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Matt, you left the pickles and onions off of your Big Mac. Crap. I knew I should have looked it up. ages ago (permalink)

you guy all are wrong. thats not what B3ngi was talking about. what he meant is if you keep the SAME FOCAL LENGHT, say 50mm for all format (it becomes wide angle on a 4x5, and tele on a digi compact) you will get the same exposition. but for some obscure reason, people say that a 50mm (f2.8) lens on a digital compact will gives MORE ) dof than a 50mm (f2.8) on a medium format 6x6. it has to do with the circle of confusion. i totally don't understand it ages ago (permalink)

Voxphoto I was comparing using one lens at one focal distance, not one field of view!!!! So please be careful with your "babble of misinformation" because you are purveying a babble of misinformation by not comparing that same thing. Now I will prove what you found with the same way I proved my point. Lets take 3 cameras with 3 different lenses that offer the same basic field of view. 35mm film w/50mm, 6X7 w/90mm and a 4X5 w/150mm. All shot at f8 focused at 10 feet. 35mm film NF=8.04, FF=13.16, DOF=5.09 6X7 NF=8.65, FF=1.84, DOF=3.19 4X5 NF=9.11, FF=11.07, DOF=1.96 NF=near focus, FF=far focus, In this case the smaller format has a greater DOF. In all honesty this is a more realistic, true to real photography, test than my first, which is more theory than practical. So Voxphoto it appears I know what I am talking about, and understand DOF just fine. Originally posted ages ago. (permalink) MJM67 edited this topic ages ago.

@Equivalence VOXPHOTO and I posted at the same time so I didn't see his post until after I posted. Regardless his answer doesn't fully explain the OP's question regarding DoF at the same focal length but differing film sizes (as the only variables). No question that VOXPHOTO's post, taking into account differing focal lengths and image size, is correct. What I was suggesting is a reason why a physically smaller lens (with smaller coverage) would have greater DoF than a physically larger lens that has to cover a larger film format - setting aside relative focal lengths, angles of view and image size on film. Which is direct response to the original question. In re-reading this thread a few times only 'luisclub' and I trying to answer the OP question. Maybe you should read the OP question and respond to that, instead of trying to correct me. ages ago (permalink)

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This is great. No one knows the correct answer to a simple question, so it turns into a debate. ages ago (permalink)

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Matthew - Enlargement is a factor in depth of field calculations, hence CoC. This is simply a matter of definition. It's like a Big Mac is two patties, special sauce, lettuce, cheese on a sesame seed bun. You can't wander in and say "I've determined that the special sauce isn't required". Take away the special sauce, no matter how confusing it is to you, and you're just not talking about Big Macs. So in the strict sense, you're wrong – CoC is always required. But there is a glimmer of truth in there – you're simply measuring something else: the amount of blur on the negative. This is, categorically, not the same thing as depth of field. It's also not any surprise to those of us who paid attention in our theory classes: lenses produce the same image regardless of what happens to be behind them. It's a real shocker, isn't it. And since you bring it up, you do get theory classes at your "school," right? They're hopefully teaching you about optics, at least a little? In other words, you're going to a school, and not just feel-good-about-your-so-called-art group therapy sessions? Because your little diversion above is a pretty fundamental mistake. I'd be sad to think you could earn a BFA in photography without knowing how depth of field is calculated. Originally posted ages ago. (permalink) matt edited this topic ages ago.

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to put it simply; remember when you pinprick a tiny hole in a paper, and when you look through, you see everything is sharp? the oibject nearer you and the object further away? that's aperture, which I assumed you understand. the bigger the aperture (hole get bigger), the less depth of field. negative/sensor size are almost exactly like aperture - the smallest sensor/negative (at F/2.8) the larger the depth of field. that's why digital; compact almost never have a narrow depth of field from a distance (usually when it come to macro, they have a noticable amount of depth of field). tiny sensor digital compact - at F/2.8 it has the depth of field of F/13 despite the speed of F/2.8 so; digital compact (tiny sensor) F/2.8 - depth of field of F/13 digital SLR (APS-C sized sensor) F/2.8 - DoF of F/4.2 digital SLR (full-frame sensor) F/2.8 - DoF of F/2.8 6x4.5 medium format F/2.8 - DoF of F/1.8 6x6 medium format F/2.8 - DoF of F/1.5 6x7 medium format F/2.8 - DoF of F/1.4 10x8 large format F/2.8 - DoF of F/0.3 That if you measure it by 35mm standard (which I think everyone does here), I'm shite at explaining thing so I hope I managed to explain it clearly. Originally posted ages ago. (permalink) edscoble edited this topic ages ago.

I'll throw in my 2 cents. I think the difference is due to the actual diameter of opening in the iris. The smaller the diameter the more "pinhole" effect (smaller circle of confusion). As a model, lets say f2.8 for a film size of 1cm by 1cm you need a hole 1cm in diameter. For film size 2cm by 2cm you need a hole that lets in four times as much light to get the same amount of light onto the film as you did to get "f2.8" on the 1x1cm film. The hole on the 2x2cm camera has to be 2cm in diameter. Same amount of light reaching the film in both cases, but much reduced pinhole effect and shallower depth of field on the larger film. (I'm sure on the theory but my math is a little stale so I may be off a little bit on the exact numbers.) As real world proof, compare the diameter of the primary objective (outermost lens) on different film/sensor sizes. On a little P&S digi-cam (small sensor) F2.8 lens is about as big as the end of your middle finger. F2.8 on a 6cm by 6cm camera is about two inches across and a f2.8 for an 8x10 is about the size of your fist. As the lens gets bigger the pinhole effect is reduced and the DoF gets smaller. NOTE I am making many generalizations here. Lens design (number of elements and groups) makes a difference - fewer elements, less light loss - smaller lens etc. I'm also taking about prime lenses only; fast, constant aperture zooms have disproportionately large primary objectives. ages ago (permalink)

GENERALLY SPEAKING, as format size increases, depth of field decreases. As format size decreases, depth of field increases. They have an inverse relationship. I should point out that you will get the SAME depth of field in both formats if you change your lens focal length and aperture proportional to the increase in format size. 135 film is 24mm x 36mm. 120 film shot on a 6x6 camera is 56mm x 56mm That's a roughly 3.6x increase from 135 to 120, right? So let's say you take a shot on your 135 with a normal 50mm lens at an aperture of f/2.8 To get the same depth of field on a 120 6x6 frame you will need to shoot at 3.6x times that - which would be 180mm at f/11 Hope that helped a little. ages ago (permalink)

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I didn't quite understand why there is a smaller DOF with MF vs 35mm. For the same Focal length, and aperture, you will have a greater DOF in MF.. is this right? Is it because the film is bigger? It was partially discussed here, but i didn't get it. I'm just curious.. Benji Originally posted at 7:25AM, 28 August 2008 PST (permalink) brichoz edited this topic ages ago.

louisclub this is what he said; For the same Focal length, and aperture, you will have a greater DOF in MF.. is this right? Is it because the film is bigger? So where did I misunderstood him? Originally posted ages ago. (permalink) edscoble edited this topic ages ago.

Sure on the film itself, of course. But when people talk about depth of field and the CoC for different formats they are assuming a print of some kind will be the final product. Sounds like you don't actually print your images. Do you just look at your slides (and negatives) through a loupe? ages ago (permalink)

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And so now we know why some satellites never make it into orbit.... ages ago (permalink)

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For Free!! go to Mamiya's netsite and download some lens manuals from their netsite for free, You can still get the older RB67 lens manuals, which have excellent information of this type. They're Acrobat files so they can print out as well for easier reading. ages ago (permalink)

Here is a link to a great little program. It has a DOF calculator and a bunch of others. Play with it and it might help you figure it out. tangentsoft.net/fcalc/ ages ago (permalink)

louisclub, you are making an assumption on behalf of the OP. He doesn't mention that the shots are taken from the same distance. Circle of confusion is what I think you mean and it isn't necessarily true. Depends on the camera. Just because a camera shoots medium format film does not mean that the lens is automatically larger. Aperture size is a ratio between the diameter of the opening and the focal length. The shorter the focal length the smaller the aperture can be and still achieve the desired f/stop. This is why 300mm prime lenses that go down to 2.8 cost a fortune, the glass has to be huge. In the end it's all geometry as I mentioned above. Originally posted ages ago. (permalink) Steve.Korn edited this topic ages ago.

eyepenn--- Actually there is a correct answer, several of us know it and have been posting it, but there is one who thinks he knows the answer and is very annoying to those of us who do!!!! But please look it up for yourself. You will see who is right. ages ago (permalink)

Actually, I'm not. I looked up the theory of CoC. And my explanation is correct, It just was not taking in the factor of CoC. And if I would have read the post all the way though, the question has been answered with basically the same explanation as i gave. And fyi your example for your depth of field calculator makes no sense. Take a 4x5 with a 150mm lens ok. focus it on your subject take the shot. then load a piece of medium format film in there, lets say u cut one piece like 6x7cm take the shot again with out even touching the camera because the focus is set already. what will you get ohhh wait a cropped version of the 4x5 no way! with the same depth of field. seriously think about it. and i know this is true because i have done it. but with 35mm film in 4x5 film holders. you are correct though if you wanted the same field of view with the formats the larger would have to be closer which would reduce the dof which I said in my post earlier. Conclusion same fstop, same focal length, same distance away from subject, and same focal point. = the same dof when your not enlarging your film for example looking at slides. The only thing different is the FoV between the formats. pwn3d MJM67 p.s. Hey by the way MJM67 where did you go to school for photography? And with all that gear you have you can actually do the experiment for your self instead of relying on a incorrect, windows only, open source pos dof converter. sorry im sort of mean sometimes. 0__o ages ago (permalink)

Area51Resident - I think you should read Voxphoto's blog post. ages ago (permalink)

Because focal length must scale up in proportion to the film format dimensions to maintain the same angle of view, the two ways of phrasing the statement are equivalent. ages ago (permalink)

I think simply B3nji got confused about what was mentioned in that thread he linked to. Someone said that for the same angle of view and F-stop, medium format has narrower depth of field. I think this is what most people are talking when they talk about medium format having less depth of field, not comparisons using the same focal length and attempting to achieve the same framing on different formats. And the term circle of confusion doesn’t have anything to do with film coverage, it's the threshold where an out-of-focus point ceases to look like a circle and appears to be a dot. This is used in determining depth of field for a given aperture and it is directly related to degree of enlargement. Medium format doesn’t have to be enlarged nearly as much for a standard size print (8x10 or whatever you want to use as your reference), so it has a larger circle of confusion than 35mm. So standing in the same position, a photo shot with an 80mm lens on 35mm film will have less depth of field than one shot with an 80mm lens on medium format for any given aperture, because you are enlarging the film more to reach a given print size. BUT if you are comparing photos shot with the ‘normal’ lens for each format, medium format will have narrower depth of field at any given aperture. ages ago (permalink)

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I tend to think of it in quite simple terms - to cover the same field of view, you're using a longer lens which will always have a reduced DoF. The 80mm 'Standard' lens on a 645 will show the same field of view as a 50mm on a 35, but it's still an 80mm lens. Same with my 135mm Optar on a 4x5 Speed Graphic - equiv 50mm field of view but it's still a 'telephoto' lens and needs to be stopped accordingly. Correspondingly, I'm on the hunt for an F2.5 178mm Aero Ektar (WWII-vintage aerial photography lens) for mounting on my Speed Graphic! Insanely narrow DoF! Originally posted ages ago. (permalink) drewleavy edited this topic ages ago.

Wow this is still going on... Having reread the comments here and VOXPhoto's blog and other sources I think I have an idea where some of the confusion (mine included) comes from. There are two factors at play - lens focal length and CoC. There are guidelines and assumptions in what is/isn't the correct CoC for a given film size - there is room for subjectivity here. However, given that focal length trumps CoC and is dominant it determining DoF I think VOXphoto's statement, from his blog, could be reworded to be clearer. "When f/stop, distance, and lens angle-of-view are all held constant, the larger the image format, the shallower the depth of field." The above could be clearer if it read: "When f/stop, distance, and lens field-of-view are all held constant, the longer the focal length, the shallower the depth of field." Larger film/sensor requires a longer focal length to produce the equivalent FoV (compared to a smaller film/sensor size). Since focal length is preeminent factor in DoF, large formats have less DoF (because they use longer lenses). (VOXphoto - Apologies in advance if I have erred in my suggested edit to your conclusion.) Comments? ages ago (permalink)

Matthew-- What DOF does is directly related to the variables that are changed. In my first example I only changed one variable---the format size, which in turn made both the FOV and DOF change. In this case the larger format would have a greater DOF In my second example I held the FOV constant and changed the lens focal length to keep the FOV the same and changed the format. In this case the smaller format has the greater DOF. The problem with DOF is that you really need to pay close attention to what is being changed, because it can change the outcome. I answered the OP--he never asked about FOV. He ask same focal length, same aperture---which my first post gave the results for (the one causing the problems). But I will admit it is not a realistic situation, FOV is the variable you would keep constant, when changing from one format to the next and wondering about how DOF will change. Good shootin to all and may all your shots be good ;) Originally posted ages ago. (permalink) MJM67 edited this topic ages ago.

For the same Focal length, and aperture, you will have a greater DOF in MF.. is this right? Is it because the film is bigger? It's basic geometry. The closer I am to my subject, the less depth of field there will be. If I shoot with an 80mm lens on both my MF and 35mm cameras, I will have to be much closer to my subject with the MF camera to frame my picture the same way I will with my 35mm camera. Therefore, because I am closer to my subject with the MF camera, the geometry is quite different between the two cameras in relation to the subject. The reason that the 80mm has a different field of view in each camera, from the same position is because the negatives are different sizes. ages ago (permalink)

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It's confusing because there are two factors: With a larger film format you need a longer lens focal length to achieve the same angle of view (thus larger format --> shallower DOF) With a larger film format, the negative requires less enlarging to yield the same-sized final image, i.e. a greater circle of confusion is permissible (thus larger format --> deeper DOF) It just happens that the focal length effect is the stronger one; so the net effect is for larger film to result in shallower DOF (all other factors held constant). I did a blog post a while back which goes into some more detail. ages ago (permalink)

B3nji: Actually your excerpt from me & VOx, if you read carefully, are working against each other ... hence I didn't mention the CoC to avoid potentially clouding the issue for some readers But the CoC enlargement factor mentioned by VOx is usually overwhelmed by the stronger DoF factor so in the net the latter still rules. An indeed, if you imaging shooting slides and looking at the resulting slides say by the same magnification loupe (say 6x) then the CoC factor is eliminated Glad my input helped =) ages ago (permalink)

woah... I already pointed out that I thought the OP misunderstood the post in the thread he linked to, which is why I posted as I did. What I was suggesting is a reason why a physically smaller lens (with smaller coverage) would have greater DoF than a physically larger lens that has to cover a larger film format - setting aside relative focal lengths, angles of view and image size on film. Which is direct response to the original question. And I think that's where you're confusing things. You could stick a 4x5 lens on a 35mm camera and at a given aperture you'd still get the same depth of field as a 35mm lens of the same focal length. Originally posted ages ago. (permalink) (mjh) edited this topic ages ago.

Thanks for your input guys.. As for what i actually ment originally, it wasn't really clear in my mind either.. i guess i was troubled by the fact that with a bigger negative format, you will have a smaller DoF. Not knowing how distance and focal length equivalents with 35mm would have an influence. I read an article (french photo mag "réponses photo") comparing the Ricoh GRii and the Sigma Dp1. Both have a 28mm fixed focal length. the Ricoh has a apt of 2.8, the Sigma f/4. Ricoh has a smaller sensor than Sigma. Comparing at same framing (hence not the same distance??), same apt (f4)(and obviously same focal length 28mm, this being, i assume the 35mm equivalent in respect to the sensor size) the sigma had a quite noticealble smaller DoF!And in the article, they were saying this had to do with the bigger sensor the sigma has. (without really explaining why, it wasn't really the aim of the article) Circle of confusion would be the right term here.. SO is it the geometry explanation? i don't really buy because you'd only have to move forward just a tad to get the same framing with those 2 cameras, and that wouldn't explain that huge DOF difference. Or is it the aperture opening having to be bigger in order to have the same amount of light hitting the sensor? why not? Or is it the the focal length effect? on wikipedia: To maintain the same field of view, the lens focal lengths must be in proportion to the format sizes. Assuming, for purposes of comparison, that the 4×5 format is four times the size of 35 mm format, if a 4×5 camera used a 300 mm lens, a 35 mm camera would need a 75 mm lens for the same field of view. For the same f-number, the image made with the 35 mm camera would have four times the DOF of the image made with the 4×5 camera. BUt there's no real explanation.. I dunno.. i'm comfused.. please help more? PS: i know i mentioned digital. i really didn't mean to.. but we're just talking about optics here.. nothing more.. :) ages ago (permalink)

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en.wikipedia.org/wiki/Depth_of_field DoF has nothing to do with the format nor the image you are trying to get. 50 mm lens closed to 5.6 and focused at 10 meters will always have the same DoF no matter if it is MF, LF or 35mm camera. It will also give you a different viewing angle but that is not the point. Do a test. Take a 80mm lens on 35mm and MF. Set the same aperture than focus it at say 4 m. You will have the same DoF. Different viewing angle but same DoF. ages ago (permalink)

Please Click on this image img84.imageshack.us/my.php?image=filmformatstq3.jpg I made this to show you the different film sizes compared to each other. If you didn't know some basic info on lens, 5.6 or any aperture for that fact doesn't matter what focal length lets the same amount of light though so a 50mm lens at 5.6 for a 35mm lets the same amount of light in as a 150mm at 5.6 on a 4x5 feild camera, the only thing different between the two is the size of the image circle thrown on to the film plane. Ok now since you know that if you look at my example of comparing the film formats most of you know the crop factor in dslrs of averagely 1.5 crop compared to 35mm. going down from 8x10 is basicly just cropping down from there as u can see in the diagram. So a 270mm on a large format will allow you to get the same depth of field as a 35mm camera but!!!! with alot wider field of view which would allow you to see more of the bokeh. As for medium format it works exactly the same, a 80mm at 2.8 on a hasselblad will give you the same depth of field as a 80mm at 2.8 on a Ae-1, Just the thing is it looks different because of the wider field of view on the hasselblad which lets you see more of the out of focus area. All of this these examples I am saying to you is given you take the photo from the same place. Composition wise if you wanted to fill the frame of your subject in both formats one the larger format would have to be closer at the same focal length to have the same composition and that fact you are closer means the depth of field will be shallower since you have to focus closer. But to basically to answer your question no the depth of field will be the same on a mf camera or 35mm camera at the same focal length and the same apture, if taken from the exactly same spot, the only thing different will be the field of view. I hope i explained this well enough and i hope my diagram i put together helps you out. its just as the crop factor on dslrs just on a larger scale. ^__^ ages ago (permalink)

@edscoble, okay what you were saying wasnt wrong, but you are not answering the question. what i think he meant is , why with a 80mm on medium format, f2.8 subject 10feet, you get less DOF than a 80mm on a 35mm , f2.8 and subject at 10 feet. SAME focal lenght, SAME aperture, SAME distance. only the film size that differ. it appear that lens designed for 6x6 has a bigger circle of conscription(?, not sure of the exact word) , which has to do with the covering film area . i don't understand why its like that, but if you check some dof calculator online you wont get the same dof for two SAME lens and subject distance, but changing only the film size. ages ago (permalink)

Matt, you left the pickles and onions off of your Big Mac. ages ago (permalink)

Peta W ".. which means MF wide angle has same DoF as a 135 film format tele lens, and we know that's kind of thin ... hence for same angle of view, MF has less ( thinner ) DoF than 135 format. This is slightly tricky argument, but not too difficult to understand." VOx "Larger film requires less enlargement to produce a same-sized final image. So the acceptable circle of confusion can be bigger; and the apparent DOF will be deeper." I think i've wrapped my head around this now.. these seem to be the most understandable and plausible explanations to the MF DoF issue. to me at least.. thanks guys for your input, really appreciate it! ages ago (permalink)

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MJM67 asked Why don't you do some test Yeah, I did, and here's what happened. 6x4.5 versus digi point & shoot. If you hold all the other factors constant (f/stop, distance, lens angle of view, image viewing size), larger film format yields shallower depth of field. I go so exasperated with the babble of misinformation in threads like this that eventually I gave up, and started my own blog.... Originally posted ages ago. (permalink) Voxphoto edited this topic ages ago.

Matthew----sorry your wrong!!! "But to basically to answer your question no the depth of field will be the same on a mf camera or 35mm camera at the same focal length and the same apture, if taken from the exactly same spot, the only thing different will be the field of view. " You are not taking in to account the theory of "circle of confusion" Lets take one lens at one aperture focused at 10 feet on 4 different formats. 90mm @ f8 on a DX, 35mm, 6X7, & 4X5 DX---Near focus 9.44ft, Far focus 10.61ft DOF=1.16ft 35mm--Near focus 9.32ft, Far focus 19.79ft, DOF=1.47ft 6X7--Near focus 8.65ft, Far focus 11.84ft, DOF=3.19ft 4X5--Near focus 7.85ft, Far focus 13.79ft, DOF=5.94ft. With those variable all equal the larger format will have a larger DOF. Again read my prior post and download the f/cal and play with it. The program is based tried and tested optical formulas. The size of the COC is also based on what is accepted in the photo industry. You will find that given the same field of view, focused at the same distance, and same F-stop the smaller format will have a greater DOF. ages ago (permalink)

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I also struggled with this topic a while back... but this sums it up quite well "When f/stop, distance, and lens field-of-view are all held constant, the longer the focal length, the shallower the depth of field." Thanks folks... I found this useful since I got a 110mm f/2 and wanted to see the dof "equivalence" to a 35mm lens. www.dofmaster.com/dofjs.html Medium format: at 110mm, f/2, 3 feet, total DOF is 0.04 ft 35mm format: (equivalent field of view is 72mm), f/2, 3 feet, total DOF is 0.06 ft. I calculated equivalent FOV roughly from this table. photo.net/photo/lens-table Have fun shooting everyone! Originally posted ages ago. (permalink) Ayoumali edited this topic ages ago.

B3nji's elaboration on his original post which mentioned the French article comparing Ricoh and Sigma contributed to much of the confusion for B3nji. Simply coz in the context of compact digital cameras, the focal lengths are often "normalized to full frame 135 format" and not the actual physical focal length. The main reason for the "normalization" practice is because the CCD or CMOS sensors has many sizes and quoting the actual focal length doesn't really mean much to anybody. The "same" 28mm on the Ricoh and the 28mm on the Sigma are simply not really the same, and not 28mm. The simplest way to visualize the DoF concept is to imagine the cone of light formed by the actual aperture ( not the f/number, but the actuall diameter, say in mm ) falling onto the film plane which is (for simplicity) at a distance equal to the focal length of the lens. For very small apertures, imagine f/90 for 50mm lens ( 50mm/90 = 0.55mm diameter ) -- the cone of light coming from a point of the subject (assume at infinity for simplicity) falling onto the film plane would be very narrow. Even when the subject is out of focus in theory, the very narrow cone of light forming the image makes it still fairly close to a point (in focus) instead of a circle ( blurred ) Imagine at this point you open up the aperture, to say 5.6, the cone of light gets much fatter ( 50mm/5.6 = 9mm for a 50mm lens ) hence DoF is much thinner. Does film size make a difference to DoF ? The "cone of light" visualization also offers an easy to understand answer -- Same physical focal length ( not the wishy washy "equivalent to 135 format" focal length often quoted in digicams ), say 50mm, and same aperture, say 5.6, then DoF for same subject distance has to be the same ... well, if we ignore the film and just talk about projecting to ground glass to eliminate the can of worms around Circle of Confusion etc. If we bring in the film size consideration, then it's easy to understand that for same focal length and same subject distance then -- 135 captures a narrower angle of view (relatively more tele like), and MF or 4x5 captures a wider angle of view (relatively more wide angle like). ... which means MF wide angle has same DoF as a 135 film format tele lens, and we know that's kind of thin ... hence for same angle of view, MF has less ( thinner ) DoF than 135 format. This is slightly tricky argument, but not too difficult to understand. Let's not bring Circle of Confusion into consideration -- Let's imagine you shoot chrome and only has 1 magnifier to disregard the complexity of considering different enlargement factor due to film size difference. There's little incremental knowledge in considering CoC influences, but very likely to get confused again -- not a good investment of time. Hope this helps. Originally posted ages ago. (permalink) peta-W edited this topic ages ago.

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the point is , if you take a 150mm lens made for 4x5 , and a 150mm made for 35mm , chances are that you won't get the same DOF because of the circle of confusion standard. of course if you keep the same lens and just crop, it will be the same dof. but that's not what we were talking about. circle of confusion is real part of optics. Matthew Avignone, you explanation missed that, so wasnt correct. ages ago (permalink)

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The answer is 42. We just haven't determined the question. ages ago (permalink)

Matthew-- I am not going to argue with you because you are wrong. DOF has always related to the final print, NOT the negative, who looks at their negatives? It has do to with the degree of enlargement. That is why larger formats will have larger DOF, they need less enlargement to make a final print, so they have out of focus points enlarged less, so it is less noticeable. Thats why different formats have different CoC's and the CoC gets larger as the format. Now that incorrect DOF calculator. Why don't you do some test. Get some DOF scales for different formats and check them against the values give in by the program. You will find out that the program is correct. It uses scientifically proven optical formulas and accepted CoC's so how can it be incorrect??? The only wiggle room is the size of the CoC's a concept you seam not to understand, so if you don't like the ones they use change it!!. I have played with DOF on my different formats it has always amazed me the amount to DOF on my 4X5 especially with a 300mm lens, Way more than 35mm film. Same with a 50mm on my RB vs 50mm on 35mm film. In both cases the 35mm film won't touch the DOF of the larger formats in the final print. So I didn't go to school for photography, I have a degree in geology, but am a Fire Fighter. I don't know if you went to school for photography, but if you did you might want to see about getting your money back and going to another. Find one that will teach DOF relating to format size and that DOF is somewhat subjective. Good day may you learn something new everyday!! Originally posted ages ago. (permalink) MJM67 edited this topic ages ago.

LOL i only like ketchup on my big macs, which actually makes them double cheese burgers sort of. and as for my examples idk what to say, i guess my logic and experiments will have to be posted some time soon. and i do enlarge my prints lol, the old fashion way on an enlarger, easel, and silver gelatin fb paper, and hopefully soon will be platinum prints on archival cotton rag. also MJM67 your numbers from your calculator actually make sence this time last time the larger formats were gaining a deeper depth of field, now they make sense. but yeah sorry for getting carried away. And i hope to get my examples up soon. Originally posted ages ago. (permalink) Matthew Avignone edited this topic ages ago.

"SO is it the geometry explanation? i don't really buy because you'd only have to move forward just a tad to get the same framing with those 2 cameras, and that wouldn't explain that huge DOF difference." You'd have to move forward more than a tad, you'd have to at least halve the distance. ages ago (permalink)

lukasz_omasta said, 50 mm lens closed to 5.6 and focused at 10 meters will always have the same DoF no matter if it is MF, LF or 35mm camera But that's not correct. Larger film requires less enlargement to produce a same-sized final image. So the acceptable circle of confusion can be bigger; and the apparent DOF will be deeper. By the way the term "circle of confusion" is a sort of grandiose way of saying "how big can the blur get on the negative before it becomes noticeable?" Circle of Confusion diameters for different film formats are not set in stone; they depend on the final viewing conditions and are somewhat subjective. But in general the larger the film, the larger the CoC that is permissible. ages ago (permalink)

Euclid discovered the law of reflection. This states that light travels in straight lines and will reflect from a smooth surface at the same angle it hit ...