Lens markings

**eccs19** · 12-18-2008, 08:31 AM

I'm curious. If I focus on something, and I look at the lens, and it tells me that I'm 10' away from the subject. Is what the lens showing me accurate, or not because of the crop factor?

newarts · 12-18-2008, 08:41 AM

Originally posted by eccs19

I'm curious. If I focus on something, and I look at the lens, and it tells me that I'm 10' away from the subject. Is what the lens showing me accurate, or not because of the crop factor?

Accurate.

The math does not involve the sensor size. Imagine an image in focus on a big sensor; it is also in focus on a smaller part of that sensor.

k100d · 12-18-2008, 08:41 AM

although the hyperfocal markings are off by about a stop

axl · 12-18-2008, 08:42 AM

the crop factor desn't change distance between you and the object, it just changes FOV for specified focal length. so if lens is telling you that you are 10 feet away, you are 10 feet away. The difference is, if you put the same lens on FF/film camera from the same 10 feet looking at the same subject you will see more in you VF...
BR

axl · 12-18-2008, 08:46 AM

Originally posted by k100d

although the hyperfocal markings are off by about a stop

please correct me if I'm wrong:
APS-C sensor sees less than full frame designed lens. That means if you focus HF on let's say f8 you are actualy wasting some space in focus (because the smaller sensor doesn't see it) and therefore you could use smaller f-stop and (f5,6 and still get into focus roughly what you need/want?
Do I understand this correctly?

Sean Nelson · 12-18-2008, 09:12 AM

Originally posted by axl

please correct me if I'm wrong:
APS-C sensor sees less than full frame designed lens. That means if you focus HF on let's say f8 you are actualy wasting some space in focus (because the smaller sensor doesn't see it) and therefore you could use smaller f-stop and (f5,6 and still get into focus roughly what you need/want?
Do I understand this correctly?

You're talking about depth of field, right? The difference in depth of field isn't anything to do with the lens, it's because you have to enlarge the image from the smaller sensor MORE to get a print or display image of the same size. This means that the slight blurring of out-of-focus areas is magnified, and so the range of objects with "acceptable blurriness" is reduced. This is comparing the SAME LENS on different sensors (which of course gives different fields of view).

What you're saying is the opposite of what it should be - f/5.6 is a "larger" f/stop than f/8 (because the iris has a larger opening at f/5.6 than at f/8). And FOR THE SAME LENS, you need to use a smaller f/stop on APS-C (ie, use f/11 vs. f/8 on full frame) to get similar depth of field.

Smaller sensors have larger depths of field at a given aperture if the FIELD OF VIEW is the same, which means using a shorter lens with the smaller sensor.

**eccs19** · 12-18-2008, 12:42 PM

Thanks for the info. I was wondering about this, because my flash lists distance on the back, and recommended F: setting, so I was hoping it was accurate. Helps a lot.

**Kerrowdown** · 12-18-2008, 01:22 PM

It should be accurate, just run out a ten foot tape measure and see, it should be there or there abouts.

Mike Cash · 12-18-2008, 02:22 PM

Originally posted by kerrowdown

It should be accurate, just run out a ten foot tape measure and see, it should be there or there abouts.

Anyone should be able to eyeball the difference between ten and fifteen feet.

k100d · 12-18-2008, 06:55 PM

Originally posted by axl

please correct me if I'm wrong:
APS-C sensor sees less than full frame designed lens. That means if you focus HF on let's say f8 you are actualy wasting some space in focus (because the smaller sensor doesn't see it) and therefore you could use smaller f-stop and (f5,6 and still get into focus roughly what you need/want?
Do I understand this correctly?

Originally posted by Sean Nelson

You're talking about depth of field, right? The difference in depth of field isn't anything to do with the lens, it's because you have to enlarge the image from the smaller sensor MORE to get a print or display image of the same size. This means that the slight blurring of out-of-focus areas is magnified, and so the range of objects with "acceptable blurriness" is reduced. This is comparing the SAME LENS on different sensors (which of course gives different fields of view).

What you're saying is the opposite of what it should be - f/5.6 is a "larger" f/stop than f/8 (because the iris has a larger opening at f/5.6 than at f/8). And FOR THE SAME LENS, you need to use a smaller f/stop on APS-C (ie, use f/11 vs. f/8 on full frame) to get similar depth of field.

Smaller sensors have larger depths of field at a given aperture if the FIELD OF VIEW is the same, which means using a shorter lens with the smaller sensor.

sounds right to me

axl · 12-19-2008, 12:56 AM

thanx for clarifying that for me guys, seems there is still a lot to learn...

anyway, since the APS-C doesn't see as much as FF (since the FOV of the same lens on two different formats is different) you may not need the same DOF, or not?
so now if I'm using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more to get everything in focus while set on HF?
Sorry, I'm just getting really confused here...

creampuff · 12-19-2008, 01:35 AM

Originally posted by axl

thanx for clarifying that for me guys, seems there is still a lot to learn...

anyway, since the APS-C doesn't see as much as FF (since the FOV of the same lens on two different formats is different) you may not need the same DOF, or not?
so now if I'm using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more to get everything in focus while set on HF?
Sorry, I'm just getting really confused here...

For a given focal length, aperture and distance, you'll get more DOF when used on a cropped sensor than on FF.

Sean Nelson · 12-19-2008, 02:16 AM

Originally posted by creampuff

For a given focal length, aperture and distance, you'll get more DOF when used on a cropped sensor than on FF.

You see, this is why poor Axl is getting confused. Your statement is incorrect, it should be "for a given FIELD OF VIEW", not for a given focal length.

The following calculations are from the DOF calculator at: Online Depth of Field Calculator using an aperture of f/4 and a subject distance of 2m:

Same focal length lens gives LESS depth of field on a smaller sensor:
50mm lens on 35mm film has a DOF of 0.38m
50mm lens on K10D has a DOF of 0.25m

Same field of view gives MORE depth of field on a smaller sensor
50mm lens on 35mm film has a DOF of 0.38m
33mm lens on K10D has a DOF of 0.59m

georgweb · 12-19-2008, 02:25 AM

Quote:

Axl said:
... using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more ... "

Yes, if you refer to the DOF scale on your Tokina lens.

This seems illogical, but it is true nonetheless. On old manual 'full-format' lens scales (=the DOF markings on the lens barrrel), if you use this lens on an APS-C camera, your DOF will shrink about 1.3 stops from what the scale tells you.

Example here: Digital Depth of Field
(scroll down til the end of the article).

So yes, if you use that old manual lens on APS-C and stop down to f/8, your DOF will shrink to something within the 5.6 markings on that lens barrrel.

Trust me :-)
Georg (the other)

Sean Nelson · 12-19-2008, 02:34 AM

Originally posted by axl

so now if I'm using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more to get everything in focus while set on HF?

As a rule of thumb, I'd stop it down one extra stop (or conversely, use the DOF markings on the lens for the aperture one stop wider than what the lens is actually set to). So if the aperture ring is set to f/8, for example, use the DOF scale markings shown for f/5.6. You can put some figures into the DOF calculator I linked to in my previous post and see that the result is very close to the DOF you'll get from the smaller sensor.

And to repeat for those aren't getting it: the reason the depth of field is smaller is because the DOF scale on the lens is designed for full-frame 35mm film. When you use the same lens on a K10D, you have to enlarge the image MORE in order to get a final print or screen image of the same size (say, 10 inches across). Because you've enlarged the image more, you've also enlarged the blurriness of the slightly out-of-focus areas - that means some of those areas that would have appeared sharp before are now revealed under the extra magnification as not-so-sharp in the final picture. The net effect is: smaller depth of field.

(Of course the prints from 35mm vs. K10D, while the same physical size at, say, 10" across, wouldn't show the same picture because the field of view on the K10D is much smaller. But that's irrelevant to the depth-of-field issue at hand).

Keep in mind that DOF is somewhat subjective and highly dependent on the size and viewing distance of the final image. It's not an absolute thing. You'll have more apparent DOF in a small print or screen image than a large one, and more DOF in a print or image viewed from farther away than from one viewed at a closer distance.

12-18-2008, 08:31 AM	#1
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510	Lens markings I'm curious. If I focus on something, and I look at the lens, and it tells me that I'm 10' away from the subject. Is what the lens showing me accurate, or not because of the crop factor?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
SMC-A 70-210 lens markings?	enoxatnep	Pentax SLR Lens Discussion	6	12-22-2009 04:02 AM
Manual lens markings?	emr	Pentax SLR Lens Discussion	3	07-05-2009 07:39 PM
Pentax 18-250mm Vs. Tamron 70-300mm, focal length markings are not the same	aweir	Pentax SLR Lens Discussion	1	04-04-2009 09:19 PM
Pentax-M 28mm F3.5 scale markings	wiseman	Pentax SLR Lens Discussion	11	03-03-2009 01:43 AM
Close-up lens markings	gamgee	Pentax SLR Lens Discussion	2	06-12-2008 06:28 AM

12-18-2008, 08:41 AM	#2
newarts Inactive Account Join Date: Dec 2008 Location: Ames, Iowa, USA Photos: Albums Posts: 2,965	Originally posted by eccs19 I'm curious. If I focus on something, and I look at the lens, and it tells me that I'm 10' away from the subject. Is what the lens showing me accurate, or not because of the crop factor? Accurate. The math does not involve the sensor size. Imagine an image in focus on a big sensor; it is also in focus on a smaller part of that sensor.

12-18-2008, 08:41 AM	#3
k100d Veteran Member Join Date: Feb 2008 Location: Toronto Posts: 3,911	although the hyperfocal markings are off by about a stop

12-18-2008, 08:42 AM	#4
axl Veteran Member Join Date: Mar 2007 Location: Nove Zamky, Slovakia Photos: Gallery \| Albums Posts: 7,183	the crop factor desn't change distance between you and the object, it just changes FOV for specified focal length. so if lens is telling you that you are 10 feet away, you are 10 feet away. The difference is, if you put the same lens on FF/film camera from the same 10 feet looking at the same subject you will see more in you VF... BR

12-18-2008, 08:46 AM	#5
axl Veteran Member Join Date: Mar 2007 Location: Nove Zamky, Slovakia Photos: Gallery \| Albums Posts: 7,183	Originally posted by k100d although the hyperfocal markings are off by about a stop please correct me if I'm wrong: APS-C sensor sees less than full frame designed lens. That means if you focus HF on let's say f8 you are actualy wasting some space in focus (because the smaller sensor doesn't see it) and therefore you could use smaller f-stop and (f5,6 and still get into focus roughly what you need/want? Do I understand this correctly?

12-18-2008, 09:12 AM	#6
Sean Nelson Veteran Member Join Date: Sep 2008 Location: Vancouver BC Canada Posts: 353	Originally posted by axl please correct me if I'm wrong: APS-C sensor sees less than full frame designed lens. That means if you focus HF on let's say f8 you are actualy wasting some space in focus (because the smaller sensor doesn't see it) and therefore you could use smaller f-stop and (f5,6 and still get into focus roughly what you need/want? Do I understand this correctly? You're talking about depth of field, right? The difference in depth of field isn't anything to do with the lens, it's because you have to enlarge the image from the smaller sensor MORE to get a print or display image of the same size. This means that the slight blurring of out-of-focus areas is magnified, and so the range of objects with "acceptable blurriness" is reduced. This is comparing the SAME LENS on different sensors (which of course gives different fields of view). What you're saying is the opposite of what it should be - f/5.6 is a "larger" f/stop than f/8 (because the iris has a larger opening at f/5.6 than at f/8). And FOR THE SAME LENS, you need to use a smaller f/stop on APS-C (ie, use f/11 vs. f/8 on full frame) to get similar depth of field. Smaller sensors have larger depths of field at a given aperture if the FIELD OF VIEW is the same, which means using a shorter lens with the smaller sensor.

12-18-2008, 12:42 PM	#7
eccs19 Site Supporter Join Date: Jul 2008 Location: Lisle, Ontario Photos: Gallery Posts: 1,510 Original Poster	Thanks for the info. I was wondering about this, because my flash lists distance on the back, and recommended F: setting, so I was hoping it was accurate. Helps a lot.

12-18-2008, 01:22 PM	#8
Kerrowdown PEG Moderator Join Date: Aug 2008 Location: Highlands of Scotland... "Hold Infinity in the palm of your hand" - William Blake Photos: Gallery Posts: 57,863	It should be accurate, just run out a ten foot tape measure and see, it should be there or there abouts.

12-18-2008, 02:22 PM	#9
Mike Cash Veteran Member Join Date: Jan 2007 Location: Japan Photos: Gallery Posts: 6,950	Originally posted by kerrowdown It should be accurate, just run out a ten foot tape measure and see, it should be there or there abouts. Anyone should be able to eyeball the difference between ten and fifteen feet.

12-18-2008, 06:55 PM	#10
k100d Veteran Member Join Date: Feb 2008 Location: Toronto Posts: 3,911	Originally posted by axl please correct me if I'm wrong: APS-C sensor sees less than full frame designed lens. That means if you focus HF on let's say f8 you are actualy wasting some space in focus (because the smaller sensor doesn't see it) and therefore you could use smaller f-stop and (f5,6 and still get into focus roughly what you need/want? Do I understand this correctly? Originally posted by Sean Nelson You're talking about depth of field, right? The difference in depth of field isn't anything to do with the lens, it's because you have to enlarge the image from the smaller sensor MORE to get a print or display image of the same size. This means that the slight blurring of out-of-focus areas is magnified, and so the range of objects with "acceptable blurriness" is reduced. This is comparing the SAME LENS on different sensors (which of course gives different fields of view). What you're saying is the opposite of what it should be - f/5.6 is a "larger" f/stop than f/8 (because the iris has a larger opening at f/5.6 than at f/8). And FOR THE SAME LENS, you need to use a smaller f/stop on APS-C (ie, use f/11 vs. f/8 on full frame) to get similar depth of field. Smaller sensors have larger depths of field at a given aperture if the FIELD OF VIEW is the same, which means using a shorter lens with the smaller sensor. sounds right to me

12-19-2008, 12:56 AM	#11
axl Veteran Member Join Date: Mar 2007 Location: Nove Zamky, Slovakia Photos: Gallery \| Albums Posts: 7,183	thanx for clarifying that for me guys, seems there is still a lot to learn... anyway, since the APS-C doesn't see as much as FF (since the FOV of the same lens on two different formats is different) you may not need the same DOF, or not? so now if I'm using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more to get everything in focus while set on HF? Sorry, I'm just getting really confused here...

12-19-2008, 01:35 AM	#12
creampuff Veteran Member Join Date: May 2007 Location: Singapore Photos: Gallery Posts: 3,953	Originally posted by axl thanx for clarifying that for me guys, seems there is still a lot to learn... anyway, since the APS-C doesn't see as much as FF (since the FOV of the same lens on two different formats is different) you may not need the same DOF, or not? so now if I'm using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more to get everything in focus while set on HF? Sorry, I'm just getting really confused here... For a given focal length, aperture and distance, you'll get more DOF when used on a cropped sensor than on FF.

12-19-2008, 02:16 AM	#13
Sean Nelson Veteran Member Join Date: Sep 2008 Location: Vancouver BC Canada Posts: 353	Originally posted by creampuff For a given focal length, aperture and distance, you'll get more DOF when used on a cropped sensor than on FF. You see, this is why poor Axl is getting confused. Your statement is incorrect, it should be "for a given FIELD OF VIEW", not for a given focal length. The following calculations are from the DOF calculator at: Online Depth of Field Calculator using an aperture of f/4 and a subject distance of 2m: Same focal length lens gives LESS depth of field on a smaller sensor: 50mm lens on 35mm film has a DOF of 0.38m 50mm lens on K10D has a DOF of 0.25m Same field of view gives MORE depth of field on a smaller sensor 50mm lens on 35mm film has a DOF of 0.38m 33mm lens on K10D has a DOF of 0.59m

12-19-2008, 02:25 AM	#14
georgweb Veteran Member Join Date: Apr 2008 Location: Berlin, Germany Photos: Gallery Posts: 1,386	Quote: Axl said: ... using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more ... " Yes, if you refer to the DOF scale on your Tokina lens. This seems illogical, but it is true nonetheless. On old manual 'full-format' lens scales (=the DOF markings on the lens barrrel), if you use this lens on an APS-C camera, your DOF will shrink about 1.3 stops from what the scale tells you. Example here: Digital Depth of Field (scroll down til the end of the article). So yes, if you use that old manual lens on APS-C and stop down to f/8, your DOF will shrink to something within the 5.6 markings on that lens barrrel. Trust me :-) Georg (the other)

12-19-2008, 02:34 AM	#15
Sean Nelson Veteran Member Join Date: Sep 2008 Location: Vancouver BC Canada Posts: 353	Originally posted by axl so now if I'm using my Tokina 28 (old manual lens from film era) shall I be stopping it down stop more to get everything in focus while set on HF? As a rule of thumb, I'd stop it down one extra stop (or conversely, use the DOF markings on the lens for the aperture one stop wider than what the lens is actually set to). So if the aperture ring is set to f/8, for example, use the DOF scale markings shown for f/5.6. You can put some figures into the DOF calculator I linked to in my previous post and see that the result is very close to the DOF you'll get from the smaller sensor. And to repeat for those aren't getting it: the reason the depth of field is smaller is because the DOF scale on the lens is designed for full-frame 35mm film. When you use the same lens on a K10D, you have to enlarge the image MORE in order to get a final print or screen image of the same size (say, 10 inches across). Because you've enlarged the image more, you've also enlarged the blurriness of the slightly out-of-focus areas - that means some of those areas that would have appeared sharp before are now revealed under the extra magnification as not-so-sharp in the final picture. The net effect is: smaller depth of field. (Of course the prints from 35mm vs. K10D, while the same physical size at, say, 10" across, wouldn't show the same picture because the field of view on the K10D is much smaller. But that's irrelevant to the depth-of-field issue at hand). Keep in mind that DOF is somewhat subjective and highly dependent on the size and viewing distance of the final image. It's not an absolute thing. You'll have more apparent DOF in a small print or screen image than a large one, and more DOF in a print or image viewed from farther away than from one viewed at a closer distance.