sgtsween
Forum Enthusiast
I'm looking for a teleconverter to try to get more reach from my Pentax 50-200 without too much degradation of image quality. Also something that allows use of AF. Anything like this out there?
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What is a good teleconverter that works with AF?
- Thread starter sgtsween
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Solution
Gerry Winterbourne
Forum Pro
The Kenko Teleplus series are generally good TCs and are fully automatic. They come in 1.4X and 2X. Tamron also do automatic TCs but I haven't used them.
It's a very rough rule of thumb that TCs degrade the image less the better the base lens: so you get better value out of them with top glass. Sometimes you get better IQ by just enlarging and cropping from the bare lens, although the TC might help you with framing.
This link illustrates how performance can vary with different lenses.
http://www.bobatkins.com/photography/tutorials/tc3.html
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Fl_Gulfer
Senior Member
If I was you I would get a Pentax DA 55-300 lens. There are only a couple of Teleconverter's that will work with AF and they are getting very hard to find and too expensive. You can get a used 55-300 for almost the same price and it's a better lens than the 50-200.
hikenhi
Forum Enthusiast
I have asked myself this question too in the past and present. After all, these things are expensive and unpredictable on DSLRs where you're mixing and matching lenses and converters on your Pentax bodies. After not having much luck with a off-brand converter on an off-brand lens on a Pentax Body, specifically a Tamron 70-200 2.8 with a Promaster 1.7x converter and a Pentax K-10D body, I said I'll just wait and see what the reviews are on the "Pentax-brand" 1.4x teleconverter due-out next year. I sold my 70-200 2.8 and replaced it with a more character-like WR Pentax DA *50-135 2.8 lens--much more suitable for my backpacking/mountaineering/climbing needs.
I liked the extra reach of the 70-200, but not a good trade-off for an extra 1lb of weight, and 3 fold of carrying bulk--see picture below.
Size-matters, but too much is not good when you have limited space needs.
Back to the teleconverter....I was debating what to do because I really do want to have that ocassional reach for my more stationary-travel needs. I like the Pentax DA* 60-250 f4 and 300 f4 lenses that are crafted in the same high-caliber professional grade attributes that I have my DA*16-50 and 50-135 DA* 2.8 lenses in specifically, but really don't want to have a 165mm gap where I have nothing in between and don't want to spend that kind of money. I really do like the 60-250 f4 lens, it's everything and then some, in terms of focal legnth that my old 70-200 had (-) minus 1-stop of available light. I think what I would do, given my experience of poor results with off-beat teleconverters is waith for the Pentax 1.4x due out next year and mount it on something like a "Pentax" lens. My DA* 50-135 f2.8 lens would become a 70-189mm f5 lens and if I choose to purchase the DA* 60-250 which is more compact than the Tamron 70-200, I'd have an awesome 84-350mm f6.3 lens which would give one some very nice options on an APS-C sensor lens w/o loosing too many stops of light--that's the most important part. I noticed that the 70-200 2.8 Tamron wouldn't fuction at all with the 2x converter that I tried in the store and the 1.7x converter would only function 50/50 in bright light. With that said, I believe your best bet is to wait for the Pentax 1.4x due out some time next year.
Fl_Gulfer
Senior Member
This is the best of the T/C's out there and you can see the price.
http://www.ebay.com/itm/Tamron-1-4x...44739416?pt=Camera_Lenses&hash=item2ec3478358
There is a DA 55-300 in the Marketplace on the other Pentax Forum for $265.00 So you can see it's a much better deal.
http://www.ebay.com/itm/Tamron-1-4x...44739416?pt=Camera_Lenses&hash=item2ec3478358
There is a DA 55-300 in the Marketplace on the other Pentax Forum for $265.00 So you can see it's a much better deal.
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KentG
Veteran Member
TC will increase the effect of mediocre lenses making them worse. Also getting a TC to AF a lens that is only as wide as F5.6 is very hit or miss. Using a TC with a 70-200/2.8 lens is infinitely better than trying to use it with a 50-200/4-5.6 kit lens. Changing to the 55-300 is a much better solution than trying to get a 50-200 to AF in all but brightly lit and contrasty situations with a TC attached.
Kent Gittings
Kent Gittings
Greyser
Veteran Member
Don't waste your money. Even best of the best TC works well only when paired with the best (and most expensive, of course) lenses.
James O'Neill
Veteran Member
I'd phrase that the other way around. A perfect TC magnifies the centre section of the image so that it fills the frame. If you have plenty of resolution in the centre part, and the aberations are small then the result will tend to be good - especially if the native resolution of the film / sensor is low relative to the lens.
Remember the rule goes 1/final res = 1/lens-res + 1/recording-res, so if you have a 100 lines per mm (lpm) lens and 50 lpm film you get 33 lpm in the final image. if the image was 36mm wide you'd get 1200 lines of res, but if print only the middle 50% your printing 600 lines. A 2x TC spreads those 100 lines out over 2mm so now you have 50lpm lens , 50lpm film : net res 25lpm but you're printing the full 36mm so you get 900 lines of res a 50% improvement.
If the lens resolution is poor, and aberations are big the TC is going to magnify those faults. So if you had a 50lpm lens and 100 lpm film/sensor you were still getting 33lpm * 36 mm , halved so 600 lines to start with. But if halve the lens res its now 25lpm lens , 100lpm film : net 20lpm x 36mm total 720 line - 20% resolution improvement is harder to see and purple fringing etc become twice the size.
And that assumes the TC is perfect, which of course it isn't.
Because the physical size of the apperture has remained the same but the focal length has doubled the f/ number halves - you lose 2 stops of light. In the old days that caused me focusing issues; and with AF if focusing without the TC is marginal, you'll strugle to get a lock with it. I don't know how well the converters above do at passing on the adjusted focal length to make SR work - without SR camera shake or subject movement for a given shutter speed will be the same on the TC'd image as one cropped to the same size, but you'll be working at 1/4 the shutter speed or turning the ISO up to compensate.
I still have my TC but I can't have used it in 10 years. Which isn't to say no one should use one ever, but get to know when doing without is better
Solution
Marc Sabatella
Veteran Member
Cropping. Costs nothing, doesn't affect AF, doesn't eat up a stop of light, doesn't reduce the effectiveness of SR, doesn't take any additional time while shooting, doiesn't take any space in your, can be applied at whatever strength you wish, and will virtually always produce better results than most TC's with most consumer lenses.
TC's made more sense back in the day when cropping required access to a darkroom.
TC's made more sense back in the day when cropping required access to a darkroom.
Good to see you posting Marc your reasoned answers as always a pleasure to read.
Lawnmower Shooter
Well-known member
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Yea if you are talking about a 2x tc, I don't even think the 50-200 will AF any more, I'm pretty sure it will add 2 stops putting you at least @F8, maybe a 1.4 would work? I am debating getting the Tamron 70-200 with a 2x tc or just getting the pentax 55-300 (the pentax is supposed to have relatively good IQ actually. Considering the Tamron option would cost me nearly $1000, I may opt for the pentax and spend the other $650 on the Sigma 17-50 I've been eyeballing.
If you are insisting on a zoom with WS then this is another story, but for pure IQ the 50-200 is a bit behind the rest.
If you are insisting on a zoom with WS then this is another story, but for pure IQ the 50-200 is a bit behind the rest.
It depends on the lens and its phase acurracy, The bigma will happily AF with a 2x on that's around F11!! whereas a 18-250 won't.
unlike cannon Pentax haven't instigated an elctronic lock so if the af module can see phase variance it will focus irrelevant of aperture.
essH
Leading Member
Generally, I'd agree with that. The 55-300 is better, though not perfect - it has a tendency to hunt for AF lock, depending on the subject. I have a Kenko Teleplus 1.5x (a rare thing to find these days - I was lucky enough to find one for £49 back in 2006). I find it works with some lenses and not others - when it doesn't, you soon know because the AF simply won't function. I was pleasantly surprised to find it has the contacts to drive an SDM lens, though I don't often use it that way. I recently used it to good effect with my 55-300.
The main advantages of a TC of course are that you can use it with more than one lens, which can cut your lens outlay (sometimes a stronger driving force than pure image quality), and it's a lot smaller and lighter than taking an equivalent lens. The argument in favour of cropping rather than using a TC hinges on how good your lens is; cropping the results from a 50-200 would be a challenge if you want a quality result.
sgtsween
Forum Enthusiast
Thank you for all of the informative answers!!! I ditched the TC idea and ordered and new DA 55-300. I've been getting really good images of birds from my 50-200, so I think this will be even better. Looking at he bigma next, but well see. I like stalking and getting close for shots.
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