DOF Calculation

[AutoFocus]

Hello, I'm the first time here..

I see on this web page interesting DOF calculator. I have some questions. It will be helpfull, probably for many of us. My dilema is, how on the rigjht way understand data need to be put into the calculator;
(Problem is also: on the DSLR with APS-C sensor is possible use FF or DX lenses)
For this purpose: Crop = 1.5x

So, if we have;
.. two DSLR, one with FF and other with APS-C sensor and
.. two lenses, one FF lens and other DX lens.

What is now equivalent, for example ;

1.
FF DSLR, 85mm FX lens, f1.8, distance 5m
APS-C DSLR, 85mm DX lens, f1.8, distance 5m

2.
FF DSLR, 85mm FX lens, f1.8, distance 5m
APS-C DSLR, 56mm FX lens, f1.8, distance 5m

3.
What about aperture: is there also necessary something to adjust for DOF calculation ?

SW:
https://www.cambridgeincolour.com/tu...calculator.htm

Thank you

[pschlute]

I have some questions.

Welcome to the forum.

For any DOF calculator you enter the camera format (eg FF or aps-c) and the focal length. Now the lenses FL is fixed when it is manufactured. It does not change if you mount that lens on a different format. So in your example above you always use 85mm.

Same for aperture. Aperture is a ratio of physical size to FL. As the FL is constant so is the aperture.

(Problem is also: on the DSLR with APS-C sensor is possible use FF or DX lenses)

I am not entirely sure what your question is here. If you mean "can I use a FF lens on a aps-c sensor" the answer is yes , as long as the mount is compatible. The image circle produced by a FF lens will always cover a aps-c size sensor. The opposite is not always true and using aps-c lenses on a FF camera may produce black irregular borders; or significant vignetting; or minor vignetting; or indeed no vignetting at all. It depends on the lens design.

[DanK]

The clearest explanation of this that I have found is this, http://bobatkins.com/photography/tec...igitaldof.html. It's helpful also that he starts with the bottom lines.

[pschlute]

You might find that worrying about exact DOF is a waste of your valuable time

I think that is the only part of your post that is actually helpful Ted.

Sorry, but the guy is asking a simple question which has a simple answer. No need to confuse him.

[DanK]

the five bullets at the top of the article I cited briefly note the things someone needs to know about DOF in practice when using two different-size sensors. All of the explanation about why these are true follows, so only the curious need to go there. The cases in the OP are addressed in the five bullets.

[AutoFocus]

Sorry, in point 2. I wrote wrong data. Correct is;
2.
FF DSLR, 85mm FX lens, f1.8, distance 5m
APS-C DSLR, 56mm DX lens, f1.8, distance 5m
(before was 56mm FF lens)

What now ?

[AutoFocus]

Thank you. Now, we are closer to situation.

Practically, what was my dilemma;

I use FF lens 70-200 f4 on my APS-C camera. I cannot put this lens to Nikon Z.
Now, I want to buy Nikkor FF 70-200 f4 lens to put him with adapter(FTZ) to FF Nikon Z and I have to be shure that BOKEH will be at least so good as my old lens on my APS-C camera at, for example; 200mm, f4,5m.
(yes, I understand that quality of BOKEH depends on many things but JUST technicaly)

Is my DOF calculation with this SW:https://www.cambridgeincolour.com/tu...calculator.htm OK ?

Crop at APS-C = 1.5x
200/1.5= 133,33

1.APS-C, 133mm, f4, 5m =23.2 cm (232 mm)
2.FF, 200 , f4, 5m = 15.4 cm (154 mm)

[pschlute]

I hope that this is not confusing.

Unless I am totally misunderstanding the original question, I believe he is asking (my paraphrasing):

"when using a DOF calculator , for a crop sensor do I change the FL of the lens I am using (85mm) by the crop factor (changing it to 56mm) ?"

The answer to that question is no.

By you giving him a DOF calculation for a non-existent 56mm lens you are , I am afraid, confusing the issue.

[pschlute]

Thank you. Now, we are closer to situation.

Practically, what was my dilemma;

I use FF lens 70-200 f4 on my APS-C camera. I cannot put this lens to Nikon Z.
Now, I want to buy Nikkor FF 70-200 f4 lens to put him with adapter(FTZ) to FF Nikon Z and I have to be shure that BOKEH will be at least so good as my old lens on my APS-C camera at, for example; 200mm, f4,5m.
(yes, I understand that quality of BOKEH depends on many things but JUST technicaly)

Is my DOF calculation with this SW:https://www.cambridgeincolour.com/tu...calculator.htm OK ?

Crop at APS-C = 1.5x
200/1.5= 133,33

1.APS-C, 133mm, f4, 5m =23.2 cm (232 mm)
2.FF, 200 , f4, 5m = 15.4 cm (154 mm)

No that is wrong.

You must use the lens FL which is 200mm for both calculations.

[pschlute]

I fold. Please take it from here ...

I am on my 5th beer....I might not be able to alone