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Extension tube with the 150mm on 645

Cuchulainn
Posted 25/01/2012 - 15:37 Link
Hi all,

I've got the 150mm f3.5 for my 645, and while it's a lovely lens, I'd like it to focus closer for tight head shots. I'm guessing the extension tube set is what I need? Looking around, I think just the tube #1 at 13mm or so should give me enough additional magnification. Has anyone any experience with this setup?
Posted 23/04/2012 - 11:38 Link
I don't have the 150 but use that trick for my 300 F4
Algernon
Posted 23/04/2012 - 12:14 Link
Extension tube or a screw in close up filter
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
Frogherder
Posted 23/04/2012 - 12:17 Link
Yes, whilst I don't have a 150mm lens, I do have 90mm, 200mm and 500mm and extention tubes will enable you to reduce the far point and simultaneously reduce the near point, thus increasing magnification. It will also reduce the depth of field accordingly.


The maths to work out the far point is D = (F+E x F)/E where
D is distant limit
E is extention length
F is lens focal length

so for a 13mm tube on a 150mm lens the far distance would be reduced from infinity to 1880mm. The near point will depend on the amount of adjustment thaat the lens travels through


regards
Bernard
Cuchulainn
Posted 23/04/2012 - 14:26 Link
That was a bump!

I'm still looking for the #1 tube - I know Pentax make some good two element diopters for the MF system, but I think I'd prefer the tube since it adds no extra glass to the system.

Thanks for the additional info everyone
hoshisato
Posted 07/09/2012 - 20:55 Link
I have used the Pentax 645 Auto Extension Tube A (14mm) on my Pentax 645 A 200mm f/4 lens with great results. I recently obtained a Pentax 645 A 150mm f/3.5 and it works well with the tube, focusing very nicely close by.
We recently had a discussion about tubes versus close up filters in the Pentax 645 group on Facebook and the conclusion was that the filter can be a bit soft on the wider apertures compared to using a tube. I picked up my Pentax 645 Auto Extension Tube for £30 at one of the online shops that normally don't even offer Pentax goods.
Cameras: Pentax 67II / 645NII / K20D / MZ-S / MZ-3 / ME
Gallery: Hans ter Horst Photography

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