K-7 shims

Lance B · 2010-03-19T00:26:53+0000

Apparently, this has been discussed here before, but I thought I would post my experiences with my K-7 with regards the focus shims and Katz Eye screen. I never knew there were focus shims used for calibrating the focus screens of the Pentax DSLR's. I did know there was a shim for the DS(? ), but I thought that was just a locating shim or some such thing. Anyway, I posted this over at the 'other forum' 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.

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Lance B Lance B

305 posts
22 years
Sydney,
Australia

Posted 22/03/2010 - 03:47 Link

golfdiesel wrote:
Good to see that Pentax charges a sensible price for the shims... I was scared that they would overprice them just like simple plastic things like lens caps, hotshoe covers and such.

You and me both. When I enquired about the price and they told me AU$2.20 each I thought he must have been quoting me just for the packaging!!

Cameras:K-7/K20D/*ist D/K10D
Lenses:DA14 f2.8, A16 f2.8, FA20 f2.8, FA31 f1.8, DA35 f2.8 macro, FA43 f1.9, FA50 f1.4, A50 f1.4, A50 f1.2, FA50 f2.8 macro, DA*55 f1.4, FA77 f1.8, DFA100 f2.8 macro, A100 f2.8, DA*300 f4, FA*300 f4.5, DA10-17 FE, DA12-24 f4, DA*16-50 f2.8, DA17-70 f4, FA*28-70 f2.8, DA*50-135 f2.8, DA*60-250 f4, FA*80-200 f2.8.
Flashes:AF540FGZ, AF360FGZ

George in Geo... George in Georgia USA

69 posts
19 years
Jonesboro,
Georgia,
USA

Posted 23/03/2010 - 20:37 Link

A most interesting thread! I'll have to check my K10d to which I have fitted a KatzEye with split image in conjunction with my 50mm f1.2. Since I also shoot a 500mm mirror lens - manual focus, of course - and a Vivitar 100mm f3.5 macro lens, also manual focus, the KatzEye was a logical purchase.

Does anyone know whether the LX which had a wide variety changeable screens available makes use of similar shims? Given that that sweet machine was largely hand made I'd suspect that any needed shims were permanently installed at the time of manufacture.

mayday mayday

652 posts
18 years
Weston-super-Mare UK

Posted 01/06/2011 - 10:47 Link

Hi,
I have fitted a Katzeye screen and had manual focus issues using the split screen. Rachael Katz was very helpful in trying to resolve the problem and advised obtaining shims for the K7.
I received the following email from the UK Pentax Service Agent:

Hello.

Thank you for your enquiry regarding Pentax K-7 spares

To supply the parts that you require would cost £16.80 and that includes P+P and VAT.

If you wish to order, please call us on 01782 753330, and have your debit/credit card details to hand.

Best Regards

Pentax UK Service
I was adivised that they have had quite a few orders for shims - for the K7. They werent able to tell me what shims were available for other models, without making enquiries direct to Pentax

Hope this info helps

Regards
David

Retired at last - now all that time for photography - you would think: wink: