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06-08-2012, 03:23 PM   #1
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lens extentsion

hi all
As I understand there is a way to make my Sigma 70-300 F4-5.6 extend out to equivalent to 600m by placing a fitting between the camera (Pentax K-7) and the lenses,is this correct?
Regards
ronmac..

06-08-2012, 03:42 PM   #2
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It's a teleconverter, but alongside increasing the focal length it also increases the aperture (1.4* for 1.4x TC, 2* for 2x TC and so on) and degrades image quality. You also lose AF since your lens is something like f/8-11 with a 2x TC (to get you to 600mm). It's not worth trying on your lens.
06-08-2012, 03:55 PM   #3
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Hi back. What Giklab says is true up to "it's no worth trying on your lens". Some are, especially if it's the difference between getting the shot with reduced IQ or not at all.
SMC Pentax-F 1.7x AF Adapter Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Lens Database (Hard to find and overpriced)
Miscellaneous Lenses for Pentax: Teleconverters (All Brands) - Pentax Lens Review Database ( some more options)

Personally, I like the Pentax auto 1.7 in some situations. But it's up to you - a reasonably cheap option to get a feel for ultra-long before investing mega-bucks in something of that range.
06-08-2012, 04:25 PM   #4
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OK I revise: It's not worth trying unless you plan to shoot the moon or something stationary, and as long as you don't pay too much for TCs (Pentax is an exception). If you go the cheapo ocassional user route might as well get one of these 3x teleconverter | eBay.

06-08-2012, 04:32 PM   #5
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Bottom line: it will look like crap on that lens (esp. at 300), and you'll have to manual focus.
06-08-2012, 04:39 PM   #6
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Thanks to all,,I have got the message.
Best wishes
ronmac
06-08-2012, 04:47 PM   #7
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To elaborate on the subject: A high-quality TC on a fast, high-quality prime lens will work pretty good. I have a 7-element (that's the better kind, as opposed to 4-elements) 2x converter. If I put it on my Sigma 70/2.8, which is one of the sharpest lenses around, results are excellent. Works ok also on some of my older manual focus 200mm primes -- they aren't as fast, but they are pretty sharp stopped down. Somewhat cumbersome to use because of the light loss, but results are decent. But on a budget zoom (where you are starting out at 5.6-6.3) to get really long reach -- looks like crap and is very hard to use. I've tried it in-fact on a Sigma 70-300 zoom (possibly same as yours, but they've made many versions) and also my 18-250 zoom. On those at the long end, it looks about the same if you just crop and magnify the image without the TC -- and often worse than that. Noticeably soft every time. And it is much harder to focus, etc.
06-08-2012, 05:23 PM   #8
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Thanks vonBaloney ,think I will have to stick to macro and doing panoramic photo's and leave the long distance stuff just for now ...Like everything else I guess you get what you pay for, lol
Best wishes
ronmac

06-08-2012, 05:24 PM   #9
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QuoteOriginally posted by ronmac Quote
Thanks vonBaloney ,think I will have to stick to macro and doing panoramic photo's and leave the long distance stuff just for now ...Like everything else I guess you get what you pay for, lol
Best wishes
ronmac
Without a TC, that Sigma will look pretty good at f8-f11. 300mm is still decent reach...
06-08-2012, 05:30 PM   #10
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Yes you are correct I'm just going out now to give it another try maybe I was doing it wrong ,only ever tried it once and it has been in the box ever since (6 months) I was that disappointed with it but here I go again with it
Many thanks
ronmac
06-08-2012, 07:44 PM   #11
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It's always tempting to go for long reach. And unless good subjects meet good technique and good glass, it's usually rather disappointing. Certain high-quality TCs (teleconverters) do well when matched with certain high-quality long primes, or with VERY few high-quality fast long zooms. Adios, mucho dinero. (Watch lotsa cash fade away.) If you have specific needs, like sports|action or birds|wildlife, then long fast extended glass may be worthwhile. Hay, it's only money!

I have some long primes (300-400-500-1000mm) and some not-too-bad TCs and I use them all too rarely. What *was* I thinking? Especially that Lil'Bigma DG 170-500? I find the 250-500mm range most useful for cowardly street shooting -- but I'm not on the right streets often enough. What did you intend to shoot with 600mm?

Some suggestions:

* As mentioned, shoot your 70-300 on a tripod with SR off and a timer delay. Keep the camera+lens rock-solid. Depending on conditions, you may need a sandbag atop them.

* Take your best, sharpest, most stabilized shot, and crop it to get the desired enlargement. IQ will be better than with any but the best and costliest superlens+TC combo.

* TCs are fine if you don't expect *photographic* results. Use them for surveillance, blackmail, crime planning, etc. Use TCs and PP when content is more important than quality.

* Move closer. A 300mm optic has an AOV (angle of view) of about 5 degrees on your camera. Position yourself so your subject is comfortably within that narrow slice of reality.

* Avoid distant subjects if the atmosphere is warm or dusty or moving. Cruddy or turbulent air really kills contrast and sharpness. Cold, dry, still air is best for far-off targets.

Just for ducks (and not too many bucks) get an A-type 2x TC on eBay. It should cost under US$30, shipped. If the results are within your pain threshold, great! If not, you can knock the glass out and use it for close and macro work. Have fun!
06-08-2012, 09:42 PM   #12
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Thanks for all that RioRico
I was going to try for wildlife shots and I think I will try for this with my 70-300 and leave it at that, It seems the bigger one goes the more complicated things get.
Once again many thanks
ronmac
06-09-2012, 04:33 AM   #13
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QuoteOriginally posted by ronmac Quote
I was going to try for wildlife shots and I think I will try for this with my 70-300 and leave it at that
That's the best option on a limited budget. Depending on the wildlife, try the approaches I mentioned: get closer; use a solid tripod and vibration-free delay. The best wildlife shooters take time to study their subjects, know where they'll be and when. Preparation wins!

QuoteQuote:
It seems the bigger one goes the more complicated things get.
More complicated or more expensive, for sure. Some big stuff is fairly simple. It merely costs a fortune. Ouch.

I suggested above that sometimes content trumps quality. Expectations can be adjusted. If I want National-Geographic or Arizona-Highways-quality shots, I use a prime or a short-focal-range zoom, and a tripod, and no TC. If I want shots than can be posterized into striking graphics, anything goes: long optics, TCs, high ISO, massive PP -- WHATEVER IT TAKES to make the picture.
06-10-2012, 05:40 AM - 1 Like   #14
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Rio Rico and some others have already made some excellent points, but I'll throw my 2 in anyway.

I think 300mm should do fairly well, I use a 200mm all the time for bird shots, but I try to get as close as I can. If you look through the shots in my gallery all of the bird shots were taken with Vivitar 200mm, Lentar 90-230mm or Sears 80-200mm. Most are also cropped fairly tight too. You can expect a little better reach with a 300mm, but the difference is not great. I've used a couple of 300mm primes and a 75-300 zoom, and was surprised that they didn't show that much difference in apparent reach. I still wanted to get as close as possible.

As already noted, get as close as you can, use a tripod if feasible, and get to know your subjects. I shoot a lot of bird shots in a local park, where they tend to be more accustomed to people being around, so I can get closer. When I'm out in the field I have to sit there and wait a while for things to settle down, then the birds will start to roam around a little, but they will still be skittish and will scatter at any sudden movement. When in the woods you can forget about good lighting, especially in summer, shadows will kill even a bright cloudless day so plan on a good flash.

More often than not a tripod is a hindrance for wildlife shots, they won't be very likely to sit around and wait for you to set it up. If it's not already set up and waiting a bird or rabbit is long gone before you can even open the legs and set it down. 99% of my shots are hand held. Including macros. Also, if you set up a tripod and a bird or squirrel shows up well to the side, it won't wait for you to pick the rig up and move it around...so if you can't swivel it around far enough, you miss the shot. I gave up on tripods pretty quick. I still have a couple and use them now and then when I can, but most days they stay in the Jeep. One exception was the Pileated Woodpecker nest, I could set it up and leave it, since I knew exactly where they would be...at the nest. I still did 95% of those hand held.

Practice with the lens you plan to use on wildflowers. They stay in one place, windy days help you learn to adjust settings to stop motion (a flash helps sometimes too) and you get some great flower shots. At 300mm you'll have to back off a few feet, but I've gotten some pretty nice wildflower shots with a 35mm ME Super and a 70-210 lens. By the time I got into digital not much practice was needed, but I still try to grab a 200mm flower shot now and then just for fun and to see if I can get it to come out decent.

Watch the lighting. Occasionally you will get a good backlit shot, but usually for wildlife you want good front lit subjects. I never shy away from a backlit bird shot, and quite a few have come out good, but I always try to keep the sun behind be or over one shoulder at least.

Take lots of shots. Digital can be deleted whereas film could get expensive. With film I tried to make every shot count. With digital you can delete anything that is not good enough. But NEVER delete them on camera, wait till they are transferred to computer. The LCD screen is good to have, but I find my pictures are often acceptable when they don't look so good on the camera.

At the ranges you'll be dealing with for wildlife, depth of field is not usually a major consideration, but I always try to shoot at least f8 so I get good depth of field, and most lenses will get better pictures at f8 to f11 than wide open. Use your lens a lot, get to know it really well, and you will usually have a good idea what the picture will look like, as long as you get good focus, before you push the shutter. With birds in flight or any animal in motion, forget about auto focus. It will usually keep searching, and you will often end up focused anywhere but where you want to be...the head. This is especially true with birds, auto focus will latch onto the wings more often than not, so try to learn to use manual focus as much as you can. It just works better.

Teleconverters...I have a couple and use them occasionally, but not often. Usually it's when I want to get a shot for ID purposes and I'm not too concerned about image quality. For good quality shots, I use a prime telephoto and get close. Even then I usually don't have time to dig the thing out and mount it so I go ahead and take a few long distance shots and cross my fingers.

Ok maybe that was 10 worth...I'll shut up now...
06-11-2012, 04:00 PM   #15
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Paleo Pete Many thanks for all that information ,the people on this site have been most helpful ,at the age of 68 I sort of think do I have the time left to learn it all ,but then do we ever know it all lol..
Best wishes to all
Ronmac
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