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03-20-2013, 09:04 PM   #1
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tele-converter questions

Hello guys!

I've seen some pentax-m 85mm f2.0 pictures and i was blown away, even the lens.. it carries such beauty...!
but there's no way i can afford that (ahha @ the 85mm * f1.4)

So i'm wondering what if i get a tele converter and use it on my smc-m 50mm f1.4

a 1.4x converter would give me a 70mm and a F value of 2.0? (1.96)

hypothetically, if there was a 70mm lens with an aperture of f2.0.. would this be *almost* the same? i know it will never be the same.. but are teleconverters usable in this fashion?
the bokeh of 70mm @ f2 must be so awesome and make a real good portrait lens.

All tips are welcome, thank you

(all of this to use on dsrl k20d)

03-20-2013, 09:55 PM   #2
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Supposing there were a 70mm f2 lens and you used a 1.4x teleconverter you would essentially have a 105mm f2.8 lens. The 1.4 teleconverter costs you one stop of exposure. There are already a good number of high quality 100mm f2.8 lenses; it would be easier to simply buy a lens with that native focal length.

Pentax makes a well respected D FA 100mm 2.8 macro lens, the latest version of which is weather resistant. The previous version can probably be found easily enough on sites like KEH.com or from a forum member in the marketplace. Sigma also made a 105mm 2.8 macro which received very good reviews. I had trouble deciding between the Sigma and a Tamron 90mm 2.8. I ultimately bought the Tamron and it has served me very well. All of these lenses have gotten great reviews. The Sigma, I believe, is no longer made, but recent enough that it can probably be found. Of course, these newer lenses all have auto focus.

However, if you were thrilled by the Pentax-M 85mm 2.0 then you probably realize that is an all-manually operated lens. If you really like that focal length and you want something with very shallow depth of field you can always go with one of the Bower/Vivitar/Samyang 85mm 1.4 lenses. They get great reviews and can be had for around $279 to $300. Here's the review PF did on the Vivitar version. There are a couple other all-manual lenses around that you could probably have for less; there are older Pentax lenses in the 100-135mm range with an aperture of 2.8, but I don't think you'll find anything with quite the bokeh characteristic of the 85mm lenses discussed here.

All-in-all, I would encourage you to check out one of the auto focus lenses I mentioned at the beginning. Because I have the Tamron I can say with great confidence it's a very nice lens - Plenty sharp wide open, very light, and comparatively affordable versus other lenses. Plus you have the added benefit of the macro focusing option. Conventional wisdom seems to be that moderate telephoto macro lenses work very well doubling as portrait lenses. I have a 50mm 2.8 Sigma macro, as well, that is fantastic. However it doesn't have quite the reach you're looking for.
03-20-2013, 11:15 PM   #3
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If you are talking about putting a 1.4X converter on a 50mm lens to try and recreate the 85mm lens you probably wont end up with what you want in the end which is photos similar to the 85mm, especially if you are talking about an A* or FA* series lens. The teleconverters tend to degrade your images in terms of quality and you would probably be better off saving the cost of the teleconvertert to put that money toward the 85mm lens that you want.

QuoteOriginally posted by Akarak Quote
the bokeh of 70mm @ f2 must be so awesome and make a real good portrait lens.
Save up for a DA ltd 70mm f2.4
03-20-2013, 11:17 PM   #4
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I think I see what you are asking. Your m 50 f1.4 + Teleconverter.
Must admit I will give it a go since I have both and see what it does...

Of course using a teleconverter you will lose a bit of IQ and the stop of aperture. Also the bokeh will not be the same as a 85 because its more than just the focal length that influences this. That said I will give it a try and report back.

03-20-2013, 11:48 PM   #5
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Ok, unfortunately I just realised I don't have a 1.4 converter at the moment - only a Tokina doubler.

Just for fun I gave the doubler + A50 f1.4 a go.

This crude snap straight out of the camera with no Post Processing at all: All sizes | Cat with doubler | Flickr - Photo Sharing!

The light was rapidly failing here (NZ Autumn) and its using ISO 1100 (and a little bit underexposed) but you get the idea. The lens is set to f1.4. The combination performs a lot better than I expected.
03-21-2013, 05:48 AM   #6
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A quick and dirty, unscientific and handheld test with my FA 50 f/1.4 and Kenko SHQ 1.4X TC with lens set at f/1.4 and f/2.2.

Crops are unprocessed, non-resized 100%:
Attached Images
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PENTAX K-5  Photo 
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PENTAX K-5  Photo 
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PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 
03-21-2013, 06:44 AM   #7
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Most folk to to use converters as a kind of last resort, when extra reach is needed usually on bigger glass, IQ is never quite the same.
03-21-2013, 07:19 AM   #8
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The above sample pics reflect my experience with (admittedly cheap) teleconverters: when used on shorter focal lengths, there is a very noticeable decrease of optical quality towards the border of the pics. So not really recommended, but it makes for a cool retro effect, especially in monochrome. Might be just right for some kinds of portraiture

Also, with a bit of patience you can grab vintage lenses for cheap on the used market. I got my m-85 f2 for a very reasonable price, less than a new teleconverter would cost!

03-21-2013, 07:34 AM   #9
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I did my experimentation with teleconverters back in the 80's and haven't willingly touched one since. About the only way you could convince me to do it would be when using one of the really long lenses that come with a matched teleconverter to make the lens really, really long.

Generally speaking, you can achieve the same effect as a teleconverter by using digital zoom - in other words, cropping. The impact on IQ is no worse and typically lower, no increase in exposure is needed*, and no worries about reduced system functionality because the teleconverter doesn't support all the mechanical and/or electrical communications between lens and body.

*The only word of advice I can pass along is when shooting with the intent of cropping, shoot like you already have that longer lens mounted - use a faster shutter speed and/or a tripod. Cropping will magnify any motion blur.
03-21-2013, 07:34 AM   #10
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Original Poster
thank you everyone for your input i have my questions anwsered, i think i will be saving alot and alot for the all manual 85mm f2.0 lens
a i only use manual lens as i dont have much $$$ to buy autofocus lens.

i tried a jupiter lens with a m42 adapter and even though the lens is "cute" my k20d looks like a frankenstein with a m42 adapter.

my manual lens are...
smc-m 35mm f2.8
smc-m 50mm f1.4

so im not scared of manual lens, they bring me an advantage to people around here that take autofocus and constant measuring for granted
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