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Forum: Pentax Film SLR Discussion 09-26-2012, 06:01 AM  
Tamron 17-50mm (and other lens) observations on MZ-7
Posted By stanislav
Replies: 9
Views: 1,195
This vignetting seem to have shape of the lens hood (more so on wide angle), so out of curiosity, did you have the lens hood on while taking these photos?
Forum: Pentax DSLR Discussion 09-25-2012, 06:08 AM  
Pentax/Ricoh: De-cripple the K-mount! PETITION
Posted By stanislav
Replies: 497
Views: 53,873
I don't see the problem with "crippled" K mount as long as there are alternative ways to tell the body what are the capabilities of the lens. In other words, it should be possible to tell the lens what is the maximum and minimum aperture (provided that there is an aperture lever). That way the body could work in all manual focus modes (aperture, shutter, sensitivity and program mode). It would be nice if it is possible to program and even calibrate a number of MF lenses so that you can simply choose from the list of lenses which one is used. That way it would work similarly to SR for older lenses (where you have to enter the focal length of the lens). So this update is strictly firmware update and if there is place to store individual lens data, this could be available even for now discontinued bodies.

On the other hand, TTL vs PTTL may require some hardware additions/changes. Which is of course desirable.

To continue the lens discussion, it would be nice in addition to handling a MF lenses to enter the lens data so that it is stored in EXIF information. So If you have a bunch of MF lenses, you can enter the model and manufacturer together with focal length and aperture capabilities, so that all is stored in EXIF. That way there is no need to actually adjust the aperture with aperture lever.

It would be also nice to have built-in GPS to geo-tag (exif tag) photos.
Forum: Pentax SLR Lens Discussion 08-31-2012, 05:29 AM  
Giving sigma bigma the boot...big time
Posted By stanislav
Replies: 21
Views: 3,069
Here is Canon 5200mm f14 prime

Ginormous 5200mm Canon Lens on eBay

The only bad part is that it's in FD mount so adapting it to Pentax K is a bit of chopping engineering, otherwise, I would go for it when it was on ebay for 45000$ :D

Well here is a nice video showing the lens in action:

You Tube

Forum: Troubleshooting and Beginner Help 08-31-2012, 03:10 AM  
How to calculate size of object on the sensor?
Posted By stanislav
Replies: 10
Views: 3,909
Your calculation is right. That provided that you shoot objects "far" away, since your calculations implicitly takes field of view into account. Note that FOV taken into account is FOV at infinity (i.e. very far away objects). However this formula is good enough for almost everything beyond macro shooting.

In macro world some other stuff comes into play, such as focus system (internal, front and/or back movement of lenses during focus), but that is completely different issue, depending much on lens design.
Forum: Pentax SLR Lens Discussion 08-30-2012, 05:28 AM  
How wide is this?
Posted By stanislav
Replies: 9
Views: 1,164
Short answer is that you efectively get 28mm focal length on a sensor of 45.6mm by 15.7mm. Now this gives you horizontal field of view just a bit shorter than 89 79 degrees (provided that you do it on digital APS-C size camera).

If you would put a lens on APS sensor to give you similar horizontal field of view, you would need a lens of about 14.5 mm in focal length.

Since you are shifting 11mm I assume that you do it in horizontal direction, since if you wold do that in vertical direction, there would be no overlap to stich panorama right?

Well, I counted it here to be just a bit shorter than 79 degrees, but I wrote 89. Well the correct answer is just a bit less then 79 :D
Forum: Pentax SLR Lens Discussion 08-30-2012, 04:40 AM  
Sigma 200mm f2.8?
Posted By stanislav
Replies: 1
Views: 776
This one is found on Swedish ebay clone (tradera). The only thing said on the add is that it is sold as is.

The description includes only: "f=28 200mm".

So I tried do google on Sigma 200mm f2.8 but only hits I get is from brand new Sigma 70-200mm f2.8 DG APO HSM (or similar). Since this looks like older piece of glas, I can just try my luck to se if anyone more experienced recognize this lens.
Forum: General Talk 07-25-2012, 04:55 AM  
Pentax app, good idea?
Posted By stanislav
Replies: 3
Views: 861
Well, the "App" could be much more than that.

Just imagine an app actually being able to take "photos" emulating the controls of the camera itself. Just imagine how nice it would be to for instance "see" and "feel" K-01, new K-30 or even 645D on your phone screen when you take "photos". I mean that the interface should look like real camera interface with all menus and sub-menus, settings and so. As new camera models appear, a simple update of app would provide new interfaces.

Of course with internet access, there could be a link to good database of Pentax and third-party lenses, reviews and so on.

Make it "free" and that should be a great global marketing channel for present and future Pentax gear.

I am aware that price for development of such app is close to price of development of new body :(
Forum: Pentax SLR Lens Discussion 07-11-2012, 11:50 PM  
I want a lens that flares REALLY bad
Posted By stanislav
Replies: 29
Views: 3,106
Helios 44 (58mm) in less than perfect condition and add some wide angle converter in front which would give you flare and spots together with focal range you desire.
Forum: Pentax K-30 & K-50 07-10-2012, 08:50 AM  
Someone has already run one under running water
Posted By stanislav
Replies: 21
Views: 2,491
Well I didn't take my K-7 to shower, but I was out in a rather heavy rain several times. Thus far there is no problem with camera. The only "bad" thing is that among some 30+ lenses the only weather sealed is DA 18-55 WR thus limiting the focal range in a matter. Maybe some day I'll get 18-135 which should give some more reach and a bit better IQ.
Forum: General Talk 07-10-2012, 07:48 AM  
Example of stupidity in Congresspeople
Posted By stanislav
Replies: 4
Views: 716
When goverments borrow money, it is just another word for raising taxes!

They make the value of the money lower (which is a sort of tax) and then spend that money which means that someone is earning that money.

IMHO it would be much better to increase the taxes to the sustainable level rather than hiding taxation through this "borrowing" acts.
Forum: Pentax SLR Lens Discussion 06-15-2012, 09:40 AM  
Anybody near Indianapolis? I need some help with a lens...
Posted By stanislav
Replies: 8
Views: 900
Why don't you just buy some cheap AF pentax film body?

You should be able to get one for under 20$ shiped. And you can test AF with the lens that you know works on your camera and compare it with your state-of-the-art Sigma.
Forum: General Talk 06-15-2012, 08:25 AM  
George Soros says three months to save the euro
Posted By stanislav
Replies: 47
Views: 2,787
Well actually the don't own land, at least not farming land. But they do pay subventions to the farmers depending on how much land they have, and what crops they grow on that land, even depending on where that land is. Sometimes they'll even pay farmers not to grow any crops.

If we are talking about milk-producers, then actually every one has a quota about how many cows he/she should have and subventions are payed for every milkilng cow. So if you have more cows than allowed then subventions are severely reduced. If you just want to start your milk producing busines from scratch then you have to buy a farm with already existing quota since it is virtually impossible to get the quota from scratch.

Surpluss is then exported or sent as humanitarian help to countries which can not export food to europe (oranges) since european producers have so big subventions.

Actually a funny part was a trade agreement between EU and Serbia about exporting serbian sugar surpluss to EU countries from some years ago. EU knew how much sugar Serbia could produce and about how big surpluss should be. The EU "internal" sugar market price was at that time about 3 times higher than the shugar price on world market. So some serbian "businesman" together with some goverment officials have exported all sugar produced that year together with some sugar from strategic reserves. To cover the deficit on the domestic market they imported sugar (at third of price) from sugar producing countries from south america (Brazil, Colombia...). Of course EU didn't like what has happened and then officials lower the quota Serbia could export to the EU market the following year... This is just to ilustrate the sicknes of the whole system :D
Forum: General Talk 06-12-2012, 11:49 PM  
George Soros says three months to save the euro
Posted By stanislav
Replies: 47
Views: 2,787
1. Personaly I do not have anything against free markets. I would rather see more free markets with less subventions. More than half of EU budget is going into subventions of food industry (farming and so on), thus destroying the "free" farming market from non-EU countries. Thus far EU is geting away with it. USA tried to do similar thing in steel industry by imposing high customs to steel imported from China. It resulted in death of once so proud american steel industry.

2. I do not have anything against gambling (or speculations) either, as long as people are gambling with their own money and as long as they now what they are doing. When they gamble with other people's money then everyone involved should know exactly what is going on. Nowadays we have all kinds of financial institutes, funds, banks, funds and so on effectivly gambling with other people's money (they call it investments). So when these fonds generate some revenue, then people in charge get well payed in form of bonusues. When they loose money, then it is someone elses money. The global problem is when these institutions became too big thus threataning the whole global financial system. So if you let one bank shut down then all others are going to have problems. So the only way out is to "bail" them out! ... or NOT. If you do bail them out then they know that all losses are going to be covered time and time again (it all hapened already) and there is noone to blame. If you just let them down then those responsible still have stash of money (board directors, executives and alike) that they are still going to be fairly unaffected.

3. So my only solution is to severely regulate "gambling" market. Or just let those responsible for gambling be there with their own assets with options to loose everything (and I really mean everything) once their gambling leads to necesity of bailouts. Moreover force them by law to put their own assets as security when they are on some key positions. Hopefully we'll get some more responsible people on high positions then.
Forum: Pentax SLR Lens Discussion 06-06-2012, 11:12 PM  
Best lens recommendations for night sky photography and long exposure < $100?
Posted By stanislav
Replies: 18
Views: 7,002
If you get lucky you can score a Zenitar 16mm f2.8 fisheye (m42 mount) for about 100$. Then you have to add M42-K converter. That would give you wider angle probably with better IQ then the kit lens, for slightly over your budget. The fish-eye effect is not so exagregated on APS-C size senzor.

Here is review of the lens Zenitar 16mm f2.8 Fisheye Lens Reviews - Russian and Zenitar Lenses - Pentax Lens Review Database
Forum: General Talk 06-04-2012, 07:25 AM  
George Soros says three months to save the euro
Posted By stanislav
Replies: 47
Views: 2,787
As a matter of fact, same people that helped Greece to falsify their own economic papers when Greece was applying to Euro are now pointing finger at Greece saying thet what they did was wrong. Well, it may be so, but more wrong was this forgery which helped Greece into Euroe to begin with, yet noboy was held responsible!

Moreover in financial circuits it was a well-known fact that Greece was on the edge of bankrupcy for long time before the crash actually happened. Yet everybody lent money willingly because they knew that somebody would have to cover for it. I would rather see that one, or several of those financial institutes go out of business and get some leading people sentenced to the life so other would be more carefull in spending other peoples money.

Do not forget that this crisis was preceeded by US home subpremie loan crash just couple of years ago. And what did the US government do? They put even more money in the system, rather than leting couple of banks go out of business. Same behaviour happens time and time again, so as long banks know that someone (states, countris and their tax-payers) are going to cover losses of risky businnes, then the risky businnes is going to continue since there is no risk at all. I would say that it is time to stop that kind of riskfull behaviour and let the banking system become servant rather than master of global economy.
Forum: Troubleshooting and Beginner Help 05-31-2012, 12:39 AM  
Question on AF on higher F numbers?
Posted By stanislav
Replies: 13
Views: 736
If you want to "simulate" AF on F8 or even higher apertures, you can try with ND filter attached.

On the other hand it is not a secret that even with fairly fast lenses, AF works better outdoors in broad daylight than indoors in dim light.
Forum: Troubleshooting and Beginner Help 05-29-2012, 10:10 AM  
Aperture Question
Posted By stanislav
Replies: 89
Views: 4,749
Well in "mathematical" terms bokeh is convolution between the aperture and the image where things more out of focus are more "convoluted" with the aperture. In practical terms it is most visible with the pointy light sources in high contrast images. If we have a round aperture, than every point is going to look like a circle. If the lens used is mirror telephoto, then the bokeh looks like rings. Actually you can get bokeh to have any shape you like by cuting a piece of cardboard or something like it and placing it right in front of the lens.

Here is an example I found on flickr:

day 10 - A Bokeh of flowers by AlexTurton, on Flickr

And here is link to more "scientific" or technical explanation and example with triangular bokeh:
Forum: Pentax Camera and Field Accessories 05-29-2012, 08:35 AM  
Distance scale on Af 540 FGZ
Posted By stanislav
Replies: 14
Views: 1,203
Lowell, I totaly agree with you! It does not matter how specific I am trying to be, there is still some misinterpretation possible ...

Well to try to be more specific here I go once again....

AF540 is a zoom flash, and zoom as such has function only (well in most cases anyway) if you point it straight to the subject. Moreover the distance shown on the flash has also no meaning of you "bounce" flash of some surface. In that case yes, the flesh is going to work fine provided it is powerfull enough to make enough light (depending on the geometry, size and reflectiv caracteristics of the room). There is also an option to have a part of scene illuminated much more than the rest and so on. It is useful if you want to experiment and if you know what you want to obtain.

Remote sensing is nice option, it certanly gives more options in lighting the scene, I totaly missed that option. On the other hand if you have all controlled in such detail, you can as well go all manual, perhaps with several "cheap" flash slave units or some combination of different light sources. Anyway knowing the "theory" behind it will not make you worse artist or photographer :D
Forum: Pentax Camera and Field Accessories 05-29-2012, 07:07 AM  
Distance scale on Af 540 FGZ
Posted By stanislav
Replies: 14
Views: 1,203
Oh well, I tried to keep it simple but....

Let's put it this way: A mode on flash will work well if:
1. You keep flash at the camera or very close to it (so that distance from flash to subject is similar to distance from camera to subject)
2. You point the flash straight ahaed (i.e. no tilt, no swivel, no bounce).

In all other cases you'll have to manually compensate for the effect you are interrested in, so I guess that the manual mode could actually work better where you control the actual output power from the flash.

Now to make it more complicated and to mention inverse square law, it applies as it is in open areas. For instance if you are in a small room with white blank walls (a toilet for instance), then more or less all the light from flash will eventually get back to the camera/lens regardless of where you point the flash. However if you are in the open or huge rooms with non-reflective surfaces (dome of a church, football stadion) than only directly lit subject is going to be visable with everything else left dark.

Now to complicate even more: inverse square law is an approximation. It says basically that the measured intensity of light from a point source (which illuminates evenly in all directions) is inverse proportional to the square of the distance from that light source. "Law" as such is rather intuitive if you think of a box wide a side of say 1 meter (or foot), and put the light source in the middle of it. Then light comming to one of the sides is covering 1 square meter. Which means thatall available light is spread on the surface of the box of 6 square meters. Now you let the box "grow" so that the side is 2 meters instead of one, than one side i 4 square meters which means that the same amount of light illuminating 1 squeare meter now has to illuminate 4 square meters (total of the whole box is 24 square meters). So just by doubling the distance the measured intensity is divided by 4. (Actually instead of the box you should think of the "sphere" which gives different numbers, but general relation still holds). Now a point light source evenly spreading on all sides is just an approximation, but it holds good in many cases being it a candle, a light bulb, moon, sun, stars or galaxies.

Note now that flas does NOT enter that definition since the light is focused in one direction and/or one area. Same holds even for scene lightning or any other source of focused light (laser for instance). So the question which arizes is what does inverse square law have to do with flashes when those are sources of focused illumination. The answer to that qustion is that an object (all objects) illuminated spread light in the same fashtion the point light sources do (of course appart from mirrors or objects with mirror-like surfaces).

So inverse square law refers actually to the intensity of the light reflected from the object that comes back to camera.

If you would use a point light source (say a flash with a diffuser) than the law would actually be inverse 4'th power law since the light intensity is inverse squared as a function of distance between the light source (diffused flash) and the object, and then inversed squared again as a function of distance between the object and the camera. This is actually a simplified (or oversimplified) example of radar equation (radar from a single source with single detector) which is another example for usage of same principles as in photography (both radar and light are electromagnetic waves).
Forum: Pentax Camera and Field Accessories 05-29-2012, 12:29 AM  
Distance scale on Af 540 FGZ
Posted By stanislav
Replies: 14
Views: 1,203
Correct! Moreover, it will need less time to recharge as well.
Forum: Pentax Camera and Field Accessories 05-29-2012, 12:10 AM  
Distance scale on Af 540 FGZ
Posted By stanislav
Replies: 14
Views: 1,203
The distance scale gives you maximum distance that flash can illuminate for a certain combination of ISO, aperture and focal length of the lens. The flash than calculates the power required to illuminate subject itself. If the subject is further away than the maximum shown at the scale, then the subject is going to be underexposed since the maximum flash power is not going to be enough to give propper illumination. If the subject is closer, the flesh should cut the power itself when it detects that certain amount of light has bounced back to the detector in the flash unit.

The focal length is used to "zoom" the flash beam so that it does not illuminate parts of scene which are not going to be captured in the frame. The difference between "35mm" and "digital" settings of the zoom are due to APS crop factor, which effectivelly givies narrower field of view, thus the focal length showed varies between the two.
Forum: Troubleshooting and Beginner Help 05-28-2012, 05:29 AM  
Aperture Question
Posted By stanislav
Replies: 89
Views: 4,749
Here is an (over)simplified explenation between aperture, ISO and shutter speed and their implication on DOF sharpnes and (over/under) exposure:

CameraSim simulates a digital SLR camera - SLR Photography Demystified
Forum: Pentax SLR Lens Discussion 05-28-2012, 03:58 AM  
Alternative lens hood for Tokina 28-80?
Posted By stanislav
Replies: 2
Views: 1,990
I do not know if this is what you were looking for, but here is a link for paper (cardboard) printable lens hood for tokina 28-80 f2.8 (not sure if this is your lens).

Tokina AT-X 280 Pro AF 28-80mm f/2.8 lens hood

And here is link to hood optimized for APS size sensor:
Forum: Photographic Technique 05-24-2012, 06:47 AM  
What do you call this type of photo effect?
Posted By stanislav
Replies: 13
Views: 2,104
Stereographic projection from a stitched panorama of 32 images. Had to watch my step carefully with the cliff just 3 feet away.

A drop of water and a pinch of earth. | Flickr - Photo Sharing!

I guess that this is the effect you were looking for, here is link to photo (just to clarify this is not my work, just somtehing I found on flickr)
Forum: General Talk 05-23-2012, 07:37 AM  
Time Magazine cover
Posted By stanislav
Replies: 18
Views: 1,585
Well all those mother-milk replacements are just that: replacements.

One thing that the mothers milk have which none of the replacements has (appart from comforting baby by being closed to the mother) is "living" part of mothers milk including bunch of feromones, good bacteria, antibodies so essential for development of imune system of newborns. If there is enough breast-milk then there is really no need for any replacement at all. Then sometimes (still debateable) between 4-6 months of age it is time to introduce other food sources as well...

That said I (having 2 kids myself) am by no means any fundamentalist oposing milk-replacement. When my wife went out to meet her friends I was more than happy to give our babies replacement food. On the other hand after some initial adjustments it seems that mother-baby system works so well that milk just starts pouring in time when baby starts to feel hunger. In our case the milk stopped by itself when there was less interest from our kids for breasfeeding (in one case at 7 months in the other at about 10 months of babies age).

As for privacy thing, I understand women which do not wont to show their "private" parts in public. On the other hand I do not have any controversy by eating myself in public - think about all reastaurants, fast-food chains, icecream stands etc that whould go out of busines if it would become controversial to eat in public in the first place. So if it is not controversial for adults, I really do not se any reason why it would be controversial for babies.
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