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01-29-2015, 09:02 PM   #1
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A110 lens tweaks

I've reduced the aperture of the A110 lenses from f/2.8 to appx f/4 (based on a one stop change in shutter speed reported in EXIF). I used a very thin washer glued to the rear element barrel to reduce the aperture by half from ~12mm diameter to ~5.5mm. The lenses involved were the 18, 50 and 70mm FLs.

Before and after comparisons at various target distances from 10-80 feet with the Q7 reveal a very noticeable increase in both sharpness and DoF for all three lenses as might be expected by reducing the maximum aperture by one f-stop.

The sharpness of the 18mm lens is not as noticeable as for the longer lenses but the increase in DoF is very apparent making this a potential landscape option.

The 70mm approximates the typical results seen with the DA 55-300 at maximum FL with a useful bump in speed to f/4.

The 50mm lens is the big winner with this modification. Used with care it approaches the results I've seen with the DA* 200 and with an equivalent FL of about 225mm at f/4 remains hand-holdable. I've adapted a Dysan hood with a 3X magnifier for using the manual focus lenses and the arrangement allows resting against the forehead as with an OVF for additional stability.

I've never had good results trying to post comparative image results after all the JPG compression in the forums but the actual images have been impressive with these 110 lenses and with very little effort needed to adjust the aperture.




Last edited by pacerr; 01-29-2015 at 09:22 PM.
01-29-2015, 09:13 PM - 1 Like   #2
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Many of us have simply used Lensbaby aperture discs -- you can get a set for about $12 and they fit perfectly into the 110-Q adapter. I think the f11 disc gets you about f/4 on the 110 lenses...
01-30-2015, 02:24 AM   #3
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QuoteOriginally posted by pacerr Quote
I've reduced the aperture of the A110 lenses from f/2.8 to appx f/4 (based on a one stop change in shutter speed reported in EXIF). I used a very thin washer glued to the rear element barrel to reduce the aperture by half from ~12mm diameter to ~5.5mm. The lenses involved were the 18, 50 and 70mm FLs.

Before and after comparisons at various target distances from 10-80 feet with the Q7 reveal a very noticeable increase in both sharpness and DoF for all three lenses as might be expected by reducing the maximum aperture by one f-stop.

The sharpness of the 18mm lens is not as noticeable as for the longer lenses but the increase in DoF is very apparent making this a potential landscape option.

The 70mm approximates the typical results seen with the DA 55-300 at maximum FL with a useful bump in speed to f/4.

The 50mm lens is the big winner with this modification. Used with care it approaches the results I've seen with the DA* 200 and with an equivalent FL of about 225mm at f/4 remains hand-holdable. I've adapted a Dysan hood with a 3X magnifier for using the manual focus lenses and the arrangement allows resting against the forehead as with an OVF for additional stability.

I've never had good results trying to post comparative image results after all the JPG compression in the forums but the actual images have been impressive with these 110 lenses and with very little effort needed to adjust the aperture.
They look very similar to my ringbinder reinforcing ring trick and that stopped down to around f4.
Something like this is well worth doing on the 110 lens.
I thought my 70mm was the one than responded least to it.
https://www.pentaxforums.com/forums/136-pentax-q/209474-adapted-lenses-tested...thread-45.html
01-30-2015, 09:03 AM   #4
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Good to hear your positive results. Another tip: if you are using a cheap 110-Q Chinese adapter, is to paint the inner surfaces of the adapter matte black or to use black flocking. Combined with the lens discs, it's like night and day.

01-30-2015, 02:39 PM   #5
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True, however later versions (the Fotodiox PTX110-PQ for instance) seem to be well blackened except for the lens release mechanism. Paint would tend to bind it up but a permanent black Magic Marker serves to kill the reflections with no problems encountered.
02-02-2015, 01:10 AM   #6
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Nice lens mod pacerr. Stopping down a full step to f4 increases lens performance quite a bit. Sharpness increases across the frame. The 110 lenses are little jewels and it is amazing how inexpensive they are. Definetly worth picking up.

thanks
barondla

ps: sent the email with battery holder pics. Hope it helps. If you need something else let me know.
02-02-2015, 11:40 PM   #7
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Has anybody compared the Pentax 110 lenses with the Pentax 06? Since I bought the 06 lens I rarely carried the 110 lenses with me for practical reasons.

In my stack of parts I found a tiny iris diafragm that just fits perfectly into the 110=>Q adapter. I can't name a source for this part though.
02-03-2015, 07:38 AM   #8
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QuoteOriginally posted by Altglas Quote
Has anybody compared the Pentax 110 lenses with the Pentax 06? Since I bought the 06 lens I rarely carried the 110 lenses with me for practical reasons.

In my stack of parts I found a tiny iris diafragm that just fits perfectly into the 110=>Q adapter. I can't name a source for this part though.
Yeah, if you have the 06, only the 50 and the 70 are longer. I also have the Soligor 1.7x teleconverter for 110 lenses, so with the 70 that gives you a nice long telephoto in a very compact package. (The TC has it's own waterhouse fixed aperture, so you don't really need a disc when using that.) I also recently picked up all the close-up filters Pentax made for these lenses (except the 70, but that takes 49mm filters so pretty easy to find something for that also), so now I can do macro-ish shots with the 110 lenses also.

Pretty versatile system really, and the lenses are all very high quality. The 20-40 zoom is even quite sharp, a poor man's 06. (The only one that isn't as good is the hard-to-find oddball 18mm pan focus, which is fairly soft relative to the others -- you have to "stop down" to a f/5.6 or smaller equivalent aperture on that one to get acceptable images, but then you also don't have to focus it.)

02-04-2015, 03:57 PM   #9
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Do you think washer has to be really thin? I'm waiting now for the adapter and my first Pentax - 110 lens I bought last week. Waiting for both I want to do something so want to prepare a "stop down solution". I have bought a washer quite good in a diameter, but it is about 2 mm thick... Unfortunatelly reinforcing rings are not available in my country.

I will look fo another washer, but I'm just curious if the "aperture" should be as thin as possible, or quite thin is thin enough
02-04-2015, 04:07 PM   #10
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QuoteOriginally posted by Piotrek K Quote
Do you think washer has to be really thin? I'm waiting now for the adapter and my first Pentax - 110 lens I bought last week. Waiting for both I want to do something so want to prepare a "stop down solution". I have bought a washer quite good in a diameter, but it is about 2 mm thick... Unfortunatelly reinforcing rings are not available in my country.

I will look fo another washer, but I'm just curious if the "aperture" should be as thin as possible, or quite thin is thin enough
If you stick it on the lens itself, it must be thin. If you fit something into the adapter (much easier), it can be thicker.
02-04-2015, 04:22 PM   #11
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I made an M43 adaptor for the Pentax 110 lenses including a stop for the 18mm.
After some experimenting the stop I made had a sharp angled, thin inner circumference.
The position of the stop behind the lens has a big influence on the sharpness at the corners.
The project is documented on PF, and should show up with a search, including a sketched diagram of the adaptor with the stop position relative to the lens register.

Here is a typical photo with the 18mm on the M43. ( posted before)
showing its quality (not as good as a K-mount lens) but it is a fun combo to use, not critical of focus, deep DOF, and in auto exposure, anybody can use it.
https://app.box.com/s/ekcx42yyv6i1y2vdzok0
02-06-2015, 01:38 AM   #12
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Do you think the thickness of the "aperture" is meaningfull for diffraction/sharpness in this case?
02-06-2015, 08:14 AM   #13
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Well, light rays passing through the aperture aren't parallel so it makes sense that the "thicker" the walls of the aperture, the more potential internal reflection angles there are -- and that ain't good. I believe good practice is to make the aperture as thin as practicable.

I won't try here to cite references but a quick look at DIY pinhole lens directions is illuminating.

I normally 'bevel' the edge of the aperture a bit and ensure there's no burrs or other anomalies in the circumference of the hole as being a good practice. One of these days I plan on experimenting with asymmetric and/or multiple apertures in a disk.

A useful illustration of 'diffraction' is to observe wave patterns as they pass through the 'aperture' in a break water or between obstructions in a stream. It's no where near an exact comparison, but watch the flow pattern behind a jet engine in after burner to see how complex the 'aperture' issue can be.
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