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03-22-2009, 09:44 PM   #106
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Here is one wide open with the 67, 200mm late model f4. I will try to get some with the 55mm f4 late model for next weekend:

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03-23-2009, 08:05 AM   #107
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Hi Jewelltrail, Those are nice pictures.

I have been reading about MF and MF lenses in general. One of the comments that I read indicated that there is a tendency to have less depth of field with a MF lens compared to a similar lens for smaller formats.

The part that was not clear from the discussions was whether they were comparing:
- 200mm MF lens on an MF film to 200mm lens for 35mm on 35mm film
- 200mm MF lens vs 200mm (designed for 35mm) on 35mm

In other words, obviously a MF lens will have a longer effective focal length on a smaller sensor / film, and longer focal length lenses tend to have less DOF, but is there something else about this as well ?

I don't notice it in your pictures, but have you seen a substantial reduction in DOF using the MF lenses for similar magnification ? I am mostly interested in "nearly wide open" performance if that affects the answer.

Thank you.
03-23-2009, 09:33 AM   #108
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QuoteOriginally posted by HarryN Quote
Hi Jewelltrail, Those are nice pictures.

I have been reading about MF and MF lenses in general. One of the comments that I read indicated that there is a tendency to have less depth of field with a MF lens compared to a similar lens for smaller formats.

The part that was not clear from the discussions was whether they were comparing:
- 200mm MF lens on an MF film to 200mm lens for 35mm on 35mm film
- 200mm MF lens vs 200mm (designed for 35mm) on 35mm

In other words, obviously a MF lens will have a longer effective focal length on a smaller sensor / film, and longer focal length lenses tend to have less DOF, but is there something else about this as well ?

I don't notice it in your pictures, but have you seen a substantial reduction in DOF using the MF lenses for similar magnification ? I am mostly interested in "nearly wide open" performance if that affects the answer.
MF lenses will have NO longer "effective" focal length at all. The focal length of a lens is a physical property which is fixed and does not change, whether you use that besaid lens on a 35mm camera, on a MF camera or on an APS-C DSLR.

Depth of field on ANY 200mm lens, for whatever film format it was made, is exactly the same at any given aperture and distance.

Ben
03-23-2009, 09:53 PM   #109
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QuoteQuote:
HarryN Hi Jewelltrail, Those are nice pictures.

I have been reading about MF and MF lenses in general. One of the comments that I read indicated that there is a tendency to have less depth of field with a MF lens compared to a similar lens for smaller formats.

The part that was not clear from the discussions was whether they were comparing:
- 200mm MF lens on an MF film to 200mm lens for 35mm on 35mm film
- 200mm MF lens vs 200mm (designed for 35mm) on 35mm

In other words, obviously a MF lens will have a longer effective focal length on a smaller sensor / film, and longer focal length lenses tend to have less DOF, but is there something else about this as well ?

I don't notice it in your pictures, but have you seen a substantial reduction in DOF using the MF lenses for similar magnification ? I am mostly interested in "nearly
wide open" performance if that affects the answer.


Thanks Harry--I have to admit I am liking the images produced by my MF lenses on the K20d.

As for DOF on MF--it is all new to me. I know very little concerning MF systems, that is why I began this thread. But as a result of DOF discussion on MF elsewhere in this forum, for example, https://www.pentaxforums.com/forums/pentax-medium-format-645-6x7/52236-p67-30...seup-work.html I too began to wonder. The discussion at this thread, or some of it, implies the MF system has less DOF. This was something I wanted to understand, especially since my intuition tells me DOF should be the same.

Towards a better understanding on the matter, I turned to our forum members who actually shoot MF--I posted this thread https://www.pentaxforums.com/forums/pentax-medium-format-645-6x7/54948-dof-6-...op-sensor.html in the MF part of our forum. Ron Boggs, a MF shooter, responds with this interesting quote " One of the most difficult transitions for me converting from 35mm to 6x7 about ten years ago was the loss of DOF. 6x7 has approximately half the DOF of 35mm and then less than that vs the crop factor sensors. So an f.4 6x7 lens has about the same DOF as an f.2.8 lens on 35mm and nearly the same DOF as an f.2 lens on the K20D sensor." But Ron makes it clear he has no experience shooting MF lenses on crop sensors, so he does not know if DOF is affected there.

A close reading of the above threads reveals nothing conclusive on the matter. But Ben's comments here are pretty clear:

"Depth of field on ANY 200mm lens, for whatever film format it was made, is exactly the same at any given aperture and distance."

Ben


But we also know a 200mm lens is a 200mm lens, no matter what system it is on. That is one way of wording it. However, clearly the images taken with the same 200mm lens on MF, 35mm & crop sensor are different--no doubt here. Some people are sensitive to the wording of how a lens behaves on different systems. However, no matter the wording, I think all sensible DSLR people know what lenses do on different systems, even if they bicker over how to word it.

That said, I am still not wholly clear on the behavior of a particular lens' DOF on different systems. But I am certainly looking forward to feedback from our learned forum members here because I love to learn.


Last edited by Jewelltrail; 03-23-2009 at 10:00 PM.
03-31-2009, 08:46 PM   #110
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Here is the 67 55mm F4, wide open, with a very large crop. Some CA wide open.
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04-03-2009, 02:58 AM   #111
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jewelltrail: here is a wording version which might help: dof depends on the focal length (physical, not equivalent, the _real_ focal length, in your case 200mm), aperture and the format on which it is used. for the same aperture and same focal length, you will have the same dof on a certain format, for example, your 50-200 at 200mm and f/5.6 will have the same dof as the 6x7 200mm at f/5.6 on your k20d.

crossing formats, it is true that the larger the format, the smaller the dof at the same aperture for the same field of view (example: the 80mm at f/2.8, which is a common standard lens on medium format systems, will have less dof than a 50mm at f/2.8 on a 35mm film system), and this is i think what ron was refering to. when comparing systems as a whole, comparing the same focal length is meaningless, it is much more usefull to compare using the field of view as a common point, however when you take a lens from one system and use it on another, that lens will behave _exactly_ as a lens of that focal length on that system (so if it's 80/2.8 it will behave like an 80/2.8 on the k20d if mounted on the k20d, or like an 80/2.8 on 35mm film if mounted on a 35mm film camera, and so on, when speaking of dof, it does not matter "where the lens is coming from"). i think this "equivalent focal length" thing has gone a bit too far, i see many people confused these days. when talking about equivalent focal length, people actualy mean "field of view", it is just more confortable to use the 35mm film focal lengths that "everybody"is used to, but i feel it would be much better to just drop this, leave focal length alone once and for all (as mentioned, it is a physical property of the lens and should be treated with respect ) and switch to field of view instead. as a reference, the "normal lens" fov is considered to be something in the range of 45 degrees (out of the 360 degrees for a circle system ), so it is quite easy to remember and start from there, i think.
04-03-2009, 10:56 PM   #112
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Nanok: I took the discussion of DOF to another section of the forum with fruitful results. A simple way to sum this up, which I take from Sean Nelson's discussion, is any focal length has varying DOF, depending upon the sized sensor with which it is paired, and this is because the FOV changes which each sensor.

For a more in depth (pun intended) discussion, see this thread here:

https://www.pentaxforums.com/forums/pentax-medium-format-645-6x7-645d/54948-d...op-sensor.html
04-04-2009, 12:19 PM   #113
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oh, okay, i'll check the thread out.

for the sake of going directly to the point: i would rephrase that a bit (it is not wrong,i hasten to add). it is not that the fov changes, but more precisely the circle of confusion changes. in human words: you need more details per square milimeter (you will enlarge more to get the same size of final result: print, digital display, whatever), this means the smaller the media you record on is, phisically, the less dof at a given focal length (as you also said). bringing fov into the discussion is not invalid or wrong (it is actually a synthetic way of summing it up i guess and easier to do transformations back and forth with), but for understanding why and how, i think it is better to go straight to the root (similarly, "field of view" and "equivalent focal length" are the "scientifically correct" and , respectively, the "easy to understand" versions of the same valid point, but it is my impression the "easy to understand" phrasing turned out to bring about a lot of confusion on the long run -- as i said above).

hope this helps, sorry to continue on this thread, i'll check out the one you mentioned asap.

04-04-2009, 12:29 PM   #114
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QuoteOriginally posted by nanok Quote
oh, okay, i'll check the thread out.

for the sake of going directly to the point: i would rephrase that a bit (it is not wrong,i hasten to add). it is not that the fov changes, but more precisely the circle of confusion changes. in human words: you need more details per square milimeter (you will enlarge more to get the same size of final result: print, digital display, whatever), this means the smaller the media you record on is, phisically, the less dof at a given focal length (as you also said). bringing fov into the discussion is not invalid or wrong (it is actually a synthetic way of summing it up i guess and easier to do transformations back and forth with), but for understanding why and how, i think it is better to go straight to the root (similarly, "field of view" and "equivalent focal length" are the "scientifically correct" and , respectively, the "easy to understand" versions of the same valid point, but it is my impression the "easy to understand" phrasing turned out to bring about a lot of confusion on the long run -- as i said above).

hope this helps, sorry to continue on this thread, i'll check out the one you mentioned asap.
Very good summary.

Ben
04-04-2009, 04:18 PM   #115
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QuoteQuote:
nanok: hope this helps, sorry to continue on this thread, i'll check out the one you mentioned asap.
I have a question for you Nanok: Are not the circles of confusion a part of the FOV?

It helps a lot and I appreciate all the excellent work you contribute to this thread. I was trying to summarize, as succinctly as possible, the many paragraphs of writing now in print at the forum on DOF on different sensors. I hope my one-sentence summary did not offend anyone.

Having spent a lot of time in higher education, I realize different levels of understanding demand different levels of explanation. It is interesting that the more we love and study something, the more demanding we become in our explanation of it.

That is why this forum is so great; it allows for multiple levels of understanding to peacefully co-exist, side by side. Best!
04-04-2009, 09:32 PM   #116
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QuoteOriginally posted by Jewelltrail Quote
Are not the circles of confusion a part of the FOV?
"Circle of confusion" essentially means "degree of blurriness".

People talk about depth of field as if it's this magic zone that goes from exactly point X to point Y in which everything is in focus. But the reality is that only ONE distance from the camera is PERFECTLY sharp - everything in front or or beyond that distance is blurry to one degree or another. The further from that particular distance, the blurrier it gets. In technical talk, the "circles of confusion" get larger. When they get large enough that you notice the blurriness, you've reached the limit of the depth of field.

So DOF is a nebulous thing. When you make a bigger print or use a larger computer monitor, it's like taking a magnifying glass to all those slightly blurry parts. Now you can notice some things that aren't in focus that you couldn't before, and the result is that you have less depth of field - even though you didn't change the camera or lens at all.
04-04-2009, 11:49 PM   #117
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QuoteQuote:
Sean Nelson: "Circle of confusion" essentially means "degree of blurriness".

People talk about depth of field as if it's this magic zone that goes from exactly point X to point Y in which everything is in focus. But the reality is that only ONE distance from the camera is PERFECTLY sharp - everything in front or or beyond that distance is blurry to one degree or another. The further from that particular distance, the blurrier it gets. In technical talk, the "circles of confusion" get larger. When they get large enough that you notice the blurriness, you've reached the limit of the depth of field.

So DOF is a nebulous thing. When you make a bigger print or use a larger computer monitor, it's like taking a magnifying glass to all those slightly blurry parts. Now you can notice some things that aren't in focus that you couldn't before, and the result is that you have less depth of field - even though you didn't change the camera or lens at all.
Sean, my question is for Nanok, and it is a rhetorical one. I do know what circles of confusion are; remember, I started the thread in the other section of the forum where this is discussed in depth. And I agree, that in reality only one distance can be "perfectly" in focus.

My question to Nanok is to get him to re-think his initial reply to my one-sentence summary of DOF on MF as being an over-simplification--that is all. Notice, my one-sentence response is a re-working of a sentence I took from you, from that other thread I started in the MF part of our forum: hence, I named you as a source. You may want to read above, unless you already have.
04-05-2009, 04:26 AM   #118
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QuoteOriginally posted by Jewelltrail Quote
I have a question for you Nanok: Are not the circles of confusion a part of the FOV?
not as such. they are connected of course, but (as somebody else here already mentioned), defining the circle of confusion is actually quite a voodoo-like art . but that's not the point, i think what you mean to point out is that your statement is valid, which i _did_ mention in my previous post. nothing to argue there. i was not arguing against your statement, i was just trying to do the same thing as you, summarize, but using a slightly different aproach (which people with a different mindset might find easier to understand).

QuoteQuote:
It helps a lot and I appreciate all the excellent work you contribute to this thread. I was trying to summarize, as succinctly as possible, the many paragraphs of writing now in print at the forum on DOF on different sensors. I hope my one-sentence summary did not offend anyone.
surely not, i cannot imagine why you would think so. it is not about being offended,
it's about trying to help to the best of my ability. i did mention what you said was fundamentally not incorrect, just potentially confusing, the explanation was not so much for you as it was for anybody who might be reading (point being: i assume that, if you are able to abstractize the fov as a measure for the circle of confusion, you understand all the steps in between already)

your input is just as helpful, but as you noted there are many angles to look at something. also, asking the right questions is in my oppinion just as important as giving the right answers, so whoever asks the questions is just as "responsible" for the overall usefulness of the discussion as people answering them (if not more). i'm just trying to do my best at my part in here
QuoteQuote:
.
Having spent a lot of time in higher education, I realize different levels of understanding demand different levels of explanation. It is interesting that the more we love and study something, the more demanding we become in our explanation of it.
agreed, and i tend to go on until i understand the "root" cause of anything, this is why i can become annoying to some people, at times . sorry about it.

QuoteQuote:
That is why this forum is so great; it allows for multiple levels of understanding to peacefully co-exist, side by side. Best!
agreed, and as i said before, the insight one can get here on various subjects is amazing (and often not only photography, but pretty much anything you can imagine)

so, to clear a small misunderstanding: i did not label your one-sentence summary as an oversimplification, actually, if you want labels, i would be more inclined to go towards "too complicated" (too abstract), but labeling of any kind was not my intention, i just wanted to help clarify things, for whomever might have been reading (which i did before reading the thread you mentioned, as i did say, sorry about that), so the point was more to give your (very brief and concentrated) statement a bit of context for people who might be reading and be a bit lost in it.

sorry again if my explanation sounded a bit scholar-like (it seems this fov vs. equiv. focal length issue is becoming somewhat of a pet peeve of mine, perhaps that's why i sounded a bit grumpy)

cheers

Last edited by nanok; 04-05-2009 at 04:34 AM.
04-05-2009, 07:03 AM   #119
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Nanok: surely not, i cannot imagine why you would think so. it is not about being offended,
I would think so because there are many, technically advanced people here. From past experience, I have learned that wording is vital to many of them.

Yes, asking the right question is at least as valuable as any answer! I was hoping, in my summary of DOF on MF, to create one, simple sentence which accurately relayed the somewhat complicated interrelationships shared with DOF on different sensors, without any technical jargon. I do not think I achieved my goal. Your commentary on my sentence shows me it needs restructuring. Please, by all means, re-work the sentence to eliminate any ambiguity or complexity I generated--I would appreciate that. Many minds coming together can achieve great things.

QuoteQuote:
Nanok: agreed, and i tend to go on until i understand the "root" cause of anything, this is why i can become annoying to some people, at times . sorry about it.
Do not apologize, I am of the same metal! That is why I was searching so hard to produce a final and simple, one-sentence summation: I'm sure many people here are thinking, okay, shut up and cut to the cheese. For those students, this is desirable. People like you and I, and I have to think Ben also, will always go and on (might be why they invented PHDs. ) BEST!
04-05-2009, 12:39 PM   #120
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QuoteOriginally posted by Jewelltrail Quote
People like you and I, and I have to think Ben also, will always go and on (might be why they invented PHDs. ) BEST!
And don't forget those of us lurking on the outside of the conversation, trying to learn something. Of course, almost 120 posts later, there might not be too many of us lurkers left.
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