First off, I'm sorry for the slide-show, but I've had this lens a long time now and I'm fed up with it. A while back I tried adjusting this ring to either extreme and couldn't see a difference.

No matter what I do I cannot get SHARP pictures with this lens. The view-finder will confirm I'm in focus. Even if I use my camera's live-view I cannot get very sharp pictures with it.

As I said I've had this lens a while and in that time I can now just "lift the camera" to my face and look at stuff, I've also gained quite a steady hand, I can usually go as low as 1/400 with 1500mm and 1/160 for 500mm before my movement becomes a problem. To eliminate that though, the 1500mm pictures were shot at 1/4000th and the 500mm at 1/1000 (the day wasn't so bright)

enter image description here

First picture, here's what I think to be some sort of calibration ring, when I first tried it (according to a guide I found online) I tried either extreme, middle, you name it but couldn't really see a difference. However it seems to move back and forth – so probably calibrates something!

The ring I am referring to here moves if the screw just to the left of "FEET" is loosened, not sure about the collar behind that.

500mm pictures 1/1000th shutter enter image description here This is probably the best one, in the view-finder I could see the circles that indicate a good focus, the rangefinder dot was on, however if you zoom there's not much detail there!

1/4000th shutter enter image description here With both of these, I took a series of pictures moving the focus ring ever so slightly, these are the best ones.

1500mm pictures All 1/4000th enter image description here enter image description here enter image description here

As you can see, they're VERY fuzzy, especially the bottom one (for some reason) – I simply cannot get better than this!

I'd really like to get nice pictures of the moon, but I really cannot get past this. I am sorry for the slide-show, I want to convey "look, it isn't just out of focus!"

Note: I had to scale these pictures quite a lot, if you want a link to a full-size one, just tell me.

  • \$\begingroup\$ Yeah, you should link the pictures to full crops if you want to talk about sharpness. Also tell us what camera you're using. \$\endgroup\$
    – feetwet
    Commented May 15, 2015 at 16:22
  • \$\begingroup\$ @feetwet I'll do that now. \$\endgroup\$
    – Alec Teal
    Commented May 15, 2015 at 17:00
  • 1
    \$\begingroup\$ Also maybe tell us which lens? \$\endgroup\$
    – inkista
    Commented May 15, 2015 at 23:02
  • \$\begingroup\$ At those focal lengths you really should be using a tripod if you want to get the best results. Are you? \$\endgroup\$
    – Michael C
    Commented May 16, 2015 at 0:26
  • 1
    \$\begingroup\$ Also, at those magnifications, atmospheric turbulence becomes an issue. Longer focal length and longer shutter speeds can dramatically increase that effect. \$\endgroup\$
    – agtoever
    Commented May 16, 2015 at 11:09

2 Answers 2


No, you don't need to calibrate it, you need to calibrate you expectations: I could be wrong, but (judging from the cap and the use of green for the metres) that looks a lot like the old Vivitar 500mm F8 from the stone age (Pentax mount?), maybe one of the cheapest and worst mirror lens ever sold, unable to be sharp even if shooting at a knife. So yes, your 500mm shots are more or less what one could expect from a mirror lens; the 1500mm shots, on the other hand, are a really an interesting mistery, as your 500mm is...well, a 500mm: how can you shot at 1500mm with a 500mm lens? Are you using a 3x teleconverter? If so...that is all the quality you can expect.

In both cases, if you just want a confirmation of its "qualities" and to just check the focus ring (but you'll need a lot of space for this) you can download from everywhere a front/back focus test image -I usually use this http://2.bp.blogspot.com/-1G5zs4s9ctQ/UwMLB2ZhJdI/AAAAAAAAAbY/f9fAF6zDQVk/s1600/Test+Focus+2.jpg - and do a bit of testing. It's easy, cheap and instructive.


Do use a sturdy support or tripod.
Focus on a point-source (a star, say) so there's no mistake about the subject interpretation.
Alternatively, you could use a laser on an optical bench to collimate your lens. Any collimated source is what you're after.
Manually, set infinity and squeeze off a shot.
Manually, find the best focus, and compare the focus-ring position difference if any.
Adjust the "ring" and compare.
Repeat until there's no difference.

I believe you will be adjusting the back-focus.


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