Alley in Pisa, Italy

by Lars Kotthoff

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I have a Nikon D3100 with the standard 18-55mm lens, and a Nikon 55-300mm lens. I bought a 2X teleconverter for the 55-300mm lens, but the TC seems to be unusable. At 300mm with the TC everything is blurred and smeared. 'Colourfully cloudy' is how I can best describe it. If I set the 55-300mm lens at about 100 (with the TC) I can get something in focus, but the quality is really bad.

Do I have to use a particular setting for the 2X TC to work well, or is it just not possible to use a 2X TC on a 300mm lens?

I didn't expect much from the TC (at £20 how could I?) but I did expect it to do something! :D

My main use for the 300mm is for astrophotography hence why I wanted the 2X.

Without:

without

With:

with

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How come, both images have the same field of view? Did you zoom inbetween? –  Unapiedra Mar 10 '13 at 16:19
    
No, I just unscrewed the 2X TC and refocused. –  Ronnie Mar 10 '13 at 16:38
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That cannot be a tele-converter if the field-of-view did not change! Unless they now make a 1X version :) –  Itai Mar 10 '13 at 20:25
2  
Am I the only person seeing an enlarged imaged with a narrower field of view? It looks more like about 1.4x, but it's clearly larger—half of the scrollwork on the fence is missing, the shrubbery stops before flat-topping, the waste bin is bigger,... –  user2719 Mar 10 '13 at 21:18

3 Answers 3

up vote 1 down vote accepted

If I had to guess, the reason for the issue is it being out of focus. I suggest you try to manually focus the lens and see if you can get a good picture. A second guess would be, as others have mentioned, a cheap teleconverter.

Teleconverters (espeically 2x) are not designed to be used on ALL lenses.

The first reason is they will cause the amount of light to be so low that you lose autofocus as the autofocus sensor doesn't have enough light to function properly. As an example, the new Nikon D7100 is claimed to have an upgraded focus sensor that will function all the way down to f/8. Which means an f/4.5 lens with a 2x converter "should" still function. I'm still waiting on reviews to see if it really holds up to this claim.

The second reason has to do with how the piece of glass at the end of the teleconverter that faces the lens may be too long and protrude too far into the back of the lens where the rear lens element resides. This is not always a factor on all lenses, meaning you may be able to physically attach the converter to the lens, but the rear element of some (espeically kit) lenses physically touch the front of the teleconverter.

As far as the Nikon brand of teleconverters, they have a chart of compatibility where your 55-300 is not a member of: http://www.nikonusa.com/en_INC/IMG/Assets/Common-Assets/Images/Teleconverter-Compatibility/en_US_Comp_chart.html

edit:clarity

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1  
The minum AF aperture thing isn't about the amount of light in an absolute sense (tht is, the sensitivity of the AF sensor) but about geometry (the layout and linear resolution of the AF sensor). That's why Minolta (Sony) was able to offer an AF 500mm/8 reflex lens when nobody else did, even though their imaging sensors' low-light performance (at the time) was execrable. You'll see the same problem on split prism focus aids on MF cameras—if the lens is slower than the prism's geometry likes, you can't see an image on both sides of the split unless you're already in focus. –  user2719 Mar 10 '13 at 18:29
2  
The TC image is clearly in focus, but very, very soft and with a lot of flare and blooming. And I mean soft in the sense of a soft-focus lens, like the old Rodenstock Imagon or the Canon EF 135mm f/2.8 SF with the SF turned up to 2. The TC appears to be adding a considerable amount of spherical aberration to the system in this combination. –  user2719 Mar 10 '13 at 18:40
    
"The TC image is clearly in focus, but very, very soft..."Agreed, sorry did not see the OPs photos before having chance to post reply hence the guess. –  ISOTropic Pixel Mar 10 '13 at 20:43

You say that the thing calls itself a "58mm Pro Digital Precision Tele converter 2.0x AF"... the 58mm part calls for some thought. Just what kind of product is this? Is it a teleconverter, a thing that you mount between the lens and the camera body, or is it a kind of secondary lens that you screw on to the front of your 55-300? (If the latter, it should come as no surprise that it gives abysmal image quality. Disregard "Pro" and "Precision" as being outright lies, and "Tele converter" as being a half-truth at best.)

As for your original question, as stated, in general it is safe to say that a 2x teleconverter (true teleconverter, the kind that mounts between the lens and the camera) is for most practical purposes (astrophotography maybe being one of the exceptions) rather useless on a 55-300 consumer lens. Tour lens is a f/4-5.6 kind of job, is it not? A 2x converter costs you two full stops of aperture, making your lens a 110-600mm f/8-11. Good luck with autofocusing anything at f/11. Plus one can expect to have to stop down the lens one or two full stops to get rid of the worst of the optical sideeffects¹ a 2x converter introduces, which makes it a total non-starter unless you are photographing at high noon in the Sahara desert or somewhere similarly well-lit.


Notes:

  1. Teleconverters tend to amplify the optical defects of the lens you use it on, and tend to throw in a few of their own. Most prime lenses² and some of the better quality zoom lenses (ie big, heavy, expensive) are good enough that you can afford this quality loss, and bright enough that you still can get autofocus to work. For consumer-level zoom lenses, it just ain't so. Given the megapixel numbers cameras output these days, you are better off just cropping the image from the lens as-is.

  2. Note that I am assuming here that teleconverters are something you put on to a long lens to get more reach. Ie using one on a wide-angle or a normal lens, while certainly possible, is really rather pointless, other than for a laugh.

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1  
Good spot: the "58mm" is likely the filter thread size. –  user2719 Mar 10 '13 at 20:06
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Great answer! I would add just one thing: getting beyond 300mm with reasonable quality and aperture gets very expensive very fast. Based on price alone I would expect this teleconverter to fall into the "novelty" market only. –  Dan Wolfgang Mar 10 '13 at 20:28

According to this, other people can take photos with the Nikon 55-300 and a teleconverter. But it seems to depend on the teleconverter.

Cjlws says:

I recently purchased a random teleconverter from eBay (Soligor brand, 1.7x) and decided to try it out with this lens. Got to say I'm surprised how well it worked - focus was a tad slow and the viewfinder image a bit dark but I got some decent AF pics of the moon. So yeah, the lens works with TCs as far as I can tell. Hope that helps.

However, he then says that it depends on the teleconverter used:

Quick update on the above - just tried this with a Sigma 2x TC and it was a non-starter. Basically the two items wouldn't physically fit together as the back of the lens sticks out a bit as does the front of the TC. So, before buying a particular model you might want to try it out with your lens. Cheers.

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The one I have just says: 58mm Pro Digital Precision Tele converter 2.0x AF –  Ronnie Mar 10 '13 at 16:15
    
Your results are so bad, maybe you could put the TC on a different lens to check that your TC works with any camera. I suspect that it is either of terrible quality or that something is wrong with the TC. But I have no experiences with TCs so I simply don't know. –  Unapiedra Mar 10 '13 at 16:31
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I'm thinking that it's just an incredibly bad TC :/ –  Ronnie Mar 10 '13 at 16:39
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I've just seen in your profile that you're from Glasgow: that explains it... ;-) –  ElendilTheTall Mar 10 '13 at 17:23
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Well that's a bit harsh. No, actually, you're probably right... :D –  Ronnie Mar 10 '13 at 18:42

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