First Tube Close-Ups

Just experimenting with new extension tubes - which then got stuck!! (see troubleshooter thread) - but I got a few shots.

Just looking for general feedback on the close-up aspects to see if the tubes are the way to go. The lens is the Pentax 'M' 75-150 f4.0, on the K7. ISOs were 800 or 1600, so pushing it a a bit on the K7, but it was just a try out.

Are these shots actually real 'close-focus'? - Is this the sort of performance I should expect from tubes ? Its not 1:1 macro, but not too far off I think? Would appreciate any technical thoughts and feedback re the close-up / macro effect. Many thanks!


























Thanks for looking and any thoughts

These are the easy ones Nigel - now it's time to try some on live subjects! It's difficult to provide any constructive comments on this set as it is purely a set of test shots. We need to see some from 'out in the field' so to speak.

Cheers
David

Thanks for looking David, you may have misunderstood me - Its the first time I've used tubes, so I want to know if they seem to have been used correctly in relation to the lens and the magnification performance. More specifically, is this the expected magnification with 3 tubes together on a 150 mm lens - does this setup seem to be working properly based on these test images? Aperture was f6.7.

You're not going to see any macro live subjects from me! I'm not at all interested in insects or scary bug shots I am interested in getting good detail close-ups of flowers though (as I was asking about in the 'Pixels or Glass' thread) - I guess the magnification I'm getting with this tube set-up would be plenty for flowers?

Do you think the DOF effect and IQ you can see (bearing in mind thes are at ISO 800 on the K7) is good, and is to the level that can generaly be expected with such a lens and tubes? Sorry to be so specific in the questions!

There is very limited DOF at close distances, so smaller apertures may be necessary. It would not be unusual to use f/22 or f/32. This needs to be coupled with very careful focusing.

I'm not quite understanding your question as to whether this is the expected magnification. Using a set up like this, what you get is the magnification you get, there's no deviation from that. So there's no sense of there being a situation where it isn't doing that.

I don't think there's necessarily a 'correct' or 'incorrect' way to use tubes Nigel, it's down to what results and effects you wish to achieve. The aperture you chose will give very shallow DOF, this may be what you want or it may not be. The tubes have certainly allowed you to magnify the image and this will be enough for most flower shots. The DOF will work against you for flowers though, as usually they require a bit more depth than the shots above are giving.

When I said 'we need to see some shots from out in the field' I wasn't necessarily meaning 'insects', I was meaning shots of your intended subjects, whatever these may be. I think you'll find it difficult in outside conditions to get the sharpness demonstrated above, as even slight breezes will mean a fast shutter speed is required and inevitable compromises start to come into play between aperture, shutter speed and ISO settings. It's all great fun though, so have a go! You might find you get on fine with it, or you might find yourself yearning for that Sigma 105 Macro which is sharp from F2.8 and has great bokeh!

Regards
David

Thanks John & David - I was just trying them out under the conditions available - that was window light, handholding, SR on, and my aperture was limited by acceptable ISO & shutter speeds. I'm happy with the 'closeness' and sharpness, so I guess thats the main thing. Obviously I'm going to struggle with shutter speeds at ISO 100 even in brighter light, and a tripod doesn't help with subject movement.

Bye the way, does anyone know if there is any effective light loss with tubes - not in the normal sense as there's no elements involved, but does the extra length make any difference? I imagine it would be very small if it did, as the light is still just travelling straight in from the rear element of the lens.

John, in relation to the question about magnification - I think I'm just looking for some reassurance that its all working as it should - based on the lens focal length and the 3 stacked tubes - that this is the sort of result that is expected. It sounds like all is OK from what you have both said, so I am pleased with that. Now I just have to learn how to get the damn mounting ring off the lens !- back to the other thread ....

There is a light loss with tubes, and you can check this by taking a meter reading with and without them. What many may not realise is that there's also a light loss with lenses that use helical focusing. The lens group is moved away from the camera body to focus closer and in effect the lens itself is a very short extension tube.

That's one reason that traditional lenses limit their magnification to about 1:10, so a 50mm lens focuses down to about 0.5 metres.

You might find this tutorial of interest.....

http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm

The same page has a handy calculator.

Also download the PDF Manual of Pentax K tubes it gives the magnification and exposure loss for each tube.

The old rule of thumb with a 50mm lens used to be.......
Light loss = 1 stop per inch of tube.

With any lens (set at infinity) you need the focal length again in
tubes for 1:1 so 50mm lens + 50mm tube = 100mm .....
Light loss = 2 stops.



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Nigel, stop worrying about technical issues - just go out and take some photos.

Personally, I like using a M75-150 f/4 with extension tubes. I find it easier to focus than using a prime. Also, esepcially at the apertures you will (probably) be using, it's as sharp as anything else you could use.

Andrew

A strange thing about the 75-150mm is that it's actually sharper
at the 150mm end than the 75mm. Most lenses are the other way around.

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No doubt about it, this little M 75-150 is a real gem, and now its going to get a new lease of life for close-ups. Thanks for those tutorials and technical tips Algi & John.

Did someone mention taking photos now ? Ah well then, you all know you're in for some treats now with many a set to come of technically proficient, sharp, low noise left-brain thinking mediocre macro images fit only for the recycle bin !!!!!!