[Jewelltrail]

Does anyone here know if the Pentax medium format lenses, like the 165mm f2.8, will work on Pentax DSLRs? Does anyone have any experience using these lenses on DSLRs. I imagine adapters are needed--is this a worthwhile pursuit? Thanks.

Regards,

Ernest


"Humanity subdues inhumanity as water subdues fire."

Mencius 6A:18

[Wheatfield]

you can adapt both 645 and 6x7 lenses to the Pentax DSLR via adapters. This was shot with the K10 and the SMC Pentax 6x7 300mm f/4.
Whether the image quality is as good as with K mount lenses, I don't know. I wouldn't expect so, but I think we get too caught up in the whole "IQ" thing (whatever that means) sometimes.
I wouldn't pursue it myself, but if you come across a cache of medium format lenses being sold really cheaply.........
You lose ALL lens automation, BTW. The 6x7 adapters have no mechanical or electrical linkages, and I am pretty sure the 645 ones don't either, though I could be wrong.

[Jewelltrail]

Wheatfield:

This is great information--thank you very much. I bumped into a mint copy of the 165mm 2.8 for little money and got to wondering. You have put the wondering to rest. I am getting used to shooting in manual mode now with the Takumars and M series lenses, so this will give me a little more practice--thank you again. BTW, this is a great shot you have posted here.


Best Regards,

Ernest

"Humanity subdues inhumanity as water subdues fire."

Mencius 6A:18.

[Zewrak]

Question is, where the heck do you find these adapters?

[christinelandon]

Zewrak, the Pentax webstore has a listing for the 645 to K mount adapter here: PentaxWebstore - SLR Lenses
Nothing listed for adapting the 6x7 lenses, though.

[Chip]

I did found all Pentax adapters quite cheap at different 2nd hand sites.
The 6x7 to 35, the 645 to 35 and the 6x7 to 645.
Here's a pic, K10D and SMC 75mm f/2.8 645 lens:




Needless to say that I'm very pleased with the combo?

[ChipB]

Using a 35mm lens on a Pentax DSLR results in the 1.5x "factor" - does this effect also apply when using medium format lenses?? If so, is it a different "factor"?

[Zewrak]

Zewrak, the Pentax webstore has a listing for the 645 to K mount adapter here: PentaxWebstore - SLR Lenses
Nothing listed for adapting the 6x7 lenses, though.

Well they only ship to USA. And niether the UK or Swedish Pentax offices have stores. Found a *300mm/4 for 645, only 400$.

[kmccanta]

Chip,

the 1.5X factor is the difference in sensor size. It has nothing to do with the lenses.

The reason it is confusing, is that people have internalized what the angle of view is for a certain focal length lens on old 35mm film sensor size. When you crop out the center of that view, its "like" zooming in by 1.5x.

It doesnt change the lens, it doesnt change the depth of field etc.. it only crops out the center of the image.

So, if you are used to shooting a 165mm lens on 645 format, then you need a different factor to understand jsut how small the DSLR sensor is compared to the larger 645 film image. If you dont know if the 165mm is "normal" or telephoto or what. Or you dont know what it would be on 35mm ... then hurray! you can forget about the factor.

All 165mm lenses will give you the same field of view on your camera, no matter how large the lens is, or for what system it was designed.

I hope I was able to explain that clearly... its hard to say but easy to understand.

[Shashinki]

There's even a 67 to 645 adapter for sale.

The size and weight (+no lenses under f/2.4) of these lenses make them kind of uhm... really not worth the price of the adapter if you don't happen to bring your DSLR with you when out taking pictures with your Pentax medium format camera.

Then its kind of useful to have a 200mm "portrait" lens on the 67 that doubles as a MF tele on your DSLR.

[ChipB]

Chip,

the 1.5X factor is the difference in sensor size. It has nothing to do with the lenses.

The reason it is confusing, is that people have internalized what the angle of view is for a certain focal length lens on old 35mm film sensor size. When you crop out the center of that view, its "like" zooming in by 1.5x.

It doesnt change the lens, it doesnt change the depth of field etc.. it only crops out the center of the image.

So, if you are used to shooting a 165mm lens on 645 format, then you need a different factor to understand jsut how small the DSLR sensor is compared to the larger 645 film image. If you dont know if the 165mm is "normal" or telephoto or what. Or you dont know what it would be on 35mm ... then hurray! you can forget about the factor.

All 165mm lenses will give you the same field of view on your camera, no matter how large the lens is, or for what system it was designed.

I hope I was able to explain that clearly... its hard to say but easy to understand.

Thanks for the explaination. I've never used any medium format lenses (or bodies, for that matter), so I have no sense of "equivelancy" - ie: a 50mm lens on a DSLR appears to be a 75mm lens due to the crop factor. Is there some sort of comparison ratio/factor for 645 (or 6x7) lenses vs 35mm lenses? OR, am I totally confused??

[Canada_Rockies]

Thanks for the explaination. I've never used any medium format lenses (or bodies, for that matter), so I have no sense of "equivelancy" - ie: a 50mm lens on a DSLR appears to be a 75mm lens due to the crop factor. Is there some sort of comparison ratio/factor for 645 (or 6x7) lenses vs 35mm lenses? OR, am I totally confused??

You are totally confused, just like the rest of us. The "crop factor" is a fiction so that we old guys and gals with aged memories can visualize the field of view. For the crop factor to have any meaning at all to you, you have to have in your memory the field of view you expect from, say, a 24 mm lens, from when you were using a film camera. The dSLR just crops out 2/3 of the field, making the lens have a field of view equivalent to a 36mm lens on film.

Since the focal length doesn't change, the field of view of a 50mm lens on a 6x7 (very wide) comes out as a normal lens on 35mm film, or a moderate portrait tele on the APS-C format of our sensors.

If you have inexpensive access to 645 or 67 lenses, and can afford the adapter, go for it. You will be using a very small area of the lens so that all the corner and edge softness and chromatic aberration will not be seen by your sensor. You will also develop good strong muscles holding up that weight.

[Wheatfield]

Using a 35mm lens on a Pentax DSLR results in the 1.5x "factor" - does this effect also apply when using medium format lenses?? If so, is it a different "factor"?

Focal length is focal length is focal length.

[kmccanta]

I think I confused you. I will now try to confuse you so much now that you will make it around the other way back to unconfused...

imagine that you are a mutant, and can shrink down small enough to crawl inside your camera. You crawl inside a 35mm film camera with a 50mm lens attached... when the mirror is flipped up, the lens will cast an image of the world outside on the film. This image is not a rectangle, it is of course a circle, because the lens is circular. the image circle has a size.

But it doesnt just "stop" at the edge, it gets darker and darker at the edges. even the bright parts of the image are a little darker the further from the center (this is called vignetting).

now someone removes the 50mm lens and attaches a different 50mm lens. the image on the rectangle of film hasnt changed. each object in the image is the same size as before... BUT this lens was designed for a 645 camera, which has a bigger film. So the image circle is bigger. Now the edges where the image gets darker are farther away from the center of the film and the vignetting of the first lens is not noticable. Most of the image circle is not falling on the film, but on the area around the film. This 50mm "wide angle" lens from the 645 camera is producing a "normal" image onthe 35mm camera without the vignetting of the smaller lens.

Now the user removes this 50mm lens and mounts the kit lens from your pentax DSLR zoomed to 50mm. The image is smaller still. It is of course large enough to cover the smaller size of an APS-C sensor chip. But here in the 35mm camera, the rectangle of film is bigger. All of the elements of the image (a person, a dog, a swingset, a mountain, whatever) are all the same size as before, but now the 50mm "short-telephoto" from your APS-C is producing a "normal" image with really bad vignetting on the rectangle of film.

It doesnt matter what camera a 50mm lens was designed for, it will alsways produce an image with a certain amount of magnification. i.e. the person in the image will be the same size as any image produced by any 50mm lens. The difference is how big of round the image will be... how much stuff around the person in the picture will be in the image? how much of that is recorded by the sensor or the film? The 645 lenses are bigger around, they have more glass in them. They are heavier than most 35mm lenses and most APS-C lenses. but the focal lengths dont change depending on the camera.

This is why the factor is fanactically called a crop factor by some. There is NO additional magnification going on. The image is cropped because the APS-C sensor is physically too small to capture the edges of the image.


The bottom line is what do you know? Are you familiar with 35mm focal lengths? if so, then maye you should translate by 1.5. I.e. whats you favorite wide angle lens for landscapes? you had better divide that by 1.5 to figure out what focal length lens to use for your APS-C camera. Are you familiar with 645 cameras? then maybe you need to use 1.5*1.5 (or something) to translate what you know is a "normal" view 75mm lens to the "normal" view of a 35mm lens on you DSLR.

If you dont have focal lengths attached to meanings in you head for some other system, then you can ignore the factor forever. It has no meaning except to help translate for someone who has memorized a different system. If you can memorize both the DSLR system and the old one ... then great! Thas probably what people did when they had both a 35mm camera system and a medium format one. They just new that the 75mm lens on the 645 was for street shots, same as the 50mm was what they wanted on the 35mm camera for the same application.

[Wheatfield]

Here, this might help. It's not 100% accurate, but it gives an idea of what happens when you put different formats behind a lens. Forgive the mis spelling of APS-C, that is intended to represent the Pentax DSLR format.