Ignorant of lens meanings

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derekh

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Pleae could anyone help?

Sorry about my ignorance oe lenses, I have acquired an optomax zoom lens, which I would like to have a play with. The markinmngs on it are as follows:-
1:3.8 f=85~205mm auto zoom. I also have a 2x tele convertor.
To start with can anyone explain in reasonably plain English what the 85~205 refer to and mean.
Also what effect would using this lens have on aperture selection, and shutter speed, and how should I calculate them.
Sorry if this is all a bit basic, but never used a zoom before and would just like to have a go and try it.

Thanks,

Derek
 
Need a bit more info really Derek. What camera will you be using this on?

A pic of the lens markings would help mate - those numbers look a tad suspect.
 
the lens markings are on the front of the lens, surrounding the lens itself.
It has an F stop ring 3.8 to 22, a zoom ring marked 85 to 205, and a focus ring marked 2 to infinity. A further ring is marked 'M'and 'A' PRESUMED MANUAL OR AUTO...CATCHING ON EH!

I will be trying it on my trusty old Zenit 11.

Not done much for a long time as you can see by the equipment, but was very satisfied with results I used to get with standard lens.

Hope you can be of further help.

Derek
 
well i'd say it was an f3.8 max aperture lens with a zoom range of 85mm to 205mm

the focus distance could be anything, feet/meters though.
 
Thanks for that, can you explain abit more in simple terms the range of 85 to 205mm.........what are we measuring here?
 
OK Derek - quick and dirty explanation.

Taking a standard 50mm 2.8 lens lens as an example it would probably be marked

50mm 1:2.8 signifying that the the lens is 50mm focal length.The 1:2.8 bit is an indication of the ratio of the diameter of the max aperture (wide open) to the focal length. If you measure the actual width of the diameter wide open it will divide into the 50 mm focal length 2.8 times, so it's an f2.8 lens. We'd say that's a moderately 'fast lens' because of it's ability to admit light. As the maximum aperture of any given lens becomes smaller we tend to think of it as a slower lens because of it's reduced ability to operate in low light.

This would indicate that the max aperture of your lens is f3.8.

The zoom markings 85-200 are easy enough, it's a useful mid range tele zoom from 85mm to 200mm.

The trouble with zoom lenses is that as you zoom the lens longer then the focal length becomes longer, meaning that your max aperture will now divide more times into the focal length, so your effective max aperture becomes smaller. For this reason zoom lenses are usually marked with something like f3.5 - f5.6 indicating how the effective aperture changes during zooming.

There are zoom lenses which have a constant aperture throughout the zoom range. It's accomplished by very expensive optical wizardry within the lens and these lenses tend not to be cheap. That's why I was doubting your original figures as I would think it unlikely that a cheap lens which the optomax is would have a constant 3.8 aperture throughout the zoom range? But hey - I could be wrong... I can't find any info on the lens. :shrug:

Using the 2X teleconverter is easy enough - you just lose two complete stops exposure. With a TTL metering camera the exposure should be taken care of automatically anyway.
 
CT said:
That's why I was doubting your original figures as I would think it unlikely that a cheap lens which the optomax is would have a constant 3.8 aperture throughout the zoom range? But hey - I could be wrong... I can't find any info on the lens. :shrug:

Using the 2X teleconverter is easy enough - you just lose one complete stop exposure. With a TTL metering camera the exposure should be taken care of automatically anyway.
Click to expand...

Ladybird has on loan from her brother a Vivitar 75-205 f3.8. This also comes with a 2x matched converter. I thinking that lenses of this kind of length/aperture were fairly common back in the 80s. :)
 
Using the 2X teleconverter is easy enough - you just lose one complete stop exposure. With a TTL metering camera the exposure should be taken care of automatically anyway
Click to expand...

Don't mean to talk bullards but don't you lose 2 f stops with a 2x teleconvertor?
Paul ;)
 
PaulBoy said:
Don't mean to talk bullards but don't you lose 2 f stops with a 2x teleconvertor?
Paul ;)
Click to expand...

Absolutely correct Paul. I typed that in a real hurry. Thanks mate. I'll amend the post. :thumbs:
 
Thanks very much everyone, i'll let you know what went wrong when i have a go tomorrow!.....or I'll ask the other questions that first use is bound to throw up.

Thanks again everyone

Derek
 
Joe T said:
Ladybird has on loan from her brother a Vivitar 75-205 f3.8. This also comes with a 2x matched converter. I thinking that lenses of this kind of length/aperture were fairly common back in the 80s. :)
Click to expand...

Good point Joe although back in the 80's Vivitar were a highly respected independent lens maker, probably as well thought of as Sigma. (So me dad tells me. ;)) They offered a real alternative to Canon, Nikon et al glass, but weren't particularly cheap. The Vivitar Series 1 were the best lenses and highly prized.
 
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