[bodhi08]

Hi

I'm quite new in photography. One thing I recently learn is that a 50mm lens is a 50mm lens regardless whether it is on film (full frame) or dSLR.

My question is this.
Suppose I have a 50mm lens. If I take a picture 1 meter away from the subject using a film camera (i.e. full frame), how far should I stand (from the subject) when I am using a dSLR to get the same field of view?

Is there a rule of thumb that allows me to estimate this distance? I want to know what the distances for 21, 35, 85 and 150mm lenses.


cheers

[sinus007]

Hi bodhi08,
If you are using Pentax DSLR, e.g. Kx, K7, then the 50mm lens "becomes" 75mm. IOW, the FOV changes by 1.5 times.

[MrApollinax]

My question is why don't you just position yourself to fill the frame how you want it to look? I think that is probably the best rule of thumb, compose your frame as you see fit. Forget all this crop factor stuff and just compose your frame.

[Wheatfield]

If you are quite new to photography and have no intention of using a film SLR, then just forget that you ever heard the term crop factor. It means nothing to you.

[bodhi08]

Thanks for the replies.

I put up this question because I don't want to be stuck in a small room with the wrong prime lens. I love my primes and I would only bring a couple to a photoshoot (mostly trial for now).
I want to be able to estimate, based on the size of the room, which prime lenses to take.

Of course I could buy all the nice prime lenses out there IF I had the money (that is a BIG if in this case ).

I am still trying to a get a feel of the different primes and I reckon this would help me get there.

Thanks for viewing this thread.

[bodhi08]

Wheatfield: I am old enough to remember I was trying to put a new film into the camera but I was not sure how to do it. And I had to try many times to get it right .
It was not an SLR but it was a film camera .

I was trying to do a studio photoshoot at home and I had learnt many great things.
One of things I learnt is that I can't really use a wide angle (the 'studio' being quite small) because of the distortion (mainly the head would not look proportional).

[grey goat]

This may or may not help, bodhi08, but here goes.

First, a 28mm lens on a Pentax DSLR is pretty useful, at least to me: it gives me a wide-normal, a field of view equivalent to what a 42mm lens would give me on a film camera. I like that.

If you want the FOV a 35mm lens would give you in 35mm film cameras (which is what most non-zoom point-and-shoots came with back then), you'd want to use a 24mm lens on your Pentax DSLR. That'd be a moderate wide-angle, and shouldn't distort much at all.

If you want the FOV a 28mm lens would give you in 35mm film cameras, you could get a 20mm lens, and it'd be pretty close. (A 20mm in digital would equate to a 30 in flim-land.)

You probably don't want to use anything smaller than that if you're hoping to avoid distortion.

I know I haven't mentioned distances, but I hope this helps. And what MrApollinax suggested makes lots of sense, too: just step back and fill the frame with what you want. If you can't step back far enough, then you need another, wider prime.

Good luck!

[DAZ]

Hi

I'm quite new in photography. One thing I recently learn is that a 50mm lens is a 50mm lens regardless whether it is on film (full frame) or dSLR.

My question is this.
Suppose I have a 50mm lens. If I take a picture 1 meter away from the subject using a film camera (i.e. full frame), how far should I stand (from the subject) when I am using a dSLR to get the same field of view?

Is there a rule of thumb that allows me to estimate this distance? I want to know what the distances for 21, 35, 85 and 150mm lenses.


cheers

@ 1 meter

21mm W 1.11m H .75m
35mm W .67m H .45m
85mm W .28m H .18m
150mm W .16m H .1m

This is the answer to the question you asked. AFAIK there is to "rule of thumb" to calculate this but I use a calculator on my cell phone.

Part of the problem is you don't have the experience to pose the question that you want but if you had the experience you’d know the answer. Well we all have to start somewhere.

You want to know what kinds of lens to use but to figure that out you have to have an idea of what you are using it for.

As an example the 150mm @ 1 meter you may need a macro lens as not all lenses can focus to 1 meter.

A better quest may be “I want to take a head portrait and a full body portrait what lens and what minimum distances do I need?”

Then you may get an answer like this. To reduce distortion of facial features you should be a minimum of 2-3 meters away with farther being better. @ 3 meters an 85mm gives you W.83m H .55m. This is OK for a head shot. For a full body @ 3 meters a 21mm gives you W3.34m H 2.23 m. These are landscape orientations rotate for portrait. An 85mm @ 3 meters using f/2.8 will give a DOF of about .13m. This should give you mostly the head in focus. It is harder to get only the subject in the DOF with a wide lens like the 21mm. An 21mm @ 3 meters using f/2.8 will give a DOF of about 2.5m so be prepared to move things farther from your subject or except/embrace them as part of the photo.

I hope this helps (and not hurts) you understanding of this subject.

DAZ

[RioRico]

Wheatfield is absolutely right. Wipe the term "crop factor" from your mind.

As was said, judgment comes from experience. Here's a way to gain experience:

Use a zoom that covers the focal lengths you're concerned with. With a display manikin, or an outline of a human figure taped to a refrigerator, stand 2m away, then 3m. Look through the zoom. See what focal lengths give your desired full-body, torso, head+shoulders, and close head shots. Write this down.

Now set the zoom to the focal length of a prime you'll be using. See what distances work for each kind of shot. (I judge distance by arm's length and stride. Or you could put measuring sticks on the floor.) Write this down. Repeat for each focal length.

If using a manikin (some thrift shops can be very accommodating about this, especially if you buy something), take photos at each of the focal lengths, so you'll have a record of the perspectives and distortions, and the visual coverage (angle of view). Print these, maybe at 4x6 inches (10x15 cm). Put these in a notebook. This will be your primer for deciding what lenses are appropriate for different situations.

The one Tom Clancy quote I agree with is: If you don't write it down, it never happened.

[bodhi08]

@sinus007:
Yes, that is the way I normally think about FOV for DSLR. Basically I want to know in advance if a room/studio is too small to be using that 50mm to get half body pics.

@MrAppolinax:
That is normally how I shoot . I like shooting wide. So lets say I reckon I'll need a 50mm lens, I'd go for 35mm just to get a bit wider. And I zoom with my feet or crop the pic later.

@Wheatfield:
That's true. That term is rather confusing at times.

@Grey Goat:
Thanks for the advice. I've seen/heard many comments that 28mm is very useful in a studio. I'll try it later.

@Daz:
You're spot on. I want to know if I am doing a full body potrait which lens to bring to get the least distortion. And to add to that, if the room is too small for a 50mm (for example) to get that half body potrait.
Your comment really helps, thanks

@RioRico:
Thanks for the advice. I have been planning to do something like that. Now, if only I can get my hands on that good but cheap Sigma 24-60mm f/2.8 zoom...

[newarts]

Hi

I'm quite new in photography. One thing I recently learn is that a 50mm lens is a 50mm lens regardless whether it is on film (full frame) or dSLR.

My question is this.
Suppose I have a 50mm lens. If I take a picture 1 meter away from the subject using a film camera (i.e. full frame), how far should I stand (from the subject) when I am using a dSLR to get the same field of view?

Is there a rule of thumb that allows me to estimate this distance? I want to know what the distances for 21, 35, 85 and 150mm lenses.


cheers

Your intuition is correct. In the situation you describe, standing 1.5 meters away with the APS-C camera will give the same field of view as the FF camera at 1 meter.

Regarding focal length selection for a 1.5 crop factor camera, here's a rule of thumb:

Let d/h be the distance/height ratio you want for a photo; consider for example a 10' high scene, 50' from the camera (d/h=5 Like a basketball court, hoop height from mid-court)...

focal_length_mm=20(d/h)

For the example given, F=20(d/h)=20*5=100mm; ie a 100mm lens from mid court would capture about floor to rim under the basket.

One way to envision these distances is to estimate them in "man-lengths", (about 2 meters.) For a particular scene make a mental estimation of how many men lying end-to-end it takes to reach the scene.

d/h = (distance_to_scene_in_man_lengths)/(height_of_scene_in_man_lengths)

[Lowell Goudge]

Hi

I'm quite new in photography. One thing I recently learn is that a 50mm lens is a 50mm lens regardless whether it is on film (full frame) or dSLR.

My question is this.
Suppose I have a 50mm lens. If I take a picture 1 meter away from the subject using a film camera (i.e. full frame), how far should I stand (from the subject) when I am using a dSLR to get the same field of view?

Is there a rule of thumb that allows me to estimate this distance? I want to know what the distances for 21, 35, 85 and 150mm lenses.


cheers

it's relitively simple, for the case where subject distance is much greater (i.e. at least 10 times) focal lenght.

image size = subject size x focal length / subject distance

the forumula is acutally much more complicated but most of this becomes neglegable at reasonable working distances

[DAZ]

Glad I could help.

@sinus007: I want to know if I am doing a full body potrait which lens to bring to get the least distortion. And to add to that, if the room is too small for a 50mm (for example) to get that half body potrait.

This statement makes me a little nervous as it has the seed of misunderstanding that could haunt you (it did me) for years.

Let see if I can explain this and not get into trouble.

All lenses distort and wider lenses tend to distort more then more telephoto lenses but this type of distortion is not usually the kind of distortion that people complain about in portraits. The kind of distortion that wider lenses give is more to making straight lines curve. If the viewer of the photo knows that the line is a straight line and not a curve then they can see the distortion. If something is curved (like people) then this kind of distortion is usually not apparent.

People are good at seeing another kind of distortion. This is s distortion of proportions and people are extremely good at seeing even small differences in the proportions of facial features even of they don’t know why. This kind of distortion is do to the difference in magnification of one part (front to back) over some other part of the subject. This is the same thing you can see in a telephoto shot where the background is bigger then it should look. Actuality the front is being magnified more then the back but as both are magnified you notice the background more. This is most noticeable if you use a wide lens close to someone’s face. There nose ends up looking bigger. Use the same lens but move back then crop the photo to the same size then there face will look flatter (generally more flattering). It is not the lens that distorts but the front to back magnification that is reduced by moving away from the subject.

If you only pick your lens based on the FOV and don’t keep distances in mind you can get some unexpected (and possibly undesirable) distortion. Even on a full length portraits this kind of thing can appear. Take someone and lay him or her on a couch. Shot them head to foot about 1 meter from their feet with like a 21mm. There feet will look huge. You can use this kind of thing to your advantage. Move to closer to their head but angled to their feet so they are only a little further away and you get some parts of her that will look bigger and her feet will look smaller.

So you must keep distance in mind not just the FoV a given lens will give you. Some time you just must have distance.

DAZ

[RioRico]

DAZ is absolutely right. And there's a plus to shooting APS-C (HF, half-frame) over 35mm film (FF, full frame) -- we tend to shoot from further back, thus reducing that closeness distortion. I put a 50mm lens on my (FF) ZX-M and shoot a face. I fill the frame at maybe 65cm, much too close. I put that same lens on my (HF) K20D, aim at the same face. I fill the frame at about 1m, much better. Maybe still too close, but at least the smaller frame forced me to move back a bit.

I think that for many lenses under 60mm or so, you probably don't want to be any closer than 1.5m-2m, unless you INTEND distortion. Or you can use a longer lens on some slight extension, and move in for partial-face closeups. Now the closeness, and the higher magnification, tend to cancel each other out. A 135mm lens on 12mm extension tubes lets you concentrate on eyes from about 65cm, for example. For shorter lenses, stay back at 1.5m-2m or further, and see the effects of different focal lengths.

And the test I mentioned earlier? The kit lens will work fine. Hey, it's just for reference! Nobody else has to know you've used it, eh?

[falconeye]

Suppose I have a 50mm lens. If I take a picture 1 meter away from the subject using a film camera (i.e. full frame), how far should I stand (from the subject) when I am using a dSLR to get the same field of view?

bodhi08,

because you confused terms in your question, you'll certainly got a lot of answers. Let me try to add precision in terminology:


1. Field of View (FoV):

This is an angle and cannot be changed by moving the camera.
It is determined by the lens' focal length and the crop factor, being proportional to ~1/(focal*crop).


2. Crop factor:

Unlike others, I think the term crop factor is a useful term. It allows to determine the equivalent lens for a system with another sensor size.

Equivalent 35mm focal length: focal*crop (cf. above, same FoV)
Equivalent 35mm f-stop: f-stop*crop

The crop-factor of Pentax digital SLR is 1.53.


3. Magnification:

This is the ratio of sensor size and imaged subject size and about equal to the ratio of focal length and subject distance.

Equivalent 35mm subject-distance (with same "frame fill factor"): subject-distance/crop

So, with the same focal length, you need to multiply distance with the crop factor to still keep the subject filling the sensor. So, you move back from 1m to 1.53m. But the perspective will be different than from 1m.