Approve the Cookies
This website uses cookies to improve your user experience. By using this site, you agree to our use of cookies. Read More.
OK
Index  •   • New posts  •   • RTAT  •   • 'Best of'  •   • Gallery  •   • Gear  •   • Reviews
Guest
New posts  •   • RTAT  •   • 'Best of'  •   • Gallery  •   • Gear  •   • Reviews
Register to forums    Log in

 
FORUMS Photography Talk by Genre Macro Talk 
Thread started 26 Jan 2018 (Friday) 10:20
Search threadPrev/next
sponsored links
(this ad will go away when you log in as a registered member)

Macro lenses and focal length

 
Dalantech
Goldmember
Avatar
4,438 posts
Gallery: 194 photos
Best ofs: 3
Likes: 299
Joined Jul 2006
Location: Bacoli, Italy
     
Jan 26, 2018 10:20 |  #1

Does anyone have a good explanation of why macro lenses with internal focusing lose focal length at minimum focus? I know it has something to do with how the lens elements are shifting, and possibly even the aperture assembly moving. Can't find any resource on the web and my "Goolge Fu" is usually pretty good.


My Gallery (external link)
My Blog (external link)
Macro Tutorials (external link)

  
  LOG IN TO REPLY
sponsored links
(this ad will go away when you log in as a registered member)
Wilt
Reader's Digest Condensed version of War and Peace [POTN Vol 1]
Avatar
40,148 posts
Gallery: 1 photo
Likes: 2012
Joined Aug 2005
Location: Belmont, CA
Post edited 3 months ago by Wilt. (6 edits in all)
     
Jan 26, 2018 11:11 |  #2

Dalantech wrote in post #18549361 (external link)
Does anyone have a good explanation of why macro lenses with internal focusing lose focal length at minimum focus? I know it has something to do with how the lens elements are shifting, and possibly even the aperture assembly moving. Can't find any resource on the web and my "Goolge Fu" is usually pretty good.

I have never seen an explanation published. I think it is perhaps good to simply think of a macro lens as 'variable focal length', like a zoom. The difference is that with zoom the photographer can choose FL at will, and the optics move to accomodate that FL. With macro, the photographer has zero direct control of FL, but indirectly affects FL via the focus control...changed FL at closes focus distance.
I don't think I have seen that a zoom like the 100mm Canon has a 'intermediate FL' setting for the optics, when the magnification achieved is 1:2 vs. the 77mm FL at 1:1.

For anyone who owns the Canon 100mm macro lens, that test is not difficult to accomplish...simply get a 1:2 image on focal plane and measure subject-to-focal plane distance! A distance different from 2*(4FL), anything other than 2*(4*77) or 2*(4*100) to accomplish 1:2 scale, is indicative of an intermediate FL setting (not 77mm, not 100mm) for the lens.

For a manual focus optic of say 8 elements in 4 groups, when you focus closer -- including macro distances -- all 8 elements in 4 groups move AS A UNIT farther from the focal plane to focus. Always moving the optics AS A SINGLE UNIT.
Because of the long 'throw' needed to make that movement away from the focal plane for macro distances, that would tax the battery unnecessarily and also make focus a much slower response. So the solution for AF lens designers was to put in a means to alter the grouping/spacing of the optics to shorten the FL so that AF throw is shortened, so that they make (4*FL) a smaller number and less taxing to the batteries!


You need to give me OK to edit your image and repost! Keep POTN alive and well with member support http://photography-on-the.net/forum/donate.p​hp
Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
  LOG IN TO REPLY
Dalantech
THREAD ­ STARTER
Goldmember
Avatar
4,438 posts
Gallery: 194 photos
Best ofs: 3
Likes: 299
Joined Jul 2006
Location: Bacoli, Italy
     
Jan 26, 2018 13:03 |  #3

Wilt wrote in post #18549406 (external link)
I have never seen an explanation published.

Same. I know that Canon's EF-S 60mm is a 37mm lens at minimum focus, cause it only takes 37mm of extension to get to 2x. My experience with the old 100mm USM macro (non L) is the same as yours -it's somewhere in the 70mm range at 1x.


My Gallery (external link)
My Blog (external link)
Macro Tutorials (external link)

  
  LOG IN TO REPLY
Wilt
Reader's Digest Condensed version of War and Peace [POTN Vol 1]
Avatar
40,148 posts
Gallery: 1 photo
Likes: 2012
Joined Aug 2005
Location: Belmont, CA
Post edited 3 months ago by Wilt. (5 edits in all)
     
Jan 26, 2018 13:12 |  #4

Dalantech wrote in post #18549527 (external link)
Same. I know that Canon's EF-S 60mm is a 37mm lens at minimum focus, cause it only takes 37mm of extension to get to 2x. My experience with the old 100mm USM macro (non L) is the same as yours -it's somewhere in the 70mm range at 1x.

I think you may be jumping to a bad a conclusion in only needing 37mm to get to 2:1.
The 60mm focuses to 0.2m and achieves 1:1 at that distance...4*FL rule means the lens is effectively acting like a 50mm lens at 1:1

OTOH, with a manual focus 50mm lens, I put it on a 50mm extension to achieve 1:1, and I put it on a 100mm entension to achieve 2:1 (both assuming the lens inherent focus mechanism is set to Infinity), so the incremental extension to go (from 1:1 to 2:1) is 50mm for a 50mm lens; so I am puzzled about incremental 37mm extension to take a so-called '50mm lens' (60mm lens effective FL) to 2:1

AF macro is so perplexing, because nobody tells you what is actually going on in the design! a bit like inferring what Apple is really doing inside its hide-it-from-the-user O/S (which Windows has become like)


You need to give me OK to edit your image and repost! Keep POTN alive and well with member support http://photography-on-the.net/forum/donate.p​hp
Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
  LOG IN TO REPLY
LordV
Macro Photo-Lord of the Year 2006
Avatar
59,509 posts
Gallery: 7 photos
Best ofs: 2
Likes: 3084
Joined Oct 2005
Location: Worthing UK
     
Jan 27, 2018 01:03 |  #5

AFAIK all macro lenses lose focal length at 1:1 whether they are internal focusing or not, Both my old Tamron 90mm and sigma 105 did it.
I think Wilt is implying this in his explanation.
Brian V.


http://www.flickr.com/​photos/lordv/ (external link)
http://www.lordv.smugm​ug.com/ (external link)
Macro Hints and tips
Canon 600D, 40D, 5D mk2, 7D, Tamron 90mm macro, Sigma 105mm OS, Canon MPE-65,18-55 kit lens X2, canon 200mm F2.8 L, Tamron 28-70mm xrdi, Other assorted bits

  
  LOG IN TO REPLY
Wilt
Reader's Digest Condensed version of War and Peace [POTN Vol 1]
Avatar
40,148 posts
Gallery: 1 photo
Likes: 2012
Joined Aug 2005
Location: Belmont, CA
Post edited 3 months ago by Wilt. (9 edits in all)
     
Jan 27, 2018 01:17 |  #6

LordV wrote in post #18549940 (external link)
AFAIK all macro lenses lose focal length at 1:1 whether they are internal focusing or not, Both my old Tamron 90mm and sigma 105 did it.
I think Wilt is implying this in his explanation.
Brian V.


Sorry, wrong interpretation on your part. All 'AUTOFOCUS macro lenses lose FL' is a statement I could buy (not having done an exhaustive analysis of minimum focus distance vs. 1:1 magnification).

But for MANUAL focus distance, I absolutely do not buy the statement "all macro lenses lose FL".
I have in my possession a Tamron 90mm f/2.5 SP Adaptall2 lens (Tamron lens ID 52BB) that focuses to 1:2, and it came with an extension tube made specifically to fit that lens so that it achieves 1:1 magnification...mounte​d on my 7DII and focused on a subject at 1:1, the distance from subject to focal plane is indeed exactly 4 * FL, 360mm in the case of this lens. I just mounted it and verified that distance!!!

In the case of the Canon 100mm f/2.8 macro, I bet that if you focused the lens at infinity and then put a 100 extension on it to yield 1:1, the subject-to-focal plane distance would indeed be 400mm.
But with the internal mechanism minimum focus distance it achieves 1:1 at 0.3m only because its FL has actually changed from 100mm to 75mm...subject-to-focal plane is 4*75mm away


You need to give me OK to edit your image and repost! Keep POTN alive and well with member support http://photography-on-the.net/forum/donate.p​hp
Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
  LOG IN TO REPLY
Bassat
"I am still in my underwear."
Avatar
7,557 posts
Likes: 2540
Joined Oct 2015
Location: Bourbon, Indiana - USA
     
Jan 27, 2018 07:44 |  #7

Two general complications:

1.) The focal length of nearly all photographic lenses is stated as 'focused at infinity'. Ponder that for a second as it relates to macro lenses.

2.) At or near 1:1 reproduction, effective aperture changes, too.


Tom,
Film gear: Elan 7NE / Elan 7 / EOS T2
Yashica FX-D (x2) & FX-3 Super 2000 / DSB 28mm f/2.8 / 50mm ML f/2 / 135mm ML f/2.8 / Sigma Zoom-gamma II 21-35mm f/3.4.2 / Yashica ML 28-85mm f/3.5-4.5 / Tokina 70-210mm ML f/4.

  
  LOG IN TO REPLY
Wilt
Reader's Digest Condensed version of War and Peace [POTN Vol 1]
Avatar
40,148 posts
Gallery: 1 photo
Likes: 2012
Joined Aug 2005
Location: Belmont, CA
Post edited 3 months ago by Wilt. (7 edits in all)
     
Jan 27, 2018 12:41 |  #8

Bassat wrote in post #18550034 (external link)
Two general complications:

1.) The focal length of nearly all photographic lenses is stated as 'focused at infinity'. Ponder that for a second as it relates to macro lenses.

2.) At or near 1:1 reproduction, effective aperture changes, too.

Bassat wrote in post #18550034 (external link)
Two general complications:

1.) The focal length of nearly all photographic lenses is stated as 'focused at infinity'. Ponder that for a second as it relates to macro lenses.

2.) At or near 1:1 reproduction, effective aperture changes, too.

Point 1 certain applies now as a caveat in the case of AF lenses. In the case of the Tamron 90mm manual focus lens, which I wrote about earlier, clearly its 6 groups of 8 elements move as a UNIT, and focus merely extends the length of the lens barrel to move the unit farther from the focus plane with zero alteration of its FL.

The effective aperture merely is a 'equivalency f/stop' that accounts for the additional 'loss of light' when photographing anything at a reproduction greater than about 1:3. We used to consult tables based upon reproduction scale, to determine the correction to be applied to handheld meter readings. Those without a correction table to consult might try to calculate effective aperture

Effective Aperture = Lens Aperture x (1 + Magnification / Pupil Magnification)

But the problem is that the Pupil Magnification varies based upon focus distance. Add to the complication the fact that the FL of the AF macro lens changes, so what is happening to the f/stop value when the FL changed?!
Now that through the lens metering (TTL metering) is in almost everything, instead of the correction tables we think of 'effective aperture' instead. Any camera that has TTL will automatically adjust the exposure to compensate for this, and will do so much better than the above equation.


You need to give me OK to edit your image and repost! Keep POTN alive and well with member support http://photography-on-the.net/forum/donate.p​hp
Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
  LOG IN TO REPLY
LordV
Macro Photo-Lord of the Year 2006
Avatar
59,509 posts
Gallery: 7 photos
Best ofs: 2
Likes: 3084
Joined Oct 2005
Location: Worthing UK
     
Jan 27, 2018 13:08 |  #9

Wilt wrote in post #18549942 (external link)
Sorry, wrong interpretation on your part. All 'AUTOFOCUS macro lenses lose FL' is a statement I could buy (not having done an exhaustive analysis of minimum focus distance vs. 1:1 magnification).

But for MANUAL focus distance, I absolutely do not buy the statement "all macro lenses lose FL".
I have in my possession a Tamron 90mm f/2.5 SP Adaptall2 lens (Tamron lens ID 52BB) that focuses to 1:2, and it came with an extension tube made specifically to fit that lens so that it achieves 1:1 magnification...mounte​d on my 7DII and focused on a subject at 1:1, the distance from subject to focal plane is indeed exactly 4 * FL, 360mm in the case of this lens. I just mounted it and verified that distance!!!

y

Ok agreed it may only apply to all AF macro lenses although there are some manual focus macro lenses it applies to eg MPE-65.
Brian V.


http://www.flickr.com/​photos/lordv/ (external link)
http://www.lordv.smugm​ug.com/ (external link)
Macro Hints and tips
Canon 600D, 40D, 5D mk2, 7D, Tamron 90mm macro, Sigma 105mm OS, Canon MPE-65,18-55 kit lens X2, canon 200mm F2.8 L, Tamron 28-70mm xrdi, Other assorted bits

  
  LOG IN TO REPLY
Wilt
Reader's Digest Condensed version of War and Peace [POTN Vol 1]
Avatar
40,148 posts
Gallery: 1 photo
Likes: 2012
Joined Aug 2005
Location: Belmont, CA
Post edited 3 months ago by Wilt.
     
Jan 27, 2018 14:23 as a reply to  @ LordV's post |  #10

The Canon MP-E 65mm is a bit of an odd duck with regard to FL...the subject-to-focal-plane distance of 0.24m at 1:1 is apropos to a lens FL that is 60mm, not 65mm.

Canon states, " A floating system preserves optical quality at different focusing distances, and features a UD-glass element." so it uncertain as to whether optics are shifting slightly primarily to optimize/preserve lens performance, or if the FL is undergoing any changes during magnfication change of the lens.


You need to give me OK to edit your image and repost! Keep POTN alive and well with member support http://photography-on-the.net/forum/donate.p​hp
Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
  LOG IN TO REPLY
LordV
Macro Photo-Lord of the Year 2006
Avatar
59,509 posts
Gallery: 7 photos
Best ofs: 2
Likes: 3084
Joined Oct 2005
Location: Worthing UK
     
Jan 28, 2018 00:23 |  #11

Wilt wrote in post #18550265 (external link)
The Canon MP-E 65mm is a bit of an odd duck with regard to FL...the subject-to-focal-plane distance of 0.24m at 1:1 is apropos to a lens FL that is 60mm, not 65mm.

Canon states, " A floating system preserves optical quality at different focusing distances, and features a UD-glass element." so it uncertain as to whether optics are shifting slightly primarily to optimize/preserve lens performance, or if the FL is undergoing any changes during magnfication change of the lens.


Can remember calculating the FL of the MPE-65 at 5:1 and think it came out at 48mm.

Brian V.


http://www.flickr.com/​photos/lordv/ (external link)
http://www.lordv.smugm​ug.com/ (external link)
Macro Hints and tips
Canon 600D, 40D, 5D mk2, 7D, Tamron 90mm macro, Sigma 105mm OS, Canon MPE-65,18-55 kit lens X2, canon 200mm F2.8 L, Tamron 28-70mm xrdi, Other assorted bits

  
  LOG IN TO REPLY
Wilt
Reader's Digest Condensed version of War and Peace [POTN Vol 1]
Avatar
40,148 posts
Gallery: 1 photo
Likes: 2012
Joined Aug 2005
Location: Belmont, CA
Post edited 3 months ago by Wilt. (2 edits in all)
     
Jan 28, 2018 11:13 |  #12

LordV wrote in post #18550661 (external link)
Can remember calculating the FL of the MPE-65 at 5:1 and think it came out at 48mm.

Brian V.

I've seen in print the formula for 1:1 subject-to-focal-plane distance (distance=4*FL), but never a formula for other magnifications.

In the case of the MP-E 65, one might speculate that subject-to-focal-plane distance at 5:1 is simply 1/5 of its 1:1 distance

so that the 65 MPE at 5:1 has its subject-to-focal-plane distance calculated to (4*48)/5 = 38.4mm rom subject...but that makes no sense since the lens is 81mm long, and then there is the thickness of the camera body, too! I found a table showing the use of extension bellows with 50mm lens, and 4:1 was achieved with a total subject-to-focal-plane distance of 313mm

What would the 5:1 subject-to-focal-plane distance be with the MP-E 65???


You need to give me OK to edit your image and repost! Keep POTN alive and well with member support http://photography-on-the.net/forum/donate.p​hp
Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
  LOG IN TO REPLY
Choderboy
I Chimp, therefore I am
Avatar
4,805 posts
Gallery: 82 photos
Likes: 1692
Joined Jul 2005
Location: Sydney, Australia
     
Jan 28, 2018 13:02 |  #13

Wilt wrote in post #18550940 (external link)
I've seen in print the formula for 1:1 subject-to-focal-plane distance (distance=4*FL), but never a formula for other magnifications.

In the case of the MP-E 65, one might speculate that subject-to-focal-plane distance at 5:1 is simply 1/5 of its 1:1 distance

so that the 65 MPE at 5:1 has its subject-to-focal-plane distance calculated to (4*48)/5 = 38.4mm rom subject...but that makes no sense since the lens is 81mm long, and then there is the thickness of the camera body, too! I found a table showing the use of extension bellows with 50mm lens, and 4:1 was achieved with a total subject-to-focal-plane distance of 313mm

What would the 5:1 subject-to-focal-plane distance be with the MP-E 65???

At 5:1 the MP-E is more like 240mm long, not 81mm. (I don't know the actual length, ballpark 240mm). It is longer the the Canon 180 macro which is about 187mm long:
https://www.the-digital-picture.com …5x-Macro-Lens-Review.aspx (external link)


Dave
https://www.flickr.com​/photos/12185187@N00/
5D4, 1D4, 1DS2. Canon, Sigma lenses
Image editing OK

  
  LOG IN TO REPLY
Wilt
Reader's Digest Condensed version of War and Peace [POTN Vol 1]
Avatar
40,148 posts
Gallery: 1 photo
Likes: 2012
Joined Aug 2005
Location: Belmont, CA
Post edited 3 months ago by Wilt. (2 edits in all)
     
Jan 28, 2018 13:23 as a reply to  @ Choderboy's post |  #14

Thanks for that information, Dave, as it helps to estimate the subject-to-focal-plane distance (since Canon document provides nothing about that).
According to Canon information on graph, at 5:1 the working distance is somewhere about 43mm.
Add the 240mm lens length estimation, add about 42mm or so for the mount-to-focal plane, and you end up with a subject-to-focal-plane distance which is perhaps in the range of 290-300mm (240+42+something)
Now comes the question of the relationship between actual lens FL, and that 5:1 subject-to-focal-plane distance

If we assume 5:1 subject-to-focal-plane distance is 300mm, and if we apply the formula

Extension tube / FL = Magnification

we can reverse compute for 5:1 we need 215mm extension with 43mm FL to get 5:1, and 43mm in front of the optic to the subject (per Canon).


You need to give me OK to edit your image and repost! Keep POTN alive and well with member support http://photography-on-the.net/forum/donate.p​hp
Canon dSLR system, Olympus OM 35mm system, Bronica ETRSi 645 system, Horseman LS 4x5 system, Metz flashes, Dynalite studio lighting, and too many accessories to mention

  
  LOG IN TO REPLY
Choderboy
I Chimp, therefore I am
Avatar
4,805 posts
Gallery: 82 photos
Likes: 1692
Joined Jul 2005
Location: Sydney, Australia
     
Jan 28, 2018 14:37 |  #15

Working Distance at 5x is 41mm. At 1x it is 101mm. As per the printing on the barrel.


Dave
https://www.flickr.com​/photos/12185187@N00/
5D4, 1D4, 1DS2. Canon, Sigma lenses
Image editing OK

  
  LOG IN TO REPLY
sponsored links
(this ad will go away when you log in as a registered member)

3,135 views & 2 likes for this thread
Macro lenses and focal length
FORUMS Photography Talk by Genre Macro Talk 
AAA
x 1600
y 1600

Jump to forum...   •  Rules   •  Index   •  New posts   •  RTAT   •  'Best of'   •  Gallery   •  Gear   •  Reviews   •  Member list   •  Polls   •  Image rules   •  Search   •  Password reset

Not a member yet?
Registered members may log in to forums and access all the features: full search, image upload, follow forums, own gear list and ratings, likes, more forums, private messaging, thread follow, notifications, own gallery, all settings, view hosted photos, own reviews, see more and do more... and all is free. Don't be a stranger - register now and start posting!


COOKIES DISCLAIMER: This website uses cookies to improve your user experience. By using this site, you agree to our use of cookies and to our privacy policy.
Privacy policy and cookie usage info.


POWERED BY AMASS forum software 2.1forum software
version 2.1 /
code and design
by Pekka Saarinen ©
for photography-on-the.net

Latest registered member is Ronaldwilliam
764 guests, 387 members online
Simultaneous users record so far is 6430, that happened on Dec 03, 2017

Photography-on-the.net Digital Photography Forums is the website for photographers and all who love great photos, camera and post processing techniques, gear talk, discussion and sharing. Professionals, hobbyists, newbies and those who don't even own a camera -- all are welcome regardless of skill, favourite brand, gear, gender or age. Registering and usage is free.