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10-22-2010, 02:22 PM - 1 Like   #16
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QuoteOriginally posted by mtroute Quote
the obvious answer would be to switch the DA 70mm to "manual" focus...
Precisely!

Todd: If you've never used Pentax FA or DA Limited lenses it is good to know that their mechanical construction is very similar to old manual lenses despite the fact that FA/DA Limiteds are AF lenses. They are great focus manually, so any real advantage of getting old MF primes would be marginal in terms of manual focusing feel (while you will be loosing exposure automation with K and M series lenses).

So indeed, as mtroute has pointed out, just use your DA 70 Limited as an MF lens and that would be exactly what you need to start with. As a plus, DA 70 is a Quick Shift AF lens, meaning you don't even have to disengage AF to apply MF correction to established AF.

10-22-2010, 02:29 PM   #17
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QuoteOriginally posted by Ivan Glisin Quote
Todd: If you've never used Pentax FA or DA Limited lenses it is good to know that their mechanical construction is very similar to old manual lenses despite the fact that FA/DA Limiteds are AF lenses. They are great focus manually, so any real advantage of getting old MF primes would be marginal in terms of manual focusing feel (while you will be loosing exposure automation with K and M series lenses).
This is very nice to know, and I'll be checking it out as soon I get it!

Still want some other focal lengths, though. The M42 lenses sound very interesting. Is there any problem with using the adapter rings (outside of stop-down metering, which I will need to learn how to do on Pentax)? Like losing infinity focus? If I want to get the Pentax-manufactured adapter ring, do I need to buy it directly from them, or can I get it at B&H, etc.?
10-22-2010, 02:34 PM   #18
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QuoteOriginally posted by Nowhere Matt Quote
See, I just learned a new phrase today. Focus throw. Used in a sentence: This Sigma lens demonstrates a very short focus throw.
Thank you. Carry on.

(I like this Todd Adamson already)
Glad to hear that even as a total n00b I can be of some use.
10-22-2010, 02:42 PM   #19
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The focus throw of my M 50mm 1:1.7 is around 190-200 degrees or somewhat over half a turn.

With Pentax A-lenses the body is in control of the aperture and therefore auto exposure modes work and aperture is recorded in the exif data. With Pentax M lenses the aperture is set by the aperture ring and the body assumes no knowledge of it so only M mode will work decently with "green button metering" which stops down the lens and sets the exposure time to suit when the button is pressed.

Third party lenses with an A-position on the aperture ring work like Pentax-A lenses. Third party lenses without that, but with the Pentax aperture lever work like Pentax-M lenses and lenses without that, such as M42 lenses work with green button metering, but without the lever, the body cannot stop them down for metering or exposure so this must be done with the lens (in which case one might need to switch back and forth for composing and focusing).

With a lens that does not have the A-position or is not set to that the body will work in the M mode as explained above. The only other mode available is Av mode, where the body meters continuously assuming exposure aperture is in effect. This makes sense for lenses without the Pentax aperture lever (such as M42 lenses), but is not so good for lenses with the Pentax aperture lever (such as M-series lenses) as the body stops these down for exposure with the shutter time set based on metering the lens wide open.

10-22-2010, 02:48 PM   #20
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I would recommend an actual Pentax K to M42 adapter if you would like to go the Takumar route. I bought mine from a local store here in town, and once in a while you see them in the forum marketplace. I would think B&H would have them.

There are a number of good articles here on the forum on how to change the setting on your K-7 to use them, managing exposure etc.

You should be safe using actual Takumar and Pentax lenses, but you might want to do a little research if you chose another obscure brand. Some will get stuck on the camera and others can interfere with the mirror. There was also a budget Takumar series of lenses that you might want to avoid. Basically the M42 screwmount Takumars are considered better than the K mount ones.

Steve
10-22-2010, 02:52 PM   #21
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QuoteOriginally posted by jolepp Quote
The focus throw of my M 50mm 1:1.7 is around 190-200 degrees or somewhat over half a turn.

With Pentax A-lenses the body is in control of the aperture and therefore auto exposure modes work and aperture is recorded in the exif data. With Pentax M lenses the aperture is set by the aperture ring and the body assumes no knowledge of it so only M mode will work decently with "green button metering" which stops down the lens and sets the exposure time to suit when the button is pressed.

Third party lenses with an A-position on the aperture ring work like Pentax-A lenses. Third party lenses without that, but with the Pentax aperture lever work like Pentax-M lenses and lenses without that, such as M42 lenses work with green button metering, but without the lever, the body cannot stop them down for metering or exposure so this must be done with the lens (in which case one might need to switch back and forth for composing and focusing).

With a lens that does not have the A-position or is not set to that the body will work in the M mode as explained above. The only other mode available is Av mode, where the body meters continuously assuming exposure aperture is in effect. This makes sense for lenses without the Pentax aperture lever (such as M42 lenses), but is not so good for lenses with the Pentax aperture lever (such as M-series lenses) as the body stops these down for exposure with the shutter time set based on metering the lens wide open.
With some Nikon lenses, I have to set the aperture ring to the smallest aperture for the body to be able to adjust aperture; is that analogous to the "A" position you're referring to? Also, the way you have described "green button metering" makes it seem a bit like aperture priority mode, is that accurate? Or can I hold down the green button for metering, as I watch an exposure meter in the VF, and set my shutter speed that way?

Heh...I'll try to take it easy on the stupid questions until I get my camera. Presumably, once I've gone through the manual, and tried some things, a lot more will be clear, and my questions will be a little more targeted.
10-22-2010, 02:54 PM   #22
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QuoteOriginally posted by Todd Adamson Quote
This is very nice to know, and I'll be checking it out as soon I get it!

Still want some other focal lengths, though. The M42 lenses sound very interesting. Is there any problem with using the adapter rings (outside of stop-down metering, which I will need to learn how to do on Pentax)? Like losing infinity focus? If I want to get the Pentax-manufactured adapter ring, do I need to buy it directly from them, or can I get it at B&H, etc.?

The Genuine Pentax Mount Adapter K allows infinity focus on Pentax m42 lenses. Know this though: the adapter has a spring clip that will lock it to the camera. You can use a pen, knife, screwdriver tip to push the clip in to remove it from the camera body.

ebay also sells pentax mount adapters, but be careful, if it's not genuine Pentax made, it may not allow infinity focus.

Pentax no longer makes the adapters. You can only find used ones or knock offs.

In fact, I just bought 3 knock off adapters from china for $12 with $10.50 shipping. They look almost like the original Pentax versions, but I will be using them with my m42 screw mount macro lenses, so infinity focus is not a major concern.

Last edited by chalion; 10-22-2010 at 03:00 PM.
10-22-2010, 03:02 PM   #23
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So, would THIS be the one to get?

10-22-2010, 03:02 PM   #24
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I second smc's recommendation: for M42 lenses, get a genuine Pentax M42 adapter. Others tend to be a pain to remove from the body (poor quality copies of the original, usually sold with a tool to remove and install) or prevent infinity focus (different design with a flange going between the lens and the body). Unfortunately the genuine adapter might be difficult to obtain.
10-22-2010, 03:23 PM   #25
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QuoteOriginally posted by Todd Adamson Quote
So, would THIS be the one to get?
Yes.....that's the one.
10-22-2010, 04:33 PM   #26
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QuoteOriginally posted by Todd Adamson Quote
With some Nikon lenses, I have to set the aperture ring to the smallest aperture for the body to be able to adjust aperture; is that analogous to the "A" position you're referring to? Also, the way you have described "green button metering" makes it seem a bit like aperture priority mode, is that accurate? Or can I hold down the green button for metering, as I watch an exposure meter in the VF, and set my shutter speed that way?

Heh...I'll try to take it easy on the stupid questions until I get my camera. Presumably, once I've gone through the manual, and tried some things, a lot more will be clear, and my questions will be a little more targeted.
The A-position is next to the smallest aperture position (=largest F-number) so this seems to be similar. The A-position operates an electromechanical contact at the mount from which the body knows that the ring is in this position though.

Logically green button metering is the same as entering aperture priority mode just long enough that the exposure time gets set to match the aperture set on the aperture ring. That is, you don't get to set the time with the help of the virtual meter in the viewfinder, but this is done for you as a result of pressing the button. You can then adjust the time normally using the set value as a starting point. The green button metering is simple enough to use, it seems that explaining it well is much more difficult :-)
10-22-2010, 07:18 PM   #27
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QuoteOriginally posted by Todd Adamson Quote
So, would THIS be the one to get?
That would be the one, but it is called Mount Adapter K not Mount Adapter B.

PentaxWebstore Mount Adapter K(35m m Screwmount to Bayonet)

I don't know why Chalion thinks they don't make them anymore. They have been in production for 35 years. Pentax must have made millions of them. I paid about $20 for mine on eBay last December.

Last edited by boriscleto; 10-22-2010 at 07:26 PM.
10-22-2010, 07:22 PM   #28
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QuoteOriginally posted by Todd Adamson Quote
Also, the way you have described "green button metering" makes it seem a bit like aperture priority mode, is that accurate? Or can I hold down the green button for metering, as I watch an exposure meter in the VF, and set my shutter speed that way?
Green button stops down the lens and sets the exposure according to the program line. The DOF preview button or whatever button you set for Optical Preview lets you watch an exposure meter in the VF.
10-22-2010, 07:56 PM   #29
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+1 for the M 50 1.7 Epic lens.
10-22-2010, 09:37 PM   #30
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OK, I think I want that M 50/1.7.

From the Pentax Lens Series Explained article:

"Some recent bodies cannot use M and K lenses or only with some limitations. An example are the *ist D and K (digital) series. In M mode you set the aperture using the aperture ring on the lens; the camera will set the shutter speed when you press the green button (or AE-L button if the camera has no green button). Or you can set the shutter speed manually (there is no exposure read out in the finder to assist you)."

So it will work on the K-7? It sounds like I select my aperture using the ring, frame my shot, and press the green button, and the shutter speed will be set (probably will vary depending on the metering mode I have chosen?)? Now, after I let up on the green button, that shutter speed is set, and I can adjust it if I want....do I have that right?

By the way, for Pentax lenses that don't have an A-position, what are the normal increments, or does it vary from lens to lens?
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