Effective Reproduction ratio 50/2.5 macro

[puttick]

After much thought, I'm buying a Canon 50/2.5 macro to use with my 300d. One "issue" often referred to with this lens is the limitation to a reproduction ratio of 1:2 - but having thought about it, while this lens was designed for full frame 35mm film, I will be using it on a dSLR with the APS-C size sensor of 22x15mm.

Consider an object with a horizontal dimension of 36mm. With the lens set for a reproduction ratio of 1:2 the size of the image at the film plane, on full-frame 35mm film (36x24mm), would be 18mm wide. The same lens on the 300d, with the same lens flange to image distance of course, will give the same sized actual image, i.e. 18mm wide. But this image will be on a 22mm wide imaging chip, so while the actual (optical) reproduction ratio remains the same at 1:2, in relation to the frame size the effective reproduction ratio becomes 22/18 or approx 1:1.22. This is quite close to the 1:1 everyone seems to want, but think they need a different lens to achieve.

There is of course no true gain in resolution for this effective gain in "magnification", but surely it is true that the best things in life are free. With the 100mm you would be getting an effective reproduction ratio of 1:0.61, a lot more than the 1:1 you thought you paid for!

Or perhaps you have a different view on this?

Incidentally, my reasons for choosing the 50mm over the 100mm:
1. Cost
2. Size
3. Fills the gap nicely between my 17-40 and 70-200
4. Greater depth of field for a given field of view due to shorter focal length

Of course I know that the working distance is less with the 50mm, and I will have to learn to live with that.

[rraman]

You may consider Sigma 50mm macro lens that gives you 1:1 macro without any additional attachments.

[Jon, The Elder]

Yep- agree with rraman-
I have the Sigma and it is a beauty !!

[Jon]

After much thought, I'm buying a Canon 50/2.5 macro to use with my 300d. One "issue" often referred to with this lens is the limitation to a reproduction ratio of 1:2 - but having thought about it, while this lens was designed for full frame 35mm film, I will be using it on a dSLR with the APS-C size sensor of 22x15mm.

Consider an object with a horizontal dimension of 36mm. With the lens set for a reproduction ratio of 1:2 the size of the image at the film plane, on full-frame 35mm film (36x24mm), would be 18mm wide. The same lens on the 300d, with the same lens flange to image distance of course, will give the same sized actual image, i.e. 18mm wide. But this image will be on a 22mm wide imaging chip, so while the actual (optical) reproduction ratio remains the same at 1:2, in relation to the frame size the effective reproduction ratio becomes 22/18 or approx 1:1.22. This is quite close to the 1:1 everyone seems to want, but think they need a different lens to achieve.

There is of course no true gain in resolution for this effective gain in "magnification", but surely it is true that the best things in life are free. With the 100mm you would be getting an effective reproduction ratio of 1:0.61, a lot more than the 1:1 you thought you paid for!

Or perhaps you have a different view on this?

Incidentally, my reasons for choosing the 50mm over the 100mm:
1. Cost
2. Size
3. Fills the gap nicely between my 17-40 and 70-200
4. Greater depth of field for a given field of view due to shorter focal length

Of course I know that the working distance is less with the 50mm, and I will have to learn to live with that.

You're sort of right on the magnification issue. The reproduction ratio is the ratio between the size of the original object and the size of the image as recorded by the film/sensor. A 36 mm object at 1:2 reproduction ratio will yield an 18 mm image on the sensor no matter what size the sensor is. But what you're talking about is the extra enlarging magnification you need to make to get a full-sized print from the 15x22.5 mm sensor of the DR vs that from a full-frame camera. You could get the same magnification by cropping the full-frame image to 15x22.5, but it's still empty magnification. It won't add any detail that wasn't captured at 1:2 but would have been at a true 1:1 reproduction ratio. This is the other end of the dreaded crop factor argument. There's no substitute for a true 1:1 reproduction of a macro, just as enlarging the 7734 out of the center of a 50 mm shot won't be as good as shooting with a 400 mm telephoto in the first place.

[tim]

I think about this slightly differently. I just ordered the Canon 100mm macro today, which is 1:1 at 6 inches. At 6 inches if I were on a full frame camera i'd be able to capture something 35mm across, on my rebel i'll be able to capture something 22mm accross. The 1.6X should more accurately be referred to as a "crop factor", as nothing is magnified, it's just cut the edges off. Like you say, you get no more detail or resolution that you would on a full frame camera, you just get less of the photo.

[puttick]

I think about this slightly differently. I just ordered the Canon 100mm macro today, which is 1:1 at 6 inches. At 6 inches if I were on a full frame camera i'd be able to capture something 35mm across, on my rebel i'll be able to capture something 22mm accross. The 1.6X should more accurately be referred to as a "crop factor", as nothing is magnified, it's just cut the edges off. Like you say, you get no more detail or resolution that you would on a full frame camera, you just get less of the photo.

Actually, at 6 inches, you'll be able to capture that 35mm object, but only see 22mm of it! The size of the image at the focal plane will be the same for both film and 300d.

I completely understand the crop factor - in fact, that's my point. The engraving on the lens barrel refers to image size, not magnification. Most users seem to think in terms of magnification in the final image. I stated there is no gain in resolution.

PS re the Sigma 50 - I'm sure it's a fine lens. But I bought the Canon because it will do what I want, compatibility is guaranteed, and it will have a better resale value (probably).

Cheers
Nigel

[tim]

Actually, at 6 inches, you'll be able to capture that 35mm object, but only see 22mm of it! The size of the image at the focal plane will be the same for both film and 300d.

That's exactly what I meant... maybe not quite what I said though ;)

[puttick]

Interestingly, in Canon's latest CPS Newsletter (no 10) there is an article on Macrophotography By Greg Basco. He writes:

"One of the things I like about the Canon 10D is its 1.6x magnification factor. This is a true gift for the macrophotographer as it allows us to gain increased magnification at a reasonable working distance. This is especially helpful when shooting close-up portraits of animals like vipers."

See: http://www.cps.canon-europe.com/home.jsp

I rest my case!

[tim]

Interestingly, in Canon's latest CPS Newsletter (no 10) there is an article on Macrophotography By Greg Basco. He writes:

"One of the things I like about the Canon 10D is its 1.6x magnification factor. This is a true gift for the macrophotographer as it allows us to gain increased magnification at a reasonable working distance. This is especially helpful when shooting close-up portraits of animals like vipers."

He's wrong: it's a crop factor, not a magnification factor. The only way to get 1.6* magnificantion is by changing the lens, adding filters, that sort of thing. The difference with the 10D is they just slapped in a smaller sensor. Sure, you get a picture that has the same content as a camera with a full frame sensor and a 1.6* greater length lens, but you miss on detail.

[Burdy]

You can use a Teleconverter 1.4 combinded with a 12mm extension tube to get 1:1.
The Teleconverter is very usefull on your 70-200!

Bram

[jylitalo]

Consider an object with a horizontal dimension of 36mm. With the lens set for a reproduction ratio of 1:2 the size of the image at the film plane, on full-frame 35mm film (36x24mm), would be 18mm wide. The same lens on the 300d, with the same lens flange to image distance of course, will give the same sized actual image, i.e. 18mm wide. But this image will be on a 22mm wide imaging chip, so while the actual (optical) reproduction ratio remains the same at 1:2, in relation to the frame size the effective reproduction ratio becomes 22/18 or approx 1:1.22. This is quite close to the 1:1 everyone seems to want, but think they need a different lens to achieve.


Just to verify something... with 20D (or 300D, 10D and other 1.6x cameras), 1:2 macro would be able to capture areas, which are only 45x30mm (without any additional cropping) ?
I currently have 17-40/4, 50/1.8 II, 70-200/4 and old 28-80/3.5-5.6 for my dSLR. None of these lenses seem to be able to win my old Canon G3, which can be used to capture 55x41mm on its small 4Mpix sensor in macro mode. With dSLR, I keep on finding myself in situations, where I am too close to target for lens to focus (70-200mm might be able to do it at 200mm end, but it needs space, relatively fast shutter speed and so on).
From what I've read on this forum, 100/2.8 is generally considered to be the better choice for macro. However, at this point, I don't want to have yet another lens to be carried with tent, sleeping bag, etc. to hiking trips, and 50mm macro could work as good replacement for my 50/1.8 II. On those trips, 50/2.5 macro would give me macro lens for plants, flowers, berries, etc. and I could use that same lens in the evening around campfire, where I need faster lens than what f4 zooms has to offer.


Incidentally, my reasons for choosing the 50mm over the 100mm:
1. Cost
2. Size
3. Fills the gap nicely between my 17-40 and 70-200
4. Greater depth of field for a given field of view due to shorter focal length


These are also good arguments for 50mm macro. Number four especially is good, since I don't normally take tripod to hiking trips, vacations, etc.. Instead of tripod, I use my hiking stick (which has screw on it) as monopod.

- Juha, http://www.ylitalot.net/