[Wild Mark]

Calling all big lens lovers!

With all the talk about legacy lenses being great/ bad, I am turning my head to the idea of 'modifying' my two big lenses (FA250-600 and F600).

Before anyone shrieks with disdain, don't worry, the modifications are not permanent.

My thoughts are to have an optics expert re-examine the optics of each lens with the view to manufacturing a custom piece of glass for insertion into the filter slot towards the rear of the lens. Probably an aspherical element to correct for aberrations or something of that nature anyway.

Such modification will come at expense, sure, but putting that negative aside, what are peoples thoughts n the idea??

[interested_observer]

There are a few optical engineers here on the forum, who are much more knowledgeable in this area. Your considering something similar to what was done with Hubble. Just thinking out loud, but I would think that the corrective optics would have a small range that the complete 250 to 600, so you might wind up with a set of corrective lenses for specific focal lengths.

Also on the larger telescopes now they have laser guides that measure the turbulence and adapt the main mirror's surface to cancel out the blurring effects of Earth's atmosphere....

• Zap! This Awesome Laser-Armed Telescope Is Fully Operational (Photos)

[Adam]

Calling all big lens lovers!

With all the talk about legacy lenses being great/ bad, I am turning my head to the idea of 'modifying' my two big lenses (FA250-600 and F600).

Before anyone shrieks with disdain, don't worry, the modifications are not permanent.

My thoughts are to have an optics expert re-examine the optics of each lens with the view to manufacturing a custom piece of glass for insertion into the filter slot towards the rear of the lens. Probably an aspherical element to correct for aberrations or something of that nature anyway.

Such modification will come at expense, sure, but putting that negative aside, what are peoples thoughts n the idea??

I'll do you one better: the K-1 includes correction profiles to compensate for the aberrations in FA* lenses

[Wild Mark]

Yes that is awesome. And yes, when finances permit I will enjoy that benefit.

Not sure if the F600/4 will be so lucky though???

[Adam]

Yes that is awesome. And yes, when finances permit I will enjoy that benefit.

Not sure if the F600/4 will be so lucky though???

Unfortunately not! If only there was a way to trick the camera to think that it's the FA* version, since the optics are the same...

[pete-tarmigan]

I'll do you one better: the K-1 includes correction profiles to compensate for the aberrations in FA* lenses

Damn! Yet another reason I'll have to buy a K-1! (I have the FA* 400mm) I never saw any rumours about this feature.

[Digitalis]

In a nutshell : yes it is feasible....but with SO many Caveats. Every element in a lens is there for a reason - a well corrected lens is a delicate balance between over/under corrections. Chucking one more element in to correct a perceived optical fault can give rise to something far worse*, if the element isn't carefully manufactured, shaped and mathematically incorporated into the optical design.

Aspherical elements are rare in 35mm lenses over 100mm. The focus field is inherently flatter than it is for wide angle lenses, Astigmatism is also usually well controlled at longer focal lengths.

I really don't see what you think you would gain by doing this.

*The reverse is also possible, however unlikely.

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Last edited by Digitalis; 05-04-2016 at 07:02 AM.

[Adam]

Damn! Yet another reason I'll have to buy a K-1! (I have the FA* 400mm) I never saw any rumours about this feature.

We posted about it on the homepage a number of times The complete details can be found here:
Pentax K-1 Lens Compatibility Guide - Articles and Tips | PentaxForums.com

Look below the compatibility table.

[pete-tarmigan]

We posted about it on the homepage a number of times The complete details can be found here:
Pentax K-1 Lens Compatibility Guide - Articles and Tips | PentaxForums.com

Look below the compatibility table.

I guess I didn't read the fine print. Those lens profiles also documented in the K-1 user manual, p. 108.

[Wild Mark]

In a nutshell : yes it is feasible....but with SO many Caveats. Every element in a lens is there for a reason - a well corrected lens is a delicate balance between over/under corrections. Chucking one more element in to correct a perceived optical fault can give rise to something far worse*, if the element isn't carefully manufactured, shaped and mathematically incorporated into the optical design.

Aspherical elements are rare in 35mm lenses over 100mm. The focus field is inherently flatter than it is for wide angle lenses, Astigmatism is also usually well controlled at longer focal lengths.

I really don't see what you think you would gain by doing this.

*The reverse is also possible, however unlikely.

As always, comments well made. In the case of both these lenses, the filter drawer and the selected filter inserted within it, is actually part of the optical path. Apparently they need to be installed for the lens to perform to spec.

So my thinking was to acknowledge this requirement but use a 'corrective' element for digital purposes rather than a filter for film purposes.

I will ponder some more.

[Digitalis]

the filter drawer and the selected filter inserted within it, is actually part of the optical path

Surely you know the difference between a lens element and a filter, sure there is provision in the lens design for a flat piece of glass in the optical path..putting a spherical/aspherical piece of glass will most likely disrupt this and can negatively impact performance.

So my thinking was to acknowledge this requirement but use a 'corrective' element for digital purposes rather than a filter for film purposes.

I what possible improvement do you hope to make? The lens is excellent, and my copy of the FA*250-600mm f/5.6 performs superbly on the K-1.

[Wild Mark]

Surely you know the difference between a lens element and a filter, sure there is provision in the lens design for a flat piece of glass in the optical path..putting a spherical/aspherical piece of glass will most likely disrupt this and can negatively impact performance.

No need to be patronising digitalis. It does seem to be your trait from time to time.

Yes I do know the difference. My thinking is augmented by the concept of putting a ghostless filter on the front of the lens as Asahi did back in the 1960's. You remember, the curved filter that went on the front of some 49mm filter thread lenses ........

What improvement? Correct for any aberrations arising from digital use. I haven't had the benefit of the K-1 as you have, but my experience on the K3 has been mixed for this lens. Unlike you, my expectation of satisfaction is not as high.

Regards

[clackers]

This seems like a nuts idea, Mark, so naturally I'm loving it. Hang on while I get the popcorn. ☺

[Wild Mark]

Yeah, probably a nuts idea, but hey I'm nuts so normal to me

No popcorn needed it would seem