Stacking

I've readed some time ago about stacking lenses to get a bigger magnification with a lens. Recently I've bought the DA 40/2.8 ltd and hold that one infront of a D-FA 100/2.8 macro to see what it does.
I like the results but since the DA 40 doesn't have an aperture ring I need to keep it open manually.

I've been looking for a lens that stays open and has a 49mm filter size so that I can screw it on the 100mm macro with a coupling ring, i've found these so far (all pentax).
M 20/4
(all) 28/2.8
M,A 28/2
(all) 35/2

Does someone have experince with these lenses stacked,
I'm afraid that some will cause vignetting when used with the 100mm.
The sharpness is also quite important but since they are primes I think that isn't a problem.

Also what is the magnification with these lenses.
I believe you can calculate it like this.
lens on camera/lens stacked = magnification, so...
100/20=5x
100/28=3.6x
100/35=2.9x

Thank you very much for your time and I hope you can give me some advice

Stefan.

As you'll be using a reversing ring then the mount on the lens won't matter, so you could save a bit of money by going for lenses that fit in the "good-but-generally-unwanted" camp. Two candidates spring to mind with 49mm filter sizes.

The first would be the Helios 44-4. A russian built 58mm f2 lens that was the "kit" lens for generations of Zenit cameras - hence they're easy to find and rarely cost more than £3-£4. Based on a pre-war Zeiss Biotar design they're extremely sharp and built like the Russian T35 tanks they were mostly recycled from. Very early versions were manual, the latest versions were/are auto but can easily be converted to manual operation in under 2 minutes. These will normally be M42 mount so with an adaptor you can turn it round and use it as a fast portrait lens (warning: the adaptor will cost approximately 5 times more than the lens! ).

The second (and I think even better) option would be a Zeiss (CZJ) Flektogon 35/f2.4. These can actually fetch quite high prices in M42 mount (not really suprising as they're excellent lenses even by modern standards), however, a fair number were also built using the obsolete Practika B Mount - which nobody wants! The B-Mount versions therefore are harder to find but fetch peanuts when they do come along, certainly worth keeping an eye out for.

If you want to keep your kit all-Pentax then the M50/f1.7 is an astonishingly sharp lens, has a 49mm filter ring, a flatter field of focus then the f1.4's and you can pick up mint ones for around £10-£15. It even has a K-mount so if you want to use it the "right" way round then there's no adaptor required!

If you want to pay more money then there is an almost limitless list of lenses that would do the job - as you've already noticed the ones with a shorter focal length will give you greater magnifications. Happy shopping!

If you cant find a 49mm thread lens, buy a different lens, and use a step down ring.

One thing I'll add is vignette is a big problem with reversing one lens in front of an other. I tried with a 28mm f2.8 in front of a 200mm set at f11 lens and the vignette was severe.

Vignette was bad even with a 50mm f1.7 reversed on the same 200mm lens.

First of all sorry for my late reply, I was quite busy
Thank you all very much for the comments and advice!

Zeis sounds always good, how hard are they to get with a B Mount. Do you see one of them monthly or is it much longer then that?

Hi Tyr,
the 28/2,8 is good avaible secondhand here, so it was my first choice before you came along with your vignette.
Was that on an analogue system, I'm using digital and I'm hoping that the smaller sensor will crop away (most of) the vignette. I didn't had noticeable problem with vignette with my combination.

I have seen a couple on eBay before but they're very rare. There's one on there now from a dealer but it's been converted to Canon mount and he's asking even more than the M42 versions normally go for! I'll be interested to see if anyone actually buys it...

You may have to wait a few weeks but one will show up sooner or later I'm sure.

After another quick scan of eBay I found this:

link

Currently standing at £15 with no bids and 3 days to run, it's a Zeiss 35/f2.4 in B mount that happens to come with a free 50/1.8, a Praktica BC1 body, some filters, manuals and a camera case. Thinking about it, you're more likely to find this lens bundled with a Praktica B-body so it may be worth your while scouring through the several hundred that are on eBay right now...

Thanks a lot Hefty,
I've never bought anything from ebay before and I just invested in a Cokin system.
I need to settle down the expense a bit but it's good to know they aren't that rare and expensive.
Will surely keep my eye open for them!