Pentax 105mm f2.4 with a Pentax 645 body? HELP!

Chris Walsh · Aug 20, 2017

Hi everyone,

I've recently acquired a Pentax 645 (original version) body and I'm looking for a lens to use with it for portrait work.

I was considering the Pentax-A 645 75mm f/2.8 to get a 50mm equivalent focal length for portraits when I heard the massive hype around the 105mm f/2.4 lens originally made for the Pentax 6x7. I'm now caught between going with the matching Pentax-A 75mm or trying to use the 105mm 2.4 with an appropriate adapter.

My question is this:

Would the 105mm f/2.4 retain it's legendary depth of field qualities when adapted to 645 format? Or would it lose some of that due to the reduced size of the negative? Would it act somewhere in between the formats of 35mm and 6x7?

Finally, if so or even if not, which lens would you advise on purchasing? What would you personally go with?

See @c_walshie on Instagram for the kind of work I like to shoot.

Thanks so much in advance!

- Chris

pentaxuser · Aug 20, 2017

Have a look on the reviews of lenses on the Pentax forums for MF. The 120( equivalent to 75mm in 35mm fomat) and the 150 (equivalent to the 94mm in 35mm) get good reviews. This might be a better bet than a 67 lens which has to be adapted.

pentaxuser

Chris Walsh · Aug 20, 2017

pentaxuser said:
Have a look on the reviews of lenses on the Pentax forums for MF. The 120( equivalent to 75mm in 35mm fomat) and the 150 (equivalent to the 94mm in 35mm) get good reviews. This might be a better bet than a 67 lens which has to be adapted.

pentaxuser

Thank you, I'm now considering this lens as well. But it does seem to be a K mount lens - can this be used natively (without an adapter) with a P645 body?

pentaxuser · Aug 20, 2017

Chris Walsh said:
Thank you, I'm now considering this lens as well. But it does seem to be a K mount lens - can this be used natively (without an adapter) with a P645 body?

I haven't got a 67 so I don't know but once again unless you get a definitive answer here from a user of a P645 who has used a P67 lens, have a look at Pentax Forums where a P67 and adaptors for its lenses for the P 645 are discussed

pentaxuser

Paul Manuell · Aug 20, 2017

I know it might be considered a bit long, but the lens I use more than any for portraits with my 645NII is the 200mm f4. On the odd occasion I need a different lens - lack of space to use the 200 for example - I use my 120mm f4 macro. I very rarely use the standard 75mm.

DREW WILEY · Aug 20, 2017

Should work great if you want a slightly longer than "normal" perspective on 645. Probably optically superior to the dedicated 645 normal. Out-of-focus rendering can be controlled by the F-stop. The 105/2.4 is a popular portrait lens, along with the 165/2.8.

Fixcinater · Aug 21, 2017

I have the original model of the 105mm, labeled Super-Takumar. It is excellent but later editions would likely have better flare resistance. That has been my experience across many many of the 35mm Takumar and later Pentax lenses. I have the factory P67:M42 adapter, the 105mm works fine on the Spotmatic bodies but it is quite large/heavy as you might imagine. I got the adapter just to try it out, and I was able to sell off a couple of teles I had doubled up on, so now I only have one 300mm and can use it on both formats, same for the 105mm.

IMO, a lot of the "magic" of that lens is shown when used on original format, so your 645 would show that better than using it on 35mm which is a waste.

I also have the 80mm f/1.9 for Mamiya 645 and it feels longer than normal, and the 110mm for that system feels longer than an 85mm does on 35mm. The 105 would be firmly in short tele territory, not so much a "normal" length.

Chris Walsh · Aug 21, 2017

Fixcinater said:
IMO, a lot of the "magic" of that lens is shown when used on original format, so your 645 would show that better than using it on 35mm which is a waste... The 105 would be firmly in short tele territory, not so much a "normal" length.

Thanks Fixcinater, that's a big help. I think I might go for the standard 75mm 2.8 that comes stock with the 645 and look at the 105mm later on, perhaps when I'm shooting a 6x7. It looks like an amazing lens by all accounts, but I'm not particularly interested in anything over 135mm in 35mm equivalents. Thanks!

wiltw · Aug 21, 2017

Chris Walsh said:
Would the 105mm f/2.4 retain it's legendary depth of field qualities when adapted to 645 format? Or would it lose some of that due to the reduced size of the negative? Would it act somewhere in between the formats of 35mm and 6x7?

Finally, if so or even if not, which lens would you advise on purchasing? What would you personally go with?

You do realize that DOF in a lens has NOTHING to do with the lens itself, but its shooting aperture and what format it is used to shoot! That is, 'the legendary depth of field' would be DIFFERENT used for 645 than 6x7.

105mm on 6x7 at a shooting distance of 13' sees 7.2' x 8.4' area with DOF of 1.75' at f/2.8
105mm on 645 at shooting distance of 17.2' sees 7.2' x 9.6' area with DOF of 2.5' at f/2.8

...you would need to shoot at 1EV larger aperture with 645 to get 'the same DOF' of 1.75' with identical framing (along the short dimension of the frame)

105mm is a rather short FL for 'portraiture' even on 645 for head and shoulders, requiring a somewhat too-close shooting distance which induces less-pleasing perspective than a longer FL. It is like using 60mm on 135.
At a shooting distance of only 5', on 645 the 105mm would frame 2.7' x 2' area...far better to shoot from about 8-10' using 170mm.

craigclu · Aug 21, 2017

I had a P67 with a decent set of lenses when I added a 645 body. I liked the brighter finder of the 645 and the general ease of handling so I added an adapter to make use of my accumulated optics (I only have the 75 and 150 of the 645 lenses). I used to go on stage at dress rehearsals of theater productions with the P645 and a 105 and a 645 rangefinder with a 65mm. I would then do the film that evening, printing lobby 8X10's the following morning. I could cover the needs of the task easily with these two rigs and I was always happy with the 105 results. The 105 had never really dazzled on the P67 (it was very competent, though) but I always liked the results on the 645 body. I don't know if the "sweet spot" was showing itself, easier focusing, film flatness on the smaller format or what was at hand but I liked the results very much.

Chris Walsh · Aug 21, 2017

wiltw said:
You do realize that DOF in a lens has NOTHING to do with the lens itself, but its shooting aperture and what format it is used to shoot! That is, 'the legendary depth of field' would be DIFFERENT used for 645 than 6x7.

105mm on 6x7 at a shooting distance of 13' sees 7.2' x 8.4' area with DOF of 1.75' at f/2.8

105mm on 645 at shooting distance of 17.2' sees 7.2' x 9.6' area with DOF of 2.5' at f/2.8

...you would need to shoot at 1EV larger aperture with 645 to get 'the same DOF' of 1.75' with identical framing (along the short dimension of the frame)

105mm is a rather short FL for 'portraiture' even on 645 for head and shoulders, requiring a somewhat too-close shooting distance which induces less-pleasing perspective than a longer FL. It is like using 60mm on 135.
At a shooting distance of only 5', on 645 the 105mm would frame 2.7' x 2' area...far better to shoot from about 8-10' using 170mm.

Hey wiltw, I do understand that DOF exists seperate to the lens, which is why I posed the question in the first place. Thanks for doing the math for me and figuring it out! I appreciate it.

Chris Walsh · Aug 21, 2017

craigclu said:
I had a P67 with a decent set of lenses when I added a 645 body. I liked the brighter finder of the 645 and the general ease of handling so I added an adapter to make use of my accumulated optics (I only have the 75 and 150 of the 645 lenses). I used to go on stage at dress rehearsals of theater productions with the P645 and a 105 and a 645 rangefinder with a 65mm. I would then do the film that evening, printing lobby 8X10's the following morning. I could cover the needs of the task easily with these two rigs and I was always happy with the 105 results. The 105 had never really dazzled on the P67 (it was very competent, though) but I always liked the results on the 645 body. I don't know if the "sweet spot" was showing itself, easier focusing, film flatness on the smaller format or what was at hand but I liked the results very much.

Thanks for the input - that does sound like a pretty sweet setup! Very cool to hear about shooting dress rehearsals, in my experience it isn't often done anymore. It's good to know that it's plausible to use 67 lenses on a 645 body, especially the 105mm. I'm keen to try it out sometime . Thanks!

Pentax 105mm f2.4 with a Pentax 645 body? HELP!

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