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Photography Question 
Kris Haskins
 

Macro work and Depth of Field


 
 
A lot of talk about depth of field going around, I'll try and mix it up with a question I've been pondering.

I currently own a Tamron SP 60-300mm with 1:1.55 macro. With this lens it is necessary to get approximately 1.25" from the subject and the lens must be fully extended to almost 12". At this position the maximum apature is ~f/5.4. In order to shoot without a tripod it is necessary for me to shoot at 1/125 minimum (and most of those are not particularly sharp) and 1/500 for clear shots. Since I am looking to enlarge the photo (11x14 or larger) I cannot afford the grain in faster films (400ASA tops).In an outdoor setting with available light I have very few choices; drop to a slower shutter, or shoot full open and accept the ~2mm depth of field. Wow, that was a lot of intro material. On to my question:

Would I notice a significant increase in depth of field with a 90mm or 60mm 1:1 macro lens? What would I get in terms of focus distance? Getting one inch from most creatures startles them, and they don't stick around for you to meter and focus. I would like to be able to get the shot from a little further away.

Any other helpful information on macro gear would be appriciated (not going to by a ring flash though... too many $$).

Thanks.


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5/28/2001 4:31:42 AM

 
John A. Lind
BetterPhoto Member Since: 9/27/2001
  Kris,
Assuming aperture is not changed:
If focus distance is held constant and the lens is shortened, the DOF will increase. However, if magnification is held constant (same size of subject on film) the DOF does not change with focal length.

When maintaining the same magnification by decreasing focal length and moving closer, the DOF shrinks at almost exactly the same rate by moving closer as it grows by decreasing the focal length. The end result is almost exactly the same DOF (assuming lens aperture also remains the same). I posted a graph here showing this for non-macro distances a while back; it's the same at macro distances too:
http://www.betterphoto.com/gallery/dynoGallDetail.asp?photoID=942
S = focus distance
Sn = near edge of DOF
Sf = far edge of DOF

The main effect from using a shorter or longer lens in making macros is being able to get closer or farther from the subject, and the perspective it has. Focus distance "S" is not from the front of the lens either. It's from a specific optical point inside the lens; how far inside the lens this point is can vary greatly by lens design (especially with modern zoom lenses). At non-macro distances greater than about 10X the focal length, it's not enough to worry about. With macros having magnfications of 1/4X and larger, exactly how far the subject distance is from the front of the lens can be much different from the optical definition of focus distance.

In short, you're boxed in a little by high magnification with very shallow DOF's and slower film speeds requiring tradeoffs between shutter speed and aperture settings.

A couple of suggestions:
1. If at all possible can you use a tripod with cable release, perhaps with a ball head? Admittedly, this would slow you down and require great patience waiting for a good shot.
2. Aftermarket ring flashes are made by Phoenix, Sunpak and Vivitar. They're less expensive than most OEM ring flashes. Don't know if these are still "too many $$" for you.

Footnote:
(I've never been a big fan of this and would not do it for personal reasons.) Wondered about how a few of the stunning insect macros I've seen were made. Discovered they were "staged" by freezing the insect and then placing it onto the plant, sometimes in a studio with highly controlled lighting and background. Allows a tripod, more light, tighter apertures and slower shutter speeds.

-- John


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5/28/2001 11:03:56 AM

 
Jim Miotke
BetterPhoto Member
BetterPhotoJim.com
Owner, BetterPhoto.com, Inc.
  Poor little bugs :) Reminds me of when I used to go around collecting insects as a kid.

Thanks for the explanation, John. Good run-down of a tough problem.


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5/28/2001 12:11:30 PM

 
Jeff S. Kennedy   As usual John has given you great information. And as usual I will sneak in at the end and add my $.02. For macro work a tripod is essential (for almost all work a tripod is essential). If you must shoot handheld then the flash is probably your best option. Although, I think it usually looks artificial.

A lot of macro shooters I know (I am certainly not one) like to shoot insects first thing in the morning. They do this because it is still cold and the insects are not moving around and often times they may be covered in dew or even frost. Which makes for really cool pictures.


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5/28/2001 12:51:25 PM

 
Kris Haskins   Thank you for all the information. So far all of my insect shots have been in the wild and completely untouched. And since my livelyhood in no way depends on getting these critters onto film, I think I would like to keep it that way. I look at it as a challenge; how fast can I get in and get a shot without scaring my subject away? It is a fun way to spend the afternoon. Unfortunately, unless I get to go on a trip, Jeff's suggestion of cold morning shooting is out of the question (I live in the desert of New Mexico).

Thanks again gentlemen.


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5/30/2001 5:53:27 AM

 
Jim Miotke
BetterPhoto Member
BetterPhotoJim.com
Owner, BetterPhoto.com, Inc.
  Doesn't it still get really cold there in the early morning? Or are you telling us it's too early :)


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5/30/2001 11:36:01 AM

 
Kris Haskins   Well, now that you mention it... I am not known for getting up early :). But I was actually refering to the temperature. It was actually nice and cool last night, I was able to put on my sheet as I slept.


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5/30/2001 3:57:25 PM

 
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