[TDvN57]

@biz-engineer. Hear hear.

@TDvN57. A way to think of the pixel resolution is to divide the pixels per mm by the ratio of object distance to focal length. Hence, 188 pix/mm at the focal plane using a 100mm lens is equivalent to 18.8 pix/mm a meter away. When using a resolution chart, particular care is needed to know just what scale the USAF test chart is actually presenting. (I'm not suggesting that you didn't do that.)

The Nyquist frequency for 188 pix/mm is 94 cy/mm. This frequency yields zero output, although the MTF has some bumps after that point. By color band, the Nyquist frequencies are at lower frequencies at half the color sampling pixel density. I have doubts that the Beyer filter function actually raises the true spatial frequency response in the color bands, but may join in creating a higher intensity MTF depending on how the nature of the estimation algorithm optimized for a particular nature fits the nature of the actual nature under observation.

For comparison, Portra 160 has at least 30% response (green, blue) at 100 cy/mm, and red is over 10% response. As noted, these respective MTFs will be modulated by the lens MTF, which varies over the field and may also vary by color.

To put it another way, with digital a field of pure red roses viewed from a particular distance might have missing blooms with the not-missing blooms having high contrast, while with film no blooms are missing, but all have lower contrast.

Shall we circle back to this discussion when we have a 100 or 150mpx on P645 FF?

[kaseki]

I fear that by then the genesis of "circle back" will be lost in the dust bin of history.

[leonine]

I fully agree with you. As I also mention in my assessment, all the lenses on the list are very good lenses, I use them all in different situations.

For portraits I use the 45-85 and the 80-160. Landscape I sometimes use the 28-45 but find I mostly use the 80-160.

Wildlife (not birds) I either go with the 150-300, or lately the fa* 300. I did a lot of wildlife with the 600mm on a gimbal and monopod. For birds I use the 600 or the 600+tc1.4.

The only time I found the 645z system inadequate was when a friend asked me to take pictures of his martial arts practice moves. In that situation I really needed a fast frame rate, and IQ and pixels were way down the list of must haves.

On the forum in earlier discussions, it was said that the 600mm Pentax 645 lens needs crazy amount of support over and above a sturdy tripod and a gimbal head, for the lens to produce images that are not blurry. The reason often quoted is the vibration induced by the shutter.

What is your personal experience in the real world with the 600mm lens? The fact that you consider it a super performer even after coupling with the 1.4X Tele converter is very surprising. Can you please share some pictures?

[TDvN57]

The other comments about stabilizing a long lens are not wrong. Any long focal length lens will become a challenge because the dof decrease and focus becomes more critical. Add to that any small movements will become large optimal swings because of the small angle of view, 5.2 degrees diagonal on digital. Consider also the distance from you to the object. The further away the larger the optical swings will be.

A stable tripod and some weight on top of the lens combined with mup will all help to minimize micro movements.

On the other hand you can also minimize some of these effects by closing down the aperture, which will help greatly with focus, and increase shutter speed to freeze a smaller amount of time, hence less negative impact from the micro movements.

Contrary to intuition I found that a gimbal is more stable than a ball head tripod head. A video fluid head is also better than a ball head, but not as good as a gimbal. I think this has to do with vibration dampening and the diameter of the shaft connecting the ball part of the ball head to the camera mounting plate.

Be that as it may, combine these and you can get fairly stable shots even with a 1.4 TC, even when you mount this on a gimbal and monopod, yes not a spelling error, monopod. When I discovered this by accident I decided to take the 600mm lens with me on a trip to Southern Africa and did a test shoot-out one afternoon. My thinking was that if it fails, then I'll put it back into my bag and use the other lenses instead. The results surprised me, considering that these pictures were taken from a safari jeep, mostly stationary during shooting, but other people moving around constantly. I placed the monopod between my legs or on my side, so that I could get the target object conveniently in view.

Here are some pictures with the 645z + 600mm some with 1.4TC, all on gimbal and monopod, from the safari jeep.

The last picture of the kingfisher I was on foot in the Philippines in one of their National parks. 645z + 600mm on gimbal and monopod.

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Last edited by TDvN57; 11-28-2021 at 11:21 PM.

[RICHARD L.]

Personally, the new 645 DFA 55 mm f/2.8 ED has given me the sharpest images I ever took with my 645Z. I always shoot meticulously : 1) optimum aperture 2) solid support 3) bright lighting conditions 4) careful focusing. This lens, I agree, is a "SUPER-PERFORMER".

[leonine]

The other comments about stabilizing a long lens are not wrong. Any long focal length lens will become a challenge because the dof decrease and focus becomes more critical. Add to that any small movements will become large optimal swings because of the small angle of view, 5.2 degrees diagonal on digital. Consider also the distance from you to the object. The further away the larger the optical swings will be.

A stable tripod and some weight on top of the lens combined with mup will all help to minimize micro movements.

On the other hand you can also minimize some of these effects by closing down the aperture, which will help greatly with focus, and increase shutter speed to freeze a smaller amount of time, hence less negative impact from the micro movements.

Contrary to intuition I found that a gimbal is more stable than a ball head tripod head. A video fluid head is also better than a ball head, but not as good as a gimbal. I think this has to do with vibration dampening and the diameter of the shaft connecting the ball part of the ball head to the camera mounting plate.

Be that as it may, combine these and you can get fairly stable shots even with a 1.4 TC, even when you mount this on a gimbal and monopod, yes not a spelling error, monopod. When I discovered this by accident I decided to take the 600mm lens with me on a trip to Southern Africa and did a test shoot-out one afternoon. My thinking was that if it fails, then I'll put it back into my bag and use the other lenses instead. The results surprised me, considering that these pictures were taken from a safari jeep, mostly stationary during shooting, but other people moving around constantly. I placed the monopod between my legs or on my side, so that I could get the target object conveniently in view.

Here are some pictures with the 645z + 600mm some with 1.4TC, all on gimbal and monopod, from the safari jeep.

The last picture of the kingfisher I was on foot in the Philippines in one of their National parks. 645z + 600mm on gimbal and monopod.

Great pics Theun. The performance of the 600mm as conveyed by you is a revealation. I will certainly try and use that lens more often and see how it goes.

[Eric Auer]

The 4585 being relegated to a paltry "great" status troubles me much, I think I have to go and lie down for a bit.

You guys go on without me, I'll catch up later...

[RICHARD L.]

It's true the 645 45-85 mm f/4.5 zoom is awesome in its own right.

@ 45 mm