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03-10-2019, 02:23 PM   #16
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QuoteOriginally posted by MrB1 Quote
So, unless there is a need/desire for shorter depth-of-field, a lens such as the excellent, relatively compact and inexpensive D-FA 28-105 f/3.5-5.6 could be used as a constant aperture zoom at f/5.6, in conjunction with setting two stops extra ISO?

Philip
That should work well enough. However, I'm not familiar with that particular lens. Some inexpensive lenses are not great at the extremes of their focal range. You'll just have to try it and find out. Of course, the amount of high ISO noise depends on sensor performance. It's up to you to decide how much noise is acceptable. With my current gear I often use ISO 800. I've been happy with that in print sizes up to 24x36 inches.

03-10-2019, 02:38 PM   #17
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QuoteOriginally posted by John Poirier Quote
That should work well enough. However, I'm not familiar with that particular lens. Some inexpensive lenses are not great at the extremes of their focal range. You'll just have to try it and find out. Of course, the amount of high ISO noise depends on sensor performance. It's up to you to decide how much noise is acceptable. With my current gear I often use ISO 800. I've been happy with that in print sizes up to 24x36 inches.
Noise, and loss of Dynamic Range, and loss of Color Depth. With my K-30, I held my breath any time I used ISO 800; yesterday I was out in pre-rain darkish conditions and used ISO 800 with my KP as routinely as I would have used ISO 200 with the K-30.
03-10-2019, 02:59 PM   #18
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Can’t forget that in general photography lenses are pretty bad for video work, and variable aperture lenses are almost unusable.
03-10-2019, 05:53 PM   #19
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QuoteOriginally posted by Turbotak Quote
Can’t forget that in general photography lenses are pretty bad for video work, and variable aperture lenses are almost unusable.
And yet Pentax's designed for video electronic aperture "for video" lens, the DA 55-300 PLM is variable aperture.

This thing about variable aperture not being good for video. If you have a PLM, set your Aperture in AV mode to 6.3 and the lens is constant aperture. Set it to 4.5 and it's not. what the issue is is beyond me. This would seem like a "I have no idea how my camera works" issue.

03-10-2019, 08:02 PM   #20
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QuoteOriginally posted by normhead Quote
And yet Pentax's designed for video electronic aperture "for video" lens, the DA 55-300 PLM is variable aperture.

This thing about variable aperture not being good for video. If you have a PLM, set your Aperture in AV mode to 6.3 and the lens is constant aperture. Set it to 4.5 and it's not. what the issue is is beyond me. This would seem like a "I have no idea how my camera works" issue.
Shoot any videos professionally and you'll soon find that a 6.3 max aperture is unacceptable. F/4 is considered slow in the cine world.

Show up on set with a 55-300 stills lens with a variable aperture and explain to the dp that it's "constant at f/6.3, should be good or you don't know how cameras work" and watch how fast they phone the next camera op to replace you.

Last edited by Turbotak; 03-10-2019 at 08:18 PM.
03-10-2019, 11:17 PM   #21
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QuoteOriginally posted by photoptimist Quote
For example, designing a variable aperture zoom and then closing down the aperture slightly at the wide end -- the Pentax SMC Pentax-A 35-70mm F4 is really a f/2.8-4 lens with the wide-end stopped down.
That's also what I thought, on a standard zoom, the max aperture of the lens is constrained by the long end (size of the front element). And for a wide angle zoom the max aperture could be constrained by the wide end due to difficulties to have homogeneous glass elements? For a lens such as 28-105, starting at 28mm instead of 24mm relaxed design constrains I suppose, making it easier to reach an optimum form factor / overall sharpness. For a lens such as 70-200, I would imagine that the design would also be constrained by the 200mm.

---------- Post added 11-03-19 at 07:20 ----------

QuoteOriginally posted by normhead Quote
It's not as hot now, but at the time it was pretty heavily corrected, 13 elements, and was a slightly ahead of the curve design.It's the best $35 I ever spent on a lens.
Excellent pictures, pleasing to see, I can see that the lens worked, there was also at work the creativity / being at the right place & time of the photographer :-)

---------- Post added 11-03-19 at 07:32 ----------

QuoteOriginally posted by John Poirier Quote
There are advantages to a 2.8 maximum aperture vs. the 3.5 or 4 common in variable aperture zooms for low-light work. This has become much less of an issue with modern sensors' high ISO performance.
f2.8 helps for focusing indoors, for example for photographing people and at concert, primes are even better. In this post I was referring to variable aperture lenses when the goal is to have all in focus frames on full frame, i.e landscape or cityscape scenes. On full frame , the DoF is such that even f4 doesn't give enough DoF, so what is the point of using an f2.8 or f4 lens in those cases? Historically people said "constant aperture lenses are better". Ok, I have the DFA24-70 and the DFA28-105, I've checked the exif of photographs taken with the DFA24-70 and realized I almost never use it at f2.8, over two years of images taken with the DFA24-70, some images are taken at f4 and 95% of images are taken between f5.6 and f16, so the 24mm is the only reason for me to use the DFA24-70. Now, wherever I go I use the DFA28-105, because it makes my K1 kit smaller, and never use aperture wide than f5.6, and it is faster to focus and it is even sharper than my DFA24-70... That is a case where I didn't find the the constant aperture lens is better than the variable aperture lens.


=> As long as a lens is good enough optically, I just don't want to carry the weight of glass area that I never use because the diaphragm is always stopped down anyway.

Last edited by biz-engineer; 03-10-2019 at 11:33 PM.
03-11-2019, 02:14 AM   #22
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Isn't it a general characteristic of lenses that they perform best when set one or two stops down from their maximum aperture? If so, for similar shots at longer focal lengths, a constant f/2.8 aperture zoom at f/5.6 should give better image quality than a variable f/3.5-5.6 aperture zoom at its maximum of f/5.6.

Philip

P.S. 1: I have no desire to carry around monster lenses. 2: The D-FA 28-105 is an excellent lens.
03-11-2019, 07:30 AM   #23
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QuoteOriginally posted by biz-engineer Quote
Now, wherever I go I use the DFA28-105, because it makes my K1 kit smaller, and never use aperture wide than f5.6, and it is faster to focus and it is even sharper than my DFA24-70... That is a case where I didn't find the the constant aperture lens is better than the variable aperture lens.
I suspect quite a few photographers have had similar experiences with the DFA 28-105 --- but the DFA 28-105 is kind of an outlier. Most f3.5-5.6 variable aperture standard zoom lenses that I'm familiar with (the Leica 18-55 f3.5-5.6 is an exception) are budget lenses with seriously compromised optics. Lens manufacturers apparently believe that they can't sell a slow variable aperture standard zoom at anything much above budget prices, so if you're shooting Nikon, Canon, Sony, etc. and you want first class optics in a standard zoom, you have no choice but to buy one of the constant aperture zooms, often at a huge price premium.

QuoteOriginally posted by MrB1 Quote
If so, for similar shots at longer focal lengths, a constant f/2.8 aperture zoom at f/5.6 should give better image quality than a variable f/3.5-5.6 aperture zoom at its maximum of f/5.6.
Yes, and that's a typical argument for f2.8 zooms by those who buy such lenses but don't need the f2.8. However, if you don't even need the f5.6, then the argument is moot. I can probably count on one hand the times I've shot the DFA 28-105 faster than f11.

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