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08-25-2011, 10:51 AM   #1
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is this one and the same lens?

First post here and looking to make sure I'm looking at the right thing.

Pentax SMC P-DAL 55-300mm f/4.0-5.8 ED Auto Focus Telephoto Zoom Lens

PENTAX DA L 55-300mm F4-5.8 F/4-5.8 ED LENS

is this one and the same lens? I am aware that pentax lens' are sometimes prefixed SMC. In all other respects the lens details are the same, just wanting to make sure.

tia

08-25-2011, 10:56 AM   #2
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Yes they are the same lens. There is a DA 55-300 (Notice no "L" in the description) that is different. The DAL version has a plastic camera mount and the DA version a steel camera mount.

Tim
08-25-2011, 11:09 AM   #3
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QuoteOriginally posted by atupdate Quote
Yes they are the same lens. There is a DA 55-300 (Notice no "L" in the description) that is different. The DAL version has a plastic camera mount and the DA version a steel camera mount.

Tim
Unlikely to be steel, it rusts
08-25-2011, 11:28 AM   #4
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QuoteOriginally posted by keithlester Quote
Unlikely to be steel, it rusts
Most Pentax lenses have a steel bayonet mount where the lens twists onto the camera body (as shown on the back of the lens in the picture below).




DAL 55-300 Lens Review

DA 55-300 Lens Review

Tim

08-25-2011, 11:29 AM   #5
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Yes it's the same. It is also optically identical to the DA 55-300 (not L). The difference with the latter is that the non-L has a metal flange, sells with a hood, and has quick-shift.
08-25-2011, 12:41 PM   #6
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QuoteOriginally posted by atupdate Quote
Most Pentax lenses have a steel bayonet mount where the lens twists onto the camera body (as shown on the back of the lens in the picture below).
You're positive that's not chrome plated brass?
08-25-2011, 12:50 PM   #7
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QuoteOriginally posted by lancer3397 Quote
Pentax SMC P-DAL 55-300mm f/4.0-5.8 ED Auto Focus Telephoto Zoom Lens
Really no need for the first Pentax...

SMCP = SMC Pentax
08-25-2011, 01:47 PM   #8
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QuoteOriginally posted by nater Quote
You're positive that's not chrome plated brass?
My 30 year old M 50 f1.4 doesn't have any brass showing through on the mount, so I would doubt it is brass (In my 30+ years as a Metallurgical Engineer humble opinion). Plus it doesn't stick to a magnet, so it is probably an austenitic grade of stainless steel (300 series of stainless). Aren't you glad you asked?

Tim


Last edited by atupdate; 08-25-2011 at 01:55 PM.
08-25-2011, 02:16 PM   #9
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QuoteOriginally posted by atupdate Quote
My 30 year old M 50 f1.4 doesn't have any brass showing through on the mount, so I would doubt it is brass (In my 30+ years as a Metallurgical Engineer humble opinion). Plus it doesn't stick to a magnet, so it is probably an austenitic grade of stainless steel (300 series of stainless). Aren't you glad you asked?

Tim
A 300 series stainless steel would have been my (metallurgical) guess as well
08-25-2011, 03:23 PM   #10
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QuoteOriginally posted by dgaies Quote
A 300 series stainless steel would have been my (metallurgical) guess as well
Talk about a thread taking a hard left turn.

Tim
08-26-2011, 10:47 AM - 2 Likes   #11
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I don't know a lot about metal, but I'll say you guys are wrong anyway. This is the inside of four loose mounts I have at the moment, some Pentax, some third-party K, various ages:



And the metal mount from an SF1:

08-26-2011, 12:08 PM   #12
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QuoteOriginally posted by Just1MoreDave Quote
I don't know a lot about metal, but I'll say you guys are wrong anyway. This is the inside of four loose mounts I have at the moment, some Pentax, some third-party K, various ages:

And the metal mount from an SF1:
Well certainly the mounts in those pictures appear to some sort of coated brass.

However, if you go to Pentax's website, under "Specifications" for the K-5, K-x, K-7, etc. and then under "Lens Mount", you'll find the following:

Lens Mount: Type/construction - PENTAX KAF2 bayonet stainless steel mount;

So it's unclear if perhaps the material used for the mounts has changed over time, if perhaps they use a different material for different mounts, or if all of them are a stainless steel with a brass core and the specifications don't specifically mention it. I suppose the next step is to remove the mount from my 55-300, take it to work, section it, and find out for sure. Then again, there is probably a better way to figure it out that doesn't include destroying my 55-300
08-26-2011, 01:26 PM   #13
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QuoteOriginally posted by Just1MoreDave Quote
I don't know a lot about metal, but I'll say you guys are wrong anyway. This is the inside of four loose mounts I have at the moment, some Pentax, some third-party K, various ages:
I would say that you have significantly more data points (based on destructive testing even) than I do, I therefore modify my initial post to "and the DA version a Metal camera mount".

Great post & worth a like from me.

Tim
08-26-2011, 01:49 PM   #14
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QuoteOriginally posted by keithlester Quote
Unlikely to be steel, it rusts
Non-treated steel rusts like crazy...
Stainless steel doesn't
08-26-2011, 02:57 PM   #15
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QuoteOriginally posted by atupdate Quote
I would say that you have significantly more data points (based on destructive testing even) than I do, I therefore modify my initial post to "and the DA version a Metal camera mount".

Great post & worth a like from me.

Tim
Notice that even though these mounts have been sitting in a drawer for a year or two and I have no idea what I might use them for, I still was not willing to scratch up the surface that would show. I don't expect anyone else to sand down their lens mounts for more data.

I have thought about design considerations. Brass might be used because it's softer or traditional or something else. It would make some sense for the sealed cameras or lenses to have a stainless steel mount as a backup to the lens seal.
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