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03-29-2010, 04:22 PM   #1
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Difference in optical formulas?

What's the difference in optical formulas between M and A lenses (and other lines as well)? I really don't know anything about this subject matter.

03-29-2010, 04:30 PM   #2
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You can't really make a general statement on the formula of A lenses vs M lenses or any other series. In fact, there are examples of different formulae WITHIN a series. Therefore, it has to be considered on a lens by lens basis.
03-29-2010, 04:45 PM   #3
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Take a look at the clickable table of normal primes at Dimitrov's site. If the formulae are shared in a cell the series are essentially the same. However even if they have the same number and arrangements, there could be other subtle differences such as ED glass etc.

Pentax Normal Prime Lenses

As you can see in this example, all of the 50mm f1.7 lenses have the same formulae but the f1.4 lenses do not even though the may have the same number of elements and groups. Damned if I know what different about the f1.4 K & M or either of those compared to the A/F/FA f1.4. It could be the size of the glass, glue and or coatings. Apparently Dimitrov had enough information to separate them in his table.

For a second example, compare the M 40mm pancake and the DA 40mm ltd pancake. In addition to some element redesign the Da has Ghostless Coating on the rear element.

M



DA ltd

03-29-2010, 04:49 PM   #4
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Here is an example of an M series lens that has 2 different versions. The 1st and 2nd M versions are different but the 2nd M version and A are the same!

The M 28mm f2.8

Version 1



Version 2





You can tell the 2 M versions apart by looking at the Face. If the serial number is on the face, its the 1st version. The second is on the outer ring typical of the A series. Some think that Pentax did this because they were out of the early elements but weren't quite ready to release the A version so they made the 2nd M version in the interim.

03-29-2010, 04:50 PM   #5
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As you can see, there is no simple answer to your question other than becoming a collector and historian of all things Pentax.
03-29-2010, 04:54 PM   #6
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QuoteOriginally posted by Blue Quote
As you can see, there is no simple answer to your question other than becoming a collector and historian of all things Pentax.
I don't mind being that! but I'm not old enough ;(. (sigh) oh well ;P I'll just base it on looks and feel then!
03-29-2010, 04:56 PM   #7
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QuoteOriginally posted by NecroticSoldier Quote
I don't mind being that! but I'm not old enough ;(. (sigh) oh well ;P I'll just base it on looks and feel then!
I didn't get to the point I am over night! Hang in there. Some time in the future you will wake up and look in the mirror and go :wowcb:
03-29-2010, 05:25 PM   #8
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QuoteOriginally posted by Blue Quote
I didn't get to the point I am over night! Hang in there. Some time in the future you will wake up and look in the mirror and go :wowcb:
Haha! Naw, "You're old, when you're old" As my dad likes to say!

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