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12-14-2010, 12:36 PM   #46
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QuoteOriginally posted by Pentaxor Quote
although you lose infinity with a diopter on, also increases whatever IQ degradation it will create (CA, distortion, loss of sharpness, vignetting, etc...).
For the type of portraiture where thinnest DOF is important, infinity is NOT an issue. And even degradation with a +1 dioptre may be little worse than using some f/1.2's wide open and close, especially when shooting 'dramatic' B&W. All I can say is, try it and see.

Another way to thin-out the DOF is to add extension. This is especially easy with M42 lenses, where a cheap safe flanged non-infinity-focus adapter's 1mm or a 42-42mm ring's 4mm thickness can dramatically alter near-focus and DOF without introducing any degradations.

And keep in mind the way our visual systems work: We generally like to see things in great detail, but we can recognize personas even with scanty detail and great distortion, to the point of becoming cartoon-y caricatures. Every picture tells a different story.

My point is: Fast lenses are good to have. Ultra-fast lenses are thus ultra-good, but their DOF effects can be simulated with tricks that aren't ultra-costly. Each trick is just another tool in my kit. It's good to have many tricks/tools available, to deal with various circumstances.

12-14-2010, 01:09 PM   #47
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Fast lens is still valuable - Especially a fast prime in the speed f1.4 to f2.0 range. With these lenses you can stop down a bit and get exceptional quality. Cameras are getting better in high ISOs but if you want the best quality it is always @ lower ISO's in terms of dynamic range etc.
Also with fast lenses combined with high ISO capable camera will allow you to stop down the lens a bit while keeping the ISO reasnably large without compromising noise performance
12-14-2010, 01:15 PM   #48
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QuoteOriginally posted by RioRico Quote
For the type of portraiture where thinnest DOF is important, infinity is NOT an issue. And even degradation with a +1 dioptre may be little worse than using some f/1.2's wide open and close, especially when shooting 'dramatic' B&W. All I can say is, try it and see.

Another way to thin-out the DOF is to add extension. This is especially easy with M42 lenses, where a cheap safe flanged non-infinity-focus adapter's 1mm or a 42-42mm ring's 4mm thickness can dramatically alter near-focus and DOF without introducing any degradations.

And keep in mind the way our visual systems work: We generally like to see things in great detail, but we can recognize personas even with scanty detail and great distortion, to the point of becoming cartoon-y caricatures. Every picture tells a different story.

My point is: Fast lenses are good to have. Ultra-fast lenses are thus ultra-good, but their DOF effects can be simulated with tricks that aren't ultra-costly. Each trick is just another tool in my kit. It's good to have many tricks/tools available, to deal with various circumstances.
I understand that this comes with certain compromises. but with regards to using a diopter, the obvious problem that is evident is it's significant loss of focusing distance even with a +1 formula. a 50-55mm + diopter +1 combo is too close for focusing and is more useful for macro rather than portraits. and you lose significant FOV. maybe a 15mm or 21mm would fit in with a diopter due to a wider FOV but there is another problem since these lenses don't possess a considerable shallow DOF. an extension is also a good alternative as you said but you will need a longer lens for that one. something around 200-300mm would give you enough room away from the subject but at the cost of losing light.

of course, there are ways to simulate certain lens effect but with compromises.

Last edited by Pentaxor; 12-14-2010 at 06:22 PM.
12-14-2010, 01:37 PM   #49
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QuoteOriginally posted by mugund Quote
Fast lens is still valuable - Especially a fast prime in the speed f1.4 to f2.0 range. With these lenses you can stop down a bit and get exceptional quality.
This philosophy is not always true, though.

For example, the FA 50 1.4 is less sharp than the DA 40 2.8 at f 2.8. Obviously, with the DA 40 you are limited to f2.8, but if you really only shoot the FA 50 at 2.8, you should not expect improved image quality at that aperture.

Pentax is doing an odd thing - they are designing lenses for ASP-C digital, which makes it hard to compare their lenses to offerings from their brethren who offer more traditional lens choices. I will not argue that one is better than the other, but rather that the concept of speed is beginning to lose ground to the concept of quality in the Pentax realm.

I think there is no other explanation for the FA limited line, which are really not all that fast, but are quite exceptional when it comes to quality. The DA limited line are an even more extreme example of this, since they are very, very good wide open, but wide open is not extremely fast.

Instead of providing larger, heavier primes which need to be stopped down to f2 or 2.8 to reach really optimal levels, Pentax seems to prefer offering a lens that is quite good from wide open, in a lighter, more compact package.

12-14-2010, 04:57 PM   #50
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QuoteOriginally posted by paperbag846 Quote
This philosophy is not always true, though.

For example, the FA 50 1.4 is less sharp than the DA 40 2.8 at f 2.8. Obviously, with the DA 40 you are limited to f2.8, but if you really only shoot the FA 50 at 2.8, you should not expect improved image quality at that aperture.

Pentax is doing an odd thing - they are designing lenses for ASP-C digital, which makes it hard to compare their lenses to offerings from their brethren who offer more traditional lens choices. I will not argue that one is better than the other, but rather that the concept of speed is beginning to lose ground to the concept of quality in the Pentax realm.

I think there is no other explanation for the FA limited line, which are really not all that fast, but are quite exceptional when it comes to quality. The DA limited line are an even more extreme example of this, since they are very, very good wide open, but wide open is not extremely fast.

Instead of providing larger, heavier primes which need to be stopped down to f2 or 2.8 to reach really optimal levels, Pentax seems to prefer offering a lens that is quite good from wide open, in a lighter, more compact package.
True, Pentax is oriented towards compact systems

My point is having fast lenses with high ISO capabilities creates lot more probabilities about capturing low light usable images that just good quality high ISO but slower lens or faster lens but not so good high ISO. Like what said about about DA 40 f2.8, it is very good @ f2.8 but uyou cannot go lower, atleast with a fast lens, you have that possibility to tradeoff high ISO Vs lens speed
12-14-2010, 05:42 PM   #51
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QuoteOriginally posted by mugund Quote
have that possibility to tradeoff high ISO Vs lens speed
Yes, this is true. In my experience though, except in very specific conditions, noise is preferable to such shallow depth of fields.

I find, even in low light, I use my fast 50's at a minimum of f2.4. I very rarely use f2, and never go below that. Everyone is different though... I've seen some rather remarkable f1.2 shots in it's respective thread. The f1.2 shots are good because of their look, though, not because they let more light in.

In my opinion, if you need speed, you should bump the ISO instead of compromising your DOF. Wide-aperture lenses are best used for the shallow depth of field effect, not so much to maximize shutter speed (anymore).
12-16-2010, 02:43 PM   #52
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QuoteOriginally posted by Winder Quote
They need faster glass and some longer glass.
135mm f/1.8 and an 85mm f/1.4 would really help the Pentax lens line up.
They do have such examples of the lenses you mention, but in manual focus and I use both of these lenses often.

I have found that in low light levels AF can struggle to lock and sometimes can be fooled in getting the right focus point i.e the mic stand in front of the face.

At the end of the day its all about image capture and for me that's manual fast lenses.

Last edited by Kerrowdown; 12-16-2010 at 02:54 PM.
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