zoom (in other words, at 50mm you would place your chosen f number next to the amber line, and at 28mm you would place your chosen number next to the blue line). To be correct in intermediate positions, you’re left with guessing a position between the blue line.

This makes logical sense but:

  • it’s a bit fiddly and one more thing to remember
  • I haven’t noticed this system used on any other zoom lens
  • In the image below, you will see there is also a blue and orange line indicating the distance at which you are focussed – but there’s also a white line and I have no idea what the white line represents!

If you are using negative film then you’re not likely to see the difference between exposures one step apart, but this is worth thinking about if you’re using slide film.

I’m guessing that modern autofocus zoom lenses use firmware to calculate the correct opening for each f number at the chosen focus length.

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