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08-19-2013, 07:56 AM   #1
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300mm, M* v A*

I've got a couple questions about the M*300/4 versus the A*300/4.

1) Are they the same lens except for the A setting? (ie, same glass, same coatings, same build materials)
2) I've found a couple A*300's for sale, but so far no M*300s. Would you expect a difference in resale price between two copies in identical condition?
3) What's the best TC to match to either one?


08-19-2013, 08:02 AM - 1 Like   #2
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I believe they optics are the same, yes. You can verify this in our lens database, but I'm fairly confident of it.

The M*'s are rarer (but not necessarily more expensive) as it was one of the first star lenses. That being said, I'd go for the A* over the M* as it's got auto aperture.

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08-19-2013, 10:45 AM - 1 Like   #3

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Hi jcdoss,

AFAIK, the optics are the same, both 8 elements in 7 groups. There appears to be a difference of about 1 oz in weight, with the A* being heavier which makes sense. I haven't followed market values closely, but from what I've seen, M*s usually start at @ $400 USD and up and A*s in similar condition start at @ $500 and up. The asking prices have been in these ranges for atl least the last 7 years, with a slight increase in average asking prices in the last few years.

I've had the A* -- replaced it with an FA* 300/4.5 for AF, better CA/PF control with the ED elements, and 2m shorter Minimum Focusing Distance -- the MFD difference is very significant for me, as I prefer to shoot close when possible.

The best TC by quite a margin, IMO is the Pentax F 1.7x Auto Focusing Adapter. This on adds AF capability to MF lenses, though with telephoto FLs, the focusing range is limited, and manual prefocusing is necessary. Some don't like this, but personally, I prefer this as it acts as a very easy to use focus limiter. The AFAs are currently pretty expensive, but worth the money if you shoot tele a lot as MF long tele lenses are significantly less expensive than AF models, and the AFA tends to pay for itself with the purchase of just one fast long tele. One caveat though -- Pentax bodies need an effective max f-stop of faster than f8 for the AF system to get enough light to work effectively, so a max aperture of @ f4.5 is about the limit for a lens you plan to use with the AFA since a TC adds to the effective FL of the lens, and you need to multiply the max aperture by the magnification factor to get the effective max aperture for the combination. This is okay though because in tele lenses, faster usually means better optics, and TCs magnify flaws in optics, so the faster, better lenses perform better with TCs. With the A*, you would retain AE and the ability to control aperture from the camera. Also, since an "A" series lens in the A position, allows you to focus wide open, then stops down automatically at exposure, it allows you to conveniently use the lens stopped to any extent. ith the M*, you could only meter stopped down, and the AF capability would be compromised quickly as you stop down past f4.5 on the lens.

Other TC choices would all be MF with either lens, and the M* would be MF and ME. The best, in order of quality are the Pentax Rear Converter A 1.4x L (if it will mount), Tamron F 1.4x PZ MC4 (this is an AF TC, but it does not add AF capability to a MF lens), and the Sigma EX 1.4x APO TC (I think the EX 1.4x APO DG will also mount and work, but am not absolutely sure -- these are also AF TCs, but they don't add AF to a MF lens)

Personally , I don't use 2x TCs as I haven't found any that perform well optically. The Pentax Rear Converter 2x L is supposed to be excellent, but I haven't tried one, so can't say from direct experience.

08-19-2013, 01:01 PM - 1 Like   #4
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I don't want to discourage you from these lenses...I had an M*300mm and it's build quality was absolutely stellar. It was also very sharp.
But, its purple fringing can be terrible, to the point where some photos were almost unusable unless I went to black and white. Just something to keep in mind.

08-19-2013, 01:17 PM   #5
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Thanks for your input, everyone! I know about CA and M lenses... I've got the 200/4 and 135/3.5, both of which are strongly affected sometimes. Lightroom seems to do a fairly decent job of cleaning up even the worst of the CA in 200/4 shots, so I'm not too concerned about it. I'm really enjoying using the M's I have so far, but I'm thinking about adding the 300/4 A* instead of the M* just because I know of a couple A*s already for sale.
08-19-2013, 02:25 PM   #6
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Like others say the optics are the same, but the M* looks better, IMHO, with the "chrome" ring on the focusing ring.
08-19-2013, 03:53 PM   #7
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Even if the number of lenses in the objectives taken into account is equal does not mean anything like they are the same in terms of optical solution. Type of glasses can be, and most likely are different, curvatures elements may also be different, which is seen in how bodies are constructed.

A real comparison can be done only in parallel, on extremely demanding topics, such as stars, or the bank of samples.

Personally, knowing that the function dictates form, I think the two are quite different.

I must stress that I have not tried neither of this lenses, and my comment came only from knowing a little about optics. And, looking at the shape of this lenses, anyone can imagine how the rays of light goes through the lens.

Last edited by JimmyDranox; 08-19-2013 at 03:59 PM.
08-21-2013, 01:38 AM   #8
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CA and PF might not be an issue.
In focus area is very sharp. Only out-of-focus area has PF.
At f4 both has minor glow. Step down half click the glow is gone.
Both are very good lenses.


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