Pano -- focus once or refocus ?

[Isaac]

I've a couple of questions, prompted by some pixel-peeping at a 3x3 pano of a hillside rising over a distance of ~1.5 miles.

At 100% there are noticeable soft-focus patches, so I've been wondering about what was different this time:

• I used less-overlap, down-to 10-15% from 25-30%
• I used single-point AF for each exposure, instead of single-point AF and then switching to MF to keep the same focus.

For a pano, do you focus once or refocus for each exposure?

Am I really noticing soft-focus caused by too little DoF (APS-C 85mm f4 1/500) when the nearest part of the photo is 1/2 a mile away, and the focus point further away?
(It's just an SLT-α35 with a budget lens -- not some fabulous optical equipment.)

[Jeremy Roussak]

I refocus as necessary, while keeping a constant exposure, although focus is most commonly at infinity anyway. I've not seen the issue you mention.

Jeremy

[Telecaster]

Since you're using f/4 I'd try stopping further down. Try making the pano in the f/5.6–11 range and see what you get. I've found with wider lenses at larger apertures field curvature can sometimes cause inconsistent spatial resolution in stitched images…never seen this in the 85mm range, though.

When making panos I've always focused just once, typically on the element in the scene I've found most interesting.

-Dave-

[Tony Jay]

I never refocus, the idea is to ensure that the DOF of field is sufficient for whatever is important.

Just a thought though - you mention that the optics are no great shakes - could it be that the edges are very soft and without the usual degree of overlap (you mention only 10-15%) substantial areas are in fact soft for this reason. Obviously, the usual way to fix this would be to stop down a couple of stops further.

Just a thought

Tony Jay

[MattBurt]

I often end up refocusing but only by accident. I think you should focus once and switch to manual focus ideally. That way even if the DOF isn't deep enough, it will at least remain consistent across your image.
I also agree stopping down should help unless you are intentionally wanting a shallow DOF (for the Brenizer method, maybe).

[Isaac]

I think you should focus once and switch to manual focus ideally. That way even if the DOF isn't deep enough, it will at least remain consistent across your image.

Yes, I assumed that consistently a little softer is why I haven't noticed the softer focus previously.

I never refocus, the idea is to ensure that the DOF of field is sufficient for whatever is important.

Perhaps I'm just conscious of pushing the budget optics to the limit, but if I can make a sharper composite front-to-back by refocusing - I will.

Just a thought though - you mention that the optics are no great shakes - could it be that the edges are very soft and without the usual degree of overlap (you mention only 10-15%) substantial areas are in fact soft for this reason. Obviously, the usual way to fix this would be to stop down a couple of stops further.

Fortunately the 85mm is a FF lens which I'm using on APS-C -- so I'm already getting the best of the image circle -- and yes I should make the most of that and increase the overlap to 30-40%.

Since you're using f/4 I'd try stopping further down.

I'll try f/5.6 ;-)


Thanks.

[Isaac]

Let me ask about this in a different way:

I suppose I assumed everything more than a couple of hundred yards away would be "acceptable".

Is it plausible that I've noticed softer focus patches caused by before-focus-behind gradation in sharpness, when the nearest part of the photo is 1/2 a mile away, and the focus point further beyond that?

f/4 128mm equiv, I'm quite willing to believe so but I'm unsure.

[Bart_van_der_Wolf]

Let me ask about this in a different way:

I suppose I assumed everything more than a couple of hundred yards away would be "acceptable".

Is it plausible that I've noticed softer focus patches caused by before-focus-behind gradation in sharpness, when the nearest part of the photo is 1/2 a mile away, and the focus point further beyond that?

f/4 128mm equiv, I'm quite willing to believe so but I'm unsure.

Hi,

Everything in the DOF zone should stitch without blur, unless there were parallax issues with the camera setup, and the stitching application making a mess of it. This does assume that a proper DOF calculation was used, one with a COC which is tuned for the sensor resolution and output magnification.

At closer ranges, there is an effect that is caused by the combined DOF zone becoming more circular than flat. When too little overlap is used, then that may become visible when the edge of the DOF range has different sharpness.

Cheers,
Bart

[BernardLanguillier]

This may help?

https://luminous-landscape.com/stitching-an-advanced-aproach/

Cheers,
Bernard

[Isaac]

This may help?

Thanks, it was interesting to look through your article again; and the situation is similar to that described for "Image 4" but without the "higher resolution sensors and better performing lenses" :-)

Thus "the desire to extract the finest possible detail when shooting at the optimum aperture (often f4 these days) vs the need to retain sufficient DoF".

However, because the nearest part of the scene was half-a-mile away, I didn't feel the need to try and change aperture front-to-back and I was careless about DoF .

[Isaac]

This does assume that a proper DOF calculation was used, one with a COC which is tuned for the sensor resolution and output magnification.

Thanks, I think the important point for me is -- "a COC which is tuned for the … output magnification".

If I was arms length from the 10,000 x 8,000 composite shown at my current screen resolution but on a 25" x 20" screen, then I wouldn't notice any softer focus -- but at the same screen resolution on a larger 50" x 40" screen, I would.

The lesson for me is that, to preserve the possibility of making larger prints with fine detail, I do need to pay attention to nearest/furthest focus when focus is at 500m and 1000m and 1500m; even when the foreground is half a mile away, not just when the foreground is close.