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Author Topic: a few basic questions regarding aperture  (Read 4503 times)
sanfairyanne
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« on: February 09, 2009, 12:13:26 PM »
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I've heard of some lenses being able to stop down to f32 while mine goes down to f22. Will I get more depth of field at f32, if so are there any disadvantages to using such a small aperture other than a longer exposure time.

Also if using a 50mm lens gives a more natural perspective is there any reason why I shouldn't just shoot two images and photostitch them together instead of buying a wider angle lens.

Many thanks.
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DarkPenguin
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« Reply #1 on: February 09, 2009, 12:37:15 PM »
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Quote from: sanfairyanne
I've heard of some lenses being able to stop down to f32 while mine goes down to f22. Will I get more depth of field at f32, if so are there any disadvantages to using such a small aperture other than a longer exposure time.

Also if using a 50mm lens gives a more natural perspective is there any reason why I shouldn't just shoot two images and photostitch them together instead of buying a wider angle lens.

Many thanks.

Diffraction will bite you in the ass at f32.  Of course it is already doing so at f22.

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k bennett
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« Reply #2 on: February 09, 2009, 07:24:15 PM »
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Assuming you are talking about a 35mm camera or digital SLR, then there is no good reason to shoot at f/22 or f/32. For technical reasons, the very tiny aperture at that setting causes an overall loss of sharpness due to diffraction of the light as it moves past the aperture blades.

Large format film cameras are sometimes shot at f/32 or even f/64 to obtain maximum depth of field.

If you are shooting with a digital SLR, you might want to limit your aperture to f/16 or even f/11. As usual, it's best to test your system. Make prints at various settings and see what happens.
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wollom
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« Reply #3 on: February 09, 2009, 11:30:18 PM »
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Quote from: sanfairyanne
Will I get more depth of field at f32, if so are there any disadvantages to using such a small aperture other than a longer exposure time.

Also if using a 50mm lens gives a more natural perspective is there any reason why I shouldn't just shoot two images and photostitch them together instead of buying a wider angle lens.

Many thanks.

Howdy, forgive me being in 'teacher mode'

As others have pointed out a smaller aperture can have several effects.  Smaller apertures (bigger f number) do give more depth of field.  At the same time, the light travelling through any aperture spreads (diffraction), this is more obvious with small apertures, and appears as reduced sharpness.  The 'benefit' of increased depth of field can be masked by diffraction; usually around f11 to f22, depending on the lens and the camera.

Stitching gives 'the same' effect (and perspective) of a wider angle lens, sort of.  A search of this forum on 'stitched panorama' will turn up a load of useful information. Because the photographs that make up a stitched image are taken at different times a moving subject can cause problems. Rotating the camera/lens/sensor to point it at different parts of the subject means that images do not join perfectly (their geometry is different) careful technique and/or special equipment can minimise the defects.

Best

Wollom
« Last Edit: February 10, 2009, 12:16:33 AM by wollom » Logged
sanfairyanne
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« Reply #4 on: February 10, 2009, 12:19:10 AM »
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Thanks guys, I was in fact talking about a SLR with a 35mm lens rather than a 35mm point and shoot. I am lucky enough to have the loan of a 5D from my father, so I'm trying to make best use of it. I found a useful webpage showing depth of field at relevant distances for this lens and I see at F/16 I can have an acceptable focus range from 9 feet to infinity. If I bare that in mind I should be able to get good landscapes with something in the foreground etc (as seems to be one of the rules).
I figure that by taking four or more images in a square pattern I can obtain a stitch which will include my desired area, then of course I'll have to crop out the rest.
I am coming to America this year to photograph the south west so I want to be well prepared.

Thank you all for taking the time to reply to me.
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marcmccalmont
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« Reply #5 on: February 10, 2009, 12:58:19 AM »
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Quote from: sanfairyanne
I've heard of some lenses being able to stop down to f32 while mine goes down to f22. Will I get more depth of field at f32, if so are there any disadvantages to using such a small aperture other than a longer exposure time.

Also if using a 50mm lens gives a more natural perspective is there any reason why I shouldn't just shoot two images and photostitch them together instead of buying a wider angle lens.

Many thanks.


In some instances the stitched photo has advantages, the wide angle lens at times captures too much sky and ground, the stitched panorama contains more "Skyline".  PS CS3 and CS4 are great to get started stitching with. I find orienting the camera vertical and taking 3 frames horizontally stitches into a very natural perspective. The sweet spot in most of my lenses is between f7.1 to f11, I aim for f8 or f9 unless depth of field or low light are considerations.
Marc
« Last Edit: February 10, 2009, 01:03:40 AM by marcmccalmont » Logged

Marc McCalmont
k bennett
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« Reply #6 on: February 10, 2009, 10:14:23 AM »
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Quote from: sanfairyanne
I found a useful webpage showing depth of field at relevant distances for this lens and I see at F/16 I can have an acceptable focus range from 9 feet to infinity.


You will definitely want to test this. The definition of "acceptable focus" varies widely among photographers. Also practice making your stitched images ahead of time. There are several complications involved in that, and you'll want to figure out the solutions ahead of time.

Have fun in the Southwest -- it's a great place to make photographs.
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sanfairyanne
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« Reply #7 on: February 10, 2009, 12:04:16 PM »
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Thank you all once again, Mark from Hawaii, I've also had good success (at least to my eye) from taking three pictures when the camera is vertically lined up. I intend to be well practised with my camera before arriving in the states.
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NikoJorj
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« Reply #8 on: February 10, 2009, 01:50:16 PM »
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Quote from: sanfairyanne
I've heard of some lenses being able to stop down to f32 while mine goes down to f22. Will I get more depth of field at f32, if so are there any disadvantages to using such a small aperture other than a longer exposure time.

Also if using a 50mm lens gives a more natural perspective is there any reason why I shouldn't just shoot two images and photostitch them together instead of buying a wider angle lens.
1) If you enjoy a bit of theory, read by yourself how diffraction interacts with depth of field (you might want to start at the beginning).
You can also just see by yourself what is diffraction.

2) Yes you can stitch, but stitching will give you back the perspective of a wide-angle.
Of course you'll end with more pixels in the print, and this is the main reason for stitching, NOT perspective.
NB In any good panorama software, you can also choose another projection as rectilinear to minimize corner distorsion but... your straight lines won't be straight anymore.
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Nicolas from Grenoble
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johngie
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« Reply #9 on: February 28, 2009, 06:20:50 PM »
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Quote from: sanfairyanne
Also if using a 50mm lens gives a more natural perspective is there any reason why I shouldn't just shoot two images and photostitch them together instead of buying a wider angle lens.

Many thanks.

Sorry for jumping in so late, but I've only just joined this forum and just seen this!

Actually the focal length of the lens does not control the perspective - the distance from the subject does! The focal length controls the angle of view - that's all!

If you take a picture with (say) a 24mm lens, then another with a 100mm from exactly the same position and crop the image taken with the 24mm so it has the same field of view as the 100mm, the two will have exactly the same perspective.

Regards

johngie
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