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10-25-2019, 02:00 PM   #1
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lens questions

Dipo 1 here, now I'm not trying to be a smart *&^ or anything but I have been looking at lens discussions and the lens data base and I'm really confused. I understand that lenses will be updated as or same as cameras what I don't understand is why so many lenses in so many millimeters so close together. Example, i looked at the lens data and found a lot of lenses such as 11mm, 24mm, 34mm, 40mm, 50mm, 55mm, 85mm 70mm, 100mm and on and on. When I bought my Spotmatic back in the day there weren't that many lenses out there that I knew about. I realize that many may have the same focal length but the apertures are different, some are some aren't.

Second question is what does macro mean, I took it to mean good for close up work, does it mean you can stand further away and use a 100mm macro to get a pic of a flower? I mean if you have a 24mm lens I assume (I know, I know) that it will be a good landscape lens. Then there is a 34mm lens is 10mm going to make that much difference in the final product. Just a little confused as to why so many lens in close proximity in mm.

As always thanks for any and all responses good or bad.

10-25-2019, 02:17 PM   #2
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edit - Q1, Jonathan (below) covered it much better.

This might help you with regards to the macro lenses:

What is a Macro Lens? Everything You Need to Know as a Beginner - BorrowLenses Blog
10-25-2019, 02:19 PM - 2 Likes   #3
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Question 1:
Different lenses have:
* Different formats - for example some lenses are good for medium format, some for fullframe and others other are APS-C only.
* As you said different maximum apertures. Faster lenses are usually more expensive.
* Different build quality. For example "*" or "Limited" grade lenses have a higher build standard and very nice to use.
* Some lenses have manual aperture, later ones have auto aperture, then AF came in and finally there are lenses with silent / quite AF
* For Pentax you have multiple generations of lenses available second hand. The lenses series flows oldest to newest (with some exceptions): Takumar (M42 mount), K, M, A, F, FA, DA / DFA
* Lens coatings (e.g. SMC etc - to control transmission performance and flare) have also improved over the years and series - although a lot of the older lenses had pretty decent coating to start with.

Question 2:
Official definitions of macro vary depending on who you talk to. Generally a lens needs to have a reproduction ration of 1 : 2 (At min focus distance object rendered haff size on the sensor / film). Although some will say "true" macro is 1 : 1 (object rendered same size on sensor / film). A lot of budget lenses will claim macro capability with less than 1 : 2 when really they are more like "close focus" lenses.
Usually macro lenses at longer focal lengths does mean than you end up further away from your subject - which is an advantage for macro work. Shorter focal length macros however have the advantage that they can be more useful for general purpose work (depending on what focal lengths you like to use).

Last edited by kiwi_jono; 10-25-2019 at 02:28 PM.
10-25-2019, 02:26 PM   #4
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QuoteOriginally posted by dipo 1 Quote
Dipo 1 here, now I'm not trying to be a smart *&^ or anything but I have been looking at lens discussions and the lens data base and I'm really confused. I understand that lenses will be updated as or same as cameras what I don't understand is why so many lenses in so many millimeters so close together. Example, i looked at the lens data and found a lot of lenses such as 11mm, 24mm, 34mm, 40mm, 50mm, 55mm, 85mm 70mm, 100mm and on and on. When I bought my Spotmatic back in the day there weren't that many lenses out there that I knew about. I realize that many may have the same focal length but the apertures are different, some are some aren't.

Second question is what does macro mean, I took it to mean good for close up work, does it mean you can stand further away and use a 100mm macro to get a pic of a flower? I mean if you have a 24mm lens I assume (I know, I know) that it will be a good landscape lens. Then there is a 34mm lens is 10mm going to make that much difference in the final product. Just a little confused as to why so many lens in close proximity in mm.

As always thanks for any and all responses good or bad.
If you look at the DA 16-85 review, there is a good pictorialization of the change in the field of view at different focal lengths.

10-25-2019, 02:46 PM   #5
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Yes, there are a lot of different lenses in a lot of different focal lengths. In theory, if one were willing to crop a lot, there'd only be a small number of widely spaced focal lengths. But if you don't want to crop and think that 50mm is too narrow and 35mm is too wide, then maybe 43 mm is the just-right or Goldlilocks choice. And "zooming with the feet" does not count if there are foreground or background objects -- each focal length has a different perspective although cropping a wider angle shot does replicate that perspective.

Note that it's the ratios that matter, not the differences. A 24mm lens really is much much wider than 34mm, about as much as the difference between 200mm and 300mm, or the difference between a lens on FF and the same lens on APS-C.

Some of the proliferation of lenses is due to different design objectives. Some lenses are optimized for a given type of photography such as portrait, macro, or landscape. Some lenses are optimized to be very fast, very compact, or very inexpensive. Some represent total redesigns to accommodate auto-focus. Some lenses are a particular designer's idea of the best focal length and rendering for something.


"Macro" does refer to the ability of the lens to reach higher magnification of the subject -- typically at least 1:2 -- but it means the lens has a much closer minimum focus distance. All 100mm lenses give the same magnification at a given distance but only a 100mm macro gets close enough for the high magnification. There are some very short focal length macro lenses that can achieve extremely high magnification but only when they are extremely close to the subject.
10-25-2019, 03:35 PM   #6
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(thread moved to get a wider/better response)
10-25-2019, 04:06 PM - 1 Like   #7
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Well this is a first....discussion about "too many" Pentax lenses
10-25-2019, 06:42 PM   #8
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As other have said, in addition to various focal lengths (FL) being ideal for certain purposes, addressing the same purpose as one is addressing with 35mm or a FF DSLR when using APS-C, this requires a lens of a different FL- to put this another way, there are lenses cut for the right opening size for a 35mm film camera, which your ancient Spotmatic was one, and now a camera having the same size digital sensor as 35mm film is called a FF (Full Frame) body vs. the APS-C size digital sensor which most DSLR cameras have. These lenses will also work fine on APS-C bodies, as they are larger than needed, so only the central area of the lens is used by the smaller APS-C sensor. Then there are also lenses cut only to match the size of APS-C sensors, which would not be adequate for FF use, since that oversized sensor would create a dark area around the edge of the frame because the lens is not physically cut wide enough for coverage (vignetting). So you might have a 50mm lens for FF use and another 50mm lens for APS-C use, which would be physically smaller. Same with 35mm lenses, etc.

Due to the size difference, the angle of view changes between FF and APS-C when using a lens having the same FL. This is why a different FL must be used by an APS-C body when addressing the same special usage as a FF body. Therefore lenses of the same FL take on different uses when mounted on APS-C vs. FF and visa-versa. For example, a 28mm lens on a FF body will provide a substantial wide angle field of view (FOV). But that same lens on APS-C bodies would no longer present any wide angle FOV at all. It would instead present a mid-FL FOV, or now be categorized as a "normal" FL lens, similar to what a 43mm lens would provide on a FF body. One would need a lens of approximately 18mm to achieve the same wide FOV with APS-C as a 28mm lens would on a FF body. So now we have 2 lenses of different FLs for the same usage, depending on which type of body it will be mounted.

These differences are there at all FLs so in order to provide comparable FOVs for APS-C bodies that have been the case with 35mm film and now FF DSLRs, lenses of various FLs have been born to accomplish this.

10-27-2019, 10:42 AM - 1 Like   #9
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Thank you all esp. luftfluss as the pictures were very illuminating. Again more beginner questions to follow, thanks again, will be reading the above many times.
10-27-2019, 10:49 AM   #10
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This is a great question as I was also overwhelmed at so many lenses overlapping their focal length when I was starting out. Luckily I have kept the same camera body for almost 10 years now and have built up my lens collection to fit my needs. And that is where I think the best place is to go from this question. Find what lenses you need in your toolkit, and try not to get overwhelmed at the other stuff. I think my first non kit lens was an older manual focus 50mm because it was cheap, and all the forums said I needed one. I replaced it last year with the cheap f1.8 version and it is so nice having autofocus on that prime.
10-27-2019, 10:59 AM   #11
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QuoteOriginally posted by Pentikonian Quote
edit - Q1, Jonathan (below) covered it much better.

This might help you with regards to the macro lenses:

What is a Macro Lens? Everything You Need to Know as a Beginner - BorrowLenses Blog
one thing to remember about " macro " lenses

true " macros " capable of 1:1

are usually very good lenses even if not being used as " macro " lenses
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