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Advice on Zenit ET
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PostPosted: Mon Sep 10, 2007 8:49 pm    Post subject: Reply with quote
Rick, you are right regarding the field of view. But for me depth of field matters and makes the difference. Otherwise I would not use a dslr but a bridge camera with the small sensor.

An example what I mean? Calculated with the help of www.dofmaster.com:

I make an open aperture portait with my 85mm Helios 40-2 at f2 using the full frame 5D - subject distance 8 feet. The total DOF is 0,31ft.

Now same FOV with a 350d/rebel xt. You will need a focal length of 53mm to overcome the crop factor of x1.6. And to get the same small DOV you will need an aperture of approximately f1.2 - sorry, such lenses are to expensive for me Very Happy
And I don't even speak of what I need if I would choose f1.5 with my Helios at the 5D - f0.9 at 350D/rebel xt? Twisted Evil

If you are shooting mostly landscapes, architecture or animals and you want your images sharp from here to eternity - then you can go for a crop camera and the discussion is really philosophical. But if you're shooting portraits with small depth of field THEN sensor size matters very much!

Michael


PostPosted: Mon Sep 10, 2007 9:04 pm    Post subject: Reply with quote
Borges wrote:

If you are shooting mostly landscapes, architecture or animals and you want your images sharp from here to eternity - then you can go for a crop camera and the discussion is really philosophical. But if you're shooting portraits with small depth of field THEN sensor size matters very much!
Michael


As an aesthetical consideration, I would add that for some purposes, such as portraits, some lenses derive their character by the contribution of the peripheral regions of the glass to the whole picture.
The Helios-40-x is a perfect example. It's most evident feature, wide open, is the combination of the blur and flare to create it's most unique "bokeh".
Shooting with a crop camera, you only use the central portion of the glass, therefore actually leaving out most of what gives the lens it's "special character". This is a case (quite singular, I admit) where the cropping of the FOV has a negative impact on the image quality (when you define as quality the goal of your efforts and not simply the result of a scientific test) - of course in 99% of the situations, where you hunt for the most detailed possible result, the cropping does increase the image quality.

And speaking widely, we can say that, for the better or the worse, the crop factor does influence the IQ in a significant way. Many of the lenses that I have, which appear perfect in a crop camera image, display corner or side problems in a full frame image.
I'd say that the whole evaluation of a lens can be mislead (for the better or the worse) if you only see it used on a crop camera. Especially with the super wide angle lenses, that are usually weakest in the corners.
OK this is not what Rick was talking about, but I think it is something that is worth considering.


PostPosted: Mon Sep 10, 2007 10:31 pm    Post subject: Reply with quote
Borges wrote:
Rick, you are right regarding the field of view. But for me depth of field matters and makes the difference. Otherwise I would not use a dslr but a bridge camera with the small sensor.

Michael


You're absolutely right, Michael - your calculation agrees with mine above, it takes 1 1/3 stops extra to equal the DOF of a full frame onto the 1.6:1 crop camera given the same field of view. The "equivalent" focal length, I believe, has always referred to the lens that produces the same perspective and field of view.... at least this is how I've always seen it refferred to regarding 4x5, medium format and 35mm full and half frame and subminiature film cameras.

It is and has always been a fact that smaller formats give greater depth of field at a given relative aperture. Whether it's practical to duplicate the DOF of a larger format onto a smaller one depends on what aperture you started out with: going from f/2 to f/1.2 is more of a challenge than going from f/2.8 to f/1.8.

: ) =


PostPosted: Mon Sep 10, 2007 10:37 pm    Post subject: Reply with quote
I join to Orio's opinion crop cameras take out lens IQ. On Olympus E-1 many lens perform worst than on Nikon D50, just the selected best ones can perform same than less good on Nikon D50. This is my personal experience.


PostPosted: Tue Sep 11, 2007 12:17 am    Post subject: Reply with quote
Trying to get a shallow DOF on a small crop camera can be a double challenge:

For example, an 85/2.0 lens is a very nice, but not extremely exotic lens on a 35mm format.... they are usually very sharp, and reasonably affordable.

Getting the equal DOF on a 1.6x crop camera is possible, you need about a 50mm f/1.2. These are available, and older ones may not be excessively costly... BUT, f/1.2 is an extreme formula, and sharpness and contrast were sacrificed in order to achieve it. To this you have to add the fact that you need to enlarge the image 60% more than the full frame has to be enlarged to make the same size print. Most f/1.2 lenses just won't hold up under this kind of enlargement to compete with the performance of an 85/2.0. So if you're accustomed to operating in this range, you will have a hard time working with a reduced format. With a 2x crop of course the situation is the same but more extreme.

Shallow DOF is not what you want in every situation, and where you want more in focus the smaller formats have the advantage (as long as you don't like wide angles).

Given the cost of large format DSLRs, this may be an area where film still has something to offer. In addition to 35mms at sinking prices, there are some interesting 6x9cm folders with 105mm lenses which give a combination of shallow DOF and a large negative that doesn't require much enlargement and so yields a sharp print with a modest lens.


PostPosted: Tue Sep 11, 2007 6:56 am    Post subject: Reply with quote
Attila wrote:
I join to Orio's opinion crop cameras take out lens IQ. On Olympus E-1 many lens perform worst than on Nikon D50, just the selected best ones can perform same than less good on Nikon D50. This is my personal experience.


Attila, I think you have misunderstood me.
I made the case of the Helios-40 as a special case, because the edge of glass contributes to the special "dreamy" quality of the lens, but normally, the crop factor cameras make lenses look better than the real, because they only use the best portion of the optics (the central part).

In your specific case, I think that what you experience has more to do with the quality of the camera than with the lenses. Probably your Nikon camera is simply better than your Olympus camera - or perhaps you just happen to simply like the Nikon results better because that is your taste.


PostPosted: Tue Sep 11, 2007 6:57 am    Post subject: Reply with quote
I see , thanks!
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