Photons to Photos Optical Bench and Focus Breathing

[RobertOToole]

If you haven't used the optical bench on Photons to Photos and you have some extra time take a look. Thanks to a friend I found the Irix 150mm and have been looking at other macro designs. Its really interesting to the optical layouts and even better to see how they older lenses focus with only extension, and some all internally.

This is the link: https://www.photonstophotos.net//Genera ... lBench.htm#

This is even better, a list of the lenses in the Optical Bench Data base:

https://www.photonstophotos.net//Genera ... nchHub.htm

To focus, follow the link, look for the focus button upper right, grab the slider and slide to the right for close fcous.

Some highlights:

Sony FE 90mm F2.8 Macro G OSS
Focal length at infinity: 92.61
Focal length at minimum : 45.88 Ouch!

Link and source for the above image: https://www.photonstophotos.net//Genera ... sO,OffAxis

Sigma APO Macro 150mm F2.8 EX DG OS HSM
Focal length at infinity: 149.99
Focal length at minimum focus: 78.23

Link: https://www.photonstophotos.net//Genera ... sO,OffAxis

Sigma APO Macro 180mm F2.8 EX DG OS HSM
Focal length at infinity: 174.60
Focal length at minimum focus: 103.47

Link: https://www.photonstophotos.net//Genera ... sO,OffAxis

Canon RF100mm F2.8 L Macro IS USM
Focal length at infinity: 100.80
Focal length at minimum focus 1x: 45.0 (WD=92)
Focal length at minimum focus 1.4x: 36.0 (WD=112)

Link: https://www.photonstophotos.net//Genera ... sO,OffAxis

Canon EF 100mm f/2.8L Macro IS USM
Focal length at infinity: 100.00
Focal length at minimum focus: 74.00 (WD=134.76)

Link: https://www.photonstophotos.net//Genera ... sO,OffAxis

Sigma Macro 105mm F2.8 EX DG OS HSM
Focal length at infinity: 101.71
Focal length at minimum focus: 75.68 (WD=144)

Link: https://www.photonstophotos.net//Genera ... sO,OffAxis

Nikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-ED Lens
Focal length at infinity: 103.97
Focal length at minimum focus: 75.87 (WD=152.47)

Link: https://www.photonstophotos.net//Genera ... sO,OffAxis


I posted more on my site:

https://www.closeuphotography.com/blog/ ... ical-bench


Be sure to check out Photons to Photos other info as well, its a huge resource of excellent information about camera sensors and lenses, and I have referenced them a few time in past posts:

https://www.photonstophotos.net/


Best,

Updated the RF to reflect figures at 1x.

[rjlittlefield]

Perfect! I was looking for this just yesterday, but had somehow lost track of it. Thanks!

--Rik

[RobertOToole]

Perfect! I was looking for this just yesterday, but had somehow lost track of it. Thanks!

--Rik

Hi Rik,

Just this morning a friend reminded about the optical bench and I didn't even know the Irix 150 was in the data base

The lens list is really useful to find things quick, Bill calls it the Optical Bench Hub:

https://www.photonstophotos.net//Genera ... nchHub.htm



Best,

Robert

[RobertOToole]

Quick update

Photons to Photo Optical Bench does not have Voigtlander 125mm SL, but I own one, so I measured myself.

Voigtlander 125mm f/2.5 SL Macro APO-Lanthar
Infinity FL: 125mm
FL at 1:1: 91mm
WD at 1:1: 380mm

If anyone runs across any interesting information on the Photons to Photo Optical Bench please share it in this thread.

Thanks in advance.

Robert

[cactuspic]

Thanks for the reference, Robert.

I suspect that one of the reasons for the dramatic change in focal length between the EF and RF versions of the 100mm macro lenses by Canon has to do with the change in the maximum magnification of the two lenses. The maximum magnification of the EF version is 1x. The RF has a max of 1.4x. I would expect that there is substantial focus breathing by the RF version as it increases its magnification from 1x to 1.4x though I don’t know if it is the sole reason for the difference.

[dickb]

I suspect that one of the reasons for the dramatic change in focal length between the EF and RF versions of the 100mm macro lenses by Canon has to do with the change in the maximum magnification of the two lenses. The maximum magnification of the EF version is 1x. The RF has a max of 1.4x. I would expect that there is substantial focus breathing by the RF version as it increases its magnification from 1x to 1.4x though I don’t know if it is the sole reason for the difference.

It isn't the sole reason. You can adjust the focus distance on the web page - you can't choose one that gives you 1:1 magnification exactly, but 1:1.05 gives you 47.67mm and 1.04:1 results in 44.98mm, so 1:1 should be around 46mm. So still a lot shorter than the 74mm of the EF version.

[RobertOToole]

Thanks for the reference, Robert.

I suspect that one of the reasons for the dramatic change in focal length between the EF and RF versions of the 100mm macro lenses by Canon has to do with the change in the maximum magnification of the two lenses. The maximum magnification of the EF version is 1x. The RF has a max of 1.4x. I would expect that there is substantial focus breathing by the RF version as it increases its magnification from 1x to 1.4x though I don’t know if it is the sole reason for the difference.

Completely forgot about the extra magnification on the RF lens! Thanks for the note!

I checked again at 1x the RF lens is 45mm.

Best,

Robert

[RobertOToole]

I suspect that one of the reasons for the dramatic change in focal length between the EF and RF versions of the 100mm macro lenses by Canon has to do with the change in the maximum magnification of the two lenses. The maximum magnification of the EF version is 1x. The RF has a max of 1.4x. I would expect that there is substantial focus breathing by the RF version as it increases its magnification from 1x to 1.4x though I don’t know if it is the sole reason for the difference.

It isn't the sole reason. You can adjust the focus distance on the web page - you can't choose one that gives you 1:1 magnification exactly, but 1:1.05 gives you 47.67mm and 1.04:1 results in 44.98mm, so 1:1 should be around 46mm. So still a lot shorter than the 74mm of the EF version.

Now that you bring up setting mag ratios!

I've had my hands on way too many lenses lately for testing so this is not something you would normally experience but people don't realize how hard it is to get a macro lens to give you 1.00 x. If you crank the lens focus ring until it stops its always 1.02 (in the case of the irix 150mm), but I've had lenses go to 1.04 or 1.05! The only problem with that is if you are testing 3 or 4 macro lenses, the mag, and crops at 100% view will have different sized details and I re-size test images is out of the question (lenses that focus with extension are very easy to set the mag exactly where needed).

I recently tested a few lenses at 1x and the Laowa and Sigma were very difficult to set the mag ratio (for different reasons). In-the-field it doesn't matter at all but for testing its a headache.

Best,

Robert

[rjlittlefield]

lenses that focus with extension are very easy to set the mag exactly where needed

I am puzzled by this distinction.

I assume that in all cases you are setting the magnification by tweaking the lens ring, then adjusting the subject distance to restore perfect focus.

So what is it about focus-with-extension that makes that process simpler than internal focus?

Are you measuring the extension and using that as a repeatable scale?

--Rik

[RobertOToole]

Hi Rik,

Was hoping someone would ask about this, I didn't want to bore people with the details but since you are asking

Do plan to go into this in more detail when I finish the page(s) on the Laowa and Sigma lenses.

lenses that focus with extension are very easy to set the mag exactly where needed

I am puzzled by this distinction.

I assume that in all cases you are setting the magnification by tweaking the lens ring, then adjusting the subject distance to restore perfect focus.

The problem with the Sigma Art 105, which is an excellent lens, so I'm this isn't meant to discourage anyone from trying or buying the lens but I do think its important to point this out, is the focus-by-wire. The ring turns without much resistance at all and worse there is a delay between the position sensor responding. So instead of 1.00 on a scale, in my case a metal 0.5mm ruler, you undershoot, then overshoot, then undershoot....0.94...1.05....0.96....1.04...you have to time the delay and take your fingers off the ring early. It takes some getting used to. This is also an issue in-the-field but in that case I use a focus rail.

The problem with the Laowa 100, which is also an excellent lens, is the calibration of the focus ring to focus (not sure the best description here, maybe come can come up with a better word) where the designer had to cram in infinity to 2x on a small ring and he didn't put much thought into it using only 100 degrees or so for the job. So in this case there is resistance and a better mechanical connect but trying to fine focus on tiny detail on a leaf or the edge of millimeter mark on a ruler for a test is tough even with the focus magnifier. The ring needs a better adjustment calibration for fine focus.

Both lenses lack the precision and feel of an all manual Voigtlander APO-Lanthar lens. Not better or worse just a lot different to use and not ideal for the work I do.

So what is it about focus-with-extension that makes that process simpler than internal focus? Are you measuring the extension and using that as a repeatable scale?

I wasn't very clear with that. With something like a lens like a Macro-Varon that uses extension only to focus, I use a threaded Thorlabs variable extension tube. I did not mean a lens with uses focus-by-extension.

All the best for the new year.

Best,

Robert

[JKT]

I heartily agree about the Sigma Art macro lenses. I have the 70 and the behaviour is similar. If you don't care about the exact magnification, you can focus by fine tuning the distance, but when that is not an option things get difficult. Additionally Sigma claims non-combatibility with Canon TC:s. Actually manual focus seems to work with at least EF 1.4x II and EF 1.4x III. However, with RF 1.4x even the manual focus won't work. That was an unpleasant surprise, which speeded the acquisition of EF 1.4x III.

[RobertOToole]

I heartily agree about the Sigma Art macro lenses. I have the 70 and the behaviour is similar. If you don't care about the exact magnification, you can focus by fine tuning the distance, but when that is not an option things get difficult. Additionally Sigma claims non-combatibility with Canon TC:s. Actually manual focus seems to work with at least EF 1.4x II and EF 1.4x III. However, with RF 1.4x even the manual focus won't work. That was an unpleasant surprise, which speeded the acquisition of EF 1.4x III.

Thanks for the TC info JKT.

All the best for 2022.

Robert

[JKT]

Thanks for the TC info JKT.

All the best for 2022.

For you as well!

Your tests are an invaluable treasure trove! Thanks for all the work you've put into them!

[rjlittlefield]

Thanks for the clarification about ease of scale adjustment.

Rephrasing what I think I'm hearing, your experiences fall into 4 major categories, ordered here by ease of precise adjustment.

1. Short-focus lenses that can be put on variable extension tubes. Example: Macro-Varon.
2. Lenses with mechanical focus rings that have lots of rotation for modest range. Example: Voigtlander APO-Lanthar.
3. Lenses with mechanical focus rings that have not much rotation for wide range. Example: Laowa 100.
4. Lenses with focus-by-wire rings that may have fiddly adjustments. Example: Sigma Art 105.

This now makes perfect sense to me.

I don't have any lenses in category 4, but lots of my kit lenses fall into category 3. For those, shooting flat subjects such as paper documents, I often rely on automatic focus because the camera can tweak focus better than I can. If I did care about exact magnification, then I might use JKT's method by tweaking the distance and letting the camera adjust focus to match. But more likely, since my cameras tether well, I would probably tether and adjust focus electronically by clicking in the GUI. None of this matches the simplicity of a good mechanical mechanism, but if the camera can adjust the lens electronically better than I can by using the focus ring, then it seems the best option.

--Rik

[Lou Jost]

For some focus-by-wire brands, there may be a way to get even higher repeatability and precision than the best mechanical lenses. Some brands of camera have tethering interfaces that allow single-microstep changes in focus distance. Thus you can get essentially perfect repeatability by focusing all the way to the lens' closest focusing distance, and then stepping the focus backwards (while counting the steps) until you get perfect 1:1. This will be repeatable by using the same number of steps and the same starting point every time (unless the temperature is very different). The Panasonic Image App works this way, and it is wireless, so you can do it from your phone without touching the camera. This makes it very precise, and the camera doesn't shake as you focus, making it even more precise (particularly with long lenses).