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DoF calculators
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PostPosted: Sat Nov 18, 2017 8:21 pm    Post subject: DoF calculators Reply with quote

Hi,
I use this online DOF calculator http://www.dofmaster.com/dofjs.html to determine the DoF produced by lenses at given focal length / subject distance / aperture.

Do you think it is valid for mirror lenses as well?
What about macro lenses or lenses attached via simple adapter or focal lens reducers? (Just need to correct by the multiplying factor?)

Thanks.


PostPosted: Sat Nov 18, 2017 9:26 pm    Post subject: Reply with quote

DOF should be the same given the same parameters of focal length and aperture regardless of lens technology.

Just one issue regarding DOF - to a degree it is a matter of judgement and restrictions of sensor technology.

There is always going to be just one point of precise focus, the rest of the field supposed to be in-focus is going to be off, good enough maybe for the sensor/film technology to be unable to distinguish between exact and good enough.

So if you have a high density sensor that you want to use for extreme cropping, a DOF calculator set up by someone who intended to shoot Tri-X for newspaper use may be rather generous. You will see something similar in DOF indicators on MF lenses, especially with wide angles. What the lens indicates as hyperfocal distance may not really be so if you pixel-peep.


PostPosted: Sat Nov 18, 2017 11:28 pm    Post subject: Reply with quote

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

http://www.cambridgeincolour.com/tutorials/dof-calculator.htm


PostPosted: Sat Nov 18, 2017 11:34 pm    Post subject: Reply with quote

This being the Manual Focus lens forum and all, and seeing that most of the folks here are mounting their MF lenses onto their digital cameras, to me this is largely a moot point, since when I mount an MF lens to my digicam -- say my Sony NEX 7 -- I am viewing the subject at the actual taking aperture. Thus Depth of Field is on display. I should be able to evaluate it just by looking at my camera's display. Yes?

Since mirror lenses have fixed apertures, what you see through the viewfinder is what you get. If you're using any sort of extension or what have you, again, you're shooting with a manual aperture, so you should be able to determine the DOF just by looking.


PostPosted: Sun Nov 19, 2017 1:56 am    Post subject: Reply with quote

Maybe, but not perfectly well.
If you intend to pixel-peep later it may not be quite what you got on the screen.

Worse, if you need to work fast by setting a hyperfocal distance and are unable to carefully check focus of all elements before shooting.


PostPosted: Sun Nov 19, 2017 2:16 am    Post subject: Reply with quote

Then there's print size and viewing distance...but the viewfinder is close enough for me too.

The calculators get used for exploring what-if scenarios too.

To actually relate seeing to the formula dynamics, getting a feel for relationships by looking is invaluable imho.


PostPosted: Sun Nov 19, 2017 1:17 pm    Post subject: Reply with quote

cooltouch wrote:
This being the Manual Focus lens forum and all, and seeing that most of the folks here are mounting their MF lenses onto their digital cameras, to me this is largely a moot point, since when I mount an MF lens to my digicam -- say my Sony NEX 7 -- I am viewing the subject at the actual taking aperture. Thus Depth of Field is on display. I should be able to evaluate it just by looking at my camera's display. Yes?

Since mirror lenses have fixed apertures, what you see through the viewfinder is what you get. If you're using any sort of extension or what have you, again, you're shooting with a manual aperture, so you should be able to determine the DOF just by looking.


There are situation when a Depth of Field calculator may be needed even with a manual focus lens and a digital camera : when you want to use the lens at the hiperfocal distance or when you want to use it focused at some fixed distances (let's say "close", "portrait" and "landscape").
But the DOF written on the lens shows only what's "sharp enough" if you use the lens on a medium resolution film. With digital sensors the "sharp enough" perception depends on the sensor resolution and the DOF scale should not be trusted. A modern DOF calculator should be more useful in such situations but, IMO, is better to test it yourself. For instance "sharp enough" for me on my Sony NEX-7 or A7R2 is 1-2 f/stops less opened than what the DOF calculator recommends.


Last edited by dan_ on Mon Nov 20, 2017 12:54 pm; edited 1 time in total


PostPosted: Sun Nov 19, 2017 9:02 pm    Post subject: Reply with quote

Yet another reason to focus and place the dof visually is https://photographylife.com/what-is-focus-shift

Also, calculators are for perfect lenses, thus ymmv...


PostPosted: Tue Nov 21, 2017 7:19 pm    Post subject: Re: DoF calculators Reply with quote

wolan wrote:
Hi,
I use this online DOF calculator http://www.dofmaster.com/dofjs.html to determine the DoF produced by lenses at given focal length / subject distance / aperture.

Do you think it is valid for mirror lenses as well?
What about macro lenses or lenses attached via simple adapter or focal lens reducers? (Just need to correct by the multiplying factor?)

Thanks.


I've use this site--excellent tool IMO. The calculation requires you to select the body which you are using, so the answer to your question (is it valid for Mirror Lenses too) I would think, must be, yes. In case you, or anyone else for that matter missed it, on the left column--you can down load a Hyperfocal Distance chart to carry in your bag. It beats the hell out of doing the math for each scenario you encounter--unless you really like math:

hyperfocal distance equation





where:


H'--is the hyperfocal distance, mm

f--is the lens focal length, mm

N--is the f-number

c--is the circle of confusion, mm


PostPosted: Sat Nov 25, 2017 12:13 am    Post subject: Reply with quote

Another factor to consider, as I found to my cost, is that an "after-market" adaptor may allow a lens to focus "beyond infinity", thereby making any depth-of-field scales on the lens redundant and any hyper-focal points inaccurate. Once you're stopped down to working aperture the viewfinder may be a little too dark to judge if the subject really is in focus Sad


PostPosted: Sat Nov 25, 2017 2:20 am    Post subject: Reply with quote

Wide angle lenses from ebay can be considerably off on infinity I have found. In either direction unfortunately. Its not always the adapter.