TC or ET for close up?

[billtils]

I have shared some images from my strict lockdown (indoor, table top, various lenses, mostly with extension tubes) and my more recent slightly relaxed lockdown (outdoor, 300mm and 1.4TC). This afternoon I had a look at how the 2 techniques compared in regard to image quality and ease of use. All the images below were taken within 30 minutes of each other, and processed as near as I could get to having the same adjustments (LR, manual exposure adjustments, lens correction, +40 sharpening, modest 'S' curve, +10 to 20 clarity). All were taken with the 300mm PF, either with a 1.4TC or a 20mm extension tube (identified as 'ET')

The geranium flowers are the same plant, just a different view point.


1: Geranium flower, TC





2: Geranium flower, ET





3: Nemesia flowers, TC






4: Nemesia flowers, ET






They are all cropped mimimally. Subjectively, the shots taken with the extension tubes seemed to allow more latitude in regard to depth of field, but there was little or not diffrence in the distance from the flower.

[xpatUSA]

After downloading all four, the shots with the TC are noticeably softer on my monitor, Bill. I did pixel-peep at 100, 200 and 400% Nearest Neighbor (no smoothing).

[billtils]

After downloading all four, the shots with the TC are noticeably softer on my monitor, Bill. I did pixel-peep at 100, 200 and 400% Nearest Neighbor (no smoothing).

Ted, thanks for the feedback, and since you have opened the subject ... I agree. First impression was "didn't expect that" but the ET shots all looked better than the TC ones. I'm hoping for some "bugs" (bees or hoverflies, or I may go on a damselfly hunt) to see how it goes with the ET, and I have yet to explore the other tube sizes, just went for the middle one to start with.

[Geoff F]

This is a bit of a complex subject, Bill.

I use both methods for my macro shots. Most, over 200 per day at this time of the year, are with TC.

Can we assume you are using a top quality TC and not one of those cut price jobs?

A TC does add extra glass and the less magnification you use, the better the results. But often, the difference is marginal. I do notice a reduction in contrast but that can be easily fixed during editing.

An ET allows you to get closer to your subject, hence a larger subject image. But while that is fine with static subjects it is a different matter with live nervous insects, etc. So for 'in the field' shots of live insects where I consider that I am doing well if I can get as close as 12 inches and many shots have to be over 2 feet, I use the TC.

I work with a Sigma 180 macro lens and most shots use flash in some form. Nearly always using a tripod. Shooting to insect identification quality on everything which comes my way for site recording work.

[billtils]

This is a bit of a complex subject, Bill.

I use both methods for my macro shots. Most, over 200 per day at this time of the year, are with TC.

Can we assume you are using a top quality TC and not one of those cut price jobs?

A TC does add extra glass and the less magnification you use, the better the results. But often, the difference is marginal. I do notice a reduction in contrast but that can be easily fixed during editing.

An ET allows you to get closer to your subject, hence a larger subject image. But while that is fine with static subjects it is a different matter with live nervous insects, etc. So for 'in the field' shots of live insects where I consider that I am doing well if I can get as close as 12 inches and many shots have to be over 2 feet, I use the TC.

I work with a Sigma 180 macro lens and most shots use flash in some form. Nearly always using a tripod. Shooting to insect identification quality on everything which comes my way for site recording work.

Geoff

Thanks for the feedback. Yes it's a Nikon TC-14E III, and absolutely not a cut price job!

I shoot all my outdoors wildlife (large and small, animal and vegetable) hand-held but pretty well always use a tripod for indoors shoots. The big attraction of the lens+TC is that the same rig works for birding, flowers, and insects, with the bonus in regard to insects that it is possible to keep far enough back not to spook them (the most recent series of damselflies I posted being a good example). Having a go outside with the extenson tubes was more or less an afterthought, and even though I was pleasantly surprised with the quality using the ET rather than the TC, I don't feel overly inclined to take the lens+TC and switch back and forth to the lens+ET, or at least not outside.

I did hint at the possibility that there may be a greater DoF with the tubes than with the TC but not sure if that would stand up to a rigorous analysis .

[Stagecoach]

Bill, I would suggest that the differences you are seeing here are not necessarily to do with degradation caused by the TC. My own TC reduces contrast slightly requiring an adjustment of around just +10% in ACR and a similar % increase of sharpening above my normal amount to make it similar to the same image taken under the same conditions without the TC.

With respect to your test examples, No 1 & 2 are two different flowers taken under different lighting conditions. Images, 3 & 4 are again under different lighting and unclear as to where your focal plane was.

With respect to DOF if the subject is framed the same the DOF will be the same. What will be noticeable will be the difference caused by the change of FOV between the TC and ET.

Some other thoughts, there will be a difference in subject distance when framing the subject identically, you will be further away when using the TC. With the TC you are losing light so to compensate (whilst retaining the same DOF) you will have to use a slower speed or greater ISO with their implications.

Unfortunately, a controlled comparison test is not the easiest to do for this.

EDIT : With respect to losing light with the TC the two test images posted below (TC and Tube) were taken at the same exposure settings with stable ambient light from a window.

[William W]

It's wonderful the variety of field tests which we can invent. Kudos to you.

I think it's not too difficult to get some control into the testing, although, a Test Target and Tripod may diminish part of the fun aspect.

Anyway my point is:

If your wandering around outside with this rig, hand held and primarily attending to "close ups" then I'd offer that you consider a starting point to be - for most practical purposes of "Close-up Photography" using either a TC or a ET will give similar outcomes.

Then consider the value of using a TC, because it will give you infinity focus: in the event that you spy something interesting which is "not close up shot", you're always primed.

I reckon that you've alluded to this in Post #5 - and I wanted to spell it out.

WW

[Stagecoach]

I think it's not too difficult to get some control into the testing, although, a Test Target and Tripod may diminish part of the fun aspect.

Well Bill, it wasn't too difficult but getting absolutely identical magnification beat me

Image No 1 was with the lens set at 200mm (280 with TC) and adjusted to 'minimum focus distance'. The camera was then moved to place the spring at the focal plane. For image No 2 the ET was fitted and the camera moved and focused to obtain as near equal framing as possible. The butterfly is about standard size

No 1


No 2


It had been my intention to 'crop' these identically in ACR and I would normally do that by selecting both and simply cropping the area I wanted. It appears this is no longer working in the recent PS ACR update and in addition the crop tool appears to be slow and very fiddly. I gave up.

[William W]

Fantastic!

Well Bill, it wasn't too difficult but getting absolutely identical magnification beat me

Like I wrote - "It's wonderful the variety of field tests which we can invent. Kudos to you", too.

***

Assuming the Lighting and the Background to Subject Distance were both consistent - the Bokeh is substantially different.

Do we put that down to Subject to Camera Distance differences? I think not.

So there's something we might consider - Bokeh: useful test shots, IMO.

WW

[billtils]

Grahame, thanks for posting the results of this much more rigorous experiment.

Overall it looks like it doesn't matter much in regard to image quality so it comes down to other factors, and the tubes lose out there.

[Stagecoach]

Assuming the Lighting and the Background to Subject Distance were both consistent - the Bokeh is substantially different.

Do we put that down to Subject to Camera Distance differences? I think not.

So there's something we might consider - Bokeh: useful test shots, IMO.

WW

Subject to background remained constant Bill.

Lighting raises a couple of questions; a) I was surprised that image brightness was so similar for both TC and ET when at the same camera settings. b) It was a fully overcast rainy day with light predominately coming from camera rear, and I always forget to move out the way, or stay in the same place

[DanK]

A very helpful thread. Thanks to all for posting.

If I am following this correctly, I think the issue isn't subject to backgound distance. It's subject-to-camera distance.

The difference in bokeh in this case is really background blur. If subject-to-background distance and framing are the same, longer FLs will have more background blur because of the narrower angle of view.

In the butterfly photos, the TC photo has a greater subject-to-camera distance. Given that the framing is the same, that means that it has a narrower AOV. Therefore, it has greater background blur.

[xpatUSA]

Subject to background remained constant Bill.

My background blur calculator for a 5m background distance gives a blur circle in the image plane of:

For 1.45m focus distance: 2.46mm
For 1.30m focus distance: 2.99mm

Not sure it accounts for added bits between lens and body, though ...

FWIW ...

[DanK]

My background blur calculator for a 5m background distance gives a blur circle in the image plane of:

For 1.45m focus distance: 2.46mm
For 1.30m focus distance: 2.99mm

Not sure it accounts for added bits between lens and body, though ...

FWIW ...

Another way to think of this is that given a fixed distance to the background, a longer focal length--that is, a smaller AOV--captures a smaller amount of the background and spreads it over the same image area.

[William W]

A very helpful thread. Thanks to all for posting.

If I am following this correctly, I think the issue isn't subject to background distance. It's subject-to-camera distance.

The difference in bokeh in this case is really background blur. If subject-to-background distance and framing are the same, longer FLs will have more background blur because of the narrower angle of view.

In the butterfly photos, the TC photo has a greater subject-to-camera distance. Given that the framing is the same, that means that it has a narrower AOV. Therefore, it has greater background blur.

Hi Dan,

We each have a disagreeing first thought one this one. Re my Post #9 - I did consider that the Subject to Camera Distance would be different.

Interesting. I am hoping Grahame will provide the Aperture that he used for each shot, please.

More thinking required - I am now questioning my first reaction.

WW

[William W]

Subject to background remained constant Bill.

Lighting raises a couple of questions; a) I was surprised that image brightness was so similar for both TC and ET when at the same camera settings. b) . . .

Hi Grahame,

Compared to using the Lens only, using the TC (a x1.4), you'll lose (approximately) 1 Stop; using a 20mm ET on a 200mm (zoom) lens, depending on the Lens's design, you could easily lose (approximately) the same.

Could you let us know the Apertures used, please.

WW

[xpatUSA]

Could you let us know the Apertures used, please.

WW

EXIF says f/11 for both, Bill ... unless you meant actual diameter?

[xpatUSA]

Another way to think of this is that given a fixed distance to the background, a longer focal length--that is, a smaller AOV--captures a smaller amount of the background and spreads it over the same image area.

Hmmm ... my calculator is for a point source of light in the background, not an area. For a longer focal length, the point source remains an infinitesimally small part of the background emitting the same amount of light. Perhaps I misunderstand ...

My formula is: blur dia equals aperture dia times magnification divided by bg dist times (bg minus focus dist).

If the longer focal length affects any of those then the blur would indeed vary. For your example, a longer focal length equals a larger aperture diameter equals a bigger blur spot.

[William W]

Thanks Ted. (dumby me - didn't think to look at EXIF)

Thinking about this is keeping me awake, so best to lay out my thoughts for you all to ponder.

I am thinking (and was initially thinking) that the Camera to Subject Distance would have very little or no impact on Bokeh / Background Blur because although the Camera to Subject Distance would change, there would be insignificant difference in the Ratio of the Distances - Camera to Subject :: Subject to Background.

The more I think about this the more I am convincing myself I am correct: I am asking for counters to this idea, please.

Additionally, and especially now that we confirmed that the Aperture used was the same, I think that the Bokeh difference is caused by (a) the different placement of the Lens Elements relative to the Sensor/Film Plane and (b) the introduction of additional Lens Elements in the TC.

Thoughts?

WW

Going back to sleep now. Will check in later tonight.

[xpatUSA]

Thinking about this is keeping me awake, so best to lay out my thoughts for you all to ponder.

I am thinking (and was initially thinking) that the Camera to Subject Distance would have very little or no impact on Bokeh / Background Blur because although the Camera to Subject Distance would change, there would be insignificant difference in the Ratio of the Distances - Camera to Subject :: Subject to Background.

The more I think about this the more I am convincing myself I am correct: I am asking for counters to this idea, please.

Bill, the ratio you are seeking is (background minus focusing distance) over background distance. The blur size is directly proportional to that, all other things being equal.

For a camera perfectly focused on the background, blur is therefore zero (ignoring diffraction, aberrations, shaky hands, etc).

For a camera focused on a very close subject with a far-off background, the blur size starts to approach the aperture diameter and could even exceed it if we get into macro territory (m greater than 1).

As to Grahame's specific comparison, I think that the only way to quantify the bokeh difference would be by ray-tracing through all the lens elements at their actual distances and thicknesses, like here , and I certainly can't do that. My calc is only for a perfect thin lens.

HTH ...