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01-10-2011, 03:45 PM   #1
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Advice on 85mm or 77mm lens

Hi

Lately I've been thinking harder and harder of buying a 77mm Ltd f1.8 or a 85mm f1.4 lens. I just love narrow dof and smooth bokeh.

I do have a mint 85mm Pentax K 85mm f1.8 lens, which is very good wide open (I use it only wide open). The thing is that I am not comfortable with a lens that does not have autofocus and have to be used fully manual.

I am primarily thinking of the Pentax 77mm f1.8 or Sigma's new 85mm f1.4. I have of course read through all the net about the Pentax 77mm f1.8 and know that one is quality. Less is written about Sigmas 85mm f1.4; so I wonder if anyone has experienced this lens?

Also, how much difference (in practical use) will there be between f1.8 and f1.4? I am not too concerned about the extra light f1.4 offers in advantage of the f1.8, rather I am interested in the out of focus qualities.

Gunnar

01-10-2011, 04:05 PM   #2
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The reduction in DOF is a little more than just aperture because 85mm is also a little longer than 77 mm. Somewhere on line is a DOF calculator you can run both and see for yourself

I have both an 85 mmF 1.4 and 1.9. I like them both but generally use them at F 2.5 or there about just to get a face only sharp
01-10-2011, 04:19 PM   #3
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Yeah, according to the dof calculator the difference is neglible. I am interested in experiences from people that have tried both, to hear if the difference is neglible in practical use too.
01-10-2011, 04:35 PM   #4
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QuoteOriginally posted by Lowell Goudge Quote
The reduction in DOF is a little more than just aperture because 85mm is also a little longer than 77 mm. Somewhere on line is a DOF calculator you can run both and see for yourself
But if you frame the shots the same (step closer with 77) then the DOF will be the same at the same aperture

01-11-2011, 06:22 AM   #5
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I don't have the 77ltd, but I've seen quite a lot of its use. I do have the FA*85 and the M85. A 85/1.4 will give more OOF rendering with its longer focal length a wider aperture. Assuming 5m subject distance for a head to shoulder portrait for the 85/1.4, DOF is 19cm. A 77/1.8 would be around 4.5m subject distance for the same FOV and DOF would be about 25cm.

However, the practical difference is not so apparent up to half body shots. The significance is the size and weight of a 85/1.4 vs a 77ltd which can be a large factor as to which is brought out of the dry cab.
The very reason why I use my M85/2 more than the FA*.
01-11-2011, 06:55 AM   #6
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Gunnar, aren't you mainly using the 85 you have now for portraits or set-up stuff? And you don't think you can get comfortable with manual focus?

Come on--of course you can. In addition, for the type of thin DOF you like, AF is going to be LESS dependable, unless you can REALLY nail your focus point with your current camera's AF. Otherwise, the best fine-tuning for this thin depth of field is going to be manual focus.

Sounds like the money could be better spent than spending it on the Sigma 85 1.4.

Now, if you want to compare IQ between your current 85 and the Sigma and 77, that's a different story, but I don't think DOF has anything to do with it.
01-11-2011, 08:11 AM   #7
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I think you should get the Sigma 85/1.4 because we need someone to review it :-)

That said, IMHO, size and narrow DOF are probably the main determinants. If you like smaller size lenses, don't get the 85/1.4. If you want very narrow DOF for full body shots (I think the 85/1.4 will do a lot better than the 77Ltd wide open for this), get the Sigma 85.1.4
01-11-2011, 11:05 AM   #8
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QuoteOriginally posted by kenyee Quote
I think you should get the Sigma 85/1.4 because we need someone to review it :-)

That said, IMHO, size and narrow DOF are probably the main determinants. If you like smaller size lenses, don't get the 85/1.4. If you want very narrow DOF for full body shots (I think the 85/1.4 will do a lot better than the 77Ltd wide open for this), get the Sigma 85.1.4
I would be glad to do some review. unfortunately, Sigma is being an ass for delaying the release of the lens for the K mount. while Canon and Nikon had already tried the lens as early as September. we are far behind for 6 months now from the time it will be released for the K-mount.

01-11-2011, 01:33 PM   #9
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QuoteOriginally posted by sewebster Quote
But if you frame the shots the same (step closer with 77) then the DOF will be the same at the same aperture
No because F1.8 on 77mm is no where near as wide as F1.4 on the 85mm lens
01-11-2011, 02:44 PM   #10
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QuoteOriginally posted by Lowell Goudge Quote
No because F1.8 on 77mm is no where near as wide as F1.4 on the 85mm lens
That's why I said "at the same aperture." I'm just point out that the focal length is irrelevant if you frame the shot the same. Of course the lenses have different max apertures...
01-12-2011, 01:13 PM   #11
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QuoteOriginally posted by pinholecam Quote
I don't have the 77ltd, but I've seen quite a lot of its use. I do have the FA*85 and the M85. A 85/1.4 will give more OOF rendering with its longer focal length a wider aperture. Assuming 5m subject distance for a head to shoulder portrait for the 85/1.4, DOF is 19cm. A 77/1.8 would be around 4.5m subject distance for the same FOV and DOF would be about 25cm.

However, the practical difference is not so apparent up to half body shots. The significance is the size and weight of a 85/1.4 vs a 77ltd which can be a large factor as to which is brought out of the dry cab.
The very reason why I use my M85/2 more than the FA*.
Your 85mm is either very long or subjects rather large. With 77mm you can fit a lot more into frame then head and shoulders from 4-4.5 meters...

I used to have M85. Liked it a lot but it had some issues and was tad slow for me. I sold it and bought 77ltd. Love it. Good speed, AF, build at least on par with M85, and the same size! I'm still very tempted by 85/1.8 or 1.4 for the sake of narrower DOF but for foreseeable future I think I'll do just fine with 77
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