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04-10-2009, 10:16 PM - 1 Like   #1
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Lens Backward Compatibility ???

newbie post here...

just a few questions.

quick preface. i really like my dads spotmatic. i am about to jump into my first dslr and i am seriously considering the k100d. in attempting to educate myself on lens backwards compatibility, i have arrived at a couple of questions.

please correct me if i my understanding of what i have read is wrong, but when shooting with older lenses, is it true that one will not obtain the same width of angle of view?

for example, if i take the 50mm prime lens from my dads spotmatic, what can i expect as a result on my k100d?

i have read that it becomes a 70-some-mm lens - but in my mind it would still retain the shallower depth of field but the ccd will capture a width of angle of a 70-some-mm lens. again correct me if i am wrong.

i have read that if i were to use the 50mm lens off of my dad's spotmatic, that metering might be a chore, but no more of a chore than metering on the spotmatic - correct? can someone explain to me how it is done on the k100d, please?

thanks for your input. i don't want to overload this posting with so many questions. i'll have to start another.

az

04-10-2009, 11:41 PM   #2
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I'll give this a crack - you've asked one of the more confusing questions about the crop sensor.

Here is a basic response to your questions
  1. Screwmont Lenses: A Spotmatic uses screwmount lenses, often called M42 lenses because of the screw thread distance and pitch in millimeters.
  2. Mountng M42 lenses: M42 lenses can be mounted to any Pentax K-mount body using the correct adapter. The adapter mounts to the body pretty much as a K-mount lens would; the M42 lens screws into the adapter just like it screws into the Spotmatic.
    1. The adapter looks like this: Link to the adapter at the Pentax Webstore They can be purchased other places, and often used here and on ebay
  3. Metering with "M" and earlier lenses: Metering in-camera with any lens made prior to development of the "A" lens contacts (which tell the camera what aperture is set manually on the lens) requires setting the camera to permit using the aperture ring (once), and using the "Green Button" on your camera. The Green Button (or the DoF preview lever) briefly stops down the lens, so the camera "knows" the aperture and meters the actual light stopped down. Open-aperture metering M42 lenses work a bit differently (using the Auto/Manual switch) than older Takumars, but that is a post all to itself. Rest assured you can make the camera and an M42 lens work together just fine.
    1. Here is a tutorial for manual K-mount lenses DP Review Tutorial
  4. A crop sensor is 2/3 the size of a frame of 35mm film. This has the effect of narrowing the Field of View obtained from a lens of any given focal length. Think of the Field of View as a rectangular section of the base of a cone at a given distance from the sensor plane - with a smaller sensor the section of the cone base is correspondingly smaller than with 35mm film. You have the appearance of using a "longer" lens by 1.5x the focal length, but the depth of field is not correspondingly the same.
    1. A 50mm lens on a crop sensor has a Field of View equivalent to that of a 75mm lens on a 35mm film camera.
I hope those answers help some. They probably just cause more questions than they answered. It took me about a month to get these straight after I got my K10D.

Last edited by monochrome; 04-11-2009 at 06:54 PM.
04-11-2009, 07:46 AM   #3
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Maybe this link will help you out more.

K100D (Super) Pictorial guide to using manual lenses [imgs] [Page 1]: Pentax SLR Talk Forum: Digital Photography Review

This post was made by Sean Nelson (he's a Forum member here) and made a good explanation about how to use manual lenses with a K100D Super (this also works with the K100D).
04-11-2009, 10:49 AM   #4
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QuoteOriginally posted by The WideBody Quote
newbie post here...

please correct me if i my understanding of what i have read is wrong, but when shooting with older lenses, is it true that one will not obtain the same width of angle of view?

az
This is true of ALL lenses, new and old. Monochrome has done a good job of explaining why.

04-11-2009, 11:22 AM   #5
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QuoteQuote:
monochrome I'll give this a crack - you've asked one of the more confusing questions about the crop sensor.

Here is a basic response to your questions

Screwmont Lenses: A Spotmatic uses screwmount lenses, often called M42 lenses because of the screw thread distance and pitch in millimeters.
Mountng M42 lenses: M42 lenses can be mounted to any Pentax K-mount body using the correct adapter. The adapter mounts to the body pretty much as a K-mount lens would; the M42 lens screws into the adapter just like it screws into the Spotmatic.
The adapter looks like this: Link to the adapter at the Pentax Webstore They can be purchased other places, and often used here and on ebay
Metering with "M" and earlier lenses: Metering in-camera with any lens made prior to development of the "A" lens contacts (which tell the camera what aperture is set manually on the lens) requires setting the camera to permit using the aperture ring (once), and using the "Green Button" on your camera. The Green Button (or the DoF preview lever) briefly stops down the lens, so the camera "knows" the aperture and meters the actual light stopped down. Open-aperture metering M42 lenses work a bit differently (using the Auto/Manual switch) than older Takumars, but that is a post all to itself. Rest assured you can make the camera and an M42 lens work together just fine.
Here is a tutorial for manual K-mount lenses DP Review Tutorial
A crop sensor is 2/3 the size of a frame of 35mm film. This has the effect of narrowing the Field of View obtained from a lens of any given focal length. Think of the Field of View as the base of a rectangular section of a cone at a given distance from the sensor plane - with a smaller sensor the base of the cone section is correspondingly smaller than with 35mm film. You have the appearance of using a "longer" lens by 1.5x the focal length, but the depth of field is not correspondingly the same.
A 50mm lens on a crop sensor has a Field of View equivalent to that of a 75mm lens on a 35mm film camera.
I hope those answers help some. They probably just cause more questions than they answered. It took me about a month to get these straight after I got my K10D.
You have done a fine job with a complicated question!
04-11-2009, 12:18 PM   #6
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QuoteOriginally posted by OregonJim Quote
This is true of ALL lenses, new and old. Monochrome has done a good job of explaining why.
QuoteOriginally posted by Jewelltrail Quote
You have done a fine job with a complicated question!
Thanks both of you - I hope it helped The WideBody.

Just trying to repay a little bit of what I have learned from all of you.
04-11-2009, 01:57 PM   #7
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Thank You.

Your answers have helped straighted out a couple of things for me. As of yet I have no gear - and as I am most interested in obtaining prime lenses for my k100d, what upgrade path would you suggest I follow after purchasing my k100d body? - providing that i can find just the body. I'm sure that my dad won't let me just have his lenses. Also, I am sure my wife would really be upset if I didn't get her a fully automatic lens for this body - maybe i should just get the kit and this would satisfy this need.

Lastly - or maybe not - if i like the look of film shots using a 50mm - should I be leaning towards something like a 35mm?

Thanks again for your suggestions. I'm sure that you'll be hearing lots from me in the future.

az
04-11-2009, 02:48 PM   #8
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QuoteOriginally posted by The WideBody Quote
I'm sure that my dad won't let me just have his lenses. Also, I am sure my wife would really be upset if I didn't get her a fully automatic lens for this body - maybe i should just get the kit and this would satisfy this need.
The 18-55mm kit lens is much better than the kit lenses from other manufacturers. In my opinion, it's greatly underrated. I'm sure your wife will be pleased with the image quality.

QuoteQuote:
Lastly - or maybe not - if i like the look of film shots using a 50mm - should I be leaning towards something like a 35mm?
Yes. Both the 31mm limited and the 35mm f/2 are highly regarded. There are several others. Check out the lens review database here.

04-11-2009, 06:45 PM   #9
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QuoteOriginally posted by OregonJim Quote
The 18-55mm kit lens is much better than the kit lenses from other manufacturers. In my opinion, it's greatly underrated. I'm sure your wife will be pleased with the image quality.

Yes. Both the 31mm limited and the 35mm f/2 are highly regarded. There are several others. Check out the lens review database here.
All that follows depends on how much you want to learn about this and how much tme you are willing to invest to learn it. For me, the learning about the lenses and the history is part of the hobby. Others think what I do is a waste of time. It is your hobby to with as you will, so I'll give you my view and let you find your own level.

You can start with old manual focus lenses, which are sometimes less expensive than the new DA lenses (although the FA50/1.4 and FA35/2 are the best values ON EARTH on a price-to-image-quality basis, and the kit lens is a very nice lens).

Take care in the Pentax 35mm range - the good ones (K35/3.5, M35/2, etc.) are as expensive as a new lens.

The 50's are much easier to get a great lens for a lower price (under $100 ).

There is a dated resource of postings to an old LIST_SERVE Group called Pentax Discuss Mailing List, a group of dedicated Pentax shooters who essentially kept the brand alive in the early 2000's. See "Stan's Pentax . . ." below. These comments will help you avoid any bad lenses and select good ones.

If you need to be discriminating about your purchases and like old, manual lenses (especially K-mount), read these resources (and others), make a budget, write down the lenses you want (in order of want) and get them one at a time. That is called a personal lens roadmap. I have one, and I don't buy lenses that I haven't planned on. It keeps me out of trouble to do it that way. (Of course, I change the roadmap all the time )

For some of us, getting old lenses is as much a part of the hobby as taking photographs with old lenses - and that's just fine.

Many people were happy 30 years ago with a combination such as 28 / 50 / 85 or 35 / 50 / 100 / 135. Zooms weren't as common then as they are now that we have computerized manufacturing processes - they were harder to design and make and tended to break due to the extra moving parts. You had to "zoom with your feet."

You have all the resources you need right here on PentaxForums.com
Resources:
PentaxFiorums Pentax Lens Review Database (and 3rd-Party database)
PentaxForums Lens Review Links List (all of the following links, plus many more)
Stan's Pentax Photography Info
Asahi Pentax (Spotmatic) Cameras and Lenses
SMC Pentax Lenses and Other Stuff (download the .zip file and you'll have everything)

Last edited by monochrome; 04-11-2009 at 06:58 PM.
04-11-2009, 10:07 PM   #10
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I think the kit lens is a good idea. It's generally quite cheap with a body purchase, good performance, inexpensive way to get wide angle coverage and fully automatic. I can't get my brother to use anything else. The kit lens also can give you an idea of what focal lengths would make useful primes.

Your dad's lenses ought to give you a good idea of what it's like using manual focus primes, vs. the convenience of a fully compatible lens. I would get the genuine Pentax adapter and borrow a lens for that experience. Some people don't feel like they are missing anything and some are much happier using only full-featured lenses. If you're not happy taking pictures, the camera just sits there, so happiness is important here.
04-12-2009, 08:41 PM   #11
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QuoteOriginally posted by Just1MoreDave Quote
Your dad's lenses ought to give you a good idea of what it's like using manual focus primes, vs. the convenience of a fully compatible lens.
i really like using my dad's spotmatic and i don't think that i'll mind manually metering and focusing on the new digital body. i also really like how budget friendly those older lenses are.

az
04-12-2009, 08:47 PM   #12
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With the kit lens, try and make sure you get the Mark II. I own the Mark I, which works fine, but lags a bit in dim conditions, like in thick woodlands, or underlit rooms.

I just read your post about manual glass being cheaper and I quite agree. I almost always have my Pentax-A 28mm f2.8 on my K100D, which I bought for 1/4 the price of a new AF.
04-13-2009, 01:46 AM   #13
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QuoteOriginally posted by The WideBody Quote
i really like using my dad's spotmatic and i don't think that i'll mind manually metering and focusing on the new digital body. i also really like how budget friendly those older lenses are.

az
Has anyone invited you to take a stroll through The Takumar Club thread yet?
04-13-2009, 09:30 AM   #14
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QuoteOriginally posted by chalion Quote
With the kit lens, try and make sure you get the Mark II. I own the Mark I, which works fine, but lags a bit in dim conditions, like in thick woodlands, or underlit rooms.
Just to be clear, version II doesn't specifically improve performance in low light at all. At least not in the sense of providing you with larger apertures to get faster shutter speeds. It is possible that in some lighting conditions, the slight differences in how they renders contrast might give one or the other an advantage, but that's going to be pretty subtle and could easily go either way depending on the lighting.

The only real advantage of version II is somewhat better sharpness at certain focal lengths and apertures, especially towards the corners. Definitely worth holding out for if you don't already have either, but not worth upgrading to in my opinion if you've already got version I.
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