Best lens for basic shoooting

[Tom Camilleri]

I inherited two lenses in addition to the 300D kit lens (EF-S 18-55), a Canon 50mm compact macro and a canon ET-62II 100-300mm. Of the three, which is best for studio shooting with tripod and general hand-held shooting?

I have not tried the 100-300mm lens with the Rebel but the compact macro works well. Are there any drawbacks to using EF lenses instead of EF-S?

[Jon]

For studio work, the 50 macro will be dynamite. It's tack-sharp and focusses extremely close. It's also the fastest of the bunch, and a good length for portraits.

There is absolutely no reason to not use EF lenses rather than EF-S lenses. An EF-S lens will only work on a limited number (DR, 20D, and DREX, in order of release) of EOS bodies, while the EF lenses will work on any EOS ever made, so you're protected against format changes.

[cactusclay]

Yea, what Jon said.

[CyberDyneSystems]

Tom,

Also,.. please take a look at the "EOS Sticky" thread and more to the point,. the "Top 10 recommended lenses" sticky thread in the EOS forum... the "Top ten" lists may be of further assistance as you contemplate these future lens decisions.

:)

[Tom Camilleri]

Thanks for replies. Question regarding the 50mm compact macro: When focusing, the lens extends depending on subject distance. Is the focal length changing or does it remain a constant 50mm?

[Tom Camilleri]

Will do. Thanks!

[slin100]

Thanks for replies. Question regarding the 50mm compact macro: When focusing, the lens extends depending on subject distance. Is the focal length changing or does it remain a constant 50mm?
It's probably increasing. You can probably check by looking through the viewfinder and noting whether the field-of-view increases or decreases as you turn the focus ring from infinity to closer distances. If the FOV increases, then the focal length is decreasing. If the FOV decreases, then the focal length is increasing.

Another way to check is to calculate the focal length using the basic lens equation 1/f = 1/i + 1/o and the published minimum focus distance and magnification at that distance. For the 50/2.5, the minimum focus distance is .230 meters at .5 magnification. Magnification is equal to i/o. The focus distance is equal to o + f. With this information, solving the lens equation for f produces f = 57 mm. So, there is a modest increase in focal length.

[DocFrankenstein]

Thanks for replies. Question regarding the 50mm compact macro: When focusing, the lens extends depending on subject distance. Is the focal length changing or does it remain a constant 50mm?
I'm be pretty damn sure it does not.

Primes changing focal lengths and pigs flying is a similar phenomenon. :confused:

[slin100]

Doc, not sure where you got the idea to the contrary, but nothing requires a lens, even a prime, to maintain a constant focal length at focus distances less than infinity.

[Jon]

Another way to check is to calculate the focal length using the basic lens equation 1/f = 1/i + 1/o and the published minimum focus distance and magnification at that distance. For the 50/2.5, the minimum focus distance is .230 meters at .5 magnification. Magnification is equal to i/o. The focus distance is equal to o + f. With this information, solving the lens equation for f produces f = 57 mm. So, there is a modest increase in focal length.
Faulty assumption here. The focus distance is actually, per Canon USA's posted specs on that lens, film plane to subject, or i+o. Now a 50 mm lens at 1/2 life size will have a total distance, film plane to nodal point (i), of 75 mm, and nodal point to subject (o) of 150 mm (i+o=225 mm). And the lens is an asymmetrical design which usually means that the nodal points for ray tracing from the front and from the back are different. With front extension focussing at max extension is well within the bounds of reason; the lens certainly doesn't become a 57 mm at 1:2. A macro that behaved so variably would be unsuitable for precision macro work, where you commonly need to photograph a subject at a known, standard, magnification.

A prime, by definition, maintains a constant focal length. If the focal length changed, they'd call it a zoom. It's remotely possible that a complex lens design, with several groups moving in different directions at the same time, will result in a lens that may vary in focal length by a percent or so across the full range, but that is a very easy problem to handle in the design stage, so if a lens did exhibit such behaviour it'd be a sign of a really cheap design.

[DocFrankenstein]

QED Jon TY

[Mike Panic]

another vote for the 50mm unless you have at least 40' of room to work w/ the 100-400

[Tom Camilleri]

Thanks for replies. Looks like the 50mm compact macro will do the trick for now. Knowing that the focal length is constant will enable me to make easy depth of field calculations.

This thread highlights the need for an understanding of optics. Can anyone suggest a book with the right level of depth? I never studied optics per se, but covered the elements in physics 101 (alas, now rusty).

[slin100]

Faulty assumption here. The focus distance is actually, per Canon USA's posted specs on that lens, film plane to subject, or i+o. Now a 50 mm lens at 1/2 life size will have a total distance, film plane to nodal point (i), of 75 mm, and nodal point to subject (o) of 150 mm (i+o=225 mm). And the lens is an asymmetrical design which usually means that the nodal points for ray tracing from the front and from the back are different. With front extension focussing at max extension is well within the bounds of reason; the lens certainly doesn't become a 57 mm at 1:2. A macro that behaved so variably would be unsuitable for precision macro work, where you commonly need to photograph a subject at a known, standard, magnification.

A prime, by definition, maintains a constant focal length. If the focal length changed, they'd call it a zoom. It's remotely possible that a complex lens design, with several groups moving in different directions at the same time, will result in a lens that may vary in focal length by a percent or so across the full range, but that is a very easy problem to handle in the design stage, so if a lens did exhibit such behaviour it'd be a sign of a really cheap design.
Jon,

Thanks for pointing out my mistake. I'm still not convinced that a prime maintains a constant focal length at all focus distances. There are certainly primes with complex lens designs and it doesn't seem far-fetched to imagine that the designers could allow focal length to vary a bit. My 50/1.8 Mk I exhibits a FOV change (i.e. zooming effect) as I twist the focus ring. Now, it may be that the nodal point is simply moving out while the focal length is kept constant.

I came across this rather interesting article by Bob Atkins on measuring focal length. In it, he states that the focal length can vary by a large amount at close distances:
Close focusing telephoto zooms with internal focus often get that close focus by reducing the focal length. So when you have your 300mm zoom focused down to 12", it's probably only really acting as a 100mm lens.
http://bobatkins.com/photography/technical/measuring_focal_length.html

True, his comment is about a zoom lens, a far cry from a prime. You may very well be right that primes never vary focal length. Unless I can find the time to perform some measurements, I'll have to concede the point. Thanks!

[Edit: Forgot to mention that also came across so-called "Variable Primes" lenses, which are used in cinematography. They are primes that can vary focal length, but are not zoom lenses. Can't quite wrap my head around that concept, though. :o ]

[Jon]

[Edit: Forgot to mention that also came across so-called "Variable Primes" lenses, which are used in cinematography. They are primes that can vary focal length, but are not zoom lenses. Can't quite wrap my head around that concept, though. :o ]

Back in the Good Old Days, many "zoom" lenses for SLRs were actually "Vari-Focal". They varied the focal length, but the point of focus shifted as you changed focal length setting. This is possibly what the cinematographers were using. Or they could be using add-on elements like P&S tele or wide converters (or the swappable front-end elements of the Canon EX). So, they can be used at any given focal length, but the focal length can't be changed while the lens is in use.