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05-26-2012, 05:09 PM   #31
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Follow up question... I am still trying to make sense of the different mounts.

What is the difference between a K and an A mount lens? "Difference" might not be a good word to use.. I want an A series lens but I need to learn how to spot one when I see it. K, A, P...I am still not able to determine which is which. I see people selling stuff all the time on craigslist and other places but they don't know the difference so they just say what they know.

Is there a gallery somewhere that will show me how to distinguish which is which if the seller doesn't know (or fails to mention it)?

05-26-2012, 05:10 PM   #32
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QuoteOriginally posted by tibbitts Quote
You do need to understand that the "cheap older Pentax lens" phenomena is to some extent a relic of the past. Pentax lagged in digital cameras for some years, but prices seemed to rebound considerably as pentax digital caught on (even to the limited extent it has vs. Canikon.) It's not impossible to find a great buy, but you can spend over a thousand dollars just building a collection of "old" 50s. Once you get past ubiquitous but uninspiring lenses like the 50/2M (not horrible, just not a favorite with most users), prices tend to increase fast, unless you patiently hunt out a bargain from someone who may not realize the market price of what they're selling.

Paul
So I am noticing. You are correct.

I will put out my feelers for the lenses but I need to know what I am looking at.
05-26-2012, 05:23 PM   #33
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QuoteOriginally posted by alamo5000 Quote
What is the difference between a K and an A mount lens? "Difference" might not be a good word to use.. I want an A series lens but I need to learn how to spot one when I see it. K, A, P...I am still not able to determine which is which. I see people selling stuff all the time on craigslist and other places but they don't know the difference so they just say what they know.
* K-series lenses say only SMC Pentax on the front, have no A aperture position nor base contacts.
* M-series lenses say SMC Pentax-M on the front and are otherwise like K-series.
* A-series lenses say SMC Pentax-A on the front, have an A aperture position and base contacts.

Those are the only Pentax bayonet non-AF lens series. A lens with a P or A(P) aperture position is either made by Ricoh, or a 3rd-party lens with Pentax+Ricoh compatibility. Many lenses are marked Auto. This has nothing to do with A-type lenses. If you want A-series or A-type, look for the A on the aperture ring.

QuoteQuote:
Is there a gallery somewhere that will show me how to distinguish which is which if the seller doesn't know (or fails to mention it)?
The lens review database here has pictures of virtually all Pentax lenses. See the menu line near the top of the screen, with HOME FORUM CAMERAS LENSES ACCESSORIES ARTICLES GROUPS PHOTOS MARKETPLACE etc? Click on LENSES, then Pentax Lens Reviews, then work your way through all the lenses. Have fun!
05-26-2012, 05:31 PM   #34
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QuoteOriginally posted by alamo5000 Quote
Follow up question... I am still trying to make sense of the different mounts.

What is the difference between a K and an A mount lens? "Difference" might not be a good word to use.. I want an A series lens but I need to learn how to spot one when I see it. K, A, P...I am still not able to determine which is which. I see people selling stuff all the time on craigslist and other places but they don't know the difference so they just say what they know.

Is there a gallery somewhere that will show me how to distinguish which is which if the seller doesn't know (or fails to mention it)?
K mount is Pentax, A mount is Minolta/Sony. When identifying K mount lenses we usually use abbreviations like KM for K and M series and KA for A series. Pentax A series lenses will be marked as SMC Pentax-A. M series will be marked as SMC Pentax-M. K series will be marked SMC Pentax.

A series lenses are styled differently than K/M series lenses, most A series lenses have their identification on the focusing ring.




This is a picture of a non-Pentax A lens with a harmless 'Ricoh Pin'.




This site show pictures of a number of older lens mounts.

SLR Lens Mount Identification Guide

This is a comparison of a Minolta MD and Minolta/Sony A.





Last edited by boriscleto; 05-26-2012 at 05:39 PM.
05-26-2012, 05:40 PM   #35
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Boriscleto---- you are an amazing person!!!

Thanks a billion!!!

That point out of that little pin and 'which pin' is exactly what I needed to know.

Now if I can find a lens with an 1.2 aperture with that little pin connector then I'm in business. I might go with the M mount or K mount or something until I can get my hands on the other one....If they are only 50 or 60 bucks thats one thing... 400 or 500 bucks is something else entirely.
05-26-2012, 05:45 PM   #36
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QuoteOriginally posted by alamo5000 Quote
Boriscleto---- you are an amazing person!!!

Thanks a billion!!!

That point out of that little pin and 'which pin' is exactly what I needed to know.

Now if I can find a lens with an 1.2 aperture with that little pin connector then I'm in business. I might go with the M mount or K mount or something until I can get my hands on the other one....If they are only 50 or 60 bucks thats one thing... 400 or 500 bucks is something else entirely.
Good luck finding an A50/1.2 for less than $500, $700-800 is probably closer to what to expect. Even when they were in production they were very rare and expensive. An A50/1.4 for around $100 is not out of the realm of possibility though.


Also beware of the A50/2 being listed as the A50/1.2. It is a common mistake because of the way the lens is marked 50:2 or 50:1.2

Last edited by boriscleto; 05-26-2012 at 05:55 PM.
05-26-2012, 11:14 PM   #37
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And don't forget to cut off the Ricoh pin if your lens has it.

I must add, the prices of some used lenses are going completely bonkers.
05-27-2012, 08:08 PM   #38
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Lens mount ID page. Very helpful if you're looking around at online lenses and don't know what they fit.

SLR Lens Mount Identification Guide

05-28-2012, 05:29 AM   #39
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Here is an (over)simplified explenation between aperture, ISO and shutter speed and their implication on DOF sharpnes and (over/under) exposure:

CameraSim simulates a digital SLR camera - SLR Photography Demystified
05-28-2012, 07:44 AM   #40
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I think one thing still missing in all this is an explanation of what Aperture really is.

Simply put, it is the mathematical relationship between the lens diameter and focal length. In the case of a variable aperture lens, the iris of the lens is placed in a point where it effectively has the same effect as changing the diameter of the lens. The aperture is expressed in terms of F numbers the bigger the aperture the smaller the number

The impact is really simple to explain, the bigger the diameter, the more light enters, and therefore the brighter the image is.

Since exposure (at any ISO) is controlled by only the total amount of light during the time the shutter is open, F Number and shutter speed have an inverse relationship. The Smaller the F Number (i.e. the bigger the aperture) , the faster the shutter speed you need to ensure the same total amount of light hits the sensor.

Now, why would you want faster lenses, i;e. those with lower F numbers.

Really there are only 2 basic reasons, you are shooting in reduced light and you want more shutter speed, so you need bigger lenses, or, you want very limited depth of field, because aside from controlling the light entering the lens, the only other major impact of the aperture is the depth of field for the lens. the higher the F number, (i.e. the smaller the aperture) the more depth of field you have. People use depth of field creatively, to either have a lot of parts of the image sharp, or to have very selective points of the image sharp and the rest soft and out of focus.
05-28-2012, 08:30 AM   #41
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QuoteOriginally posted by Lowell Goudge Quote
Now, why would you want faster lenses, i;e. those with lower F numbers.

Really there are only 2 basic reasons, you are shooting in reduced light and you want more shutter speed, so you need bigger lenses, or, you want very limited depth of field, because aside from controlling the light entering the lens, the only other major impact of the aperture is the depth of field for the lens. the higher the F number, (i.e. the smaller the aperture) the more depth of field you have. People use depth of field creatively, to either have a lot of parts of the image sharp, or to have very selective points of the image sharp and the rest soft and out of focus.
Ka-BLAM! Bingo!

And hence why I went out and kicked some Ebay rear end to get a larger size aperture lenses...that creativeness... that bokeh...the depth of field...

You see--I work in a relatively mundane job and day in and day out I feel like the dunkin donut guy...'time to make the donuts'....so I want that creative option as an outlet to counteract the crap factor of my day job. This is my art pallet to keep me from going bonkers...when I am stationed for a week out in a West Texas town of 1,200 people---when I get off work I can take pictures rather than watch cable.

I have always been interested in photography and even took some classes long ago--and recently read a bunch of books getting me 'more' up to speed on things like 'digital'...

it also doesn't hurt that I am friends with some really good photographers (as in shooting Nat Geo features, major magazine covers, etc --that kind of good)...yes, peer pressure mixed in with a bit of admiration and curiosity (plus an ingrained interest)

When the economy turns around (if ever) and I am able to travel to more interesting places and do more interesting stuff I will have a skill that I can carry over. I have been to the interesting places doing the interesting stuff but most of my photos consisted of saying 'push that big button on the top there' while doing sign language and speaking real slow because the other guy doesn't speak english...

My initial question though was sort of misleading... in that some were thinking I was asking 'what is it' but really I am asking a more technical question...

Would a f1.4 create a better bokeh than an f1.7? What about an f1.2?

Another topic that I might have to do some old fashioned trial and error on will be creating bokeh with a telephoto lens shooting high speed objects with a fast shutter speed... IE shooting a man galloping on a horse at 300mm zoom where I want him in focus and sharp but the background with bokeh....

Last edited by alamo5000; 05-28-2012 at 08:38 AM. Reason: more info...
05-28-2012, 08:47 AM   #42
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QuoteOriginally posted by alamo5000 Quote

Would a f1.4 create a better bokeh than an f1.7? What about an f1.2?
Since I am trying to learn here let me try and answer my own question---please let me know if I am right or wrong (in theory)...

In sheer 'theory' the 1.2 aperture will give a lot greater range of options for bokeh so forth...BUT it depends largely on conditions.

It also depends on the lens itself... different types or brands of lenses, different focal lengths all make a difference in how the camera ultimately manipulates and records the light.

But if I had two 50mm lenses one with a 1.4 aperture and one with a 1.7 aperture each of those lenses essentially will have its own personality and/or 'sweet spot'... so although it might be a 1.4 aperture lens its 'sweet spot' might be stopped down a little...it depends on the make the brand the glass the whatever...

Yes? No? Warm?
05-28-2012, 08:53 AM   #43
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QuoteOriginally posted by alamo5000 Quote
Ka-BLAM! Bingo!
glad you liked my comment
QuoteQuote:
snip.....

My initial question though was sort of misleading... in that some were thinking I was asking 'what is it' but really I am asking a more technical question...

Would a f1.4 create a better bokeh than an f1.7? What about an f1.2?
I personally consider bokeh and aperture in this way i.e. better and worse as a function only of aperture.

Bokeh is very much dependent on the actual lens design, aperture design, and a whole host of other things, that can cause two lenses of identidal focal length and shooting at identical apertures to have considerably different bokeh. Remember bokeh is a term used to subjectively/qualitatively describe the out of focus qualities, not quantitatively describe them, although there is at least one forum member attempting to do so.

Depth of field, on the other hand is a quantitative measure of a definitive behavior. A lens shot at F1.2 will have less DOF than the same lens shot at F1.4, 1.7, ...etc.the smaller the aperture the more depth of field you get.

QuoteQuote:

Another topic that I might have to do some old fashioned trial and error on will be creating bokeh with a telephoto lens shooting high speed objects with a fast shutter speed... IE shooting a man galloping on a horse at 300mm zoom where I want him in focus and sharp but the background with bokeh....
Maybe you should replace the use of the word bokeh with blur.

Something else to consider and this was a suprise to me when I did the calculation, but someone asked about the relationship between focal length, image size and depth of field, i.e. specifically if you change focal lengths and shooting distance to retain the same image size for a given subject, the distance to the background for the same out of focus impact remains constant for the same aperture.

Therefore for you, and wanting blur / out of focus behind your subject start looking at ensuring there is enough subject to background distance. Also, if you want to have blur in the background, just have the person on the horse move, and you pan the image at a relitively slow shutter speed. the panning will have the image relitively sharp and the background streaked by motion
05-28-2012, 09:11 AM   #44
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Excellent comment Lowell...on another forum I go to sometimes they have an actual calculator where you punch in your sensor crop factor, your focal length, aperture and so forth and it will tell you numerically what your dept of field will be....

For example a quick look there tells me that if I am focusing on an object 100 meters away from me at 300mm focal length with an aperture of f4 I will have an 18.83 meter depth of field...

Anything 91.4 meters out to 110.2 meters will be in acceptable focus....beyond 110 meters it starts to blur. These online gadgets and gizmos work awesome.

It might not be 'perfect' but gives me an idea of what to look for...

You can punch in any focal length any f any distance to the subject you want and it will tell ya straight up...
05-28-2012, 09:18 AM   #45
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Another interesting calculation is if I am shooting my soon to be delivered 50mm f1.4....

If I focus on an object 1 meter away with my 1.5 crop factor sensor at a full f1.4 my total depth of feild will be .022 meters or just under an inch of total depth of feild.

At f2 the total depth of field is 1.18 inches...

Tricky but doable.
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