Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-30-2013, 07:53 AM   #1
Veteran Member




Join Date: Mar 2010
Location: NewYork
Posts: 899
anybody used a 420-800mm (opteka/kenko), mine has a problem

I was actually looking for a little bit better cheapo preset long lenses and impulse bought an opteka 420-800mm (curious how the cheapest of the cheap compared at 800mm to a little bit better 400mm cheapo and a semi cheapo 2x telconverter). It was cheap on ebay.

So its got a possible functional problem (or cheap design) and I was wondering if anyone had used one, and if theirs did it. When you want to zoom, you turn a lock ring and it just push pulls. When I zoom it though, its got a dragging sound. If you have ever had a push pull lens of any kind where one of the metal tubes scrapes along the inside of another it sounds like that. In other words, on many tubes lenses are made of, there are fine rings from it being machined. If you have even taken apart some push pull zooms or perhaps other types to, you have probably heard this sound putting it back together. Its like you were dragging your finger nail or a piece of metal lightly across those rings. Its not gouging and doesn't seem broken. The lens seems almost new so I was wondering if they were just this quality level or if this was actually their idea of anti zoom creep on the cheap. Its very distinct and I have hard it lots of times, even working on older but very good quality lenses (of course they don't do it once thy are fully assembled).

Here is the weird part. I took it apart and the main tube is oversize with a large piece of very thin felt like material glued in place covering the whole inside of the tube to provide tighter tolerances (a rather cheap way of doing it but it seems to work). There is no metal to metal contact that I can find, so how am I getting that metal to metal noise? There is a helix but its movement is minimal so it couldn't be inside. All I can think is a bur dragging somewhere or its is by design to stop zoom creep?

07-30-2013, 09:17 PM   #2
Veteran Member




Join Date: Mar 2010
Location: NewYork
Posts: 899
Original Poster
I would still be interested in knowing if anyone else has this lens and if it does it, but it was bugging me too much so I took it apart the rest of the way and found the problem. It was in fact in the helix. The machining was too rough on one part with sharp edges (the center assembly that holds the rear elements) and it was in the helix. Based on its minimal movement and kind of loose fit in its tube, It probably won't ever cause a problem other than being annoying, but also due to its minimal movement it will probably never wear in unless the lens gets substantial use. I gave it a light polishing but that didn't help. I may give it a heavier polishing later Or I may just ignore it. The lens looks like new or close to it so I think its just the way its made (its a very cheap lens after all). It won't effect function.

As far as the lens, I had anticipated it having unusable image quality (bought it on a whim cheap and wasn't expecting much). I was pleasantly surprised (relative to what I was expecting). I think it might be a bit better than my tou five star 500mm (which isn't saying much other than usable but not great or anything). It of course had a nice purple edge when I shot a crescent moon on the round edge (actually not that bad without pixel peeping but quite visible zoomed in). Oddly, I tried it on white vehicles with a telescope adapter in bright sunlight (didn't take any pictures of that yet) and didn't see any purple fringing? that usually causes it a lot with the tou five star 500mm.

For $25 shipped, it will be a fun toy to play with a little (moon shots or even just as a telescope with a telescope adapter for the kids). I'll have to see how nasty the image gets with a teleconverter or two, lol. the image quality actually seemed decent enough with a telescope adapter (which doesn't seem to be so demanding as a camera). Plenty good enough for the kids anyway.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
cheapo, k-mount, lenses, metal, pentax lens, piece, push, quality, rings, slr lens, sound, tube, tubes
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Anybody with A 50 1.2 and K30? I have a problem. simbon4o Pentax K-30 & K-50 20 04-17-2013 05:04 AM
Has anybody else had such a bad experience with a Kr mellenby Pentax K-r 7 11-11-2012 11:43 AM
K10D- what a great camera mine has been... lesmore49 Pentax DSLR Discussion 16 03-03-2012 08:04 AM
Has anybody had success in using a "Powermonkey" to charge a D-Li90? Roughrider Pentax K-5 6 12-31-2011 05:23 AM
Has anybody used a Wacom Bamboo Fun tablet? heatherslightbox Digital Processing, Software, and Printing 7 05-13-2008 03:49 AM



All times are GMT -7. The time now is 08:51 AM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top