Best perfomance with TC's

[eric_m4]

<p>When shooting with an f/2.8 lens the optical "sweet spot" is suppose to be 2-3 stops down from that - somewhere around f/8. But if a 2x TeleConverter is attached the widest opening is now f/5.6. Does this mean that the optical sweet spot is now 2-3 stops from f/5.6 (around f/16) or is it still in the f/8 vicinity? And does the "sweet spot" concept even make a difference with TC's? Thanks.</p>

[Wouter Willemse]

<p>The optical sweet spot is where it is; for some lenses it is wide open or just one stop down. The mantra that it's 2-3 stops down is very outdated. TCs usually require further stopping down than you'd usually would, but also here it depends a lot on the combination.<br>

Personally, I do not worry too much about sweet spots. Good lenses (and most are) have a wide range of apertures where they perform well. The tiny differences between the optimal and near optimal are not going to make or break your photo; stopping down too far and introducing a lot of background clutter *might* make or break your photo. So I prefer to set aperture based on needs/wants rather than the pursuit of optical excellence.</p>

[ShunCheung]

<p>Presumably you are already using a fairly long lens to begin with, e.g. at least 200mm, most likely longer. After you add a 2x TC, you'll have a really long lens. With such a long lens, you want some faster shutter speed to stop motion and vibration, and f16 is practically useless under such conditions, not to mention that at f16, diffraction is going to rob a lot of your sharpness.</p>

<p>If you start with an f2.8 tele, with the 2x TC you'll have max f5.6. You might want to stop down by one stop to regain some sharpness, but you need to balance that against subject motion blur and vibration. How to compromise highly depends on each particular shooting condition. There is no one-size-fits-all answer.</p>

[JDMvW]

<p>In my not-so-humble opinion, and not to be so polite as the earlier responders, once you've got into the magic world of teleconverters - good as the best of them can be <em>sometimes</em>-- you're well off the "sweet spot road" and mired in the slough of "not so sharp as it would be without this extra piece of glass".<br /> In short, I wouldn't worry. Getting the picture is the important thing; and if you need the TC to do it, well, so be it.</p><div></div>

[sarah_fox]

<p>In my experience with a big Takumar 500 and a 2x TC, there's a distinct sweet spot that is the same number of stops open from max aperture, with or without the TC. The lens has a sweet spot of f/8, and with the TC, that becomes f/16. Of course with the TC, I get shoved up against diffraction limits, but that f/16 is still the sweet spot.</p>

[JDMvW]

<p>I do have to acknowledge that when your TC use is with reflex (mirror) lenses, you don't have to worry much about what aperture you're going to shoot at. :)</p>

[ilkka_nissila]

<p>Which lens, which TC, and which camera body are you planning on using?</p>

<p>I think one stop down from the maximum aperture is a good place to start when using TCs. In most cases you have to consider shutter speed as well.</p>

[Rick Waller]

<p>Why don't you just take out your rig and see for yourself where the 'sweet spot" is? Better solution than asking such a broad question on a photo forum, wouldn't you think?</p>

[eric_m4]

<p>Because I don't have a 2x TC.</p>

[dan_brown4]

It's worth comparing a cropped image to one shot with a teleconverter. For example, on a D800, the cropped image is

sometimes noticeably better.

[ShunCheung]

<p>I have both the TC-20E (original version) and the TC-20E III (new and improved). Don't expect any 2x TC to be the silver bullet. You double the focal length to something (typically) really long and reduce the maximum aperture by two stops. Just the combination of those two things is going to make the combo very difficult to use, not to mention that all the optical flaws in your lens are magnified.</p>

<p>At least I rarely use my 2x TCs. Usually you use you lens wide open so that you don't need to use a really slow shutter speed or a very high ISO. You don't usually have the luxury to stop down by even 1 stop, let along more.</p>

[eric_m4]

<p>I don't think any TC + lens is going to give what its equivalent prime will give, whether it's focal length, f/stops or whatever. That's why they cost about $500 compared to, for example, a $10,000 400mm f/2.8 lens. I realize some compromise is necessary but I would just like to minimize my losses as much as possible anyway I can. I agree with JDM - "Getting the picture is the important thing." Even if it's not tack sharp it's probably still better than no picture at all. BTW JDM, considering what it is, that's pretty impressive detail from that 600mm Sigma + Vivitar 2x.</p>