Another hover

[DaveW]

Had a go at another hover fly. Don't know if the images are getting any better or worse! Still cannot seem to get both wings pin sharp. Guess I do need to go to flash hand holding so I can stop down further. This was 1/160th sec. at f9 using Shutter Priority so hand holding speed with my 70-180 Micro Nikkor was not too low.



DaveW

[MacroLuv]

Nice one Dave.
Maybe increasing distance could help?

[DaveW]

Isn't depth of field solely dependent on magnification and aperture (f-stop) though?

The above picture is obviously a crop anyway.

DaveW

[rjlittlefield]

Isn't depth of field solely dependent on magnification and aperture (f-stop) though?

Yes. At least, that's right for any particular sensor size and for reasonable assumptions about how the f-stops are marked. We've had many pages of discussions about those aspects in the past; no need to repeat here.

But maybe Nikola just means that for this particular picture, the focus plane looks a bit low on the fly. The end of the abdomen is crisp, and so are a couple of knees. It looks like backing off by 1 mm or so might have pulled the wings and eyes into perfect focus, as well as reducing the blur on the back of the thorax.

I agree that you'd be better off with flash. f/9 is perfectly reasonable for a compact digital point-and-shoot, but with a larger format DSLR, f/9 is pretty wide for single-shot photos. From f/9, you have some room to stop down farther to improve the overall sharpness, before diffraction starts to become a problem. But you do need more light to stop down, or shutter speed will become a problem.

BTW, I always recommend finding a dead fly to experiment with. That way you can isolate the various issues like focus placement, aperture setting, subject alignment, etc.

--Rik

[MacroLuv]

Hmmm... I think that the image magnification is defined as the ratio of the image size to the object size, but it is related to the object distance and the image distance.
Depth of field is directly proportional to the f-number, but doubling the object distance makes the depth of field four times as large. Isn't it right?
Yes Rik I meant that also. It is important to place the subject right inside DOF range.

[DaveW]

But if you increase the object distance with the same lens aren't you simply decreasing the magnification? If you blow the two images up to the same size having used the same f-number will they not both have the same DOF?

I just tried using f22 and Aperture rather than Shutter Priority and got too much camera shake, will have to keep increasing the aperture until it is acceptable

DaveW

[MacroLuv]

But if you increase the object distance with the same lens aren't you simply decreasing the magnification?...

DaveW

Yes, that is right. But I didn't even think that you will keep same magnification by increasing the distance.
Blowing images... maybe in theory...not a good idea in practice in terms of quality.
Maybe we need to involve the flash in ours macro setups.

[beetleman]

it does look like the focus fell on the abdomen. I know sometimes my autofocus does not want to go where I point it. I always try and take as many shots as I can (if you can). I also hear of people setting the camera on manual focus and moving the camera to focus.

[salden]

I always manual focus and move the camera to within the focus distance.

[rjlittlefield]

But if you increase the object distance with the same lens aren't you simply decreasing the magnification? If you blow the two images up to the same size having used the same f-number will they not both have the same DOF?

Well, no. Here's why...

Let's use "depth of field outside the box" analysis as explained by Dick Lyon .

Think about the cone formed by all the light rays that come from a spot on the subject and pass through the aperture of the lens.

DOF depends on the thickness of that cone (its "cone angle"), and also on the total magnification (ratio of final image size to subject size).

At the same total magnification, a thinner cone (smaller angle) will give more DOF.

You can make the cone thinner by reducing the aperture diameter (stopping down).

You can also make the cone thinner by moving farther away from the subject, leaving the aperture diameter unchanged.

So, increasing the object distance with the same lens at the same f-number does not simply decrease the magnification. It also makes the cone thinner, so you get more DOF even after enlarging the smaller sensor image to get the same total magnification.

As always, there are some awkward tradeoffs here. Backing away gives you a skinnier cone and more DOF at the same shutter speed, or even faster. But it also makes the sensor image smaller. The extra enlargement needed to keep same total magnification then exposes more noise and may also expose resolution problems due to lens aberrations and/or sensor pitch. I don't know any theory that accurately predicts which approach will produce a better picture in any particular circumstance.

Looking back at earlier posts in this topic, I see that I wrote an incorrect answer to your question the first time. Sorry about that. Hopefully this cone-angle description will help clear things up.

--Rik

[DaveW]

Thanks Rik, will try that as well.

DaveW