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Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
 

Digital Lens Confusion HELP!!


I popped into a speciality store today and was chatting about lenses, when the fundi told me that (Sigma DC lenses) which I thought were specifically for Digital, still have a 1.6x conversion factor - so..... I thought my 18-200 was a TRUE 18-200, does this mean its actually a 29 - 320?? I'm now totally confused. I give up on this 'glass' story - I wish there was a lens which was a 2.8 and covered Macro through VERY wide angle till about say.... 500 zoom - now wouldn't that make sense :)


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2/22/2006 11:43:57 AM

 
Jon Close
BetterPhoto Member Since: 5/18/2000
  You're both right. The 18-200 is a "true" 18mm-200mm focal length _AND_ the 1.6x conversion factor applies to any and all lenses you mount on your (Canon?) DSLR. The lens focal length does not change when you put a lens on your camera. The 1.6x conversion is simply to give an equivalency for the angle of view that your camera will see with that lens.

Most people are not familiar with thinking in degrees of angle of view, but are familiar with the view given by various focal lengths on a 35mm film camera. So the conversion, "a 18mm lens on my DSLR is like a 29mm (18mm x 1.6) lens on a film camera" is useful.

Your "1.6x" camera captures 64.5 horizontal angle of view with an 18mm lens. Getting the same view on a 35mm film camera would require a 29mm lens. 200mm on your camera gives 6.5 angle of view. That's the same angle of view that a 320mm lens gives on a 35mm film camera.


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2/22/2006 12:16:41 PM

 
Christopher A. Vedros
BetterPhoto Member Since: 3/14/2005
  Take a deep breath, Robyn.

Let's see if this makes sense.

Your 18-200mm lens is an 18-200mm lens. Lenses don't actually have a conversion factor, it's the camera that you mount it on that does. Lenses are always marked with their "actual" focal length, because the lens itself doesn't know what size sensor is in your camera.

If your camera has a 1.6x conversion factor, then your lens will have a Field of View equivalent to a 29-320mm lens on a 35mm camera. If it has a 1.5x factor, then it will have a 27-300mm FOV.

The fact that your lens is a DC lens for digital only, just means that it could be constructed differently. Since it doesn't need an image circle large enough to fill a 35mm frame, it can be more compact (and less expensive) than an 18mm lens for a 35mm camera.

Does this help?

Chris


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2/22/2006 12:26:12 PM

 
Christopher A. Vedros
BetterPhoto Member Since: 3/14/2005
  I started typing before Jon's response was in, but I had to answer the phone.

Between the two of us, I think we've got it covered.

Chris


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2/22/2006 12:29:01 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Chris and Jon, I'm now going to cut my wrists!!! Between conversions and trying to make collages in Photoshop I've decided I'm cerebrally inferior!! (aka really 'doff') I think I will just take pretty pictures, apply some basic PS that I've learned - but in the meantime, I think I should go to sleep, as my brain is fried!! LOL - thanks for the explanations though, I will try to digest this slowly!


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2/22/2006 12:40:57 PM

 
David Earls   Camera manufacturers don't make this any easier. To wit:

I just purchased a Canon 10-22mm EF-S wide angle zoom for my Canon 20D. It is a true 10-22mm lens, but of course is subject to the 1.6x APS-C conversion factor.

Seems simple until you realize that this lens cannot be used on any Canon can only be used on the Digital Rebel and the 20D. Both of those cameras have less than full-frame sensors. So the lens performs as 16-35mm lens.

The irony is that the lens cannot be attached to a camera where it will function as a true 10-22mm lens.


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2/22/2006 2:04:57 PM

 
Jon Close
BetterPhoto Member Since: 5/18/2000
  Confusion continues. The EF-S 10-22 DOES function as a TRUE 10mm-22mm on 20D. Your 20D has a smaller image sensor than 35mm. It is a different format size, just as 35mm is smaller than 120 film.

On a 35mm film camera 50mm is a "normal" lens, but on a 120 film camera 50mm is very wide angle. And even if a 50mm lens from a 35mm film camera could fit on a medium format camera, it would not project an image circle wide enough to fill the 60mm x 70mm film frame.

Same situation with 20D and EF-S lenses. 20D has smaller format (15mm x 22.5mm) than 35mm. If the EF-S lens could fit on a 35mm film camera, it would not project an image circle wide enough to cover the 24mm x 36mm film frame.


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2/22/2006 3:21:04 PM

 
David Earls   Jon,

Yes, confusion reigns. All the reviews of the 10-22mm EF-S lens I've read say it performs as a 16-35mm.

I have both the EF-S 18-55mm EF-S lens and a Canon 50mm macro lens. I just shot two photos of my kitchen as tests, one using the 50mm prime and the second with the 18-55mm EF-S. Except for a slight variation in shot due to minor turning of the camera while changing lenses, the shots are identical. If the EF-S lens were performing as a true 50mm, wouldn't the field of view be wider?

I'm not sure what we're accomplishing with the flange-enclosed backfocus mechanism in the EF-S lenses, but it doesn't appear we're getting closer to "full-frame" performance.

If you'd like, I'd be happy to post them to my gallery.


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2/22/2006 4:05:52 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Dave, I'd like to see your posts. But then your answer also begs the quetion - why an 18-55 AND a 50mm macro lens? Is one faster than the other, what is the difference, if you're saying your kitche shot was identical? I'm seriously confused, and would like to get another Sigma (can't afford Canon EF-s) lens - I'd like to do more in the wedding/portraiture field, BUT I also enjoy Macro more and more - so.... do I go with a 2.8 I think its about a 28-50 or something, or just with a 50mm prime, and then could I use it for portraiture? Thanks


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2/22/2006 11:53:56 PM

 
David Earls   Robyn,

The 18-55mm lens is the kit lens that came with the camera. The 50mm lens is Canon's macro - better glass, closer focusing, higher magnification.


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2/23/2006 2:52:36 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Ok, I'm looking at getting the Sigma 27-70 2.8 lens (about R4800.00 here, which is about USD738) any thoughts on this. If you look at my gallery I'm enjoying portraiture/macro and will be doing 2 weddings soon. I would love the Canon 70-200 L Series, USM - its F4, and I know its got the USM etc., but I feel I need a 2.8. Do you know this lens?


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2/23/2006 11:29:48 AM

 
Christopher A. Vedros
BetterPhoto Member Since: 3/14/2005
  Robyn, what corner of the world are you in? I thought you were Down Under. I know photo equipment in Australia is marked up quite a bit.

I bought the Sigma 24-70mm f/2.8 EX and Sigma 70-200mm f/2.8 EX a couple of weeks ago and so far I love them both.

The 24-70mm was USD399 and the 70-200mm was USD789.

I read a lot of reviews and opinions on these lenses before the purchase. A lot of people had commented that the 24-70mm Sigma had a noisy focus motor. Compared to other lenses, I admit that it is noisier, but it doesn't bother me. It focuses quickly and precisely, it doesn't hunt around like my 28-300mm zoom would in low light. I used it at a Baptism last weekend and no one was distracted by it, so it's not THAT noisy.

Chris


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2/23/2006 12:01:28 PM

 
Christopher A. Vedros
BetterPhoto Member Since: 3/14/2005
  Okay, I just saw on another thread that Robyn is in S Africa. Looks like you guys are getting robbed worse than the Australians. ;-


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2/23/2006 12:06:31 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Chris - I'm in Johannesburg, South Africa (where the weather is generally great and the cricket is crap!!) The Rand/Dollar is about 6.08 - so hang on.... R2406.00 - with import duties etc its going to cost me R4 800.00!! - Also those soft box covers you spoke about (for diffusing) apparently Canon don't make them for their flashes ? I thought it was like a small paper shower cap, that just gets slipped over the flash. The Canon 5D has just been launched here and is retailing for about R30 000.00 (USD4975.00) - just to give you an idea. I also battle with the 28-300 (and 18-200) in low light, which is why I'm drawn to this 2.8 lens. Did you have to swop lenses during the baptism, or did you use it throughout?Thanks for your input.


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2/23/2006 12:10:20 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Chris, glad you feel my pain. We were given the run-down on how small the South African market is in comparison to USA etc recently, coz everyone was bitchin' - we are a spit in the ocean- getting the goods here, the import duties etc are what whack it up unfortunately. I know that if I got it overseas it'd be cheaper, but then by the time you buy the international warranty, you might as well just have bought it here!! I'm going to bed now, will check in the morning. BTW John, I often see your posts and appreciate them, but if you're a BP member, why no link to your gallery, I'd love to see what you shoot!


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2/23/2006 12:21:56 PM

 
Christopher A. Vedros
BetterPhoto Member Since: 3/14/2005
  Robyn,
I used the 24-70mm the whole time at the Baptism.

The softbox that I have for my Canon flash is made by Lumiquest.

Chris


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2/24/2006 1:23:48 PM

 
Craig m. Zacarelli
BetterPhoto Member Since: 2/3/2005
  think of it like this Robbs. Take your lens and put it on a 35mm camera, take a pic, load it into PS and crop out the center x1.6 ( if im explaining it right) whats in the center of that crop is what youll get on digital. just like zooming in on a bird in a tree, as you zoom the outer edges of the scene start to "dissapear" out of the frame. Only, with digital, you just lose the edges but the bird will stay the same size.
Craig-


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2/25/2006 4:49:46 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Craig - so... lets say I took a pic (on film), had it printed, would I say crop about 6mm off the pic all round, and that would be the effect of the lens on a digital, ie is that how much I would lose, or do you think it would be more? I've just traded in one of my Canon EOS 300 slrs, a Canon 80-200 lens (nothing fancy just an EF, plastic mount etc ), the stand 28-90 lens, a Canon 540 Flash, (really burns my bum that its not TTL with my digital!!!) and a cheap tripod, all against the price of the 2.8 Sigma lens - which leaves me with about R1940.00 outstanding - I figured I might as well get something for it all while I can, as the trade in on film camera's is falling quicker than the rand against the dollar!! Should get it Tuesday!!


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2/25/2006 6:19:38 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Oh, one more thing, they said the reason why there is DC on the digital lens and DG on the normal lens (although they're all interchangeable I think?) is something to do with the coating on the lens, so stop flare. Just thought I'd add that one to the confusion :)


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2/25/2006 6:27:29 AM

 
Craig m. Zacarelli
BetterPhoto Member Since: 2/3/2005
  maybe, I never heard that but its probably true...lol I know digital only means they either wont mount to a film body or the image on film will be surrounded by black
craig-


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2/25/2006 8:17:07 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  no, most of them will mount to a film body - and then its a true 18-200 (even tho it says DC for digital!) thats what got me. Anyway, I'm just going to wait for my new lens and shoot myself silly all week, as I'm using it as a backup to a wedding photographer on Saturday, so I need some practice! Thanks for all the advice and comments here :)


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2/25/2006 1:54:35 PM

 
Christopher A. Vedros
BetterPhoto Member Since: 3/14/2005
  Robyn,
For Sigma lenses, DG means that it is optimized for digital with additional coating on the rear elements. This prevents glare from the reflective sensor.

A DC lens is intended for reduced-sensor digital SLRs only. It has a smaller image circle because that's all that is needed on these cameras. It is similar in design to the EF-S lenses from Canon.

I'm not sure if it's an actual EF-S mount, though. That might be a proprietary Canon thing. So a Sigma DC lens might be able to mount on a Canon film SLR, but it would make a vignetted image on the film like Craig said.

Chris


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2/25/2006 5:27:51 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Chris - sorry my emails been down, just catching up now. I know that in 2 years time, I'll think why didn't I buy the Canon lens (coz then the price of the 5D will have come down, and we'll all have full frame sensor camera's......) In the meantime I just can't squeeze the bucks, so will wait for Tues for my new lens :)


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2/26/2006 12:30:11 PM

 
John G. Clifford Jr
BetterPhoto Member Since: 8/18/2005
  As someone pointed out, 'digital' lenses are the manufacturer's term for a lens that does not provide a full, 35mm film-sized image circle. Manufacturers make lenses like this because they can use designs that trade edge sharpness and light rolloff for other lens attributes... and if the lens image circle edge is out beyond the sensor's area it's wasted anyway.

Re focal lengths and crop factors, focal length is focal length, period. The crop factor is a way of giving the consumer some idea of the effective field of view of a lens, as compared to what they'd see on a 35mm full-frame camera. In other words, a 24mm lens on a 1.6x crop factor dSLR gives the same field of view as a 40mm lens (okay, 38.4mm) lens on a 35mm film SLR.

Re full-frame dSLRs, I don't think this is the wave of the future. There are some real advantages to having smaller sensors. For instance, the Nikon D2x has a 12 MP sensor with a 1.6x crop factor, while the 12 MP Canon 5D is full-frame. The Nikon's pixels are smaller, meaning it has much higher resolution (about 90 lp/mm, as compared to the 5D's 60 +/- lp/mm). What does this mean? It means that, although a 50mm lens on a D2x gives the same image as an 80mm lens on the 5D, the Nikon image will be sharper. On the Nikon, the lens will be the limiting factor, whereas on the 5D the sensor is the limiting factor. And, many good lenses will be limited by the 5D's sensor.

Additionally, if I were buying a Sigma lens in the focal lengths you're looking at, I'd go with the 24-70/2.8 EX DG instead of the 28-70. The 24-70 is the sharpest Sigma lens in this focal length grouping (24-60, 24-70, 28-70), and gives you the widest focal length range. It's also NOT a 'digital' lens, and provides full-frame coverage so it can be used on a full-frame camera also.


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2/26/2006 7:38:50 PM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks John :) I just checked back in the thread, and it was a typo, it is the 24-70 2.8EX ( I think DG, will check that), that I've ordered. So.... watch this space :)


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2/26/2006 8:00:02 PM

 
Craig m. Zacarelli
BetterPhoto Member Since: 2/3/2005
  Hey Robyn, I have the 24-70 EX-DG macro..youre gonna love it. One thing though, Test the heck out of it before you shoot asnything important. If you using a canon (and I think you are) this lens will be very close to the 24-70 L by canon... IF YOU GET A GOOD COPY!
these lenses have a history of either front focusing problems or rear focusing problems..straight out of the box. Be sure to do a test and be sure it is shap. Sigma will take it back and re-callibrate it for you without any hassels if its not right.
Good luck!
Craig-


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2/27/2006 4:46:41 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  I'm so excited to get it, but how will I know if its sharp enough or not!!?? Shadowing a wedding on Sat - my niece's, so yes it needs to perform!


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2/27/2006 4:59:19 AM

 
Craig m. Zacarelli
BetterPhoto Member Since: 2/3/2005
  either google for a lens test or print out some nice sharp print like a news print and hang it on the wall and shoot it at all the different f stops and shutter speeds and use the different settings from 24 to 70mm and look at them to see if its sharp or not and on what settings (youll have to keep track in a note book) then stand to objects (like batteries ) up on a table, one in front and one behind (but a little off to the side) then focus on the front one and shoot a couple shots, then focus on the rear one and shoot again then check to be sure the lens actually did focus where it was supposed to. Not only will it tell you if there are any problems, it will tell you at what settings the lens is its sharpest. mine is around f 11 if I remember correctly (its been so long sinse ive used it, I love my 28-135 IS too much)
good luck and let us know what you get,
Craig-


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2/27/2006 5:05:21 AM

 
Craig m. Zacarelli
BetterPhoto Member Since: 2/3/2005
  start here robyn....

http://medfmt.8k.com/mf/resolution.html

craig-


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2/27/2006 5:06:29 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  Thanks Craig, I'm hopefully picking it up tomorrow, then I'm off to the bush to look for wildlife - just for the night and the next day !! Hopefully will find some lions, leopards, rhino, ellies, giraffes, zebra's :) Will prob use my 28-300 more though !! Tks for all the advice


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2/27/2006 7:38:53 AM

 
Craig m. Zacarelli
BetterPhoto Member Since: 2/3/2005
  Ohhhh! can I come too?
lol
good luck and happy hunting!
Craig-


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2/27/2006 7:52:11 AM

 
Craig m. Zacarelli
BetterPhoto Member Since: 2/3/2005
  Robyn, I think your e-mail hates me... I just sent you an e-mail and it appears to have come back to me... let me know if ya got it.
Craig-


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2/27/2006 10:03:30 AM

 
Robyn Gwilt
BetterPhoto Member Since: 7/15/2005
  LOL and yet when I get to work its on the server - very strange! Try to send to robyn@cinet.co.za, let me see if I get it at home tonight!


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2/27/2006 10:17:24 AM

 
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