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02-10-2018, 12:15 PM   #1
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Is it worth upgrading from a 200mm f/4 manual lens to a 150mm f/3.5 manual lens

Hi. I just got a Pentax 645. I normally shoot digital, but liked how film looks and figured go big (ish) or go home. My 645 came with a 75mm f/2.8 and 35mm f/3.5. I have seen a lot of praise for both of these lenses, especially at f/8. The third lens my camera came with was a 200mm f/4. This one doesn't seem to be as praised on the internet as the other 2. My question is more or less, does it have sufficient sharpness at the more wide open apertures to create those shallow DOF medium format portraits or should I upgrade to a 150mm f/3.5 which I see much more praise for? This is an original model 645 so it has no auto focus.

02-10-2018, 01:06 PM   #2
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QuoteOriginally posted by dudemanbro Quote
My question is more or less, does it have sufficient sharpness at the more wide open apertures to create those shallow DOF medium format portraits or should I upgrade to a 150mm f/3.5 which I see much more praise for?
I have all four lenses that you mention and love the 35mm and 75mm, but have never been satisfied, despite many attempts, to like the 200mm f/4. It is just too soft and low contrast for my taste and doesnʻt render bokeh that is in anyway special. The 150mm f/3.5 is a much better lens, especially for portraits. YES, itʻs worth the upgrade.

The 200mm MF is equivalent to a 135mm FF and the 150mm MF is equivalent to a 100mm FF. With FF, I prefer to shoot portraits in the 80-100mm range, so the 150mm MF makes more sense in terms of focal length and not only gets you closer to your subject, but throws the background bokeh more OOF.

If I get a chance, I can shoot and post a comparison for you, but it might take a few weeks till I get around to it.
02-11-2018, 02:13 AM   #3
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Just in case it hadn't crossed your mind.....give some consideration to the 67 165/2.8 (with adapter).

Bob
02-17-2018, 07:42 AM   #4
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QuoteOriginally posted by Alex645 Quote

The 200mm MF is equivalent to a 135mm FF and the 150mm MF is equivalent to a 100mm FF. With FF, I prefer to shoot portraits in the 80-100mm range, so the 150mm MF makes more sense in terms of focal length and not only gets you closer to your subject, but throws the background bokeh more OOF.

If I get a chance, I can shoot and post a comparison for you, but it might take a few weeks till I get around to it.
I thought I had seen somewhere( maybe here?) that the conversion factor from MF(645) lenses to lenses for 35mm cameras was 0.62 which makes the 200 the equivalent of 124 and the 150 equivalent to 93. Have I got the wrong factor?

A comparison would be very useful for those of us such as I who have wondered about the 200 v 150, Thanks

asahijock

02-17-2018, 08:14 AM   #5
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The mount doesn't affect the length of the lens, 200mm is 200mm. The only thing affected is the 35mm equivalence field of view. But 200mm APS_c , 200mm FF or 200mm 645 are all the same focal length. The only thing that changes is the size of the image circle.
02-17-2018, 09:09 AM   #6
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The crop factor is a bit messy because of the aspect ratio differences:


1) Do you want to take a 4:3 ratio picture (or squarer) on both 645 film and 35 mm film?

If so, the crop factor is 24/41.5 = 0.58 (So 200mm on MF film has the same field of view as 116mm on 35 mm film)


2) Or do you want to take a 3:2 ratio picture (or skinnier) on both 645 film and 35 mm film

If so, the crop factor is 36/56 = 0.64 (So 200mm on MF film has the same field of view as 128mm on 35 mm film)


(Note: crop factors for digital 645 are different because most 645 sensors are crop sensors.)
02-17-2018, 12:15 PM   #7
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QuoteOriginally posted by asahijock Quote
I thought I had seen somewhere( maybe here?) that the conversion factor from MF(645) lenses to lenses for 35mm cameras was 0.62 which makes the 200 the equivalent of 124 and the 150 equivalent to 93. Have I got the wrong factor?
asahijock
QuoteOriginally posted by normhead Quote
The mount doesn't affect the length of the lens, 200mm is 200mm. The only thing affected is the 35mm equivalence field of view.
Yes, to clarify, "the focal length is the focal length", so I interpreted the question in regards to field of view.

The correct factor will be based on the actual film or sensor sizes.

I was referring to 645 film, which despite the name, is not 60mm x 45mm (6x4.5cm). The actual image size on the film is 56mm x 41.5mm. The sensor size on the 645D and 645Z is not the same, but smaller at approx. 44mm x 33mm.

So when doing any equivalence math to FF at 36mm x 24mm, the factor would be different.

But in the real world, Iʻm not a math guy and Iʻve learned not split hairs. Even lens focal lengths are approximations. Try comparing an 18-55mm zoom at 55mm, a 55-300mm at 55mm, and with the camera locked down on a tripod, compare that to a DA* 55mm FOV. They will be close but not identical.

According to Ken Rockwell, the 75mm has a FOV FF equivalence of 45mm. My own experience comes from the darkroom where I would find a 50mm enlarger lens for a 35mm neg had an equivalence to a 75mm enlarger lens for 645. With 6x6, Iʻd use an 80mm. As @photooptimist notes, the aspect ratio does make equivalence ʻmessyʻ.
02-19-2018, 09:49 AM   #8
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QuoteOriginally posted by photoptimist Quote
The crop factor is a bit messy because of the aspect ratio differences:


1) Do you want to take a 4:3 ratio picture (or squarer) on both 645 film and 35 mm film?

If so, the crop factor is 24/41.5 = 0.58 (So 200mm on MF film has the same field of view as 116mm on 35 mm film)


2) Or do you want to take a 3:2 ratio picture (or skinnier) on both 645 film and 35 mm film

If so, the crop factor is 36/56 = 0.64 (So 200mm on MF film has the same field of view as 128mm on 35 mm film)


(Note: crop factors for digital 645 are different because most 645 sensors are crop sensors.)
Can't you just compute crop factors of different aspect ratios by comparing the diagonals?

02-19-2018, 10:24 AM   #9
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QuoteOriginally posted by timw4mail Quote
Can't you just compute crop factors of different aspect ratios by comparing the diagonals?
Yes you can and you'll get the 0.62 number that is commonly cited.

For most applications, the diagonal crop factor is good enough.

But if you really want the equivalent field of view than you need to consider the creating the equivalent aspect ratio with the relative effects of horizontal versus vertical field of view.

If you have a more demanding application (e.g., setting up cameras for technical photography of museum art or industrial machine vision), then the aspect ratio matters. The difference in crop factors will also matter if you are photographer who likes to shoot a specific aspect ratio and are considering the crop factor for two different formats.

Someone who always shoots square images or prints 4:5 ratio (8x10, 16x20) would use the 0.58 crop factor between 35 & 645.

Someone who always shoots panorama aspect ratios would use the 0.64 crop factor between 35 & 645.
02-19-2018, 12:58 PM   #10
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QuoteOriginally posted by dudemanbro Quote
Hi. I just got a Pentax 645. I normally shoot digital, but liked how film looks and figured go big (ish) or go home. My 645 came with a 75mm f/2.8 and 35mm f/3.5. I have seen a lot of praise for both of these lenses, especially at f/8. The third lens my camera came with was a 200mm f/4. This one doesn't seem to be as praised on the internet as the other 2. My question is more or less, does it have sufficient sharpness at the more wide open apertures to create those shallow DOF medium format portraits or should I upgrade to a 150mm f/3.5 which I see much more praise for? This is an original model 645 so it has no auto focus.
I have both the 150mm and 200mm lenses. The 200mm doesn't get much love, but it is a nice lens. I'd high recommend shoot with what you have for a while before buying more lenses. I did "single in april" in 2016 with a (original model) 645 and the 200mm lens. It was a bit brutal as the lens + camera package is verging on quite large, but I can definitely say the lens has nice IQ.

At wide open it is a challenge hitting focus dead on. At f4 there isn't much wiggle room at 200mm on a 645.
02-20-2018, 11:25 AM   #11
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QuoteOriginally posted by bobbotron Quote
I have both the 150mm and 200mm lenses. The 200mm doesn't get much love, but it is a nice lens.
I have both, and I agree. Neither is razor-sharp wide open but both are very usable.
02-21-2018, 08:55 AM   #12
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QuoteOriginally posted by baro-nite Quote
I have both, and I agree. Neither is razor-sharp wide open but both are very usable.
I really like them both at f5.6. Sharp, and both have very shallow DOF at f5.6, at portrait distances.

I'm not sure, this is probably at f4 or f5.6 with the 150mm.


This is the 200mm at f4
02-21-2018, 02:21 PM   #13
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Thanks for posting, bobbotron. These shots would suit my requirements. On the point of hard to focus which was made, doesn't the green hexagonal light to show focus which you get from the A lenses take away most of not all difficulties in focusing. I only have the 75mm and 45mm lenses but the green light makes it relatively easy to obtain focus, although I can imagine that you might need a more delicate touch to get the light on with a 150/200mm lens - less leeway while moving the focus.

PS the top animal is welcome at my house anytime. The lower one I am less sure of

asahijock
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