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07-15-2011, 10:53 PM   #16
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QuoteOriginally posted by Blue Quote
What are you saying no to? It can still be useful. Go back and re-read my post. I didn't say to multiply the dof by 1.5, I said the focus distance. The dof markings on the lenses are estimates anyway. The marks can still be used for hyper focusing with the 1.5x.

However, on an aps-c sensor, an equivalent field of view will have more dof than the equivalent on 135. For example on film, the dof for the fa 77 focused on a person at 15 feet @f16 has a dof 17.5' whereas the A 50mm at the same distance aperture will have 26'. However, the hyperfocal distance for the A 50 @ f16 is 17.3 on film and 25.8 on the Pentax aps-c.

Edit:

DOF for the A 50 focusing on a person at 15' @f16 will have 7' in front 99' behind the subject, 105.8 total, 8' near and 114' far.
DOF for the A 50 focusing on a person at 15' f16 will have 5.5' in front and 20.6' behind a total of 26.1' with 9.5' near and 35.6 far.
Er, yes, but you've just changed the lens from a 77 to a 50. If take a lens with a given focal length and mount it on a FF camera and an APS-c camera, all things being equal, the DOF will be shallower for a the APS-c. You can check this easily using this calculator:

Understanding Depth of Field in Photography

or here:

A Flexible Depth of Field Calculator

You can view the situation as a lens producing an image onto smaller pixels than the FF case, so OOF blur covers more pixels, and so is more visible. Of course, as has been hinted at already, the DOF scale is all rather arbitrary, as it depends on the resolution of the film or sensor, how big you print the image, and how closely you view the image - but I think most people have success when the scale is used conservatively by about 2 stops. You definitely can't use the scale as it is though.

07-16-2011, 07:09 AM   #17
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QuoteOriginally posted by m42man Quote
Er, yes, but you've just changed the lens from a 77 to a 50. If take a lens with a given focal length and mount it on a FF camera and an APS-c camera, all things being equal, the DOF will be shallower for a the APS-c. You can check this easily using this calculator:

Understanding Depth of Field in Photography

or here:

A Flexible Depth of Field Calculator

You can view the situation as a lens producing an image onto smaller pixels than the FF case, so OOF blur covers more pixels, and so is more visible. Of course, as has been hinted at already, the DOF scale is all rather arbitrary, as it depends on the resolution of the film or sensor, how big you print the image, and how closely you view the image - but I think most people have success when the scale is used conservatively by about 2 stops. You definitely can't use the scale as it is though.
That is not what I was saying. Furthermore the numbers I posted came from a dof on my android. What do you think happens to the dof of printed images at 8x10 from the same lens on aps-c and 135 and 8x10 printed from a 50 on aps-c and from a 77mm on 135?

P.S. I already posted links to dof calculators.

Edit: The point I was making is that at equivalent fields of view, the dof is greater on aps-c. That is one of the key arguments for people that want a ff dSLR. The second is the fov on wide angle and ultrawide angle lenses.
07-16-2011, 10:12 PM   #18
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QuoteOriginally posted by Blue Quote
That is not what I was saying. Furthermore the numbers I posted came from a dof on my android. What do you think happens to the dof of printed images at 8x10 from the same lens on aps-c and 135 and 8x10 printed from a 50 on aps-c and from a 77mm on 135?

P.S. I already posted links to dof calculators.

Edit: The point I was making is that at equivalent fields of view, the dof is greater on aps-c. That is one of the key arguments for people that want a ff dSLR. The second is the fov on wide angle and ultrawide angle lenses.
That a smaller sensor has greater DOF for a lens with the same FOV is common knowledge.

The discussion is actually about the DOF scale on an old lens. You made this statement "I know if I have adequate dof for film, I have it covered on my digital aps-c bodies". This is incorrect: you won't have it covered for APS-c bodies. That's all I was pointing out.

Have you tried using a DOF calculator for a lens of a given FL, focus distance and aperture, whilst varying the sensor size?
07-17-2011, 07:11 AM   #19
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QuoteOriginally posted by m42man Quote
That a smaller sensor has greater DOF for a lens with the same FOV is common knowledge.

The discussion is actually about the DOF scale on an old lens. You made this statement "I know if I have adequate dof for film, I have it covered on my digital aps-c bodies". This is incorrect: you won't have it covered for APS-c bodies. That's all I was pointing out.

Have you tried using a DOF calculator for a lens of a given FL, focus distance and aperture, whilst varying the sensor size?
If you go back and look, I stated that 1.5x the focus distance and hyperfocal distance when I use the film scale on aps-c. I also use the marks for the wider apertures. Furthermore, if you look at these scales and have used them, you will realize that they are no where near enough of them to be as accurate as calculations, plus the distance has to be estimated or measured with a tape measure. While I do have a nice 150' tape measure, I don't carry it around in the bag. Sometimes depending on the conditions and subject distance I actually do use the original marks since the ultimate goal is to get the subject in focus and a 0.5' of extra distance in front can be sacrificed then tweak it with the screen and or focus confirmation. Lastly, the marks are used for Hyperfocal focusing as well and I was also mentioning that.

Furthermore, your statement of 'No' in reference to the marks not being useful was your opinion and not a fact.

But back to the last question that you sidestepped regarding the print out comparison. How is the dof effected in actual print? The output is more important than what is in the viewfinder unless you plan show people rear screen.

BTW, have you tried reading, I already answered that and gave an example.


Last edited by Blue; 07-17-2011 at 08:38 PM.
07-17-2011, 11:08 PM - 1 Like   #20
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Look, I've collected up some of your postings:

QuoteOriginally posted by Blue Quote
This is correct for a lens made for film and used on aps-c in that the lens will have more depth of field on the APS-c than 135 film at an equivalent fov. For Pentax sensors, this is about 1.5x. (the same for Nikon and Sony, 1.6 for canon and 1.7 for Sigma) Just the opposite would be true for the DA 70mm Ltd used on a film body.
The phrases "a lens made for film and used on aps-c" and "at an equivalent fov" are mutually incompatible. The phrase "the lens will have more depth of field on the APS-c than 135 film" is wrong (note: fact, not opinion).

QuoteOriginally posted by Blue Quote
You can still use it. I even don't bother with conversion when I am using digital unless I am trying for shallow dof because I know if I have adequate dof for film, I have it covered on my digital aps-c bodies. Other wise just use the 1.5x conversion factor on the focus distance.

Edit: There is a section in the hyperfocal section of this article.

Hyperfocal Focusing With APS Sized Sensors
As I said before, the phrase "I know if I have adequate dof for film, I have it covered on my digital aps-c bodies" is wrong (note: fact, not opinion).

QuoteOriginally posted by Blue Quote
That is not what I was saying. Furthermore the numbers I posted came from a dof on my android. What do you think happens to the dof of printed images at 8x10 from the same lens on aps-c and 135 and 8x10 printed from a 50 on aps-c and from a 77mm on 135?

P.S. I already posted links to dof calculators.

Edit: The point I was making is that at equivalent fields of view, the dof is greater on aps-c. That is one of the key arguments for people that want a ff dSLR. The second is the fov on wide angle and ultrawide angle lenses.
You are now changing focal lengths in order to equalise the FOV; this is entirely irrelevant to the discussion, which is about DOF for a single lens.

QuoteOriginally posted by Blue Quote
Furthermore, your statement of 'No' in reference to the marks not being useful was your opinion and not a fact.

But back to the last question that you sidestepped regarding the print out comparison. How is the dof effected in actual print? The output is more important than what is in the viewfinder unless you plan show people rear screen.

BTW, have you tried reading, I already answered that and gave an example.
I used the word "no" to emphasise the fact that what you're saying is wrong (you said that if you use the DOF markings as they are, then you're covered for APS-c). I never said the marks were not useful - they're particularly useful if you're using hyperfocal focusing, but only if you understand that you'll get less DOF than the scale implies (because it's a 135 film lens). RioRico said it very succinctly, of course.

Regarding print size, yes, this is important, and DOF figures make assumptions about size and viewing distance. You have to keep print size and viewing distance constant if you're comparing DOFs.

Do us all a favour, and put the following into this DOF calculator:

Understanding Depth of Field in Photography

50mm lens, f2, 20m focus distance; camera type 35mm. Press "calculate" and note the DOF result. Now, without changing anything else, change the camera type to "digital SLR with CF of 1.5x". Press "calculate" and note the results.
07-18-2011, 07:19 AM   #21
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QuoteOriginally posted by m42man Quote
Look, I've collected up some of your postings:



The phrases "a lens made for film and used on aps-c" and "at an equivalent fov" are mutually incompatible. The phrase "the lens will have more depth of field on the APS-c than 135 film" is wrong (note: fact, not opinion).



As I said before, the phrase "I know if I have adequate dof for film, I have it covered on my digital aps-c bodies" is wrong (note: fact, not opinion).



You are now changing focal lengths in order to equalise the FOV; this is entirely irrelevant to the discussion, which is about DOF for a single lens.



I used the word "no" to emphasise the fact that what you're saying is wrong (you said that if you use the DOF markings as they are, then you're covered for APS-c). I never said the marks were not useful - they're particularly useful if you're using hyperfocal focusing, but only if you understand that you'll get less DOF than the scale implies (because it's a 135 film lens). RioRico said it very succinctly, of course.

Regarding print size, yes, this is important, and DOF figures make assumptions about size and viewing distance. You have to keep print size and viewing distance constant if you're comparing DOFs.

Do us all a favour, and put the following into this DOF calculator:

Understanding Depth of Field in Photography

50mm lens, f2, 20m focus distance; camera type 35mm. Press "calculate" and note the DOF result. Now, without changing anything else, change the camera type to "digital SLR with CF of 1.5x". Press "calculate" and note the results.
I tell you what, you do us a favor and answer the damn question about the out put dof on a 8 x10 print or monitor image.


QuoteOriginally posted by Blue Quote
You can still use it. I even don't bother with conversion when I am using digital unless I am trying for shallow dof because I know if I have adequate dof for film, I have it covered on my digital aps-c bodies. Other wise just use the 1.5x conversion factor on the focus distance.

Edit: There is a section in the hyperfocal section of this article.

http://www.cjcom.net/articles/hyperfoc.htm
Here is what I said. I didn't say it was more just that it was usually enough. I also qualified it by adjusting the focus distance when working with shallow dof by "Other wise just use the 1.5x conversion factor on the focus distance." (see link below) You obviously never read the link I posted or you wouldn't be running off with diarrhea of the mouth and realize that I agreed with you from the beginning regarding the image on the aps-c sensor and 24x36 film. The problem here is that you are arguing about precise calculations via online dof calculators when the markings on the barrel aren't the precise as already pointed out by others in this thread. When only the lens barrel is used, the distance to the subject has to be guessed and that also has to be approximated on the barrel. Lastly, the past 6-mos I actually use my droid if I want to calculate the f# and use the barrel marking for approximating distance. It gets real interesting when taking a DA 21 Ltd mounted on a e-p1. On a stationary set, it is easy, use the 150' tape measure and use the calculator and the barrel marks aren't needed. However, they were intended for use on the go such as street shooting etc. where that isn't practical or the numbers aren't known. Using them is just like marksmanship, it takes practice with the "piece" at hand.

See the addendum at the bottom of this page for an idea of what I am talking about.

http://www.bobatkins.com/photography/technical/digitaldof.html

Notice the distance mark on 135 and then on the aps-c 1.6 sensor of the Canon 10d.

Last edited by Blue; 07-18-2011 at 12:39 PM.
07-18-2011, 11:04 PM   #22
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(I dread to think what Adam and his moderators are making of our little discussion!)

QuoteOriginally posted by Blue Quote
I tell you what, you do us a favor and answer the damn question about the out put dof on a 8 x10 print or monitor image.
Look, I've already said that it's common knowledge that, for lens/sensor combinations with the same FOV, the APS-c will have more DOF than the 135. But why is this relevant to the discussion? Surely it just confuses the issue - we're talking about a given lens with different sensor sizes, not a given FOV.


QuoteOriginally posted by Blue Quote
Here is what I said. I didn't say it was more just that it was usually enough. I also qualified it by adjusting the focus distance when working with shallow dof by "Other wise just use the 1.5x conversion factor on the focus distance." (see link below) You obviously never read the link I posted or you wouldn't be running off with diarrhea of the mouth and realize that I agreed with you from the beginning regarding the image on the aps-c sensor and 24x36 film. The problem here is that you are arguing about precise calculations via online dof calculators when the markings on the barrel aren't the precise as already pointed out by others in this thread. When only the lens barrel is used, the distance to the subject has to be guessed and that also has to be approximated on the barrel. Lastly, the past 6-mos I actually use my droid if I want to calculate the f# and use the barrel marking for approximating distance. It gets real interesting when taking a DA 21 Ltd mounted on a e-p1. On a stationary set, it is easy, use the 150' tape measure and use the calculator and the barrel marks aren't needed. However, they were intended for use on the go such as street shooting etc. where that isn't practical or the numbers aren't known. Using them is just like marksmanship, it takes practice with the "piece" at hand.

See the addendum at the bottom of this page for an idea of what I am talking about.

Depth of Field, Digital Photography and Crop Sensor Cameras - Bob Atkins Photography

Notice the distance mark on 135 and then on the aps-c 1.6 sensor of the Canon 10d.
OK, I should have followed the link, because it does explain some of your subsequent statements which were baffling me. I also have to say I think the content of the article, whilst technically correct, is an absolutely awful way of handling the DOF/hyperfocal issue. It's so much easier to make use of the DOF scale (if your lens has one, that is) directly, with the proviso that you will need to be conservative by a couple of stops (or possibly a bit less if you're not going to be pixel-peeping). No tape measures needed!

The reason I kept mentioning use of DOF calculators was that I had the strong impression that you actually were disagreeing with the my post about shallower DOFs, and they're just a quick and easy way of confirming what I was saying. If we're actually in agreement, then they're not needed.

Anyway, it's been an, er, interesting debate, and sorry if I ended up causing any offence - it's easily done in the heat of the moment, and you always end up feeling bad about it afterwards...
07-19-2011, 01:27 AM   #23
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I heard the FA35/2 and the DA35/2.4 are optically the same.
Do they have the same DOF? or they actually DO have the 1/2 stop difference?

07-19-2011, 05:51 AM   #24
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QuoteOriginally posted by MegaPower Quote
I heard the FA35/2 and the DA35/2.4 are optically the same.
Do they have the same DOF? or they actually DO have the 1/2 stop difference?
While they are very similar optically, it doesn't really matter since they are the same focal length. The DOF is going to depend on the the film sensor size, aperture, focal length, subject distance etc. Both lenses will behave the same on Pentax dSLR bodies. The DA 35/2.4 AL lacks the focus scale.

Last edited by Blue; 07-19-2011 at 06:34 AM.
07-19-2011, 06:01 AM   #25
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I think the moderators are o.k. as long as we are. Strong debates are o.k. as long as they end up without resulting in animosity. Most of the time have found the focusing distance marks to be more useful and mainly on wide angle and normal lenses anyway. For me the M 85mm/2 would be pushing my upper distance estimation especially on aps-c. Even then I use them for quick adjustment in street photography situations or setting up a landscape shot. Otherwise the charts (cheat sheets) or now the droid app works better for me.

QuoteOriginally posted by m42man Quote
(I dread to think what Adam and his moderators are making of our little discussion!)



Look, I've already said that it's common knowledge that, for lens/sensor combinations with the same FOV, the APS-c will have more DOF than the 135. But why is this relevant to the discussion? Surely it just confuses the issue - we're talking about a given lens with different sensor sizes, not a given FOV.




OK, I should have followed the link, because it does explain some of your subsequent statements which were baffling me. I also have to say I think the content of the article, whilst technically correct, is an absolutely awful way of handling the DOF/hyperfocal issue. It's so much easier to make use of the DOF scale (if your lens has one, that is) directly, with the proviso that you will need to be conservative by a couple of stops (or possibly a bit less if you're not going to be pixel-peeping). No tape measures needed!

The reason I kept mentioning use of DOF calculators was that I had the strong impression that you actually were disagreeing with the my post about shallower DOFs, and they're just a quick and easy way of confirming what I was saying. If we're actually in agreement, then they're not needed.

Anyway, it's been an, er, interesting debate, and sorry if I ended up causing any offence - it's easily done in the heat of the moment, and you always end up feeling bad about it afterwards...

Last edited by Blue; 07-19-2011 at 10:36 AM.
07-19-2011, 06:45 AM   #26
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QuoteOriginally posted by Blue Quote
Most of the time have found the focusing distance marks to be more useful and mainly on wide angle and normal lenses anyway. For me the M 85mm/2 would be pushing my upper distance estimation especially on aps-c.
Quite right. I've successfully used the distance marks (adjusted) for hyperfocusing on lenses up to 100mm; beyond that they're not useful, as DOF becomes too thin at most apertures.

Let me mention DOF INDEX. This is a comparative (not absolute) measure of DOF at different focal lengths and apertures. To find the index, just divide focal length by aperture: FL/AP. The larger the FL/AP index, the thinner the DOF; and two lenses with the same index will have similar DOF. So a 50/2 lens and a 100/4 have similar DOF (index=25) and thicker DOF than a 50/1.4 or 100/2.8 (index=35.7). And a 200/4 (index=50) has thinner DOF than an 85/2 (index=42.5). Whereas a 24mm lens with aperture at f/11 (index=2.18) has really really thick DOF.

My point is, you can judge the difficulty of hyperfocusing using the distance marks (adjusted) by looking at the FL/AP number. Smaller is easier, larger is harder.
07-20-2011, 07:39 AM   #27
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QuoteOriginally posted by Blue Quote
While they are very similar optically, it doesn't really matter since they are the same focal length. The DOF is going to depend on the the film sensor size, aperture, focal length, subject distance etc. Both lenses will behave the same on Pentax dSLR bodies. The DA 35/2.4 AL lacks the focus scale.
so FA 35/2 wide open on DSLR = f2.4?
DA35/2.4 wide open on DSLR = f2.4?


I just bought a FA35/2.
I shoot some film sometime but not that often. Not sure if it is a good idea to pay the extra for the A ring.
07-20-2011, 07:54 AM   #28
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QuoteOriginally posted by MegaPower Quote
so FA 35/2 wide open on DSLR = f2.4?
DA35/2.4 wide open on DSLR = f2.4?
The FA35/2 wide-open on a dSLR is f/2.
The DA35/2.4 wide-open on a dSLR is f/2.4.
At any aperture, they will have the same FOV
Wide-open, the 35/2 will have thinner DOF.

QuoteQuote:
I just bought a FA35/2.
I shoot some film sometime but not that often. Not sure if it is a good idea to pay the extra for the A ring.
With the 35/2, you are paying extra for 2/3 f-stop, lack of vignetting on FF, and greater control.
07-20-2011, 11:42 AM   #29
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QuoteOriginally posted by MegaPower Quote
so FA 35/2 wide open on DSLR = f2.4?
DA35/2.4 wide open on DSLR = f2.4?


I just bought a FA35/2.
I shoot some film sometime but not that often. Not sure if it is a good idea to pay the extra for the A ring.
When I answered your question, I thought you were asking about the focus scale. Of course the .4 difference in maximum aperture between the 2 lenses. The focal length is the same and the number of elements and grouping is the same in the lenses but the elements are slightly smaller in diameter and thickness which probably accounts for that loss of .4. The both have Ghostless Coating on the rear element.

The A ring is a nice feature and personally, I like the build of the FA better then the DA AL, not to mention it is slightly faster which will also effect the dof some on dSLR but more so on the film bodies.

For Example on film focusing on a subject at 10 feet:

The near focus at f2 is 8.7 and the far at 11. 7 with a total depth of 3.02. feet. (Hyperfocal at 67.1 feet)
The near focus at F2.4 is 8.5 and the far at 12.2 with a total depth of 3.66 feet. (hyperfocal at 55.9 feet.)

On Pentax APS-C:

The near focus at f2 is 9.1 and far 11.1 with a total of 1.99 feet (Hyperfocal at 100.6)
The near focus at f2.4 is 8.9 and far 11.3 with at total depth of 2.39 feet (Hyperfocal 83.8)

Notice the Hyperfocal distance changes by 1.5x between film and aps-c.

Last edited by Blue; 07-20-2011 at 11:47 AM.
07-21-2011, 10:56 AM   #30
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What is that 'pearl' like white thingy in the same ring with red diamond mark

QuoteOriginally posted by sany Quote
Just to help me point out as an example, please see the image of lens <a href="https://www.pentaxforums.com/lensreviews/SMC-Pentax-M-85mm-F2-Lens.html" target="_blank">here</a><br />
<br />
I know the first ring is for aperture setting (on the left) and on extreme right is the distance setting, what is the ring in center for - the one with the red diamond. Please can somebody explain as I am soon receiving a copy of this lens.<br />
<br />
And anything that I may have to know from your point if you have used this particular lens already. This will become my first manual lens so any knowledge sharing on this lens and in general the M series will be of much help for me, thanks in advance<br />
<br />
thanks
Can somebody also tell me what is this 'white pearl' like object in the same ring with the 'red diamond' mark (reference image). Sorry to have not asked this before.
Is this some sort of clutch to rotate something?
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