I am an underwater photomacrographer soon to be getting my first dSLR system (yay!). Unless something earth-shattering occurs, I'll be getting a Nikon body.
My subjects are generally .5-5cm by their longest dimension, and while they aren't likely to "fly away", they tend to sway or reposition themselves fairly regularly. Add in the fact that there is no tripod, and the camera and its user are often floating freely, there is a real trade-off between getting the magnification I want and having a DOF that will capture the subject with reasonable certainty.
Being new to the SLR world, I'm having difficulty deciding/understanding what lens(es) will best suit my purposes. Generally, I am able to get within 10-30 cm of my subject (or even closer), and a depth of field around or greater than 1.5 cm would be ideal. I aim to make large prints of these little critters, so I want to get as close to 1:1 as possible.
I'm hoping to get some suggestions for a lens (and accessories) that might suit my needs. The AF 60mm f/2.8 has caught my attention, and at a distance of 40cm and f/11 I can get a DOF of 1.71 cm. Though I'm not sure what the magnification would be. Seeing as I can get so close to my subject, would an accessorized wide-angle give a reasonable magnification?
Thanks,
Ryan
balancing DOF and magnification
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Ryan,
Hello, and welcome to the forum!
Regarding DOF, the key thing to know is that for your purposes DOF depends only on the final magnification (e.g. subject size versus print size), how sharp you need the image to be, and on the aperture used for shooting. Choice of lens and accessories -- for example focal length, extension tubes, closeup lenses -- generally makes no difference in how much DOF you can get, only in exactly how you have to set the aperture to get it.
I agree that for subjects as small as 0.5 cm, you will be wanting 1:1 or even more. There are many "true macro" lenses that will focus continuously from infinity to 1:1 and have focal lengths around 60 mm, which will give you 1:1 at about 10 cm from your subject. (You will not get anything approaching 1.5 cm DOF at that magnification, however!)
For underwater use, a key element will be what you can fit into a waterproof case. It is critical to note that different macro lenses have different focusing mechanisms. Some of them focus by extending; others focus by moving lens elements internally. Internal focusing will make your life a lot easier.
If you want further discussion of DOF tradeoffs, just ask and I will track down the references. It has been discussed at length in this forum and elsewhere. Bottom line is that the law of diffraction imposes a strict tradeoff between magnification, resolution, and DOF in a single exposure. See http://www.janrik.net/insects/ExtendedD ... deoff.html for an illustration at 1:1.
For static subjects, one can get larger DOF by "stacking" images from multiple exposures having different focus points. Quite a few of the images in our forum are using this technique now. (Hopefully they are all labeled as such.) But of course that technique won't help in your situation.
--Rik
PS. Sure, I can move your post to a different forum. How about Equipment Discussions?
Hello, and welcome to the forum!
Regarding DOF, the key thing to know is that for your purposes DOF depends only on the final magnification (e.g. subject size versus print size), how sharp you need the image to be, and on the aperture used for shooting. Choice of lens and accessories -- for example focal length, extension tubes, closeup lenses -- generally makes no difference in how much DOF you can get, only in exactly how you have to set the aperture to get it.
I agree that for subjects as small as 0.5 cm, you will be wanting 1:1 or even more. There are many "true macro" lenses that will focus continuously from infinity to 1:1 and have focal lengths around 60 mm, which will give you 1:1 at about 10 cm from your subject. (You will not get anything approaching 1.5 cm DOF at that magnification, however!)
For underwater use, a key element will be what you can fit into a waterproof case. It is critical to note that different macro lenses have different focusing mechanisms. Some of them focus by extending; others focus by moving lens elements internally. Internal focusing will make your life a lot easier.
If you want further discussion of DOF tradeoffs, just ask and I will track down the references. It has been discussed at length in this forum and elsewhere. Bottom line is that the law of diffraction imposes a strict tradeoff between magnification, resolution, and DOF in a single exposure. See http://www.janrik.net/insects/ExtendedD ... deoff.html for an illustration at 1:1.
For static subjects, one can get larger DOF by "stacking" images from multiple exposures having different focus points. Quite a few of the images in our forum are using this technique now. (Hopefully they are all labeled as such.) But of course that technique won't help in your situation.
--Rik
PS. Sure, I can move your post to a different forum. How about Equipment Discussions?
Ryan,
I am no underwater photographer but I believe lenses behave differently regarding their apparent focal length in water to air. Anyway see:-
http://www.camerasunderwater.info/optics/lenses.html
http://www.nikonians.org/dcforum/DCForu ... 15100.html
http://www.daveharasti.com/articles/d80.htm
I use the 60mm f2.8 Micro Nikkor on my Nikon D200 and it produces first class images, as do any of the top marque macro lenses. Here is a review of it:-
http://www.photozone.de/8Reviews/lenses ... /index.htm
Seemingly, unlike conventional macro photography, it is advisable to get as close to the object as possible to minimise the amount of water you are shooting through, so it would seem the extra working distance of a longer focal length is not such an advantage in your case.
DaveW
I am no underwater photographer but I believe lenses behave differently regarding their apparent focal length in water to air. Anyway see:-
http://www.camerasunderwater.info/optics/lenses.html
http://www.nikonians.org/dcforum/DCForu ... 15100.html
http://www.daveharasti.com/articles/d80.htm
I use the 60mm f2.8 Micro Nikkor on my Nikon D200 and it produces first class images, as do any of the top marque macro lenses. Here is a review of it:-
http://www.photozone.de/8Reviews/lenses ... /index.htm
Seemingly, unlike conventional macro photography, it is advisable to get as close to the object as possible to minimise the amount of water you are shooting through, so it would seem the extra working distance of a longer focal length is not such an advantage in your case.
DaveW
Thank you both for your quick responses. Yes, a switch to Equipment Discussion would be appreciated! Until then I'll keep reading your posts (and the links) until this all makes a bit more sense to me 
I've played around with the idea of a weighted tripod to take with me... but I can only imagine that would be more hassle than it'd be worth, unless I had a very specific objective. In a month or two the waters will be at their clearest (and coldest), but I have to admit I don't take my best pictures when the water temperature is -1.8 degrees! In the summer the visibility can be very poor (< 1m) so light quality and suspended particles have a tremendous impact on my shots.
With the strobes I'll be using, I can work comfortably down/up? around f/32. Dave, what is your experience with resolution/sharpness at this aperture for the 60mm?
Thanks again
I've played around with the idea of a weighted tripod to take with me... but I can only imagine that would be more hassle than it'd be worth, unless I had a very specific objective. In a month or two the waters will be at their clearest (and coldest), but I have to admit I don't take my best pictures when the water temperature is -1.8 degrees! In the summer the visibility can be very poor (< 1m) so light quality and suspended particles have a tremendous impact on my shots.
With the strobes I'll be using, I can work comfortably down/up? around f/32. Dave, what is your experience with resolution/sharpness at this aperture for the 60mm?
Thanks again
You really need to find out for yourself what apertures are going to give what you require. You may the extra depth of field outweighs the increase in diffraction - although f/32 would not be where I work, most likely around f/8. So as you are working, make a few exposures with different apertures.
BTW, you do not need to worry about the final display size. Most depth of field calculators assume an 8x10 final print. But this does not really impact a larger or smaller print size as viewing conditions are assumed to change. DOF calculators are assuming nothing is cropped.
BTW, you do not need to worry about the final display size. Most depth of field calculators assume an 8x10 final print. But this does not really impact a larger or smaller print size as viewing conditions are assumed to change. DOF calculators are assuming nothing is cropped.
Will
Depends on your magnification and the use you will put the shots to. I do use f32, in spite of theoretical diffraction problems when posting for the Internet because the low screen resolution hides the softness a print would show. I believe a computer monitor or digital projection screen cannot show any greater resolution than that obtained from a 2 Megapixel camera?
It is really the effective aperture you are working at that matters, and Nikon's are one of the few cameras that actually show the lenses effective aperture it is working at, not that marked on the aperture ring. My camera at times has shown apertures smaller than f32, though that is the smallest marked aperture on the lens.
I personally usually work around f16-f22 for my plants unless I am forced to use a wider stop. And of course on a Nikon when the camera says f22 that's what the aperture actually is, not the relative aperture marked on the lens other makes show. Not much point in having smaller apertures if you always use a lens wide open at it's theoretical sharpest aperture unless photostacking, because if that is the case both Nikon and Canon may as well have made far cheaper single aperture f8 macro lenses.
I believe the range of stops on a lens were put there to use unless there is a very good reason, like diffraction, not to use them at higher magnifications.
DaveW
It is really the effective aperture you are working at that matters, and Nikon's are one of the few cameras that actually show the lenses effective aperture it is working at, not that marked on the aperture ring. My camera at times has shown apertures smaller than f32, though that is the smallest marked aperture on the lens.
I personally usually work around f16-f22 for my plants unless I am forced to use a wider stop. And of course on a Nikon when the camera says f22 that's what the aperture actually is, not the relative aperture marked on the lens other makes show. Not much point in having smaller apertures if you always use a lens wide open at it's theoretical sharpest aperture unless photostacking, because if that is the case both Nikon and Canon may as well have made far cheaper single aperture f8 macro lenses.
I believe the range of stops on a lens were put there to use unless there is a very good reason, like diffraction, not to use them at higher magnifications.
DaveW