Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
02-11-2011, 01:30 AM   #1
Veteran Member
lguckert79's Avatar

Join Date: Jun 2010
Location: Pittsburgh, PA
Photos: Gallery | Albums
Posts: 586
some ?? about the asp-c sensor compared to 35mm negative

Well when you use a 35mm negative with a lens made for a film camera, lets just say the "A" 50mm F2 and then you use the same lens on an asp-c sensor digital camera with the whole 1.5X crop factor. Would that not effect the aperture also would it not let more light in on the sensor since the sensor is 1.5X smaller than the original 35mm negative, like when i use my "A" 50mm F for film on my digital camera would it now become f1.3 which would be 2/1.5=1.3 because their is less sensor area to cover than with the 35mm negative so wouldn't that mean more light on the sensor?? or maybe i don't know what I'm talking about and this is just going to screw people up and I'm sorry if that happens i just want to know. thanks Larry

02-11-2011, 02:13 AM   #2
Forum Member




Join Date: Jan 2011
Location: Leipzig
Photos: Gallery | Albums
Posts: 64
Hi Larry,
the crop factor does not affect the aperature related f-number.
The reason for the confusion - I guess- is that commonly people often say that a "50mm becomes a 75mm" and so on...
BUT: the crop factor does not really change anything concerning the optical properties of the lens: the focal length STAYS 50mm and the diameter of the entrance pupil also doesn't bother what crop factor you'll have.
Since the f-number is simply the focal length divided by the diameter of the entrance pupil, and both are not affected by the crop factor, your f-number remains unchanged!
(N = f/D with f = focal length and D = the diameter of the entrance pupil)

--> The crop factor only refers to "how much surface" you cover in your image plane (were the sensor/film is located).
This really is just the same effect as cropping a picture in photoshop...
If you'll take an "old" picture taken with a 50mm lens at f/2 and you crop it, it appears like "zooming in". This means it might "appear" as taken with a 75mm lens, but the underlying picture, of course remains the 50mm f/2 image and it will not get any brighter or darker (and the f-number remains, too).

Hope I could help to answer your question.

Last edited by FH_le; 02-11-2011 at 02:36 AM.
02-11-2011, 02:25 AM   #3
Inactive Account




Join Date: Aug 2008
Location: Michigan, USA
Photos: Gallery | Albums
Posts: 7,485
That would be an awesome thought if it were true. My f1:1.2 would become an f0.8 (by your math) :drool:

If you must think of Crop Factor, think of it as just that. A Crop. Nothing optical changes with it or as a result of it. Then forget you ever heard the term and go on about taking photos. If you are use to 35mm cameras you will soon become accustomed to the APS-C and won't give it a second thought.

02-11-2011, 02:44 AM   #4
Forum Member




Join Date: Jan 2011
Location: Leipzig
Photos: Gallery | Albums
Posts: 64
Just another thought on this issue:

as mentioned before, the f-number is a lens characteristic that is not changed by the crop factor.
What does change is the depth of field (DoF) when compared to "full format"!
But unfortunately this changes towards the opposite direction mentioned:
When using your f/2 lens on your 1.5xcrop factor camera, its depth of field will more likely look like f/3 when compared to full format .

02-11-2011, 04:20 AM   #5
Senior Member




Join Date: Mar 2008
Location: Lisbon
Posts: 142
QuoteOriginally posted by FH_le Quote
What does change is the depth of field (DoF) when compared to "full format"!
But unfortunately this changes towards the opposite direction mentioned:
When using your f/2 lens on your 1.5xcrop factor camera, its depth of field will more likely look like f/3 when compared to full format .
IIRC the DoF depens on the distance of the subject, the absolute aperture and the enlargement. So, ceteris paribus, you will get less DoF with a crop camera when you enlarge to the same size, but you won't get the same photo.

The confusion starts when you want to get the same photo. You will need a wider lens or to stay further from the subject. A wider lens means that you will have smaller absolute aperture for the same relative aperture (or f value) therefore more DoF. Longer distance also means more DoF.

This leads to an important conclusion. The DoF indicated on the old lenses is over estimated when used on a APS-c camera. So if you want to use those indication you should close the lens one stopmore than indicated.

Luis
02-11-2011, 06:45 AM - 1 Like   #6
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,346
Oh No, Not Another Crop Factor Thread

I thought this had died a well justified death.

There is no such thing as crop factor.

For any given lens there are really only 3 fundamental characteristics, Focal length, aperture, and image circle.

Focal length is pretty self explanatory, it is the distance from the focal plane at which the image of a point source of light appears as a point (as opposed to a circle)

Aperture is the ratio of diameter to focal length, and relates to the illumination per square unit area

Image circle is the diameter of the circle that a lens can project onto, without curring the edges of the image due to mechanical restrictions of the lens both in front of and behind of the first element.

None of these change as a function of sensor size placed behind the lens,

Now, as to crop factor. the size of the image you capture in total also changes nothing about the image.

Take any 4x6 print. cut the middle 2x3 iches out of that print. Have you changed anything at all, NO, the depth of field has not changed, the brightness has not changed, all that has changed is you are looking at less of the total image.

That is all that the crop factor really means.

there are two spots where the confusion comes in,
- first, for the example above we then enlarge that middle portion of the image more to get a big print. As a result of increased enlargement, yes depth of field, sharpness, blurr from camera motion all appear to get worse, only because we are enlarging it more.

- second, when looking in the view finder, or when framing a subject, from any set distance, you need a lens with a shorter focal length on an ASP-C sensor to fit the same field of view into the frame. The difference in focal length is the direct proportion of the "crop factor" of the sensor relitive to what ever format you are comparing it to. in the typical case of DSLRs, to a 35mm frame. (or more importantly the image circle or diagonal of that frame)

The big problem people have is they do not realize that depth of field and what was considered acceptable depth of field (for being in focus) was all based upon making a single print size (8 inch by 10iinch) from full frame (24x36mm) formats . If you want to make a 16 x 20 print, the depth of field is reduced because you are printing the image bigger. But did changing the print size change the lens at all, NO it did not.

We should all forget about crop factor, because it is not related to the lenses at all. we should simply talk about lens characteristics, and print sizes.
02-11-2011, 06:59 AM - 1 Like   #7
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
Oh yes, another Crap Factor thread

The beast that never dies, right alongside I JUST GOT A CAMERA, WHAT SHOULD I UPGRADE THE KIT LENS TO? Let us find whomever coined the term, and lynch them. Also lynch the corporate wonks who decided to put "35mm equivalencies" on P&S's. Or the "macro zoom" label on lenses that only go to 1:5. These marketing terms are sources of endless confusion.

They give us something to rant about though, eh?
02-11-2011, 01:13 PM   #8
Pentaxian
enoeske's Avatar

Join Date: Jul 2009
Location: Surprise, Az
Photos: Gallery
Posts: 1,897
does this help explain anything? I just made this to try to illustrate crop factors. The lens and image circle don't change. All that changes is the "sensor" that records the image circle. So, field of view changes because different sensors are different sizes, but the lens and its characteristics don't.


*not to scale

02-11-2011, 01:18 PM   #9
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,346
QuoteOriginally posted by enoeske Quote
does this help explain anything? I just made this to try to illustrate crop factors. The lens and image circle don't change. All that changes is the "sensor" that records the image circle. So, field of view changes because different sensors are different sizes, but the lens and its characteristics don't.


*not to scale
glad you put not to scale at the bottom, a P&S is actually a whole lot smaller

Good shot to explain it,

As I said, nothiong about the image changes due to the sensor, only how much of it you see,.
02-11-2011, 03:17 PM   #10
Pentaxian
hoanpham's Avatar

Join Date: Nov 2009
Location: Strand
Photos: Gallery | Albums
Posts: 1,361
We should welcome new members, not cry out loudly ;-)

Another job to redesign a tutorial section of this forum. It's so hidden, as you mentioned, these kind of thread won't die quietly. So what can we do in order to ease the search of a topic?

Hi there, don't worry be happy
02-12-2011, 05:41 AM   #11
Loyal Site Supporter




Join Date: Mar 2009
Location: Southern Indiana
Photos: Gallery
Posts: 15,327
Eventually people will stop talking about "crop factor." It is only useful for people who are used to shooting with 35mm and how their lenses behaved on that and then begin shooting APS-C. If you are used to 24 mm being a wide angle lens, then you need to convert things in your mind to realize that on APS-C you need a 16 mm lens to get the same field of view.

Equivalence includes depth of field as well, so that a 55mm f1.4 on APS-C will take the same photo as an 85mm f2 lens on 35mm, but if you aren't used to shooting film or digital full frame, who cares?
02-12-2011, 07:34 AM   #12
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
Devil's advocate

So I'm this person that has decided for whatever valid and/or invalid reasons to switch from his Olympus SP500UZ (10x P&S, 6MP) to an APSc dSLR and I'm wondering which lenses to get. I'm considering the 1-lens kit or 2-lens kit with 50-200 or the 2-lens kit with 55-300.

I know that I can get that elephant at x meters fill the photo when I zoom in to the max. with the Olympus and I want to be able to achieve the same with this new APSc dSLR and one of those kits. I will tell you that my camera says 6.3-63mm 1:2.8-3.7 on the lens and that the manual somewhere says 38 to 380mm FF equivalent (oh confusion).

Which kit do you advise (to get that elephant at the same distance fill the frame)? And why?
02-12-2011, 08:26 AM   #13
Loyal Site Supporter




Join Date: Mar 2009
Location: Southern Indiana
Photos: Gallery
Posts: 15,327
QuoteOriginally posted by sterretje Quote
So I'm this person that has decided for whatever valid and/or invalid reasons to switch from his Olympus SP500UZ (10x P&S, 6MP) to an APSc dSLR and I'm wondering which lenses to get. I'm considering the 1-lens kit or 2-lens kit with 50-200 or the 2-lens kit with 55-300.

I know that I can get that elephant at x meters fill the photo when I zoom in to the max. with the Olympus and I want to be able to achieve the same with this new APSc dSLR and one of those kits. I will tell you that my camera says 6.3-63mm 1:2.8-3.7 on the lens and that the manual somewhere says 38 to 380mm FF equivalent (oh confusion).

Which kit do you advise (to get that elephant at the same distance fill the frame)? And why?
With the 18-55 lens you have a 27 to 80-ish equivalent and with the 50-200 you would have 75 to 300mm equivalent, while the 55-300 would take you to 450mm.

Just as far as image quality, the 55-300 is worth the extra money over the 50-200, in my opinion.
02-12-2011, 09:45 AM   #14
Veteran Member
sterretje's Avatar

Join Date: Dec 2008
Location: Roodepoort, South Africa
Photos: Gallery | Albums
Posts: 3,534
QuoteOriginally posted by Rondec Quote
With the 18-55 lens you have a 27 to 80-ish equivalent and with the 50-200 you would have 75 to 300mm equivalent, while the 55-300 would take you to 450mm.

Just as far as image quality, the 55-300 is worth the extra money over the 50-200, in my opinion.
Rondec, glad you answered. How did you get to those numbers? I guess you used the crop factor. So that thing will never die as it is important in these scenarios.

02-12-2011, 11:44 AM   #15
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by sterretje Quote
How did you get to those numbers? I guess you used the crop factor. So that thing will never die as it is important in these scenarios.
Except that the pictures taken won't be the same. The elephant may fill the frame at 63mm on your Oly and 250mm on a Kx but the DOF will differ rather a bit. That's even more noticeable at the other end, with 6.3mm on the Oly and 25mm on the Kx. Especially if the Oly is stopped down a bit -- for the Kx to have similar DOF, it would be stopped down way past the diffraction limit, so the Kx shot will have lousy sharpness. Yeah, yeah, sharpness is a bourgeois conceit -- but short lenses on tiny sensors have near-infinite DOF, and equivalent lenses on APS-C sensors, don't.

And that's why I hate this crap about 'equivalencies' applied to P&S vs dSLR optics. Naive users think their 6.3-63mm P&S is equivalent to 38-380mm on FF and 25-250mm on APS-C, and IT AIN'T. They expect a larger-format lens will have the same sharpness and DOF as their P&S, and IT DON'T. Especially if they've started with just the 18-55 kit lens. Then they whine, "My kit lens sucks, what should I upgrade it to?" And the managers and stockholders of lensmaking firms smile as the money rolls in.

If lensmakers labeled their products by AOV (angle of view) per frame format, that would be fine -- it would actually indicate something important about how a lens will work. But that's apparently Too Much Information for targeted customers. So we get this equivalency and crap.factor stuff, and rampant confusion without much hilarity. [expletive deleted]
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
50mm, asp-c, camera, dslr, film, lens, light, photography, sensor
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
about the asp-c sensor lguckert79 Troubleshooting and Beginner Help 10 01-29-2011 06:28 PM
35mm negative scanning progress: Me vs. Walgreens ismaelg Film Processing, Scanning, and Darkroom 9 08-27-2010 02:12 PM
35mm negative scanning: Emulsion side up, down or.... ismaelg Film Processing, Scanning, and Darkroom 4 08-23-2010 06:07 PM
Sigma 17-35mm f/2.8-4 EX ASP HSM (ver. 1) - opinions? ajuett Pentax SLR Lens Discussion 13 05-02-2010 09:45 PM
Can I still get 35mm Negative binder Sheets? konraDarnok Pentax Film SLR Discussion 8 01-02-2008 11:02 PM



All times are GMT -7. The time now is 03:06 AM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top