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Old Mar 16, 2004, 6:49 AM   #1
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Default Question on flash metering terminoligy

When viewing camera specs, what do the terms i-TTL and D-TTL mean? I notice the Nikon D70 has both, the Canon 300D is listed as n/a.

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Old Mar 16, 2004, 8:12 AM   #2
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TTL stands for "Through The Lens"

What it means is that the way the camera uses to decide how to use the flash (how much power and, I think, for how long) is done by metering the light as it goes "Through The Lens".

How what the "i" and "d" mean I don't fully know. I know that D-TTL was added for Nikon's digital cameras, but does it "require" digital in some way? Or was it some technology that they came up with at the time they were releasing a digital camera so they called it "d-ttl" (the D being for digital.) I don't know. I don't believe that the "d" is for distance.... I thought that Nikon uses the distance to the subject before "d-tll" came out.

I believe that d-ttl requires special flashes, but I couldn't be wrong.

Canon has its own "e-ttl", and now "e-ttl2" but I couldn't tell you what the difference is between "e-ttl" and "ttl"which is an older method of metering for flash. e-ttl2 uses the distance to the subject, something Nikon cameras have been doing for a long time but Canon cameras haven't.

Eric
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Old Mar 16, 2004, 9:08 AM   #3
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The Nikon TTL distance to subject measurement started (I think) with the Nikkor P lenses. So in that case even if the focusing is manual the camera still knows the distance to the subject.

D-TTL (simply) uses the distance information from the lens to allow the camera to instruct a fill-in flash how much power to use.

I-TTL allows the camera and four groups of "inteligent" flash guns to work together. Nikon say that this will allow the co-ordination of up to 160 (?) flash guns in 4 groups via wireless comms. I can only assume that they all know where they are in relation to eachother and to the camera, and that the lens distance metering does the rest.

Regards,
Graham.
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Old Mar 16, 2004, 9:20 AM   #4
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So, I assume the reason for the comparison chart showing N/A in the Canon column means it has neither, but rather it's own system. I think they call it E-TTL.

I'm just moving into digital after years of film cameras (Nikon) and have to learn a lot.

Nikon used a system of reading the flash exposure off the film surface, but I assume that since digtal came along, an entirely new approach became necessary, such as "distance to subject". I assume Canon's E-TTL is about the same as Nikon's D-TTL.

If I'm catching on correctly, the TTL almost seems an inappropriate term, since the camera is measuring the distance to the subject rather than the light stiking the sensor. Perhaps it measures the ambient light entering the camera and adds the appropriate amount of flash power, making the TTL term more accurate.

By the way, Graham, those are some nice photos you have on your site. I love the color in the wedding pictures, especially the group shot. Really looks like a happy time.

I assume that's not straight out of the camera. There must be some color correction, at least. Surely digital cameras don't do that good right in the camera?
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Old Mar 16, 2004, 9:52 AM   #5
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Quote:
Originally Posted by Deane Johnson
If I'm catching on correctly, the TTL almost seems an inappropriate term, since the camera is measuring the distance to the subject rather than the light stiking the sensor. Perhaps it measures the ambient light entering the camera and adds the appropriate amount of flash power, making the TTL term more accurate.
The way I think it works is as follows. The camera meters on the basis of the light received, but you've given it the option to fill-in with a flash. As a result it uses the distance to the subject to calculate the old inverse square law. As a result it can deliver a fill-in flash. How successful ? that's another question. I've never used it in anger.

Quote:
Originally Posted by Deane Johnson
By the way, Graham, those are some nice photos you have on your site. I love the color in the wedding pictures, especially the group shot. Really looks like a happy time.

I assume that's not straight out of the camera. There must be some color correction, at least. Surely digital cameras don't do that good right in the camera?
Thanks Deane, I'm realy pleased that you like them. The group shot was taken by my girlfriend (I'm third from the right as you look at the picture, next to my neice in the orange dress). Lesley caught the moment when somebody said something that disolved us all.

In terms of colour correction, I don't recall doing any. It was a lightly cloudy day and all I remember doing was a little subsequent exposure adjustment to the RAW files and a little Unsharp Mask. When I published for the web I changed from Adobe 1998 to sRGB colour space. That was it. A lot of the reviews I read about the D100 referred to its amazing colour range, and that was a key factor for me in considering it along side the Cannon 10D.

Regards,
Graham.
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Old Mar 16, 2004, 10:08 AM   #6
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Thanks for the details. It helps an old film guy learn the characteristics of the digital medium.

I just purchased a Sony DSC-T1 to carry in my pocket, but I'm researching various possibilities for a more serious camera, in the USD $1000 to $1,500 range. The Canon 300D is one that's high on the list. I'm watching for Steve's review on the new Nikon D70 as another possibility. Nikon is near and dear to my heart as I've used many of their film cameras since my first one, a Nikon F purchased in 1970.

Being an old film guy, accurate color is a serious consideration for me.
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Old Mar 16, 2004, 11:14 AM   #7
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Deane, the general concensous here is to go with the system that you have the lenses for.

They are both very good systems and for the majority of people it isn't worth the financial hit that you'd take in selling the old System A stuff to switch to System B stuff. The D70 is too new to say for sure, but I bet it will be a winner.

Your comment about taking ambient light entering the camera + distance (used to calculate flash power) to handle the flash is (I believe) accurate. So TTL is still an accurate term.

Any chart that compares flash features of Nikon vs canon will have holes on both sides. Nikon doesn't have E-TTL nor "E-TTL2", but I don't believe Canon has I-TTL, and it certainly doesn't do D-TTL. Since those are not industry terms/standards what matters more is if the camera does what you need. Other than the use of subject distance E-TTL and D-TTL are basically the same (I believe.)

It is my understanding that Nikon bodies (because of the use of distance info) have generally produced better flash results. Canon has finally added the use of distance info in E-TTL2, but only their absolutely newest DSLR body supports it (a $4,500 pro body, the 1D-Mark 2.) But if you need wireless flashes, the D100 can't do it.

Eric
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Old Mar 16, 2004, 12:57 PM   #8
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Eric, you've summed it up nicely, as I now understand things.

Regarding systems and existing lenses, I stopped buying Nikon (or any other SLR system about 10 years ago). As a result, my newest Nikons are FA, meaning all of my lenses are old manual focus. For this reason, whether I go with Nikon or Canon, each is starting from scratch.

No question, the Canon 300D is a darn good camera, and a good one to compare against. They have set a new price point for an SLR with a basic zoom lens. It's now a $1000 SLR world.

One thing that is attracting me to the Canon is the Canon CP-300 portable printer. I assume it only works with the Canon cameras. In my wife's work, it would be desirable for her to take a picture at a customers house and leave a 4 x 6 print. i'm not sure any other brand has the package of a $1,000 SLR and a printer that are completely portable in a small package. But then, I'm learning something new everyday from Steve's site and this forum.

Thanks again.
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Old Mar 16, 2004, 2:07 PM   #9
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Well, since I own a Canon I'm certainly not against people buying them. Read the review of the DRebel closely. They made some design choices to separate it from the 10D in the area of human interface that would drive me nuts... but doesn't bother other people. Worth reading about. There are many threads about this in the Canon dslr area.

I don't know of other portable printers, but it's an interesting question. Most DSLRs are designed around the idea that the user will post-process the picture. Add sharpening, contrast, whatever and then print. You can change some of the in-camera settings to do this, but you should be aware that the image out-of-camera might not look as sharp as you might like... but it will be able to take a good amount of sharpening in a program like Photoshop.

That might hamper you idea of direct-from-camera printing. But you also might find a good set of settings in the camera to alleviate this

Eric
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Old Mar 17, 2004, 6:13 AM   #10
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Quote:
Originally Posted by Deane Johnson
Being an old film guy, accurate color is a serious consideration for me.
Deane, the digital colours may be varied, vibrant, and rich, but accuracy can be an issue. Matching the colour profiles through from the subject to the screen and printer output devices is getting a little easier, but exactly how faithful the colours are to the original is another question. That's where direct printing may let you down.

I've only experimented with direct printing to an Epson 895 using my Nikon CP4500 but I was disapointed with the results. The colours were garish and the images were soft. As Eric points out you can use your camera settings to possibly get around some of the softness issues, but to my mind the colour profile that your camera supports could well be an issue for direct printing.

You could experiment with the colour profile used in your camera (my D100 gives me a choice of three) and see what the direct printing results are like....

Regards,
Graham.
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