PHOTOGRAPHIC THREADS: camera queries, any photo tech stuff!

[Maggi Young]

Many thanks for taking the time to explain this stuff to me, Guys... much appreciated... I'm sure others will have learned from you, too.

[ArnoldT]

Mike:

If I back the camera up there is less of a focus proble.  My handbook says 1.5 inches for close-up.

[David Pilling]

Maggi - put it this way, if the image coming out of the camera is 4000 pixels wide and all you want is to put something 400 pixels wide on the forum, you don't care if the flower only takes up a tenth of the frame.

Another aspect is that all these photos are compressed using JPEG, and often some sharpness is lost in that process.

But if you want maximum detail, or the flowers are very small you end up very close to the target with a suitable lens.

Immediately after I bought my close up lenses I bought a tripod and a shutter release cable - you want a greater depth of field, so you want to take longer exposures.

Below is a picture of a teasel, as close as I could get with my 18-70mm lens, about a foot. What comes out of the Sony A200 is 3872 pixels wide. I have reduced it to 20% to upload here. The second photo is a piece of the original with no reduction in size, 500 pixels wide. Third photo was taken with the close-up lens fitted, again it is reduced to 20%. Finally see that bug - the last photo shows it at maximum size - close up lens photo with no reduction. You can read off the pixel dimensions below.

[Maggi Young]

Every picture worth a thousand words, David!  

[Mike Ireland]

Arnold
just had a try with Scene/Close up, and about 2inches from the lens seems to be as close as mine will go.
You could try moving away from the subject and using the zoom to go in close as that would also, in scene mode, increase the depth of field as the lens stops down.

Mike

[gote]

There are several considerations i closeup photo
#1: It is a question of information. As pointed out above. Your software can insert missing pixels but not create information that was not there. If we increase the number of pixels using appropriate software and then decrease the scale (by viewing from further away or otherwise) we are back to square zero. We want to have as much information in the picture as possible so therefore we try to use as much of the sensor as possible. The so called digital zoom is nothing but cropping in the camera. You can as well use a pair of scissors on the print.
#2: The depth of field in the subject depends upon the scale of magnification - not on the distance to the subject. A 250mm lens 2.5 meters away will give the same depth of field as a 25mm lens 25 cm away.
#3: A closeup picture does not need to be close. If we look to an oldfashioned plate camera with bellows we get the same size on the negative with 250mm lens 2.5 meters away as with a 25mm lens 25 cm away. The old camera (including also 35mm with fixed focus lens) focuses closeup by increasing the lens-film distance. If you wanted higher magnification the negative you simply moved the lens away from the film - using the bellows or rings or whatever.  Modern zoom lenses do not focus by changing the distance between lens and sensor so this simple method is not feasible. The lens manufacturer sometimes sacrifies the ability of close focussing in tele-mode so the photographer has to use wideangle and get uncomfortably close to the subject.
For this reason it is much better to use additional closeup lenses with tele-setting as recommended above. The alternative is to get a special macro lens and that is many times more expensive.
#4: If we want to increase depth of field we can
A: Stop down the lens (if the camera allows this; most do). This has two disadvantages: Longer exposure time (use a tripod and hope the day is not windy)  And loss of definition due to diffraction if we stop down too much (as I have shown in an earlier post). Maximum definition is usually achieved at f:11 or thereabouts. Stopping down to f:22 is, however, usually acceptable. (There used to be an f:44 club of landscape photographers but they used negative formats of 18x24cm and did not enlarge their pictures very much)
B: Use less magnification on the film/sensor. This is of course to step back in magnification of the subject but if we use a fine grained film or a sensor with higly packed sensors we get an improvement. The drawback is the lower sensitivity to low light levels. The smaller pixels/silver halide grains do not catch as many photons as the bigger ones. The high degree of pixel packing (in pixels/mm2) is the reason why depth of field is quite good in many modern small digital cameras.

My advice is always: Use a tripod. Fill the frame. Use the longest lens available and the longest distance that will fill your frame. If the lens does not focus down to that distance use a cheap closeup lens in front. 

I hope I have not expressed myself too cloudily.
Göte
   

[Peter Maguire]

Excellent summary Göte.

I would just add one thing for those with too much (computer) time on their hands. As the optimum aperture for maximum sharpness is in the range f8-f11 (because the lens maunfacturers design them that way), then if this isn't going to give you front-to-back sharpness of the subject you can take a series of images with slightly different points of focus and merge them in the computer - a procedure known as focus stacking. There are even relatively inexpensive progammes that will preform the job for you whilst you make a cup of coffee or go and do some light weeding. 

[David Pilling]

I recall reading a good post by Göte in which he showed the effect of diffraction at small aperture. Alas I've failed to find it again.

Attached are two sets of three photos taken at f2.8, f11 and f32, the first set show that as the aperture decreases depth of field increases. The second set show sharpness peaks in the middle.

Photos are of a 1mm laser printed grid, taken with Minolta 50mm f2.8 macro lens at closest focusing distance.

[gote]

Excellent summary Göte.

I would just add one thing for those with too much (computer) time on their hands. As the optimum aperture for maximum sharpness is in the range f8-f11 (because the lens maunfacturers design them that way), then if this isn't going to give you front-to-back sharpness of the subject you can take a series of images with slightly different points of focus and merge them in the computer - a procedure known as focus stacking. There are even relatively inexpensive progammes that will preform the job for you whilst you make a cup of coffee or go and do some light weeding. 

Thank you. I assume that such a program will also re-center the pictures since ther will be inevitable movement between each exposure.
Göte

[gote]

I recall reading a good post by Göte in which he showed the effect of diffraction at small aperture. Alas I've failed to find it again.

Attached are two sets of three photos taken at f2.8, f11 and f32, the first set show that as the aperture decreases depth of field increases. The second set show sharpness peaks in the middle.

Photos are of a 1mm laser printed grid, taken with Minolta 50mm f2.8 macro lens at closest focusing distance.

I think your pictures show the point more clearly than mine did. I get the impression that 2.8 is nearly better than 11 (if we disregard the effect of the distance) that is a very good lens indeed.
Göte

[Maggi Young]

I cannot trace that post you mention from Göte ... might it have been in the "old" Forum? 

[gote]

I cannot trace that post you mention from Göte ... might it have been in the "old" Forum? 

It was this summer but showed Epimedium I think. I have not the time to dig it up today


By the way have anice weekend all of you
Göte

[David Pilling]

Hi,

This is Göte's example

http://www.srgc.org.uk/forum/index.php?topic=54.msg200906#msg200906

I just needed the clue 'epimdium'.

[Maggi Young]

Well done, David.
The search didn't find it for me .... it did with Epimedium brachyrrhizum but not with epimedium alone. Blasted thing is temperamental!

[Peter Maguire]

I assume that such a program will also re-center the pictures since ther will be inevitable movement between each exposure.

I had to check that Göte , as the program that I use (Helicon Focus) was developed for macrophotography Out of doors, I've only used it on fungi which don't usually move in the wind. However, according to the website it does align images automatically. (You can tell that I havene't used the program much yet)