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10-03-2011, 10:30 AM   #1
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I am new here and in need of help !


I am new to group today. I have played with cameras for a few years but I now want to try new things and make it more of a hobby. I have owned a Pentax MZ 50 for around 15 years, got it out a few nights ago and it has something wrong with it. So I have purchased a new body as the lens on my original one was very expensive when I purchased it.
Yesterday I decided to by a Asahi Pentax spotmatic we think about the age of 1969. What I am wondering however is. I have found a lens on ebay which is a Asahi PK mount ( what does that mean ? ) and I have been told it will work with the MZ 50 but not the spotmatic ? Also when reading books and things what does the f mean ?
This is all new to me, I usually press and go ! I am so intrested in making this my hobby. Hope some one will help me.

Anyway my name is Marilynn I am in the UK and been married for 20 years. I have shown and bred pedigree cats for almost 16 years. We are off to Las Vegas next August to visit Grand Canyon for 4 nights then off to Nashville for 25 nights. I would love to be able to take some stunning pictures while we are away.

I do also own a Canon digital SLR and a small pentax digital. I hope I will get to know some of you. Thanks for your time Marilynn

10-03-2011, 10:53 AM   #2
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The Spotmatic has a M42 screw mount (you screw the lens onto the body). The PK mount is also known as a bayonet mount. The PK lenses mount to the body with a quarter turn of the lens.

They have adapters for mounting a M42 lens to a PK body but I have never heard of a PK lens adapter for mounting to your Spotmatic.

10-03-2011, 11:20 AM   #3
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Hi Tim

Thanks for that. That is what we thought when reading the manual. I assume it would fit the MZ50 then. Marilynn
10-03-2011, 11:50 AM - 1 Like   #4
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Yes, both PK bayonet mount lenses, and M42 screwmount lenses (with a simple adapter), will fit the MZ50 and any other bayonet-mount Pentax camera, up to the new dSLRs. But PK lenses will NOT fit on an M42 screwmount camera like a Spotmatic. There ARE adapters for both PK and M42 to fit a Canon EOS mount, although certain lenses and bodies are incompatible because of mirror fouling.

What does f mean? It is a ratio. Lenses are rated by their maximum aperture, the opening of the iris that, with the shutter, controls the amount of light entering the camera. Any specific iris setting is called an f-stop, a measure of the ratio between the aperture opening and the lens' focal length. So if a 100mm lens has its aperture set to f/4, the iris opening is 1/4 of 100mm, or 25mm.

Knowing that opening size isn't important; knowing the f-stop IS meaningful. Wider openings allow more light, so you can shoot in lower light or with faster shutter speeds. And wider openings cost money. I buy and sell old lenses, mostly cheap. I've bought 50-55mm f/1.4 lenses for under US$15, and slower lenses of f/2.0-2.8 for under US$5. My slightly faster f/1.2 lens cost US$250 and was a bargain at the price.

Lenses with small f-stop numbers, like the f/1.2-1.4 gems, are prized not just because they allow faster and dimmer shooting, but also because they have very thin DOF, depth of field, the range from the camera where a subject is in focus. Slow short lenses have thick DOF; everything is sharp. Fast long lenses have thin DOF; we can isolate a subject from their surroundings, so only the subject is sharp and everything else is fuzzy, OOF (out-of-focus). The quality of those OOF areas, whether the blurring is soft or harsh or whatever, is called the bokeh. Fast lenses give us great control over DOF and bokeh. More money, please!

Let us know before you come stateside and we'll gladly suggest must-see goodies. Have fun!

10-03-2011, 12:03 PM   #5
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We are flying out 19th August 2012 to Las Vegas then 23 August to Nashville until 18 Sept 2012... We have been to Nashville before but I wanted to do the civil war tours etc. Thanks very much for your reply. I will re read it, time and time again so I get to understand it. x
10-04-2011, 04:45 AM   #6
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Here are a couple of free on-line camera simulators that will help you visualize the relationship between ISO - Aperture - Shutter Speed (f-number).

The SimCam: Film and Digital Camera Simulator -

Aperture, shutter and ISO value | SLR Camera Simulator

This one even has a couple of camera modes, aperture priority (Av) and shutter priority (Tv)

SLR Camera Simulator | Simulates a digital SLR camera


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