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Forum: Pentax SLR Lens Discussion 11-27-2022, 11:23 AM  
Need a 24mm prime lens. Any recommendations?
Posted By marcusBMG
Replies: 26
Views: 965
There are lots of decent/similar 28mm, at 24mm two lenses keep on being mentioned/referred to (apart from oem lenses that are not relevant being incompatible) : the sigma superwide and the tamron adaptall 2 01B. Consensus suggests that the sigma is better across the frame (corners) and has closer focus, the tamron has better rendering and is very good centre frame. I have posted pics with the 01B in the adaptall mount club thread. if you can find one in K mount the fast vivitar 24mm f2's are good stopped down, soft at f2, and have strong colours.
Forum: Lens Clubs 10-30-2022, 09:48 AM  
300mm plus Lens Club: discuss your long lenses
Posted By marcusBMG
Replies: 39,019
Views: 4,123,006
canon SZ70: 3.8 – 247.0 mm (35 mm equivalent: 21 – 1365 mm), 20MPx, RAW. 600or less here in UK.

These bridge cameras just get better and better - probably already the practical option for most snappers of wildlife etc. That image speaks for itself basie. Was the camera on a tripod? What was the ISO (still the weak point with these smaller sensors)? Was it out of teh camera or did you PP?
Forum: Pentax SLR Lens Discussion 10-22-2022, 02:28 AM  
Fungus in rear elements Sigma Mini Wide 28mm f2.8
Posted By marcusBMG
Replies: 3
Views: 387
I'm not sure what the difference between the first miniwide and the II are - in general terms they are very similar. I would be surprised if they weren't more or less the same: take off the mount and the rear element housing will unscrew (somehow). Nail varnish remover (acetone) may be useful for softening any thread locker. Then you may need to ease or tap the elements out NB note which way round they go - put it back in back to front and you wil be wondering what on earth has happened to your images. sometimes it is sufficient to just reach in once you have access to the affected side of teh element - bit of tissue on a cocktail stick, lens pen to finish.
I use a drop of mould and mildew remover in meths and a dried out paper lens cleaning tissue - basically anything wit detergent effect will clean the fungus right off and kill it. Then just normal lens cleaning stuff - tissues, blower etc to finish off. With small elements it is even more pertinent to use plastic gloves and avoid getting fingerprints etc on the glass.
Forum: Pentax SLR Lens Discussion 10-21-2022, 10:48 AM  
Fungus in rear elements Sigma Mini Wide 28mm f2.8
Posted By marcusBMG
Replies: 3
Views: 387
Forum: Pentax K-30 & K-50 10-20-2022, 08:33 AM  
Pentax K-30/50 for micrography
Posted By marcusBMG
Replies: 9
Views: 519
Just doing a bit of reading on photomicrography - there are some similarity of principles with digiscoping. Seems to me you have similar choices: eyepiece projection (no lens on the camera) or, as you have been doing with the Olympus, taking a picture of the exit pupil with the camera plus lens afocal coupling (knew there was a term for this thanks to @Not A Number for posting informative links below). There is some set up involved with a dslr, the larger sensor means more tinkering with distances and mounting to reduce/avoid vignetting. For afocal coupling with a scope, a favoured lens is the compact SMC-M 40mm f2.8.
I think the K30/50 is a pretty good choice of camera, it has magnified live view which I can suggest is essential, however it doesn't have an articulated lcd. The model for that would be the KS1 or KS2. Alternatively you could consider a later model G series Lumix - G5, G6, G7. The later M43 sensors have much better iq and ISO performance than the earlier ones, quite close to apsc and are similar price bracket to a K30/K50. And of course these are mirrorless so completely avoid vibrations from that source.
Forum: Pentax SLR Lens Discussion 10-15-2022, 12:22 PM  
Weird diaphragm issue on Tamron 90mm Macro
Posted By marcusBMG
Replies: 8
Views: 480
if you mean the aperture ring doesn't click, that is due to the ball bearing not the spring. Did you replace the ball bearing correctly (see pic #4 in my post in the linked thread on mflenses)?
Forum: Pentax SLR Lens Discussion 10-10-2022, 02:11 PM  
Weird diaphragm issue on Tamron 90mm Macro
Posted By marcusBMG
Replies: 8
Views: 480
Frankly, I don't know. Most camera repair shops don't work/are no longer familiar with old MF lenses. You might find a techie who is "old school" or willing to have a go. it's not difficult to go as far as I did. I suggest diy.
Forum: Pentax SLR Lens Discussion 10-10-2022, 08:41 AM  
Weird diaphragm issue on Tamron 90mm Macro
Posted By marcusBMG
Replies: 8
Views: 480
OK you have the later 52BB adaptall 90mm. Sticky iris is a known issue with this lens. I have tried fixing this myself with partial success. Check out:

Adaptall diaphragm

It's not really clear to me what the problem is exactly. I don't notice oil or anything obvious on the iris blades. When done manually with a finger the mechanics seem ok. Tweaking the spring position seems to help. I have the impression that the mechanism is finely balanced and with age, a little bit of dirt/dust or something, this starts to happen.
Forum: Monthly Photo Contests 10-03-2022, 07:08 AM  
A night in the orchard
Posted By marcusBMG
Replies: 7
Views: 337
Very good. Did you do some illumination of the trees like "painting" with a flashlight?
Forum: Troubleshooting and Beginner Help 10-01-2022, 10:37 AM  
Confirm aperture block failure in K-70
Posted By marcusBMG
Replies: 12
Views: 828
Could be but not entirerly clear from those examples. With aperture block failure the image is usually really dark, because the lens iris remains closed - F22. Your image exif says f8 so thats 3 stops : yeah could be 3 stops under but ...
Try setting the lens to min F wide open.
Certainly in its early stages this can be inconsistent and intermittent in its occurence (but gets worse and persistent) - I set the RAW/Fx button on my KS2 to stop down preview and a couple of presses of that would free up the solenoid allowing me to keep using it for a while longer. But thats not a fix or particularly recommended.
Have a look at teh relevant thread here:

How to detect aperture-block failure/stuck solenoid on Pentax K-70 - PentaxForums.com
Forum: Troubleshooting and Beginner Help 10-01-2022, 09:20 AM  
Pentax K mount lenses
Posted By marcusBMG
Replies: 12
Views: 799
Hi Roger, welcome.

Pentaxes are the best for legacy lens compatibility. I am pretty sure that all chinon camera bodies were K mount (1st gen: K-M). Pentax I think had a notion that the mount could be an open standard and made the mount generally available. Ricoh and Cosina and others (see here) also made K mount cameras.
I have a nice K30 with the green solenoid already replaced with the good white one, if you are interested (the K30's are probably the most liable to the "aperture block failure" caused by the lower quality of the green solenoid, causing dark images, not a difficult fix but a hassle, and expensive through a commercial repairer).
Forum: Pentax SLR Lens Discussion 09-27-2022, 10:11 AM  
Where have all the f/3.5-4.5 zooms gone?
Posted By marcusBMG
Replies: 21
Views: 1,115
Main reason is optics. The definition of F-stop is:
f/stop = focal length / diameter of effective aperture (entrance pupil) of the lens
The kit lens is 18-55mm f3.5-5.6. That's a 3 x zoom ie 3 x 18 = 54. There would nominally be a commensurate corresponding shift in F number of 3 stops. However lenses are typically designed to have a lesser change than the change in focal length would warrant. You can get an impression of how much you can zoom before the f-stop changes with the lens on the camera, metering off eg a white wall (an approximate measure, the camera exposure changes in steps of 1/2 or 1/3 stop depending on your camera settings).

Old film kit lenses were typically something like 28-70mm, =2.5x zoom, and f3.5-4.5 would have been pretty typical for these. I guess it was relatively straightforward to design these lenses like this, specifically because they were typically retrofocus designs with a large negative front element, so I guess the entrance pupil could also change while zooming through the wide angle focal range. There are also lenses where you can see the iris change size as you zoom.
Forum: Lens Clubs 09-25-2022, 08:04 AM  
Vivitar Lens Club - share the beauty
Posted By marcusBMG
Replies: 1,018
Views: 197,993
While you can see from the pics I have posted that the vivitar 35-70mm f2.8-3.5 is a good lens, when I did some test pics of the castle those highlighted some "decentering* " - pics when scrutinised were softer on the right side. Then I spotted one in PKA mount, which I doubted even existed though a reviewer on the review page reported one. So I was prompted to make a move and put in an offer, this manouvre was successful.



Another nice minty one, and I am now keen to see if this one tests better.
*there are a number of different optical causes of this, decentering as strictly defined (optical lens elements that are either moved or tilted from the principal axis of the lens) is just one, but decentering tends to be used as a generic desciption of a lens showing softer on one side.
Forum: Pentax SLR Lens Discussion 09-15-2022, 01:28 AM  
Very mysterious problem mount Vivitar lens, please help!
Posted By marcusBMG
Replies: 10
Views: 569
Forum: Pentax SLR Lens Discussion 09-04-2022, 01:34 AM  
Tamron Adaptall adapters
Posted By marcusBMG
Replies: 12
Views: 586
I think that PCS is an M42 screw thread mount?
Check the review section here - describes and differentiates the adapters available:

Tamron Adaptall Lenses for Pentax: Adaptall Adapters - Pentax Lens Review Database

"Better" rather depends on how you want to use the lens. All the original adapters are good quality. The M42 ones all work the same for adapting to DSLR. Note the point about the iris not being actuated on adaptall-2 and SP adaptall lenses in the M42 mount description.
Forum: Pentax SLR Lens Discussion 09-03-2022, 06:35 AM  
Vintage lenses for video
Posted By marcusBMG
Replies: 2
Views: 439
BKSpicture (Begt Sandberg) has done a lot of reviews including a video test:

BKSPicture's Camera and Lens Reviews

There is also: https://www.vintagelensesforvideo.com/about/
Forum: Lens Clubs 09-03-2022, 06:07 AM  
Post your HD PENTAX-D FA 150-450mm F4.5-5.6 ED DC AW pictures!
Posted By marcusBMG
Replies: 3,251
Views: 447,622
That's a pretty clear difference. It's going to become more and more about what you can do with the image processing ...
There is a section for post processing but I think you are perfectly justified in X-posting in relevant lens threads.
Forum: Lens Clubs 09-01-2022, 06:42 AM  
300mm plus Lens Club: discuss your long lenses
Posted By marcusBMG
Replies: 39,019
Views: 4,123,006
New toy for Gaz :) great pics of saturn and jupiter
are you going to try this on some long range birds??
Forum: Lens Clubs 08-28-2022, 01:55 AM  
300mm plus Lens Club: discuss your long lenses
Posted By marcusBMG
Replies: 39,019
Views: 4,123,006
Great to see results from this combo.
Forum: Lens Clubs 08-26-2022, 12:46 PM  
Vivitar Lens Club - share the beauty
Posted By marcusBMG
Replies: 1,018
Views: 197,993
Bright and sunny yesterday so I took these snaps with the vivitar 35-70mm f2.8-3.8. Middling F's. Just crop and exposure adjust (and speck removal) on most of these in faststone.

Very pleasing results actually, I was inclining to a notion of "good for close up" but check out the 1:1 pixel peep crop below from the panoramic crop of the estuary and Great Orme. Discount the evident atmospheric blur: sharp, no significant fringing or coma.
Forum: Pentax SLR Lens Discussion 08-25-2022, 07:09 AM  
Adapt 135/2.8 Elmarit-R Leicaflex telephoto lens to K-mount
Posted By marcusBMG
Replies: 1
Views: 282
Leica R mount has a registration distance of 47mm as opposed to K mount 45.46mm. So you can have infinity focus. There have been previous discusions of this:

Leica lens to pk mount adapter that will focus to infinity? - PentaxForums.com

it seems that although there is just about 1.5mm space for an adapter, the bayonet flanges etc get in the way so leitax mount swap is only solution.
Forum: Pentax SLR Lens Discussion 08-24-2022, 10:20 AM  
Adapter for mounting Zeiss C/Y lenses
Posted By marcusBMG
Replies: 6
Views: 405
The adapters linked to above are not recomendable, the additional optics make the adapter into effectively a small teleconverter and negate the idea of enjoying the IQ of classic lenses, lowering the iq significantly.

The adaptist multimount is discontinued, so only chance would be old stock or s/h one, howevr CY mount was one of the mounts it would work with. It is said that CY and OM were derived from PK hence have very similar registration distances and the bayonet fit is very close, but won't go on a pentax as is.

Rather than mod the mount on the lens, if you can't find an adaptist multimount then I would look at modding a camera mount (the main silver metal plate ring - it's a standard part usually) obtained off a junk dslr ( I have several actually off cameras scavenged for solenoids). It would make more sense to do this to a second camera however, rahter than probably compromising the mounting of pentax lenses (loose?) on your main camera.
Addendum: alternative is a mount swap - leitax see post below.
Forum: Pentax SLR Lens Discussion 08-22-2022, 02:10 AM  
Sigma APO Tele 400f5.6 vs DA*300f4 + TC1.4
Posted By marcusBMG
Replies: 4
Views: 540
Always scrutinise those 400 - apo's for hazed cemented group deep in the lens - see review description. Never seen one that wasn't!
Da 300 f4 + tc - you're already set, you're only going to get something more/bit different from options like a 300 f2.8; DFA 150-450mm.. The main point to eg vintage sigma 400-5.6 is cheapness: getting 400mm for minimal $$.
Forum: Lens Clubs 08-21-2022, 02:28 PM  
Vivitar Lens Club - share the beauty
Posted By marcusBMG
Replies: 1,018
Views: 197,993
Another close up shot with the viv 35-70mm - max 1:4 repro 70mm, f6.7 (=f9.4).
I did some test pics of the castle, the resolution looked good, some cloud meant the pics were backlit and the lens showed a significant loss of contrast and some flare. I'l post some more ideal test pics.
Forum: Maintenance and Repair Articles 08-21-2022, 10:55 AM  
Notes on disassembling Vivitar 400mm f5.6
Posted By marcusBMG
Replies: 13
Views: 9,862
You mean you have separated the helicoid? When you do this, it is common to have to count rotations, mark the point at which the halves separate, and so on in order to reassemble correctly. if you haven't done this it may be a difficult exercise to re-assemble involving repeated trial and error reassemble points, to get the lens functioning correctly with correct infinity focus etc.
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