|
Forum: Lens Clubs
03-12-2009, 05:31 PM
|
| |
The A lenses were probably the most beautifully engineered lenses that Pentax ever did. A joy to manually focus.
"A" lenses that I still have:
A16mm f2.8:
A50mm f1.2:
A50mm f1.4:
A100mm f2.8 non macro:
"A" lenses that I had, but sold:
A28mm f2.8:
A100mm f2.8 macro
A*200mm f2.8
A*300 f4
 |
|
Forum: Pentax DSLR Discussion
03-18-2010, 04:59 PM
|
| |
I did post this over at the "other forum" but thought it worth posting here as well:
I just purchased a Katz Eye focus screen for my K-7 and received it yesterday. The screen is a ground glass screen with 1/3rd grid lines for composition and Opti-Brite treatment. There are no other focus aids other than the ground glass screen, there is no split prism or microprism collar.
This screen is wonderful as it is simple and very effective for getting that "snap intop focus" look throught he VF.
I did some preliminary tests as far as exposure and manual focus accuracy. Exposure looks spot on but I noticed an issue with the manual focus accuracy. When the focus is correct in the VF, the resultant recorded image on the sensor was focused in front of the intended target. This was using the A50mm f1.2 lens which will obviously have very narrow DOF and allow such accurate focusing ability.
My first thought was that the focus screen is too thick and therefore the image was being focused in front of the correct focus plane, but on reflection and talking to Rachael Katz from Katz Eye, this is of course an incorrect assumption. Silly me!! The focus screen thickness is irrelevent as the focusing takes place on the ground glass surface which is on top of the screen next to the pentaprism, just the same as the original screen focus would be and therefore has no bearing on the issue.
My second thought was that the pentaprism is out of calibration, but Rachael Katz advises that there is a shim between the focus screen and the pentaprism bottom face and these shims come in various thicknesses so as there is adjustment available!
I removed my shim and measured it and found that it was .40mm. When removed, the resultant image target recorded on the sensor was now behind the focused target image in the VF by about the same margin as it was in front with the shim installed.
So, it would appear that the correct shim thickness should be about .20mm to .25mm and this is borne out by what Rachael Katz has found with her dealings with the K-7. Apparently, some K-7's are shipped with the .40mm shim and some with .20mm and .25mm. It looks as though mine should have been with the .20mm or .25mm shim and this is why it is out of calibration.
Rachael also states that using the Katz Eye screen due to it's excellent focusability, you can see where even as little as .05mm can make the difference whether you have the focus accuracy exactly spot on! I would suggest that you need a very fast lens to utilize this sort of focus accuracy with the Katz Eye screen, probably sub f2.
What I did notice is that the DA*16-50 f2.8 lens was less susceptible to slight focus inaccuracies due to the extra DOF, but it would still be advantageous to have the correct focus shim applied. I think my point here is that you are less likely to see focus inaccuracies with an f2.8 lens or slower than if you used a faster lens(obviously).
The Katz Eye screen seems to give better focus "snap" and therefore better focus accuracy, me thinks. I mean, I never really noticed that I had any focus inaccuracies previously, but using the Katz Eye certainly pointed it out quite easily. Maybe this is why a did get a few ever so slightly misfocused shots (but within realms of acceptibility) previously and put it down to user error. The "inaccuracies" may be, and probably are, masked by the extra DOF afforded by using smaller apertures like f4 etc.
If your shim is incorrect, this may also play a part in any focus anomolies experienced when trying to adjust for AF Adjustment and why some people find it difficult to accurately get correct AF using the AF adjustment feature. I am not saying that the shim issue is prevalent, but it may be worth checking if you are having any issues with focus and discount this part of the equation.
It is a reasonably simple exercise to swap shims and not much different to changing the focus screen, if you are reasonably competent. I would be very careful when doing it as you may damage the bottom of the pentaprism if you are not careful. Use a plastic set of tweezers rather than anything metal. Katz Eye supply an excellent set of plastic tweezers for swapping the focus screen, so you can utilize this for the job.
|
|
Forum: Pentax News and Rumors
05-12-2010, 11:15 PM
|
| |
True, but the same advantages applied to APS C sensors to better the IQ can be applied to FF making the difference the same once again. The laws of physics stipulate that the advantages will always be there, so if APS C looks good at ISO 3200, then FF will look good at say, ISO5000 which will be great for capturing low light fast moving images.
I can guarantee that entry level cameras will still be small, like the K-7, because there is a market that dictates that size of camera. In fact, the APS C sensored camera will still be very much used for the foreseeable future, IMO.
|
|
Forum: Pentax News and Rumors
05-09-2010, 04:00 AM
|
| |
In 12 months it will be 2 years and therefore not the near future. ;)
Most lenses can be used on APS C and FF, especially the telephots which are not smaller but the same sice as required on APS C. The DA*20 f2.8 is the same size as the FA*200 f2.8, in fact it is the exact same optical formula. It is really only the wide angle lenses that are different and here is the crunch, the DA14 f2.8 is bigger than the FA20 f2.8!
Also, Pentax has many lenses already in production for FF, the FA31, FA43, FA50, FA77, DFA50 macro, DFA100 macro, DA*200 f2.8 (fits FF), DA*300 f4 (fits FF), DA*60-250 f4 (fits FF apparently). The A50mm f1.2 is also still in production.
 Quote: Now an APS-C pro camera will also be a lot more affordable than a FF pro camera. Anyone remembers how much a D3X or a 1Ds MkIII cost? (And don't tell me about the D700 or 5D MkII: these aren't pro bodies. If they were, they would have 100% coverage viewfinders, a faster AF [for the 5DII, that is — the D700 is fine there], and a built-in vertical battery grip, just to name a few). Sensor prices are falling. People who are advanced amateurs are going to go for the best IQ for the money that they have to spend and that mark is about the US$1,500 point. Once FF cameras can be made to this price point, then Canon, Nikon and Sony will all have smaller FF cameras at this level and entice advanced amateur/semi pro APS C users to this market.
Quote: (Now that doesn't mean such cameras can't be used by pros. In fact, a lot of pros choose such cameras because they don't need the faster AF or the built-in battery grip. The 5DII is the best example of a high end enthusiast camera used by pros. But such a FF camera is still quite expensive, at 2500$, yet its AF is slower and its weather seals are cheaper than the more affordable 7D.)
By making its pro camera APS-C, Pentax can manage to keep the price at a more affordable level and grab a larger share of the advanced enthusiast and budget-oriented pro. As I said previously, FF cameras will come down to the $1,500 price point which is the domain of advanced amateurs and semi pros. They will still spend this amount and if there is a FF camera at this level then that is what they will purchase.
Also, FF cameras at the moment are really only large and heavy as this is what the pro market demands. They have to be robust to stand up to the rigours of pro use and they usually have to be large for use with lerge lenses, accommodate large batteries, dual card slots, high memory and advanced electronics. Once the price comes down, then the need for them to be as robust and large also can be reduced. It won't happen before hand as the price for them will keep them in the domain of professional use, and only well heeled advanced amateurs who will put up with the size and weight penalty, who will purchase them.
Quote: For all these reasons, I believe the Pentax pro body will be APS-C.
But I could be wrong, of course. I really hope it's going to be a full-frame!
:)
Here's my guess at the specs: - 12 to 18 Mpix APS-C sensor
- 8 fps burst speed
- Improved AF performance, especially in AF-C
- 100% coverage viewfinder
- Advanced weather seals and larger than K-7, magnesium-alloy body
- ISO 100-12800, extended ISO 50-25600
- Improved flash/ambient light metering
- Improved SR, DR, Liveview, etc.
- Improved, full HD video (hopefully with full manual control, so I'll keep my Pentax gear instead of selling it all for a Canon 5DII)
Just my bet. Feel free to come up with yours!
;) |
|
Forum: Pentax News and Rumors
05-04-2010, 11:24 PM
|
| |
MF is a larger format and requires larger lenses. FF lenses are already availabale for all the manufacturers cameras whereas MF lenses are a complete new lens lineup. Also, FF is now a standard and the cameras are about as big as pro's would want them.
Canon, Nikon and to a lesser degree Sony are the market leaders and manipulators and therefore Pentax needs to make sure they can keep pace with their offerings. Pentax are the tail and C, N and S are the dog, so I doubt that Pentax can wag the dog.
As I keep saying, if Canon, Nikon and Sony release a FF camera at the $1,500 mark, then Pentax will have to have a FF camera in this area otherwise it Pentax will lose purchasers to C, N and S. If Nikon released a FF camera at $1,500 that had all the features of the K7 and was about the size of the K20D, then I would probably jump ship, as I am sure others here would too.
|
