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Shorter macro lens with internal focus?

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Post Options Post Options   Quote dCap Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 11:57
Good that the OP is still involved (and welcome to the forum).

Are you looking for a lens that maintains a smaller size? Looking for a video lens that doesn't breathe? Or just looking for a 50-ish (or shorter) with good working distance? Working distance with 50mm (and less) has always been a challenge and explains why the '100mm' was always the more popular macro. Do you need 1:1?
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 12:07
Originally posted by Harm vb Harm vb wrote:

But the Sony FE2,8/90 Macro OSS G (SEL90M28G) that I own, is remaining its length when focussing. I guess that it means that the front lens dosn't move towards of from the subject.

Does it have internal focussing then?


Yes, see the database entry for this lens

There's also a simple trick you can determine if a macro lens has internal focussing in case the Minimum Focus Distance (MFD) at 1:1 is given.

Devide the MFD by 4, if the outcome is the same as the stated focal length it does not have internal focussing. In case the outcome is smaller the lens has internal focussing. In the latter case it can still be combined with extension (like for instance the Minolta/Sony 100/2.8 or Sony FE 50/2.8) or no extension at all (like your Sony FE 90/2.8)
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 12:23
Why this infatuation with internal focussing? It's virtually impossible to make a 1:1 macro lens without moving most of the elements forward, for the simple reason that unless you can magically halve the focal length, the principal planes have to double their distance from the sensor to get 1:1. The thin lens approximation makes this easier to understand (see lots of descriptions on the web).

I guess you can stick a piece of curved glass at the very front which doesn't move, does hardly anything optically*, and serves mostly to hide the apparently wasted length there which is actually needed to house the moving elements and support tubes. Hey presto! An 'internal focussing' macro lens with a constant length. The engineers will laugh behind their hands but the sales people will be so pleased!

You will note that 'internal focussing' lenses which genuinely only move a few of their elements have a very restricted focus range with a long MFD. They don't get to 1:1 unless they fake it as described above.

Personally I blame the current infatuation with AF speed, which has led to in-lens AF motors with an adjustment range that is deliberately restricted to benefit AF speed at the expense of usability.

* several macro lenses already have such a piece of glass at the back, possibly described as a field corrector, but this doesn't change the fact that the bits of glass that do the actual focussing have to move forward a LONG way, and the more of them you move and the further they have to travel, the slower the AF will be ...

Oh, and the bits of plain glass at each end do the useful thing of keeping the dust and rain out, I guess. Is that the concern?

Edited by Miranda F - 28 January 2021 at 12:37
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 12:41
Originally posted by Miranda F Miranda F wrote:

What's with the infatuation with internal focussing? It's virtually impossible to make a 1:1 macro lens without moving most of the elements forward, for the simple reason that unless you can magically halve the focal length, the principal planes have to double their distance from the sensor to get 1:1. The thin lens approximation makes this easier to understand (see lots of descriptions on the web).

I guess you can stick a piece of curved glass at the very front which doesn't move, does hardly anything optically, and serves mostly to hide the apparently wasted length there which is actually needed to house the moving elements and support tubes. Hey presto! An 'internal focussing' macro lens with a constant length. The engineers will laugh behind their hands but the sales people will be so pleased!

You will note that so-called 'internal focussing' lenses have a very restricted focus range with a long MFD. They don't get to 1:1 unless they fake it as described above.

Personally I blame the current infatuation with AF speed, which has led to in-lens AF motors with an adjustment range that is deliberately restricted to benefit AF speed at the expense of usability.


I think you're overlooking the possibility that most IF lenses use, i.e moving the elements in such a way that the focal length of the entire combo is reduced.

For instance the Sony FE 90/2.8 macro lens is a notable exception to your statements.

Looking at the optical scheme (see the database page linked above) it doesn't meet your description, it doesn't have a thin lens in front but 5 groups / 7 elements close together so it can't move most elements to the double distance from the sensor. Still it does not get longer and only reduces it's focal length at MFD to 70 mm. It also does not have a "restricted focus range with a long MFD"

Similar remarks can be made about for instance the Sigma 180/3.5 IF telemacro, allthough there the focal length reduction at 1:1 is a bit more and comes out at 115 mm.

But I agree, if the "internal focussing" does not reduce the focal length then extension (or moving most elements further from the sensor) is the only way to achieve focus, but if I look in the database most Internal Focus lenses reduce their focal length as you focus closer.
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Post Options Post Options   Quote QuietOC Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 13:21
The thin lens formulas can be quite inaccurate at high magnification with actual lenses.

I wonder why macro lenses without focus breathing do not exist. They would make focus stacking simpler. My reducing focal length with close focus macro lenses don't reduce their focal lengths enough to keep constant angle-of-view. It might reduce the working distance more. Like the Sigma 400mm F5.6 APO Tele Macro I just bought. It is internal focus with a 1.6 meter closest focus. It seems like that could be reduced a bit to allow no angle-of-view change.

Sony doesn't really market the lack of focus breathing of their lenses which lack focus breathing. Maybe it is because manufacturing variation causes every copy to be a bit off.

Edited by QuietOC - 28 January 2021 at 13:26
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 19:29
Originally posted by pegelli pegelli wrote:


Similar remarks can be made about for instance the Sigma 180/3.5 IF telemacro, allthough there the focal length reduction at 1:1 is a bit more and comes out at 115 mm.

But I agree, if the "internal focussing" does not reduce the focal length then extension (or moving most elements further from the sensor) is the only way to achieve focus, but if I look in the database most Internal Focus lenses reduce their focal length as you focus closer.


Clearly some of the macro lenses deliberately reduce the focal length, presumably by bringing a negative element forward as a kind of extremely non-parfocal zoom lens. You can achieve something similar with an extension tube as I mentioned above. I guess it has several advantages.

But I still feel that equating 'internal focussing' with constant-length is a bit silly. E-mount lenses all have an internal focus motor and they all move internal elements (not just the front group as in cheap A-mount zooms) so it doesn't rally matter to anyone except the designer which elements they move.    
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 19:33
Originally posted by QuietOC QuietOC wrote:

Sony doesn't really market the lack of focus breathing of their lenses which lack focus breathing. Maybe it is because manufacturing variation causes every copy to be a bit off.

Good point. They've missed a trick there, or maybe few customers understand what focus breathing is...

I'd be interested to know if the internal-zoom macro lenses which don't change length much also show much less change in aperture than an all-moving design. If so, that would be another benefit. Speaking of which - does the internal aperture iris adjust to correct the recorded aperture as they move to 1:1?
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Post Options Post Options   Quote pegelli Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 19:59
Originally posted by Miranda F Miranda F wrote:


Clearly some of the macro lenses deliberately reduce the focal length, presumably by bringing a negative element forward as a kind of extremely non-parfocal zoom lens. You can achieve something similar with an extension tube as I mentioned above. I guess it has several advantages.
I don't think adding extension tubes will shorten the focal length, so it's not really similar. And by moving groups you could also achieve some of the "floating element" advantages to allow a better performance across the whole focus range from infinity to macro, I think some of the more expensive macro lenses also do that.

Originally posted by Miranda F Miranda F wrote:


But I still feel that equating 'internal focussing' with constant-length is a bit silly. E-mount lenses all have an internal focus motor and they all move internal elements (not just the front group as in cheap A-mount zooms) so it doesn't rally matter to anyone except the designer which elements they move.    
I agree that internal focussing does not necesarily lead to constant length, some lenses use both. I personally don't mind that lenses get longer when focussing but some people do, I don't find that silly but just a different opinion.
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Post Options Post Options   Quote QuietOC Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 21:06
Originally posted by Miranda F Miranda F wrote:

Originally posted by QuietOC QuietOC wrote:

Sony doesn't really market the lack of focus breathing of their lenses which lack focus breathing. Maybe it is because manufacturing variation causes every copy to be a bit off.

Good point. They've missed a trick there, or maybe few customers understand what focus breathing is...

I'd be interested to know if the internal-zoom macro lenses which don't change length much also show much less change in aperture than an all-moving design. If so, that would be another benefit. Speaking of which - does the internal aperture iris adjust to correct the recorded aperture as they move to 1:1?

Looking at sony.com today Sony does advertise minimal breathing for a few lenses.

I've heard that Nikon bodies show the effective aperture with at least their own macro or micro lenses.

I was wondering the same thing about the focal reducing macro lenses. It shouldn't be too hard to test.
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 28 January 2021 at 22:58
Originally posted by pegelli pegelli wrote:

Originally posted by Miranda F Miranda F wrote:


Clearly some of the macro lenses deliberately reduce the focal length, presumably by bringing a negative element forward as a kind of extremely non-parfocal zoom lens. You can achieve something similar with an extension tube as I mentioned above. I guess it has several advantages.
I don't think adding extension tubes will shorten the focal length, so it's not really similar. And by moving groups you could also achieve some of the "floating element" advantages to allow a better performance across the whole focus range from infinity to macro, I think some of the more expensive macro lenses also do that.

My point was (I think) that adding an extension tube means that zooming out shortens the focussing range. So if you push the main focussing group out a bit and then zoom out, you can get a similar effect to pushing a constant-FL prime lens a lot more. From the discussion here, that sounds to me like what some of them are doing.

Agree with your other poiont.
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Post Options Post Options   Quote dbrusco Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2021 at 02:06
Originally posted by pegelli pegelli wrote:

Internal focus and barrel extension are not mutually exclusive.

For instance the Sigma 105/2.8 and Minolta 100/2.8 do both. With those lenses focus is achieved partly by the internal focussing (shortening the focal length) and partly by extension, which can be less than without the internal focus action.

But my question is why you want a shorter focal length with internal focussing? With shorter lenses you need to get closer to the subject for the same magnification and internal focus will even further shorten the focus distance.


I'm often trying to take photos of tiny things that by nature tend to be in places where there isn't bright light, and in that circumstance I put the camera in APS-C mode to get more crop. It's just really awkward when something is that small and possibly moving. I managed to get decent handheld photos of some <2mm ants (they were cold and in post-rain soil) at minimum focus distance, but I had to do it without my DIY flash diffuser and with the help of a flashlight. I need more than two hands! And yes, I have a tripod but that wouldn't have worked there.

Closer to the subject is ok as long as There's enough room for light (need a different flash, as well)--I also have a Laowa wide-angle macro, but so far I haven't found a suitable subject, large enough not to have the subject practically touching the lens, and something that will be still long enough.
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Post Options Post Options   Quote dbrusco Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2021 at 02:23
Originally posted by Miranda F Miranda F wrote:

How short do you want to go? And what macro ratio do you want?
Tamron do a range of 1:2 macro lenses from 20mm upwards, though the 45mm hasn't made it to E-mount yet.
If a lens is sharp near MFD (many aren't, but macros usually are), an extension tube will get you closer and with more magnification.

Have you considered a non-AF for macro? IME AF is not that useful in macro so i usually turn it off.


I have a Sony APS-C 50mm macro from before this camera, but I don't like having to use the bulky adapter plus the barrel extends. I suppose I should try it with those ants I mentioned.

I had an older Tamron 90mm macro, but it was really noisy. Using the Sony is a dream compared to that.
I use the AF more than not since it's usually more accurate than my eyes are with peaking. (It was easier using the old-fashioned optical viewfinder where you line things up. I wasn't doing macro back then though). But for some reason it seems like I can get a little closer if I do MF, so I do that with tiny things where I can prop myself.

I'm heading more and more towards not having enough magnification though...
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Post Options Post Options   Quote addy landzaat Quote  Post ReplyReply Direct Link To This Post Posted: 30 January 2021 at 09:32
A standard macro is 1:1 - the picture is life sized on the sensor. If you want more magnification, there are some manual lenses that have double the magnification. Take a look in the lensdatabase at the Venus Optics Laowa 60mm F2.8 2X Ultra-Macro and Venus Optics Laowa 100mm F2.8 2X Ultra Macro APO and maybe google for some reviews.
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Post Options Post Options   Quote Miranda F Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2021 at 21:49
An easy and cheap way to get more than life size is to find an old non-AF moderate wide angle lens with preset aperture and reverse it onto the front of a medium telephoto (front to front). 28mm on 135mm gives you about 5:1 macro; 35mm on 135mm gives you 4:1, and 35mm on 100mm gives you 3:1. You may lose some of the field of view, though and you have to experiment with the apertures on each.
I tend to use a MF lens on a long bellows adapter, but the rig is not really up to nature photography.
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