Teleconverters

anyte · Aug 2, 2004

Does a teleconverter affect the aperture or DOF - or anything else the uneducated photographer might want to know about?

Thank you

David A. Goldfarb · Aug 2, 2004

A teleconverter transforms the lens into a lens of longer focal length by whatever the conversion factor is (usually 1.4X, 2X or occasionally 3X). Meanwhile, the physical diaphragm does not change in size, so if you have a 1.4X converter, the effective f:stop is one stop less than what it says on the aperture dial, and with a 2X converter you lose two stops, and the DOF will be the DOF for a lens of the focal length you get with the converter at the aperture calculated with the converter for the applicable subject distance and format.

If you are metering through the lens, you don't really need to think about this--just use the converter and do what the meter tells you. If you are using an external meter or a non-TTL auto flash or manual flash, then you need to include the exposure factor. If you are not metering through the lens, you might also want to test for transmissive light loss with the converter, which can sometimes be as much as half a stop, which is important if you shoot slide film.

Converters also reduce image quality somewhat by magnifying the flaws of the main lens, but sometimes the tradeoff for convenience is worthwhile.

Flotsam · Aug 2, 2004

Another feature that you might be interested in is that the the minimum focusing distance remains the same so you wind up with a longer lens that focuses unusally close. This helps if you like to do occasional macro photography.

anyte · Aug 2, 2004

Thank you for the input. That helps me out quite a bit.

Nige · Aug 2, 2004

The beauty of my 2X teleconvertor is that it's guts (the glass elements) screw out, leaving it functioning as an lengthy extension ring... the only way I use it What is silly, is that I always screw the inards back in afterwards... I should throw them away but it's hard to break a 20 year old habit

anyte · Aug 2, 2004

I know what a teleconverter does, but what does an extension ring do?

TPPhotog · Aug 2, 2004

anyte said:
I know what a teleconverter does, but what does an extension ring do?

Quick answer is allows the lens to focus closer to the subject and give greater magnification for macro working.

Must check mine and see if it un-screws LOL

glbeas · Aug 2, 2004

I used to have one like that for the old Minolta. If you mount a teleconverter, then the "extension tube" then the normal lens you can get even better magnification, in my case I got a 7/8" field of view.

Unfortunately, the EOS teleconverters are way too pricey to do this with so I went ahead and got some bona fide extension tubes on Ebay to use.
Then theres the Bronica......$$$$

Jorge Oliveira · Aug 2, 2004

Just a reflection re teleconverters:

Image quality suffers, but in my experience, if one enlarge a photo from a given distant subject not using a TC to the same size of one taken with a TC, the final quality is better with the TC.
And TC's shall not be used with short lenses. They fare better making tele lens longer.
This is valid for 2X TCs - 3x TCs give lousy results...

This said, TCs shall only be used if a longer lens is not available.

Jorge O

25asa · Feb 15, 2005

Jorge Oliveira said:
Just a reflection re teleconverters:

Image quality suffers, but in my experience, if one enlarge a photo from a given distant subject not using a TC to the same size of one taken with a TC, the final quality is better with the TC.
And TC's shall not be used with short lenses. They fare better making tele lens longer.
This is valid for 2X TCs - 3x TCs give lousy results...

This said, TCs shall only be used if a longer lens is not available.

Jorge O

I know this is an old thread and under 35mm, but it's the only one relevant.

I have been scratching my head over this since I did lens test.

I took my Hassy out with the 250mm and a 2x converter. I shot a distant brick wall using a tripod, mirror lock-up and a cable release.

With the converter I shot frames at 5.6 (11), 8 (16), 11 (22), . .up to 45 (90)
Without the converter I shot frames at 11, 16, 22, 32, and 45 to coincide.

Magnifying the bricks to where they are the same size, the 2x converter shots show better resolution and accutance.

Can anyone explain this?

Thomas Wagner · Feb 15, 2005

My Vivitar actually "Macro-Focuses". Allows all my lenses to function in an adjustable macro mode. Biggest probem I had with conventional teleconvertors is that they could not be used in close focus situations. I like being able to get really close with some of my tele-zoom lenses.

TW

127 · Feb 16, 2005

25asa said:
With the converter I shot frames at 5.6 (11), 8 (16), 11 (22), . .up to 45 (90)
Without the converter I shot frames at 11, 16, 22, 32, and 45 to coincide.

Magnifying the bricks to where they are the same size, the 2x converter shots show better resolution and accutance.

The most obvious thing is the area of film you're using.

If you're magnifying/cropping to the same final image, then the 2x image is using the full 66 frame, while the regular image is cropped so you're only using the centre - perhaps equivalent to a 35mm neg.

Ian

Teleconverters

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