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12-15-2010, 06:02 PM   #1
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FA 150f2.8 on 645d...anyone try?

I am thinking about picking this lens up but want to know if it is worth it. I know the 120mm macro is known for its sharpness, but I think the 150mm focal length would add a little more to my portraits.

So if you have used this lens with the 645D please let us know how it performs.

Thanks!

12-15-2010, 08:06 PM   #2
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I was thinking the same until I learned that the 55mm f/2.8 is the only 645 lens to feature a completely rounded diaphragm.

According to Pentax that "creates a natural, beautiful “bokeh” (out-of-focus rendition), while minimizing the streaking effect of point light sources."

I've heard, second hand, that the 120mm and 150mm bokeh is less than optimal.

The 150mm have been selling on e Bay for the mid $400s, so I am consistently tempted to buy one. Therefore, I am interested in some empirical data regarding this lens as well.
12-16-2010, 07:30 AM   #3
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gotta remember, the 150 will become the equivalent of a 195 while the 120 becomes a 156 on the crop. and I think the price of all FA glass is going to start climbing now that the camera has actually shown up.
12-16-2010, 08:09 AM   #4
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Man your not joking about that. I wish I would of bought some used lenses 3 weeks ago...the prices on ebay now are 2-3 times more.

The 150 f2.8 I was looking at is now sold

I really want this lens or the macro but cannot find any under $700


Last edited by Shuttershane; 12-16-2010 at 08:41 AM.
12-16-2010, 12:10 PM   #5
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I probably bought it.

I'll test the teles in-studio at some point and add that to my review. The 150mm is interesting because of the max. aperture. Having seen some stuff off the Leica S teles lately, though, I'm getting jaded. Same price as the 150mm pentax too, give or take $5,500.

In 35mm terms, the 120mm works out to about 100, and the 150 works out to something like 120mm, so both right in the portrait sweet-zone.

- N.
12-16-2010, 02:00 PM   #6
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Ndevlin,

That would be awesome. Currently my bread and butter lens for my canon system is the 100mm Macro f2.8 IS. Yes it is a macro but it is my sharpest lens and focuses fast enough for studio portraits. I am hoping the 150mm f2.8 is as sharp as the canon lens....with all the benefits of Medium format

So far I only have 3 lenses. fa 80-160mm, fa 75mm and the new 55mm
12-16-2010, 04:23 PM   #7
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I do not have the 645D, but can confirm from personal experience that the FA 2.8/150mm is tack sharp. I'm not so sure about the bokeh, though. May depend on your background, but I had some where I did not particularly like it.
12-16-2010, 04:35 PM   #8
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hsteeves wrote "...the 150 will become a 195, while the 120 will become a 156 on the crop".
This is incorrect. To determine the approximate 35mm equivalent focal length, multiply the focal length by .8. Therefore using the 150 on the 645D will approximate a 120mm lens on a FF 35mm sensor, while the 120 macro is equivalent to 96mm.

12-16-2010, 04:48 PM   #9
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QuoteOriginally posted by surfotog Quote
hsteeves wrote "...the 150 will become a 195, while the 120 will become a 156 on the crop".
This is incorrect. To determine the approximate 35mm equivalent focal length, multiply the focal length by .8. Therefore using the 150 on the 645D will approximate a 120mm lens on a FF 35mm sensor, while the 120 macro is equivalent to 96mm.
I agree with you but maybe the reference point for him was not the approximate 35mm equiv but the approximate 645 "film full-frame" equivalent.

Coming from a 5d, in my mind, the 150 is equivalent to a 120 (the 55 is 43.5 etc.) but in his frame of reference, coming from medium format film, it works the opposite.

I cannot say whether he is correct or not, but that is my explanation for the misunderstanding/miscommunication.
12-18-2010, 04:28 PM   #10
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QuoteOriginally posted by Shuttershane Quote
I know the 120mm macro is known for its sharpness, but I think the 150mm focal length would add a little more to my portraits.
So if you have used this lens with the 645D please let us know how it performs.
Here you can find a lot of samples of different lenses on 645D
Pentax 645D - - iXBT

FA 150/2.8 is a "bokeh king" - as for me.
FA 120/4.0 is not only "macro lens for closed apertures" - portraits are not bad too.
I use both of this lenses from film era and tested them on 645D.

Here you can find several samples
Pentax 645D "" - managger - - iXBT
No sharpness in the camera or in the Photoshop !
QuoteOriginally posted by hsteeves Quote
gotta remember, the 150 will become the equivalent of a 195 while the 120 becomes a 156 on the crop. and I think the price of all FA glass is going to start climbing now that the camera has actually shown up.
Of course not.
You must divide on 1.61 if you want to understand equivalent on 645/645N/645NII.
150/1.61 ~ 93mm in 36x24 terms. Pure portrait lens.
You must divide on 1.27 if you want to understand equivalent on 645D.
150/1.27 ~ 118mm in 36x24 terms. Little bit tele portrait lens.
12-18-2010, 04:59 PM   #11
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So the 135mm LS becomes interesting on the 645D, as it would be ca. 106 in the 36x24 world.
The 120mm of course is about 95mm, but its character would make it a situational choice rather than default portrait, perhaps.
12-19-2010, 03:11 AM   #12
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the 150mm f/2.8 is a sharp lens on the 645D it has a 35mm equivalent of a 117mm with the DOF of a f/1.1* lens. I expect pentax to update this classic portrait prime with WR SDM and a circular aperture. But that shouldn't prevent you from buying the current 645 FA 150mm f/2.8 it is very sharp at f/2.8 at f/4 it is razor sharp. If you like the FA77 f/1.8 on APS-C the 645 150mm f/2.8 will give you a similar FOV on the 645D.

The 120mm f/4 macro has often been criticised for having harsh bokeh, I haven't used this lens personally but from print samples I have seen the bokeh is ok - but at certain subject to background distances things can get ugly. On the 645D the 120mm f/4 macro will give you a 35mm equivalent focal length of 96.5mm with equivalent DOF of an f/2.3 lens.


*taking into account the sensor of the 645D is 1.7X larger than a 24X36mm sensor. Subtract 1.7 from the aperture value of the lens and that will give you a rough idea of the DOF you will get at f/2.8. Same thing works for APS-C cameras, which have a sensor that is 1.5X smaller than a full frame sensor, you multiply 1.5 to get an idea of DOF you will be working with. Nothing is being changed with the lenses themselves it is just the size of the sensor that is altering the apparent DOF.

QuoteOriginally posted by managger Quote
You must divide on 1.27 if you want to understand equivalent on 645D. 150/1.27 ~ 118mm in 36x24 terms. Little bit tele portrait lens.
I prefer to multiply the lens focal length by 0.78X to get the 35mm equivalent it is simpler.

Last edited by Digitalis; 12-19-2010 at 03:25 AM.
12-20-2010, 06:17 AM   #13
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QuoteOriginally posted by Digitalis Quote
the 150mm f/2.8 is a sharp lens on the 645D it has a 35mm equivalent of a 117mm with the DOF of a f/1.1* lens. I expect pentax to update this classic portrait prime with WR SDM and a circular aperture. But that shouldn't prevent you from buying the current 645 FA 150mm f/2.8 it is very sharp at f/2.8 at f/4 it is razor sharp. If you like the FA77 f/1.8 on APS-C the 645 150mm f/2.8 will give you a similar FOV on the 645D.

The 120mm f/4 macro has often been criticised for having harsh bokeh, I haven't used this lens personally but from print samples I have seen the bokeh is ok - but at certain subject to background distances things can get ugly. On the 645D the 120mm f/4 macro will give you a 35mm equivalent focal length of 96.5mm with equivalent DOF of an f/2.3 lens.


*taking into account the sensor of the 645D is 1.7X larger than a 24X36mm sensor. Subtract 1.7 from the aperture value of the lens and that will give you a rough idea of the DOF you will get at f/2.8. Same thing works for APS-C cameras, which have a sensor that is 1.5X smaller than a full frame sensor, you multiply 1.5 to get an idea of DOF you will be working with. Nothing is being changed with the lenses themselves it is just the size of the sensor that is altering the apparent DOF.



I prefer to multiply the lens focal length by 0.78X to get the 35mm equivalent it is simpler.
The F equivalent (DOF 35mmFF) for the 150/2.8 is 2.2 more or less, not 1.1, and the F equivalent (DOF 35FF) for the 120/4 is 3.2 more or less.

http://i.pbase.com/o2/50/276250/1/124042570.TobCsfQ4.PENTAX645EQ7.jpg


Ramn
12-20-2010, 04:38 PM   #14
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QuoteOriginally posted by Ramn Quote
The F equivalent (DOF 35mmFF) for the 150/2.8 is 2.2 more or less, not 1.1, and the F equivalent (DOF 35FF) for the 120/4 is 3.2 more or less.
could you explain the math you used to get that conclusion?
12-20-2010, 06:21 PM   #15
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He must be using the 645D multiplier to get that number: 2.8 x 0.78 ≈ 2.2

So one can roughly say that the 150/2.8 on the 645D has the DOF of a 150/2.0 on 35mm film.

This is approximately correct. Even in film days, MF shows a DOF about 1 f-stop less than 35mm (and 4x5 camera, about 3 to 4 f-stops less DOF).

To be more accurate, the DOF comparison should also include the Circle of Confusion (COC), which is a function of the pixel size. So when comparing sensors with same size pixels, it can be reasonably ignored. But if comparing the 645D to a 35mm FF with different pixel dimensions, then the COC will affect the DOF comparison. (Even the COC is dependent upon what estimate for image sharpness is chosen.)

A more complete formula is:

DOF = [(f-stop * COC) / (magnification)^2] * (magnification + 1),

where the magnification = the ratio of image size over subject size. As I recall, the typical COC for 35mm film is 0.03mm and 0.1mm for 4x5 film.
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