Basic or not? On occassion , I use older manual focus lenses on my Pentax K-x. According to instructions, the focal length of the lens should be dialed into camera. For purposes of...

sirlensalot Loc: Arizona

On occassion , I use older manual focus lenses on my Pentax K-x. According to instructions, the focal length of the lens should be dialed into camera. For purposes of this discussion, we'll use a standard 50mm f/2 lens. The Pentax has a crop factor of 1.5, so I dial in 75mm.
A fellow photographer tells me not necessary, that the setting can be set to 50mm. First part of this is which setting is correct? Second part is what impact would the difference have on the image if settings are not adjusted to the crop factor? I don't seem to see a difference in photos.
Should images look a lot different? Any feedback will be appreciated.

MT Shooter Loc: Montana

A 50mm lens is ALWAYS a 50mm lens. With a crop sensor camera you are simply only using the center portion of the lens rather than the whole thing.

sirlensalot Loc: Arizona

Would you know what the necessity is for inputting the focal length of any lens then if lens only uses the center portion, or am I missing how to understand this? I appreciate your input MT Shooter.

MT Shooter Loc: Montana

sirlensalot wrote:

Would you know what the necessity is for inputting the focal length of any lens then if lens only uses the center portion, or am I missing how to understand this? I appreciate your input MT Shooter.

I am unfamiliar with "inputing" a lens, I simply mount a lens on my Nikons and it recognizes what lens I am using and shoots with it, the EXIF data even shows the serial number of my lenses along with all their other information including the 35mm equivalent of it. Must be something with the Pentax that you have to tell the body what lens you are using. In either case I think I would enter exactly what the lens is, not the equivalent length as, like I said before, a 50mm lens is always a 50mm lens no matter what body you put it on and no matter what your sensor size is.

sirlensalot Loc: Arizona

Thanks MT Shooter. I think I will call Pentax tech service tomorrow to see what they say. Telling the camera what lens you are using is only needed when using older film lenses with no connections for auto focus. Mostly the older "M" lenses. All of the newest lenses work pretty much as your Nikon does. Let you know what they say.

Nikonian72 Loc: Chico CA

sirlensalot wrote:

According to instructions, the focal length of the lens should be dialed into camera . . . so I dial in 75mm.

Exactly how do you "dial" a lens into a camera? What is the process?

sirlensalot wrote:

I don't seem to see a difference in photos. Should images look a lot different? Any feedback will be appreciated.

Same scene photographed twice with the same lens should look identical, except for any ISO, aperture, or shutter duration changes that you make.

sirlensalot Loc: Arizona

On my K-x when you mount an older manual lens which cannot receive information from the camera, two things are required per PG. 130 of the manual. First in menu settings, user must "permit" the use of the aperture ring to be used manually. That triggers a window which allows user to input focal length of the manual lens. Then after setting, you are ready to shoot. I can't find any further explanation.

GC-FineArt Loc: WDC

sirlensalot wrote:

On my K-x when you mount an older manual lens which cannot receive information from the camera, two things are required per PG. 130 of the manual. First in menu settings, user must "permit" the use of the aperture ring to be used manually. That triggers a window which allows user to input focal length of the manual lens. Then after setting, you are ready to shoot. I can't find any further explanation.

I shoot with a Pentax-K20D and am not really familiar with the K-x but as far as I know, all Pentax DSLR's have a "Shake Reduction" function built into the camera body. In order for this to work properly with older lenses, the camera needs to know the physical dimensions of the lens in use. So, rather than ask you to input the actual dimensions, the camera simply asks for "focal length" to use as a "best appoximation," so to speak.
Also, in line with this, not only is there no need to do any "effective focal length" calculations, as your friend says, you SHOULD not since this gives the shake reduction function incorrect data.
Regards,

Dean Sturgis

GC-FineArt wrote:

quote=sirlensalot On my K-x when you mount an old... (show quote)

One of the functions of the contacts on the back of the lens is to tell the camera body what the focal length is. Setting the focal length is to enable best operation of the shake reduction system. Since shake shake reduction is not needed at high shutter speeds say above 1/125 sec or with a rigid tripod, you might not need to set it every time you put on a old lens. I just checked with my Pentax K10D to see what happen with a old lens. If you set the focal length for shake reduction the EXIF data will report the focal length, If you don't set it the EXIF data may report 0mm, lor possibly a wrong length from a earlier setting.

Historical note: I believe the K10D was the first model with shake reduction, the *ist series of cameras didn't have it.

dsturgis

GC-FineArt Loc: WDC

I misspoke. You're absolutely right about the K10D being the first Pentax DSLR with "Shake Reduction" while the earlier *istD does not have this feature.
Regard,

Greg Loc: Maryland

MT Shooter wrote:

quote=sirlensalot Would you know what the necessi... (show quote)

Yes MT, but these are not older manual lenses like sirlensalot is using. If you put one of my older lenses on your D7000, it won't recognize it. It will still work, but everything is manual (well on the D7000, almost everything, you can use Aperture priority, but some older Nikkor lenses will not let even the D7000 do that). I did a search, and from the little I found it looks like you are basically telling the body to:

This setting allows easy and accurate exposure metering using older lenses without an "A" setting on the aperture ring. When the Green button is pressed in Manual exposure mode, the lens "stops down", the camera's meter measures the light passing through the lens, and an appropriate shutter speed is automatically set based on that measurement.

MT Shooter Loc: Montana

Greg wrote:

quote=MT Shooter quote=sirlensalot Would you kno... (show quote)

Actually they are. I have several old Nikkor AIs lenses from the 70's and 80's from my old F2 and FM days, and they all are recognized in focal length and aperture range on my D7000. Since I almost always shoot in Aperture priority anyway they work quite well.

Greg Loc: Maryland

MT Shooter wrote:

quote=Greg quote=MT Shooter quote=sirlensalot W... (show quote)

I don't see how they are recognized for focal length as they aren't cpu lenses. Aperature will work with ani AI lens, but the D7000 does not have the input mechanism for F mount lenses. They'll work in full manual, but they don't have the AI encoder.

sirlensalot Loc: Arizona

Sorry everyone, but was unable to contact Pentax today. Will try tomorrow. Thanks for discussion.

professorwheeze Loc: Maine, USA

sirlensalot wrote:

On occassion , I use older manual focus lenses on ... (show quote)

It is hard to give-up on the old glass. I actually use, albeit infrequently, and 80 mm lens from my Bronica SQ-Ai on a Nikon D3100. Obviously it needed an adapter that was $$, but it allowed to use the lens anyways. It fits tightly. Unfortunately, the camera will stop-down ( or is it step-down) to the largest aperture on the 80 (f2.8). Everything is manual. But, heck, I use the VDU on the camera backside.

There is 3 no Vibration-Reduction as Nikon placed that function in the lens and not the body, like your Pentax. Sure does help to sell those Nikon lenses!

As other's have said don't confuse the camera by telling it is a lens of a longer length. Great question.