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SLR Lenses on DSLRs
Hi all..

Have just stepped back into the frame of casual photography. Have purchased a near new Pentax K10 body. I previously owned pentax SLRs so this seemed a good choice. My question (no doubt the first of many) is;.

What is the guts of using SLR lenses on DSLR cameras. Can you utilise them, or are there factors which make them too impractical to use..

In particular can I run my Sigma lenses for my old SLR on the K10, they are:.

Sigma EX Aspherical IF 20 - 40 1 :2.8 82mmSigma EX 105mm MacroSigma 70-300mm F4-5.6 APO.

I understand that the focal length is reduced by a factor of 1.5. i.e. a 300mm SLR lens = 200mm on a DSLR camera. Does this have any other effects on the operation of the lense/quality of image?.

Appreciate your helpAaron..

Comments (5)

Aaron H wrote:.

Hi all.Have just stepped back into the frame of casual photography. Havepurchased a near new Pentax K10 body. I previously owned pentax SLRsso this seemed a good choice. My question (no doubt the first ofmany) is;What is the guts of using SLR lenses on DSLR cameras. Can you utilisethem, or are there factors which make them too impractical to use..

The whole point of an SLR camera is the benefit of interchangeable lenses. This maximizes your ability to shoot scenes at a distance, close up, wide, etc..

In particular can I run my Sigma lenses for my old SLR on the K10,they are:.

Sigma EX Aspherical IF 20 - 40 1 :2.8 82mmSigma EX 105mm MacroSigma 70-300mm F4-5.6 APO.

I am not familiar with the Pentax DSLR. If the lenses safely mount and are other wise compatible, you should be able to use them. You need to research if the lenses are designed to fit Pentax, and if so, if the camera doesn't have limitations with certain lenses, etc..

I understand that the focal length is reduced by a factor of 1.5.i.e. a 300mm SLR lens = 200mm on a DSLR camera. Does this have anyother effects on the operation of the lense/quality of image?.

Wrong! Focal length is focal length is focal length. And, at that, you have it backwards. Because the Pentax, and many other DSLRs have a cropped sensor (when compared to the film standard), the field of view is effectively "magnified." This, because the smaller sensor captures less of the scene than a full-sized sensor. With the Pentax's 1.5 crop factor, if you were using a 100mm lens, you see through the viewfinder and scene captured would be similar to that of a lens of 150mm focal length..

Appreciate your helpAaron..

Comment #1

Aaron,.

You have it a little backwards because the sensor on your K10D is smaller than 35mm film frame, the equivalent field of view of a 300mm on your digital is equal to that of a 450mm lens on 35mm film. Please bear in mind that it's the field of view that changes the focal length is still the same..

In practical terms this means that your 20-40mm lens on your K10D gives you the same field of view as a 30-60mm would on film..

As for using the lenses, assuming they have an "A" setting on the aperture ring (or are autofocus), they should work fine with the K10D. You'll be utilizing the "sweet spot" of the lens, not the extreme edges, which should actually improve certain aspects of performance (vignetting in particular)..

Hope this makes sense.....

Jim.

Http://www.downeffect.com/jim/portfolio..

Comment #2

Thanks Jim...makes perfect sense. My lenses do have'A' and auto focus so appear to function well on the K10..

Appreciate your input..

Aaron..

Comment #3

You can use virtually any Pentax fit lens on the K10D in some form or another, even M42 screw lenses with an appropiate adaptor. KA mount lenses will "talk" to your camera to allow automatic exposure control, older lenses will still work in manual exposure mode. You can use MF mode for manual lenses or AF mode with manual lenses (focus trap mode) Autofocus lenses work fine. Search the Pentax SLR forum for info on specific lenses, there are a number of sites with comprehensive lists and user reviews of Pentax's rich back catalogue!Just stay off e-bay or you may succumb to LBA! (Lense Buying Addiction): )Everything changes..

Comment #4

Stephenhampshire wrote:.

You can use virtually any Pentax fit lens on the K10D in some form oranother, even M42 screw lenses with an appropiate adaptor. KA mountlenses will "talk" to your camera to allow automatic exposurecontrol, older lenses will still work in manual exposure mode. Youcan use MF mode for manual lenses or AF mode with manual lenses(focus trap mode) Autofocus lenses work fine. Search the Pentax SLRforum for info on specific lenses, there are a number of sites withcomprehensive lists and user reviews of Pentax's rich back catalogue!Just stay off e-bay or you may succumb to LBA! (Lense Buying Addiction): )Everything changes.

This pretty much covers it. There is some dispute about whether non A series Pentax MF lenses (ie M and K series lenses) meter accurately on a K10 (check the Pentax forum) but the suggestion is the errors are consistent so easily compensated for..

Pentax lens quality historically is pretty sound (many good ones, not many dogs). Whatever you do do not ever attatch a Ricoh P mount lens onto a Pentax body. The lensmount is the same but it has an extra camm which locks and jams & it's a major repair job to separate them!Shay son of Che..

Comment #5

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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