[normhead]

Magnification of different lenses at 8 feet.

(Or it's hot, how can I feel like I'm doing something without actually moving.)

Magification is the size an object in real life, compared to the size it is on the sensor. SO a 1:1 macro, a small fly will be exactly the same size on the sensor as it is in real life. Of course when you blow the sensor image up to 11x14 for your screen it will by hundreds of times life size, but, that's the standard.

If magnification was 1:6, the image would be 1/6th life size etc.

A 135 mm lens is 135 mm at infinity, that's how they are measured. So if it's a simple lens the light coming into the lens, the photons will be functionally parallel. That's what infinity means optically. With a simple 135 mm lens, the light will focus, 135mm from the optical centre of the lens. As you ficus a simple lens, if the focal plane is constant, you have to move closer to the subject, to maintain the subject in focus, with a simple lens, to keep the subject in focus therefore, you are functionally enlarging it.

With my 70-210 as I focus, the front element moves closer to the subject, and the effect of that is more magnification. With my 60-250, the front element remains in the same place and internal elements move, meaning there is not as much magnification even though they would create the same result at infinity. Since almost all lenses have more than one piece of glass in them, some having 8 to 13 elements as part of their CA correction design, each lens focusses to different levels of magnification at different distances from the subject, except for focussed on something at infinity, which should produce the same result.

OK here I've run a brief test for you, to show the new glass old glass thing.

The oldest.... all taken 8 feet from the ruler from the same tripod position.

Vivitar M-135... showing 17 real inches of image.


F 70-210, set to 135mm shows 17 inches of real image


The DA* 60-250 @ 250 mm shows 13.5 inches of real image.


The DA* 18-135mm shows 21 inches of real image


The DA* 60-250 shows @ 135mm shows 20.5 inches of real image.


Hence at 8 feet, I'm getting less magnification from my 60-250 at 135.. than I did with my Vivitar 135 or F 70-210 at 135mm. And the DA 18-135 is like a half inch better than the 60-250 both at 135mm.

Want more magnification from your DA*60-250, you have to use the HD DA 1.4 TC which gives you 350mm and 10 real inches, and in all fairness, the 1.4 works well with the 60-250, purples fringing becomes an issue on the 18-135 and Vivitar 135 and F 70-210, , and probably will with any lens that extends it's front element when focusing. so a TC not really an options on those lenses


Or really want to crank it up use the DA*60-250 and F 1.7 x AF converter at 425mm... 8 inches...


Of course, the most magnification close in is going to be my A-400 first by itself at 5 inches...


And then with the 1.4 TC at 3.5.


But for some real magnification you want something like this...SIgma 70 with the HD DA 1.4 TC walked right in to the 1:1 setting - 16mm on a 22mm sensor..
That's about .4 better than 1:1. The DoF is so narrow, the ruler goes out of focus where the blade is slightly sloped.

As general observation based on my own shooting practice, if you are shooting small birds and animals close to you, use older glass, or, a TC on your newer glass. At least with my images, older glass equals more magnification close up, newer glass equals reduce magnification. If you are used to an F 70-210 you're going to be disappointed with the magnification of your new 60-250. The 70-210 is more magnification at 8 feet, than the 60-250.

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Last edited by normhead; 07-11-2015 at 12:38 PM.

[JimmyDranox]

That's a really interesting article, with some unexpected results.

If would be even more interesting if you can repet the tests with a target at more than 50x the maximum focal length, to get valid results for infinity.

[normhead]

That's a really interesting article, with some unexpected results.

If would be even more interesting if you can repet the tests with a target at more than 50x the maximum focal length, to get valid results for infinity.

There's a church with a big white cross across the valley from me, probably a Km away. But it's obscured by leaves right now. I can look for something else.

[starbase218]

But for some real magnification you want something like this...SIgma 70 with the HD DA 1.4 TC walked right in to the 1:1 setting - 16mm on a 22mm sensor..

But that's not at 8 feet, right?

[normhead]

But that's not at 8 feet, right?

That's like 2 cm.

what I meant by "walked right in" was I set the lens to 1:1 and then walked the lens until it was in focus, or focused with my feet instead of zoomed with me feet.

Thats probably an odd concept to people not used to trying to get the most magnification out of a macro, lens.

[JimmyDranox]

A building with glass and steel wall, from a bigger distance will be good.

[starbase218]

That's like 2 cm.

what I meant by "walked right in" was I set the lens to 1:1 and then walked the lens until it was in focus, or focused with my feet instead of zoomed with me feet.

Thats probably an odd concept to people not used to trying to get the most magnification out of a macro, lens.

It's not. I had a macro lens, but then decided it wasn't my kind of photography.

[MikePerham]

This test should really be run at infinity which is how focal length is rated. Also, you will find differences due to focus breathing ...lot's of articles on the web about that.

[transam879]

I believe that with lens that focus internally, the magnification of the image varies, since the front element is fixed at a particular focal length. The focusing is done by moving an element(s) inside the camera, thus altering the magnification. I remember a post awhile back on here that mentioned that the 60-250 is actually closer to 200mm (while extended to 250mm) depending on the distance of the subject. I believe it's only truly 250mm when focused at infinity. Something close it's more likely to be equivalent to 200mm despite being set at 250mm. Just wanted to throw that out there and if anyone with more technical knowledge can clarify, please do so. I'm trying to recall a previous post that I read on a similar topic with the 60-250.

[normhead]

This test should really be run at infinity which is how focal length is rated. Also, you will find differences due to focus breathing ...lot's of articles on the web about that.

No it shouldn't be run at infinity, although I did that. And the reason is at infinifty every 135 I've tested has been close to the same magnification. But at 10 feet , they are different. So if most of you shooting is done from 10-20 feet, like many of my bird images, then you need to know which 135mm lens will give you the biggest little birds.

Some of us like our porch birds filling the frame, even if they are 5 times life size. This is my A-400, the DA*60-250 even with the 1.7 AF TC wouldn't have given me as much magnification, even though it's technically 425mm. Some of us take our porch bird images very seriously.

[ScooterMaxi Jim]

Nice image, Norm.

I do believe that internal focus (modern lenses) are going to be more likely to exhibit focus breathing. Achieving internal focus does involve serious design compromises - and that's a big part why some old zooms with rotating front element and projecting barrels are optically superior to several current designs (without naming names). Bottom line, the 60-250 is nearly 5:1 and yes, you have focus breathing. That's probably its worst fault. I don't have the lens, but I am fairly sure that - based on the images I've seen from the lens and its relatively solid history - it qualifies as the best overall Pentax zoom over its several years of use. The new zooms are also promising.

[southlander]

Firstly, the distance to target measurement is correctly done from the plane of the film or sensor, not from the position of the front element. There is a little mark on the camera to show where this is. Depending how a lens manages its focusing once it moves off infinity towards minimum focus in terms of what lens elements are getting moved about, magnification changes may vary from lens to lens. Internal focussing lenses, particularly zooms, tend to reduce effective focal length as they are focussed closer. The DA*60-250 is fairly well known for showing more of this effect than most but it can be observed on other internal focussing lenses as well.

Older prime lens often just move all of the elements forward - in effect the helicoil is simply mimicking the adding of extension tubes.

[Lowell Goudge]

Sadly, this issue has been beaten to death already. It is a well established fact that many lenses which use internal focusing, not just zooms but primes alter their focal length as you focus closer, resulting in lower than expected magnifications.

Focal length is only tested at infinity, and sadly, there is no lens testing standard that requires makers to publish charts of effective focal length vs focus distance

This issue, I believe was first discussed at the release it the Pentax K28/2 with Fixed rear element design (the forerunner of internal focusing) in the 1970's It keeps coming up as people forget the trade off you make for internal focusing

[normhead]

Sadly, this issue has been beaten to death already. It is a well established fact that many lenses which use internal focusing, not just zooms but primes alter their focal length as you focus closer, resulting in lower than expected magnifications.

Focal length is only tested at infinity, and sadly, there is no lens testing standard that requires makers to publish charts of effective focal length vs focus distance

This issue, I believe was first discussed at the release it the Pentax K28/2 with Fixed rear element design (the forerunner of internal focusing) in the 1970's It keeps coming up as people forget the trade off you make for internal focusing

It comes up every time someone gets blindsided by less than expected magnification from a new lens. It's not like this information is readily available to new users.