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Forum: Pentax SLR Lens Discussion 01-23-2022, 07:01 AM  
K and M 135mm shootout: a comparison nobody needed
Posted By glasbak
Replies: 10
Views: 890
You do not mention the camera used, I found out that the differences between the M and K 135mm lenses is in the corner performance of 35mm, on APS-C this difference is not very obvious.
Forum: Pentax SLR Lens Discussion 09-14-2021, 12:36 PM  
No lens diagram information for the Pentax-F zooms
Posted By glasbak
Replies: 9
Views: 615
Forum: Pentax SLR Lens Discussion 07-24-2021, 08:07 AM  
K28 f3.5 Vs M28 f2.0
Posted By glasbak
Replies: 27
Views: 1,807
But not identical twins.
Forum: Pentax SLR Lens Discussion 05-27-2021, 09:52 AM  
FA 80-320mm, repair attempt
Posted By glasbak
Replies: 29
Views: 1,703
Always funny, to see my own posts back after years, the middle document is a (google?) translation (cannot remember to have posted this to an english site) of my original post (oct-2012) to a dutch pentax forum.

I hope it helps someone to repair a broken lens.
Forum: Pentax SLR Lens Discussion 10-20-2020, 03:02 PM  
Weight of the K series 105mm F2.8
Posted By glasbak
Replies: 17
Views: 1,234
I identified three slightly different versions of the M 1:1.7 50mm lens long (20 years?) ago.
Somewhere I must have a picture explaining those, but where...
It was mainly in the finish, the oldest version had the best finish/engravings.
Forum: Pentax Full Frame 08-07-2020, 07:50 AM  
1000mm and 1200mm lenses
Posted By glasbak
Replies: 27
Views: 3,362
I did some testing in the past with some of the above mentioned lenses (on APS-C):

3x1000mm -

Pentax, Sigma and Leitz 500mm..560mm optics -

Pre ED optics will have serious chromatic aberations, except mirror optics, but they have different problems (donut bokeh)
Forum: Flashes, Lighting, and Studio 06-28-2020, 01:20 PM  
Pentax Flash Guide - 1st Development Thread
Posted By glasbak
Replies: 44
Views: 5,528
I am a bit late to this discussion, but shortly after I bought my K5 (2011?), I contacted the (dutch) pentax service with a wireless p-ttl problem when using A type lenses.
Camera at AV, popup as control, 360fgz as slave, short object distance:
50mm 1.7 A lens very dark
50mm 1.7 F lens right exposure.

And later I found out that I could get the same dark exposure by focussing the F lens manual to infinity.
So somehow the camera uses the object distance in its flash calculation, and A lenses who do not communicate object distance are probably considered at infinity.
I cannot remember I had these problems with my K10D.

Never got a decent solution from pentax, and now I rarely use P-TTL anymore, just manual and make some test exposures to get it right.
Forum: Pentax SLR Lens Discussion 06-24-2020, 09:15 AM  
120mm- M vs K
Posted By glasbak
Replies: 24
Views: 1,390
Although I did not test these against each other, I expect the behavior to be like most K versus M lenses : K better image over the whole 24x36 frame, the M good in the centre, less in the edges/corners.
Forum: Pentax SLR Lens Discussion 04-24-2020, 12:45 PM  
Which 50mm 2.8 Macro would you pick.
Posted By glasbak
Replies: 42
Views: 2,392
The macro A 50/2.8 is not a big chunk of glass, and it also has a floating element.

My DFA 50/2.8 (optical the same as the FA and F, if I remember correctly), is much sharper than my A 50/2.8, but the DFA has a mechanical flaw, too flimsy with its double heliocoid (which makes it compact though) to keep the optics propper centrated, especially noticible in portret mode shots.
If I stumble over a FA or F 50/2.8, I will probably replace the DFA.
Forum: Pentax SLR Lens Discussion 11-15-2019, 12:36 AM  
How is the sharpness of your K 500mm f4.5 on digital, if you have one?
Posted By glasbak
Replies: 29
Views: 2,139
Forum: Pentax SLR Lens Discussion 11-13-2019, 01:02 PM  
Spots in pictures from my SMC PENTAX DA 18-55 lens
Posted By glasbak
Replies: 19
Views: 1,220
Do the spots change when zooming to a different focal length ?
Forum: Pentax SLR Lens Discussion 11-02-2019, 03:53 AM  
What new lens would you purchase on release?
Posted By glasbak
Replies: 72
Views: 3,707
high end 50mm 1:2.8 macro with aperture ring (bellows usage) and proper mechanics to keep the optics aligned, so no crappy plastic as on the dfa50 macro..
Forum: Pentax SLR Lens Discussion 11-02-2019, 03:39 AM  
mm for shooting the moon
Posted By glasbak
Replies: 12
Views: 999
Rule of thumb : diameter of the full moon (or sun) on the sensor is 1% of the focal length.
Forum: Pentax SLR Lens Discussion 08-10-2019, 06:39 AM  
Which Pentax 100 macro?
Posted By glasbak
Replies: 31
Views: 2,358
And here they differ (look at the optical diagrams) : Pentax Short Telephoto Prime Lenses | The K-Mount Page
So, who to believe ?

And you are talking about the DFA100 WR, I have no experience with that lens, I did mention clearly the plastic aperture ring versions and never the WR version.

Some other hints for demanding macro photographers :
Avoid lenses with a plastic filter thread (easily damaged when attaching the lens in reverse, or attaching a ring flash)
Avoid lenses without aperture ring if you want to reverse a lens, or use it on bellows, controlling aperture becomes a nightmare.
Forum: Pentax SLR Lens Discussion 08-10-2019, 06:06 AM  
Which Pentax 100 macro?
Posted By glasbak
Replies: 31
Views: 2,358
The F and FA are quite metal, and of a very good build quality.
If I remember correctly, the FA 100 and DFA 100 have a different optical formula, the FA 50 and DFA 50 the same.
The DFA 50 and 100mm (the ones with aperture rings), are very plastic and built with double heliocoids, which keeeps the design compact, but as drawback an extra increase in play.

If you notice problems with these plastic lenses will depend on what you use them for.
If you shoot flowers and insects, or have an APSC sensor size, the drop in image quality goes probably unnoticed.
On my K1 and using it for reproduction, it is quite obvious, especially the portret mode shots show the most drop in resolution out of center.
Putting the camera on a reproduction stand, with the lens pointing down, so gravity does not pull the optics out of alignment give the best results.
The problem is not unique to the DFA 50 macro etc. Lots of optics with a lot of play in them suffer from the same problem (remember the DA 16-45 ? Pentax DA 16-45mm 1:4 ED/AL review: Digital Photography Review)
Forum: Pentax SLR Lens Discussion 08-10-2019, 02:39 AM  
Which Pentax 100 macro?
Posted By glasbak
Replies: 31
Views: 2,358
If you are serious about optical quality, avoid the plastic DFA 50 and DFA 100mm, the optics are OK, but the mechanics are not able to keep the optics proper aligned. If I can find a good FA50 macro, I will toss out the DFA50 macro.
Forum: Pentax SLR Lens Discussion 08-09-2019, 12:14 PM  
Pentax 50mm 1:1.4 m vs 50mm 1:1.4
Posted By glasbak
Replies: 19
Views: 1,951
The K version has the better mechanics(brass on aluminum in the focus heliocoid) and the radioactive yellowing/browning glass (hence the warmer cast),
Forum: Pentax SLR Lens Discussion 06-09-2019, 08:02 AM  
Which 135mm one to keep? smc pentax-m 3.5, Takumar (Boyonet) 2.5 or smc Takumar 3.5
Posted By glasbak
Replies: 18
Views: 2,547
The screw mount takumar is optical the best of the three on 'full frame', the lower edge performace of the M goes unnoticed on apc-c, build quality of the screw mount is the best, the bayonet takumar the worst (mine keeps getting grease on the aperture blades, even after several cleanings).
Forum: Pentax SLR Lens Discussion 05-26-2019, 10:52 PM  
Weird lens behaviour on Pentax K Mount (film SLR)
Posted By glasbak
Replies: 11
Views: 1,200
Could the error be lens speed related ?
Maybe something has come loose which prevents light of low speed lenses reach the light sensor in the chinon..
Forum: Pentax SLR Lens Discussion 05-08-2019, 11:39 AM  
SMC Pentax-m 35-70mm 2.8-3.5 Focus/ aperture mark not line up.
Posted By glasbak
Replies: 9
Views: 1,097
loosen the 3 screws in the knurled part, and then you can re position the barrel, or shift it up to see some internals.
Forum: Pentax SLR Lens Discussion 08-07-2018, 10:48 AM  
Faulty SMC Pentax AF Zoom 1:2.8 35~70mm
Posted By glasbak
Replies: 7
Views: 795
And this page may be of interrest too, clean the contacts ?
Forum: Pentax SLR Lens Discussion 01-14-2018, 02:19 AM  
Are K lenses better than their M and A counterparts?
Posted By glasbak
Replies: 23
Views: 2,637
So, you found my very first webpage, with the pictures I made 20 years ago !

About mechanical finish, there is a degradation in finish of the M lenses over the various production batches (cost cutting), the very first generation of the M 1:1.7 50mm has the best finish.
Forum: Pentax SLR Lens Discussion 01-13-2018, 06:24 AM  
Are K lenses better than their M and A counterparts?
Posted By glasbak
Replies: 23
Views: 2,637
Already in the film days (20 years ago?) I had the next statement :

No M lens which replaced a similar K lens, optically outperforms that K lens, they are usually worse.

Why ?
The M generation had as major selling point compactness, and that had its optical consequences for the edges of the image field.
Central performance of a M lens is generally good, that is why the APS-C users don't notice this difference, on 24x36 thats different.
Lots of A lenses are repackaged M lenses.

Mechanically the K lenses which had their roots in takumars have brass in their focus heliocoid, the M generation has aluminum only. Aluminum on aluminum goes very bad without grease.
Forum: Pentax SLR Lens Discussion 10-12-2017, 10:12 AM  
throium glass lenses
Posted By glasbak
Replies: 60
Views: 6,710
I think it is just the takumar optics with bayonet, and not a repair job, because one of these lenses is more that 30 years in my possession, so probably less that 10 years old when I bought it, deteriorating cement takes usually more time,
Forum: Pentax SLR Lens Discussion 10-12-2017, 07:09 AM  
throium glass lenses
Posted By glasbak
Replies: 60
Views: 6,710
I have two PENTAx-K 1:1.4/50 lenses, both suffer from browning and are radioactive (verified with a radiation meter), just as their smc takumar predecessors.
So it is not strange they perform similar.
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