Z7/ 300mm PF / 1.7 TC Question

I was out last night shooting the moon through the trees, experimenting to see if I could get a shot that allowed both the moon and trees to be reasonably in focus. According to the specs for this lens, the minimum aperture is f32. However, I was able to get f57! When imported into Lightroom, the metadata also indicated f57. I’m sure this must be the affect of the 1.7 TC. So, am I actually looking at a photo shot at f57? By the way, LR and the Z7 indicates the focal length to be 500mm instead of 510mm.

Here a pic of the info from the z7

The TC multiplies the f-number by the TC factor, so it's 1.7*32 = 54.4. f/57 might be the closest the camera can display. 510mm might not be an option the camera can display. Or, the actual focal length of the lens might be slightly below 300mm and if the camera knows that, it could display a more accurate focal length. I suspect 500mm is just something available and 510mm might not be, so this could just be a rounding error. (The original focal length is typically rounded, too, to some well-known focal length for convenient marketing).

Diffraction is proportional to the relative (i.e., f/stop) aperture. At f/57 on a FF sensor, resolution would be severely degraded. If you wish to get near and distant objects in sharp focus, at reasonable apertures, I suggest image stacking. I use StarryLandscapeStacker for subjects like this, but other focus stacking programs, like HeliconFocus, may be better because masking is more flexible than for the sky alone, and can handle multiple planes.

...I suggest image stacking. I use StarryLandscapeStacker for subjects like this, but other focus stacking programs, like HeliconFocus, may be better because masking is more flexible than for the sky alone, and can handle multiple planes.

The Nikon Z7 shares the focus shift feature with the D850, so the OP does not need any additional software. Nikon allows you to stack up to 100 images and set the focus step manually.

 

Several Nikon cameras report some extended focal lengths with TCs slightly wrong. They round it off sometimes, but I have not given much thought to at which focal lenght they start.

 

My D850 reports my 600 f/4G VR as follows:

Bare: 600mm (so the camera does not know the lens’s true focal lenght)

With TC-14EIII: 850mm (which really is 840mm)

With TC-17EII: 1000mm (which really is 1020mm)

With TC-20EIII: 1200mm (which is correct)

 

While I have not used the TC-17EII with the 70-200 f/2.8 VRII, 70-200 f/2.8 E FL and 300 f/2.8G VR, I know the D850 reports the right focal lenghts with the 1.4x and 2x TCs and those lenses.

Edited September 10, 2019 by heimbrandt

When using focus shift, you still need to calculate the stacked image on a computer using third party software.

Or, the actual focal length of the lens might be slightly below 300mm and if the camera knows that, it could display a more accurate focal length.

Or the TC-17EII's magnification isn't 1.7x but 1 2/3x ;)

Or the TC-17EII's magnification isn't 1.7x but 1 2/3x ;)

Really?

 

Somehow I thought 1.4x teleconverters are actually the square root of 2, i.e. 1.414.... 2x TC is the square root of 4, which is indeed 2.

 

Wouldn't 1.7x TC be the square root of 3, more like 1.732...?

The view shown isn't really appropriate for focus stacking, as such.

 

There's absolutely nothing between the branch and the moon to 'get sharp'.... not even an arty cloud or two. !!

 

A simple blend of two frames shot @ f8 would suffice... and you'd get down to ISO sensible too.:)

Really?

 

Somehow I thought 1.4x teleconverters are actually the square root of 2, i.e. 1.414.... 2x TC is the square root of 4, which is indeed 2.

 

Wouldn't 1.7x TC be the square root of 3, more like 1.732...?

 

Edit: Okay, so much for HTML superscripting...

 

I think I'd expect 2^(2/3) (1.587...). Or maybe that's what the TC16 did, and a TC17 is 2^0.75 (1.682). Or (I think there's an arguable geometric justification for this) 2 ^ sqrt(0.5) (1.633). I'm sure it's all fairly approximate anyway.

f/57 coincides nicely with aperture-value increments in 1/3 steps. IIRC, however (I no longer own the TC-17EII), then the maximum aperture of the 300/4 with TC-17EII attached is reported as f/6.7 (indicating 1/2-stop increments) and not f/6.3 (for 1/3 stop increments).

 

A simple blend of two frames shot @ f8 would suffice

I guess the 238,900 miles distance between earth and moon falls outside any possible "DOF extending from x ft to infinity":D - the moon is thus "beyond infinity":p

f/57 coincides nicely with aperture-value increments in 1/3 steps.

 

Wait... it does? Oh, sorry, 11 2/3 stops down from f/1. Okay, with you. (Sorry, as a power of two, 5.83 didn't look enough like a sixth to me, but as a power of sqrt(2), 11.666 seems quite definitive. Maths, huh?)

 

IIRC, however (I no longer own the TC-17EII), then the maximum aperture of the 300/4 with TC-17EII attached is reported as f/6.7 (indicating 1/2-stop increments) and not f/6.3 (for 1/3 stop increments).

 

I was going to say something about Nikon making f/4.5 300mms, and maybe it was to do with that... but actually, no, no idea why there's the disagreement. I think we had a discussion once about how it would be nicer if we described things in terms of the log (base sqrt 2) of the f-stop. We might end up converting Americans to the ISO paper sizes. :)

 

Incidentally, I vaguely wonder why Nikon don't let you set stops in sixths. I've never been quite keen enough to select 1/2 stop steps just to get at the half way point between two thirds, but it seems like an obvious option.

 

I guess the 238,900 miles distance between earth and moon falls outside any possible "DOF extending from x ft to infinity":D - the moon is thus "beyond infinity":p

 

If you have a hyperfocal distance, you need a better lens and more pixels. :) Somehow I doubt Buzz Lightyear's helmet is all that good optically. (Or it really is, in old versions of RenderMan not diffracting anything.)

I was out last night shooting the moon through the trees, experimenting to see if I could get a shot that allowed both the moon and trees to be reasonably in focus. According to the specs for this lens, the minimum aperture is f32. However, I was able to get f57! When imported into Lightroom, the metadata also indicated f57. I’m sure this must be the affect of the 1.7 TC. So, am I actually looking at a photo shot at f57? By the way, LR and the Z7 indicates the focal length to be 500mm instead of 510mm.

Time to experiment with your camera's "Peaking Stack Image" feature: YouTube tips (

).

 

Good luck! We'd like to hear the results.

Two shots at f/anything and a quick composite in PhotoShop, or practically any other image editor, would have done the trick. No need for stacking software when there's clear space around what you're trying to 'stack'.

 

Only issue would be the inevitable slight exposure change due to lens 'breathing' between focus points.