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06-09-2008, 05:16 PM   #16
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I thank you all for trying to educate this old brain. Tough job!!

I'm always on the look-out for new and different lenses to try out, but after seeing the price of the 645-->K-Mt adapter, I think I'll cross those babies off my list!! Besides, there's a plethora of old M42's, etc to play with - and I haven't even gotten into the various German lenses!

06-09-2008, 10:13 PM   #17
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Thanks everyone for some good discussion. The 67 to k-mount adapter isn't cheap either--here is a link.

Pentax 67 6X7 lens adapter to pentax K PK K20D K200D - eBay (item 160248655270 end time Jun-14-08 06:50:33 PDT)


Regards,

Ernest

"Humanity subdues inhumanity as water subdues fire."

Mencius 6A:18.
06-09-2008, 10:25 PM   #18
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ChipB Lens factor??

--------------------------------------------------------------------------------
Using a 35mm lens on a Pentax DSLR results in the 1.5x "factor" - does this effect also apply when using medium format lenses?? If so, is it a different "factor"?

________________________________________________________________


I would like to return to Chip's original question, because I'm not so sure I am %100 with the program here. I'll try to simplify what I'm asking in three steps--hope this works:

1) a 50mm lens on a 35 mm camera acts like a 50mm lens

2) a 50mm lens on a Pentax DSLR acts like a 75mm lens (due to 1.5 crop factor of aps-c sensor)

3) a 50mm lens, from medium format system, acts like a 75 mm lens too (due to 1.5 crop factor of aps-c sensor)

Is the third statment above true? Thanks.


Regards,

Ernest


"Humanity subdues inhumanity as water subdues fire."

Mencius 6A:18.
06-09-2008, 11:09 PM   #19
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QuoteOriginally posted by Jewelltrail Quote
ChipB Lens factor??

--------------------------------------------------------------------------------
Using a 35mm lens on a Pentax DSLR results in the 1.5x "factor" - does this effect also apply when using medium format lenses?? If so, is it a different "factor"?

________________________________________________________________


I would like to return to Chip's original question, because I'm not so sure I am %100 with the program here. I'll try to simplify what I'm asking in three steps--hope this works:

1) a 50mm lens on a 35 mm camera acts like a 50mm lens

2) a 50mm lens on a Pentax DSLR acts like a 75mm lens (due to 1.5 crop factor of aps-c sensor)

3) a 50mm lens, from medium format system, acts like a 75 mm lens too (due to 1.5 crop factor of aps-c sensor)

Is the third statment above true? Thanks.


Regards,

Ernest


"Humanity subdues inhumanity as water subdues fire."

Mencius 6A:18.
Yup, thats it in a nutshell if you want to use crop factors. The best idea though is to try to stop making the comparison and think of the lens the way it works on the format you are using, as opposed to thinking of how it would work on a different format, were it a different lens.

06-10-2008, 09:05 AM   #20
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QuoteOriginally posted by Jewelltrail Quote
[I]ChipB Lens factor??

....

3) a 50mm lens, from medium format system, acts like a 75 mm lens too (due to 1.5 crop factor of aps-c sensor)

Is the third statment above true? Thanks.
No. you have been following the explanations here. But what there is a subtle but important difference between what was/is been said and whats true.

The 50mm lenses NEVER act like a 75mm lens. focal length is focal length is focal length. As someone else pointed out above. Look at the nice picture with crop lines above. This is the best way to understand whats going on.

The focal length of the lens (and aperture and subject distance etc..) establish what the image looks like. i.e whats in focus, how big things look. The format is now just a question of how much of the image to crop out. If we had and infinite format camera, and an infinitely large 50mm lens, then you could capture the universe. but instead we have to crop something out. The different crop lines above illustrate how much you cut out by using a smaller format camera.

The only reason to ever think about crop factor is if you are transitioning from a different camera system, and are trying to learn the new system

Once you have learned the new system, forget about crop factor. It has nothing to do with the lens the camera or photography. Its a language tool. If you know english and are learning italian, you carry around a book to translate. Once you have learned Italian, you can forget about the book.

The Crop factor is only used to translate form your old system that you know to the new one that you are learning

If you know that you used a 24mm lens on your old MX film camera to capture a sunset scene years ago on vacation. But you are now going on vacation with your new K20 instead... what lens do you need to take along to take in the same scene? If you put the 24mm lens on the K20, you will get the same depth of field etc... but the edges of the photo will be cropped out. So instead, you can take along a 16mm lens and get the same scene captured. The 16mm is more wide angle than the 24mm. But since the k20 sensor is smaller, the effect is it crops the center out, you are left with the same image elements as with the 24mm on the MX.
06-10-2008, 10:01 AM   #21
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QuoteOriginally posted by kmccanta Quote
No. you have been following the explanations here. But what there is a subtle but important difference between what was/is been said and whats true.

The 50mm lenses NEVER act like a 75mm lens. focal length is focal length is focal length. As someone else pointed out above. Look at the nice picture with crop lines above. This is the best way to understand whats going on.

The focal length of the lens (and aperture and subject distance etc..) establish what the image looks like. i.e whats in focus, how big things look. The format is now just a question of how much of the image to crop out. If we had and infinite format camera, and an infinitely large 50mm lens, then you could capture the universe. but instead we have to crop something out. The different crop lines above illustrate how much you cut out by using a smaller format camera.

The only reason to ever think about crop factor is if you are transitioning from a different camera system, and are trying to learn the new system

Once you have learned the new system, forget about crop factor. It has nothing to do with the lens the camera or photography. Its a language tool. If you know english and are learning italian, you carry around a book to translate. Once you have learned Italian, you can forget about the book.

The Crop factor is only used to translate form your old system that you know to the new one that you are learning

If you know that you used a 24mm lens on your old MX film camera to capture a sunset scene years ago on vacation. But you are now going on vacation with your new K20 instead... what lens do you need to take along to take in the same scene? If you put the 24mm lens on the K20, you will get the same depth of field etc... but the edges of the photo will be cropped out. So instead, you can take along a 16mm lens and get the same scene captured. The 16mm is more wide angle than the 24mm. But since the k20 sensor is smaller, the effect is it crops the center out, you are left with the same image elements as with the 24mm on the MX.
Yep...you hit the nail on the head. It appears that most (including myself) still use the 35mm as "The Standard". And since digital sensor size seems to change over time (aren't they getting larger?), we still need a standard to fall back on. It would be nice if the digital SLR manufacturers would start cranking out reasonably priced 35mm sized senors in the majority of their cameras.
06-10-2008, 10:11 AM   #22
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Its only in the digicams and cell phones that the sensors are changing.

Under a $1000, DSLRs with few exceptions are all on the APS-C format. Pentax and Nikon used the same Sony sensors for years (Nikon got them first with some custom tweaks). Canon's sensors are a little bit differnt size (1.6x v.s. 1.5x) but not enough to matter in this discussion. Olympus uses the infamous 4/3 size which is smaller still.

I had a 35mm camera for years... but I didnt have a lens wider than 28mm. So crop factor is still useless to inform me of how wide is the 16mm end of the 16-45mm zoom lens? 24mm on film was not in my experience... so all anyone could do is say its wider. Or here are two shots showing how it looks from my front porch... but that doesnt really teach my brain to "See" what the 16mm end of my camera will see.

just the same now... how can you tell me if I should get the 28-75 or the 50-135 for my sons basketball games? If I dont have those focal lengths... its trial and error. You may now what you need... but its hard to get inside my head and describe what I would be seeing...
06-10-2008, 11:54 AM   #23
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Hmmmm....all makes sense to me now.

I do like the idea of imagining that I'm a shrunking down mutant though...

c[_]

06-10-2008, 10:05 PM   #24
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Kmccanta, it is good to have your input here—thanks for enriching the discussion. Yes, I have been following the discussion. But, no, there is never a subtle difference between truth and falsehood. Clearly, a 50mm lens is always a 50mm lens—I think you possibly are reading more into the posts here than need be.

I carefully selected the words “acts like” for the discussion because I am aware that acting like something and being something are two different things. For example, in a play, I could act like I’m kmccanta—however; I could never really be you. It can often be difficult to use words to express complicated ideas: this is a good example. Almost everywhere you read, when focal lengths are discussed, you will see the use of “acts like” or “is the equivalent of” when comparisons of APS-c (CROP) sensors are compared to 35mm film. Yes, Wheatfield’s picture tells at least a thousand words, but that is just it—it is a picture—not words. Bringing this picture into words, accurately, is an art in itself. Here is another picture.


Regards,

Ernest



Humanity subdues inhumanity as water subdues fire.”


Mencius 6A:18.

Last edited by Jewelltrail; 08-31-2008 at 07:42 AM.
06-10-2008, 10:55 PM   #25
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kmccanta
QuoteQuote:
The 50mm lenses NEVER act like a 75mm lens. focal length is focal length is focal length. As someone else pointed out above. Look at the nice picture with crop lines above. This is the best way to understand whats going on.

Okay, at Wikipedia, in their paragraph on Focal Length, here are their precise words on the matter. Hopefully they will stand up better to our scrutiny.

"The impact of sensor size on field of view is referred to as the "crop factor" or "focal length multiplier", which is a factor by which a lens focal length can be multiplied to give the full-frame-equivalent focal length for a lens. Typical APS-C sensors have crop factors of 1.5 to 1.7, so a lens with a focal length of 50mm will give a field of view equal to that of a 75mm to 85mm lens on a 35 mm camera."

Regards,

Ernest


Humanity subdues inhumanity as water subdues fire

Mencius 6A:18
06-11-2008, 09:51 AM   #26
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Thanks for the diagram of sizes! facts always help. I think we totally agree here.

the Wikipedia explanation is good, because it precisely discusses field of view. Which is more correct than vaguely saying the lens acts like another lens. The other major difference between the 50 and 75mm lens is the depth of field. I didnt want to derail the discussion of crop factor by throwing in another difference. But it is important. Thats one reason why one might choose a medium format camera or a digicam instead.

-k
06-11-2008, 11:17 PM   #27
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Thanks K:


Yes, facts are, indeed, good--but mere tools! They do not guarantee objectivity because in the communication and interpretation of those facts, subjectivity gets the better of them.

There is a specification sheet (pure facts) which accompanies the K20 and other DSLRs. But it is the actual subjective experience of holding and using the K20 which, for many, sells it.

I bought my K20 for reasons which transcend the realm of pure fact, though I must admit I love the facts which accompany the camera.


Regards,

Ernest



"Humanity subdues inhumanity as water subdues fire."

Mencius 6A:18.
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