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01-06-2013, 09:14 AM   #31
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Are any Pentax lenses not now assembled in Vietnam?

01-08-2013, 01:29 PM   #32
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QuoteOriginally posted by simbon4o Quote
About 18-135 - If we look at the lens it is 18mm with streching to 135mm, my theory is that removing some elements from the long end made the lens 135mm instead of 250mm and that's why the 18-135 is so poor performer after 50mm. Sigma 18-250 also look like possible donor, it even zooms the right way(like the pentax).

My point for this thread was - does pentax develops lenses now days or they use other companies for the job and just re badge them.
Changing a lens' focal length, does not involve eliminating one or two lens elements. It is about changing the primary lens group's optical properties. So, if you remove a couple of lenses from "the longer end" of a 18-250mm lens, you don't get a shorter fl 18-135, but a defective 18-250...

Obviously there is some similarity between the Sigma and the Pentax super zoom, but simply, because they both follow they same basic design concept with a zoom group (the varietor group and the comnpensator (relay) group. Some add special field flattening lenses at the rear, and ofcourse the compensator varies with the zoom type (variable focal plane and aperture or fixed) - but the basics is very much the same with almost any zoom lens. No wonder, you detetct similarities.

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01-08-2013, 09:53 PM   #33
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QuoteOriginally posted by Ben_Edict Quote
you don't get a shorter fl 18-135, but a defective 18-250




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01-09-2013, 12:58 AM   #34
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QuoteOriginally posted by Ben_Edict Quote
Changing a lens' focal length, does not involve eliminating one or two lens elements.
Apparently the Auto Takumar 35/2.3 is an exception to that general rule:

"On some samples it is quite easy to unscrew the front element without tools : you get a ~50/4 lens with . . . around 1:2 reproduction ratio"

@CarbonR on:
Auto Takumar 35mm F2.3 Reviews - M42 Screwmount Wide-Angle Primes - Pentax Lens Reviews & Lens Database

01-09-2013, 04:40 AM   #35
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QuoteOriginally posted by lytrytyr Quote
Apparently the Auto Takumar 35/2.3 is an exception to that general rule:

"On some samples it is quite easy to unscrew the front element without tools : you get a ~50/4 lens with . . . around 1:2 reproduction ratio"

@CarbonR on:
Auto Takumar 35mm F2.3 Reviews - M42 Screwmount Wide-Angle Primes - Pentax Lens Reviews & Lens Database
Sounds like another way of saying that you get a broken ~50/4 lens (no infinity focus). Why not just add a short extension tube to get the same thing and leave the poor Auto Tak intact!


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01-09-2013, 05:09 AM   #36
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QuoteOriginally posted by stevebrot Quote
Why not just add a short extension tube to get the same thing and leave the poor Auto Tak intact!
1. To avoid getting dust into the camera while you set up the extension tube?

2. Because you've been using the 35/2.3 as a walkaround lens,
and don't have an extension tube with you?

3. To keep the semi-automatic functionality for macro use?

Anyway, it sounds like kind of a cool thing to do.
01-09-2013, 07:48 AM   #37
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QuoteOriginally posted by Unsinkable II Quote
Are any Pentax lenses not now assembled in Vietnam?
At least the K-mount lenses are except for FA 50/1.4 and FA 35/2 stock that was assembled in Japan. I don't know where the Pentax 645D lenses are assembled but assume Vietnam.
01-09-2013, 07:54 AM   #38
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QuoteOriginally posted by simbon4o Quote
I was thinking these days something like conspiracy theory .

We all know that Pentax have many lenses made by/with/... Tokina and Tamron. But do we know about all of them?
I have started to think about it and looking for information.

My guesses are:

Pentax 35 2.8 Macro Limited - it could be Tokina 35 2.8 Macro

Pentax 18-135WR - it could be modified Tamron 18-250 with some lens elements removed. I'm thinking about this tamron because it has the same shape, same front element, absolutely identical optical quality from 18mm to 50mm, after that the tamron is way better. We know that Pentax 18-250 is actually Tamron, not officially but I think it is almost 100%. Now Pentax announced that the new Pentax 18-270 is Tamron officially...

Pentax 17-70 4.0 - could it be Sigma 17-70 2.8-4.0 or more likely the optically identical older one 17-70 2.8-4.5 version? I think it could, it looks like it, the only difference is the opposite ring rotation. The sharpness and distortions are the same, the flares(something typical for sigma) are huge problem with the pentax 17-70 which is not typical for SMC coatings...

Pentax DFA 100 2.8 - Tokina 100 2.8 macro? If we look back the FA 100 2.8 is much better lens than the DFA successor, so is it possible the later model to be taken from other company?


So anybody else with guesses, I'm serious. For example DA 35 2.4 - it is the same as FA 35 2.0, but DA 50 1.8? Who made the DA 50 1.8?

PS Is Pentax a lens manufacturer or it isn't from a big period of time?
This is incorrect. Pentax licensed a few lenses from Tamron and also collaborated with the design on some. Same thing with Tokina. The Tokina 35/2.8 Macro was licensed TO Tokina along with several other lenses. The 100mm macro lenses are a Pentax design. Forget about Sigma. Pentax builds their own lenses including the few the licenses from Tammy and Tokina. Likewise, Tokina builds the ones they licensed from Pentax. Pentax has been making lenses a long time. Ever hear of Asahi Optical and Takumar?

01-09-2013, 08:12 AM   #39
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Here is the factory.

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21.030563,105.918494
01-09-2013, 08:39 AM   #40
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QuoteOriginally posted by lytrytyr Quote
1. To avoid getting dust into the camera while you set up the extension tube?

2. Because you've been using the 35/2.3 as a walkaround lens,
and don't have an extension tube with you?

3. To keep the semi-automatic functionality for macro use?

Anyway, it sounds like kind of a cool thing to do.
You may avoid dust on the sensor, but how will you avoid getting dust between the lens elements - how do you protect the single lens element, in the field, without risking scratches etc.? There is a reason, why even in large format lenses, the idea of convertible lenses, which were quite common until the 1960s or so, did not survive. There are still some exceptions and you can get a Cook or Taylor-Hobbs (the brand escapes me now) set lens even today, if you have enough money to invest. I even use an old Schneider Symmar, which you can convert from 300/5.6 to 500/12 (or so), which is not bad, but even these specifically made lenses always presented the problem of storing the removed lens element in the field.

-- Instead of removing the frontal lens element, I would simply add an achromatic close-up lens to the 35/2.4. I bet, the image quality is at least as good as with the crippled 50/4 and you also avoid the possibility of getting dust on the sensor.

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01-09-2013, 09:05 AM   #41
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I have a Sears 135mm 2.8 macro that allows you to screw the front element in closer, giving 1:7, 1:6 or 1:5 macro. You do lose infinity focus though, and macro performance is not even close to what you can get by adding a Raynox DCR-150 diopter.
01-09-2013, 11:38 AM   #42
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QuoteOriginally posted by Ben_Edict Quote
You may avoid dust on the sensor, but how will you avoid getting dust between the lens elements
I don't have the 35/2.3 myself,
but the part between the front element and the rest
should be easier to dust off than the inside of a camera.

QuoteOriginally posted by Ben_Edict Quote
- how do you protect the single lens element, in the field, without risking scratches etc.?
. . .
-- Instead of removing the frontal lens element, I would simply add an achromatic close-up lens to the 35/2.4.
How do you protect the achromat from getting scratched?
01-09-2013, 12:28 PM   #43
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QuoteOriginally posted by lytrytyr Quote
How do you protect the achromat from getting scratched?
If the achromat get scratched I throw it away and buy a new one. If the front lens element gets scratched, I throw it away...

Ben
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