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Old Jan 13, 2004, 8:10 AM   #1
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Default Macro Question and Flash Question

Hi all

Something that I have never understood is this.... I have a 50mm f1.8 lens that I cherish...! I was thinking about getting the Sigma 50mm f2.8 Macro (any of you guys have this lens?) after reading many good things about it. The question is, what makes one lens a macro and the other not....? Is it just that one has better optics than the other or that the focusing system is wider or something else....? I mean the 50 f1.8 gives superb image quality at everything bar wide open where it only drops in quality a bit but it doesnt let me focus closely enough to make shots appear as macro shots.....? So it must be down to the focusing system right.....?

Second question is a flash one... I have seen this come up on many forums. Underexposing by up to 1 - 1.5 stops seems to be the norm with my 300D and many others. I spent about 2 hours on Saturday night testing various settings in the creative modes but I couldnt get a decent exposure with the inbuilt flash or with my Sigma DG ST flash. The best results i got where in P and Manual mode but even these were not perfect. I had a look back at some prints off my old Eos 50e with a Metz flash and they where all exposed almost perfectly. I have tried using FEL off a midtoned grey and yes that does help but seems a bit akward. I also read that massive article over at Photonotes which is brilliant but this problem i believe lands in Canon's lap. Do you guys think there is a possibility of a firmware update with a Flash Exposure Compensation from Canon...? Or could someone else write one..? I think this would be the best option. Do you know if the 10D has the same problems...? (but of course it has FEC....!)

Thanks in advance and Happy new Year to ye all....!

Richie
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Old Jan 13, 2004, 8:23 AM   #2
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Richie,
Concerning the "macro" lens; Macro lenses permit closer focusing while keeping the image field relatively flat. It is the design of the lens that makes the difference. If you use an extension tube on a "normal lens" to get a closer focus you introduce distortion. You can use a normal lens in the reverse direction(with the appropriate adapters) and get a flat field closeup.
I prefer to use the "macro lens" for closeup work. The only reason I would use the reverse lens approach is to get "extreme" closeups (greater than 1:1).
Ted
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Old Jan 13, 2004, 8:31 AM   #3
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Richie,
One more point about "macro" lens. Some prefer the 100mm macros because you can work farther from the subject such as in insect photography. I use the 50mm Canon macro and a 200mm Tamron macro.
Ted
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Old Jan 13, 2004, 9:18 AM   #4
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Thanks Ted

So basically then it is the physical internal design of the lens that is different... Thats interesting....

Cheers

Richie
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Old Jan 13, 2004, 12:45 PM   #5
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I've tried at the store using your lens and an extension tube and gotten quite nice results. Because the image sensor on the 10D and Rebel is smaller than a 35mm frame you'll avoid some of the distortion you'd nomally get using that setup on film.

What a macro lens would give you is better reproduction across the entire image. If you're photographing documents or stamps you'd need this. But if you're shooting three dimensional objects (flowers) you won't see any problems because the depth of field is so shallow.

A 100mm macro lens will give you more working distance (space between lens and object) so it is likely a better choice and use your f1.8 on extension tubes. That way you'll have two lens at different focal lengths both of them high quality optics. You can use macro lenses for 'normal' photography without any problems, the only downside is that some people find the lens to be too sharp.

By the way - my understanding is that the 1.6x factor will act to magnify the image ie (1:1 becomes 1.6:1) not make the lens act like a 80mm macro as far as working distance and depth of field goes.
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Old Jan 14, 2004, 8:05 PM   #6
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Hi Ursa,

Regarding your underexposed flash photos, someone wrote a Flash Exposure Compensation software fix. I downloaded and increased the FEC by 2/3 and it has really worked wonders. it's free - check it for yourself and let me know if you have any luck. Just follow the directions - you must put the camera in P mode.

Paul

http://revolution.cx/rcx/fecset.htm
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Old Jan 15, 2004, 10:25 AM   #7
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Default Sigma DG ST flash

The Sigma DG ST flash might be part of your problem. The Sigma model that works with the digital Canons is the Sigma EF 500 DG SUPER flash. I am not up on all the differences but my Super works well and I had been warned to avoid the ST as it would only be partially compatible with my 300D.

On Macro: No lens is corrected perfectly for more than one subject distance. On a normal lens, that might be 20 feet and give great results from a fraction of that to infinity. It would remain useable for macro use to a degree but might suffer from a less than flat field or some other minor problem. Macro lenses are supposedly corrected for a closer spot so their range spans down to a closer point possibly at the expense of their worth at infinity. This last has never struck me as a problem probably because the relatively lower speed of macros (f/2.8 or slower) will help mask little abherrations. Macro lenses intended for the very close range (like the Canon 65mm) might show more of the problem than lenses only good to 1:1 but I have not tested one and have no idea if you would ever see the difference. For the most part, the big difference in a macro lens is that it comes with a mount that will let you focus both to infinity and very close without having to add accessories. That is a big advantage if you are shooting bees and an eagle lands 10 yards away! (Dreaming here.)
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Old Jan 16, 2004, 2:52 AM   #8
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Thanks Doug and everybody else that replied. Its not that i didnt know what a Macro did it was just that i was interested in how the internal makings of lens where different. I now have some type of an idea as to why a macro is a macro......!

As far as the flash is concerned.... yes the Sigma EF 500 DG ST (http://www.sigmaphoto.com/html/flashes.htm) is completely compatable with the 300D. It has full e-TTL support but not the bells and whistles of the Super version (which i probably should have bought only for i was tight for cash at that stage). Anyway the problem of underexposure occurs even with the built-in flash so i dont think its an incompatability issue.

Anyway Thanks for the help

Richie
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Old Jan 22, 2004, 1:02 AM   #9
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I noticed the same problem (at least, one full stop underexposure) with Digital Rebel and the new MR-14EX ring flash. Fortunately, the flash itself has exposure compensation feature.

Anyway, I'm very disappointed.
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Old Jan 22, 2004, 1:05 AM   #10
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Quote:
Originally Posted by M-O
I noticed the same problem (at least, one full stop underexposure) with Digital Rebel and the new MR-14EX ring flash. Fortunately, the flash itself has exposure compensation feature.

Anyway, I'm very disappointed.

What mode are you shooting in that you're underexposing? I get good exposure with the 420EX and the DRebel. I generally shoot in M mode for flash.
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