need some new lenses

[surfnvb7]

i've been thinking about getting some new lenses for my XTi for a while and need some advice on which.

with the canon 100mm macro, things need to be pretty close to the glass in order to get a good shot without cropping it sounds like. my cube tank at home, is 24" deep...and theres alot of stuff in the back i would like to be able to get macro pics of without having to crop and lose quality.

i would obviously need to get some of those extendors...but was wondering how much quality i would lose in the picture, and how much "zoom" i would get from these extendors....i.e. is it really worth it?

shoot, by the time i get the cannon 100mm + the extension set...thats putting it at the price range of the Sigma 150mm.

so i guess what i'm asking, with a tank as deep as mine...should i just go for the Sigma 150mm macro?

is this it?

http://www.bhphotovideo.com/bnh/con...422&is=USA&addedTroughType=categoryNavigation

also, i would like to replace my piece of crap kit lens that came with my cannon XTi. it actually came with a tiny *knick* on the inner most lens, but i didnt feel like going through the hassel of getting it exchanged etc...b/c i was going to the georgia aquarium in a week after i got the camera...and didnt want to be camera-less. that, and after testing it out the knick didnt seem to mess up the pictures any.

i would like something that can take good pictures of people standing 10feet away, as well as "sight seeing" type of pictures. just every day normal stuff like if you were on vacation. and of course other things like: if i visited an aquarium, or took regular pics of a friends tank or tank at a LFS, pictures of people and panoramic scenes if i went skiing etc.

would the Sigma 50-150mm work well? or is there a cheaper alternative as i'm not going for as much "high quality" with an all purpose lens that is going to get some wear and tear on it.

is this it?
http://www.bhphotovideo.com/bnh/con...438&is=REG&addedTroughType=categoryNavigation


any and all advice is much appreciated!

 

[gregr]

Regarding the extenstion tubes- I think you've got the idea a little backwards. The tubes will decrease the minimum focus distance of the lens- thereby increasing the magnification.
In your case you want a longer lens (more telephoto/more millimeters) not a shorter minimum focus distance, so the 150mm macro lens would be a good idea. The one you linked to is the correct Sigma macro lens to be looking at. Both lenses (150 and 100mm) will do true macro 1:1 magnification, but the 150 will allow you to get that magnification from 15" away, as opposed to 5.9" for the Canon 100mm macro lens.
I think that answers your question right?

 

[surfnvb7]

<a href=showthread.php?s=&postid=9834154#post9834154 target=_blank>Originally posted</a> by gregr
Regarding the extenstion tubes- I think you've got the idea a little backwards. The tubes will decrease the minimum focus distance of the lens- thereby increasing the magnification.
In your case you want a longer lens (more telephoto/more millimeters) not a shorter minimum focus distance, so the 150mm macro lens would be a good idea. The one you linked to is the correct Sigma macro lens to be looking at. Both lenses (150 and 100mm) will do true macro 1:1 magnification, but the 150 will allow you to get that magnification from 15" away, as opposed to 5.9" for the Canon 100mm macro lens.
I think that answers your question right?

pretty much, i just figured with any kind of "add-on", you are gonna lose a little bit of detail or quality in the image by adding another lens for light to pass through.

if the sigma 150mm can reach up to 15" away, how far can the longest extension for the cannon 100mm reach up to?

also, with the sigma 150mm, if i want to take a macro picture of something up close to the glass, will i have to set the camera further back from the tank to get the whole coral in the picture instead of taking a picture of a single polyp, like on an sps?


what about a good all-purpose lens?

 

[gregr]

Generally an all-purpose lens is one that is decently wide to decently long, like Canon's 28-135. It's a good lens though some people have reported not liking it (Beerguy for one). I had one for a while and thought it was good for the money. There are options out there besides that one lens- take a look at the Sigma's too. I think Sigma makes a good fast [f2.8] all purpose lens that is reasonably priced.
Extension tubes have no glass- they're just empty tubes. They increase the distance between the sensor and the rear element of the lens- that's how come the lens focuses closer. You lose a little light but there's not really any significant quality loss, optically speaking. I think you may have extension tube and extenders confused. Here's what I wrote in another thread on the same topic:

Extension tubes and teleconverters (aka extenders, aka converters) are two different pieces of equipment that can increase your magnification. Tubes are just that- empty tubes that increase the distance between the rear element of the lens and the sensor, thereby decreasing your minimum focus distance. With the 100mm macro lens and no tubes your minimum focus distance is 5.9". With extension tubes you can greatly decrease that distance, thereby increasing magnification (the closer the lens is to the subject the greater the magnification). Teleconverters increase the focal length by their magnifcation rating. They generally come in two choices: 1.4x and 2x. Add a 1.4x extender to your macro lens and you now have a 140mm macro lens. 2x gets you a 200mm macro lens. With the 1.4x your minimum aperture becomes f4 and with the 2x it'll be f5.6. With that much magnification though, you'll be using a tripod and tiny apertures so the light loss isn't the end of the world. Sharpness loss will be fairly significant with the 2x and not bad with the 1.4x. Here's the thing though- I can't recall if the converters work directly with the macro lens. You may need a small extension tube in between because the converters stick out a bit in front and may not fit inside the opening at the back of the macro lens. I can't check right now but can later if you need to know.

 

[surfnvb7]

yup, i think i got it backwards. i see what you are saying about the tube going b/w the sensor and the glass. that makes sense....

i'm not very good with understanding optics, i keep taking notes, then get a grasp of what i'm doing...but if i dont use the knowledge i just learned, for a couple weeks....i forget it all again. was never very good with optics in physics either...



it sounds like from what you are saying, the cannon 100mm with the set of extension tubes (or converters) offers a better versatility than does the sigma 150mm.

1) will adding these to a cannon 100mm help me with being able to take macro pictures towards the back of the 24" tank?

2) if i got the sigma 150mm, would i have alot of headaches trying to take pictures of things closer to the front of the tank than by using the cannon 100mm?

-basically just trying to figure out the pros and cons b/w the two setups, whichever one gives me the most versatility in taking good macro pictures of everything in my tank is the one i'm probably going to choose, even if i have to trade off a little bit of sharpness.

 

[gregr]

1) will adding these to a cannon 100mm help me with being able to take macro pictures towards the back of the 24" tank?

The 150 will be better for the farther away stuff and the 100 will be better for the stuff that is close. Adding tubes to the 100 will make it good only for things that are very close to the lens- it'd still focus on something at the back of the tank but the 150 will give you much more magnification [better close-ups].
The 100 is much more hand-holdable than the 150 so it'll be better for fish pictures, people portraits etcs. You'll probably find that you will need a tripod when you use the 150 for close-ups and although the same goes for the 100, it's quite a bit easier to hold steady than the bigger 150. You'll still be able to use the 150 on things that are close to the glass in the front of the tank-- you'll just have to move back a bit. Plus you could add extension tubes to the 150 and get extreme close-ups in the middle and front of the tank, whereas with the 100 you can only get extreme close-ups of things that are less than six inches away from the lens.

i keep taking notes, then get a grasp of what i'm doing...but if i dont use the knowledge i just learned, for a couple weeks....i forget it all again.

I know exactly what you mean... that's why the best learning tool is practice

 

[surfnvb7]

<a href=showthread.php?s=&postid=9835556#post9835556 target=_blank>Originally posted</a> by gregr
You'll still be able to use the 150 on things that are close to the glass in the front of the tank-- you'll just have to move back a bit.

are there any downsides with having to move the camera away from the tank? i know i've always been advised to put the lens up as close to the tank glass as possible. i already shoot with a tripod, so thats not a big deal.

do i need to make sure to have the rest of the room dark? i'm just thinking if the camera is too far away from the tank, does ambient room lighting play a role in how the lighting in your picture will turn out? (maybe i'm thinking in my mind i'll have to move the camera back alot further from the tank than i'll really need to in reality).

i shouldn't have to move it further back than 12" from the tank for a picture of something in front of the tank, right?

 

[gregr]

Yep- it will only be a foot or so. Ambient light will have minimal impact on the picture but reflections can be a hassle. Like you said, the closer you are to the tank the less you have to deal with reflections, but a foot isn't that much.
The downsides of the 150 are the weight and loss of ability to handhold at slower shutter speeds and the cost. The upside is the extra reach. If you like to shoot things like dragonflies and flowers and such, it will be better than the 100 for that. The 100 is cheaper, more hand-holdable, better for portraits and fish shots, and though I've not got to play with the Sigma, the Canon probably focuses faster. I'm sure there are other considerations I'm not remembering but the bottom line is they both have their strong and weak points... these decisions are rarely easy.
One thing to check on is if you can use extenders [teleconverters] with the Sigma without having to have a small extension tube in between.