APO 2x extender with non-APO lenses?

[farnz]

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Can anybody tell me, is there any downside (other than price of course) to using an APO 2x extender with non-APO lenses?

 

I realise that this wouldn't completely correct the image apochromatically but would it partly do so and would there be any other optical effects to beware of?

 

Thanks,

Pete.

[masjah]

Pete, I think that the APO designation means that the Extender won't introduce any significant chromatic aberration of its own, but I doubt that it would do anything to sort out chromatic aberration introduced by the lens at its front. Indeed, if it did, it would be introducing CA of ts own, since it would be refracting rays of different wavelength in different ways! So I suspect that any CA from the lens itself would simply get magnified by the Extender.

[jaapv]

No- it will perform better than an older one.

[leicamr]

Many years ago I purchased the non APO version. I returned it to the dealer straight away. I do use the 1.4x and 2x APO's and they are superb.

 

Mark

[farnz]

Gents,

 

Thanks for your replies, which give me food for thought.

 

 

John, that's an interesting angle - it hadn't occurred to me that the APO-extender actually might magnify any inherent CA from the non-APO lens (without it adding any of its own) but logic suggests that the very process of magnification of the image might also magnify any aberrations.

 

I was looking at it from a purely additive and subtractive point of view where the lens would have a positive CA constant and the APO-extender would have a smaller negative CA constant by virtue of its being APO-corrected but this model may be a little simplistic. Hmm ...

 

 

Jaap, when you say "better" I've assumed that you mean that CA will be slightly corrected but I may have misinterpreted. Is this based on experience fromyour R lenses and R9/DMR kit?

 

 

Mark, since you mention the APO 1.4x extender, which I believe can only be used on a small number of APO lenses (although I'm happy to be corrected ), it's not clear to me whether your experiences were with APO or non-APO lenses; would you kindly let me know please?

 

Pete.

[jaapv]

I used to have a "normal" 2x extender. When I replaced it by an Apo-extender, the difference was rather spectacular.It is not just the "APO" designation, it is simply optically superior. I think you must interpret the designation that it will not add any additional CA, as opposed to the non-APO extender. It was still in the film days and the lens I used it on was the 280/4.0 APO. I don't think there is a non-APO 1.4x extender. It can be used on quite a number of lenses, provided the rear lens element is not placed too far rearward.