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06-29-2011, 11:58 AM   #196
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QuoteOriginally posted by DragonLord Quote
Okay, so here's what Falk Lumo said when I PMed him:


This is consistent with the following post:



The problem is that we had all failed to consider ISO in the 35mm equivalence discussion. I hope we can get back to on-topic discussion now.

--DragonLord
That certainly makes more sense, and had Class A said that, the discussion would have been done with.

Regardless, I didn't think it was all that off topic, as my point was primarily that in real world usage, the lens on the Q isn't "slow", and a barrage of inaccurate claims followed that assertion.

I still will wait and see actual images from the Q before dismissing it.

06-29-2011, 12:07 PM   #197
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QuoteOriginally posted by jstevewhite Quote
That certainly makes more sense, and had Class A said that, the discussion would have been done with.

Regardless, I didn't think it was all that off topic, as my point was primarily that in real world usage, the lens on the Q isn't "slow", and a barrage of inaccurate claims followed that assertion.

I still will wait and see actual images from the Q before dismissing it.

my feeling exactly
we've been surprised (both good and bad) by sensor performance in the past (not just with Pentax)
I'm not looking at it for DOF that's for certain
but if it performs well enough (and the price drops a bit) i can be tempted. - though at current prices with the Q-kit I'd want (prime,+3toys) I'd just buy an X100 and live with less lens choice
06-29-2011, 12:30 PM   #198
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Pentax Q don't have viewfinder. Darn it.
06-29-2011, 01:38 PM   #199
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QuoteOriginally posted by DragonLord Quote
The problem is that we had all failed to consider ISO in the 35mm equivalence discussion.
I didn't mention ISO a lot because we were talking about 35mm-equivalent lenses (not cameras).

Note that I did write "This means that you either have to increase the exposure time and/or the ISO value as well.".

Anyhow, kudos to you for having been open to alternatives views on the matter and for getting a second "opinion".

06-29-2011, 01:45 PM   #200
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QuoteOriginally posted by jstevewhite Quote
That certainly makes more sense, and had Class A said that, the discussion would have been done with.
Note that I pointed you to the "Equivalence" essay which makes the point about adjusting ISO values.

Also note that
  • we weren't talking about equivalent cameras.
  • I mentioned the need to adjust shutter speed and/or ISO.
The only statement I initially made -- that you have to multiply the f-stop value by the crop-factor as well -- is, of course, confirmed by Falk.


QuoteOriginally posted by jstevewhite Quote
Regardless, I didn't think it was all that off topic, as my point was primarily that in real world usage, the lens on the Q isn't "slow", and a barrage of inaccurate claims followed that assertion.
Nothing I said was inaccurate and/or inconsistent with what Falk wrote. Please pick your position. You cannot agree with Falk and still claim that I was making inaccurate statements and that the 8.5/1.9 lens isn't slow.

N.B., I don't think that the discussion was "off-topic". I think it is relevant to discuss what kinds of images you can take with the 8.5/1.9 lens on the Q-camera. The only unfortunate circumstance was that it took so many posts for this topic to be settled.

Last edited by Class A; 06-29-2011 at 01:59 PM.
06-29-2011, 01:48 PM   #201
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So, if I understand the thrust of this discussion, in order to get the same image (in terms of exposure) out of an 8.5mm f/1.9 lens on the Q as a 47mm f/1.9 lens on a FF, the ISO of the Q sensor would have to be 47/8.5*[ISO of the FF sensor]. So if the sensitivity of the FF is 200, then the sensitivity of the Q would be 1106?
06-29-2011, 02:10 PM   #202
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QuoteOriginally posted by Designosophy Quote
So, if I understand the thrust of this discussion, in order to get the same image (in terms of exposure) out of an 8.5mm f/1.9 lens on the Q as a 47mm f/1.9 lens on a FF, the ISO of the Q sensor would have to be 47/8.5*[ISO of the FF sensor]. So if the sensitivity of the FF is 200, then the sensitivity of the Q would be 1106?
The other way 'round. The ISO of the FF would have to be set to the multiplied ISO, because to get the same DOF, you have to use f10.5.
06-29-2011, 02:26 PM   #203
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QuoteOriginally posted by jstevewhite Quote
The ISO of the FF would have to be set to the multiplied ISO, because to get the same DOF, you have to use f10.5.
Correct.

Note that he was only looking for the "same exposure" though. To achieve the same exposure (not considering that the images won't have the same DOF), none of the exposure parameters need to be changed. The 47mm f/1.9 lens on FF lets in a lot more light than the 8.5mm f/1.9 lens on the Q-system but this is counteracted by the FF-camera using a correspondingly lower ISO value (ISO 200 instead of ISO 1100 (<- the FF-equivalent of the ISO 200 on the Q-camera)).

06-29-2011, 02:34 PM   #204
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QuoteOriginally posted by Class A Quote
Note that I pointed you to the "Equivalence" essay which makes the point about adjusting ISO values.

Also note that
  • we weren't talking about equivalent cameras.
  • I mentioned the need to adjust shutter speed and/or ISO.
The only statement I initially made -- that you have to multiply the f-stop value by the crop-factor as well -- is, of course, confirmed by Falk.
Actually, you said:

QuoteOriginally posted by Class A:
A 50mm f/1.9 is not slow, AFAIC. In order to be able to take the same images (DOF, exposure, given a fixed shutter speed and iso setting), you'd need a 9mm f/0.3 lens in the Q-system. Such lens does not exist. This is the reason why the Q-system is limiting.
Perhaps you didn't MEAN "given a fixed shutter speed and iso setting", but that's what you kept saying, and that's why I kept arguing about that point.

QuoteQuote:
Nothing I said was inaccurate and/or inconsistent with what Falk wrote. Please pick your position.
Except the bit I quoted above.

QuoteQuote:
You cannot agree with Falk and still claim that I was making inaccurate statements and that the 8.5/1.9 lens isn't slow.
I can, absolutely, agree with Falk about the assessment of making "equivalent images"; AND not agree with your assertion that the Q lens is "slow". Falk makes (in that PM) no definition of the word "fast" or the word "slow". Like I said, that's a terminology problem; that's not what "slow" means, nor what "fast" means. Those terms have everything to do with shutter speed (which does not change) and nothing to do with DOF.

That said, I understand why you object to the use of 45mm/f1.9. OTOH, it's still accurate to say it's an f1.9 lens (for calculating exposure) and equivalent in FOV to 45mm (for calculating FOV) and 45mm f10.5 (for calculating DOF, if your DOF calculator doesn't do 8.5mm lenses @ f1.9).

Equivalence is an *analogy*, not some characteristic of the universe. In the end, the Q's lens is an 8.5mm f1.9 for all purposes, and uses the same exposure as any other f1.9 lens.
06-29-2011, 02:38 PM   #205
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QuoteOriginally posted by Class A Quote
Correct.

Note that he was only looking for the "same exposure" though. To achieve the same exposure (not considering that the images won't have the same DOF), none of the exposure parameters need to be changed. The 47mm f/1.9 lens on FF lets in a lot more light than the 8.5mm f/1.9 lens on the Q-system but this is counteracted by the FF-camera using a correspondingly lower ISO value (ISO 200 instead of ISO 1100 (<- the FF-equivalent of the ISO 200 on the Q-camera)).
Wait. That reads like you're saying that to get the same exposure irrespective of DOF, you need to use lower ISO on FF. Is that what you're saying? That to get the same exposure with both lenses set to f1.9 and the same shutter speed on both cameras, you'd have to set a lower ISO on the FF camera?

edit: and just for the record, an ideal (that is, disregarding the absorption of the glass used) f1.9 lens lets in the same amount of light regardless of focal length - that's why exposure doesn't change when you switch from a 50mm lens to a 20mm lens.

Last edited by jstevewhite; 06-29-2011 at 03:12 PM. Reason: Clarity
06-29-2011, 04:03 PM   #206
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Very silly.

Surely the point is that the 8.5mm f1.9 lens can never give you as a shallow depth of field that a 45mm f1.9 lens can. At best (wide open) it will be like a 45mm stopped down to f10.5 or whatever. Of course it follows that if you do that to a 45mm lens you will have to increase your exposure accordingly to get a similarly exposed image - by using a slower shutter speed or by turning up the gain (ISO).

Last edited by kh1234567890; 06-29-2011 at 04:32 PM.
06-29-2011, 04:14 PM   #207
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QuoteOriginally posted by Laurentiu Cristofor Quote
Your earlier statements that I quoted above include at least 3 factual errors: 1) some people need compact sensor cameras or there wouldn't be a market for them if they could just use their phones 2) the Q has a larger sensor than phones do and 3) you aren't necessarily able to use small apertures on an SLR for an equivalent result to that of a compact, because the high ISO setting needed for equivalence might not be available to you. You called my arguments flawed, you implied I'm a biased Pentax fan, you ended up resorting to fallacies in your rhetoric, and now you're offended that I asked you to grow up and judge a camera against its peers.
Laurentiu, we would probably agree more than we disagree, except that you have to demonise me for some reason. You assume I said things I never did. And your primary device is to over-emphasise my points. I never said anything about people not needing compact cameras. YOU MADE THAT UP. I have used no fallacies -- you have yet to name them (except the straw man I did not use -- YOUR MISUNDERSTANDING of what I wrote). And of course I will be offended that you resort to such phrases as "grow up" since it is DESIGNED TO BE OFFENSIVE.

Sheesh! Can we ever get back on topic? (Oh sorry, there is no topic any more.)
06-29-2011, 04:27 PM   #208
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It looks like this is starting to become a flame war. Can everyone here be a bit more civil?

--DragonLord
06-29-2011, 04:31 PM   #209
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QuoteOriginally posted by jstevewhite Quote
Perhaps you didn't MEAN "given a fixed shutter speed and iso setting",
You are right. I meant to say "given a fixed shutter speed and equivalent ISO setting".

QuoteOriginally posted by jstevewhite Quote
...but that's what you kept saying, and that's why I kept arguing about that point.
In the hundreds of words I wrote, I missed one word. The post in which I made that omission was a rather late one as well. Fact is that you kept rejecting the notion that one has to convert f-ratios between formats. Fact is that you have to (see Falk's post) for equivalent images. One can make all sorts of statements about images that are not equivalent but this then literally becomes an "apples vs oranges" discussion which, AFAIC, serves no purpose.

QuoteOriginally posted by jstevewhite Quote
Like I said, that's a terminology problem; that's not what "slow" means, nor what "fast" means. Those terms have everything to do with shutter speed (which does not change) and nothing to do with DOF.
Wrong. Obviously "fast" and "slow" are terms derived from the shutter speeds made possible with a lens. But photographers frequently use phrases like "... need a faster lens to obtain less DOF...". They do it justifiably so because there is no way in which a lens can let more light in without decreasing the DOF (or vice versa) [leaving different t-stops aside].

Anyhow, I'm out of this debate now for good. I chimed back in again because I thought progress had been made, but this is way too laborious to continue.

Last edited by Class A; 06-29-2011 at 06:10 PM.
06-29-2011, 05:09 PM   #210
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QuoteOriginally posted by eddie1960 Quote
we've been surprised (both good and bad) by sensor performance in the past (not just with Pentax)
Who do not make sensors.
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