Protective filter on MP-E yes/no?

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ChrisR
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Post by ChrisR »

Yes yes, but what's missing is any effect of changing the Working Distance, keeping the NA the same.
Maybe there isn't one, but I suspect there is.
I'll go measure some objectives!
These LWD objectives appear at first consideration, to be similar to retrofocus design camera lenses, where the exit pupil ( I think that's the right term) of say a 20mm lens, is in the middle of the mirror box somewhere.

rjlittlefield
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Post by rjlittlefield »

I agree, it seems to me too that working distance should matter.

My rationale goes like this: Both long and short WD lenses accept light from the same angles (presuming same NA). The immediate effect of the extra glass is to shift oblique rays sideways, and of course the shift will be the same for both lenses. However, the curvatures of the long and short WD lenses will be different, so the same sideways shift will result in different angular errors for the two lenses. At that point, it seems like everything gets different.

Of course it could also be that those differences get canceled by other differences farther downstream, so the overall error ends up being the same. Too complicated for me! This is a case where some careful tests could be very instructive. But I don't have appropriate objectives either, so this is definitely a job for somebody else.

--Rik

augusthouse
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Post by augusthouse »

Thanks for all the detailed info regarding the use of a UV/protective filter on an MP-E 65mm.

I've purchased a B+W 58mm MRC UV filter from:

http://www.mainlinephoto.com.au (that way I know it is genuine).

They also carry a reasonable selection of Novoflex gear for anyone in Australia who may be looking for such equipment.

Craig
To use a classic quote from 'Antz' - "I almost know exactly what I'm doing!"

DaveW
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Post by DaveW »

DQE's Lester Wareham link contains some other useful links. One that I had pointed out to me, an in depth test of filters where it proved that expensive can often be worse than cheap! In fact in the test Hoya filters came out best of all beating the most expensive for that particular type of filter. See:-

http://www.lenstip.com/113.1-article-UV ... ction.html

No doubt for other types of filters than UV ones others might come top, but we were discussing "transparent lens caps", though I understand now Nikon do produce a clear glass filter (no doubt coated) rather than a UV specially for digital cameras in a range of sizes. Though it does say UV protection lower down, but I believe clear glass stops some UV anyway does it not?

http://www.adorama.com/NK52C.html

DaveW

g4lab
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Post by g4lab »

Clear glass usually blocks almost 100% of UV when you get to the 360-380nanometer wavelength. But it stilll leaves some UVA longwave UV.

As important is the use of water white glass uncontaminated by iron which is what gives glass the greenish appearance when viewed edge on. This can add all sorts of wiggles to the transmission spectrum that you don't want.
Last edited by g4lab on Fri Dec 04, 2009 2:40 pm, edited 1 time in total.

g4lab
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Post by g4lab »

I sent a note to Roger Hicks about this thread to see if I could get a pdf of his article. Today I received this reply.
Thanks for the kind words. That article was a LONG time ago now, probably too long for Shutterbug to have it on their site, and I can't even recover it because it was written in Wordstar on a deceased 386 computer.

Since writing the article, I have seen nothing to change my opinion about resolution -- only window-glass detectably reduced that -- but I'm told (I've not tried it) that the effect may be detectable with longer focal lengths (over 100mm or perhaps 200mm) though I have my doubts. Others swear that filters give them problems with reflections but all I can say is that unless I'm shooting straight into the sun, with the sun in shot, I leave the filters on and don't get problems.

If I get around to it (an ever-lengthening list) I may repeat the experiment with something like my 200/3 Vivitar or 200/4 Nikkor and see what happens. But with anything like a standard lens, I am convinced that the objections are more theoretical than actual.
and:
By all means post it. I didn't add that as far as I recall, Ctein, a far better experimentalist than I, found exactly the same thing when he tried the same experiments.

I suppose I should add that I didn't do any research on filters and macro either, though I'd have thought that for macro qua macro, you'd not use protective filters anyway.

The BAT
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Post by The BAT »

Hi Guys,

As is usual for this site, the scientific communtity has taken this question to the outer boundaries of what is humanly possible and left most readers completely confused. . . IMHO
I use Tiffen Digital HT (hi-trans) ultra clear protective filters on my 'outdoor' lenses. Will these filters visibly affect the quality/resolution of my images at magnifications of no more than 2:1?
I'm certainly not complaining about the scientific discussions that take place, but I believe that there are fewer members who don't understand, than there is of those of you, who do understand. . . .
With respect,
Bruce

rjlittlefield
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Post by rjlittlefield »

The BAT wrote:I use Tiffen Digital HT (hi-trans) ultra clear protective filters on my 'outdoor' lenses. Will these filters visibly affect the quality/resolution of my images at magnifications of no more than 2:1?
Translating and summarizing...

Your filters are not a problem.

Just keep 'em clean, of course (says the man who stopped down to about f/90 to run some test, and then wondered where the dark blobs were coming from...)

--Rik

The BAT
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Location: Ballarat, Australia

Post by The BAT »

rjlittlefield wrote:Translating and summarizing...

Your filters are not a problem.

Just keep 'em clean, of course (says the man who stopped down to about f/90 to run some test, and then wondered where the dark blobs were coming from...)

--Rik
Thanks Rik. . . . . :D :D :D

Bruce

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