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FORUMS Photography Talk by Genre Macro Talk 
Thread started 27 Nov 2017 (Monday) 19:59
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Help sigma 105mm vs canon 100mm L. Clinical Oral Photography

 
ANDFlow
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Post edited 7 months ago by ANDFlow.
     
Nov 27, 2017 19:59 |  #1

Dears,

I'm a bit complicated since I bought the EOS 6d and now I have to decide what macro to buy for Oral Clinic photography (I'm a dentist).

Formerly I had a 500d with a macro of 60 mm, and I was handling with very small openings (f stop) since I need great depth of field (f / 22, f / 28, f / 32). It turns out that now I wanted to buy the "Sigma 105mm 2.8 Ex Os Macro" lens mainly for its value compared to "Canon EF 100mm f / 2.8L IS USM Macro", but I realized that the minimum aperture of the Sigma diaphragm is f / 22 (Canon's is f / 32).
I'm afraid that the Sigma will not give me the depth of field I want (the front teeth and the back ones will be focused) .. But the truth is that I do not have macro frame experience with Full Frame and maybe that f / 22 sigma is not very different from the f / 32 of the canon, or perhaps it can be very different ...

I would like to know your opinion, because if there were not so many differences I would prefer to save money and buy the sigma




  
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MalVeauX
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Nov 27, 2017 20:18 |  #2

Hello,

I think you're approaching this from a hard angle. You're wanting to shoot at F22, or smaller, for depth of field. You'll find you don't gain much depth of field at F22 compared to F8 or F11 for the distance you need (front teeth to back teeth being greater than a few millimeters, upwards of over an inch or more needed). I would suggest you take the images from farther away from the subject, that alone will increase depth of field considerably and use the 20MP+ resolution of your camera to your advantage and crop down.

It would help to know more about how you're setting this up, how you are photographing the subject(s) (such as live in the chair, or specimens not in a host, etc). It also helps to know if you have lighting for this or not. It also helps to know what you're doing with the subject matter.

Very best,


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Wilt
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Post edited 7 months ago by Wilt.
     
Nov 27, 2017 20:37 |  #3

But DOF has more to do with object MAGNIFICATION than shooting distance!

Whether I achieve 1:2 scale with 100mm or 50mm FL results in same DOF

Yashica Dental Eye film camera used a 100mm macro with minimum 6 in focus


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ANDFlow
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Nov 27, 2017 20:50 as a reply to  @ MalVeauX's post |  #4

I shoot to stationary mouths ( people on chair) with a ring flash. I need minimum of f20 to have ok, but not enought or excelent DOF. Thanks for your answer but i still dont know if is worth going for the canon L with f/32 instead of the signa 105 f22.




  
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MalVeauX
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Nov 27, 2017 21:12 |  #5

ANDFlow wrote in post #18505554 (external link)
I shoot to stationary mouths ( people on chair) with a ring flash. I need minimum of f20 to have ok, but not enought or excelent DOF. Thanks for your answer but i still dont know if is worth going for the canon L with f/32 instead of the signa 105 f22.

You don't have to spend money to trial & error and find out. It's measurable and calculable.

Thing is, you're not photographing a detail on a single tooth smaller than your sensor size. You're photographing something that is larger than your sensor, so you actually don't even need a macro lens really. You could do this without a macro lens with a standard longer telephoto lens even. It's just probably more practical with a close focusing lens because of the smaller size of your studio (your clinical room in this case).

On a full frame sensor, at 105mm, focusing from 12 inches away, at F22, your DOF is approximately 0.3 inches.
Same thing, but at F32 is 0.42 inches.

You will not benefit from stopping down further. And you won't benefit from buying a new lens to get that. So don't bother with a 100L or anything like that.

You need a different approach.

I would use a wider angle macro lens (if you even feel the need for a macro lens). A Canon 50mm F2.5 macro lens for example, at F11 and 12 inches from subject will have 0.83 inches of DOF and at F16, it will have 1.18 inches of DOF. And that lens like $250.

https://www.keh.com …97&aid=1052997&​rmatt=tsid (external link):|cid:873153775|agid:464​88731400|tid:pla-367604578034|crid:2048​69092037|nw:g|rnd:1597​5733734759495663|dvc:c​|adp:1o1&gclid=EAIaIQo​bChMIoL7Q1qTg1wIVjrXAC​h3ldgwmEAYYASABEgJs8_D​_BwE
https://www.amazon.com …-Macro-Lens/dp/B00006I53V (external link)

And there are even wider angle lenses that would give you even more DOF options. There's 15mm macro lenses that would give you tons of depth of field at just F4.

Really depends on what you're trying to produce.

If you could share an example of what you produce, that would help.

Very best,


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ANDFlow
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Post edited 7 months ago by ANDFlow. (4 edits in all)
     
Nov 27, 2017 22:08 as a reply to  @ MalVeauX's post |  #6

thanks you again for your time a exceptional explanation. My answers:
Sometimes i need to take a picture with more detail, i think i need the macro for that, but most of the times i took "general" pictures. As you said, i have a college who use the 18-55 kit lens for the "general" picture, its works fine but his picture is much worst quality compared with a 60mm fixed or a 100L or sigma 105mm, and i like quality and good detailed pictures. I take the pictures with my hands, the macro, camera and ringflash weight make me shake a little, also the patient move a bit so i think a stabilization is good since i can't have a tripod on the dental box.

So you said that the f22 is enought? go for the sigma 105?

Look at the first picture, i took it with f f20 and the back is little blurry, i dont find it a good picture, so i need to work with f25 or maybe f32, or as you said move backward and zoom it, but the detail is gona be worst, so i prefer to change the f stop.


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Dalantech
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Post edited 7 months ago by Dalantech.
     
Nov 28, 2017 02:19 |  #7

MalVeauX wrote in post #18505568 (external link)
...I would use a wider angle macro lens (if you even feel the need for a macro lens)...


That's where you lost me. Depth of field is strictly a function of magnification and Fstop. It seems to me that you'd want to keep magnification to a minimum to increase depth, hence a longer focal length would be better to decrease the field of view (to get the subject as large as possible in the frame with the lowest magnification). You mentioned using a longer telephoto lens earlier in your post (and I agree), so is the wide angle macro lens recommendation a typo?

For the OP: It's really tough to tell if an additional stop is really going to make a difference at the magnifications that you're shooting at. I do agree with MalVeauX's math. Typically a one stop change in aperture is going give you a ~50% change in depth of field, and you have to move two stops to roughly double the depth (or cut it in half).

In my experience most people make these posts because they want someone to make them feel good about buying something that they've already decided to purchase. In terms of optical quality both lenses are pretty much equal, with the 100mm L giving you less distortion and better contrast than the Sigma. But for the type of images that you're taking those qualities don't matter that much. It's up to you, but it's a lot of money for very little gain.


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Post edited 7 months ago by Wilt.
     
Nov 28, 2017 12:09 |  #8

Using the dimensions of my own mouth as an example of what OP might be trying to accomplish:
Capture a 85mm width full mouth photo (similar to photo 1 in post 6) onto a 36mm wide FF sensor: 0.45x

  • at f/32 the DOF is determined by an effective aperture of f/46, giving DOF of 14.66mm
  • at f/22, the DOF is determined by an effective aperture of f/32, giving DOF of 10.08mm


Note that the FL does NOT enter into the above calculation, as DOF is entirely dependent upon the MAGNIFICATION of the subject area, as already stated earlier (and the f/stop used).
Subject distance (which is a function of FL used) does not enter into the above calculation either, when the resulting imaged area is identical in size (i.e. 'same magnification')

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Bassat
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Nov 28, 2017 15:28 |  #9

SLR? Seems like a very large cumbersome tool for a very tight space. Have you considered that you are using the wrong tool for the job? Google is your friend: http://sotaimaging.com …20Uwv2EAAYASAAE​gIZv_D_BwE (external link)


Tom

  
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ANDFlow
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Nov 28, 2017 19:05 |  #10

Wilt wrote in post #18505920 (external link)
Using the dimensions of my own mouth as an example of what OP might be trying to accomplish:
Capture a 85mm width full mouth photo (similar to photo 1 in post 6) onto a 36mm wide FF sensor: 0.45x

  • at f/32 the DOF is determined by an effective aperture of f/46, giving DOF of 14.66mm
  • at f/22, the DOF is determined by an effective aperture of f/32, giving DOF of 10.08mm


Note that the FL does NOT enter into the above calculation, as DOF is entirely dependent upon the MAGNIFICATION of the subject area, as already stated earlier (and the f/stop used).
Subject distance (which is a function of FL used) does not enter into the above calculation either, when the resulting imaged area is identical in size (i.e. 'same magnification')

So, you think that the 100L is not worth it?




  
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MalVeauX
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Nov 28, 2017 19:16 |  #11

ANDFlow wrote in post #18506278 (external link)
So, you think that the 100L is not worth it?

No. You're not gaining anything with it. If you value sharpness and detail, shooting at F32 isn't the way to go.

You can frankly do it with what you already have (the Sigma). The Sigma at F16 at 24 inches will have 1.06 inches of DOF. At 30 inches, 1.72 inches of DOF. You don't need a new lens. With 20MP+ sensor, you'll have plenty of pixels on the target for a large representation.

Very best,


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Wilt
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Post edited 7 months ago by Wilt.
     
Nov 28, 2017 23:01 as a reply to  @ ANDFlow's post |  #12

Why would I think the 100L is 'not worth it', when it allows f/32 which gives you almost 5mm more DOF?!

The trade off of more DOF is simply the fact that f/32 is affected by diffraction limitations of the very small aperture becoming visible when you magnify the 24x36mm frame to fill an 8x10" print, but the tradeoff is yours to decide.


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Post edited 7 months ago by Wilt. (2 edits in all)
     
Nov 28, 2017 23:07 |  #13

MalVeauX wrote in post #18506291 (external link)
No. You're not gaining anything with it. If you value sharpness and detail, shooting at F32 isn't the way to go.

You can frankly do it with what you already have (the Sigma). The Sigma at F16 at 24 inches will have 1.06 inches of DOF. At 30 inches, 1.72 inches of DOF. You don't need a new lens. With 20MP+ sensor, you'll have plenty of pixels on the target for a large representation.

Very best,

shooting at 30" will give you 20% smaller magnification of the dentition than 24" will, which is the reason that DOF appears to be deeper at the 30" distance. Yet another trade off! And shooting at the 24mm distance will make for the 85mm field width filling only HALF the frame! Filling frame with 85mm field width is 0.45X with DOF approaching 15mm, as stated earlier

A 100mm lens which focuses to 13" will allow a capture of the 85mm wide field


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Nov 29, 2017 03:31 |  #14

The better solution is to decrease the magnification to increase the depth of field, so neither lens is optimal.

Pretty tough question to ask a bunch of macro photographers since we're typically shooting at 1x and higher mag, something that you won't be doing in you dentist office...


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Post edited 7 months ago by Wilt.
     
Nov 29, 2017 11:35 as a reply to  @ Dalantech's post |  #15

But -- for a DENTIST -- what is the point of 'decreased magnification' shot, if the mouth full of teeth no longer fills the frame?!


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Help sigma 105mm vs canon 100mm L. Clinical Oral Photography
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