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11-10-2010, 04:34 PM   #1
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? about a lens i just got

I just got a "Osawa 28 mm Wide Angle m42 Lens f2.8" does any one know any thig about this lens? thank you


Last edited by lguckert79; 11-10-2010 at 05:27 PM.
11-10-2010, 05:08 PM   #2
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Can you please edit your post to a smaller type size?

Hit the edit button below your post, select all of your text, use the "Sizes" pull-down menu above your post, and select "1."

It looks like you're shouting at us.
11-10-2010, 05:16 PM   #3
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Well what is it that you would like to know about it?
It's a basic wide angle screwmount lens that will fit on a Pentax camera via a K-mount adaptor for screwmount lenses. Good thing is you don't have to stop-down meter with this lens - you just set aperture on your lens, set on any auto mode on the camera and shoot away.
11-10-2010, 05:18 PM   #4
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I believe that same lens also came in a K-mount for which specs are located here:

Osawa f2.8 28mm.jpg photo - Steve Flynn photos at pbase.com

Also note that Osawa lenses are the same as Mamiya lenses with Osawa Brand name on them.

11-10-2010, 05:24 PM   #5
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QuoteOriginally posted by Ash Quote
Well what is it that you would like to know about it?
It's a basic wide angle screwmount lens that will fit on a Pentax camera via a K-mount adaptor for screwmount lenses. Good thing is you don't have to stop-down meter with this lens - you just set aperture on your lens, set on any auto mode on the camera and shoot away.
If it's an M42, it's not going to work in any auto mode.

Only Av mode, or manual with the button.
11-10-2010, 06:11 PM   #6
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another thing i have a k100d and i have been trying to find out what is the multiplier for the lens to camera body is i heard that you take like the 28mm and times it by 1.5 and end up with a 42mm lens is this true?
11-10-2010, 06:30 PM   #7
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QuoteOriginally posted by lguckert79 Quote
another thing i have a k100d and i have been trying to find out what is the multiplier for the lens to camera body is i heard that you take like the 28mm and times it by 1.5 and end up with a 42mm lens is this true?
No, You use 28mm for a 28 mm lens. If there is no exact number for a given lens you have, go the next step Up (That's what I do anyway). Probably one of the worse things manufactures ever did was release information about that silly multiplier. Your 28mm is a 28mm and that's all it ever will be. If you want to know where the Crop Factor becomes important with respect to lenses, look for information on Field Of View (FOV).

Enjoy your lens and show us what you can do with it.

11-10-2010, 06:36 PM   #8
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thank you that sounds about right. i just heard that you had to compensait for the fov cropping and the image stabalizer

11-10-2010, 09:53 PM   #9
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Maybe the following explains the crop factor once and for all (see image below).

The solid vertical red line at the left is the 35mm film (or a full frame sensor). The size of this film or sensor is 36x24mm. In this post, I will refer to this as 'film'

Your subject is at the right (consisting of both the solid and dashed black lines). What you will see on the photo is given by the thin red diagonal lines.

I have taken a lens with an (arbitrary) focal length of 50mm. This is the distance between the lens and the film.

Next we put the same lens on a camera with an APSc sensor and keep distance to the subject the same; the sensor in the current Pentax dSLRs is 24x16mm (so 1.5 times smaller in each direction). This sensor is shown in blue at the left hand side. What you will see in the photo is indicated by the thin blue diagonal lines.

You can see (in this example) that you will only get the tree in the picture. And please note that the focal length has NOT changed.

To get that same picture with the film camera, you need to increase the distance between the film and the lens (as said earlier, this is the focal length). I have extended the diagonal blue lines (dashed) and the distance needs to be increased till the film fits in the extended lines (the dashed vertical red line). Simple (or not so simple) mathematics will tell you that the distance will now be 75mm (which is 50x1.5).

So a 50mm lens on an APSc based camera will give you the the equivalent field of view of a 75mm lens on a film camera.

And that's all that there is to the crop factor.

Note:
The crop factor is only important if you're familiar with one 'system' (e.g. SLR or P&S) and want to switch to another system; e.g:
  • You come from a film SLR and want to switch to a dSLR; simply divide the focal lengths of the lenses that you have by (for Pentax) 1.5
  • You switch from a 10x P&S to a dSLR; find the equivalent focal length (e.g. 38-380mm) in the specs of your current camera and divide by (for Pentax) 1.5.
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12-15-2010, 03:16 PM   #10
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Thank you. I finally understood what I should tell my camera when it asks what the focal length is of the manual lens I just attached. What would be the case with a bellows or a tube extension? Or a zoom lens?
12-15-2010, 03:51 PM   #11
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QuoteOriginally posted by Pepe Guitarra Quote
Thank you. I finally understood what I should tell my camera when it asks what the focal length is of the manual lens I just attached. What would be the case with a bellows or a tube extension? Or a zoom lens?
With bellows or tubes, chances are you're shooting on a tripod, where you have to have Shake Reduction OFF anyway. Once you turn SR off, it won't prompt you to input a length for a manual lens.

If you ARE shooting with bellows or a tube handheld...and people actually do it here but I don't know how...just use the lens's actual focal length (FL). The shortest FL you input is the safest, since it activates less shake reduction. If you have SR set too high, it can screw you up.

As far as zooms go, it's a real problem with manual lenses. To truly learn what you're doing and for the best photos while also developing your technique, unless you're going to only use one FL of your zoom--or keep changing your SR FL setting--you're better off turning the damn thing off and shoot via holding the camera steady and choosing the right ISO and aperture to get to the shutter speed need to safely handhold your zoom at any particular FL.

Please remember that shake reduction is only ONE part of your equation, and does nothing anyway to help with moving subjects. People shot for years and years without it to ill effect, and a lot of people nowadays are getting too dependent on it.

SR can help you do some great things, but in the grand scheme of things, it's the least important of your settings, and you should turn it off with manual zooms.

What's important is ISO, aperture, shutter speed, and learning to hold the camera steady when you take the picture.

Also remember that the Kx, Kr and K5's incredibly clean high ISO settings make SR even more irrelevant, since they allow you to shoot at high shutter speeds anyway. And it's high shutter speeds that you need for safe handheld shooting, totally irrespective of whether SR is on or off.

Last edited by Ira; 12-15-2010 at 04:16 PM.
12-15-2010, 05:57 PM   #12
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you still looking for a potato masher flash
12-15-2010, 07:30 PM   #13
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QuoteOriginally posted by lguckert79 Quote
you still looking for a potato masher flash
Five minutes ago, I won a Sunpak 555 on eBay, and I'm going to be buying a REALLY old Strobonar from a member here.

You have a good memory!!!
12-16-2010, 08:51 AM   #14
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thats cool i have an old sunpak 933 im just to afraid to use it on my camera with out an adapter i dont want to fry my camera
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