[nandadevieast]

MFD of afs 85 1.8 G = 2 feet/23 inches

MFD of DP3 Merrill = 9 inches

But DP3 is F4 vs 1.8 of Nikon for full frame


Which one is more suitable for small flowers?

Thanks

NDE

[Brightcolours]

Both have very different FOV. You first have to pick your desired FOV and desired magnification, then choose a lens. The desired FOV is taste and vision dependent.

 

Just wanting to compare two totally different lenses does not make too much sense.

[nandadevieast]

FOVs are not different.

Sigma is 75mm

Nikon is 85mm

[soLong]

....But DP3 is F4 vs 1.8 of Nikon for full frame


Which one is more suitable for small flowers?

Thanks

NDE

....you might not want f/1.8 when taking pictures of small flowers at a 9" distance....unless you're Bc and like soft things(and there's nothing wrong with that :-)....could be f/8 will also do the job....on the other hand....maybe not

[Brightcolours]

It depends on you... According to you, the Sigma focusses closer. How much the FOV will change while focussing closer is an unknown factor, but will get smaller flowers bigger in the image. 

The depth of focus choice is also up to you. At the same distance, the Nikon is capable of a much more shallow DOF. Its maximum aperture is 56.7mm, from the Sigma 17.9mm. So the Nikon will give you more artistic freedom, when needed.

 

So that is your choice, between these two unlikely candidates. If you want to get closer, the Sigma offers that. If you want to have the possibility to get a more shallow depth of focus, the Nikon offers that.

 

Of course, the Nikon with a Sigma 70mm f2.8 macro lens gives more depth of focus range, and goes closer than the DP3.

[arvydas]

If "more suitable" means "close-ups", I'd go with higher magnification (i.e. Sigma DP3, 1:3, while Nikkor 85mm f 1.8G is just 1:8) for flowers.

 

A.

 

P.S. I am thinking... If we know FOV for infinity, and magnification for MFD, isn't that enough data to calculate FOV at MFD for that particular lens?

[Brightcolours]

If "more suitable" means "close-ups", I'd go with higher magnification (i.e. Sigma DP3, 1:3, while Nikkor 85mm f 1.8G is just 1:8) for flowers.

 

A.

 

P.S. I am thinking... If we know FOV for infinity, and magnification for MFD, isn't that enough data to calculate FOV at MFD for that particular lens?

No, at least not exactly. You can not be sure about the focal length at MFD nor FOV at MFD (those are not linked 1 on 1).

It is very difficult to determine the actual focal length... And even if the focal length stayed constant, you would get a more narrow FOV at MFD than at infinity... 

[arvydas]

No, at least not exactly. You can not be sure about the focal length at MFD nor FOV at MFD (those are not linked 1 on 1).

It is very difficult to determine the actual focal length... And even if the focal length stayed constant, you would get a more narrow FOV at MFD than at infinity... 

 

   Hm....  For macro lenses at MFD (_well, usually_) we have ratio 1:1, so 36mm object projects on 36mm sensor at the MFD, and what actually means the same FOV for different macro lenses at this magnification (1:1). Sensor size doesn't change, and we know both MFD and magnification (and thus max. object size, that could be projected on the sensor at that particular distance) for every lens from manufacturer's specifications. So, we have isosceles trapezoid  with further calculations arising from it, instead of classic calculation of the FOV, where we need FL. Of course, indicated magnification may not be very precise (Popphoto tests), but we can measure it more easily than real FL, and on this approach we even do not need focal length of the lens.

    Unfortunately, I am not so good in math to further elaborate that.

 

A.

[Brightcolours]

   Hm....  For macro lenses at MFD (_well, usually_) we have ratio 1:1, so 36mm object projects on 36mm sensor at the MFD, and what actually means the same FOV for different macro lenses at this magnification (1:1).

You are confusing main subject size and FOV. FOV is about the angle of the view, not the size of the subject (with varying distance..). So no, not all lenses at 1:1 have the same FOV (not even close, actually). 

Sensor size doesn't change, and we know both MFD and magnification (and thus max. object size, that could be projected on the sensor at that particular distance) for every lens from manufacturer's specifications. So, we have isosceles trapezoid  with further calculations arising from it, instead of classic calculation of the FOV, where we need FL. Of course, indicated magnification may not be very precise (Popphoto tests), but we can measure it more easily than real FL, and on this approach we even do not need focal length of the lens.

You can indeed calculate FOV with subject size and distance to the subject (although even this is tricky, as for distance to the subject you have to use the focal point to get it exact. And that focal point is somewhere within the lens system, and hard to determine. Some use the aperture position as seen from the front of the lens).

    Unfortunately, I am not so good in math to further elaborate that.

 

A.

[arvydas]

You are confusing main subject size and FOV. FOV is about the angle of the view, not the size of the subject (with varying distance..). So no, not all lenses at 1:1 have the same FOV (not even close, actually).

There is some disambiguation. If to be precise, according to Wiki, field of view is "the extent of the observable world that is seen at any given moment", so at 1:1 it doesn't differ between the lenses (like on this example from dpreview); FL only defines the distance, at which it is achieved; so angular extent, or angle of view will differ between lenses with different FL. Yes, FOV usually is expressed as angular size, but sometimes it is more convenient to express it in other metrics (like this example). IMO this difference is the key to bypass FL.


A.