How do you focus Pentax SMC F 35-70 macro Zoom lens?

[jun]

I have a SMC F 35-70mm zoom lens by Pentax, i am using it on a sony nx via adaptor so autofocus is not available.

i am used with other zoom lens where in you can set the zoom level 35, 50, 70 or anything in between then afterwards you turn the focus ring to make the images sharp.

on this particular lens there is no "focus" ring? the zoom and focus ring are the same? so in effect you are getting a sharp image by turning the zoom level ring?

i am sure if i have the name for the parts of the lens right.

am i missing something in how this lens operate? there is another ring on the front of the lens but turning this has no effect on my image.

[TBaker]

Does it look like this one?



If so I imagine the front ribbed ring is the focus.

[Spotmatic]

I have the transparent version of that lens

http://i385.photobucket.com/albums/oo293/spotmatic/sfxtransparent/IMGP1127.jpg

Indeed, the front ring is the focus ring. Make sure the zoom ring isn't in macro mode otherwise you can't focus up to infinity.

[TBaker]

Really? They sold a transparent version? Man Pentax are out there.

[jun]

yes that is indeed the same model as my lens. i tried turning the front most ring but there is really no effect on my images.

are you using this on a pentax body that can autofocus the lens?

i am thinking that the front ring is an electronic sensitive ring. meaning the focus is transmitted to the motor as the user turns this ring on a pentax body that has autofocus control on the lens.

the sf1 body where this lens came from is "dead" so i can't test it .
thanks

[Spotmatic]

@Tbaker: yup, this was a demonstration model. The lens is fully functional, the body isn't (because of the transparent back).

The focusing ring is not electronically coupled to a motor inside the lens. Please look at the back of the lens, in the bayonet. In the bayonet a small slot for the screwdrive focus should be visible. You can turn this with a small screwdriver. While you are turning the focusing ring should rotate (as it is directly coupled).

If nothing happens then I think your lens is defective.

[jun]

@spotmatic

i just checked the lens and indeed there is a small screw on the back of the lens that also turns as i rotate the front ring. so everything is properly atached but i can't focus using this ring.

i am now only using this as a macro lens since i am able to focus properly using the focal ring (not the front focus ring) when doing close up shots or when the focal ring is in the macro green area on the left.

[nemesis101]

Weird!

I have three (all came as kit lenses on film SLR cameras) and all focus on my Pany L1 by merely turning the ribbed ring.. it's easy to check as the lens barrel goes in and out!

Doug

[jun]

hi

when you say ribbed ring are you referring to the middle ring with the markings - macro - 70 50 35?

or

the front ring that moves the words in the clear plastic panel?

i am able to focus using the middle ring but it focuses as the ring goes from 70-50-35. somewhere within this range the image would focus although not sharp or difficult to get sharp pictures. it's a hit or miss.

i am wondering if you could say set the focal length to 50mm and then focus the image using the front ring.

this is not how a zoom lens work right?

i have a sigma 80-200 and you first set the desired focal length then you turn the barrel to focus your image.

[Spotmatic]

I'd say that somehow the "macro" setting got coupled to the 35-70 range, instead of after the "70" range. Could this be possible? When you want to enter the macro range there should be a firm "bump" at 70mm, with a little more force you can move beyond 70 and then enter the macro range. Does this still work in your lens?

[jun]

^Yes you need to exert a slight force to enter the macro range. the macro range is fine. i find it easy to focus in the green section. actually i focus using only the middle ring.

[RioRico]

Focus: Turn the very front ring, the one with very fine knurling.

'Macro': At 70mm, closest focus is about 40cm / 16in. Go past the bump, and you can no longer reach infinity focus. At maximum 'macro', closest focus is about 20cm / 8in. At least as I measured, in crude tests.

Go here [ http://www.pentaxforums.com/lensreviews/SMC-Pentax-F-35-70mm-F3.5-4.5-Macro-Zoom-Lens.html ] for user reviews.