Aperture/focusing distance changes at different FL for zoom lenses?

Started Mar 21, 2013 | Discussions
pavinder
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Aperture/focusing distance changes at different FL for zoom lenses?
Mar 21, 2013

So I went out to test a number of M4/3 zoom lenses today and was majorly disappointed by 2 things as I zoomed to higher focal lengths:

Many seemed to rapidly close down the aperture, and some had very long minimum focusing distances.

Of course I expect these things to change, but was surprised at how quickly they did so.  For example with the Olympus 14-42 kit zoom it seemed that just by zooming slightly the aperture was suddenly at 5.6, and I couldn't focus at closer than about 90cm (my estimates, not measured precisely...).  These are absolute dealbreakers for me.

1. Is there any chart/guide which shows at what focal lengths a lens closes down to smaller maximum apertures?

2. Comparing lenses on this site side-by-side, the "minimum focusing distance" seems to be that at the widest end.  Is there any chart/guide to show the minimum focusing distance at different focal lengths?

Martin.au
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to pavinder, Mar 21, 2013

So I went out to test a number of M4/3 zoom lenses today and was majorly disappointed by 2 things as I zoomed to higher focal lengths:

Many seemed to rapidly close down the aperture, and some had very long minimum focusing distances.

Of course I expect these things to change, but was surprised at how quickly they did so. For example with the Olympus 14-42 kit zoom it seemed that just by zooming slightly the aperture was suddenly at 5.6, and I couldn't focus at closer than about 90cm (my estimates, not measured precisely...). These are absolute dealbreakers for me.

1. Is there any chart/guide which shows at what focal lengths a lens closes down to smaller maximum apertures?

2. Comparing lenses on this site side-by-side, the "minimum focusing distance" seems to be that at the widest end. Is there any chart/guide to show the minimum focusing distance at different focal lengths?

Are you after any particular requirements?

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pavinder
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to Martin.au, Mar 21, 2013

Are you after any particular requirements?

As you can imagine, I'd like to have the focusing distance remain as short as possible, and the aperture remain widest as the FL increases.

I know the Panasonic zooms have constant f2.8, but it's the other zooms I'd like to compare.

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revio
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to pavinder, Mar 21, 2013

So I went out to test a number of M4/3 zoom lenses today and was majorly disappointed by 2 things as I zoomed to higher focal lengths:

Many seemed to rapidly close down the aperture, and some had very long minimum focusing distances.

Of course I expect these things to change, but was surprised at how quickly they did so. For example with the Olympus 14-42 kit zoom it seemed that just by zooming slightly the aperture was suddenly at 5.6, and I couldn't focus at closer than about 90cm (my estimates, not measured precisely...). These are absolute dealbreakers for me.

1. Is there any chart/guide which shows at what focal lengths a lens closes down to smaller maximum apertures?

2. Comparing lenses on this site side-by-side, the "minimum focusing distance" seems to be that at the widest end. Is there any chart/guide to show the minimum focusing distance at different focal lengths?

Strange, since most af zoom lenses I´ve had the opportunity to use have hade exactly the same minimum focus distance at all focal lenghts (Olympus, Nikon, Canon, a few others, and in Oly both m4/3 and regular 4/3)

(Some older zoom lenses I have owned had varying minimum focus distance vs f-length, though)

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pavinder
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to revio, Mar 21, 2013

Strange, since most af zoom lenses I´ve had the opportunity to use have hade exactly the same minimum focus distance at all focal lenghts (Olympus, Nikon, Canon, a few others, and in Oly both m4/3 and regular 4/3)

Really?  I've never had a zoom with a constant minimum focusing distance throughout.  At the wide end they always focus closer.

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Ulric
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to pavinder, Mar 21, 2013
Many seemed to rapidly close down the aperture, and some had very long minimum focusing distances.

It's not that the aperture closes down, but that the focal length increases.

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pavinder
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to Ulric, Mar 21, 2013
It's not that the aperture closes down, but that the focal length increases.

Of course the aperture closes down!  As the focal length increases, the aperture closes.

That's what it means when the number goes from 3.5 to 4 to 5.6 etc!

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BBbuilder467
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14-45 & 45-200
In reply to pavinder, Mar 21, 2013

My 14-45 focuses at 30 CM easily at any focal length and down to f/22. The 45-200 focus at 1 meter regardless of the focal length and aperture. Actually less if I get particular. I'm measuring to the tripod mount. Both focus at the minimum focus distance advertised.

I can get a little closer than the minimum spec at wide end of the 45-200, but the minimum listed matches the long end.

They can miss a target and get lost if the subject is close and you don't pay attention, but I've never had a real problem getting the minimum focus distance at any focal length if the subject is solid, not like a tree branch or bush that it can see through or past, and there is some contrast.

The 14-45 is f/3.5 at 14, f/4 at 18, f/4.9 at 25, f/5.5 at 35 and f/5.6 at 40.

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Ulric
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to pavinder, Mar 21, 2013
It's not that the aperture closes down, but that the focal length increases.

Of course the aperture closes down! As the focal length increases, the aperture closes.

That's what it means when the number goes from 3.5 to 4 to 5.6 etc!

Remember that the f-number is the ratio of the focal length to the entrance pupil. Take for example the very nice M.Zuiko 40-150 mm zoom. At 40 mm, its relative aperture is 4.0 => 40/4.0 = 10 mm. At 150 mm, its relative aperture is 5.6 => 150/5.6 = 27 mm. No closing down there.

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revio
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to pavinder, Mar 21, 2013

So I went out to test a number of M4/3 zoom lenses today and was majorly disappointed by 2 things as I zoomed to higher focal lengths:

Many seemed to rapidly close down the aperture, and some had very long minimum focusing distances.

Of course I expect these things to change, but was surprised at how quickly they did so. For example with the Olympus 14-42 kit zoom it seemed that just by zooming slightly the aperture was suddenly at 5.6, and I couldn't focus at closer than about 90cm (my estimates, not measured precisely...). These are absolute dealbreakers for me.

1. Is there any chart/guide which shows at what focal lengths a lens closes down to smaller maximum apertures?

2. Comparing lenses on this site side-by-side, the "minimum focusing distance" seems to be that at the widest end. Is there any chart/guide to show the minimum focusing distance at different focal lengths?

I found, after writing my first comment, I wanted to try my lenses out for these parameters. Of course I had quickly went beyond the "comment editing time limit". Thus, here comes my observations of my 4 available zoom lenses:

All, except one, have linear "aperture darkening" as I zoom upwards. The one exception was the Zuiko 14-54mm/2,8-3,5 which maintained a full F:2,8 from 14mm up to and including 18mm.

My Micro Zuiko Digital 12-50/3,5-6,3 was, on the other hand, the one exception to the norm among the 4 lenses I tried in that it did have variable minimum focusing distance. All the other lenses had exactly the same minmum focusing distance kept at all f-lenghts, allowing a difference of a few millimeters.

(Within for example a centimeter, or two, I´d still consider a lens to have, in practise for most uses, a "fixed" minimum focus distance. Maybe I´d be interested to make a more severe test, but I think I´m not very much in need of knowing that. In practise it wouldn´t be of a major importance to me)

My assortment tried today:

Zuiko Digitals: 14-54/2,8-3,5,  40-150/4-5,6,  14-42/3,5-5,6

M-Zuiko Digital 12-50/3,5-6,3

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Dr_Jon
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to pavinder, Mar 21, 2013

Things worth noting...

Firstly the Minimum Focusing Distance is usually (always I think) quoted from the sensor, not the end of the lens, so if you do look up distances then remember that. For example I was amazed by the close focusing distance of the 12-35 f2.8 as I hadn't looked it up, actually it is just under 9" (from the sensor).

Secondly you possibly don't care. What you might actually care about is the Maximum Magnification, which says what is the largest size it can project something onto the sensor. For example if it is 0.2x that means at the closest focusing distance at some focal length it can project a 20mm high object as 4mm high on the sensor. On m43 that's about 1/3 of the image height. (So a lens with a MM of 0.2x and closest focusing of 50cm will enable a larger image of an object than a lens with 0.1x and 15cm. Also if the subject is alive it may be easier to take the photo as won't have to get so close.)

The aperture going down with focal length is how you keep lens size and cost down, both being important in lenses being sold to consumers.

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revio
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to Ulric, Mar 21, 2013
It's not that the aperture closes down, but that the focal length increases.

Of course the aperture closes down! As the focal length increases, the aperture closes.

That's what it means when the number goes from 3.5 to 4 to 5.6 etc!

Remember that the f-number is the ratio of the focal length to the entrance pupil. Take for example the very nice M.Zuiko 40-150 mm zoom. At 40 mm, its relative aperture is 4.0 => 40/4.0 = 10 mm. At 150 mm, its relative aperture is 5.6 => 150/5.6 = 27 mm. No closing down there.

Closing down physically or not, the usable F:no, seen as "usabel light input", decreases as F:no gets changed from 3,5 to 5,6 for example

F:5,6 demands a longer shutter time (or "slower speed", if that is better understood) than F:4.

Most amateur users don´t even have to know that aperture expressed as F-number is a ratio of entrance pupil vs f-lenght, but, of course, it´s never bad TO know 

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revio
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to pavinder, Mar 21, 2013

Strange, since most af zoom lenses I´ve had the opportunity to use have hade exactly the same minimum focus distance at all focal lenghts (Olympus, Nikon, Canon, a few others, and in Oly both m4/3 and regular 4/3)

Really? I've never had a zoom with a constant minimum focusing distance throughout. At the wide end they always focus closer.

I note, by that, you have never owned a Zuiko Digital zoom (?)

I have only owned 5 Zuiko Digital zooms, and one Micro Zuiko Digital zoom. The Micro was the one that had variable minimum focus distance (the 12-50/3,5-6,3)

A number of Canon, Nikon, Tokina, Sigma to note most of what I have owned, have most of them had fixed minimum focal distance. Max one or two of the AF-lenses, but more or most of the older, manual focusing, lenses I´ve owned did have variable minimum focusing distance, though.

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pavinder
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to revio, Mar 21, 2013

That may explain something, most of my lenses being s few years old. And all Canon EOS mount as I haven't yet bought M4/3.

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pavinder
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Re: Aperture/focusing distance changes at different FL for zoom lenses?
In reply to revio, Mar 21, 2013

I'm at the store now, testing the M Zuiko 75-300mm 4.8-6.7.
At 75mm minimum focusing distance is 90cm.
At 300mm the minimum is closer to 1.7m.

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