Why bother?


Horst

Link Posted 28/06/2014 - 05:39
This is a portion of an add for an Tamron lens:

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Lightweight, compact fast standard zoom designed exclusively for digital SLRs, with 17mm wide-angle coverage
Exclusive design for digital SLR cameras achieves a fast standard zoom lens that covers virtually the same angles as focal lengths of 26-78mm when converted to a 35mm format. The wide-angle focal length is established at 17mm (26mm equivalent) to obtain a wider angle of view than ordinary standard zoom lenses, while maintaining the remarkably lightweight and compact size of the earlier full frame zoom lens model. Since the lens is designed exclusively for APS-C sized digital cameras, the image circle diameter has been reduced.

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What I don't understand is why the reference to the 35mm is given on a lens which is specifically designed for APS-C.

The reference to 35mm seems to be completely completely irrelevant for a lens which can not really to its full capability be used with a full frame camera.

I notice this all the time in lens reviews and descriptions.

Why would anyone give a hoot what the lens would be on 35mm if it is and can only be used on APS-C?

Regards, Horst

gartmore

Link Posted 28/06/2014 - 06:44
I quite agree. I have never understood the obsession of converting focal lengths of any lens to 35mm equivalent. Why don't we convert 35mm lenses to their medium format equivalent?
Ken
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -

bwlchmawr

Link Posted 28/06/2014 - 06:53
I think because a lot of photographers, self included, are old and spent years using mainly 35mm film cameras and their different focal length lenses. With the advent of digital, there were, and indeed are, so many different sensor sizes that in order to make sense of what one might see looking through a viewfinder, we needed to convert focal lengths back to 35mm equivalent. Thus, when I bought my MX-1 the fact that it had a 6-24mm lens meant nothing until I knew it was equivalent to 28-112 in 35mm terms.

But you're right, with APSC sized sensors dominating DSLRs we ought by now to understand that, for example, 18mm equals 27mm. Damn, I've just done it again.

Of course, people who own lenses designed specifically for cropped sensor cameras will be a bit stuck when/if Pentax ever make a "full" frame camera, whereas those with old glass will be happy to get their wide angle lenses back.
Best wishes,

Andrew

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johnriley

Link Posted 28/06/2014 - 08:05
I think the reason is that we needed a frame of reference for what a lens would do, in the early days of digital photography. At this point cameras were compacts or bridge cameras and they all had different sensor sizes. This meant the focal lengths meant almost nothing to anybody, so the idea of "35mm equivalent" was born.

I'm pleased that at least Pentax continued to mark the actual focal lengths on their lenses though, because some makers label them with the "35mm equivalent" and I find that quite annoying.
Best regards, John

Horst

Link Posted 28/06/2014 - 08:18
Well, the first thing I want to say, This time I am not trying to sell the advantages or disadvantages of the FF format.

bwlchmawr wrote:

Quote:
I think because a lot of photographers, self included, are old and spent years using mainly 35mm film cameras and their different focal length lenses. With the advent of digital, there were, and indeed are, so many different sensor sizes that in order to make sense of what one might see looking through a viewfinder, we needed to convert focal lengths back to 35mm equivalent. Thus, when I bought my MX-1 the fact that it had a 6-24mm lens meant nothing until I knew it was equivalent to 28-112 in 35mm terms.

But you're right, with APS-C sized sensors dominating DSLRs we ought by now to understand that, for example, 18mm equals 27mm. Damn, I've just done it again.

You have a point there, But what happens when us old Ex35mm users Get to old to hold the camera steady or conk it all together?
Doe this mean when the lens manufacturers bring out new 35mm lenses, they the do the opposite and say: 50mm equals 75mm on APS-C?

Back to the original question.

there is still a difference between using a 50mm lens on FF to using the equivalent lens :33mm on APS-C. You may get the same amount of the object on to your sensor, but: it looks quite different in the viewfinder.
It does not look life size anymore, but to fit the same amount on the Sensor , the image on the view finder is quite a bit smaller.

so if you where comfortable with the life size image, the 33mm lens is not equal to 50mm on APC-S.
In addition, It has more barrel distortion than the 50mm lens.
This is even more pronounced with the wider focal length.
So i suppose the conversion is correct if you just look the amount of picture you get on to your sensor. But that is all.
I suppose the Dof is also different. (I may be wrong), but a 33mm focal length is still a 33mm focal length. No matter what the size of the sensor.

And what about the F-stop? does that stay the same? or does that need to have a correction factor too?

Therefor I still believe , the only time a accurate correction is given, when a FF designed lens is used on APS-C is to state the actual angle of view in degrees.
But not when an APS-C only lens is designed. No other figures should be used except the focal length, Dof and the correct f-stop for this lens.

Having said all this, maybe I am to picky and therefore I will be sitting back with a glass of Cognac and thinking about other more important things.

Kind regards, Horst
Last Edited by Horst on 28/06/2014 - 08:25

vic cross

Link Posted 28/06/2014 - 08:27
Ken. When I had my 645 then I used to convert 35/645 and 645/35 lenses.
645 standard is 75mm lens = 35 standard 50mm lens now = APSc standard 35mm lens.
At that time I also had a converter and sometimes put my 645 lenses on my 35mm Z1p. I found it nice to know what the basic (standard = eye) lens length was. Having said all that I'm now used to the 1.5 crop sizes as that is all I use.
As Andrew says some of us are getting older (no one said anything about wiser) and still remember £.s.d. and feet and inches, and PINTS.
CHEERS Vic.
Born again biker with lots of Pentax bits. Every day I wake up is a good day. I'm so old I don't even buy green bananas.

Algernon

Link Posted 28/06/2014 - 08:37
As long as they don't start quoting what the equivalent
lens is on an iPHONE I'm quite happy with the 35mm equivalent

I still convert degC to degF

Strange that when the weather gets hot the papers, TV and radio
start quoting the temperatures in degF

--
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi

Algernon

Link Posted 28/06/2014 - 08:49
The Kodak Professional Photoguide (1975) has a very nice colour illustration showing angle of view equivalents for.....
8x10 inch
5x7 inch
4x5 inch
6x8 cm
6x7 cm
6x6 cm
35 mm

From that you can see that the equiv. of a 28mm (on 35mm) on 10"x8" is 200mm etc.

It also has rotating DOF calculators for all of the above.

--
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
Last Edited by Algernon on 28/06/2014 - 08:51

Horst

Link Posted 28/06/2014 - 09:10
Quote:
I still convert degC to degF

Strange that when the weather gets hot the papers, TV and radio
start quoting the temperatures in degF

.

I am glad we are a bit more advanced in the colonies.

only deg C here , only metric here and only dollars and cebnts.

All imperial measurements are gone.

Except the gas pipe threads.


Regards, Horst

MrB

Link Posted 28/06/2014 - 09:44
I do find the 35 mm equivalents helpful, and particularly on the small sensor compact cameras, e.g. MX-1.

(Off topic - the one I can't get used to is 'litres per 100 kilometres'. 'Miles per gallon' - now that's meaningful.)

Cheers.
Philip
Last Edited by MrB on 28/06/2014 - 09:46

Algernon

Link Posted 28/06/2014 - 10:12
I prefer miles and MPG as well..... The odd thing is that in the UK we have to convert one or the other to get fuel consumption either Litres to Gallons or Miles to Kilometres

Handy conversion site for lens focal lengths + Km/miles etc.

http://www.metric-conversions.org/length/kilometers-to-miles.htm

--
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi

McGregNi

Link Posted 28/06/2014 - 10:19
That's right Philip, its a needed reference... A lot of low-end cameras still use the rather meaningless '8x / 12x zoom' designations, which only indicate a multiplication factor, but without any real start point!

I suppose another question would be, does the 35mm reference only have meaning to the 'older' photographer now? I mean those who are serious, and there must be plenty of younger ones in that category... Aren't there? ...

And can we really expect the aps-c size to become a new reference in this changing world? Is it not the case that the 35mm sensor size is slowly becoming the new norm for increasingly more cameras, not just those at the professional end of the market. And surely soon enough we Pentaxians will not have to worry about any focal length crop factor as well ...
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Last Edited by McGregNi on 28/06/2014 - 10:23

1stEverPentax

Link Posted 28/06/2014 - 10:23
I'm an 'old timer' too...still use imperial for everything except currency which I have to agree is far more logical than using bases of 12 and 20. (plus you don't have a choice in this !). I can convert to metric from imperial but using imperial means more to my brain and more quickly. When I see metric I only end up converting it mentally to imperial and then using that info....might just as well cut out the middleman!

So, it should come as no surprise that i find the whole '35mm equivalent thing' very logical and useful...its a common standard in a constantly changing world.

bwlchmawr got it spot on in his comment.

Karlo

PIRATE

Link Posted 28/06/2014 - 19:20
Ahoy!

On one hand you're quite right, but there is one point that I'm sure a lot of APS-C users don't consider, and that is 'what you actually capture'. What I mean is this:

Lets take a 47" TV and call it full frame. Now take a 32" TV and we'll call this APS-C. Put the 32" in front of the 47". Now when using a FF lens on an APS-C camera, the bulk of the image is lost as the smaller 32" TV isn't big enough to capture the whole image that the lens is producing, though you'll get whatever can fit on the 32" APS-C TV which is the same size as what the 47" TV see's, but the smaller sized 32" captures less of the overall image, which is where full frame comes into it's own . . the cropping power.

The 1.5x crop factor only relates to the fact that you would have to be 1.5x further away with a full frame lens on an APS-C camera to see the same area captured on a full frame camera or 47" TV, though the subjects will be much smaller, so to say a 100mm full frame lens on an APS-C body is 150mm APS-C equivalent is bogus. There is no multiplication applied, you just don't get the full picture, though one benefit is that you see through the 'meat' of the lens and likely will not have any IQ fall-off towards the edges. So, a 300mm lens on APS-C isn't 450mm it's 300mm but you only see the 32" TV portion and not the whole 47" TV portion that the larger sensor would otherwise capture. What the smaller sensor doesn't capture is just lost.

That being said, with a zoom lens is where things do change as say a Tamron 17-35mm on an APS-C body cannot see the full width, so you lose the effective width which is why it's best to use a cropped WA zoom on an APS-C body so you get the whole picture and not just a portion of it.

Does anyone here actually use FF K-Mount lenses?
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K10D

Link Posted 30/06/2014 - 00:43
[quote:3496ace15f="Horst"]
Quote:
I am glad we are a bit more advanced in the colonies. only deg C here , only metric here and only dollars and cebnts. All imperial measurements are gone.

Except the gas pipe threads.


Regards, Horst

The pubs in Perth sell pints but charge in Fahrenheit figures as they are numerically larger, especially that 100/212 version where a 100% of cost outside of Australia means 212% in Perth.

To Mark:
I still use FF K-mount lenses, 28mm, 31mm, 43mm, 50mm and every M & A series lens I own. I specifically avoid buying cropped glass where possible.

Best regards
Last Edited by K10D on 30/06/2014 - 00:47
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