yes I know, I only calculated one with the hand and the rest with that thing

Thanks John for you agreement it took me 4 hours to write this thing.

If you read the part of the CoC you will see I've included the print resolution and viewing distance. It's also why you can magnify prints more on your computer screen then on prints but I didn't cover that part.
I also discover that not many lenses will benefit from a higher density sensor since when the density increases the more imperfection you will see in it goes up equally I believe. Your kitlens for example wouldn't preform better on K20D as it did on the K10D, only the higher end zooms and almost all primes will benefit from a sensor with more pixels but you can increase the sharpness of you kit lens by inlarging the sensor size. Maybe an APS-H for the K30D isn't such bad idea afterall

I aint so sure I wont to go further into it, I rather just shoot photos and see what happends then calculate it. I was simply interested to see how the DA* 55mm compares on digital to the FA* 85mm on film since it would be the lens to replace that one. I already started it for the DA* 55 topic but it became to large I think

Not a review but a comparison link

Just make a topic out of the matter of comparing the FA* 85mm f/1.4 and the DA* 55mm f/1.4 on differend sensorsizes in the general chat.
There is a difference in depth of field because of these points;
- If the sensor is smaller you lens need to have sharper to capture the same amount of detial as with a large sensor, you have more tolerance so to say.
- Since the size of the image is smaller you need to magnify it more to get the same final image size also causing more blur.

No comments on this here but in the topic please, thank you!
https://www.pentaxuser.com/forum/topic/The-impact-the-sensor-size-has-on-the-len...

When reading the the question again how the lens would be on digital compared to on a 35mm format I began to calculate the DOF and discover it does make a diffrence.

I will take the FA* 85mm f/1.4 and the DA* 55mm f/1.4 because of the smaller ASP-C sensor the DA* 55mm will have an angle of view as 84.15mm on 35mm so they will be almost the same.
If we mount both lenses on the Pentax k10D this would be the DOF if we focus on a subject 10m away;
the FA* 85mm f/1.4 will give you a DOF of 77.7 cm while wide open
the DA* 55mm f/1.4 will give a DOF of 187.6 cm while wide open.
Okay clearly a difference but the 85mm will make a differend photo as the 55mm so we need to step away from the subject to get the same image, to 15.45m to be exact so lets calculate the DOF again.
The FA* 85mm f/1.4 at 15.45m wide open would give you a DOF of 186.5 cm.
Compared to the DA* 55m there isn't much diference.

But we always so that a lens will act like a ... on a 35mm, lets try that.

The FA* 85mm on a 35mm camera and the DA* 55mm on a Pentax K10D.
Because the 55mm doesn't give the same angle of view as the FA* 85mm, we need to stand just a bit closer. The subject distance for the FA* 85mm is 10m and for the DA* 55mm 9.9m, with these distance the subject will be the same length on both photos.
With the distance given above and both wide open f/1.4 the;
DA* 55mm would have a DOF of 183.8 cm on the K10D
FA* 85mm would have a dof of 116.8 cm on 35mm film
So the DA* 55mm would not replace the FA* 85mm for his DOF

Now we are going to look purely on what the sensor size does for the DOF so the FA* 85mm on the pentax K10D and on 35mm film with a focus on a subject 10m away and both wide open;
Pentax K10D would give you a DOF of 77.7 cm
35mm camera would be a DOF of 116.8 cm
so clearly the same lens will not be the same on both formats.
The difference is cause by the diffrence in circle of confusion.

Since it's already 4:30am here I will cut it short, sorry.
The circle of confusion is in the formula of depth of field so that's why it effects it. I'm going to explain what circle of confusion is and going to bed right afterwards.

The circle of confusion is the largest blur circle that will still be perceived by the human eye as a point when viewed at a distance of 25 cm.
3 things make up the CoC and that is visual acuity, viewing conditions & Enlargement from the original image and there we have it. All three factors are accommodated with this formula:
CoC Diameter Limit (mm) = anticipated viewing distance (cm) / desired print resolution (lp/mm) for a 25 cm viewing distance / anticipated enlargement factor / 25
You can see it as the amount of blur an image may have while it still looks sharp, so also the sharpness of the lens comes into account but also the size of the sensor that records it. Since the area of a APS-C is smaller compared to 35mm you will see more inperfections when the final image is viewed on the same size since the enlargment is greater with a APS-C sensor.

I will end it here since I can't think anymore, please correct me if I'm wrong somewhere, certainly the chapter about CoC can be wrong so please look at that for me.
I hope it makes some sence and with that I hope the matter is some clearer but I don't think so since just saying that the lens will be the same and the angle of view only change was far simpeler.

Enjoy the read and dont get a headache like me now

if you turn the camera off and press the shutter release you won't hear the mirror flappy thingy, does this solve the problem?

wow awesome photo

Peter, why don't you just tape that mirror flappy thing down, it won't make any noise anymore if you do that.

yeah maybe a bit off from the top but to be honest ilike it so.
you have the dark forground on the lower third, the green hills and the city in the middle third and the clouds and mist in the higher third half. Thats why I said I like but you're right Gwyn, there is just a bit to much sky in it to make it a perfect third.

that looks quite nice, good composition

You can also send him a PM if you need some info

The kitlens on the K200D is the mkII version, it's sharper on the edges, see here the topic https://www.pentaxuser.com/forum/topic/1855-kit-lens--mk1-v-mk2-9734

If you live in the UK this month you will get some cashback on the K200D and the K20D

Since you have older lenses the K200D and the K20D would be better since the K10D had some eposure problems I believe, I mostly use DA lensses and only borrowed some older lenses but I shoot with them on Manual mode.

I'm sure other users can tell you more about the problems