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View Full Version : focus shifting with changing temperature?!?


Falk
11th June 2011, 10:11 AM
With the E-30 you are able to fine adjust the AF. Something I was really locking forward to, when I upgraded from the E-520. And every lense I own, with the exception of the ZD35 Macro, needed a little adjustement to get the focus spot on. It has all worked fine so far!

Yesterday I did a walk about to take some 'macros'. Any kind of insect, but especially looked for butterflies, grass hoppers, dragon flies and beetles.
For this sort of shooting I like to use the ZD70-300. It's my most used lense as it allows me to not miss the occasional bird, helicopter or wild boar ... anything which was not on the list in the first place.

After having a look on my photos taken yesterday, I just reconfigured the 70-300 AF-adjusment setting to: T 0, W+2 - because many of my 'macros' had a slight back focus and I had to delete an awfull lot of them :mad:
Since several weeks (with modest temps: 5-20C) I had the AF-adjustments set to: T+1, W+2
... but, I came here from formerly using T+2, W+4 - in late winter to early spring times (with temps always below 5C).

I guess my question to the forum is this:
Has anybody ever noticed a shift in focus adjustment with changing temperature?!? Could temperature really be the explaination for what I observe?!?

Any thoughts and ideas welcome!

David Morison
11th June 2011, 10:56 AM
This is an interesting observation. Sometimes on certain days notice that my E5/300mm combination doesn't give as sharp results as others, I haven't thought about ambient temperature being a factor but I will take a thermometer when I go out to see if there is any correlation.

Thanks

David

Ross the fiddler
11th June 2011, 11:57 AM
I would think that is a valid consideration with the amount of variation in temperature. I haven't played with any adjustments yet but perhaps a thorough check may reveal a need for some adjustment perhaps.

Thanks for sharing this.
*chr

Naughty Nigel
17th June 2011, 07:48 AM
I wonder, is this why a certain competitor's Long Lenses are painted white? :)

Thinking about it, heat causes expansion in all materials, and especially in light alloys, so the focal length of a long lens will presumably be slightly longer when it is hot? I presume this could affect focus; but what if manual focusing is used?

However, I have noticed a different problem which may be what you are seeing. Just once or twice I have found that photographs taken on my E1 were not as sharp as I have come to expect. These were all taken using my 14 ~ 54 Mk1 lens, and all were taken in warm (25 C +) summery conditions. Some of the photographs were taken at the wide angle end of the zoom range, where focusing is not at all critical.

When I look at the images they just don't look sharp, and in some cases also look slightly flat. However, close examination on the computer screen shows that nothing in the image is completely sharp, and in any case I would be using apertures of f5.6 or f8.0, so I don't think this is a focusing issue. And in any case, I tend to focus manually most of the time.

I also doubt that this effect would be caused by camera shake as even with a polarising filter, in bright sunlight I would be using exposures of 1/250 or shorter at 100 ASA.

I should stress that this seems to affect multiple images taken around the same time, and is not limited to a single exposure, which of course we can all get wrong from time to time.

I have heard of others who have seen similar effects on the E1, and more recently on the E3, but I have never found a cogent explanation for it.

Aggressive sharpening in Photoshop improves things slightly, but still does not produce the sharpness that I have come to expect from this equipment. Could this be a diffraction effect? Somehow I doubt it, as it only seems to happen on odd occasions and not all of the time. I will have a look for the raw images in question and will post one or two here.

Naughty Nigel
17th June 2011, 10:22 AM
As promised, please see two samples showing the effects described above. As you will see, nothing looks really clear or in focus, and the colours are washed out. Yet, the third image, which I took shortly afterwards was much, much better. These were all processed normally in PS from the original raw files.

http://e-group.uk.net/gallery/data/500/Sample_6206436_.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/35543)

http://e-group.uk.net/gallery/data/500/Sample_6206430_.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/35541)

The same field a few minutes later! Could this really have been taken on the same day?

http://e-group.uk.net/gallery/data/508/Poppies_6206442_.jpg (http://e-group.uk.net/gallery/showphoto.php/photo/11377)

Falk
17th June 2011, 06:44 PM
I wonder, is this why a certain competitor's Long Lenses are painted white? :)

I guess it is, yes.

Thinking about it, heat causes expansion in all materials, and especially in light alloys, so the focal length of a long lens will presumably be slightly longer when it is hot? I presume this could affect focus; but what if manual focusing is used?

I certainly knew the fact, that almost anything will expand with heat ;)
But, the lenses have more hard plastics then aluminum etc. to them, which might react to temperatur change very little!?
I was thinking of the AF-sensor itself might be affected!?

With manual focus, any issue with the AF is of course obsolete. I use the magnifying eye piece on my camera, but the viewer does in general not allow me to fine tune the focus this small fraction of what I am talking about here. My findings are based on 'post mortem' examinations on the computer screen. And often was I surprised to find out, that a photo what I thought I had taken all fine, was just out of focus - back or front - not all over the place.

Thanks for your input! I'll need to read and then answer to your second post later ...

Falk
17th June 2011, 06:58 PM
Well Nigel, your stunning photo postcard (#3) was taken with the sun in your back - but in the first two photos you were shooting more into the sun, right? Seems to me as if this might be at least a part of the equation!?
Other then that, I would think it is an IS issue. Sometimes I hate the IS and think it is not working properly, blurring the whole pic :mad: but then it goes again :confused: and I am happy I have a body equipped with one *yes

A little uncertainty is always left, but I tend to use IS most of the time, as I most often work on the longer end of my lenses.

Naughty Nigel
17th June 2011, 07:20 PM
Well Nigel, your stunning photo postcard (#3) was taken with the sun in your back - but in the first two photos you were shooting more into the sun, right? Seems to me as if this might be at least a part of the equation!?
Other then that, I would think it is an IS issue. Sometimes I hate the IS and think it is not working properly, blurring the whole pic :mad: but then it goes again :confused: and I am happy I have a body equipped with one *yes

A little uncertainty is always left, but I tend to use IS most of the time, as I most often work on the longer end of my lenses.

Well; all were taken with the E1, so I don't think IS would be an issue.

The first two photographs were taken looking more or less due west, whilst the third was taken looking north west. All were taken at about 2.30 pm on a hot June afternoon. Indeed, if you look at the clouds towards the right of the first two shots you will see the same clouds to the left of the third shot; and yet the two shots are nothing like the same in terms of either sharpness or colour. I cannot work it out. :confused:

DerekW
17th June 2011, 07:55 PM
See some of the discussion in this thread
http://photography-on-the.net/forum/archive/index.php/t-925671.html

Cannon use(d) a specific type of flourite based glass that is temperature sensitive and so white outer colouring was used to reflect heat. It may be interesting to follow up the 106,000 results Google came up with - but I remember reading about the flourite and heat sensitivity quite a while ago -

The marketing aspect of the colour is also interesting ie long big white lens is a Cannon

I would have expected that on all lenses the auto focus would be expected to compensate for any shift in length of the barrel.

Re Nigel's photos - speculation mode on

He said he was pointing in different directions relative to the sun, so I wonder if the lenses are slightly polarising in their way of working and so give a sharper image if the reflected light from the subject is polarised in a restricted angle - end of speculation.
however why does my optician say that my prescription polarised glasses will give an added sense of sharpness compared to regular prescription lenses - is it because polarised light gives a less confusing image for the eye to focus on and the brain to resolve.

Total end of random thinking

Naughty Nigel
17th June 2011, 08:24 PM
however why does my optician say that my prescription polarised glasses will give an added sense of sharpness compared to regular prescription lenses - is it because polarised light gives a less confusing image for the eye to focus on and the brain to resolve.

Total end of random thinking

........ Because a polarising filter increases contrast and colour saturation, and reduces reflections?

David M
17th June 2011, 10:38 PM
Canon use(d) a specific type of flourite based glass that is temperature sensitive and so white outer colouring was used to reflect heat.

The fluorite used by Canon (and others) is a synthetically-grown crystal (calcium fluoride) not glass.

It's also supposed to be affected by water and I've heard fluorite elements need to be sealed to keep moisture out.

The 180mm f2, 250mm f2 and 350mm f2.8 OM Zuiko lenses were mostly white. Some early versions of the 250mm and 350mm were built in black before they started making them in white.