Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Sony Alpha dSLR / Konica Minolta dSLR, Sony SLT

Reply
 
Thread Tools Search this Thread
Old Dec 25, 2009, 12:27 PM   #1
Member
 
Join Date: Apr 2006
Posts: 45
Default General-purpose zoom for a100 kit lens replacement?

Helo.

I was thinking about replacing the kit lens of my A100 (or rather, replacing a 50mm/2.8 Sigma as general-purpose lens; I don't like the kit lens' optical properties very much). A fixed 50mm is too narrow as often as it isn't long enough, and the slingshot bag I have can't be carried all the time.

These two are my main contenters at the moment:
Sigma 17-70mm 2.8-4.5, and
Minolta 24-105mm 3.5-4.5.
Both can be had for aproximately the same price(∼350USD; I'm in Europe.) The Minolta mightn't be wide enough (36mm 35mm equiv. on the aps-c a100), on the other hand 36mm is noticably better than 50mm, and it has better reach than the Sigma. Still, I think 17-70 is the more attractive range for this purpose, though the bokeh of the Sigma 50mm I already own isn't absolutely great, and if the Minolta's is anything like the beercan's..

The other lenses in my bag, for additional information, are the kit lens (seldom used), the 'beercan', and a tamron 11-18 (which I can but seldom achieve the sharpness I want with and which overdoes contrast and underexposes a tad too heavily).

Last edited by Lindinblade; Dec 25, 2009 at 12:37 PM.
Lindinblade is offline   Reply With Quote
Sponsored Links
Old Dec 25, 2009, 9:09 PM   #2
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,543
Default

Both the Minolta 24-105 and the Sigma 17-70 are very good lenses. The Sigma more closely duplicates the 18-70 kit lens you want to replace, it's faster, a lot sharper, and it is a 1:2.3 macro lens to boot. The Minolta only goes to 24mm, which, on an APS-C body, isn't very wide. It would leave a significant gap in your range, between the 24mm focal length (62 angle of view), and the 18mm focal length (77 angle of view) of the Tamron.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Dec 26, 2009, 4:48 AM   #3
Member
 
Join Date: Apr 2006
Posts: 45
Default

Sooth.

11-18mm, 36-157mm, 105-315mm (35mm-lens-on-35mm-body equiv., by how I understand it) is a bit more redundant & gap-filled than
11-18mm, 17-70mm, 105-315mm.

I wonder how these two would compare, iq-wise?

The Minolta 24-105mm gives results identical to the (now discontinued too) Sony version, yes? From what I've read, this means ok sharpness when stopped down a bit, quite neutral colors, and ok, if not beercan, bokeh.

The Sigma is supposedly rather sharp and can of course focus from a closer distance, which is mostly a plus. I don't mind 'Sigmaish colors', but the bokeh of my 50mm prime isn't as neat as the beercan's, and I wonder if that is somewhat the same for these two. Edit: At this very moment, the 24-105mm is around 330USD, while the 17-70 is at approx 415USD. Ebay prices are in a constant state of flux though, of course.

Last edited by Lindinblade; Dec 26, 2009 at 6:35 AM.
Lindinblade is offline   Reply With Quote
Old Dec 26, 2009, 10:04 AM   #4
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,543
Default

Quote:
Originally Posted by Lindinblade View Post
11-18mm, 36-157mm, 105-315mm (35mm-lens-on-35mm-body equiv., by how I understand it) is a bit more redundant & gap-filled than
11-18mm, 17-70mm, 105-315mm.
Not quite.

The focal length of a lens is the focal length of a lens; it doesn't change with the camera body it's mounted on. If you're going to apply the crop factor to obtain the 35mm equivalent focal length, you need to do it for all your lenses. Depending on the choice you make, you'd have 11-18, 24-105 &70-210 or 11-18,17-70 & 70-210. Or, if you prefer, 16-27, 36-157 & 105-315 or 16-27, 25-105 & 105-315.

As I said, they are both very good lenses, and, yes, the Minolta is the same as the newer Sony. The only difference might be that the Sony will have the coatings on the rear element that will prevent ghosting and flare from the digital image sensor, which is more reflective than film. It is unlikely that the Minolta would have those same coatings.

And you can't judge the bokeh of one lens by the bokeh you've seen on another, whether they're fromt he same manufacturer or not. You shouldn't use your experience with an earlier Sigma lens to presume how a different Sigma lens will perform.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Dec 26, 2009, 11:17 AM   #5
Member
 
Join Date: Apr 2006
Posts: 45
Default

Quote:
Originally Posted by TCav View Post
Not quite.

The focal length of a lens is the focal length of a lens; it doesn't change with the camera body it's mounted on. If you're going to apply the crop factor to obtain the 35mm equivalent focal length, you need to do it for all your lenses. Depending on the choice you make, you'd have 11-18, 24-105 &70-210 or 11-18,17-70 & 70-210. Or, if you prefer, 16-27, 36-157 & 105-315 or 16-27, 25-105 & 105-315.
I see; I guess I haven't exactly understood that bit yet. I thought aps-c lenses were 'cropped' to fit aps-c sensors, and that a 50mm aps-c lens on an aps-c body would give the same view as a 50mm ff lens on an ff body;
and that you applied the crop factor (multiplier) when using an ff lens on an aps-c body simply because the sensor saw only a center portion of the ff lens. The aps-c body wouldn't 'crop' an aps-c lens, so why would you apply a 'cropping factor'? (I'm not asking to be argumentative - I do believe you're right 'cause I've heard that line before, I'm just asking on the off-chance that you might be able to explain it so that it makes sense to me )



Quote:
Originally Posted by TCav View Post
And you can't..
Thus the 'I wonder' part of the sentence

Last edited by Lindinblade; Dec 26, 2009 at 11:31 AM.
Lindinblade is offline   Reply With Quote
Old Dec 26, 2009, 11:47 AM   #6
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

A 50mm lens is a 50mm lens. ;-)

With your A100, you'd get the same angle of view you'd have using a 75mm lens on a 35mm camera. It doesn't make any difference if that lens was made for a 35mm camera, or if it was designed for a camera with an APS-C size sensor. The angle of view is going to be the same either way on your camera (with a 50mm focal length, you'd have the same angle of view you'd have using a 75mm lens on a 35mm camera). Just multiply the focal length by 1.5x to see what focal length would be needed on a 35mm camera to give you the same angle of view.

The difference between them is that the lens designed for an APS-C size sensor doesn't need to project a larger image circle needed for a larger sensor or film size. That allows manufacturers to make a smaller and lighter lens for a given focal length. When you use a lens designed for a 35mm camera on a camera with a smaller sensor, the entire image circle being projected is not used (since the sensor is smaller). On the downside, you can't use the lens designed for an APS-C size sensor on a camera with a 35mm film or sensor size without vignetting or cropping (because the image circle isn't large enough to cover the larger sensor or film size).
JimC is offline   Reply With Quote
Old Dec 26, 2009, 11:52 AM   #7
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

See the photo on the right side of this page showing how a smaller sensor doesn't use the entire image circle being projected:

http://en.wikipedia.org/wiki/Crop_factor

The smaller sensor is only using the center portion of it.

The difference is that a lens designed for an APS-C size sensor will project a smaller image circle to begin with (versus one that is large enough to cover a 35mm size film or sensor) . But, the angle of view for a given focal length is going to be the same with either lens type on your camera.
JimC is offline   Reply With Quote
Old Dec 26, 2009, 12:21 PM   #8
Senior Member
 
mtclimber's Avatar
 
Join Date: Oct 2005
Location: Oregon, USA
Posts: 18,143
Default

For over a year, I used a Sigma 18-125mm lens on my A-230 with excellent results.

Sarah Joyce
mtclimber is offline   Reply With Quote
Old Dec 26, 2009, 2:42 PM   #9
Member
 
Join Date: Apr 2006
Posts: 45
Default

Quote:
Originally Posted by JimC View Post
Explanation
Thanks.

I've been staring at http://en.wikipedia.org/wiki/File:Fu...e_vs_APS-C.svg for 17 minutes straight now, and I thought I just heard something rasp into place.
A few spontaneous queries: (Using my own terminology :/ )

Why did they use a 50mm and a 70mm lens, with the goal of "Explaination why a 50mm lens on APS-C amounts to a 80mm in full-frame"? Wouldn't a 50mm and an 80mm lens have been slightly easier to understand?

If the answer to that is "It's clear enough anyways, but you are right in theory", then, (still relating to the picture) if a 50mm lens shows a larger part (shaped as a rectangle) of a subject if on a 35mm sensor, and a smaller rectangle if on an aps-c sensor- both scenes are represented by the same amount of pixels- so the 'enlargened' aps-c view (third picture from top in right hand column) isn't of less quality than the corresponding (kind of) view in a 35mm sensor(fourth picture from top in right hand column), correct?

And the only thing that makes aps-c lenses different is that they 'see' less of a subject, but 'from the same distance' so to speak as the 35mm lens.

There are more conclusions to draw from that, but for now, I think (hope) I have the gist of it. But if 'a drawn picture' didn't help then gods alone know what could

Mtclimber: Thanks for the advice 18-125 is a very useful range. I shall check what is written about it.

Last edited by Lindinblade; Dec 26, 2009 at 2:48 PM.
Lindinblade is offline   Reply With Quote
Old Dec 26, 2009, 3:04 PM   #10
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

If you use a smaller sensor or film size, the angle of view will be narrower (more apparent magnification) for any given focal length.

If you use a larger sensor or film size, the angle of view will be wider (less apparent magnification) for any given focal length.

The only reason to even have a so called crop factor or focal length multiplier is so that users familiar with using lenses on 35mm cameras have a better understanding of how angle of view compares using a DSLR with a sensor smaller than 35mm film.

If 35mm cameras were not so popular, there would be no need to use them at all.

Since you have the same lenses for use on 35mm or smaller sensors with DSLR models from Nikon, Canon, Olympus and Sony giving angle of view is more difficult (since you don't know the camera the lens will be used on with most designs).

Nikon started giving Angle of View for DX lenses assuming an APS-C size sensor would be used (since their DX series are similar to Canon's EF-S series lenses, or KM/Sony's DT lenses, or Tamron's Di II lenses, or Sigma's DT lenses) and they will only work on a camera with a sensor smaller than 35mm film without vignetting).

For example, the Nikon specs for the widest angle of view for the Nikkor 18-70mm f/3.5-4.5G ID-IF AF-S DX lens is shown as 76 degrees at a focal length of 18mm (as you would expect when a lens with a focal length of 18mm is used on a DSLR model with a smaller sensor).

If you look at a non-DX lens, the angle of view shown in the specifications for a given focal length assumes it will be used on a 35mm model.For example, the Nikkor 18-35mm f/3.5-4.5DED-IF AF lens (non DX lens) shows an angle of view in it's specifications of 100 degrees at a focal lenth of 18mm (as you would expect when an 18mm lens is used on a 35mm camera).

The focal length at the widest setting for both lenses is identical. What changes is the angle of view, depending on the size of the sensor/film the lens is being used with.

If you used the non-DX lens (designed for 35mm cameras) on a DSLR, the angle of view would be identical to the DX lens (digital only lens design) for the same focal length setting.

Since we have lenses that can be used on cameras with more than one sensor or film size, it's tougher to give angle of view for these (although they could give multiple angle of views in the specs, showing it for multiple sensor/film sizes).

If 645 format was more popular than 35mm, we may have be seeing "focal length multipliers" to help medium format users make the transition to 35mm, so that users could understand that a lens will have more apparent magnification (narrower angle of view) for any given focal length when used on a 35mm camera versus a medium format model. ;-)


If you really want to know the forumla, here it is:
  • Angle of View = 2 * ArcTan(Film Dimension / (2 * Focal Length * (1 + Magnification)))
If you want some simple formulas for how larger format films compare to 35mm for a given focal length lens, here some are::

645 focal length x 0.62 = equivalent 35mm focal length
6x6 focal length x 0.55 = equivalent 35mm focal length
6x7 focal length x 0.48 = equivalent 35mm focal length

If you use a lens designed for a given format (as in the new "digital only" lenses designed for a DSLR with a smaller sensor), you don't crop it (as the image circle is designed to match up to the film or sensor). But, you still have to use the exact same formulas for angle of view comparisons for a given focal length lens.

For example, if you use a 50mm lens on a 645 format camera, you'll have a wider angle of view (less apparent magnfication) compared to a 50mm lens on a 35mm camera (it would be like using a 31mm lens on a 35mm camera from an angle of view perpective). You'll have a wider angle of view on 645 film.

Or, to put it another way, you'd have a narrower angle of view (more apparent magnification) using any given focal length lens on a 35mm camera versus a medium format model. You'd need to multiply the focal length of a lens used on a 35mm camera by around 1.7x to compare to the focal length needed on a 645 camera for the same angle of view.

A lens designed for a 35mm camera will behave exactly the same on DSLR from an angle of view perspective as a digital only lens of the same focal length on that same DSLR from an angle of view perspective (apparent magnfication, what you see on the resulting image).

You'd still need to multiply the actual focal length of the lens by 1.5x if a lens is used on a DSLR with an APS-C size sensor to see what focal length you'd need on a 35mm camera for the same angle of view.

Where the confusion comes in, is because lenses designed for a 35mm camera have a larger image circle compared to lenses designed for a DSLR with an APS-C size sensor.

That doesn't have anything to do with the angle of view you see for a given focal length lens. In the case of a lens originally designed for a 35mm camera, the extra space in the image circle just isn't used with a DSLR using an APS-C sensor.
JimC is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 11:08 PM.