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Forum: Pentax Medium Format
10-29-2021, 08:21 AM
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Indeed!
"Equivalence" is too strong a word because crop-factor affects different photographic attributes in different ways:
Using f/2.8 on lens on fullframe does not provide a similar exposure (for most subjects*) as an f/2 on a lens on APS-C. (no crop-factor effect)
Using a lens with a focal length of F on fullframe does provide a similar angle of view as using a lens of focal length of 0.67*F on APS-C. (crop-factor effect)
Using f/2.8 on a lens with a focal length of F on fullframe does provide a similar depth-of-field as f/2 on a lens of the same angle of view on APS-C. (crop-factor effect)
Thus crop-factor has no effects on exposure settings, but it does affect the focal length needed to create images of similar angle of view and does change the f/stop setting of the lens needed to get a similar depth of field, hyperfocal distance, or diffraction.
In engineering, the attributes of a design will have a set of scaling relationships - double all the dimensions in the design and some attributes will double, grow by 4X, grow by 8X, be unchanged, or perhaps even decrease as the size of the designed object increases.
For cameras and lenses, doubling all the dimensions (e.g., scaling a 24 MPix micro4/3 camera and 25mm f/1.4 lens) has the following effects:
Some things grow:
• Focal length: 2X
• Pixel size: 2X
• Pixel area: 4X
• Sensor area: 4X
• Lens aperture area: 4X
• Total weight: 8X (assuming no changes in relative sizes such as the grip)
Some thing don't change:
• wide-open f/stop: unchanged
• exposure settings: unchanged
• base ISO: generally unchanged
Some things decrease:
• Pixel Noise: 1/2X
• Frame Rate: lower ("it's complicated")
• Depth-of-field: 1/2X (for better or worse!)
The deeper point is that different formats are different in different ways -- nothing is really fully equivalent. But if photographers with one format of camera want to create images (or styles of images) which are similar in some way to images created in another format, then understanding how crop factor changes some attributes (but not others) can help.
* Note: For stars and other point-like objects, using f/2.8 on a lens of focal length F on fullframe does provide a similar exposure as using f/2 on a lens of the same angle of view on APS-C. Bigger format lenses and cameras see much brighter stars than do smaller format ones. For example, the primary mirror of the Hubble Space Telescope has only an f/24 aperture but its focal length is 57,600 mm meaning the physical aperture is 2.4 meters across and it collects 4,500 times more light (12 stops!) from each star than does a 50mm f/1.4 lens.
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Forum: Pentax Medium Format
10-28-2021, 07:08 AM
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Ya, that.^
Nothing has created as much confusion as ƒ2.8 on FF is the same as ƒ/2 on APS-c. Because ƒ/stops are exposure values, not DoF values. It's an abuse of the terminology perpetrated by click bait artists.
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Forum: Pentax Medium Format
10-21-2021, 07:26 AM
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Everything you need to know, you can see in the viewfinder.
There is no equivalence that resolves exposure value, field of view and depth of field.
AN example....
 2021-10-09-LumixZS100-group-snapshot - 1 by Norm Head, on Flickr
Lumix ZS100 at ƒ3.2, 1/125s
1/125s is the preferred speed for freezing people in informal snapshots.
If I want to take this with my K-1 I have to use ƒ/16.
The resultant shutter speed would be 1/6s.
In other words, if you try and include DoF in equivalence, you get shutter speeds that aren't functional. Practically you can't take that shot with the same results.
Better to just realize some sensor sizes are better than others and use the cameras to their strength. Don't take snapshots on dull days with large sensor cameras, don't take landscapes with large DR values with small sensor cameras. NeIther large format nor small format can be used interchangeably. In that sense equivalence including DoF is a complete lie.
There simply is no equivlance that can resolve both exposure values and DoF values. And if shutter speed, aperture and ISO and DoF are not all equivalent, (which they aren't) there is no equivalence.
For depth of field ƒ/2.8 small sensor might be 16 FF.
But there is no scenario where ƒ/2.8 small sensor is the same as ƒ/16 FF for exposure. One will be 1/8 the other. You can shoot more depth of field at faster shutter speeds with a small sensor.
Equivalence including DoF does not coincide with equal exposures. Equivalence including DoF is a myth when looking at a camera systems. And pretty much useless in any case.
What I do is get to know my lenses. Shoot a "base" ƒ/5.6 on APS-c, ƒ/8 on full frame and base ƒ3.2 or 2.8 on my small sensor cameras. Experience has taught me what that looks like at various distances. So when I approach a scene, my internal discussion is "do I need more than my base aperture or less? " This is based on my understanding of taking an image with different sensor sizes. There is no way to make this less complicated, using some formula. You have to learn your gear.
You need to understand what you'r base aperture is for each camera...after that, you'll never need to work with equivalence again.
Field of view equivalence you need when you buy a lens if you use multiple systems if you don't understand one of those systems.
The whole "will provide the same image on different systems" is bogus to start with. First of all, if you're taking the same picture with both systems you are by definition making a mistake. Different systems have different strengths. Selecting the right system is the way to go, not trying to take the same image with two different systems. If what you are trying to do is something nobody ever does, maybe you need to rethink the utility of the proposed information.
It's kind of like,"If I have to push my car a km to the nearest gas station a smaller car is better." Finding one isolated reason for buying a smaller car, doesn't make it a better choice overall. There are other factors to consider. It is so annoying to see DoF equivalent proponents excluding exposure time and claiming that a difference of 1/125s is somehow equivalent to 1/6s exposure time. It's not. The whole thing is a fallacy.
How people can with a straight face claim ƒ/2.8 small sensor is equivalent to ƒ/16 FF without mentioning the problem created by shooting 1/8 the shutter speed on the FF is beyond me. It's a clear misstatement of the issues at hand to the point of being intentional mis-information. IN the image above, it could not have been taken with my K-1. There is no equivalent FF image to be had. There is no equivalent image taken on an FF nor could there have been one, given the conditions that day. Equivalence applies only to field of view and focal length. And even then, with two different systems, both will have strengths and weaknesses. They are never truly equivalent.
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Forum: Pentax Medium Format
10-20-2021, 10:50 AM
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Watching this thread now. I see no need to close it yet. The forums allow for dreary topics that aren't political, just not mean ones. As long as no name calling starts and the thread remains respectful, it can go on. Probably if it becomes dull it will wither away on its own.
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Forum: Pentax Medium Format
10-25-2021, 08:56 AM
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So what? This is a discussion forum, not just an information database.
I don't see what the problem is. :confused2:
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Forum: Pentax Medium Format
10-20-2021, 09:09 AM
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They are talking about
1) Depth of field. Depth of field of an f/4.0 lens on a 6x7 camera is roughly the same as the depth of field of an f/2.0 lens on a 35mm (or "full frame") camera. Whether the lens itself is a 6x7 lens or a full frame lens makes no difference.
2) Field of view. The field of view of a 100mm lens on a 6x7 camera is roughly the same as the field of view of a 50mm lens on a 35mm camera. Again, whether the lens itself is a 6x7 lens or any other lens, doesn't matter. If you put a 50mm 6x7 lens on a 35mm camera, it will have the same field of view as a 100mm 6x7 lens on a 6x7 camera.
Since depth of field and field of view are two very important properties, and for some shooters, like portrait shooters, wedding shooters, etc, they are basically what matters, you'd hear things like "a 100mm f/4 lens on 6x7 is the same as 50mm f/2 lens on a 35mm camera". While that statement is incomplete, it allows you to quickly compare properties of cameras and lenses from different systems.
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Forum: Pentax Medium Format
10-21-2021, 08:29 AM
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To the OP: This is the correct answer. You can read this and move on with your life.
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Forum: Pentax Medium Format
10-20-2021, 06:41 PM
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The digital world did not introduce the issue. Photographers have shot in multiple formats since the beginning.
Forget translating one format to another, which imposes mental gymnastics (easy for some, not so for others) every time reach into the bag for a different lens.
The way multi-format photographers have done it in the past starts with the diameter of the film. Yes, I said diameter--what's the distance across a circle that just touches the corners of the frame. Those diagonal measurements are (nominally, which means no intention or need for exactitude):
APS-C: 29mm
24x36: 43mm
33x44: 55mm
645: 75mm
6x6: 80mm
6x7: 90mm
6x9: 105mm
4x5 (inches): 160mm
8x10: 320mm
Lenses with these focal lengths are considered "normal" lenses, which simply means that they are the same focal length as the diameter of the format (and that's all it means--it says nothing about the design of the lens, which is and should be a whole separate taxonomy).
Once we establish the normal lens, everything else is a ratio of that.
(Sidebar for geeks--OP should skip: It's a mistake of terminology to refer to shorter-than-normal lenses as "wide angle" and longer-than-normal lenses as "telephoto". Those terms apply to the design of the lens. A wide-angle lens's physical glass is centered ahead of its optical center, which is necessary for cameras with reflex mirrors to get the glass in front of the mirror. Another term for these is "reversed telephoto" or "retrofocus" and the design was first commercialized in the late 40's by Angenieux It made possible short-focal-length lenses on the new SLR design that had just emerged--the Exakta. Telephoto lenses sit further back than their optical center, making it possible to have a physically shorter lens for a given focal length. They did by adding a magnification corrector behind a conventional lens, which forced a few compromises. These terms aren't as clear for modern lenses on smaller cameras because of the complexity of the designs. But they don't mean "short" and "long". It's quite possible to have a wide-angle lens with a longer focal length--the 55mm lens for the Pentax 67 is a wide-angle lens, even when it's adapted to an APS-C camera, on which it would be nearly double the diameter of the format. And a 45mm wide-angle lens for the 67 makes a perfectly usable normal lens when adapted to a 35mm camera, but it's still a wide-angle design, despite that the smaller format can't make use of that fact. Fun fact: Most lenses used on large-format cameras are neither wide-angle nor telephoto, being approximately centered physically around their optical center. Some are wide-field designs, confusingly called wide-angle, because their coverage angle is greater than about 45 degrees. That means simply: greater than is needed by a lens of normal focal length to cover the format. This allows shorter lenses to cover the format and provide for movements. I routinely use a 300mm lens on my 4x5 camera when I want a lens about twice normal, even though that particular lens was really marketed for use on 8x10 cameras. And so on. The point of the fun fact is that large-format photographers are as interested in lens design as in focal length, because it dictates what they can do with it on a view camera with movements. End of sidebar.)
"Standard" lenses are not exactly "normal" lenses, though the terms are used interchangeably. The "standard" lens for a 35mm camera is traditionally 50mm, while the normal lens is 43mm. The standard lens for 8x10 is traditionally 12" (305mm), while the normal lens is a bit longer. But here's what you should remember: The normal lens will provide a similar field of view on its respective format as any other format's normal lens. So, a lens that is one half the focal length of the normal lens will provide the same wide field of view on its respective format. The 28mm end of the 28-45 zoom on the 645z is right at one-half of the normal lens. A 21mm lens on a 35mm camera is very close to one-half of the normal lens on that format. A 75mm large-format lens on a 4x5 camera is not far from one half of the normal lens for that format. And they will all provide similar fields of view, as long as one compensates for the shape of the format.
I know what lenses that are one-half of the normal lens do on some of my cameras, and so I can know about what they will do on all of my cameras. By "know what they do" I can tell from looking at the scene that it's the lens I want to use.
Going longer than normal: A popular focal length for portraits is not quite twice the normal focal length, say, 80mm on a 35mm camera (when twice the normal focal length would be closer to 90). On a 645z, with a normal focal length of 55mm, not quite double that is--shazam!--105mm, which is why a certain fast "standard" lens for the P67 is particularly popular for adaptation. And it's why the preferred portrait lens for the P67 is the 165/2.8 (and why Pentax designed a lens of that focal length with such a large aperture). And it's why the 50/1.4 "standard" lenses for 35mm make such good portrait lenses for APS-C. I know what a lens a little less than twice the normal focal length does on any camera--and it does about the same thing on all cameras.
Greater precision than "half" and "about twice" is a waste of arithmetic--it will get you no closer to a worthwhile conclusion. But it will help you decide which lens to grab. Your feet can make further adjustments.
Now, about the f/stop and aperture--a rabbit hole if there ever was one. The aperture is the size of the hole as projected to the rear of the lens, but nobody ever measures that diameter. It doesn't matter. What matters is the ratio of that diameter to the focal length of the lens, because that's what describes how much light is getting through no matter what that focal length happens to be. So, f/4 on one lens moves the same light as f/4 on any other lens no matter the focal length (roughly speaking--there are differences in transmission efficiency that work at the margins). Format size has no role in defining the f/stop. Format size is just how much of the scene projected by the lens we happen to be recording.
BUT...(and there's always a "but"), some people are interested in matching the rendering of the out-of-focus areas between lenses sized for different formats. Depth of field is dictated by focal ratio (f/stop) and magnification (focal length). To get the same degree of blur in that distant background, you can't change one without changing the other. A lens of low magnification (as in, shorter than normal) needs a lower f/stop than a lens of high magnification. This is why a lens that twice-normal portrait lens needs a wider aperture (i.e., lower ratio, or f/number) to achieve the same degree of out-of-focus blur. One can consult depth of field tables to determine the similarities, and I agree with the point upthread that similarities are the best you'll get. Experience with specific lenses will take you the rest of the way--there are too many confounding factors at the subtlety level.
Rick "working in multiple formats for 45 years" Denney
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Forum: Pentax Price Watch
06-10-2019, 04:56 PM
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Pentax K-1 Mark II with Pentax D-BG6 Battery Grip is sold at B&H at $1 above the price of a body alone: $1797:
Pentax K-1 Mark II DSLR Camera Body with Battery Grip Kit B&H
I believe the body alone has been running at $1796 for several months now. So, you get the $200 grip for just $1.
PS. I wonder if it is a sign for an upcoming price reduction for the body.
I don't see a reason why: It seems to me that it would be too soon for a new body to come out at this point, especially since there were no rumors, whatsoever.
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Forum: Welcomes and Introductions
06-15-2018, 12:58 AM
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Welcome to the forum, many of us older film guys know where your coming from. ;)
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Forum: Welcomes and Introductions
06-15-2018, 06:38 PM
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Welcome from Australia. :)
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Forum: Welcomes and Introductions
06-24-2018, 04:58 AM
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G'day mate and welcome to the forum :)
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Forum: Welcomes and Introductions
06-27-2018, 06:04 AM
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welcome to the forum. congrats on your goodwill find!
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Forum: Welcomes and Introductions
06-27-2018, 10:10 AM
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Forum: Welcomes and Introductions
06-27-2018, 08:34 AM
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Welcome to the forum! Your camera find is a nice way to get started.
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Forum: General Photography
04-20-2019, 11:53 AM
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I have one of those lenses, bought for $5 from a secondhand goods shop. Finally, I know what the XR stands for. :lol:
It is a very fast (moving) lens as well:
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Forum: General Talk
04-16-2019, 08:07 AM
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The value of the Pentax forum is it's ability to reach out to people who are having problems, but haven't made up their minds and are still open to being influenced. Many come here looking for answers, not to state their opinions. The ones that give us the most trouble are those who state an opinion as a prelude to telling us what problem they are having, a very round about way of asking for help. We don't know if they've made up their minds and just want to argue, or if they are honestly looking for help.
PF is a tremendous resource, because many people who have had to figure things out on their own over days weeks and months, can pass on that knowledge in single post. It's an amazing resource. Pentax is small so, a good percentage of the people in the world who know much about Pentax are accessible here. Regardless of what you want to shoot, someone here has done it. I'm willing to bet for other brands, you wouldn't find the level of expertise you find here on a public forum. Just based on some of the amazing posts, my guess is there is a higher percentage of technically knowledgeable people here than most camera forums.
Honestly, framed the right way, I've never had a question someone couldn't answer.
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Forum: Pentax Full Frame
04-11-2019, 09:24 PM
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The DA 55-300 PLM is very good. Yeah, it’s a crop lens, but that’s not a bug, it’s a feature. It crops to 450mm on the long end. It’s relatively small and the focus is fast. Very fast. F/6.3 on the long end is a definite drawback in non-daylight conditions. Other than that it’s a terrific lens.
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Forum: Pentax Full Frame
04-11-2019, 10:43 PM
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just sharing quick thoughts.
If "weight" is an important factor (let's not even get into 'size'), then you can definitely cross out the DFA 150-450.
Although "weight" is subjective, since a 1.5kg lens might be considered 'relatively light' to a person and may also be considered "relatively heavy" to another person".
But becuz you indicated that the FA* 70-210 being "already heavy", Thats why i can say you can already cross out the DFA 150-450.
(Do you mean the FA* 80-200? Becuz not sure if there is FA* 70-210).
Theres no "best way".
What suits one person, may not suit another.
But a good backpack should help go some way to lugging around lenses (something like a Lowepro Flipside 400 perhaps?).
As for prime or zoom, only you can best answer which might better suit what you have in mind.
The thing is, too many paxes always try looking for a perfect product/item.
There's none.
People got to remember, "there is no perfect solution, only a perfect compromise".
Without really knowing some other factors that you need to consider, i could picture the Sigma 100-300 f4.0 to be the "perfect compromise" that you might want to consider.
But honestly, if "weight" is something you think you can overcome and just live with it, and finances are flexible (ie, you can and don't mind to go upwards to USD1500-1800), the DFA 150-450 should be as perfect as you can hope for.
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Forum: Pentax Price Watch
02-26-2019, 07:56 AM
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It was me, thank you very much! A friend of mine will bring it to my place in about two weeks.
Thanks again
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Forum: Pentax SLR Lens Discussion
04-06-2019, 02:32 PM
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"I'm going to start exercising", "I'm going to eat better", "I'm going to get a different job", "I'm only going to buy one more lens"
All great quotes overheard at a new years eve party...:)
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Forum: Pentax SLR Lens Discussion
04-06-2019, 01:56 PM
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@Craigbob, Craigbob, Craigbob, haven't you been reading the Pentax Forums Advice column?
Rule Number One: Never -- never -- display all of your lenses at one time in one place. Although you might assume that your GF is out shopping, she could come through the door at any time and face that wall of goodies.
Rule Number Two: If you do feel obliged to gather all of your lenses on one table, remove all lens hoods to make the collection look smaller. Maybe she won't notice.
;):lol:
- Craig
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Forum: Pentax Price Watch
03-20-2019, 12:01 PM
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Forum: Pentax Price Watch
03-18-2019, 12:13 PM
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Forum: Pentax Price Watch
03-18-2019, 02:12 PM
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Got it, thank you so much!
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