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Forum: Pentax SLR Lens Discussion 09-30-2020, 07:28 AM  
APS-C/FF speed booster
Posted By leodp
Replies: 11
Views: 1,183
YES, and that's because such a converter is designed with a working distance for a Nikon F mount camera -->46.5mm from flange to focal plane, similar to Pentax K 45.46mm


I think also that said before is not fully correct,including the Wikipedia article on Telecompressors (the note on back focus).
I see that in astronomy people regularly utilize telecompressors, and that what matters is the "telecompressor working distance" or back focus requirements, which is specific only on how the telecompressor is built:
Agena's Guide to Focal Reducers
also here:
Optical Enhancements: Focal Reducers, Field Flatteners and Coma Correctors - Camera Concepts & Telescope Solutions
Some people which have a poorly built telescope and cannot focus at infinity even utilize telecompressors with a great working distance, in order to regain infinity focus.

I made a test with a 2x Vivitar MC Teleconverter, on my K-70, with a Porst 55mm/F1.2 lens.
At infinity the focus did not change at all: no need to change the lens focusing.
At minimum focusing distance also no change at all. (images attached: 55mm, 55mm*s, central areas rescaled, compared)

--> The TC does not change the focusing of the lens at infinity or at minimum focus distance, and the lens focusing behaves as it would without the TC.
So why should it change with a telecompressor?

---------- Post added 09-30-20 at 04:35 PM ----------

Bottom line: if anything usable exists, both mounts probably need to be exchanged and it's going to cost a lot of money, which are better invested in, for example, a used FF K-1.

Thanks to all for helping to clarify.
Leo
Forum: Pentax SLR Lens Discussion 09-30-2020, 05:34 AM  
APS-C/FF speed booster
Posted By leodp
Replies: 11
Views: 1,183
Not with tele converters. I used one to magnify astro shootings. The moon is not at infinity, but it's enough for the reach I need :-)
Forum: Pentax SLR Lens Discussion 09-30-2020, 05:19 AM  
APS-C/FF speed booster
Posted By leodp
Replies: 11
Views: 1,183
Why? Teleconverters up to 2x exist freely, you can even stack them. It should not be different for focal reducers.
Forum: Pentax SLR Lens Discussion 09-30-2020, 03:07 AM  
APS-C/FF speed booster
Posted By leodp
Replies: 11
Views: 1,183
Hi,
has anybody any experience of using speed boosters on an APS-C Pentax camera?
I cannot find any model with K-mount on camera and on lens side, what they sell is intended to adapt K-mount lenses on a bunch of non Pentax mirrorless and less than APS size sensors.
Maybe there's one easy to adapt (even if loosing auto aperture) and that accepts the longer flange length of Pentax DSLRs.

I own some old manual, or better: mechanical :-) lenses and would like to see how much I gain in terms of light gathering in low-light situations, and how does bokeh change.

Thanks, Leo
Forum: Photographic Industry and Professionals 09-30-2020, 02:14 AM  
Pentax K-3 II successor on September 2020
Posted By leodp
Replies: 961
Views: 84,110
And maybe electronic shutter, to avoid shutter shock in short exposition, extra long focal length fotography (birdwatching, astro imaging, ...)
Forum: Pentax Full Frame 08-06-2020, 01:28 AM  
1000mm and 1200mm lenses
Posted By leodp
Replies: 27
Views: 2,387
I own a K-70 and a 1000mm f10 mirror tele lens. The combination is different from what you're interested in, but a mirror lens is a cheap way to go if you wish to find out what the challenges are with such a tele lens: vibrations, correct focusing, finding out where your subject is in such a narrow field of view, ...
As example: I took some shots of the moon and even with a sturdy tripod the shutter release vibrations (not the mirror mechanical vibrations, as I do 2-seconds-delay photo) may cause blurred images.

You can easily find an used MC MTO-11CA 10/1000 (aka Russentonne) in some of its variants between 100 and 250$. They're not the best in sharpness and contrast, but before investing a few thousands they allow you to explore this focal range.
Leodp
Forum: Monthly Photo Contests 08-05-2020, 05:16 AM  
Alignments
Posted By leodp
Replies: 15
Views: 209
Le Rhône, with aureole of moon with incomplete moon aureole, surmuonted by Jupiter, Saturn following.
Versailles, August 2020
Forum: Pentax SLR Lens Discussion 09-20-2019, 05:23 AM  
Chinon lens won't stop down on K3
Posted By leodp
Replies: 21
Views: 2,872
Hi,
I have the same problem on a black-anodized flange on an old Porst 55mm f1.2 mounted on a k-70 body, with firmware version 1.11

Using "M" mode, with the camera set to allow the use of the aperture ring, fixed ISO setting: the green button works intermittently, probably due to a not good contact.

I scratched the flange in correspondence of where the digital communication contact is (exactly opposite to the red dot). This was sufficient to let the camera aknowledge that a lens is attached.
Now the green button correctly stops-down the iris when it should.
Thanks for the thread, it helped me a lot.
Leodp
Forum: Sold Items 12-21-2018, 12:38 AM  
For Sale - Sold: Pentax & Tamron Lens: SMC DA 50mm f1.8 (Tamron Lens Sold)
Posted By leodp
Replies: 4
Views: 960
Hi, I would take the Tamron 70-200, if you deliver to Europe for reasonable prices.
Forum: Pentax SLR Lens Discussion 08-04-2017, 07:54 AM  
How clean the insides of a Sigma 17-70 -
Posted By leodp
Replies: 9
Views: 18,091
No need to order the tool...
...if you're the average italian.
Just use a 6-cups coffee-machine replacement ring. It works perfectly.
Place it on the objective, then turn it upside-down, and turn it pushing gently on a clean surface: the objective ring will come out without problems.
There are 6 small screws, and once you remove the main lens you'll see three metal rings: remember (or photograph, or note down) their precise position, in relation to the lens and objective, otherwise you'll sweat to get them back in place.
Dust is gone, speckles in the sky also!
Forum: Sold Items 07-22-2013, 01:31 AM  
For Sale - Sold: Pentax K-m + 50-135 + F 100 macro + sigma 17-70 + 50-150 + tamron 17-50 + metz 50 AF
Posted By leodp
Replies: 11
Views: 4,544
PM sent
Forum: Monthly Photo Contests 02-02-2013, 09:24 AM  
Forward protection
Posted By leodp
Replies: 0
Views: 392
A quiet evening by friends.
I like the way this lens renders out-of focus subjects when wide open.
In this photo the attitude of the baby's mother can still be discerned, without distracting from the main subject.
A bit soft, with the K10D at f1.4 and low light I have always found it difficult to precisely focus.

Leodp
Forum: Pentax SLR Lens Discussion 01-14-2013, 03:54 AM  
Disassembling the Sigma AF 2,8-4,5/17-70 DC Macro (no HSM)
Posted By leodp
Replies: 1
Views: 7,326
Hi,

I have a defective Sigma AF 2,8-4,5/17-70 DC Macro, Pentax mount, bought in beginning of 2007 (the one without HSM motor).
The front lens is heavily damaged and the focal length is wrongly acquired by my K10D camera (minimum focal acquired is around 55mm).

As a result I cannot set the aperture as I wish, because
the minimum value is now f4.0 (probably because above 55mm the f number cannot be lower).
The lens has done around 12000 shots.

I decided to open the lens to look for the problem myself.
I'm going to post the photos taken during the opening, maybe they are useful for somebody else.
Please note that I am writing this only to help anybody which should decide to open the objective.
I do not advise you to perform a disassembling: it may lead to an unusable objective.

Now the photos.

01: the mount.
Three screws. (The smallest one can be left in place)

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/120s

ISO
80






02: removing the mount ring. The long stab is for controlling the aperture

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/24s

ISO
50






03: the focusing mechanism (left bottom) can be easily removed

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/30s

ISO
50






04: taking out protecting rings and a small metal stopper (fixed with the small screw in the first image)

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/60s

ISO
50






05: Longer screws are accessible. Then the focus gears and the electronics can be removed

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/24s

ISO
50






06: 2 screws for the focusing gear and 3+2 to hold in place the focal-length regulating ring




07: there are two different screws lengths

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/20s

ISO
50







08: By turning the ring slightly two more (quite short) screws are accessible. They act as mechanical stoppers (for the ring rotation) and have to be removed anyhow in order to correctly re-assemble the objective

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/20s

ISO
80







09: ring removed: contacts can be seen in the lens body

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/20s

ISO
200






10:The contacts are quite dirty, probably some grease leaked. Maybe this is causing contact issues leading to a wrong readout of the focal length

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/20s

ISO
320






11: zoom on the running contacts. ATTENTION: it's fairly easy to damage them by removing the ring

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/20s

ISO
320






12: The ring is composed of two parts. They are joined together and kept in place by "a guide and three teeth" which are positioned on the side of the ring which is closest to the lens mount.
Also here there are contacts, which can be damaged even more easily than the others.

Attention to the flexible circuit strip: it can get hung when you remove the inner ring from the outer one and get damaged.

Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/20s

ISO
50





13: During the opening I have slightly bent the running contacts. They could be put back in place. However, the metal they are made of can easily crack, if you bend them too many times.
The green arrow points to the site where the post for regulating the focal length should sit.
The post is clearly visible and protruding from the main lens body. It is made out of a goldish metal.
If the post does not slip into this site, turning the ring does not move the objective focal.


Camera
iPhone 4S

Focal Length
4.28mm

Aperture
f/2.4

Exposure
1/15s

ISO
500






The most difficult part of reassembling the lens is having the two (inner and outer) focal length rings back in place, without damaging the running contacts.
The way I have done it is:

First put the inner ring in place, protecting the contacts with a piece of paper 'till the ring is in place, then carefully removing it.
At this point I fix it with the main body wit one screw (of the 3+2 set shown in pict.06)

The outer ring can be then put in place.
Let the focal length post in the main body enter through the "cut/opening/guide" visible in internal, bottom part (the side farthest from the mount ring) of the outer ring. Keep the running contacts protected with a piece of paper.
Rotate the ring along the circular guide (a circular cut just above the running contacts in the image 13) toward the site for the post, in the LONGEST DIRECTION to reach it.
Check on the upper side of the rings when the three teeth can slip into the cuts (one is visible below the running contacts in image 1), then remove the paper carefully and push the two rings together.
If I rembemer correctly now you should screw again the two short screws seen in pict. 08.
Continue rotating 'till the two rings come to a stop.
Push harder to have the post enter the site.

Then you can put everything back together.

If you do everything carefully you MAY have a functioning objective.
Mine still has problems, minimum focal length readout is now 45mm. Better but not solved.


Ciao,
leodp



P.S: I do not know for how long the photos will e accessible on my website. I attach also them as zipped file.
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