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02-24-2009, 03:46 AM   #16
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QuoteOriginally posted by gazonk Quote
I can't understand why they did that. Just another "me too"? (I guess at least Canon doesn't provide hoods with their cheaper lenses)
I think its a simple cost saving measure. If you buy the plastic contraption separately it costs another 25 Euros, which is a joke - about half the price of the lens on its own.

Ben

02-24-2009, 03:55 AM   #17
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QuoteOriginally posted by Ben_Edict Quote
This article very clearly states, that the culprit is the filter, though it makes reference to the film as a mirror for the incident light.
The thing is, here it needs two to tango: The filter and something else (most likely film/sensor) acting as mirrors.

QuoteOriginally posted by Ben_Edict Quote
Anyway: if the sensor would be a major contributor to this kind of ghosting and flare, there wouldn't be much, we could do about it. Luckily, at least my personal experience with Pentax DSLRs is otherise, as I never have seen any sensor induced flare in my images. All the flring I have had could easily be traced to the lens in question, for example the old K 15/3.5, which is a wonderfully sharp and contrasty lens, but very prone to flaring.
But these observations are compatible with the hypothesis that the sensor acts as a (weak) mirror. Without a filter or "bad" lens acting as a second mirror, the light reflected by the sensor does no harm.

QuoteOriginally posted by gazonk Quote
I can't understand why they did that.
I guess they are saving every penny possible. Or is there another explanation for the dreadful rubber slide on -- and in particular slide off -- rear lens caps?

In Pentax' defence, a (static) lens hood for a zoom is not going to be very effective for anything but the widest angle. I agree that it should be part of the package anyhow but perhaps it is somewhat excusable to not include a part that a fraction of users actually use and which doesn't do its job properly for most of the time.
02-24-2009, 10:49 AM   #18
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QuoteOriginally posted by Class A Quote
The thing is, here it needs two to tango: The filter and something else (most likely film/sensor) acting as mirrors.
QuoteOriginally posted by Class A Quote
But these observations are compatible with the hypothesis that the sensor acts as a (weak) mirror. Without a filter or "bad" lens acting as a second mirror, the light reflected by the sensor does no harm.
Ah, you see - if the sensor reflects anything at all (obviously any plane surface reflects a bit of incident light and as the incoming and outgoing angles are equal, light that falls near perpendicular to the sensor plane will obviously be reflected). That was as much valid with film as it is with digital sensors. Nevertheless the article makes very clear, that this reflection is without consequence, unless there is the front filter, which is also plano-parallel (quite in contrast to the curved surfaces of the lens) and which seems to act like a projection screen to some degree.

But whether the sensor reflects anything or wheteher there is a lens internal reflection is basically of not much importance, because the culprit - as the article states very clearly - is the filter.

My original thinking was, that any remaining flare/ghosting/reflection, after removing the filter, might quite possibly be caused by the lens - especially as the original poster used a super-zoom with many lenses. Obviously we cannot remove the sensor from the equation, nor can we "remove" the lens. But using a lens with fewer lens elements usually reduces reflections drastically. This is as much a common sense approach as it is based on photographic experience and lastly optics. Wheteher the lenses/lens groups are the originators of these reflections or whether they re-reflect light coming from the sensor is secondary, if we are only concerned, how we can reduce flaring and ghosting.

Ben
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