macro lens question

[Destin]

To expand upon HelenB's point you might want to have a read here: Macro Camera Lenses

Depth of field for macro shots remains the same from 35mm macro at 1:1 to 300mm macro at 1:1 magnification. What will change, however, is the background blurring; with shorter lenses giving less blur to the background whilst longer lenses will render with a much more blurred effect. However you need to compare extremes to really see big differences in this.

Also consider the nature of the 50mm and 100mm lenses. Most of the 50mm macro lenses I'm aware of are cheaper build and quality, aimed at being budget friendly; heck Canon's 50mm macro isn't even a real macro until you purchase and add its lifesize adaptor. The 100mm options are often much better built and featured (eg things like fulltime manual focusing or OS/IS/VR tech).

That is all in addition to the increased working distances (distance from the front of the lens to the subject) that longer focal length macro lenses offer. This not only makes it easier to work with as you won't scare your subject as much (if working with bugs) but also makes lighting easier as you are less able to shadow the shot with the camera/lens combo when working with longer focal length macro lenses.

Look at Ron's example shots. The depth of field is ABSOLUTELY less on the 100mm shot than the 50mm shot. There is no arguing that point. Proof is in the photo.

 

[Overread]

Check the site I linked to again, plus google around; there is a lot of documented info on this. Sadly you can't cheat the system to get more depth of field from different focal length lenses. The closest you get is the reduced background blur at very short focal length macro lenses, which can appear to have given more depth when they haven't.
Tests for this can also have problems, even a small shift in the angle of the camera being used could easily misslead into showing what might appear to be more or less depth of field in a shot - sending out confusing messages to people when they compare them against each other.

 

[Helen B]

Look at Ron's example shots. The depth of field is ABSOLUTELY less on the 100mm shot than the 50mm shot. There is no arguing that point. Proof is in the photo.

Yes, that point is arguable, and the proof is not in the photos.

I've just sliced the two images up into strips and put the strips side-by-side, adjusting for the difference in focus point, and see very little difference in DoF. What I do see is a difference in brightness - the 50 shot is darker than the 100 shot. That might be because Ron used different settings in post, or because the originals have different brightnesses. Just because the marking on the lens says f/8, or the EXIF says f/8, doesn't mean that the effective aperture is f/8. The difference between the aperture at infinity and the effective aperture depends on the image magnification and the pupillary magnification (which can be different for two different lenses), so two different lenses can be used at the same image magnification and same marked f-number yet have different effective apertures.

If you trust any of the online DoF calculators, try plugging in some numbers.

 

[Ron Evers]

My quick comparison was not critically performed. I moved both subject & camera between shots to aproximate the same view. I raised the camera & moved the subject farther away for the 100mm shot so the angle of the camera relitive to horrizontal is likely somewhat different. One would have to accurately measure the angle of declanation of the camera to make this comparison precise.

My personal cursory assessment of the result was that the DOF was esentially the same for each lens.

 

[Ron Evers]

Delete duplicate post

 

[jake337]

To expand upon HelenB's point you might want to have a read here: Macro Camera Lenses

Depth of field for macro shots remains the same from 35mm macro at 1:1 to 300mm macro at 1:1 magnification. What will change, however, is the background blurring; with shorter lenses giving less blur to the background whilst longer lenses will render with a much more blurred effect. However you need to compare extremes to really see big differences in this.

Also consider the nature of the 50mm and 100mm lenses. Most of the 50mm macro lenses I'm aware of are cheaper build and quality, aimed at being budget friendly; heck Canon's 50mm macro isn't even a real macro until you purchase and add its lifesize adaptor. The 100mm options are often much better built and featured (eg things like fulltime manual focusing or OS/IS/VR tech).

That is all in addition to the increased working distances (distance from the front of the lens to the subject) that longer focal length macro lenses offer. This not only makes it easier to work with as you won't scare your subject as much (if working with bugs) but also makes lighting easier as you are less able to shadow the shot with the camera/lens combo when working with longer focal length macro lenses.

Look at Ron's example shots. The depth of field is ABSOLUTELY less on the 100mm shot than the 50mm shot. There is no arguing that point. Proof is in the photo.

I got put in check in this thread:
http://www.thephotoforum.com/forum/beyond-basics/267282-focal-length-depth-field.html

I also was confusing focal length with magnification when dealing with DOF.

 

[Helen B]

My quick comparison was not critically performed.
...

... but thanks for doing it and posting it anyway.

Are you familiar with a moderately well-known quote from 1950: in The Art of Scientific Investigation William Ian Beardmore Beveridge wrote "no one believes an hypothesis except its originator but everyone believes an experiment except the experimenter."

 

[Destin]

I just had one of those DUH moments in photography. I was taught.. my reputable members of this forum, and reputable books, that the longer the focal length, the less the DOF. But this doesn't seem to be the case based on what's been said in this thread, and what I've just read online.

So if I take a photo with a subject distance of 10 feet with my 50mm lens at 2.8, on my D80, I'll get a DOF of 1.36 feet. If I switch out to my 70-200 and take a photo at 200mm and f/2.8, and change the subject distance to 40 feet (x4, multiplying by the same value by which focal length was increased), I'll get the same DOF of 1.36 feet.

So what is actually affecting my depth of field is the magnification, and not the focal length? Yet longer focal lengths will still appear to have a thinner DOF due to the more magnified bokeh?

Am I correct, or am I still missing the mark here? It's a bit of a shocker to realize that the way I was taught, and believed this to work over the last 2 or 3 years is false and I'm having a hard time viewing it from a different angle than the (apparently incorrect) one that I'm used to.

 

[Ron Evers]

My quick comparison was not critically performed.
...

... but thanks for doing it and posting it anyway.

Are you familiar with a moderately well-known quote from 1950: in The Art of Scientific Investigation William Ian Beardmore Beveridge wrote "no one believes an hypothesis except its originator but everyone believes an experiment except the experimenter."

No Helen but I can understand the sentiment.

I spent years involved in research & totally understand the need of properly controlled & executed comparisons. However, this is no longer a resource I have access to, so I just wing an approximation.

I find you intriguing, as I have posted previously, I would love to see your CV. You do not reveal yourself in your profile.

 

[erotavlas]

I'm not sure I can see much difference except for a bit more blurring at the top and bottom for the Takumar, is that what I'm seeing?
I do like the Minolta image much better

I think that a 100mm macro would compress perspectives compared to a 50mm macro given they are used on the same size format. However, I don't have an example of a 50 and a 100 to test so it is all just conjecture.

I do, here is a quick comparison. The scale has 1/8" increments.


1. Minolta 50/3.5, 1:2 macro @ minimum focus distance. f8

2. SMC Takumar 100/4.0, 1:2 macro @ minimum focus distance. f8

 

[Helen B]

Ron, I'm mulling it over. As one of my friends says, I've worked long and hard for my obscurity and I don't give it up easily!

I just had one of those DUH moments in photography. I was taught.. my reputable members of this forum, and reputable books, that the longer the focal length, the less the DOF.

Hmmm. I wonder what 'reputable' books have said this. Try reading Lester Lefkowitz' Manual of Close-Up Photography, one of the classics on the subject. You should be able to get a used copy very cheaply.

So what is actually affecting my depth of field is the magnification, and not the focal length?

It's roughly true until one of the lenses in the comparison approaches its hyperfocal distance, as the difference in DoF becomes more and more significant.

Yet longer focal lengths will still appear to have a thinner DOF due to the more magnified bokeh?

Once it looks out of focus, it is outside the DoF. Standard DoF calculations do not take the effect of the comparative appearance of the rest of the image into account. Whether that is right or wrong probably depends on the individual image.

 

[djacobox372]

And the normal lens thing... well you're kind of right. 35mm is normal FOV on DX, and 50mm is normal FOV on FX, however this is simply referring to the width of the frame compared to the width (FOV) that our eyes see. If we're talking about which lens produces proper compression to what our eyes see, the answer is the 50mm regardless of sensor size.

Cropping does not affect depth of field, or compression. Doesn't matter if it's cropped by a smaller sensor, or in post.

Your understanding is wrong, "compression," or forshortening, has nothing to do with focal length, only distance to subject change this. A 50mm on fx is considered "normal" because it produces compositions that look correct due to the distance to subject in relation to the composition. If u use a 50mm lens on a crop camera u have to stand further away from the subject increasing "compression" to something that looks less natural.

A 50mm on fx produces the same compression as a 35mm on aps, 80mm on 645, or 150mm on 4x5" film. The photos are identical, the only thing that changes is dof at a given aperture, due to the physics of light hitting a larger surface.

The easiest way to see this is to look through a zoom lens, as u zoom in and out (change focal lengths) the size relationships between the subjects in frame do not change, changing focal lengths has the same affect as a post process crop.

 

[Helen B]

Aren't you forgetting the last step in the process - the conditions under which the final image is viewed? (See my explanation above) If you stood in the same place and took a series of images with lenses of different focal lengths (on the same camera) then printed them to the same image size (eg made them all 8x12s or whatever) they would have different perspective compression if viewed at the same distance.

 

[immafreebeetch]

Hi! Sorry if i will ask differently from the thread subject but how will I post photos here too?