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06/15/2006 09:32:16 PM · #26 |
Originally posted by wavelength:
Sorry to digress, but you DOF is dependant on you Sensor or Film size also, so the body does matter. Actually, the smaller the sensor, the smaller the DOF should be at the same f/, but SLR's have much higher f/ available in general, pressed against the fact that Compacts are using 35mm equivalents for focal length, not true number. Meaning that they usually start at 7mm and go up to about 50mm, so many of them will have greater DOF at any range, and about the same DOF fully extended as a 50mm macro. I probably made a few mistakes on that, but you get the gist I hope. |
Sorry if this comes across as a bit argumentative, but you did actually make a few mistakes here...
DOF *IS* entirely dependent on aperture size and focal length.
Chiqui has it right.
The difference in the sensor size has to do with the crop factor.
This means that if you are 100mm using a lens on a 35mm film body, you will end up with 100mm focal length... This 100mm focal length compared with the aperture size will determine your focal length...
BUT if you are using a 350XT, in order to get 100mm, you will get a 100mm EFFECTIVE focal length when your LENS is set to around 63mm focal length... Therefore, the DOF will be deeper (DOF gets shallower as the focal length increases).
Likewise, in order to get 100mm on an A80 (which has roughly a 5x crop factor if memory serves), you will achieve the EFFECTIVE 100mm focal length when the LENS is at 20mm actual focal length... The DOF will be much deeper...
In this way, it can be very confusing for people who are talking about DOF between these different cameras... If you look at the front of the camera/lens, you will see the ACTUAL lens characteristics, although they tend to be somewhat cryptic to many users as they are usually just a bunch of numbers...
My S2 IS has a 6-72mm lens. If I wanted to calculate the DOF from that, I would use those numbers... I would not need to further add any strange complications with the sensor size...
Using EFFECTIVE Focal length only comes in handy when trying to figure out minimum shutter speeds and a couple of other things...
When working out DOF, Focus, Magnification and a few other things, you will generally need to consider only the characteristics of the lens.
Chiqui's comment that most DSLR's are roughly the same as far as DOF is sound because most of them are 1.5X or 1.6X crop factors, so basically they all play in the same ballpark as to effective DOF... I doubt that the OP was considering a FF digital camera with a budget of 500 bucks.
Oh and the 6 megapixel 300D has been compared to the 8 megapixel sensor of the 350XT and 20D.
The general concencus was that the actual increase in detail is quite insignificant...
Large prints made from the 350XT will be of very similar quality when compared to those from a 300D...
Both are very good cameras... there are some who still use the 300D and prefer it over the 350XT.
The only real difference is startup time (and playback time), and sensor noise at higher ISO's... If you want to do most of your shooting in bright situations, the 300D will probably be good for ya.
Both cameras are worth consideration for the battery grip... The 300D for the extra battery life, and the 350XT for the size...
I've found that most people who are put off by the size of a 350XT that do actually get it are usually quite happy with the way they adjust after a few days/weeks...
Even using a big lens... The lens is usually supported by the left hand anyhow...
Using a battery grip is usually enough even for the die-hards in this matter.
Message edited by author 2006-06-15 21:34:11. |
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06/15/2006 10:51:00 PM · #27 |
Originally posted by eschelar:
Sorry if this comes across as a bit argumentative, but you did actually make a few mistakes here...
DOF *IS* entirely dependent on aperture size and focal length.
Chiqui has it right.
The difference in the sensor size has to do with the crop factor.
This means that if you are 100mm using a lens on a 35mm film body, you will end up with 100mm focal length... This 100mm focal length compared with the aperture size will determine your focal length... {sinp} |
Okay, then explain why when you go to a DOF calculator and put in an f/ and a focal length, the DOF will change dependant upon the size of film/sensor you choose?
At 50mm f/2.8 on APS size, focused to 20 feet out, you will have 7 foot depth of field. With 8x10, your DOF changes to 8.45 feet to infinity. What you are trying to say doesn't mesh with that at all.
Since the OP mentioned their P&S just doesn't have the same DOF, well.. change the sensor to that of a Powershot A80, and you go down to 1.64 ft of total DOF.
Or are you trying to explain something more esoteric than the static idea I have of it?
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06/15/2006 11:20:28 PM · #28 |
Originally posted by eschelar:
DOF *IS* entirely dependent on aperture size and focal length.
Chiqui has it right. |
While your argument may be technically correct, for practical purposes it is misleading, IMO.
The bottom line, for practical purposes, is this: if you photograph the same scene with both a point and shoot camera and a dSLR, the photo made with the point and shoot will have a deeper depth of field.
Yes, this is due to the fact that the point and shoot camera uses a very short focal length, BUT, the reason that you have to use such a short focal length is that the sensor is so small. So sensor size does affect DOF when photographing any given scene, in that it dictates what focal length you must use.
Or am I way off?
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06/15/2006 11:28:47 PM · #29 |
Originally posted by Keith Maniac:
Originally posted by eschelar:
DOF *IS* entirely dependent on aperture size and focal length.
Chiqui has it right. |
While your argument may be technically correct, for practical purposes it is misleading, IMO.
The bottom line, for practical purposes, is this: if you photograph the same scene with both a point and shoot camera and a dSLR, the photo made with the point and shoot will have a deeper depth of field.
Yes, this is due to the fact that the point and shoot camera uses a very short focal length, BUT, the reason that you have to use such a short focal length is that the sensor is so small. So sensor size does affect DOF when photographing any given scene, in that it dictates what focal length you must use.
Or am I way off? |
I don't thik you're off at all. I *think* what eschelar was trying to say was that the equivalencies of focal length moot the sensor/film size argument. Meaning, I would have to use a lens that is 9.09 times the actual magnification on an 8x10 to capture the same scene, which would decrease my DOF significantly. The converse, as you stated, is true of a 6x7mm P&S sensor vs. an APS sensor.
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06/15/2006 11:44:21 PM · #30 |
Ah, okay, using the virtual focal length magnifier....
APS size at 110mm, f/2.8, you get about 1.2 feet of DOF on a 20ft focus distance.
8x10 film, at a 9.09x the size of APS, I would neet a 9.09x longer lens to get the same scene, thus a 1000mm lens is neccessary. I would have to jack the f/ to 28 to get the dof UP to 1.2feet around the subject.
I probably screwed that up. oh well, someone correct me again. I feel like gettin mah learn on. :P
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06/16/2006 12:03:06 AM · #31 |
Oof. I guess it really did sound argumentative... I don't feel like arguing today. I'm sorry if it sounded offensive. I'm just trying to be clear.
The OP's question: Is the Canon Rebel XT the camera for me?
The presumed purpose: The OP is looking at the DSLR market and comparing from brand to brand.
The reason: She wants to improve the DOF characteristics of her pictures.
She already understands that DOF is going to be much shallower on DSLRs over her P&S camera.
Chiqui mentioned that she didn't like the 350XT because it was too small... One would guess that she therefore isn't recommending that the OP stick with P&S cameras which are even smaller. She is recommending the OP to look at other entry level DSLRs. Amongst this field, DOF characteristics are a minor issue because they are all subject to roughly the same crop factor and the original objective (that of using a shallow DOF) is achieved at a 1.5 OR a 1.6 crop factor. The difference in DOF characteristics between a D50 and 350XT are negligible.
It is worthy of note that because DOF is directly tied to focal length and aperture, choosing amongst the DSLRs is less important than choosing lenses. Which a possible reason that Chiqui said that DOF is tied to your lens.
Therefore, the point was that within the DSLR world, it's probably something of a moot point... I think that she just wanted more, not so much that she wanted a specific DOF value.
The DOFMaster site also uses the circle of confusion to measure DOF... I always viewed that as kind of more about sensor pixel pitch thing, referring to the sensors ability to differentiate between an in-focus point and an out-of-focus point. Kind of like an 'as good as' or 'good enough' value for the 'reasonable sharpness' value which determines the very definition of DOF itself.
I guess I too could be wrong there though... They certainly do seem to use crop factor for their COC calculation... I had kind of felt that this was a bit of an oversimplification because COC had to do with generally accepted standards of film resolution... I guess I have to do some more reading...
I guess I will have to retract this one until further notice:
Originally posted by my big mouth:
DOF *IS* entirely dependent on aperture size and focal length. |
However, none of this really changes the fact that we are definitely splitting hairs WAY too fine for the purpose of this thread.
EDIT to add.
Keith, your explanation is excellent.
Message edited by author 2006-06-16 00:04:52. |
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06/16/2006 09:51:00 AM · #32 |
As far as IQ between the 300D and 350D, they're about the same -- see //www.dpreview.com/reviews/canoneos350d/page22.asp
Since you mention Disneyland, there are some good reasons to get the 350D:
1. Selectable AF - The 300D can only do AI servo AF in "Sports" mode, so you're limited to ISO 400 unless you install one of the hacks. The 350D has One-Shot, AI servo and AI focus in all the creative modes.
2. More shots in burst mode.
3. Faster writing to the CF card, so its less likely you'll miss a shot because the buffer's full.
4. more metering options.
5. Better control of flash from the camera. |
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06/16/2006 10:25:28 AM · #33 |
| Getting ready to run out the door right now for a little while...but I have the 350D Rebel XT, GREAT camera, just a little too heavy for me and my 'slight" disability. I have the kit lens 18-55mm, plus the 75-300mm mark III, a 1.7 teleconverter lens, all lens caps, original box and software, a 1 GB card, camera case, battery and battery charger, and to sweeten the pot, jars of my HOMEMADE Strawberry Jam and Peach Preserves to go with it. LOL!! You'll probably love the jam more than the camera!!! But, PM me if you are interested...I'll be back shortly and I am definitely willing to barter!!! |
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06/16/2006 11:44:15 AM · #34 |
Originally posted by sugarandspice:
Does...the 2 extra megapixels between the Rebel 300D, and the XT ...make a huge difference when getting big pictures printed out for the wall? Or does it not really matter? Say, 16x24? |
What the extra megapixels will allow you to do is to crop the original photo down to just the right scene with enough resolution left over to make a larger print that will be satisfactory. |
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06/16/2006 05:00:22 PM · #35 |
| I think the xt has improved enough to justify the price. ive played around with just about ever prosumer digital out there, and im soo happy to be back to shooting with an SLR. nothing compares. ive found that even the kit lens isnt too bad for a kit lens |
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06/16/2006 05:07:34 PM · #36 |
Originally posted by a1leyez0nm3:
ive found that even the kit lens isnt too bad for a kit lens |
That's an understatement. It actually is a pretty decent piece of plastic.
:) |
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