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04-04-2010, 09:02 PM   #1
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how to guesstimate focal length?

Hi all
I am using the bellows with 2 extension rings and for some reason the camera ( KM ) now wants to know the focal length? It may have something to do with me tightening things up on the lens's ( danged plumbers tape didnt last!)

So is there some sort of math doohey that I can use to work it out? Would a tape measure help?

Is this foggy look cause I guessed at 100mm? I know its not in focus either!



or some other reason? The rose hasnt had any pp just from LR to PSP to jpg.......
When I upped the blacks in LR it looked fine so I must ahve done something wrong?? Oh and the exif data should be back! PSP has had a patch!
if only i could work out how to make the link work
cheers
Jan

04-04-2010, 09:07 PM   #2
Ole
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The focal length is not affected by a bellows unit.

However, the camera only needs the focal length in connection with shake reduction, and shake reduction will not work well when you do macro photography. Best is to turn shake reduction off and use a tripod.

Your photo is sharp at the edge of the green leaf. The depth of field is very narrow at this magnification. To increase it you should use a small aperture, like f/11 or f/16.

I don't know what lens you used. If it is not a dedicated macro lens sharpness may increase if you reverse the lens. An adapter like this comes in handy when reversing a lens:

https://www.pentaxforums.com/accessoryreviews/showproduct.php?product=672&cat=105

Last edited by Ole; 04-04-2010 at 09:13 PM.
04-04-2010, 09:33 PM   #3
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To use shake reduction for hand-held macros, with tubes or bellows or a manual lens, add the extension to the focal length. For instance, if you put a 50mm lens on 25mm of tubes, your SR length is 75mm. And when I screw my M42 Vivitar 90mm macro out to full extension for 1:1 magnification, my SR length is 180mm.
04-04-2010, 10:00 PM   #4
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it has a dedicated lens..spiritone macrotell 1:4.5 f=150mm hmmmm didnt see that bit....shake reduction is off but a slight breeze blew up.........using a seriously heavy tripod......the head alone weighs a tonne!

so if f=150mm + 35mm in extension tubes focal length is 185mm?

ok I am lost......I am in manual focus and manual capture........when I am looking at the info screen there is no f stop? it just says f----- and the shutter speed is 0.8.........

Ok i see........this is where the stopdown metering comes into play..........


Last edited by janstew; 04-04-2010 at 10:08 PM. Reason: light bulb moment
04-05-2010, 03:52 AM   #5
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QuoteOriginally posted by ricstew Quote
it has a dedicated lens..spiritone macrotell 1:4.5 f=150mm hmmmm didnt see that bit....shake reduction is off but a slight breeze blew up.........using a seriously heavy tripod......the head alone weighs a tonne!
Yes, if you're on a tripod, SR must be turned off.

QuoteQuote:
so if f=150mm + 35mm in extension tubes focal length is 185mm?
Well, sort of. 180 (closest possible to 185) is what you TELL the SR robot when you're going to shoot handheld.

QuoteQuote:
ok I am lost......I am in manual focus and manual capture........when I am looking at the info screen there is no f stop? it just says f----- and the shutter speed is 0.8.........
I assume you're using inexpensive tubes that don't communicate between lens and camera. In that case, the camera doesn't know what f-stop you've set the lens, so the info screen says f-----.

QuoteQuote:
Ok i see........this is where the stopdown metering comes into play..........
Hey, now you're getting the hang of it!!
04-05-2010, 09:36 AM   #6
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QuoteOriginally posted by ricstew Quote
I am using the bellows with 2 extension rings and for some reason the camera ( KM ) now wants to know the focal length? It may have something to do with me tightening things up on the lens's ( danged plumbers tape didnt last!)
Unless these are very rare bellows and extension tubes that transmit lens information, then it's normal that the camera would ask for focal length. It's what it does for all manual aperture lenses (lenses where the aperture is set using the aperture ring rather than the controls on the camera).

QuoteQuote:
Is this foggy look cause I guessed at 100mm? I know its not in focus either!
I'd guess flare, or a light leak in your bellows.
04-05-2010, 01:10 PM   #7
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Am I missing something, or perhaps indeed, the OP a) doesn't really understand how shallow DOF can get at these magnifications, and b) Spiratone lenses and things, while a sincere effort at making good stuff affordable, and often by present plastic standards, on the low end of 'They don't make em like that anymore,' ...Not ever having been things one would really call 'Top quality optics?'

Before there was Ebay, there was Spiratone. They'd sell in sort of catalog form, mirror attachments that would ostensibly allow you to photograph people in bikinis without them noticing, alongside all manner of connectors and things retail wouldn't necessarily bother to stock.

Their in-house lenses were actually made by some people considered respectable brands today. But not necessarily their best.
04-05-2010, 01:36 PM   #8
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flare is what it is! worked it out when I shifted around the light source........

As for question/ supositions on the focus......i know this is out of focus! it was just a grab from a series........to show what turns out to be flare!
and of course I know this is not a $$ lens.............its just for playing with........im dumb but not stupid)
I have to say this is my first use of a digital camera..........and I didnt "do " macro with film......so the actual usage of all the dials and switches are new to me!
cheers
Jan

04-05-2010, 02:59 PM   #9
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I have some suggestions:

You've already found that flare isn't your friend. Make sure that direct light doesn't hit your lens. Your light source should be behind you, and beside or above you.

You've probably read the Sticky.post atop this forum on using manual lenses. I often use trap-focus with manual lenses. Go into the Custom Menu and set Catch-In-Focus ON. Set the Focus Mode to AF.S. This enables trap-focus with manual lenses; automatic lenses ignore it. To disable trap-focus, just set Focus Mode to AF.C or MF. On my K20D, that's a simple flick of a switch.

For tripod macro work, set the camera to M(anual) mode, with SR off, and Focus Mode to MF. Set the Drive Mode to 2- or 3-second self timer, and I recommend using a remote. Focus on the subject with the aperture wide-open, get a green focus confirmation light, then stop the aperture down, hit the Green button to get the exposure reading, and shoot.

For handheld macro work, tell the SR robot the focal length plus the extension length. Set the Focus Mode to AF.S to enable trap-focus. Now aim at your subject. Set your aperture to an f-stop where you can see it well. Hold the shutter down. Slowly bring the subject into focus. When it's in focus, the shutter will automatically snap. That's trap-focus, the poor man's AF.

I hope this helps. You should be able to get decent results, even with a Spiratone lens, as long as the aperture is stopped-down a bit. Have fun!
04-05-2010, 11:39 PM   #10
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Thankyou so much Rico! Thats confirmation that I was doing it correctly.......
My light source was way too bright.....I was outside even with the sun shielded thru a white cloth it was still too bright. I could hardly see thru the eyepiece and not see the screen much at all.......
and I am after ' decent' results...not world beaters....at least untill i work it out ......
thanks
again
Jan
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