macro lens question

[erotavlas]

why would someone prefer a 100mm macro lens over a 50mm one?

 

[Destin]

Because it allows you to get the same results, and be twice the distance from the subject. So you don't have to get your lens right up against the subject.

EDIT: Also gives a thinner depth of field, which isn't neccesarily a good thing for macro work.

 

[greybeard]

I do and I don't. I like that I can get close up without being close up (if you get what I mean) however, sometimes the compressed prospective and shallower perceived depth of focus of a tele isn't what you want when shooting 3 dimensional subjects. I guess that is why they make macro lenses in normal and short tele focal lengths. lol

 

[erotavlas]

I don't understand the difference in the depth of field. If a 50mm and 100mm both have an apeture of say 3.5, wouldn't the out of focus parts look roughly the same?

 

[LightSpeed]

The aperture has nothing to do with it.
The shorter focal length will give greater depth of field.
You can close the aperture down on either lens for even greater depth of field.
There are three things that effect depth of field.

!- distance to subject.
2- focal length
3- Fstop

 

[greybeard]

When you use a "normal" lens. For a DX camera that is roughly 35mm. For 35mm it is roughly a 50. objects front to back will appear (big to small, near to far) in the correct perspective. Meaning that something behind will appear smaller. When you shoot with a tele, objects front to back will appear to be compressed meaning that objects in the background will appear closer or bigger than they should. You can get the exact same effect by cropping a photograph taken with a normal lens. Why objects behind the prime point of focus appear fuzzier with a tele is because they appear closer (bigger) than they would be if taken with a normal focal length lens.

 

[erotavlas]

so basically the one with the longer focal length magnifies the out of focus regions making it appear more out of focus than an equivalent non magnified image shot with a short focal length lens?

 

[LightSpeed]

so basically the one with the longer focal length magnifies the out of focus regions making it appear more out of focus than an equivalent non magnified image shot with a short focal length lens?

No.
Both lenses are designed for close up work.
The 100mm lens will give you a closest working distance of around 1 foot, give or take.
The 50mm lens will give you a closest working distance of roughly half that........6-7 inches.

 

[Destin]

When you use a "normal" lens. For a DX camera that is roughly 35mm. For 35mm it is roughly a 50. objects front to back will appear (big to small, near to far) in the correct perspective. Meaning that something behind will appear smaller. When you shoot with a tele, objects front to back will appear to be compressed meaning that objects in the background will appear closer or bigger than they should. You can get the exact same effect by cropping a photograph taken with a normal lens. Why objects behind the prime point of focus appear fuzzier with a tele is because they appear closer (bigger) than they would be if taken with a normal focal length lens.

This is not accuarate. You CANNOT achieve the same look by cropping, each focal length has it's own characteristics for depth of field, and compression.

Longer focal lengths provide thinner DOF due to the way physics work, not because the objects in the background appear larger or closer to the subject.


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.

Here's a DOF calculator. Playing with one for a bit is the best way to gain an understanding of what affects your DOF. Online Depth of Field Calculator

 

[Destin]

so basically the one with the longer focal length magnifies the out of focus regions making it appear more out of focus than an equivalent non magnified image shot with a short focal length lens?

Kind of. But the way you're saying it almost makes it sound a bit wrong. If I'm reading right, you are correct... it's just that this isn't how most people look at it.

Read this for a better understanding of DOF. Depth of Field: What Affects it and How to Control it

 

[greybeard]

When you use a "normal" lens. For a DX camera that is roughly 35mm. For 35mm it is roughly a 50. objects front to back will appear (big to small, near to far) in the correct perspective. Meaning that something behind will appear smaller. When you shoot with a tele, objects front to back will appear to be compressed meaning that objects in the background will appear closer or bigger than they should. You can get the exact same effect by cropping a photograph taken with a normal lens. Why objects behind the prime point of focus appear fuzzier with a tele is because they appear closer (bigger) than they would be if taken with a normal focal length lens.

This is not accuarate. You CANNOT achieve the same look by cropping, each focal length has it's own characteristics for depth of field, and compression.

Longer focal lengths provide thinner DOF due to the way physics work, not because the objects in the background appear larger or closer to the subject.


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.

Here's a DOF calculator. Playing with one for a bit is the best way to gain an understanding of what affects your DOF. Online Depth of Field Calculator

Really? I beg to differ, take two shots of the same subject with a lot of front to back depth, like buildings etc. take one with a "normal" lens and the other with a tele. Now crop the normal shot to match the tele, meaning they should have roughly the same content. The perspective will be the same. I've have done it a thousand times. As for the NORMAL thing, each size format requires a certain focal length for a normal field of view and normal perspective. For a 35mm it is roughly 50mm. For a 2 1/4 it is roughly 80mm. My 4x5 view camera had a 150mm Schneider and that produced a NORMAL field of view. The DOF of the 150mm on the 4x5 was not the same as the DOF of the 50mm on my 35mm camera. The DOF of the 150 on the 4x5 was much shallower. That is just the way it works. I have a Sony F828 with a really small sensor. I can't remember exactly what it is but it is really small and it sucks for low light because of it. However, zoomed to the max which is 200mm equivalent and wide open (F2) it still has pretty descent DOF because it's focal length is so short because of the really small format.

 

[Helen B]

The aperture has nothing to do with it.
The shorter focal length will give greater depth of field.
You can close the aperture down on either lens for even greater depth of field.
There are three things that effect depth of field.

!- distance to subject.
2- focal length
3- Fstop

That's not true, is it? In the macro/close-up region the DoF is the same for different focal lengths if the magnification is the same (and the same effective f-number, same max CoC criterion). Of course a lot of modern macro lenses shorten their focal length as they focus closer, so your "100 mm" lens might not have a focal length of 100 mm when focused very close.

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.

Neither of those statements are true. The 'normal' lens* for a format does depend on the format. Cropping does affect DoF if the cropped images are enlarged to the same physical size, which is the usual way of comparing images.

*ie the lens that produces a viewed image, when the camera image is printed full frame, that has the same perspective as that seen from the lens' position in the real world, under a standard set of viewing conditions. Here's something I wrote earlier:
"One way of judging what is a 'neutral' focal length would be to imagine a print held in front of you at a comfortable viewing distance for the size of the print. For example, an 8x10 sized print is commonly viewed at about 12 inches. If you held that print in front of the real-life scene it represents, and the perspective matches (ie each object in the scene lines up with its image on the print) then you could say that the lens used to make that image had a neutral focal length.

That example gives an easy result for an 8x10 camera - a 300 mm (12 inch approx) lens would be 'neutral'. In general, by considering similar geometry, it works out that this effect occurs when the focal length of the lens is roughly equal to the diagonal of the film/sensor (eg 43 mm for 24 mm x 36 mm film).

That does not explain why a 50 mm lens is considered the normal for Standard 35 mm motion picture - which has a significantly smaller frame size than the standard 24x36 frame size of still film. Movie theaters typically had 100 mm projection lenses on the 35 mm projector, so someone sitting in the middle of the audience would see a natural perspective if the image had been taken with a 50 mm lens."

 

[greybeard]

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.

 

[Ron Evers]

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

 

[Overread]

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.