Macro and Crop Factor

[milster]

Not sure if this is in the right forum.

I'm hopefully going to purchase the Tamron 90mm macro today so I've been thinking about this (not that it's going to effect my purchase).

The Tamron I believe works on both full frame and crop sensor cameras, so my question is, what does the "crop factor" effect in terms of the lens? I presume you can only reach a magnification of 1:1 on either sensor so the crop factor is just effecting the working distance? So, if that's the case on the new d7100 there will be a 1.3 crop mode on that which will make the crop 1.95 effectively, so will that give me a greater working distance or greater magnification? My thoughts are that I'd end up with what would effectively be a 175mm ish 1:1 lens, is that right?


Hope this makes sense.

Cheers,

Gary.

 

[Phil V]

Given the variable focal length and minimum focusing distance of that lens, it'll take some smart maths to create a table to give technical specs to answer your questions.

But simply, as far as the crop factor and 'effective focal length' are concerned, it only offers confusion because it's not technically correct.

You'll be at the same working distance when you reach 1:1 ratio, but your field of view will be narrower, so the object takes up more of your frame - but is the same size on the sensor.

I'll leave the rest of my 'crop sensor equivalence' rant apart from to say, why does it matter - you're fitting a 90mm Macro to a crop camera. What does it matter that it'd be different on a FF body?

 

[milster]

Thanks for the reply Phil.

I'll leave the rest of my 'crop sensor equivalence' rant apart from to say, why does it matter - you're fitting a 90mm Macro to a crop camera. What does it matter that it'd be different on a FF body?

I know what you're saying and it doesn't make any difference to me, I was really just wondering if I'd end up with a greater working distance when I hopefully upgrade to the d7100 really

 

[PaulButler]

No, the working distance will remain the same on the D7100, D7000 or an FX body

 

[Canon Bob]

The working distance at a specific magnification will be the same as it's a property of the lens. If you have a subject that is bigger than your sensor then the working distance to fill the frame will be greater on a cropped sensored body than a full frame body (but the resultant optical magnification will be less)

Bob

 

[woof woof]

I presume you can only reach a magnification of 1:1 on either sensor so the crop factor is just effecting the working distance?

Personally I've never worried about the magnification factor and I've always used macro lenses to allow me to fill more of the frame with smallish subjects so whilst I wont attempt to answer the question I can give you my experience as a psudo macro shooter ...

When moving from a 20D to a 5D and using my Sigma 150mm f2.8 I obviously had to decrease the camera to subject distance to get the equiv view that I got with the 20D. The decreased camera to subject distance in turn meant that I had to use smaller apertures with the 5D to get the equiv DoF that I got with the 20D. Using smaller apertures then can have implications for shutter speeds and ISO settings.

 

[milster]

Thanks for the replies guys. I think I'm beginning to get it now