Why isn't there a TC with IS?

[yakim_peled1]

I wonder........

 

If we suppose that it will not be used with IS lenses, no

stabilization conflicts will occur, right? If so, I see no technical

reason to consider TC with IS impossible to make, do you?

 

After all, IS works by moving one of the elements inside the lens.

Therefore, why can't they make a TC in which one of the elements

moves to compensate for shake?

 

Is there something that I overlooked or that Canon simply doesn't

want to do this because of some obscure marketing considerations? I

guess that whatever the reason is, it relates to all TC makers like

Tamron, Sigma, Nikon etc.

 

Thanks for your thoughts.

 

 

Happy shooting,

Yakim.

[johnb]

Yakim, <br>

My first guess would be Canon wouldn't want to do it.<br><br>

Why?<br><br>

Because if my 2xtc had IS then I could put any 400mm <br>

on it and get the value of IS instead of putting my<br>

100-400L IS on.<br>

<br>

If it was made well though I would grab one.<br>

I would put my 2xtc with IS on my telescope, <br>

1200mm x 2 = 2400mm IS? :+)<br>

<br>

At least a 2xtc works well with a lens that has IS, <br>

it doesn't make the IS not usable.<br>

[olivier_de_lame]

Well, I think the best solution is what Minolta did: put stabilization on the body.

 

Regards,

 

Olivier

[stefan_deisz]

My guess would be that the best place for the IS element(s) depends on the actual lens being used. Maybe a general IS converter is simply impossible?

The Minolta way of IS seems most practical, but have there been good comparisons between the 2 systems?

 

Regards, Stefan.

[mark u]

There are several reasons why it would not be a good idea to locate IS in a TC. Most obviously, what if you want to use a lens without a TC, especially if you don't want to lose infinity focus?

 

The IS group is usually not too far from the point where the principal rays cross within the lens. This has the advantage that much smaller movements are required for the IS group to correct angular shake, saving battery power and causing minimum upset to the optical design.

[ky2]

Marketing. Marketing. Marketing.

 

Did I mention Marketing?

[mark_chappell]

<I>Most obviously, what if you want to use a lens without a TC, especially if you don't want

to lose infinity focus?</i><P>

 

I follow the rest of your argument, but TCs used in the normal way (without extension tubes)

don't cause loss of infinity focus.

[bobatkins]

Simple answer. Canon don't want to make one. That's all there is to it.

[wgpinc]

I'm going to assume that this is a serious question. I think the main answer, besides the fact that obviously Canon doesn't want to make a converter with IS, is that the TC is a passive system unlike the lens which is an active system with a lot of automation in that it can be focused and change aperture automatically. The expense to build automation into a converter would greatly exceed the demand. JMNHO, cheers.

[straightarm]

you get a light loss and hence slower shutter speeds, which rather defeats the object of IS.

 

Simon

[kelvin_wong3]

to 'straight arm'

 

er..., not really. tc is to help you magnify/increase focal length without buying another lens; while IS is to negate vibrations which may lead to unsharp images.

 

not all canon lenses can use the tc's, and thus limits its appeal; and as image quality drops when you use a tc, wouldn't it be reasonable to say that a IS's tc would cause a further drop in resolution? i mean, look at the 70-200 f2.8 and the 70-200 f2.8 IS mtf chart, or the reports of 300 f4 being sharper than it's IS counterpart.

[mark_chappell]

<I>you get a light loss and hence slower shutter speeds, which rather defeats the object

of IS.</i><P>

 

I don't think this is very logical since (a) slow shutter speeds are where you MOST benefit

from IS, and (b) IS works very well -- better than autofocus, in fact -- when you add TCs

to an IS lens (IS keeps right on working even if the effective aperture drops below the AF

limit). To speculate further, why not build a stabilized optical unit that physically

resembles a TC, but with no (or very little) magnification? Not being an optical engineer

I'm not sure how realistic that might be. More generally, it seems logical that one can

achieve the best results from a given stabilization technology if it is designed specifically

for particular lenses, rather than a one-size-fits-all approach.

[bobatkins]

Technically it's quite possible to build a zero power (or low power) optical relay system with built in image stabilization. I'm not saying it would be easy but I am saying it could be done.

 

The trick might be to get it to operate both with short and long focal length lenses equally well since the system tuning parameters would be different. But with EOS lenses, the lens info is available electronically from the ROM in the lens, so the converter could tune itself to the lens in use.

 

But like I said, Canon (and the rest of the industry) don't want to. I assume it's because of a mix of both technical and marketing reasons.

 

It might be very expensive and difficult to design and build and it might also affect sales of other products.

 

Maybe what the world needs are smaller, lighter and less expensive mechanical gyro stabilizers (remember them?). Bolt one to the bottom of any camera and you have a stabilized system.

[mark_ryan2]

Yakim,

 

I asked the same question a few weeks ago on Fred Miranda's site and got similar answers.

 

The one here I find most interesting is the one about he rays axis and where the IS unit needs to be. Sounds like an IS unit almost works on the "leverage" principle and works best in sweet spot.

 

I like the idea of the unit. I think as you add a TC, you are more likely to need IS. Most of the IS lenses are slow f4-5.6, so adding it to a f2.8 and faster prime doesn't seem unreasonable. If it worked, I could see Canon's reluctance to bring it out since they get about $500 bucks more for IS on a 70-210/2.8 with IS than with out (if I remember B&H pricing right).

 

I would think the best bet would be someone like SIGMA bringing one out since they have less invested in OS (?) lenses.

 

I like the idea of a 1.4TC IS on a 50/1.4 and get a 70/2 with IS.

[johnclinch]

I assume canon Is relies on an image circle from the lens that is larger than the sensor/film, this may cause problems if the lens wasn't originally designed for this. Other than that moving a diverging lens (which is what a tc is) should provide IS. However you would need to move all the elements together which could be rather alot of mass to move quickly

[bobatkins]

There's no need for a larger image circle. The image is only being moved by small fractions of a mm when IS is operating.

[johnclinch]

Thanks Bob I always assumed it was quite alot.

 

That perhaps explains why the minolta 7d can use the reduced image circle sigma lenses.I asumed the camera got the sensor central but travelling in the correct direction before tripping the shutter.

[ron c sunshine coast,qld,a]

I'm not so sure Bob.

<BR>Don't IS lenses have to be redesigned to cope with IS? I know this is the case with the 75-300 IS but i don't know about the others- the 70-200/2.8 for example

<BR>The 75-300 IS has larger rear element groups compared to the non IS version (these are completely seperate to the optical stabilization group)

[jean_jacques_lemaire]

Maybe simply ask this (excellent) question to Sigma, Tamron, .. or other third-party manufacturers :D<BR><BR>

 

I guess that Canon's IS device is put in a place where chromatic abberation is minimal in the lens (but I'm just guessing).<BR><BR>

 

The "Minolta alternative" has as a downside that movements of the correcting elements are maximum compared to the other systems.<BR>

But they could certainly provide a "non-IS" mode with resolution enhancement (like medium-format backs, where you can make half-pixel or quarter-pixel shifts).

[yakim_peled1]

>> But like I said, Canon (and the rest of the industry) don't want to. I assume it's because of a mix of both technical and marketing reasons.

 

 

While I could understand the marketing reasons for Canon and Nikon to be reluctant of such a product, I don't think the same applies for third-party makers. Even if they will price it at 500$ this could be a major hit.

 

Happy shooting,

Yakim.