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Old Sep 23, 2009, 7:57 PM   #21
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Originally Posted by tclune View Post
Thanks, TCav. This is very helpful. But you fail to appreciate the depth of my ignorance. When I see an 18-200mm Sigma lens with apertures of 3.5 to 6.3, and apply what I think I have learned from your comments, it appears that the Sigma should be a much brighter lens than 3.5 at the wide end. The marble is still not falling in the hole for me.
I presume you're considering the focal length of 200mm and the aperture of f/6.3 and calculating a pupil diameter of about 32mm, and wondering why that same pupil diameter only results in an aperture of f/3.5 at 18mm.

Short answer: It's complicated. Trust me.

Long answer: The measurement of a lens' aperture is based on the simple measurement of the diameter of a single, circular, convex lens. If two lenses have the same focal length but one is twice the diameter of the other, the larger lens focuses 4 times as much light as the smaller lens.

In a photographic lens, the light path is more complicated than that of a simple convex lens. The light is refracted and the path that light takes is constricted. As the focal length of a lens changes, the degree of constriction varies. The aperture blades are located where the light path is constricted, so the pupil diameter is not actually 32mm at a focal length of 200mm. But at 18mm, the light path is constricted to a much greater degree, so the relative size of the pupil at a focal length of 18mm is larger than at 200mm, even though, mechanically, the pupil diameter remains constant as the lens is zoomed.

So ... it's complicated. Trust me.
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Old Sep 24, 2009, 3:09 AM   #22
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The X times zoom as you refer to it is a ratio of the low end to the high end, or 55 / 18 = 3.05 So its essentially a 3X zoom.

In terms of zooms for dSLRs the general rule of thumb is about 4. The reason why 4 is used, is that its is a zoom range that provides a reasonable amount of zoom, but also does not compromise the optical quality of the lens design.

For instance a 18 - 250 lens is almost 14X zoom (250/18=13.8) It provides a lot of versatility, however if you stretch that range across 2 lens (18-55, and 50-200 or 50-300) you receive a set of lenses that are usually have a much better set of optical quality (or image quality). That said, of course the single lens usually is better for walking around (less equipment to haul around), so there are trade offs to be made.

Sorry, about the long answer to your short question...
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This is an indication that Sarah's explanation missed its mark.

The "X times zoom" is just the ratio of the shortest focal length to the longest. The 18-55mm lens would be a 3X zoom, but since dSLRs have interchangeable lenses, the "3X zoom" doesn't tell the whole story. Yes, the 18-55mm lens is a 3X zoom, but so is a 100-300mm lens, though the angle of view each lens gives is quite different. P&S Digicams only have one lens, so the "X times zoom" is all there is, and it doesn't tell the whole story there either.

Thanks guys that was helpful...


Can I say that this thread (and there are others as well..) are extremely helpful to us new folks...thanks so much for your efforts....

Awesome group you have here...
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Old Sep 24, 2009, 1:40 PM   #23
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I agree that we have an awesome group her

Sarah, Jim C, TCav, John G, Mark and numerous others are very experienced and very helpful. I know I am not in a league with them but I also try to help out because I have gotten loads of help from them in the past. Also the moderators such as Billy etc do a great job to keep spammers out of here as well.

dave
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Old Sep 24, 2009, 2:05 PM   #24
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Another thought to add:

When entering into the DSLR world, there is no single best camera/system. Doesn't exist. It's also important to realize that a DSLR is NOT a point-and-shoot. Some of the benefits of DSLR photography can only be realized when using specific lenses, flashes, or other accessories. So, if you have specific areas of interest (love macro or want to shoot portraits or want to shoot sports, etc...) I strongly recommend getting input from people that actually shoot what you want to shoot. It's those people that can best speak to what gear features are desirable and what lenses will be required. And, better yet, when you look at a given system you want to get first-hand recommendations on what gear you would need in that system. There are 2 reasons for this:
1) You really want hands-on experience not just someone with an opinion. A macro shooter can comment on types of shots a 1:4 is good for, a 1:2 is good for and a 1:1 is required. They can talk about the benefits of flash use, they can talk about extension tubes and how well they work. People, like me, that don't shoot macro can't give good advice on what the feature and equipment needs/options are. While I and other non-macro shooters can provide basic information our advice isn't as valuable as someone who does it.

2) You want to be sure your expectations and the gear you're buying are in-line. Buying a camera and kit lens in any system isn't going to get you great bird-in-flight shots. Nor is it going to allow you to take good indoor gymnastics shots. Talking to people who shoot what you shoot will give you an idea of the gear you'll need so you can properly set your expectations. That way you're not disappointed when you plunk down $1200 on a new DSLR and find out that kit isn't going to let you take the photos you want. What do you mean I need to buy an external flash? Nobody told me that. So, a lot of us can provide general advice but make sure if you have specific needs you get advice from people who have hands-on experience.

So, how do you know who knows what they're talking about? That's easy - this is all about photography. Anyone telling you what you need to buy to shoot portraits should have portrait shots to share with you. Anyone telling you what you should buy to shoot night time football should have some nighttime football shots to share. You get the idea.

That way you don't end up with either buyer's remorse or shock of realizing after your initial purchase you really need to spend another $XXX to do what you wanted to do. And, it's not always about spending MORE money, it can often be about proper allocation of money to begin with. It may be that for what you want to shoot, an eperienced photographer can help explain why taking the money you were going to spend on a 2nd lens would be better spent on an external flash or tripod instead.

Finally - watch out for all of us on here. We all have biases and brand loyalties. It's something we're all guilty of - even those of us who own cameras in multiple systems. We're happy with our latest toy and want everyone else to share that happiness so we'll try to convince you to buy a camera in our system. So keep us in check and be wary when someone always seems to be pushing cameras from their brand.
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Old Sep 24, 2009, 4:48 PM   #25
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I'd like to interject something into this discussion that I think is important yet hasn't been mentioned so far. An important part of selecting a dSLR is the type of photography it will be used for. And many people want to make the move from P&S to dSLR because thay have a particular purpose in mind.

As an example, if the buyer wants to do macrophotography handheld, Canon and Nikon only have one stabilized macro lens a piece, and they are very expensive, but since Olympus, Pentax and Sony have stabilization in the camera body, all their macro lenses, and all the macro lenses from third-party manufacturers, will be stabilized. This should put those brands ahead of Canon and Nikon on the list of bodies the buyer should consider.

Conversely, if the buyer wants to shoot indoor sports, only Canon, Nikon and Sony have a selection of lenses that are appropriate for that purpose, and the ones from Sony are very expensive. This should put Canon and Nikon at the top of the list of brands and bodies the buyer should consider, followed by Sony (for those with deep pockets.) The buyer shouldn't even consider anything from Pentax and Olympus, because, without an appropriate lens, the best camera body can't do what they want.
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Old Sep 25, 2009, 12:52 AM   #26
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WOW..JohnG and TCav......super info there, and very valuable!!!

Sometime a newby like me can't decide what he's gonna major in...I wanna do some macro, I wanna do more scenery and I like the odd portraits not the staged ones so much but the street ones or the unique cowboy etc...Animal shots are cool too...

I my work I am a generalist...so I guess in my hobby I'll be the same...I suspect that's harder then if one were to specialize..
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Old Sep 25, 2009, 12:26 PM   #27
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LittleJohn-

There is nothing wrong at all with being a generalist. JohnG and TCav were posting about specific camera and lens requirements that are sometimes found only in one camera brand.

As a generalist, you have a choice of all the DSLR cameras out there. You currently trying out a Sony A-230 camera if I remember correctly. It is a good choice for a generalist. The kit lens, the Sony 18-55 mm lens is capable of many macro situations as it will focus quite closely. It you need 1:1 or 1:2 ratios, Sony makes the well priced 30 mm macro lens which sells for under $200.00.

The other lens you might want to add would be the Sony 55-200 mm lens for some zoom reach. It is also well priced and very highly rated or reviewed. It also sells for less than $200.00.

Let us know if we can be of further help to you and thanks for posting. Have a great day.

Sarah Joyce
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Old Sep 25, 2009, 12:59 PM   #28
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It you need 1:1 or 1:2 ratios, Sony makes the well priced 30 mm macro lens which sells for under $200.00.
It may seem like I'm picking on Sarah here, but I want to illustrate the point I was trying to make. This is EXACTLY the kind of generalist advice that is dangerous. Throwing out a 30mm macro lens solution as if that's the solution for all macro work. There is more to it than just 1:1 or 1:2. The focal length should be appropriate for the type of macro work. This is exactly why, if something like macro were important to you, you want to get advice from macro shooters - even if you are a 'generalist' but your macro shooting desires lean towarad insects. Is a 30mm macro lens a good solution for insects? I honestly don't know. But that's the problem with gear advice from people that don't have hands-on experience and don't take the time to find out your specific needs before they suggest a camera solution.

So it's not my intent to pick on a particular poster - especially since Sarah started this thread and is a very positive contributor here. But in my opinion it's a risk with getting advice from people on the web. Especially when you see the number of their posts, or in my case a 'moderator' tag.

It's also the reason why threads like this are not made 'stickys' more often. TCAV, myself, Sarah and others have voiced opinions. But with all due respect to all of us, none of us are an authority on selecting the right DSLR and suggesting specific cameras / lenses people should purchase. We all like to think we are from time to time, myself included.

So I'll re-iterate: any time you see someone suggest a certain piece of gear for a certain type of photography - ask for their photos of that type of photgraphy. Don't be timid. These are important decisions and your money is precious. Don't let titles, # of posts or anything else sway you -all us 'experts' are all guilty of giving advice in areas we have no business giving it. And remember, just because I own Camera X - doesn't mean I use it to shoot the types of things you want to shoot or at the quality you want to shoot it. So, when I or anyone else suggests how you should spend your money ask to see the photos.

So, please don't misunderstand - I am not trying to attack Sarah because I know she is only trying to help and is a valuable asset here. But I do warn people to watch out for those pieces of advice when the source doesn't have details of what you want to shoot and get photographic evidence. This is NOT a contest of who is a better photographer either - so my intent is not that we all start including shots in this thread as a 'pissing contest'. It's my advice to people that when you do post your 'what DSLR should I buy" thread for the things to look for from those of us who will give you advice. Lord knows I've given bad advice to people in the past - but I'm fairly confident this little piece is good stuff. Lots of opinions on the net. You need to be able to determine which you should trust in a given situation. Myself as an example - I shoot a lot of sports. If I advise you what camera to get for sports shooting you're welcome to see my photos to judge the weight you should give my opinion. You WONT see my advise you on specific gear to buy for macro shooting. At best I'll mention broad principles but if I advise you what camera or lens to buy, it's a safe bet you should not pay attention to my advice
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Old Sep 25, 2009, 6:54 PM   #29
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Default Macro Photo Sample

LittleJohn-

This is the kind of macro or close-up photo that I was posting about in my previous post. Flowers are my favorite macro subjects, so I have lots more sample photos if you desire.

Sarah Joyce
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Old Sep 25, 2009, 9:51 PM   #30
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and that was done with the a230 and the 30 mm macro?

Its a beautiful photo... if I can do that with my setup.....wow...

I hear John G loud and clear, and its actually advice I follow...in most things, and I appreciate John G posting it as its just good advise for all new people.

In the little time I've been here, I've certainly received a LOT of good information, even for those who think they don't have much to offer..even the questions lead me to thinking! This is an great group of folks, and hopefully I can repay you all............by giving freely what you've taught me.

But Damn that flower looks good....
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