Elements in teleconverters...

I'm after a 2x teleconverter to go with my 100mm macro lens... The plan is to make little things 'bigger' (than 1:1)

Not too fussed about AF for this purpose (but it might be a plus in some situations) but it must have contacts for retaining aperture control in-body ('cos I want that!!)... So my options are already fairly limited


The thing is... Some teleconverters have 5 elements and some have 7... What differences are the 2 extra (or less) elements going to bring (or lose) in real terms?

Does an MC5 give more or less in terms of IQ than an MC7???

I don't get it... Help me understand...

I'd be concerned about the loss of 2 stops in terms of potential depth of field. Are TCs really designed for this?

Why not just use macro tubes?

I'd go with extension tubes too, and they are available with contacts.

I think i have seen someone get a 2 x af teleconverter then take the glass out to use it as a ka macro tube.

Perhaps the OP wants a 100mm as opposed to 50mm in order to be further away?

I've used the Vivitar x2 macro TC and it did a splendid job with virtually no noticeable IQ degradation.

And this?





I have a 100mm macro (Samsung version of DFA100 2. lens but shooting bugs I have to crop quite considerably...
I tried a 2xTC in my local shop and it effectively doubled the size of the subject (in this case a counter screw) while also increasing (although only slightly) minimum focusing distance...


The TC I tried was a Kenko Teleplus 2x it has AF (f4 or brighter) but was a tad expensive at £180... It's a 7 element one...

Looking at the auction site it appears 7 element TCs are more expensive... Is the IQ considerably better than 5 element versions?

If so... Why is that?

7 element converters offer better corrections. As you are magnifying the image you are also magnifying the lens defects, so the TC needs to be top quality and suited to the lens ideally. This is why there are some converters matched to lenses, but they can be as expensive as the lenses.

Converters that are not from marque ranges can vary between fairly good and abysmal.

It is a recognised technique though to use a converter to make a macro lens. For example, a 50mm f/2 lens with a 2x converter becomes a 100mm f/4 lens that still focuses just as close (not closer) - focusing distance is measured from the camera film/sensor plane.

Macro converters were used in dental photography, allowing very high magnifications. These are converters that also offer some focusing movement to give these high magnifications.

I would forget 4 element converters.

have you seen the Teleplus 2x macro converter in classifieds, they are designed to give 1:1 with 50mm lens what it would do with your macro i do not know. , davidxgreen is the seller he may be able to help. it has the electrical contacts for in body aperture control and is £65
1 have full manual version, not used much, this was with the FA50 @ f1.7 attached

Just like it is with lenses there is no guarantee that one with more elements will be better quality, just more complex. That said the additional elements allow the possibility of correcting extra aberrations and where a manufacturer offers both 5 and 7 element models you can be pretty certain that the 7 element one is the more expensive and (probably) better one. Which isn't the same as saying all 7 element converters are better than all 5 element ones

As has been said a 2x teleconverter will double the focal length without significantly changing minimum focusing distance, so the achievable magnification ratio is also doubled. The same increase in magnification ratio can be achieved by using simple extension tubes (or teleconverters with the glass removed) or bellows which allow closer focus without altering the focal length or reducing image quality due to the extra glass elements of the teleconverter.

If you are going to get serious (or just want to play) and want to go beyond 1:1 as originally stated, it is possible to use a reversing ring and attach an extra lens backwards in front of your main macro lens i.e. you are using both lenses together. Something like an old manual 28mm lens works well (the wider the angle the greater the overall magnification) and it doesn't even have to be a Pentax one - anything from a junk shop will do to experiment

I have one of these interesting thingies as well. They are sort of like a 2x teleconverter and variable extension tube combined and are designed to not only work as a 2x teleconverter but also give 1:1 macro with a standard 50mm lens when that lens if focused at infinity. This ought to mean a 100mm macro lens focused at infinity would give a smaller 1:2 ratio. Of course these ratios are with the lens focused at infinity, you can then start to focus the lens itself closer as well thus increasing the magnification ratio further but you'll have to test to see how far you can push this with the specific lens in question. I regard my one as a useful and versatile bit of kit, but not something that would give me the same quality as a straight macro lens, or an extension tube, or a reversed lens.

Tubes all the way, there is nothing between the lens and the sensor to muddy the picture. The key to macro photography is light and you will loose light with either setup but adding the additional glass will harm your images.

Pentax A 50mm on 75mm of tubes with contacts and Catch in focus link

Although I answered the poll saying I use one, I also use other techniques and combinations of techniques, most often recently would be stacking lenses (a prime reversed infront of another longer lens).

As others have mentioned there are TCs with built in variable extension designed for macro.
Neither of mine work well for distant subjects being very soft when supposedly focused at infinty.

Yes TCs magnify any imperfections in your lens as well as potential introducing loads of their own. But remember even extension magnifies the aberations of your lens - if it didn't you wouldn't get a bigger image! The big advantage for TCs is they don't effect the minimum focusing distance of the lens used on them few 100mm lenses will focus as close as a std 50mm lens. The extra magnification also means you don't need to get quite so close for skitish subjects.

If you use them with extension tubes as well you get an increased flexibility in your system without increasing your bag weight as magnication will be different depending if the TC is before or after the tube(s). The combinded affect on lens aberations may well make it a pointless excercise though.

I can't seem to find any with contacts... Saw a review of some 'Jessops' ones but I can't find any going...

Kenko do them (via SRS) in every mount except Pentax...

I think tubes will be a useful addition but for bugs I worry that having to go closer to the subject might be a disadvantage... Is this the case or is my thinking all wrong?